Photochromic heterocyclic fulgides. Part 2. Electrocyclic reactions of (E)-α-2,5-dimethyl-3-furylethylidene(alkyl-substituted methylene)succinic anhydrides
The pale yellow title compounds undergo reversible photochemical conrotatory electrocyclic reactions to give in quantitative yields deep red 7,7a-dihydrobenzo[b]furan-5,6-dicarboxylic anhydrides, which are stable at 100 °C. These photochromic systems, which have high quantum yields for photocolouration, are highly resistant to photodegradation and retain their photochromic properties in a variety of solvents.