NUCLEOPHILIC ADDITIONS TO PYRIDINIUM SALTS - REDUCTION OF THE INTERMEDIATE DIHYDROPYRIDINES

Reduction of indolyldihydrodyridines 4 and 5 satisfactorily Save the corresponding tetrahydropyridines 6 and 7. A similar reduction of 4-(2-indolylmethyl)-1,4-dihydropyridines 3 was inefficient. In contrast, dihydropyridine 19 was reduced to 23 and then cyclized to pentacycle 24. Direct cyclization of 19 resulted in the formation of imide 21.