Carbanion rearrangements. Collision-induced dissociations of enolate ions derived from 3-ethylpentan-2-one

Abstract

Reaction of HO^– with MeCOCHEt₂ produces two enolate ions, MeCOEt₂ and ^–CH₂COCHEt₂. The primary carbanion competitively eliminates C₂H₄ and C₄H₈, and forms C₂HO^–. The elimination of C₂H₄ is a stepwise reaction proceeding through a six-membered transition state; the first step (deprotonation) is rate-determining. The loss of C₄H₈ is a rearrangement reaction ^–CH₂COCHEt₂ [graphic omitted] ^–CH₂COMe + EtCHCH₂. The tertiary carbanion competitively eliminates H₂, CH₄, and C₃H₈. The losses of CH₄ and C₃H₈ are stepwise processes occurring through six- and five-membered transition states, respectively. A double isotope fractionation experiment (²H, ¹³C) shows that both steps of the CH₄ elimination are rate-determining.