CHIRAL SYNTHESIS VIA ORGANOBORANES .24. B-ALLYLBIS(2-ISOCARANYL)BORANE AS A SUPERIOR REAGENT FOR THE ASYMMETRIC ALLYLBORATION OF ALDEHYDES

Hydroboration of (+)-2-carene, readily available via the base-induced isomerization of (+)-3-carene, provides bis(2-isocaranyl)borane, which can be readily transformed into B-allylbis(2-isocaranyl)borane (2-dIcr2BAll). This new reagent undergoes asymmetric allylboration with a variety of aldehydes and affords the corresponding homoallylic alcohols in 94-99% ee. The enantioselectivities realized with this reagent are significantly higher than those realized with the previously explored reagents, B-allyldiisopinocampheylborane (dIpc2Ball) and B-allylbis(4-isocaranyl)borane (4-dIcr2BAll). © 1990, American Chemical Society. All rights reserved.