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The influence of buffer type, co‐solvent type, and acyl chain length was investigated for the enantioselective hydrolysis of racemic 4‐arylbut‐3‐en‐2‐yl esters using Lecitase Ultra (LU). Immobilized preparations of the Lecitase Ultra enzyme had

The enantioselective 1,2-reduction of α,β-unsaturated ketones was achieved using a NiH catalyst in the presence of pinacolborane. This mild process represents a general method to access a wide variety of structurally diverse α-chiral allylic alcohols in excellent yields and enantioselectivity, as well as very high levels of ambidoselectivity for 1,2- over 1,4-reduction. Furthermore, for reactions on a 10 mmol scale, catalyst loadings as low as 0.5 mol % could be employed to deliver product without any detrimental effect on the yield, enantio-, or ambidoselectivity.

Resolving the issue: A near-perfect Pd-catalyzed kinetic resolution of 1,3-disubstituted unsymmetrical allylic acetates uses silyl enol ethers as nucleophiles to access the important 3-substituted-furanone scaffold (see scheme; DACH=diaminocyclohexyl, dba=dibenzylideneacetone). The reaction proceeds under mild conditions and provides the desired products with excellent chemo-, regio-, and enantioselectivity. Copyright

A series of vinylchlorohydrins are resolved by enzymatic kinetic resolution. The resulting R-alcohols, obtained in up to 99% ee, are stereoselectively converted into vinyloxiranes in high yield. The S-acetates, obtained in up to 99% ee were either deprotected to S-alcohols, or cyclized directly to vinyl oxiranes under basic conditions, with moderate to no loss in ee. The results are consistent with a racemization mechanism involving reversible migration of the acetate during deprotection. Georg Thieme Verlag Stuttgart.

A new asymmetric transesterification of secondary alcohols catalyzed by feruloyl esterase from Humicola insolens has been found. Although alcohols are not the natural substrates for this enzyme, a high R enantioselectivity was observed. Stereochemical studies showed that variations in substrate structure lead to strong variations in enantioselectivity. The highest enantioselectivities are obtained when the β-carbon of the secondary alcohol is tertiary or quaternary.

Described is the asymmetric synthesis of the allylic alcohols 11 (85% ee), 15 (99% ee), 17 (93% ee), 19 (61% ee), and 21 (69% ee) through a Pd-catalyzed reaction of the unsymmetrical carbonates rac-10, rac-12, rac-14, rac-16, rac-18, and rac-20, respectively, with KHCO3 and H2O in the presence of bisphosphane 6. Similarly the allylic alcohols 23 (99% ee) and 25 (97% ee) have been obtained from the symmetrical carbonates rac-22 and rac-24, respectively. Reaction of the meso-biscarbonate 26 with H2O and Pd(0)/6 afforded alcohol 27 (96% ee), which was converted to the PG building block 32. The unsaturated bisphosphane 33 showed in the synthesis of alcohols 36, 37, and 39 a similar high selectivity as 6. The formation of alcohols 11, 15, and 17 involves an efficient dynamic kinetic resolution.

This report describes a high-throughput method for measuring the enantiomeric excess of allylic acetates. Such methods are useful tools for screening libraries of potential catalysts for enantioselective reactions. This technique, which is called EMDee fo

The RuCl2(η1-Ph2PCH2CH 2OCH3)2(diamine) complexes 2L1-2L5 have been prepared in high yields from the reaction of equimolar amounts of RuCl2(η2-Ph2PCH2CH 2OCH3)2 1 with various kinds of chelating diamines L1-L5 to form five-membered chelates with ruthenium. These novel ruthenium(II) complexes have been used as catalysts in the asymmetric hydrogenation of the prochiral ketone trans-4-phenyl-3-butene-2-one 3, using 2-propanol and different types of cocatalysts. Whereas complexes with achiral diamines afforded the racemic alcohols, complexes with chiral diamines (R,R or S,S) allowed the formation of the corresponding enantiomerically enriched secondary alcohol (S or R) with ee values of 45%. In order to obtain the secondary alcohol with ee of >99%, the kinetic resolution of enantiomerically enriched trans-4-phenyl-3-butene-2-ol 3 was performed in a consecutive approach using either the lipase-catalyzed enantioselective transesterification of the alcohol with isopropenyl acetate as the acyl donor in toluene or the enantioselective hydrolysis of the corresponding acetate in buffer. The determination of the enantiomeric excess (ee) of the resulting enantiomerically enriched secondary alcohols was performed by gas chromatography using heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin as the chiral stationary phase.

The enzymatic kinetic resolution of (RS)-trans-4-phenyl-3-butene-2-ol was investigated by screening a range of lipases both for enantioselective transesterification and for enantioselective hydrolysis of its acetate. The lipase from Pseudomonas cepacia immobilized on diatomaceous earth (PSL-D)-catalyzed asymmetric transesterification was performed on gram scale using isopropenyl acetate as an innocuous acyl donor in organic media affording the (S)-alcohol in high enantiomeric excess (>99% ee) and enantiomeric ratio E >150. The lipase (Candida antarctica B, CAL-B)-catalyzed asymmetric hydrolysis of the racemic acetate was performed on gram scale in phosphate buffer affording the (R)-alcohol in high enantiomeric excess (>99% ee) and enantiomeric ratio E >150. The investigation demonstrates that the transesterification of the racemic alcohol in organic solvent was faster than the hydrolysis of the corresponding acetate in phosphate buffer. A GC method was developed to achieve an effective analytical separation of the enantiomers of both substrate and product in one analysis using the chiral stationary phase heptakis(2,3-di-O-methyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin.

The binuclear Mo(II) and W(II) complexes 28a,b and 29a,b have been developed as pre-catalysts for allylic substitution with β-dicarbonyl nucleophiles. These complexes are reduced in situ to Mo(0) and W(0) catalytic species 30a,b and 31a,b by excess of NaH, employed to generate sodiomalonate nucleophiles, or by DIBAL-H. 1,3-Dioxolane and 1,4-dioxane, when used as solvents, substantially accelerate the reaction. These new catalysts exhibit "traditional" Mo regiochemistry, i.e., the nucleophilic attack occurring preferentially at the more substituted carbon (5 → 9; 37 → 38), unless an additional factor, such as further coordination to another moiety of the allylic electrophile takes part (41), as in the case of the geranyl-type substrates (32 or 33 → 36).

A planar-chiral DMAP derivative is shown to serve as an effective catalyst for the kinetic resolution of allylic alcohols; to illustrate its practical utility, the catalyst is applied to the resolution of two alcohols that have been employed as intermedia