Studies for the enantiocontrolled preparation of substituted tetrahydropyrans: Applications for the synthesis of leucascandrolide A macrolactone.

Strategies for the stereocontrolled preparations of 2,6-cis-and 2,6-trans-substituted tetrahydropyrans have been devised. These studies have explored methodology for asymmetric induction in SE' reactions using chiral 1,3,2-diazaborolidine controllers. Reactions with aldehydes at -78 °C yield nonracemic 1,5-diols for chemoselective internal backside displacements. This concept is developed as a flexible and reliable strategy in studies toward leucascandrolide A macrolactone 2 via the sequential applications of SE' reactions leading to the C1-C9 aldehyde 14, and the bis-tetrahydropyran 59, respectively.