Decarboxylative [4+2] Cycloaddition by Synergistic Palladium and Organocatalysis

A novel reaction based on synergistic catalysis, combining palladium- and organocatalysis has been developed. The palladium catalyst activates vinyl benzoxazinanones via a decarboxylation to undergo a [4+2] cycloaddition with iminium-ion activated ,-unsaturated aldehydes. The reaction is demonstrated to proceed for a number of combinations of vinyl benzoxazinanones reacting with ,-unsaturated aldehydes, providing highly substituted vinyl tetrahydroquinolines in good to high yields, and excellent enantio- and diastereoselectivities (>98% ee and >20:1 d.r.). The palladium catalyst used in the synergistic catalysis can be re-used in a one-pot sequential coupling reaction with an aromatic boronic acid forming the coupling product in 95% yield, >20:1 d.r. and 99% ee.