Overcrowded molecules. Part VII. Thermal and photochemical reactions of photochromic (E)- and (Z)-benzylidene(diphenylmethylene)-succinic anhydrides and imides

The photochromic (E)- and (Z)-benzylidene(diphenylmethylene)succinic anhydrides and imides undergo reversible photochemical conrotatory ring closure reactions to form 1,8a-dihydronaphthalene intermediates, which ring open by a disrotatory mode yielding (Z)- and (E)-isomers, respectively, and rearrange to 1,2-dihydronaphthalene derivatives in two competing thermal processes. Product distribution depends on the temperature at which the photochemical reaction is carried out. The stereoselective Stobbe condensation of succinic esters with aromatic aldehydes is explained by Zimmerman's ‘overlap control’ mechanism.