Synthetic Studies on Podophyllum Lignans: Tributyltin Hydride-induced Radical Cyclization and Intramolecular Heck Reaction of a-Benzylidene-b-(o-bromobenzyl)-g-lactones

Abstract

Tributyltin hydride-induced radical cyclization of the (Z)-α-benzylidene-β-(o-bromobenzyl)-γ-lactone (16) gave the 6-endo cyclization product, (±)-deoxyisopicropodophyllin (18), and the 5-exo cyclization product (19). On the other hand, the intramolecular Heck reaction of 16 provided (±)-γ-apopicropodophyllin (20) as a sole cyclization product