Pyrrole studies. Part 26. A novel thermochromic and photochromic pyrrole system

Abstract

2-Dichloromethyl-3,5-bisethoxycarbonyl-4-methylpyrrole (3) yields a thermally labile 5,10-methylenedioxy-5H,10H-dipyrrolo[1,2-a;1′,2′-d]pyrazine (1) when heated with 6% aqueous potassium hydroxide. Upon being heated at 160 °C the colourless dipyrrolopyrazine is converted into a red bis-(1-azafulvene) system, which can be reconverted photochromically into the dipyrrolopyrazine via a [6π+ 6π] cycloaddition reaction.