Automated three-component synthesis of a library of γ-lactams

• Erik Fenster,
• David Hill,
• Oliver Reiser and
• Jeffrey Aubé

Beilstein J. Org. Chem. 2012, 8, 1804–1813, doi:10.3762/bjoc.8.206

• %) observable in the 13C NMR spectra of the final products (Supporting Information File 1). Such products were deemed suitable for screening purposes. Finally, enantiomeric purity measurements were obtained for six selected γ-lactam products, which ranged between 62 and 84% es. Overall, the results of the

Asymmetric desymmetrization of meso-diols by C₂-symmetric chiral 4-pyrrolidinopyridines

• Hartmut Schedel,
• Keizo Kan,
• Yoshihiro Ueda,
• Kenji Mishiro,
• Keisuke Yoshida,
• Takumi Furuta and
• Takeo Kawabata

Beilstein J. Org. Chem. 2012, 8, 1778–1787, doi:10.3762/bjoc.8.203

• acylpyridinium ion A, and b) the calculated structure of A. Asymmetric desymmetrization of 5 with catalyst 3. Preparation of a small library of chiral C2-symmetric PPY catalysts (reference, see [12]). Amplification of enantiomeric purity of the major enantiomer produced at the step of asymmetric desymmetrization

Organocatalytic asymmetric addition of malonates to unsaturated 1,4-diketones

• Sergei Žari,
• Tiiu Kailas,
• Marina Kudrjashova,
• Mario Öeren,
• Ivar Järving,
• Toomas Tamm,
• Margus Lopp and
• Tõnis Kanger

Beilstein J. Org. Chem. 2012, 8, 1452–1457, doi:10.3762/bjoc.8.165

• catalyst IX, all of the reactions became sluggish at room temperature (Table 3, entries 5, 8, 11 and 14). The reaction times were unreasonably long and the yields remained low. However, in the case of reactions with electron-withdrawing groups, the enantiomeric purity of the products was higher (Table 3

Stereoselective, nitro-Mannich/lactamisation cascades for the direct synthesis of heavily decorated 5-nitropiperidin-2-ones and related heterocycles

• Pavol Jakubec,
• Dane M. Cockfield,
• Madeleine Helliwell,
• James Raftery and
• Darren J. Dixon

Beilstein J. Org. Chem. 2012, 8, 567–578, doi:10.3762/bjoc.8.64

• but with the intention of targeting a piperidin-2-one ring-containing polycyclic scaffold, cyclic imine 5a was added at the second stage. Tetracyclic spiro-lactam 2a was isolated in high enantiomeric purity (90% ee) in good chemical yield (62%, Scheme 8) [111][112]. For the products of the nitro

Efficient and selective chemical transformations under flow conditions: The combination of supported catalysts and supercritical fluids

• M. Isabel Burguete,
• Eduardo García-Verdugo and
• Santiago V. Luis

Beilstein J. Org. Chem. 2011, 7, 1347–1359, doi:10.3762/bjoc.7.159

• were achieved for the second step (17–35%) the corresponding acetate was obtained in high enantiomeric purity (ca. 99%). b) Biocatalysts immobilized in ionic liquids (ILs) The discovery of the possibility to immobilize biocatalysts in ionic-liquid phases has been a recent breakthrough that can be

Synthesis of enantiomerically enriched (R)-¹³C-labelled 2-aminoisobutyric acid (Aib) by conformational memory in the alkylation of a derivative of L-alanine

• Stephen P. Fletcher,
• Jordi Solà,
• Dean Holt,
• Robert A. Brown and
• Jonathan Clayden

Beilstein J. Org. Chem. 2011, 7, 1304–1309, doi:10.3762/bjoc.7.152

• amino acids was used to introduce a 13C label into one of the two enantiotopic methyl groups of 2-aminoisobutyric acid (Aib) by retentive alkylation of L-alanine with 13CH3I. Conditions were identified for optimization of yield and enantiomeric purity, and the absolute configuration of the labelled

• % yield from 3. The 1H spectrum of 6* in CD3OD consisted of a 3H CO2Me singlet at 3.85 ppm, plus two coincident signals centred on 1.47 ppm: A 3H doublet (3JHC = 4.3 Hz) for the unlabelled Me, and a 3H doublet (1JHC = 130 Hz) for the labelled Me. The enantiomeric purity of the products was quantified by

• ratio of diastereoisomeric isotopomers. Portion of 13C NMR spectrum of 8 showing location of 13C label in the less shielded methyl group. Portion of 1H NMR spectrum of 8 showing greater 1JHC coupling in the less shielded methyl group. Alkylation of L-alanine. Determining enantiomeric purity and absolute

Single enantiomer synthesis of α-(trifluoromethyl)-β-lactam

• Václav Jurčík,
• Alexandra M. Z. Slawin and
• David O'Hagan

Beilstein J. Org. Chem. 2011, 7, 759–766, doi:10.3762/bjoc.7.86

• benzylic cleavage. Enantiomeric purity analysis of the resultant β-lactam 1 was evaluated by 19F NMR using a europium chiral shift reagent [Eu(hfc)3]. The comparison of a racemic sample of 1 and then a sample after diastereoisomer separation of 5b as described above, indicated that β-lactam 1 was prepared

Complete transfer of chirality in an intramolecular, thermal [2 + 2] cycloaddition of allene-ynes to form non-racemic spirooxindoles

• Kay M. Brummond and
• Joshua M. Osbourn

Beilstein J. Org. Chem. 2011, 7, 601–605, doi:10.3762/bjoc.7.70

• provided the propargyl acetate 7 in quantitative yield (Scheme 2). The enantiomeric purity of propargyl acetate 7 was determined based on treatment of the compound with the chiral shift reagent (+)-Eu(hfc)3. Figure 1 shows the 1H NMR of the racemic as well as the enantiomerically enriched propargyl acetate

Asymmetric synthesis of tertiary thiols and thioethers

• Jonathan Clayden and
• Paul MacLellan

Beilstein J. Org. Chem. 2011, 7, 582–595, doi:10.3762/bjoc.7.68

• product 6 (Scheme 2). The low yields can be attributed to the formation of β-phenylthioesters 7 by elimination followed by conjugate addition. Even in the presence of the adjacent carbonyl group, competing SN1 dissociation of the benzylic leaving group leads to a loss of enantiomeric purity in some cases

• a variety of thiols to a range of nitroalkenes 49 proceeds to give 50 and hence 51 in good yield and good enantioselectivity (Scheme 19). α-Arylthio-β-amino acid 54 was prepared from Michael adduct 52 in three steps (Scheme 20) in good yield and with full conservation of enantiomeric purity. Palomo

• -butyllithium in diethyl ether and TMEDA at −78 °C for 2.5 hours and quenched with MeOD (Scheme 28). Deuterated thiocarbamate 78 was isolated with an enantiomeric ratio of 72:28, indicating almost full conservation of enantiomeric purity and hence demonstrating that the more congested organolithium 80 is now

Synthesis of chiral mono(N-heterocyclic carbene) palladium and gold complexes with a 1,1'-biphenyl scaffold and their applications in catalysis

• Lian-jun Liu,
• Feijun Wang,
• Wenfeng Wang,
• Mei-xin Zhao and
• Min Shi

Beilstein J. Org. Chem. 2011, 7, 555–564, doi:10.3762/bjoc.7.64

• solution of compound 11 (76.6 mg, 0.20 mmol) in DCM (0.6 mL) was added to the resulting solution and the mixture stirred at rt for 36 h. Column chromatography of the reaction mixture gave the desired product. The enantiomeric purity of the product was determined by chiral HPLC analysis. Monodentate NHCs

Towards racemizable chiral organogelators

• Jian Bin Lin,
• Debarshi Dasgupta,
• Seda Cantekin and
• Albertus P. H. J. Schenning

Beilstein J. Org. Chem. 2010, 6, 960–965, doi:10.3762/bjoc.6.107

• , samples were collected over time and the enantiomeric purity was measured. Racemization was not observed in the gel state (5 mM) after 18 hours, whilst after heating and cooling precipitation was observed. At a concentration of 1 mM, where self-assembled fibers are present, the ee of the solution

Chiral amplification in a cyanobiphenyl nematic liquid crystal doped with helicene-like derivatives

• Alberta Ferrarini,
• Silvia Pieraccini,
• Stefano Masiero and
• Gian Piero Spada

Beilstein J. Org. Chem. 2009, 5, No. 50, doi:10.3762/bjoc.5.50

• and magnitude of the pitch of the cholesteric helix depend on the structure, concentration, and enantiomeric purity of the dopant. Enantiomeric pairs induce oppositely handed cholesteric phases. At low concentration, the helix pitch is inversely proportional to the molar fraction of the dopant; the

Large- scale ruthenium- and enzyme- catalyzed dynamic kinetic resolution of (rac)-1-phenylethanol

• Krisztián Bogár,
• Belén Martín-Matute and
• Jan-E. Bäckvall

Beilstein J. Org. Chem. 2007, 3, No. 50, doi:10.1186/1860-5397-3-50

• mixture afforded enantiopure acetate 3 in 97% yield after 20 h. Careful analysis of the enantiomeric purity of acetate 3 revealed that it was >99.8% ee. This result is remarkable since only a very low catalyst loading is employed and in addition, only 150 mL of toluene as the solvent is used to produce

An asymmetric synthesis of all stereoisomers of piclavines A1-4 using an iterative asymmetric dihydroxylation

• Yukako Saito,
• Naoki Okamoto and
• Hiroki Takahata

Beilstein J. Org. Chem. 2007, 3, No. 37, doi:10.1186/1860-5397-3-37

• -4 with high enantiomeric purity (amplification) for the major diastereomer via iterative AD reaction of terminal olefins. [8] Results Actually we developed a general access to 5-substituted indolizidines 10 (all four stereoisomers of indolizidine 209D) with high enantio-enhancement (92–98% ee) via a

A convenient allylsilane- N-acyliminium route toward indolizidine and quinolizidine alkaloids

• Roland Remuson

Beilstein J. Org. Chem. 2007, 3, No. 32, doi:10.1186/1860-5397-3-32

• conditions led to a 7:3 mixture of the two diastereomeric alkaloids (+)-myrtine and (-)-epimyrtine. These alkaloids were obtained in five steps from (S)-2-(2-hydroxypropyl)allylsilane 32 with an overall yield of 23% and a high enantiomeric purity. This synthesis constitutes the first total synthesis of

• cyclisation of N-acyliminium ion (S)-49. (-)-Lasubine I and (-)-lasubine II were obtained in six steps with overall yields of 7 and 14% respectively. (+)-Subcosine was prepared in seven steps with an overall yield of 9%. These three compounds were obtained with high enantiomeric purity. These results

Chiral trimethylsilylated C₂-symmetrical diamines as phosphorous derivatizing agents for the determination of the enantiomeric excess of chiral alcohols by ¹H NMR

• Anne-Sophie Chauvin and
• Alexandre Alexakis

Beilstein J. Org. Chem. 2006, 2, No. 6, doi:10.1186/1860-5397-2-6

• derivatising agents, prepared from C2 symmetric trimethylsilylated diamines, for the 1H NMR and 31P NMR determination of the enantiomeric composition of chiral alcohols is described. Introduction NMR spectroscopy is one of the most frequently employed methods used for determining the enantiomeric purity of

Stereoselective α-fluoroamide and α-fluoro- γ-lactone synthesis by an asymmetric zwitterionic aza-Claisen rearrangement

• Kenny Tenza,
• Julian S. Northen,
• David O'Hagan and
• Alexandra M. Z. Slawin

Beilstein J. Org. Chem. 2005, 1, No. 13, doi:10.1186/1860-5397-1-13

• reagents, either using asymmetric enolates, [3][4] asymmetric fluorinating reagents[5][6] or asymmetric Lewis acids.[7][8][9] Most recently organocatalysis mediated asymmetric fluorinations have been explored[10] and this has resulted in the efficient preparation of α-fluoroaldehydes in high enantiomeric

• purity.[11] Successes in this area has advanced methodology in organofluorine chemistry considerably over the last decade or so.[1][2] In this paper we explore an alternative approach for the preparation of α-fluorocarbonyls using an asymmetric zwitterionic aza-Claisen rearrangement on appropriate

Synthesis of 2,6-trans- disubstituted 5,6-dihydropyrans from (Z)-1,5-syn-endiols

• Eric M. Flamme and
• William R. Roush

Beilstein J. Org. Chem. 2005, 1, No. 7, doi:10.1186/1860-5397-1-7

• enantiomeric excess of only 25% e.e. while the enantiomeric purity of the starting diol 2a was 91% e.e. This result suggests that the selectivity for displacement of the two hydroxyl groups of 2a is only ca. 2 : 1 under these conditions. Examination of molecular models indicates that in order for the activated