The Stevens rearrangement: an antiaromatic pericyclic reaction?

Abstract

The possibility that the Woodward–Hoffmann rules may break down quite generally for very exothermic reactions is discussed. MINDO/3 Calculations for a pericyclic mechanisms for the Stevens rearrangement support this possibility. Although a concerted mechanism for the Stevens rearrangement is formally ‘forbidden’ according to the Woodward–Hoffmann rules, the calculated activation energy is extremely small (17 kJ mol^–1). The calculated structure of a benzoyl-stabilized nitrogen ylide is reported and the electrostatic energy of the ylide is estimated.