Chemoenzymatic synthesis and biological evaluation of enantiomerically enriched 1-(β-hydroxypropyl)imidazolium- and triazolium-based ionic liquids

• Paweł Borowiecki,
• Małgorzata Milner-Krawczyk and
• Jan Plenkiewicz

Beilstein J. Org. Chem. 2013, 9, 516–525, doi:10.3762/bjoc.9.56

• derivatives 9a and 10a. Comparison of the 1H NMR spectra of these two species for this particular alcohol (+)-5a shows that the phenyl ring of the chiral auxiliary reagent projects its magnetic anisotropy strongly toward the H(2’) proton in the (S)-derivative 9a, while the same proton in the (R)-MPA ester 10a

• correlation of MPA esters 9a, 9b and 10a, 10b. The 1H NMR spectra of the derivatives of two unreacted chiral alcohols (+)-5a (top) and (+)-5b (bottom). Symbols marked in green represent protons shielded by the phenyl ring of chiral auxiliary (MPA); blue labels stand for unaffected protons. Synthesis of

Asymmetric Diels–Alder reaction with >C=P– functionality of the 2-phosphaindolizine-η¹-P-aluminium(O-menthoxy) dichloride complex: experimental and theoretical results

• Rajendra K. Jangid,
• Nidhi Sogani,
• Neelima Gupta,
• Raj K. Bansal,
• Moritz von Hopffgarten and
• Gernot Frenking

Beilstein J. Org. Chem. 2013, 9, 392–400, doi:10.3762/bjoc.9.40

• theoretically the mode of action of the chiral auxiliary in directing the complete diastereoselectivity of the DA reactions. The following model DA reactions (Scheme 5) were calculated at the DFT (B3LYP/6-31+G*) level. Computational calculations It has been reported that for determining activation free energies

One-pot tandem cyclization of enantiopure asymmetric cis-2,5-disubstituted pyrrolidines: Facile access to chiral 10-heteroazatriquinanes

• Ping-An Wang,
• Sheng-Yong Zhang and
• Henri B. Kagan

Beilstein J. Org. Chem. 2013, 9, 265–269, doi:10.3762/bjoc.9.32

• , especially for one chiral nitrogen center and one chiral boron center. The configurations of the stereogenic centers in 5a are deduced from the configuration of the chiral auxiliary (S)-(−)-1-phenylethylamine to be S, 3S, 6R, 9S (chiral B atom) and 10R (chiral N atom), respectively. This novel tandem

The multicomponent approach to N-methyl peptides: total synthesis of antibacterial (–)-viridic acid and analogues

• Ricardo A. W. Neves Filho,
• Sebastian Stark,
• Bernhard Westermann and
• Ludger A. Wessjohann

Beilstein J. Org. Chem. 2012, 8, 2085–2090, doi:10.3762/bjoc.8.234

• properties (Scheme 3) [13]. Since the MCR results in racemates, we decided to investigate the applicability of a chiral auxiliary MCR approach for the asymmetric synthesis of viridic acid (1). The Ugi-4CR is not specifically prone to asymmetric induction, but at least some auxiliaries are known to result in

trans-2-(2,5-Dimethoxy-4-iodophenyl)cyclopropylamine and trans-2-(2,5-dimethoxy-4-bromophenyl)cyclopropylamine as potent agonists for the 5-HT₂ receptor family

• Adam Pigott,
• Stewart Frescas,
• John D. McCorvy,
• Xi-Ping Huang,
• Bryan L. Roth and
• David E. Nichols

Beilstein J. Org. Chem. 2012, 8, 1705–1709, doi:10.3762/bjoc.8.194

• would also need to be mindful that their selectivity for 5-HT2A over 5-HT1A is only about 70-fold. The most efficient approach appears to be the synthesis of the chiral cyclopropane carboxylic acids, followed by derivatization at the 4-position. This approach would be most appealing if a chiral

• auxiliary was used in the cyclopropanation step [8]. We also note that compound 4 was less stable than 5 under recrystallization conditions, an instability we did not observe during our earlier work with 3. We have observed even greater instability in 2-(indol-3-yl)cyclopropylamines [8][9], suggesting that

Synthesis and structure of tricarbonyl(η⁶-arene)chromium complexes of phenyl and benzyl D-glycopyranosides

• Thomas Ziegler and
• Ulrich Heber

Beilstein J. Org. Chem. 2012, 8, 1059–1070, doi:10.3762/bjoc.8.118

• carbohydrate-derived chromium complexes that have been described in the literature so far. Complexes of type A and B were obtained from the corresponding glycopyranosides and were studied as substrates for chiral-auxiliary-directed asymmetric ortholithiation and as catalysts for enantioselective Diels–Alder

Carbohydrate-auxiliary assisted preparation of enantiopure 1,2-oxazine derivatives and aminopolyols

• Marcin Jasiński,
• Dieter Lentz and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2012, 8, 662–674, doi:10.3762/bjoc.8.74

• known protocols employing terpene units [62] and carbohydrate-derived auxiliaries [63][64] for the asymmetric synthesis of the 1,2-oxazine derivatives. More recently, the use of (–)-menthol as a chiral auxiliary was presented for the separation of diastereomeric 6H-1,2-oxazines [65][66]. Subsequent

Development of the titanium–TADDOLate-catalyzed asymmetric fluorination of β-ketoesters

• Lukas Hintermann,
• Mauro Perseghini and
• Antonio Togni

Beilstein J. Org. Chem. 2011, 7, 1421–1435, doi:10.3762/bjoc.7.166

• experienced by synthetic chemists in their struggle to prepare a desired fluoroorganic target [18]. A major synthetic challenge of fluoroorganic chemistry is the enantioselective generation of fluorinated stereogenic carbon centers [2][19][20]. Initially, chiral auxiliary approaches and diastereoselective

Efficient syntheses of 25,26-dihydrodictyostatin and 25,26-dihydro-6-epi-dictyostatin, two potent new microtubule-stabilizing agents

• María Jiménez,
• Wei Zhu,
• Andreas Vogt,
• Billy W. Day and
• Dennis P. Curran

Beilstein J. Org. Chem. 2011, 7, 1372–1378, doi:10.3762/bjoc.7.161

• amide 10 and alkyl iodide 11 afforded amide 12 in 95% yield. The chiral auxiliary was then removed with BH3·NH3 (92%) [34], then the resulting primary alcohol was oxidized under Swern conditions to provide aldehyde 13 (86%). A Marshall palladium-catalyzed addition reaction [35] between aldehyde 13 and

A practical route to tertiary diarylmethylamides or -carbamates from imines, organozinc reagents and acyl chlorides or chloroformates

• Erwan Le Gall,
• Antoine Pignon and
• Thierry Martens

Beilstein J. Org. Chem. 2011, 7, 997–1002, doi:10.3762/bjoc.7.112

• stereogenic center would be located very close to the impending asymmetric carbon and may thus serve as a valuable chiral auxiliary. Consequently, we envisage the implementation a further study which would be dedicated to the evaluation of well-recognized chiral inductors such as Ellman- [40][41] or Davis

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

• steroidal systems [38][39] and intermolecular addition directed by substrate stereochemistry [40][41] or a chiral auxiliary [42][43]. Despite these examples, there are very few general procedures for the preparation of chiral tertiary thiols and thioethers by this method. This may be attributed to three

Effects of anion complexation on the photoreactivity of bisureido- and bisthioureido-substituted dibenzobarrelene derivatives

• Heiko Ihmels and
• Jia Luo

Beilstein J. Org. Chem. 2011, 7, 278–289, doi:10.3762/bjoc.7.37

• . For example, the achiral derivative 1b crystallizes in the chiral space group P212121, and irradiation of the chiral crystals gives dibenzosemibullvalene 2b with a high enantiomeric excess, >95% ee [33]. Since achiral molecules crystallize only very rarely in chiral space groups, the ionic chiral

• auxiliary strategy was developed by Scheffer et al. which allows to influence the stereoselectivity of solid-state photoreactions by chiral counter ions [34]. This is accomplished by providing the chromophore under investigation with a carboxylic acid functionality and then by attaching a chiral

Benzyne arylation of oxathiane glycosyl donors

• Martin A. Fascione and
• W. Bruce Turnbull

Beilstein J. Org. Chem. 2010, 6, No. 19, doi:10.3762/bjoc.6.19

• reported an elegant chiral auxiliary-based glycosylation protocol for the synthesis of 1,2-cis-α-glycosides [12]. Completely stereoselective glycosylation was achieved when a thiophenyl-containing chiral auxiliary was attached to O-2 of an imidate glycosyl donor 1 (Scheme 1a). Low temperature 1H NMR

• utilising the inherent chirality of the sugar to determine the stereochemistry of the key benzylic centre in the chiral auxiliary, and also facilitates regioselective attachment of the auxiliary group to O-2. The benzylated oxathiane ether 18 also afforded a glycosyl acetate 25 in 57% yield but on this

• of novel oxathiane glycosyl donors can be achieved using a combination of 1-ABT and lead tetraacetate. Following arylation, glycosylation with an acetate anion takes place with a high degree of stereoselectivity to afford 1,2-cis-α-acetates. a) Boons’ chiral auxiliary-based approach to α

Recent progress on the total synthesis of acetogenins from Annonaceae

• Nianguang Li,
• Zhihao Shi,
• Yuping Tang,
• Jianwei Chen and
• Xiang Li

Beilstein J. Org. Chem. 2008, 4, No. 48, doi:10.3762/bjoc.4.48

The role of an aromatic group in remote chiral induction during conjugate addition of α-sulfonylallylic carbanions to ethyl crotonate

• Shlomo Levinger,
• Ranjeet Nair and
• Alfred Hassner

Beilstein J. Org. Chem. 2008, 4, No. 32, doi:10.3762/bjoc.4.32

• -(phenylsulfonyl)allylic carbanions bearing a chiral auxiliary [1]. Transmission of asymmetry, though four atoms removed, was striking and was found to depend on the presence of an aromatic nucleus bound to the stereogenic center attached to N in 1. Thus, addition to crotonate 2 of the lithio derivative of amino

Synthesis of new triazole- based trifluoromethyl scaffolds

• Michela Martinelli,
• Thierry Milcent,
• Sandrine Ongeri and
• Benoit Crousse

Beilstein J. Org. Chem. 2008, 4, No. 19, doi:10.3762/bjoc.4.19

• applied our strategy to the enantiopure trifluoromethyl-propargylamine 3 bearing the removable (R)-phenylglycinol chiral auxiliary (Scheme 2) [30][31][32]. The reaction was carried out under the same condition with azidoacetic acid methyl ester and afforded the cycloadduct 4 in good yield (79%) and as a

Stereoselective synthesis of (2S,3S,4Z)-4-fluoro- 1,3-dihydroxy- 2-(octadecanoylamino)octadec- 4-ene, [(Z)-4-fluoroceramide], and its phase behavior at the air/water interface

• Gergana S. Nikolova and
• Günter Haufe

Beilstein J. Org. Chem. 2008, 4, No. 12, doi:10.3762/bjoc.4.12

• configuration (2S,3S) of the products is controlled by the chiral auxiliary. In recent years several studies on cell membrane lipid models suggested that ceramide could act indirectly as a messenger by modulation of membrane properties. The membrane lipids (mostly sphingomyelin) together with cholesterol are

The use of chiral lithium amides in the desymmetrisation of N-trialkylsilyl dimethyl sulfoximines

• Matthew J. McGrath and
• Carsten Bolm

Beilstein J. Org. Chem. 2007, 3, No. 33, doi:10.1186/1860-5397-3-33

• enantioenriched S-chiral sulfoximines but both methods lack generality due to the limited availability of the appropriate chiral sulfoxides and the limited scope for cleavage of the chiral auxiliary in the latter process. [6][7][8][9][10][11][12][13][14][15] Selective substitution of one of the enantiotopic

Asymmetric aza-Diels- Alder reaction of Danishefsky's diene with imines in a chiral reaction medium

• Bruce Pégot,
• Olivier Nguyen Van Buu,
• Didier Gori and
• Giang Vo-Thanh

Beilstein J. Org. Chem. 2006, 2, No. 18, doi:10.1186/1860-5397-2-18

• )-(-)-methylbenzylamine chiral auxiliary. However, all reactions had to be performed in an organic solvent under an inert atmosphere and required stoichiometric loadings of Lewis acid promoter, the use of which is not recommended under 'green chemistry' conditions. Having established the high efficiency of chiral ILs is

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

• rearrangement (S)-2(methoxymethyl)pyrrolidine 22 was then explored as the chiral auxiliary.[25] This auxiliary was selected to include a co-ordinating oxygen in place of the bulky diphenylmethane group in 14 to compare steric versus co-ordination effects. Allylation then gave 23 as the required aza-Claisen

Methods for the synthesis of polyhydroxylated piperidines by diastereoselective dihydroxylation: Exploitation in the two-directional synthesis of aza-C-linked disaccharide derivatives

• Andrew Kennedy,
• Adam Nelson and
• Alexis Perry

Beilstein J. Org. Chem. 2005, 1, No. 2, doi:10.1186/1860-5397-1-2

• chiral auxiliary. The source of the asymmetry means that the approach would be amenable to the synthesis of the enantiomeric aza-C-linked disaccharide derivatives. A key feature of the approach was the potential to switch between one- and two-directional synthetic steps, allowing the selective