Alan John Collis

Ring expansion of aziridines to piperidines using the aza-wittig rearrangement

Abstract A one-pot, two-step synthesis of unsaturated piperidines from 2-keto aziridines is reported, Treatment of a range of 2-keto aziridines with two equivalents of a phosphonium ylide generates intermediate vinyl aziridines which rearrange by a [2,3]-sigmatropic shift to create a new carbon-carbon bond with concomitant ring opening of the aziridines to give the unsaturated piperidines. This three- to six-membered ring expansion allows the synthesis of N -unsubstituted piperidines and pipecolic acid derivatives.

Synthesis of 4-phenylpiperidines by tandem Wittig olefination–aza-Wittig rearrangement of 2-benzoylaziridines

A number of routes to 2-vinylaziridines are reported. N-Alkylation of a range of 2-benzoyl-3-alkylaziridines with tert-butyl bromoacetate followed by Wittig olefination gave directly a range of 4-phenylpiperidines. The intermediate 2-vinylaziridines rearrange by a [2,3]-aza-Wittig rearrangement to give the 4-phenylpiperidines.