Nonracemic -Lactones from the Sharpless Asymmetric Dihydroxylation of ,-Unsaturated Carboxylic Esters

Since Sharpless' discovery of the asymmetric dihydroxylation of C=C double bonds in the late 1980s this reaction has become a powerful tool of synthetic organic chemistry. As a consequence, this transformation has been reviewed repeatedly and extensively. The present microreview focuses on Sharpless' asymmetric dihydroxylations (from here on SADs) of ,-unsaturated carboxylic esters. These SADs differ from most others in that they provide not nonracemic 1,2-diols but follow-up products thereof. Bearing ester groups at appropriate distances, the SAD-based 1,2-diols obtained from ,-unsaturated carboxylic esters lactonize readily under SAD conditions. Accordingly, SADs of ,-unsaturated carboxylic esters furnish nonracemic -hydroxy--lactones in a single operation. We show that this SAD route represents a - or even the most - potent easy-to-handle route to nonracemic butanolides and butenolides of almost all kinds. The span covered is from pioneering racemic work to applications in natural product synthesis. Some non-butanolide and non-butenolide target syntheses are included, especially those of tetrahydrofurans.