Strict reagent control in the asymmetric allylboration of N-TIPS-alpha-amino aldehydes with the B-allyl-10-TMS-9-borabicyclo[3.3.2]decanes

Abstract

The allylboration of enantiomerically pure N-triisopropylsilyl-alpha-amino aldehydes (2) with B-allyl-10-trimethylsilyl-9-borabicyclo[3.3.2]decanes (1) proceeds cleanly at -78 degrees C, exhibiting essentially complete reagent control. After an oxidative workup, an HOAc-mediated N-->O TIPS rearrangement facilitates the clean formation of stable O-TIPS protected beta-amino alcohol derivatives 3 which are isolated in 60-83% yields in > or = 96% de and > 99% ee. For the leucinal series (R = i-Bu), an efficient entry to either statine (8aSS) or epi-statine (8aRS) is reported illustrating the versatility of this potent 1/2 combination.