Configurational and Conformational Effects on Tin−Lithium Exchange in α-Aminoorganostannanes by Rapid-Injection NMR

Abstract

The kinetics of tin−lithium exchange in heterocyclic α-aminoorganostannanes have been studied using 119Sn rapid-injection NMR. By comparison of the observed relative rate constants, the effects of ring size, configuration, and conformation can be discerned. Stannylpyrrolidines transmetalate extremely rapidly, whereas the rate of transmetalation of stannylpiperidines varies from negligible transmetalation to rapid transmetalation. The evidence suggests that only one conformation of N-methyl-2-(tributylstannyl)piperidine transmetalates. N-Boc stannyl piperidines transmetalate at rates that vary somewhat, due in part to conformational effects.