Diastereoselective synthesis of chiral α-aminoorganotributyltins via ring-opening of 2-tributylstannyloxazolidines

Reactions of 2-tributylstannyloxazolidines 2a-d (cis or trans), derived from (R)-phenylglycinol protected as N-carbamate, with lithium diorganocuprates in presence of boron trifluoride in diethyl ether provide the corresponding functionalized tributylstannyl-β-aminoalcohols 3-10 with diastereoselectivities close to 85:15 in favour of the (S,R)-isomer. The stereochemical trend is preserved using allyltributyltin as nucleophile and TiCl2(Oi-Pr)2 as Lewis acid in dichloromethane. The assignments of the (S,R) or (R,R) configurations in 3-10 were achieved on the basis of physicochemical data combined with a radiocrystallographic structure. Stereochemical preferences were rationalized by consideration of the interactions occurring in the iminium intermediates.