ACYL RADICALS - INTERMOLECULAR AND INTRAMOLECULAR ALKENE ADDITION-REACTIONS

A full study of the use of phenyl selenoesters as precursors to acyl radicals and their subsequent participation in intermolecular and intramolecular alkene addition reactions is detailed. Primary alkyl-, vinyl-, and aryl-substituted acyl radicals generated by Bu3SnH treatment of the corresponding phenyl selenoesters participate cleanly in intermolecular addition reactions with alkenes bearing electron-withdrawing or radical-stabilizing substituents at rates that exceed those of the potentially competitive decarbonylation or reduction. Similarly, their intramolecular addition to activated or unactivated alkenes proceeds without significant competitive reduction or decarbonylation and at rates generally greater-than-or-equal-to 1 x 10(6) s-1 with some occurring at rates greater-than-or-equal-to 3 x 10(7) s-1. Consistent with their behavior in intermolecular addition reactions, the 5-exo-trig cyclizations of secondary and tertiary alkyl-substituted acyl radicals to an unactivated olefin acceptor may be accompanied by varying degrees of decarbonylation, even under low-temperature free-radical reaction conditions. Studies are presented which suggest that the intramolecular additions of acyl radicals to alkenes under the conditions detailed herein may be regarded as irreversible, kinetically controlled processes which exhibit regioselectivity that is predictable based on well-established empirical rules set forth for the analogous free-radical cyclization reactions of alkyl radicals.