N- to C-sulfonyl photoisomerisation of dihydropyridinones: a synthetic and mechanistic study

Abstract

The scope and limitations of a photoinitiated N- to C-sulfonyl migration process within a range of dihydropyridinones is assessed. This sulfonyl transfer proceeds without erosion of either diastereo- or enantiocontrol, and is general across a range of N-sulfonyl substituents (SO₂R; R = Ph, 4-MeC₆H₄, 4-MeOC₆H₄, 4-NO₂C₆H₄, Me, Et) as well as C(3)-(aryl, heteroaryl, alkyl and alkenyl) and C(4)-(aryl and ester) substitution. Crossover reactions indicate an intermolecular step is operative within the formal migration process, although no crossover from C-sulfonyl products was observed. EPR studies indicate the intermediacy of a sulfonyl radical and a mechanism is proposed based upon these observations.