Azomethine ylides, alkynyl cyclic

Alkynyl azomethine ylides containing an aryl bridge have been shown to undergo cyclization. Thus, tautomerization of imine (137) afforded an azomethine ylide which cyclized to give two diastereomeric dihydropyrroles and traces of aromatized product (Scheme 42).56 The activated cyclic ylide (138), generated via the desilylation route, underwent cyclization to afford dihydropyrrole (139) in 42% yield.67b The structure of (139) is closely related to erythramine. The structurally related non-stabilized azomethine ylide (140) did not cyclize, tautomerizing to the corresponding enamine instead. 

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