A2-Pyrroline ring

Generalization of this result to imines of conjugated aldehydes provides a good synthesis of the A2-pyrroline ring. The intermediacy of an ylid is confirmed by trapping with iV-phenylmaleimide, which takes place with excellent stereocontrol.330... 

The type-2 systems are the basis of a new type of very potent photochromic compounds. Several routes to this type of system have been developed recently. Incorporation of a A2-pyrroline ring into a more complex molecule has led to a very efficient new class of photochromic compounds (Scheme 2). 

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