Sodium borohydride cyclic acid anhydrides

Reduction of cyclic anhydrides. Although acid anhydrides are reduced to only a slight extent by sodium borohydride, cyclic anhydrides are reduced to 8- and y-lactones in 51-97% yield. Hydride attack occurs principally at the carbonyl group adjacent to the more highly substituted carbon atom.7... 

Dihydroxypyrrolidinones, which can be considered as cyclic GABA derivatives, are potential nootropic drug candidates. All four possible diastereomers 794—797, as shown in Scheme 174, can be prepared from tartaric acid. Treating L-tartaric acid sequentially with acetyl chloride, methyl glycinate, and then acetyl chloride provides in 81% overall yield the C2-symmetric succinimide 790. In order not to reduce the methyl ester, the very mild treatment with sodium borohydride at —40 °C is employed to prepare the cw-hydroxylactam 791 in an 80% isolated yield. Esterification of 791 with trifiuoroacetic anhydride followed by triethylsilane reduction yields to the extent of 79% the pyrrolidinone 792. This is deprotected with sodium methoxide to provide in 97% yield (3i ,45)-3,4-dihydroxy-A -methoxy-carbonylmethyl-2-pyrrolidinone (793). Ammonolysis of 793 affords (3i ,4 S)-3,4-dihydroxy-2-oxopyrrolidine-A -acetamide (794) in 60% yield. Subsequent modifications to 793 allow for the preparation of (35, 4S)-3,4-dihydroxy-2-oxopyrrolidine-A/-acetamide (795), (3R,4R)-3,4-dihydroxy-2-oxopyrrolidine-A -acetamide (796) and (35, 47 )-3,4-dihydroxy-2-oxopyrrolidine-7V-acetamide (797) [234]. 

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