Tetrahydroquinoline syntheses induced with catalytic amounts of viologen additives

The viologen N,N′-dicyanomethyl-4,4′-bipyridinium·2PF6 was found to induce an aza-Diels–Alder reaction of N-arylimines with N-vinylpyrrolidinone or N-vinylcarbazole, producing tetrahydroquinoline derivatives with high cis/trans selectivities and yields.

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