Preparation and homologation of Cedranediol boronic esters

(-)-Cedranediol boronic esters 3, a series of asymmetric homologation reage nts were prepared from a new chiral director (-)-cedranediol 1 and boronic acids. 1 was easily synthesized by the dihydroxylation of ( -)-alpha-cedren e 2 with OsO4. Homologation of cedranediol boronic esters 3 with (dichlorom ethyl) lithium resulted in (R)-alpha-chloro boronic esters 4, with R/S-rati os over 25:1. It is easy to recover cedranediol for its boronic esters pron e to rapid hydrolysis. The absolute configuration of cedranediol (R)-1-chlo ro-2-phenylethylboronate 4cR was determined by X-ray diffraction, The disto rtion of the five-membered 1,3,2-dioxaborolane ring of 4cR tvas found and d iscussed.