Cinchona-derived ammonium salts-catalyzed aza Diels–Alder reaction of Danishefsky’s diene with imines

Described is the efficiency of cinchona-derived quaternary ammonium salts as Lewis acid organocatalysts in aza Diels–Alder reaction of Danishefsky’s diene 1 with imines 2 and 16, providing 1,2-dialkyl-2,3-dihydro-4-pyridinones 3 and cyclic dihydropyridones 17, respectively. Among the nine of cinchonidine-derived quaternary ammonium catalysts prepared, N-2′,3′,4′-trifluorobenzyl-O-benzylcinchonidinum bromide (6) exhibited the highest chemical yield (up to 99%). Systematic study on structure-catalytic efficiency relationship revealed that 2′,3′,4′-trifluorobenzyl, quinuclidine, and quinoline moieties are essential.