Allylboration of some ketones and aldehydes with 2-allyl-1,2-oxaborolane. Isolation of their intermediate adducts and synthesis of homoallylic alcohols

Abstract

2-Allyl-1,2-oxaborolane ( II), prepared by the reaction of 2-allyloxy-1,2-oxaborolane ( I) with allylmagnesium bromide in ether, is an extremely reactive allylborane. This cyclic borinate ester II is a BCCO-type organoborane and can be used as a novel allylborating reagent. As is usual with allylboranes, II can also add smoothly to various ketones or aldehydes, and when followed by deboronation with diethanolamine gives the corresponding homoallylic alcohols IV. The adducts III, formed via a six-centre cyclic mechanism and allylic rearrangement, have been isolated and identified as a kind of 2-alkenoxy-1,2-oxaborolane.