ON THE FORMATION AND REACTIVITY OF 2-ALKYLIDENE-BENZOPYRANS AND THEIR2-AMINO-5,6-BENZO-2H-PYRAN PRECURSORS

A series of 2-amino-substituted 5,6-benzo-2H-pyrans 14, 2-alkylidene-5 ,6-benzo-2H-pyrans 15, and their dimers 17 are obtained, depending on the condition used, by the reaction of 2-hydroxy-benzaldehydes I with enamines 9 derived of (cyclo)aliphatic ketones. Compounds 14, 15, and 17 can be transformed into 2-alkyl-benzopyrylium salts 16 or 2-[1-(2-h ydroxyphenyl)-alken-2-yl]-benzopyrylium salts 23 by treatment with min eral acids. With aromatic aldehydes or the Vilsmeier reagent the compo unds 14, 15, or 17 are transformed into deeply colored 2-(aryl-alkenyl )-benzopyrylium perchlorates 25 or 2-(2-dialkylamino)-alkenyl-benzopyr ylium salts 26, respectively.