Synthesis of 2-aminochromene derivatives from 1-(2-imino-2H-chromen-3-yl)pyridin-1-ium perchlorates and nitromethane in basic medium

Novel 2-amino-4-(nitromethylidene)chromenes were obtained as a result of the reaction of 1-(2-imino-2 H -chromen-3-yl)pyridinium perchlorates and nitromethane by the action of DBU at reflux in trifluoroethanol. The starting 2-iminochromenes are readily accessible from the corresponding salicylic aldehydes and quaternary cyanomethyl pyridinium salts. The reaction is tolerant to substituents of different nature (alkyl, alkoxy, halogen); a limitation is the presence of strong electron-withdrawing substituents in the benzene ring of chromene. During the reaction, the products precipitate and can be isolated by filtration.