Asymmetric homologation of cedranediol boronic esters and X-ray structure of cedranediol 1-chloro-1-phenylmethylboronate

Homologation of cedranediol boronic esters 1, RBO2C15H24, with (dichloromet hyl)lithium resulted in the formation of (alpha R)-alpha-chloro boronic est ers 3, RCHClBO2C15H24, consistently yielding (R)/(S)-ratios over 25:1. The absolute configuration of cedranediol (R)-1-chloro-1-phenylmethylboronare 3 dR was determined by X-ray diffraction. The distortion of the five-membered 1,3,2-dioxaborolane ring of 3dR from planarity was found. The reason why t he cedranediol boronic esters are prone to hydrolysis has been discussed.