Ylids, nitrogen formation

A closely related reaction is formation of nitrogen ylids from quaternary ammonium salts (see 17-7) ... 

Although there is no direct evidence for the postulated intermediate 3 in this example, there is evidence for the existence of analogous ylids in the aziridine series (see Section II, B), and in some reactions of pyridine-type heterocycles with DMAD intermediates corresponding to 3 have been trapped. The formation of intermediates similar to 3 is the commonest first stage in reactions of nitrogen-containing heterocycles with activated acetylenes. 

When the aziridine nitrogen is substituted, Michael-type addition to the acetylene is not possible. Reactions are then usually preceded by ring cleavage with the formation of an azomethine ylid. The product obtained depends on the nitrogen substituent. Heine and co-workers 45,46 used m-l,2,3-triphenylaziridine (27) with DMAD, DEAD, EP, and EPP. The DMAD gave 98% of compound 28 after refluxing in toluene... 

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