β-(phosphatoxy)alkyl and β-(acyloxy)alkyl radical migrations studied by laser flash photolysis

A number of beta-(phosphatoxy)alkyl and beta-(acyloxy)alkyl radicals have been generated by laser flash photolysis of the corresponding Barton PTOC esters. Time resolved studies permitted the determination of late constants and kinetic parameters for their rearrangement in benzene, THF, and acetonitrile. Migrations are accelerated by electron-donating groups on the alkyl moiety, electron-withdrawing groups on the migrating group, and more polar solvents. All reactions showed strictly first order kinetics. The results are interpreted in terms of concerted mechanisms occurring through three electron, three center and five electron, five center mechanisms. (C) 1999 Elsevier Science Ltd. All rights reserved.