Andreas Onistschenko

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

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⊖.

Reactions with aziridines - 39 : Ring opening of activated 2,2-dimethylaziridines by grignard reagents. A mechanistic study

Abstract Reaction of activated 2,2-dimethylaziridines 1 with Grignard reagents RMgHal in boiling THF can yield the products 2 of normal aziridine ring opening, the rearranged opening products 3 , and the methallylamides 4 (isomers of 1 ). The product distribution depends on R, Hal, and experimental conditions, and very strongly on the nature of the activating group A. It is shown that 1 is opened (reversibly for A = sulfonyl) forming 10 through a Lewis acid assisted attack of Halθ on the tert carbon of 1 (abnormal opening by Halθ ). Evidence is presented to show that 4 as well as 3 come from this intermediate.

Aziridines, 61. Ring Opening of 2,2-Dimethyl-l-sulfonylaziridines by Anilines: Regioselectivity and Revised Structure of Main Products

It is shown (1) that in most reactions of anilines 2 with 1-sulfonyl-2,2-dimethylaziridines 1 both isomeric products 3 and 4 are formed, (2) that the “normal” product 4 obtained by attack on position 3 of 1 usually arises in a small or negligible amount that seems to decrease with decreasing basicity of 2, and (3) that the amount of 4 strongly increases with increasing steric demand of 2. Formation of 4 is explained by a lag of bond making in SN2.