Reduction of Functionalized Carbonyl and Dicarbonyl Compounds

When a-heterocyclic substituted ketones have been subjected to yeast-mediated reductions, yields and enantiospecificity were low for 2-acylthiazoles [149], ketoisox-azoles [160], and 5-acetyl-2-isoxazolines [161]. 

The reduction of aromatic nitro compounds has been performed as early as 1914 by A. Neuberg [162,163] and is well documented [17,96,164], but there seems to be no example for the reduction of an aliphatic nitro group this functional group was stable during the reduction of carbonyl groups, with an exception of those nitro 

Several of these products [189-191] have been prepared and used for the total synthesis of natural products [185-187]. The formation of by-products was observed quite often during these reductions. This might be due to the slow rates of the reaction. Hence, the addition of activators has been suggested [191]. These activators (most often a,p-imsaturated alcohols, ketones, or nitriles) seem to act as suicide substrates for several oxidoreductases [192, 193], whereas, for the reduction of cyclopentanoid 1,3-diketones, stereoselectivity was high, and most often [194] low selectivity was observed for cyclohexanoid 1,3-diketones [184, 194-197]. 

High recovery yield was observed, however, for the reduction of cyclic 1,3-diketones being part of a medium-sized ring [198]. Low yields and fair to moderate ee and de values have been obtained for the reduction of cyclic 1,4-diketones or quinones [199-203]. 

Better results were obtained for the reduction of acyclic diketones acyclic 1,2-diketones are excellent substrates for baker s yeast. The selectivity, however, is often rather low [121,179, 204-207]. An effective way to improve stereoselectivity of the reduction process was the introduction of a sterically demanding sulfur-containing group [208,209]. 

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