The aza-[2,3]-Wittig sigmatropic rearrangement of acyclic amines: Scope and limitations of silicon assistance

The inclusion of a C-2 trialkylsilyl substituent into allylic amine precurs ors allows the base-induced aza-[2,3]-Wittig sigmatropic rearrangement to p roceed in-excellent yield and diastereoselectivity. The rearrangement precu rsors require a carbonyl-based nitrogen protecting group that must be stabl e to the excess of strong base required for the reaction. The N-Boc and N-b enzoyl group are very good at stabilizing-the product anion and initiating deprotonation. The migrating groups (G) need to stabilize the intial anion by resonance and require G-CH3 pK(a) > 22 in order for the initial anion to be reactive enough for rearrangement. Products 7, 20b-d,f,g, and 23 are fo rmed with high (10-20:1) anti diastereoselectivity. Product 23 containing t he morpholine amide group is useful for preparing other carbonyl derivative s.