Acylated 2,2-dimethylaziridines: regioselectivity of ring opening by sodium thiophenolate; borderline SN2 due to planarization of nitrogen pyramid

Pen yuan Lin, Konstantinos Bellos, Helmut Stamm, Andreas Onistschenko

Research output: Contribution to journalArticle

38 Citations (Scopus)

Abstract

2,2-Dimethylaziridines 1 carrying a COR group on nitrogen are opened by PhS⊖ with a regioselectivity RS = abnormal:normal ≥ 20 in MeOH and 5-16 in THF. Practically no influence of COR on RS was found except for the poorest oxidant 1g (R = tBu) that gave the highest RS (95, MeOH). This rules out an SET mechanism for the abnormal opening. Absence of homolytic ring opening is directly shown by the failure to detect products resulting from cyclization of a homolytically formed radical when COR is cinnamoyl (1f). Direct nucleophilic attack is indicated by suppression of any reaction with PhS⊖ when the steric hindrance is increased (N-benzoylaziridine 13). The observed SN2 borderline behaviour with 1 is explained by reaction in a flattened nitrogen conformation of the otherwise poorly reactive 1. Carboxamide resonance in this (nearly) planar conformation generates a substantial positive charge on N which will shift the mechanism closer to SN1 by partial heterolysis of the N-CMe2 bond prior to attack by PhS⊖.

Original languageEnglish
Pages (from-to)2359-2372
Number of pages14
JournalTetrahedron
Volume48
Issue number12
DOIs
Publication statusPublished - Mar 20 1992
Externally publishedYes

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Keywords

  • aziridines
  • leaving group quality of N-acylaziridines
  • nucleophilic attack
  • planation of N pyramid.
  • preferred abnormal opening

ASJC Scopus subject areas

  • Biochemistry
  • Organic Chemistry
  • Drug Discovery

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