Alkenes Bakers yeast reduction

Very few enzyme-catalysed reactions involving the reduction of alkenes have achieved any degree of recognition in synthetic organic chemistry. Indeed the only transformation of note involves the reduction of a, (3-unsaturated aldehydes and ketones. For example, bakers yeast reduction of (Z)-2-bromo-3-phenylprop-2-enal yields (S)-2-bromo-3-phenylpropanol in practically quantitative yield (99 % ee) when a resin is employed to control substrate concen-tration[50]. Similarly (Z)-3-bromo-4-phenylbut-3-en-2-one yields 2(5), 3(,S)-3-bromo-4-phenylbutan-2-ol (80% yield, >95% ee)[51]. Carbon-carbon double bond reductases can be isolated one such enzyme from bakers yeast catalyses the reduction of enones of the type Ar—CH = C(CH3)—COCH3 to the corresponding (S)-ketones in almost quantitative yields and very high enantiomeric excesses[52]. 

Mele, A., Sarra, A., Allegrone, G., and Barbeni, M. (1993) On the mode of baker s yeast reduction of C-7-C-10 2-alken-4-olides. Tetrahedron Lett., 34, 6467-6470. 

COOH or NHCOCH3, for example, 2-phenyl-l-butene. Enantioselective reduction of certain alkenes has also been achieved by reducing with baker s yeast. Hydrogenation with Ni2B on borohydride exchange resin (BER) has also been... 

Scheme 13.17 depicts a synthesis based on enantioselective reduction of bicyclo[2.2.2]octane-2,6-dione by Baker s yeast.21 This is an example of desym-metrization (see Part A, Topic 2.2). The unreduced carbonyl group was converted to an alkene by the Shapiro reaction. The alcohol was then reoxidized to a ketone. The enantiomerically pure intermediate was converted to the lactone by Baeyer-Villiger oxidation and an allylic rearrangement. The methyl group was introduced stereoselec-tively from the exo face of the bicyclic lactone by an enolate alkylation in Step C-l. 

Reduction of 1-nitro-1-alkenes with fermenting Baker s yeast proceeds enantioselectively to give optically active nitroalkanes (Eq. 3.53).81... 

A short enantioselective synthesis of (-)-(R,R)-pyrenophorin, a naturally occurring anti-fun-gal 16-membered macrolide dilactone, is prepared from (S)-5-nitropentan-2-ol via the Michael addition and Nef reaction (Scheme 4.23).162 The choice of base is important to get the E-alkene in the Michael addition, for other bases give a mixture of E and Z-alkenes. The requisite chiral (S)-5-nitropentan-2-ol is prepared by enantioselective reduction of 5-nitropentan-2-one with baker s yeast.163... 

Enantioselective reduction of certain alkenes has also been achieved by reducing with baker s yeast. ... 

Saceharomyces cerevisiae (baker s yeast) is able to reduce the carbon - carbon double bonds to a,/S-unsaturated primary alcohols and aldehydes (see Section 2.5.1.3.1.2.), to a,/ -unsaturated ketones (see Section 2.5.1.3.1.3.) and to unsaturated a-keto acids (see Section 2.5.1.3.1.4.). On the other hand, only a few examples are known for the reduction of alkenic compounds that are substituted differently. 

The asymmetric reduction of (Z)-3-chloro-3-alken-2-ones with baker s yeast to give the corresponding a-chloroketones and further reduction to the chlorohydrins is shown in the following diagram54. 

The reduction of carbon-carbon double bonds to single bonds has been studied with various substrates. For example, Ohta et al. demonstrated that the reduction of a number of 1-nitro-l-alkenes by fermenting baker s yeast was enantioselective, resulting in the formation of optically active 1-nitroalkanes as shown in Fig. 10.13(a).On the other hand, Fuganti et al. reduced a,/3-unsaturated y-lactones to produce enantiomerically pure (-1-)-(J )-goniothalamin (Fig. 10.13(b)), which shows central nervous system activity. They also performed the kinetic resolution of the corresponding embryotoxic epoxide with yeast. 8... 

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