Elemental iodine catalyzed [4 + 2] cycloaddition reactions of o-quinomethanes: an efficient synthesis of trans-fused pyrano[3,2-c]benzopyrans

Abstract

Elemental iodine has been utilized as an efficient catalyst for the intramolecular[4 + 2]cycloaddition of o-quinomethanes generated in situ from o-hydroxybenzaldehydes and unsaturated alcohol in the presence of trimethyl orthoformate to afford the corresponding trans-annelated pyrano[3,2-c]benzopyrans in high yields with high diastereoselectivity