Intramolecular 6-endo Heck cyclization of 3-(2-iodophenoxy)methylbenzofurans: A novel approach to pterocarpene isoflavonoids

ORGN 718

Gary W. Morrow, gary.morrow@notes.udayton.edu and Kathryn J. Fowler. Department of Chemistry, University of Dayton, 300 College Park, Dayton, OH 45469
Pterocarpenes 4 are unsaturated members of the pterocarpan family of oxygenated tetracyclic heterocycles possessing a unique benzofuranyl-benzopyran ring junction. The pterocarpene group includes flemichapparin B (R1 = R2 = OCH2O, R3 = H, R4 = OCH3), isolated from pea petals, and erypoegin H (R1 = H, R2 = OCH3, R3 = CH2CH=C(CH3)2, R4 = OH), isolated from the ornamental plant Erythrina poeppigiana and which exhibits broad spectrum activity against Gram-positive bacteria as well as significant activity against vancomycin-resistant strains of enterococci. We will present a novel synthetic approach to pterocarpenes 4 via an unusual intramolecular 6-endo Heck cyclization of 3-(2-iodophenoxy)-methylbenzofurans 3, which in turn are readily prepared via Mitsunobu coupling of o-iodophenols 1 with 3-hydroxymethylbenzofurans 2.