ALLYLBORATION OF SOME KETONES AND ALDEHYDES WITH 2-ALLYL-1,2-OXABOROLANE - ISOLATION OF THEIR INTERMEDIATE ADDUCTS AND SYNTHESIS OF HOMOALLYLIC ALCOHOLS

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