(Alkoxyalkyl)boronic Ester Intermediates for Asymmetric Synthesis

The use of boronic ester chemistry in the construction of synthetic intermediates containing two or three chiral centers corresponding to steric relationships in the macrolide leuconolide has been explored. A four-carbon chain with a substituent at each carbon has been built from each end, and the effects of different chiral directors and masking groups have been compared. Exceptionally facile debenzylation of a benzyloxy group separated by four carbon atoms from a boronic ester function has been observed and may account for the failure of earlier attempts to synthesize sugars via analogous chemistry. A novel method of reducing α-chloro boronic esters to alkylboronic esters with sodium hydride in DMSO has been found.