Regioselective photochemical cycloaddition of enamine-carbaldehydes and alkenes; synthesis of 1,4-Dihydropyridines and 2-hydroxy-1,2,3,4-tetrahydropyridines

Abstract Photocycloaddition of enamine-carbaldehydes 1 and alkenes 2 with an electron-withdrawing or an electron-donating group 2 a-f and 2 g-h regioselectively yields and 4-substituted and the 3-substituted 2-hydroxy-1,2,3,4-tetrahydropyridines 3 respectively. Dehydratisation of 3 with electron-withdrawing groups at C-4 gives the 1,4-dihydropyridines 4 .