A Route to 2‐Alkenyl‐3‐(tert‐butyldiphenylsilyl)amines and Application to the Construction of a Tricyclic Ring System

N-Tosyl 3,3-dialkyl-2-(tert-butyldiphenylsilylmethyl)azetidines rearrange smoothly into the corresponding 2-alkenyl-3-(tert-butyldiphenylsilyl)amines upon exposure to BF3·OEt2 in CH2Cl2. The reaction involves sequential σC–N bond cleavage, 1,2-migration of the N-tosyl-aminomethyl group, and deprotonation of the resultant tert-carbenium ions. For the instance in which the carbenium ion formed from migration of the N-tosyl-aminomethyl group is highly stable by virtue of being, for example, tertiary as well as benzylic, the migration takes place in sync with σC–N bond cleavage, which leads to high configurational control at the tert-butyldiphenylsilylmethyl-bearing carbon atom in the product.