Asymmetric synthesis with the robust and versatile 10-substituted 9-borabicyclo[3.3.2]decanes: Homoallylic amines from aldimines

Abstract

The asymmetric allylboration of N-H aldimines, generated from either N-trimethylsilyl or N-diisobutylalanyl precursors, with B-allyl-9-borabicyclo[3.3.2]decane is described. The desired homoallylic amines are obtained efficiently (60-90 %) and selectively (60-89 % ee). A non-oxidative work-up procedure has also been developed for this new method, which permits the recovery of the air-stable pseudoephedrine (PE) complex (50-70 %), which is conveniently converted back to B-allyl-9-borabicyclo[3.3.2]decane (98 %) with allylmagnesium bromide in ether for its reuse in the asymmetric allylboration process. Additional studies were conducted to better understand these processes and the origin of the observed enantioselectivity.