REDUCTIVE RADICAL CYCLIZATIONS OF HALOALKENES PROMOTED BY SAMARIUM DIIODIDE - SEQUENTIAL CYCLIZATION INTERMOLECULAR CARBONYL ADDITION-REACTIONS

A sequential radical cyclization/intermolecular carbonyl addition process promoted by samarium(II) iodide (SmI2) is reported. Treatment of appropriate haloalkenes with SmI2 in the presence of a variety of ketones leads to products resulting from cyclization followed by intermolecular addition of the resultant anion to the carbonyl electrophiles. Although several mechanisms can be envisioned, this process is most likely initiated by SmI2-induced formation of a hexenyl radical. Intramolecular addition of this radical to the tethered alkene leads to generation of a new alkyl radical, which can be reduced in situ to the corresponding organosamarium species. This organosamarium adds to the carbonyl electrophile, completing the tandem process. In this study, 2-(allyloxy)ethyl iodide and 2-(allyloxy)-l-iodobenzene were the most thoroughly examined radical precursors. The anion intermediates ultimately derived from these starting materials were trapped with a range of ketones to yield the corresponding heterocyclic derivatives. © 1990, American Chemical Society. All rights reserved.