Coumarins. VI. The Acid-catalyzed Reaction of Phenols with β-Aminocrotononitrile

Abstract A new synthesis of 4-methylcoumarins has been developed by means of the acid-catalyzed condensation of phenols with β-aminocrotononitrile. Such monohydric phenols as phenol or cresols reacted with β-aminocrotononitrile in polyphosphoric acid (PPA) to give 4-methylcoumarins in poor yields, along with a good yield of 6-amino-3-cyano-2,4-lutidine (III). In contrast, 7-substituted-4-methylcoumarins were obtained in 23–44% yields from resorcinol and its monomethyl ether. On the other hand, when β-aminocrotononitrile was heated in PPA, the lutidine (III) was obtained in a high yield. Its precursor, 4-amino-1,3-dicyano-2-methylpenta-1,3-diene (XI), was isolated under mild conditions. These results suggest that β-aminocrotononitrile may undergo the preferential self-dimerization to the lutidine (III) rather than the intermolecular condensation with phenols.