Palladium (II) catalyzed 5-endo epoxynitrile cyclizations: total syntheses of enokipodins A and B

New total syntheses of the cuparenic sesquiterpenes enokipodins A and B were accomplished. The key step involves a novel, cationic-controlled and palladium (II) improved, 5-endo cyclization of an α-aryl-δ-epoxynitrile. The cyclization occurs with unmatched regioselectivity and high stereoselectivity. The synthesis is completed in 5 steps achieving yields of 50% for enokipodin A and 55% for enokipodin B.