Inter- and intramolecular pathways for the formation of tetrahydrofurans from β-(phosphatoxy)alkyl radicals. Evidence for a dissociative mechanism

Article abstract of DOI:10.1021/jo991570o

β-(Phosphatoxy)alkyl radicals generated by photolysis of Barton PTOC esters in the presence of allyl alcohol and tert-butyl mercaptan undergo nucleophilic substitution followed by 5-exo-trig radical ring closure leading to tetrahydrofurans in good yield and with high trans selectivity. β- (Phosphatoxy)alkyl radicals obtained by intramolecular hydrogen 1,5- abstraction with an alkoxyl radical undergo nucleophilic displacement providing tetrahydrofurans. The ensemble of results, including the effects of leaving groups and substituents, strongly support a dissociative mechanism for these radical nucleophilic displacement reactions.