Reaction of aromatic N-oxides with dipolarophiles. IV. Factors affecting the 1,3-cycloaddition of pyridine 1-oxide with phenyl isocyanates.

Abstract

Pyridine 1-oxide was subjected to 1, 3-dipolar cycloaddition with phenyl isocyanates having an ortho, meta or para substituent group. The reaction conducted at 90°C in dimethylformamide gave the 2, 3-dihydropyridine-form cycloadduct, although the reaction of pyridine 1-oxide with phenyl isocyanate directly affords 2-anilinopyridine. An increase of the reaction time led to increases in the yields of 2-anilinopyridine and 1-phenyl-carbamoyl-2-phenylimino-1, 2-dihydropyridine, while the yield of the cycloadduct tended to decrease. The reaction at 150°C resulted in an increased yield of 2-anilinopyridine. The reactions of 2-anilinopyridine and 5-methyl-2-anilinopyridine with phenyl isocyanate at room temperature afforded the corresponding 1-phenylcarbamoyl-2-phenylimino-1, 2-dihydropyridines, whereas the reactions of 3-methyl- and 3, 5-dimethyl-2-anilinopyridines with phenyl isocyanate at 90°C afforded 2-(N-phenylcarbamoylanilino) pyridine derivatives.