Azomethines enolizable

Confalone and Earl have reported a series of intramolecular azomethine ylide cyclizations employing a-dithiolanyl aldehydes (Scheme 35).60 Thus, reaction of the aldehydes (115a-b) with ethyl sarcosinate at 140 C provided the 5,6-fused bicyclic pyrrolidines (116a-b), presumably via cyclization of the singly stabilized azomethine ylides. The dithiolanyl group could be removed by standard reactions this route then provides bicyclic pyrrolidines which cannot be prepared directly from enolizable aldehydes. 

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