Methine-type isoindolinones

In comparison with their azomethine analogs described above, methine-type isoindolinones have gained Htde significance as pigments, although bismethine iso-indoline pigments constitute commercially important yellow-to-red products [21]. 

Methine isoindolinones of generic structure 23 can be prepared by the reaction of active methylene compounds with either phthahmides [22], or iminoisoindoh-nones [23], or a-cyanobenzoates by analogy with the methods described above for azomethine-type isoindolinones. 

Methine isoindolinones have also been prepared by treatment of the corresponding phthalildes with ammonia [24]. 

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Formal replacement of the two hydrogen atoms at the 3-position by a substituted nitrogen atom yields an azomethine (>C=N-) linkage at this position - the ensuing product being conveniently referred to as an azomethine-type isoindolinone derivative. If, however, the two hydrogen atoms are replaced by an appropriately substituted carbon atom to yield a C=C double bond, the resulting semicyclic amidine derivative is classed as a methine-type isoindolinone. 

The methine type comprises isoindoline derivatives which, like tetrachloro-isoindolinone pigments, have only recently been described. One or usually two equivalents of a compound containing an activated methylene moiety are attached to one equivalent of isoindoline. The list of compounds featuring activated methylene groups includes cyanacetamide or heterocycles such as barbituric acid or tetrahydroquinolinedione. 

Further, stable 2 1 transition metal complex pigments 27 (C.I. Pigment Yellow 177) and 28 (C.I. Pigment Yellow 179), featuring six-ring chelates, have been prepared from methine and azomethine type isoindolinones l... 

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