Ylids, nitrogen rearrangement

When the migrating group is allyl, an additional concerted ([2,3] sigmatropic) pathway for rearrangement becomes available. In this an allylic shift must also occur. Nevertheless, the radical pathway is not always excluded. For example, rearrangement of ylids such as 36 (R = CHs.CO) leads to product 37 (R = CH3.CO) in which the allylic protons adjacent to the amido-nitrogen atom appear in emission (D. G. Morris, 1969). No polarization is observed in the much readier... 

Essentially the same mechanism is likely to be involved in an electrochemical version of the Stevens rearrangement. The mechanism of this reaction is not known with certainty however, it is known to be intramolecular and to involve deprotonation of quaternary ammonium salts to give nitrogen ylids which rapidly rearrange. The scheme set out in Scheme 9 is therefore entirety plausible. 

Heterocyclic nitrogen-derived ylids behaviors have been studied.373 For instance, pyridine derivatives lead exclusively to [2,3]-sigmatropic rearrangement (Sommelet-Hauser) products. 

In an nmr study of the reaction of N,N-dimethylbenzylamine with benzyne, Lepley 98> observed a free radical intermediate (path 8) which is formed from the ylid and which rearranges to N-methyl-N-(a-phen-ethyl)aniline via a Stevens rearrangement. Prior to this report 8 ") radical intermediates had not been observed in the Stevens rearrangement but their presence had been suggested m>. This radical path must be considered in all reactions of nitrogen ylids for it may be the route by which many rearrangement reactions occur. 

Acknowledgement I wish to thank the National Institute of Health for support of much of my research on nitrogen ylids. I wish to thank Dr. Stanley L. Pine for a preprint of a review article entitled, "The Basic Rearrangement of Quaternary Ammonium Salts, which will soon be published in Organic Reactions. I especially thank Dr. Arthur R. Lepley for several preprints of his work on radical intermediates and for his valuable comments on the manuscript. 

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