A GENERAL, EFFICIENT, CONVENIENT SYNTHESIS OF CHIRAL BIS(TERPENYL)HALOBORANE REAGENTS, VALUABLE FOR ASYMMETRIC-SYNTHESIS VIA ORGANOBORANES

The chiral, sterically-varied bis(terpenyl)haloboranes (Ter(2)BX; X = Cl, Br, and I), potentially important reagents for asymmetric synthesi s, are conveniently prepared in essentially quantitative yield by the in situ tandem reduction-hydroboration under mild conditions of boron trihalide, trialkylsilane, and representative terpenes (Ter). Use of e thyl ether (EE) as solvent accelerates the formation of the sterically bulkier Ter(2)BCl derivatives. Typically the reaction is over in less than 2 h in comparison with the literature procedure requiring 36 h a t room temperature. Copyright (C) 1996 Published by Elsevier Science L td