Asymmetric Homologation of Cedranediol Boronic Esters and X-Ray Structure of Cedranediol 1-Chloro-1- Phenylmetylboronate

Abstract

Homologation of cedranediol boronic esters 1, RBO,C₁₅H,_4l with (dichloromethyl)lithium resulted in the formation of (αR)-α-chloro boronic esters 3, RCHCIBO₂C₁₅H₂₄, consistently yielding (R)/(S)ratios over 25:1. The absolute configuration of cedranediol (R)-1-chloro-1-phenylmethylboronate 3dR 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 the cedranediol boronic esters are prone to hydrolysis has been discussed.