Asymmetric Propargylation with Trimethylsilyl-9-borabicyclo[3.3.2]decanes

Significance

The group of Soderquist recently reported a number of very elegant and versatile synthetic methods, based on the readily available synthetic auxiliary 1. This chiral auxiliary reacts smoothly with allyl, crotyl or allenyl Grignard reagents, giving chiral boron derivatives, which react with carbonyl compounds with almost complete diastereoselectivity. The steric bulk of the TMS group allows the preparation of propargyl Grignard reagents practically without the formation of allenylic impurities. The synthesis of the chiral boron species and further reaction with aldehydes give α-TMS allenyl carbinols with excellent enantioselectivities and yields. The TMS group can be easily cleaved from the products to provide the almost enantiomerically pure parent allenylic alcohols.