Allyl ketenimines

A series of carbocyclization cascades of allyl ketenimines initiated through a thermal aza-Claisen rearrangement of A-phosphoryl-A-allyl ynamides has been reported where interceptions of the cationic intermediate via Meerwein-Wagner rearrangements and polyene-type cyclizations are observed (Scheme 17) ... 

An unusual domino process was observed by Biehl and coworkers [69] in the reaction of 2-bromo-l-naphthol 4-196 with arylacetonitriles in the presence of LDA or LiTMP by employing 3-thienylacetonitrile 4-197, the tetracyclic compound 4-200 was obtained in 57% yield (Scheme 4.43). The reaction probably includes the formation of an aryne and a ketenimine which undergo [2+2] cycloaddition to give 4-198, followed by rearrangement and allylic addition to the intermediately formed aryl cyano compound 4-199. 

There is no unity of opinion in the literature concerning a classification, i.e, whether to call these transformations aza-Claisen or aza-Cope rearrangements. It is accepted that the term aza-Claisen should be reserved only for those processes in which a carbon atom in the allyl vinyl ether system has been replaced by nitrogen357. Three different types of aliphatic 3-aza-Cope reactions which were studied theoretically are the rearrangements of 3-aza-l,5-hexadienes (610, equation 262), 3-azonia-l,5-hexadienes (611, equation 263) and 3-aza-l,2,5-hexatrienes (612, equation 264) (the latter is a ketenimine rearrangement )357. 

Monocyclic imino-ketenimines, in which the reactive functionalities are linked by an allylic or vinylic tether connecting the imino and ketenimino nitrogen atoms, undergo a formal intramolecular [2+2] cycloaddition to yield fused tricyclic 2-iminoazetidines, namely, azeto[l,2-a][l,3]thiazolo[4,5-rf] [pyrimidines 10 <02EJO4222>, and azeto[l,2-... 

DeKorver, K. A., Hsung, R. R, Song, W. Z., Wang, X. N., Walton, M. C. (2012). An intramolecular 2-1-2 cycloaddition of ketenimines yia palladium-catalyzed rearrangements of N-allyl-ynamides. Organic Letters, 14, 3214-3217. 

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