Search results
Search for "quaternary ammonium salt" in Full Text gives 17 result(s) in Beilstein Journal of Organic Chemistry.
Synthetic study toward tridachiapyrone B
- Morgan Cormier,
- Florian Hernvann and
- Michaël De Paolis
Beilstein J. Org. Chem. 2022, 18, 1741–1748, doi:10.3762/bjoc.18.183
- , treatment with KH in DMSO at room temperature caused the degradation of 17. Scarcely examined for this purpose, hydroxide of quaternary ammonium salt was next evaluated to promote the anionic oxy-Cope rearrangement with the prospect that non-coordinating organic cations could facilitate the transformation
- -cyclohexadienone followed by an oxidative anionic oxy-Cope rearrangement promoted by hydroxide of quaternary ammonium salt. Moreover, the coupling of lithiocyclopentadiene to α,α’-dimethoxy-γ-pyrone was demonstrated, enlarging the scope of nucleophiles grafted to the pharmaceutically relevant α’-methoxy-γ-pyrone
Graphical Abstract
Scheme 1: Routes to crispatene, photodeoxytridachione, aureothin, and tridachiapyrone B.
Scheme 2: Desymmetrization of 2.
Scheme 3: Addition of lithiocyclopentadiene to pyrone 2.
Scheme 4: Plan to reach 2,5-cyclohexadienone 5.
Scheme 5: Preparation of 2,5-cyclohexadienone 5.
Scheme 6: Attempts to perform the conjugate addition.
Scheme 7: Updated route to tridachiapyrone B.
New synthesis of a late-stage tetracyclic key intermediate of lumateperone
- Mátyás Milen,
- Bálint Nyulasi,
- Tamás Nagy,
- Gyula Simig and
- Balázs Volk
Beilstein J. Org. Chem. 2022, 18, 653–659, doi:10.3762/bjoc.18.66
- -toluenesulfonate followed by reduction of the N-methylated quaternary ammonium salt 25 with sodium borohydride gave tetrahydroquinoxaline 26. Since N-amination of the latter with hydroxylamine-O-sulfonic acid [14] had been unsuccessful, we tried to achieve our target via the N-nitroso derivative 27, which was
- . Reduction of the quaternary ammonium salt 28 with sodium borohydride gave tetrahydroquinoxaline 29. Its reaction with trifluoroacetic anhydride (TFAA) to give 30 and removal of the benzyl group by catalytic hydrogenation afforded N-trifluoroacetyl-1,2,3,4-tetrahydroquinoxaline (31). Compound 31 was then
Graphical Abstract
Figure 1: Structure of lumateperone.
Scheme 1: First synthetic route leading to lumateperone (1).
Scheme 2: Alternate synthesis of lumateperone.
Scheme 3: Alternate synthetic approaches leading to racemic lumateperone ((±)-1)).
Scheme 4: Planned new synthesis of key intermediate (±)-9a.
Scheme 5: New synthesis of key intermediate (±)-9a.
Scheme 6: Trifluoroacetylation of tetrahydroquinoxaline (37).
Prins cyclization-mediated stereoselective synthesis of tetrahydropyrans and dihydropyrans: an inspection of twenty years
- Asha Budakoti,
- Pradip Kumar Mondal,
- Prachi Verma and
- Jagadish Khamrai
Beilstein J. Org. Chem. 2021, 17, 932–963, doi:10.3762/bjoc.17.77
- cyclization reaction of allyl bromide (228) with a carbonyl compound promoted by BBIMBr/SnBr2 complex under solvent-free conditions has been explored [97]. The mechanism of the reaction was shown to include a Barbier reaction of allyl bromide with an aldehyde in the presence of SnBr3 and a quaternary ammonium
- salt to produce allyltin compound 230, which subsequently reacts with an aldehyde to generate intermediate 231. This intermediate could be hydrolyzed by water during workup to afford 232, which does not give the required THP product. Desired product 235 was obtained only in the anhydrous conditions
Graphical Abstract
Scheme 1: General strategy for the synthesis of THPs.
Scheme 2: Developments towards the Prins cyclization.
Scheme 3: General stereochemical outcome of the Prins cyclization.
Scheme 4: Regioselectivity in the Prins cyclization.
Scheme 5: Mechanism of the oxonia-Cope reaction in the Prins cyclization.
Scheme 6: Cyclization of electron-deficient enantioenriched alcohol 27.
Scheme 7: Partial racemization through 2-oxonia-Cope allyl transfer.
Scheme 8: Partial racemization by reversible 2-oxonia-Cope rearrangement.
Scheme 9: Rychnovsky modification of the Prins cyclization.
Scheme 10: Synthesis of (−)-centrolobine and the C22–C26 unit of phorboxazole A.
Scheme 11: Axially selective Prins cyclization by Rychnovsky et al.
Scheme 12: Mechanism for the axially selectivity Prins cyclization.
Scheme 13: Mukaiyama aldol–Prins cyclization reaction.
Scheme 14: Application of the aldol–Prins reaction.
Scheme 15: Hart and Bennet's acid-promoted Prins cyclization.
Scheme 16: Tetrahydropyran core of polycarvernoside A as well as (−)-clavoslide A and D.
Scheme 17: Scheidt and co-workers’ route to tetrahydropyran-4-one.
Scheme 18: Mechanism for the Lewis acid-catalyzed synthesis of tetrahydropyran-4-one.
Scheme 19: Hoveyda and co-workers’ strategy for 2,6-disubstituted 4-methylenetetrahydropyran.
Scheme 20: Funk and Cossey’s ene-carbamates strategy.
Scheme 21: Yadav and Kumar’s cyclopropane strategy for THP synthesis.
Scheme 22: 2-Arylcylopropylmethanolin in centrolobine synthesis.
Scheme 23: Yadav and co-workers’ strategy for the synthesis of THP.
Scheme 24: Yadav and co-workers’ Prins–Ritter reaction sequence for 4-amidotetrahydropyran.
Scheme 25: Yadav and co-workers’ strategy to prelactones B, C, and V.
Scheme 26: Yadav and co-workers’ strategy for the synthesis of (±)-centrolobine.
Scheme 27: Loh and co-workers’ strategy for the synthesis of zampanolide and dactylolide.
Scheme 28: Loh and Chan’s strategy for THP synthesis.
Scheme 29: Prins cyclization of cyclohexanecarboxaldehyde.
Scheme 30: Prins cyclization of methyl ricinoleate (127) and benzaldehyde (88).
Scheme 31: AlCl3-catalyzed cyclization of homoallylic alcohol 129 and aldehyde 130.
Scheme 32: Martín and co-workers’ stereoselective approach for the synthesis of highly substituted tetrahydrop...
Scheme 33: Ene-IMSC strategy by Marko and Leroy for the synthesis of tetrahydropyran.
Scheme 34: Marko and Leroy’s strategy for the synthesis of tetrahydropyrans 146.
Scheme 35: Sakurai dimerization/macrolactonization reaction for the synthesis of cyanolide A.
Scheme 36: Hoye and Hu’s synthesis of (−)-dactyloide by intramolecular Sakurai cyclization.
Scheme 37: Minehan and co-workers’ strategy for the synthesis of THPs 157.
Scheme 38: Yu and co-workers’ allylic transfer strategy for the construction of tetrahydropyran 161.
Scheme 39: Reactivity enhancement in intramolecular Prins cyclization.
Scheme 40: Floreancig and co-workers’ Prins cyclization strategy to (+)-dactyloide.
Scheme 41: Panek and Huang’s DHP synthesis from crotylsilanes: a general strategy.
Scheme 42: Panek and Huang’s DHP synthesis from syn-crotylsilanes.
Scheme 43: Panek and Huang’s DHP synthesis from anti-crotylsilanes.
Scheme 44: Roush and co-workers’ [4 + 2]-annulation strategy for DHP synthesis [82].
Scheme 45: TMSOTf-promoted annulation reaction.
Scheme 46: Dobb and co-workers’ synthesis of DHP.
Scheme 47: BiBr3-promoted tandem silyl-Prins reaction by Hinkle et al.
Scheme 48: Substrate scope of Hinkle and co-workers’ strategy.
Scheme 49: Cho and co-workers’ strategy for 2,6 disubstituted 3,4-dimethylene-THP.
Scheme 50: Furman and co-workers’ THP synthesis from propargylsilane.
Scheme 51: THP synthesis from silyl enol ethers.
Scheme 52: Rychnovsky and co-workers’ strategy for THP synthesis from hydroxy-substituted silyl enol ethers.
Scheme 53: Li and co-workers’ germinal bissilyl Prins cyclization strategy to (−)-exiguolide.
Scheme 54: Xu and co-workers’ hydroiodination strategy for THP.
Scheme 55: Wang and co-workers’ strategy for tetrahydropyran synthesis.
Scheme 56: FeCl3-catalyzed synthesis of DHP from alkynylsilane alcohol.
Scheme 57: Martín, Padrón, and co-workers’ proposed mechanism of alkynylsilane Prins cyclization for the synth...
Scheme 58: Marko and co-workers’ synthesis of 2,6-anti-configured tetrahydropyran.
Scheme 59: Loh and co-workers’ strategy for 2,6-syn-tetrahydropyrans.
Scheme 60: Loh and co-workers’ strategy for anti-THP synthesis.
Scheme 61: Cha and co-workers’ strategy for trans-2,6-tetrahydropyran.
Scheme 62: Mechanism proposed by Cha et al.
Scheme 63: TiCl4-mediated cyclization to trans-THP.
Scheme 64: Feng and co-workers’ FeCl3-catalyzed Prins cyclization strategy to 4-hydroxy-substituted THP.
Scheme 65: Selectivity profile of the Prins cyclization under participation of an iron ligand.
Scheme 66: Sequential reactions involving Prins cyclization.
Scheme 67: Banerjee and co-workers’ strategy of Prins cyclization from cyclopropane carbaldehydes and propargy...
Scheme 68: Mullen and Gagné's (R)-[(tolBINAP)Pt(NC6F5)2][SbF6]2-catalyzed asymmetric Prins cyclization strateg...
Scheme 69: Yu and co-workers’ DDQ-catalyzed asymmetric Prins cyclization strategy to trisubstituted THPs.
Scheme 70: Lalli and Weghe’s chiral-Brønsted-acid- and achiral-Lewis-acid-promoted asymmetric Prins cyclizatio...
Scheme 71: List and co-workers’ iIDP Brønsted acid-promoted asymmetric Prins cyclization strategy.
Scheme 72: Zhou and co-workers’ strategy for chiral phosphoric acid (CPA)-catalyzed cascade Prins cyclization.
Scheme 73: List and co-workers’ approach for asymmetric Prins cyclization using chiral imidodiphosphoric acid ...
Synthetic reactions driven by electron-donor–acceptor (EDA) complexes
- Zhonglie Yang,
- Yutong Liu,
- Kun Cao,
- Xiaobin Zhang,
- Hezhong Jiang and
- Jiahong Li
Beilstein J. Org. Chem. 2021, 17, 771–799, doi:10.3762/bjoc.17.67
- atom transfer) occurs in nitrogen radical 14 to give radical 16, which further transforms to radical 17 after the addition of sulfur dioxide. Finally, HAT happens between 15 and 17, yielding quaternary ammonium salt 18 and product 12, respectively. In 2017, Chen and colleagues [47] accomplished the
Graphical Abstract
Scheme 1: The electron transfer process in EDA complexes.
Scheme 2: Synthesis of benzo[b]phosphorus oxide 3 initiated by an EDA complex.
Scheme 3: Mechanism of the synthesis of quinoxaline derivative 7.
Scheme 4: Synthesis of imidazole derivative 10 initiated by an EDA complex.
Scheme 5: Synthesis of sulfamoylation product 12 initiated by an EDA complex.
Scheme 6: Mechanism of the synthesis of sulfamoylation product 12.
Scheme 7: Synthesis of indole derivative 22 initiated by an EDA complex.
Scheme 8: Synthesis of perfluoroalkylated pyrimidines 26 initiated by an EDA complex.
Scheme 9: Synthesis of phenanthridine derivative 29 initiated by an EDA complex.
Scheme 10: Synthesis of cis-tetrahydroquinoline derivative 32 initiated by an EDA complex.
Scheme 11: Mechanism of the synthesis of cis-tetrahydroquinoline derivative 32.
Scheme 12: Synthesis of phenanthridine derivative 38 initiated by an EDA complex.
Scheme 13: Synthesis of spiropyrroline derivative 40 initiated by an EDA complex.
Scheme 14: Synthesis of benzothiazole derivative 43 initiated by an EDA complex.
Scheme 15: Synthesis of perfluoroalkyl-s-triazine derivative 45 initiated by an EDA complex.
Scheme 16: Synthesis of indoline derivative 47 initiated by an EDA complex.
Scheme 17: Mechanism of the synthesis of spirocyclic indoline derivative 47.
Scheme 18: Synthesis of cyclobutane product 50 initiated by an EDA complex.
Scheme 19: Mechanism of the synthesis of spirocyclic indoline derivative 50.
Scheme 20: Synthesis of 1,3-oxazolidine compound 59 initiated by an EDA complex.
Scheme 21: Synthesis of trifluoromethylated product 61 initiated by an EDA complex.
Scheme 22: Synthesis of indole alkylation product 64 initiated by an EDA complex.
Scheme 23: Synthesis of perfluoroalkylation product 67 initiated by an EDA complex.
Scheme 24: Synthesis of hydrotrifluoromethylated product 70 initiated by an EDA complex.
Scheme 25: Synthesis of β-trifluoromethylated alkyne product 71 initiated by an EDA complex.
Scheme 26: Mechanism of the synthesis of 2-phenylthiophene derivative 74.
Scheme 27: Synthesis of allylated product 80 initiated by an EDA complex.
Scheme 28: Synthesis of trifluoromethyl-substituted alkynyl product 84 initiated by an EDA complex.
Scheme 29: Synthesis of dearomatized fluoroalkylation product 86 initiated by an EDA complex.
Scheme 30: Mechanism of the synthesis of dearomatized fluoroalkylation product 86.
Scheme 31: Synthesis of C(sp3)–H allylation product 91 initiated by an EDA complex.
Scheme 32: Synthesis of perfluoroalkylation product 93 initiated by an EDA complex.
Scheme 33: Synthesis of spirocyclic indolene derivative 95 initiated by an EDA complex.
Scheme 34: Synthesis of perfluoroalkylation product 97 initiated by an EDA complex.
Scheme 35: Synthesis of alkylated indole derivative 100 initiated by an EDA complex.
Scheme 36: Mechanism of the synthesis of alkylated indole derivative 100.
Scheme 37: Synthesis of arylated oxidized indole derivative 108 initiated by an EDA complex.
Scheme 38: Synthesis of 4-ketoaldehyde derivative 111 initiated by an EDA complex.
Scheme 39: Mechanism of the synthesis of 4-ketoaldehyde derivative 111.
Scheme 40: Synthesis of perfluoroalkylated olefin 118 initiated by an EDA complex.
Scheme 41: Synthesis of alkylation product 121 initiated by an EDA complex.
Scheme 42: Synthesis of acylation product 123 initiated by an EDA complex.
Scheme 43: Mechanism of the synthesis of acylation product 123.
Scheme 44: Synthesis of trifluoromethylation product 126 initiated by an EDA complex.
Scheme 45: Synthesis of unnatural α-amino acid 129 initiated by an EDA complex.
Scheme 46: Synthesis of thioether derivative 132 initiated by an EDA complex.
Scheme 47: Synthesis of S-aryl dithiocarbamate product 135 initiated by an EDA complex.
Scheme 48: Mechanism of the synthesis of S-aryl dithiocarbamate product 135.
Scheme 49: Synthesis of thioether product 141 initiated by an EDA complex.
Scheme 50: Mechanism of the synthesis of borate product 144.
Scheme 51: Synthesis of boronation product 148 initiated by an EDA complex.
Scheme 52: Synthesis of boration product 151 initiated by an EDA complex.
Scheme 53: Synthesis of boronic acid ester derivative 154 initiated by an EDA complex.
Scheme 54: Synthesis of β-azide product 157 initiated by an EDA complex.
Scheme 55: Decarboxylation reaction initiated by an EDA complex.
Scheme 56: Synthesis of amidated product 162 initiated by an EDA complex.
Scheme 57: Synthesis of diethyl phenylphosphonate 165 initiated by an EDA complex.
Scheme 58: Mechanism of the synthesis of diethyl phenylphosphonate derivative 165.
Scheme 59: Synthesis of (Z)-2-iodovinyl phenyl ether 168 initiated by an EDA complex.
Scheme 60: Mechanism of the synthesis of (Z)-2-iodovinyl phenyl ether derivative 168.
Scheme 61: Dehalogenation reaction initiated by an EDA complex.
Multicomponent reactions (MCRs): a useful access to the synthesis of benzo-fused γ-lactams
- Edorta Martínez de Marigorta,
- Jesús M. de Los Santos,
- Ana M. Ochoa de Retana,
- Javier Vicario and
- Francisco Palacios
Beilstein J. Org. Chem. 2019, 15, 1065–1085, doi:10.3762/bjoc.15.104
- = OH, conditions B, Scheme 9) instead of diketones and a quaternary ammonium salt as catalyst in water. In this multicomponent decarboxylative alkylation/cyclization process, they prepared several lactam derivatives 36 with good yields. While the first research group suggests that the reaction would
Graphical Abstract
Figure 1: γ-Lactam-derived structures considered in this review.
Figure 2: Alkaloids containing an isoindolinone moiety.
Figure 3: Alkaloids containing the 2-oxindole ring system.
Figure 4: Drugs and biological active compounds containing an isoindolinone moiety.
Figure 5: Drugs and biologically active compounds bearing a 2-oxindole skeleton.
Scheme 1: Three-component reaction of benzoic acid 1, amides 2 and DMSO (3).
Scheme 2: Copper-catalysed three-component reaction of 2-iodobenzoic acids 10, alkynylcarboxylic acids 11 and...
Scheme 3: Proposed mechanism for the formation of methylene isoindolinones 13.
Scheme 4: Copper-catalysed three-component reaction of 2-iodobenzamide 17, terminal alkyne 18 and pyrrole or ...
Scheme 5: Palladium-catalysed three-component reaction of ethynylbenzamides 21, secondary amines 22 and CO (23...
Scheme 6: Proposed mechanism for the formation of methyleneisoindolinones 24.
Scheme 7: Copper-catalysed three-component reaction of formyl benzoate 29, amines 2 and alkynes 18.
Scheme 8: Copper-catalysed three-component reaction of formylbenzoate 29, amines 2 and ketones 31.
Scheme 9: Non-catalysed (A) and phase-transfer catalysed (B) three-component reactions of formylbenzoic acids ...
Scheme 10: Proposed mechanism for the formation of isoindolinones 36.
Scheme 11: Three-component reaction of formylbenzoic acid 33, amines 2 and fluorinated silyl ethers 39.
Scheme 12: Three-component Ugi reaction of 2-formylbenzoic acid (33), diamines 41 and isocyanides 42.
Scheme 13: Non-catalysed (A, B) and chiral phosphoric acid promoted (C) three-component Ugi reactions of formy...
Scheme 14: Proposed mechanism for the enantioselective formation of isoindolinones 46.
Scheme 15: Three-component reaction of benzoic acids 33 or 54, amines 2 and TMSCN (52).
Scheme 16: Several variations of the three-component reaction of formylbenzoic acids 33, amines 2 and isatoic ...
Scheme 17: Proposed mechanism for the synthesis of isoindoloquinazolinones 57.
Scheme 18: Three-component reaction of isobenzofuranone 61, amines 2 and isatoic anhydrides 56.
Scheme 19: Palladium-catalysed three-component reaction of 2-aminobenzamides 59, 2-bromobenzaldehydes 62 and C...
Scheme 20: Proposed mechanism for the palladium-catalysed synthesis of isoindoloquinazolinones 57.
Scheme 21: Four-component reaction of 2-vinylbenzoic acids 67, aryldioazonium tetrafluoroborates 68, DABCO·(SO2...
Scheme 22: Plausible mechanism for the formation of isoindolinones 71.
Scheme 23: Three-component reaction of trimethylsilylaryltriflates 77, isocyanides 42 and CO2 (78).
Scheme 24: Plausible mechanism for the three-component synthesis of phthalimides 79.
Scheme 25: Copper-catalysed three-component reaction of 2-formylbenzonitriles 85, arenes 86 and diaryliodonium...
Scheme 26: Copper-catalysed three-component reaction of 2-formylbenzonitriles 85, diaryliodonium salts 87 and ...
Scheme 27: Proposed mechanism for the formation of 2,3-diarylisoindolinones 88, 89 and 92.
Scheme 28: Palladium-catalysed three-component reaction of chloroquinolinecarbaldehydes 97 with isocyanides 42...
Scheme 29: Palladium-catalysed three-component reaction of imines 99 with CO (23) and ortho-iodoarylimines 100....
Scheme 30: Palladium-catalysed three-component reaction of amines 2 with CO (23) and aryl iodide 105.
Scheme 31: Three-component reaction of 2-ethynylanilines 109, perfluoroalkyl iodides 110 and carbon monoxide (...
Scheme 32: Ultraviolet-induced three-component reaction of N-(2-iodoaryl)acrylamides 113, DABCO·(SO2)2 (69) an...
Scheme 33: Proposed mechanism for the preparation of oxindoles 115.
Scheme 34: Three-component reaction of acrylamide 113, CO (23) and 1,4-benzodiazepine 121.
Scheme 35: Multicomponent reaction of sulfonylacrylamides 123, aryldiazonium tetrafluoroborates 68 and DABCO·(...
Scheme 36: Proposed mechanism for the preparation of oxindoles 124.
Scheme 37: Three-component reaction of N-arylpropiolamides 128, aryl iodides 129 and boronic acids 130.
Scheme 38: Proposed mechanism for the formation of diarylmethylene- and diarylallylideneoxindoles 131 and 132.
Scheme 39: Three-component reaction of cyclohexa-1,3-dione (136), amines 2 and alkyl acetylenedicarboxylates 1...
Scheme 40: Proposed mechanism for the formation of 2-oxindoles 138.
A simple and effective preparation of quercetin pentamethyl ether from quercetin
- Jin Tatsuzaki,
- Tomohiko Ohwada,
- Yuko Otani,
- Reiko Inagi and
- Tsutomu Ishikawa
Beilstein J. Org. Chem. 2018, 14, 3112–3121, doi:10.3762/bjoc.14.291
- volume of solvent, to minimize the cost. The results are summarized in Table 2. Phase transfer catalysts (PTCs), such as quaternary ammonium salt, are effective catalysts for the alkylation of less reactive OH functions, such as a hydrogen-bonded phenolic group [41][42]. However, treatment of 2 with 6
Graphical Abstract
Figure 1: Structures of quercetin pentamethyl ether (QPE, 1) and quercetin (2).
Figure 2: Selected HMBC correlations of 6-methyl-3,5,7,3',4'-penta-O-methylquercetin (5).
Figure 3: Three representative conformers of neutral quercetin (2). Top and side views are shown. The relativ...
Figure 4: Structures of oxyanions derived from quercetin (2) by deprotonation of a single OH group. Top and s...
Figure 5: Deprotonation energy of the OH group at 5 position in neutral 2A and tetra-O-methylated quercetin 4A...
Figure 6: Structures and energies of C-methylated products of the tetra- 4 and the penta-O-methyl quercetins 1...
Recent applications of chiral calixarenes in asymmetric catalysis
- Mustafa Durmaz,
- Erkan Halay and
- Selahattin Bozkurt
Beilstein J. Org. Chem. 2018, 14, 1389–1412, doi:10.3762/bjoc.14.117
- sequence including protection/deprotection steps for the benzyl groups. The catalytic efficiency of calix[4]arene-based phase-transfer catalyst 7 was evaluated in the benchmark reaction (Scheme 3) and compared with that of the chiral quaternary ammonium salt 8. The results obtained when 7 used as
Graphical Abstract
Figure 1: Inherently chiral calix[4]arene-based phase-transfer catalysts.
Scheme 1: Asymmetric alkylations of 3 catalyzed by (±)-1 and (±)-2 under phase-transfer conditions.
Scheme 2: Synthesis of chiral calix[4]arene-based phase-transfer catalyst 7 and structure of O’Donnell’s N-be...
Scheme 3: Asymmetric alkylation of glycine derivative 3 catalyzed by calixarene-based phase-transfer catalyst ...
Figure 2: Calix[4]arene-amides used as phase-transfer catalysts.
Scheme 4: Phase-transfer alkylation of 3 catalyzed by calixarene-triamide 12.
Scheme 5: Synthesis of inherently chiral calix[4]arenes 20a/20b substituted at the lower rim. Reaction condit...
Scheme 6: Asymmetric Henry reaction between 21 and 22 catalyzed by 20a/20b.
Figure 3: Proposed transition state model of asymmetric Henry reaction.
Scheme 7: Synthesis of enantiomerically pure phosphinoferrocenyl-substituted calixarene ligands 27–29.
Scheme 8: Asymmetric coupling reaction of aryl boronates and aryl halides in the presence of calixarene mono ...
Scheme 9: Asymmetric allylic alkylation in the presence of calix[4]arene ligand (S,S)-29.
Figure 4: Structure of inherently chiral oxazoline calix[4]arenes applied in the palladium-catalyzed Tsuji–Tr...
Scheme 10: Asymmetric Tsuji–Trost reaction in the presence of calix[4]arene ligands 36–39.
Figure 5: BINOL-derived calix[4]arene-diphosphite ligands.
Scheme 11: Asymmetric hydrogenation of 41a and 41b catalyzed by in situ-generated catalysts comprised of [Rh(C...
Figure 6: Inherently chiral calix[4]arene 43 containing a diarylmethanol structure.
Scheme 12: Asymmetric Michael addition reaction of 44 with 45 catalyzed by 43.
Figure 7: Calix[4]arene-based chiral primary amine–thiourea catalysts.
Scheme 13: Asymmetric Michael addition of 48 with 49 catalyzed by 47a and 47b.
Scheme 14: Enantioselective Michael addition of 51 to 52 catalyzed by calix[4]arene thioureas.
Scheme 15: Synthesis of calix[4]arene-based tertiary amine–thioureas 54–56.
Scheme 16: Asymmetric Michael addition of 34 and 57 to nitroalkenes 49 catalyzed by 54b.
Scheme 17: Synthesis of p-tert-butylcalix[4]arene bis-squaramide derivative 64.
Scheme 18: Asymmetric Michael addition catalyzed by 64.
Scheme 19: Synthesis of chiral p-tert-butylphenol analogue 68.
Figure 8: Novel prolinamide organocatalysts based on the calix[4]arene scaffold.
Scheme 20: Asymmetric aldol reactions of 72 with 70 and 71 catalyzed by 69b.
Scheme 21: Synthesis of p-tert-butylcalix[4]arene-based chiral organocatalysts 75 and 78 derived from L-prolin...
Scheme 22: Synthesis of upper rim-functionalized calix[4]arene-based L-proline derivative 83.
Scheme 23: Synthesis and proposed structure of Calix-Pro-MN (86).
Figure 9: Calix[4]arene-based L-proline catalysts containing ester, amide and acid units.
Scheme 24: Synthesis of calix[4]arene-based prolinamide 92.
Scheme 25: Calixarene-based catalysts for the aldol reaction of 21 with 70.
Scheme 26: Asymmetric aldol reactions of 72 with cyclic ketones catalyzed by calix[4]arene-based chiral organo...
Figure 10: A proposed structure for catalyst 92 in H2O.
Scheme 27: Synthetic route for organocatalyst 98.
Scheme 28: Asymmetric aldol reactions catalyzed by 99.
Figure 11: Proposed catalytic environment for catalyst 99 in the presence of water.
Scheme 29: Asymmetric aldol reactions between 94 and 72 catalyzed by 55a.
Scheme 30: Enantioselective Biginelli reactions catalyzed by 69f.
Scheme 31: Synthesis of calix[4]arene–(salen) complexes.
Scheme 32: Enantioselective epoxidation of 108 catalyzed by 107a/107b.
Scheme 33: Synthesis of inherently chiral calix[4]arene catalysts 111 and 112.
Scheme 34: Enantioselective MPV reduction.
Scheme 35: Synthesis of chiral calix[4]arene ligands 116a–c.
Scheme 36: Asymmetric MPV reduction with chiral calix[4]arene ligands.
Scheme 37: Chiral AlIII–calixarene complexes bearing distally positioned chiral substituents.
Scheme 38: Asymmetric MPV reduction in the presence of chiral calix[4]arene diphosphites.
Scheme 39: Synthesis of enantiomerically pure inherently chiral calix[4]arene phosphonic acid.
Scheme 40: Asymmetric aza-Diels–Alder reactions catalyzed by (cR,pR)-121.
Scheme 41: Asymmetric ring opening of epoxides catalyzed by (cR,pR)-121.
Bromide-assisted chemoselective Heck reaction of 3-bromoindazoles under high-speed ball-milling conditions: synthesis of axitinib
- Jingbo Yu,
- Zikun Hong,
- Xinjie Yang,
- Yu Jiang,
- Zhijiang Jiang and
- Weike Su
Beilstein J. Org. Chem. 2018, 14, 786–795, doi:10.3762/bjoc.14.66
- , suggesting the bromide ion plays an important role in ameliorating the reaction selectivity (Table S1, entries 9–11). Further investigating the alkyl chain (R) of NR4+Br− showed that the medium-length butyl was most efficient (Table S1, entries 5–7). In order to see whether the quaternary ammonium salt had
Graphical Abstract
Scheme 1: Representative pharmaceutically useful indazoles.
Scheme 2: Model Heck reaction of 3-bromo-N-methyl-1H-indazole (1a) and n-butyl acrylate (2a). (173 stainless-...
Figure 1: Investigation of additives in the Heck reaction: 1a (1.5 mmol), 2a (2.25 mmol), Pd(OAc)2 (5 mol %),...
Scheme 3: The control experiments. aTEA (1.8 mmol), silica gel (5.0 g), bPd(OAc)2 (5 mol %), PPh3 (10 mol %),...
Scheme 4: Plausible reaction pathway.
Figure 2: Influence of milling time and rotation speed on the Heck reaction: 1a (1.5 mmol), 2a (2.25 mmol), P...
Figure 3: Influence of the milling ball filling degree with different size on the Heck reaction: 1a (1.5 mmol...
Scheme 5: Examination of the substrate scope. Reaction conditions: 1 (1.5 mmol), 2 (2.25 mmol), Pd(OAc)2 (5 m...
Scheme 6: Synthesis of axitinib by mechanochemical Heck–Migita coupling. Reagents and conditions: (i) NBS, Na...
Mannich base-connected syntheses mediated by ortho-quinone methides
- Petra Barta,
- Ferenc Fülöp and
- István Szatmári
Beilstein J. Org. Chem. 2018, 14, 560–575, doi:10.3762/bjoc.14.43
- intermediate reacts with the nucleophile (dienophile) species in different reactions to form a wide range of heterocyclic compounds. Reactions with C=C dienophiles Reactions of o-QMs with different C=C dienophiles are listed in Table 3. Osyanin et al. reported the efficient reaction of quaternary ammonium salt
Graphical Abstract
Scheme 1: Formation of amidoalkylnaphthols 4 via o-QM intermediate 3.
Scheme 2: Asymmetric syntheses of triarylmethanes starting from diarylmethylamines.
Scheme 3: Proposed mechanism for the formation of 2,2-dialkyl-3-dialkylamino-2,3-dihydro-1H-naphtho[2,1-b]pyr...
Scheme 4: Cycloadditions of isoflavonoid-derived o-QMs and various dienophiles.
Scheme 5: [4 + 2] Cycloaddition reactions between aminonaphthols and cyclic amines.
Scheme 6: Brønsted acid-catalysed reaction between aza-o-QMs and 2- or 3-substituted indoles.
Scheme 7: Formation of 3-(α,α-diarylmethyl)indoles 52 in different synthetic pathways.
Scheme 8: Alkylation of o-QMs with N-, O- or S-nucleophiles.
Scheme 9: Formation of DNA linkers and o-QM mediated polymers.
Chiral phase-transfer catalysis in the asymmetric α-heterofunctionalization of prochiral nucleophiles
- Johannes Schörgenhumer,
- Maximilian Tiffner and
- Mario Waser
Beilstein J. Org. Chem. 2017, 13, 1753–1769, doi:10.3762/bjoc.13.170
- last millennium then witnessed an increasing interest in the design of new chiral ammonium salt phase-transfer catalysts, with remarkable contributions especially by Maruoka’s group, who developed very efficient and highly versatile chiral binaphthyl-based quaternary ammonium salt catalysts [12][13][14
- -workers demonstrated the potential of asymmetric cation-based phase-transfer catalysis to control the absolute configuration of the newly-installed stereogenic centre in this rearrangement reaction [141]. By using their spiro-quaternary ammonium salt catalyst B5 they were able to control the Neber
Graphical Abstract
Scheme 1: Generally accepted ion-pairing mechanism between the chiral cation Q+ of a PTC and an enolate and s...
Scheme 2: Reported asymmetric α-fluorination of β-ketoesters 1 using different chiral PTCs.
Scheme 3: Asymmetric α-fluorination of benzofuranones 4 with phosphonium salt PTC F1.
Scheme 4: Asymmetric α-fluorination of 1 with chiral phosphate-based catalysts.
Scheme 5: Anionic PTC-catalysed α-fluorination of enamines 7 and ketones 10.
Scheme 6: PTC-catalysed α-chlorination reactions of β-ketoesters 1.
Scheme 7: Shioiri’s seminal report of the asymmetric α-hydroxylation of 15 with chiral ammonium salt PTCs.
Scheme 8: Asymmetric ammonium salt-catalysed α-hydroxylation using oxygen together with a P(III)-based reduct...
Scheme 9: Asymmetric ammonium salt-catalysed α-photooxygenations.
Scheme 10: Asymmetric ammonium salt-catalysed α-hydroxylations using organic oxygen-transfer reagents.
Scheme 11: Asymmetric triazolium salt-catalysed α-hydroxylation with in situ generated peroxy imidic acid 24.
Scheme 12: Phase-transfer-catalysed dearomatization of phenols and naphthols.
Scheme 13: Ishihara’s ammonium salt-catalysed oxidative cycloetherification.
Scheme 14: Chiral phase-transfer-catalysed α-sulfanylation reactions.
Scheme 15: Chiral phase-transfer-catalysed α-trifluoromethylthiolation of β-ketoesters 1.
Scheme 16: Chiral phase-transfer-catalysed α-amination of β-ketoesters 1 using diazocarboxylates 38.
Scheme 17: Asymmetric α-fluorination of benzofuranones 4 using diazocarboxylates 38 in the presence of phospho...
Scheme 18: Anionic phase-transfer-catalysed α-amination of β-ketoesters 1 with aryldiazonium salts 41.
Scheme 19: Triazolium salt L-catalysed α-amination of different prochiral nucleophiles with in situ activated ...
Scheme 20: Phase-transfer-catalysed Neber rearrangement.
A new protocol for the synthesis of 4,7,12,15-tetrachloro[2.2]paracyclophane
- Donghui Pan,
- Yanbin Wang and
- Guomin Xiao
Beilstein J. Org. Chem. 2016, 12, 2443–2449, doi:10.3762/bjoc.12.237
- was stirred at 300 rpm. Me3N was generated by heating an aqueous Me3N solution (40% w/w, 15 mL) and passed into the flask for 4 h. The product was precipitated as a white solid. Then the mixture was stirred at room temperature overnight and the quaternary ammonium salt was obtained on a Büchner funnel
Graphical Abstract
Figure 1: Chemical structures of parylene N, parylene C, and parylene D.
Figure 2: Chemical structures of [2.2]paracyclophane and 4,7,12,15-tetrachloro[2.2]paracyclophane.
Scheme 1: Synthesis of substituted (4-methylbenzyl)trimethylammonium bromides from substituted (4-methylbenzy...
Mutagenic activity of quaternary ammonium salt derivatives of carbohydrates
- Barbara Dmochowska,
- Karol Sikora,
- Anna Woziwodzka,
- Jacek Piosik and
- Beata Podgórska
Beilstein J. Org. Chem. 2016, 12, 1434–1439, doi:10.3762/bjoc.12.138
- mutagenicity test; quaternary ammonium salt; Introduction Carbohydrates and alditols occur broadly in nature and possess many biological functions essential to living organisms. Sugars not only contribute as energetic substances, but also serve as building materials for fungi, microbes, plants, and animals
- ammonium salt (QAS) derivatives of glucopyranosides with an elongated hydrophobic hydrocarbon chain. The new N-[6-(β-D-glucopyranosyloxy)hexyl]ammonium bromides and their O-acetyl derivatives were analyzed via 1H and 13C NMR spectroscopy. The mutagenic activity of the newly synthesized QAS was investigated
- Faculty of Biotechnology, University of Gdańsk and Medical University of Gdańsk, Antoniego Abrahama 58, 80-307 Gdańsk, Poland Department of Molecular Evolution, University of Gdańsk, Wita Stwosza 59, 80-308 Gdańsk, Poland 10.3762/bjoc.12.138 Abstract This paper presents a study on a series of quaternary
Graphical Abstract
Scheme 1: Reagents and conditions; I: HO(CH2)6Br, BF3·Et2O/CH2Cl2, 1 h 0 °C → 3 h, rt, ([32] compound 2 36% yield...
Figure 1: Mutagenic activity of the QASs in the Vibrio harveyi A16 strain bioluminescence assay. A, 4a; B, 4b...
Figure 2: Mutagenic activity of the QASs in the Ames test with histidine-dependent Salmonella typhimurium TA9...
Bifunctional phase-transfer catalysis in the asymmetric synthesis of biologically active isoindolinones
- Antonia Di Mola,
- Maximilian Tiffner,
- Francesco Scorzelli,
- Laura Palombi,
- Rosanna Filosa,
- Paolo De Caprariis,
- Mario Waser and
- Antonio Massa
Beilstein J. Org. Chem. 2015, 11, 2591–2599, doi:10.3762/bjoc.11.279
- base organo-catalysts and when using quaternary ammonium salts. In the latter case, however, only 46% ee was obtained using the bifunctional urea-containing ammonium salt catalyst introduced by Dixon's group [30]. Readily available commonly used quaternary ammonium salt catalysts gave racemic mixtures
Graphical Abstract
Figure 1: Some chiral, bioactive isoindolinones.
Scheme 1: This work: 1) trans-1,2-cyclohexane diamine-based bifunctional ammonium salts 8 in the asymmetric s...
Scheme 2: Asymmetric cascade, crystallization and decarboxylation reaction.
Scheme 3: Proposed racemization pathways of isoindolinones 9 via retro-Michael process.
Scheme 4: Asymmetric synthesis of (S)-PD172938.
Scheme 5: Coupling of chiral acid 9 with p-tolylpiperazine and CuI arylation of chiral isoindolinones.
Control over molecular motion using the cis–trans photoisomerization of the azo group
- Estíbaliz Merino and
- María Ribagorda
Beilstein J. Org. Chem. 2012, 8, 1071–1090, doi:10.3762/bjoc.8.119
- . An illustrative example is described by Trauner, Kramer and co-workers to control the K+ channels in neuronal cells (Figure 4) [88]. The azobenzene 1 is a terminal quaternary ammonium salt, thus when 1 adopts the trans configuration, the flow of K+ ions is blocked. After irradiation with λ = 380 nm
Graphical Abstract
Figure 1: Photoisomerization process of azobenzene.
Figure 2: Representative example of an UV spectrum of an azocompound of the azobenzene type (blue line: trans...
Figure 3: Mechanistic proposals for the isomerization of azobenzenes.
Figure 4: Representation of the photocontrol of a K+ channel in the cellular membrane based on the isomerizat...
Figure 5: (a) MAG interaction with iGluR; (b) photocontrol of the opening of the ion channel by trans–cis iso...
Figure 6: Photocontrol of the structure of the α-helix in the polypeptide azoderivative 2. Reprinted (adapted...
Figure 7: Recognition of a guanidinium ion by a cis,cis-bis-azo derivative 3.
Figure 8: Recognition of cesium ions by cis-azo derivative 4.
Figure 9: Photocontrolled formation of an inclusion complex of cyclodextrin trans-azo 5+6.
Figure 10: Pseudorotaxane-based molecular machine.
Figure 11: Molecular hinge. Reprinted (adapted) with permission from Org. Lett. 2004, 6, 2595–2598. Copyright ...
Figure 12: Molecular threader. Reprinted (adapted) with permission from Acc. Chem. Res. 2001, 34, 445–455. Cop...
Figure 13: Molecular scissors based on azobenzene 12. Reprinted (adapted) with permission from J. Am. Chem. So...
Figure 14: Molecular pedals. Reprinted by permission from Macmillan Publishers Ltd: Nature, 2006, 440, 512–515...
Figure 15: Design of nanovehicles based on azo structures. Reprinted (adapted) with permission from Org. Lett. ...
Figure 16: Light-activated mesostructured silica nanoparticles (LAMs).
Figure 17: Molecular lift.
Figure 18: Conformational considerations in mono-ortho-substituted azobenzenes.
Scheme 1: Synthesis and photoisomerization of sulfinyl azobenzenes. Reprinted (adapted) with permission from ...
Figure 19: Photoisomerization of azocompound 22 and its application as a photobase catalyst.
Figure 20: Effect of irradiation with linearly polarized light on azo-LCEs. Reprinted by permission from Macmi...
Figure 21: Chemically and photochemically triggered memory switching cycle of the [2]rotaxane 25.
Figure 22: Unidirectional photoisomerization process of the azobenzene 26.
An overview of the key routes to the best selling 5-membered ring heterocyclic pharmaceuticals
- Marcus Baumann,
- Ian R. Baxendale,
- Steven V. Ley and
- Nikzad Nikbin
Beilstein J. Org. Chem. 2011, 7, 442–495, doi:10.3762/bjoc.7.57
- to circumvent the formation of the undesired regioisomer, a strategy that is often used is to react the corresponding benzyl bromide component first with 4-amino-1,2,4-triazole (266) to form a quaternary ammonium salt. The latter can be deaminated to give anastrozole with no isomeric impurities
Graphical Abstract
Figure 1: Structures of atorvastatin and other commercial statins.
Figure 2: Structure of compactin.
Scheme 1: Synthesis of pentasubstituted pyrroles.
Scheme 2: [3 + 2] Cycloaddition to prepare 5-isopropylpyrroles.
Scheme 3: Regiospecific [3 + 2] cycloaddition to prepare the pyrrole scaffold.
Scheme 4: Formation of the pyrrole core of atorvastatin via [3 + 2] cycloaddition.
Scheme 5: Formation of pyrrole 33 via the Paal–Knorr reaction.
Scheme 6: Convergent synthesis towards atorvastatin.
Figure 3: Binding pocket of sunitinib in the TRK KIT.
Scheme 7: Synthesis of sunitinib.
Scheme 8: Alternative synthesis of sunitinib.
Scheme 9: Key steps in the syntheses of sumatriptan and zolmitriptan.
Scheme 10: Introduction of the N,N-dimethylaminoethyl side chain.
Scheme 11: Japp–Klingemann reaction in the synthesis of sumatriptan.
Scheme 12: Synthesis of the intermediate sulfonyl chlorides 62 and 63.
Scheme 13: Alternative introduction of the sulfonamide.
Scheme 14: Negishi-type coupling to benzylic sulfonamides.
Scheme 15: Heck reaction used to introduce the sulfonamide side chain of naratriptan.
Scheme 16: Synthesis of the oxazolinone appendage of zolmitriptan.
Scheme 17: Grandberg indole synthesis used in the preparation of rizatriptan.
Scheme 18: Improved synthesis of rizatriptan.
Scheme 19: Larock-type synthesis of rizatriptan.
Scheme 20: Synthesis of eletriptan.
Scheme 21: Heck coupling for the indole system in eletriptan.
Scheme 22: Attempted Fischer indole synthesis of elatriptan.
Scheme 23: Successful Fischer indole synthesis for eletriptan.
Scheme 24: Mechanistic rationale for the Bischler–Möhlau reaction.
Scheme 25: Bischler-type indole synthesis used in the fluvastatin sodium synthesis.
Scheme 26: Palladium-mediated synthesis of ondansetron.
Scheme 27: Fischer indole synthesis of ondansetron.
Scheme 28: Optimised Pictet–Spengler reaction towards tadalafil.
Figure 4: Structures of carvedilol 136 and propranolol 137.
Scheme 29: Synthesis of the carbazole core of carvedilol.
Scheme 30: Alternative syntheses of 4-hydroxy-9H-carbazole.
Scheme 31: Convergent synthesis of etodolac.
Scheme 32: Alternative synthesis of etodolac.
Figure 5: Structures of imidazole-containing drugs.
Scheme 33: Synthesis of functionalised imidazoles towards losartan.
Scheme 34: Direct synthesis of the chlorinated imidazole in losartan.
Scheme 35: Synthesis of trisubstituted imidazoles.
Scheme 36: Preparation of the imidazole ring in olmesartan.
Scheme 37: Synthesis of ondansetron.
Scheme 38: Alternative route to ondansetron and its analogues.
Scheme 39: Proton pump inhibitors and synthesis of esomeprazole.
Scheme 40: Synthesis of benzimidazole core pantoprazole.
Figure 6: Structure of rabeprazole 194.
Scheme 41: Synthesis of candesartan.
Scheme 42: Alternative access to the candesartan key intermediate 216.
Scheme 43: .Medicinal chemistry route to telmisartan.
Scheme 44: Improved synthesis of telmisartan.
Scheme 45: Synthesis of zolpidem.
Scheme 46: Copper-catalysed 3-component coupling towards zolpidem.
Figure 7: Structure of celecoxib.
Scheme 47: Preparation of celecoxib.
Scheme 48: Alternative synthesis of celecoxib.
Scheme 49: Regioselective access to celecoxib.
Scheme 50: Synthesis of pazopanib.
Scheme 51: Syntheses of anastrozole, rizatriptan and letrozole.
Scheme 52: Regioselective synthesis of anastrozole.
Scheme 53: Triazine-mediated triazole formation towards anastrozole.
Scheme 54: Alternative routes to 1,2,4-triazoles.
Scheme 55: Initial synthetic route to sitagliptin.
Figure 8: Binding of sitagliptin within DPP-IV.
Scheme 56: The process route to sitagliptin key intermediate 280.
Scheme 57: Synthesis of maraviroc.
Scheme 58: Synthesis of alprazolam.
Scheme 59: The use of N-nitrosoamidine derivatives in the preparation of fused benzodiazepines.
Figure 9: Structures of itraconazole, ravuconazole and voriconazole.
Scheme 60: Synthesis of itraconazole.
Scheme 61: Synthesis of rufinamide.
Scheme 62: Representative tetrazole formation in valsartan.
Figure 10: Structure of tetrazole containing olmesartan, candesartan and irbesartan.
Scheme 63: Early stage introduction of the tetrazole in losartan.
Scheme 64: Synthesis of cilostazol.
Figure 11: Structure of cefdinir.
Scheme 65: Semi-synthesis of cefdinir.
Scheme 66: Thiazole syntheses towards ritonavir.
Scheme 67: Synthesis towards pramipexole.
Scheme 68: Alternative route to pramipexole.
Scheme 69: Synthesis of famotidine.
Scheme 70: Efficient synthesis of the hyperuricemic febuxostat.
Scheme 71: Synthesis of ziprasidone.
Figure 12: Structure of mometasone.
Scheme 72: Industrial access to 2-furoic acid present in mometasone.
Scheme 73: Synthesis of ranitidine from furfuryl alcohol.
Scheme 74: Synthesis of nitrofurantoin.
Scheme 75: Synthesis of benzofuran.
Scheme 76: Synthesis of amiodarone.
Scheme 77: Synthesis of raloxifene.
Scheme 78: Alternative access to the benzo[b]thiophene core of raloxifene.
Scheme 79: Gewald reaction in the synthesis of olanzapine.
Scheme 80: Alternative synthesis of olanzapine.
Figure 13: Access to simple thiophene-containing drugs.
Scheme 81: Synthesis of clopidogrel.
Scheme 82: Pictet–Spengler reaction in the preparation of tetrahydrothieno[3,2-c]pyridine (422).
Scheme 83: Alternative synthesis of key intermediate 422.
Figure 14: Co-crystal structures of timolol (left) and carazolol (right) in the β-adrenergic receptor.
Scheme 84: Synthesis of timolol.
Scheme 85: Synthesis of tizanidine 440.
Scheme 86: Synthesis of leflunomide.
Scheme 87: Synthesis of sulfamethoxazole.
Scheme 88: Synthesis of risperidone.
Figure 15: Relative abundance of selected transformations.
Figure 16: The abundance of heterocycles within top 200 drugs (5-membered rings).
Enantioselective nucleophilic difluoromethylation of aromatic aldehydes with Me3SiCF2SO2Ph and PhSO2CF2H reagents catalyzed by chiral quaternary ammonium salts
- Chuanfa Ni,
- Fang Wang and
- Jinbo Hu
Beilstein J. Org. Chem. 2008, 4, No. 21, doi:10.3762/bjoc.4.21
- imines has been realized with PhSO2CF2H and related reagents, there are still no reports on the enantioselective nucleophilic reactions. Results With a chiral quaternary ammonium salt as the catalyst and KOH as the base, we describe the first enantioselective difluoromethylation of aromatic aldehydes
- difluoromethylation reaction of aromatic aldehydes with Me3SiCF2SO2Ph or PhSO2CF2H in the presence of a cinchona alkaloid-based chiral quaternary ammonium salt. Results and Discussion Enantioselective nucleophilic difluoromethylation of aromatic aldehydes with Me3SiCF2SO2Ph We started our investigation with the
- reported the nucleophilic difluoromethylation of aromatic aldehydes with PhSO2CF2H under the phase transfer condition using Aliquat 336 (a commercially available quaternary ammonium salt) as the phase transfer catalyst [35]. With most aldehydes, the reaction affords moderate to excellent yields of products
Graphical Abstract
Scheme 1: Structure of chiral quaternary ammonium salts.
Scheme 2: Determination of the absolute configuration of (+)-3a.
A divergent asymmetric approach to aza-spiropyran derivative and (1S,8aR)-1-hydroxyindolizidine
- Jian-Feng Zheng,
- Wen Chen,
- Su-Yu Huang,
- Jian-Liang Ye and
- Pei-Qiang Huang
Beilstein J. Org. Chem. 2007, 3, No. 41, doi:10.1186/1860-5397-3-41
- substitution occurred firstly, and the formation of the quaternary ammonium salt K [40] then favors the reductive debenzylation. This mechanism is supported by the following observations. First, in a similar case, Thompson et al observed that the formation of a mesylate resulted in spontaneous quarternization
- leading to the bicyclic indolizidine.[40] Second, we have also observed that the tosylate of 8 is too labile to be isolated, and mesylate 12 decomposed upon flash column chromatography on silica gel, which are due to the spontaneous formation of a polar quaternary ammonium salt. In addition, the presence
Graphical Abstract
Scheme 1: The skeletons of useful aza-spiroketals and some naturally occurring hydroxylated indolizidines.
Scheme 2: Synthetic strategy based on N,O-dibenzylmalimide (4).
Scheme 3: Stereoselectivity synthesis of aza-spiropyran 7.
Figure 1: The observed NOE correlations (in part) and the region expanded NOESY spectrum of compound 7.
Scheme 4: Stereoselective synthesis of (1S,8aR)-1-hydroxyindolizidine (ent-3).
Scheme 5: One-pot synthesis of ent-3 from amino alcohol 8.
