Chiral synthesis via organoboranes. 35. Simple procedures for the efficient recycling of the terpenyl chiral auxiliaries and convenient isolation of the homoallylic alcohols in asymmetric allyl- and crotylboration of aldehydes

Asymmetric allyl- and crotylboration of aldehydes, RCHO, with terpenyl-based allyl- and crotylborane reagents Ter 2 * BAll (1), Ter 2 * BCrt Z (2), and Ter 2 * BCrt E (3, Ter * =Ipc, 4-Icr and 2-Icr, All=allyl and Crt=crotyl), afford Ter 2 * BOCH * (R)C * ( 1 R)( 2 R)CH=CH 2 intermediates 4