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

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