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 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. beta-(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.
Crich
D
Department of Chemistry, University of Illinois at Chicago, 845 West Taylor Street, Chicago, Illinois 60607, and Department of Chemistry, Wayne State University, Detroit, Michigan 48202, USA.
Huang
X
Newcomb
M