Photoinduced electron-transfer reaction of α-bromomethyl-substituted benzocyclic β-keto esters with amines: selective reaction pathways depending on the nature of the amine radical cations

Photoinduced electron-transfer reaction of alpha-bromomethyl-substituted benzocyclic beta-keto esters with tertiary amines was investigated. Debrominated beta-keto esters and ring-expanded gamma-keto esters were obtained as major products. On the basis of mechanistic experiments it was concluded that these products are formed via a reaction sequence of selective carbon-bromine bond cleavage and subsequent competitive hydrogen abstraction and Dowd-Beckwith ring-expansion of the resulting primary alkyl radicals. The characteristic product distribution observed for the type of amine used is rationalized on the basis of selective reaction pathways of generated radical intermediates that depend on the nature of the amine radical cations.