A computational study of anionic alkoxide–allene and amide–allene cyclizations

Abstract

Computational studies have been performed on potassium alkoxide-allenes, as well as potassium and lithium amido-allenes to probe the mechanism of their cyclizations to dihydrofurans and to 2,5-dihydropyrroles. A long-standing proposal envisaged electron transfer from dimsyl anions (formed by deprotonation of the solvent DMSO) but this pathway shows an exceptionally high kinetic barrier, while direct 5-endo-trig cyclization of the alkoxides and amides is much more easily achievable. The energy profiles for 4-exo-trig cyclizations onto the allenes are also explored, and the preferred formation of the observed five-membered products is rationalized