Activation and stabilization of aldimines by an ortho-trifluoromethyl substituent in direct vinylogous Mannich-type reactions

Lewis acid catalyzed direct vinylogous Mannich-type reaction with a weak nucleophile dienol, generated in situ by ring-opening and rearrangement of vinyloxiranes, could be demonstrated in excellent yields under mild conditions using benzylidene(4-methoxy-2-trifluoromethyl)aniline (MTMA) as an electrophile. The o-trifluoromethyl substituent can stabilize imines by a steric effect and activate by an electron-withdrawing effect. It proved to be an easily deprotectable protecting group for direct Mannich-type reactions.