Arylidene Derivatives of Fulgides ArF

CH3) have been studied by an X-ray diffraction method. In their stereochemical description, fulgides are treated as derivatives of succinic acid. The trans arrangement of a substituent and the carbonyl group with respect to the C=C double bond is referred to as the F configuration, and the cis arrangement as the Z configuration. 

Three isomeric forms of ArF are available EE, EZ, and ZZ. These three isomers are capable of photochemical intertransformations and cyclization. Cyclization only occurs from a sterically strained E form, and its efficiency depends on the structure of the F-isomer. 

According to the selective rule of orbital symmetry preservation, cyclization of an F-isomer involves the methylene carbon atom of one benzylidene group and 

Photochemical cyclization occurs by a conrotatory mechanism, while thermal cyclization occurs by a disrotatory one. In the symmetrical fulgide / 7 -ArF2, the phenyl substituents of both benzylidene groups participate in the reaction with equal probability. In unsymmetrical benzylidene(diphenylmethylene)-succinic anhydride, -ArFl, only one phenyl substituent of the diphenylmethylene moiety participates both in thermo- and in photochemical reactions. The selectivity of such a transformation is not determined by a rule of orbital symmetry preservation, so it was suggested that it may be related to the specific spatial structure ofArFl.81 

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