A new 2-phenyl-4H-1-benzopyran (flav-2-ene) synthesis

Abstract

Phenoxymagnesium bromides react with cinnamaldehyde selectively in the position ortho to the oxy-substituent to yield diphenyl(styryl)methane derivatives (III). When a suitable substituent is located near the position of electrophilic attack, the reaction leads to mixtures of 2-phenyl-4H- and 2H-1-benzopyrans in a ratio which depends on the experimental conditions. The 2H-compounds are converted into the 4H-isomers when heated with alkoxy- or phenoxy-magnesium bromides. This method is the most straightforward route to 2-phenyl-4H-1-benzopyrans (flav-2-enes).