Imino carbenes, rearrangement

The intermediate produced by loss of nitrogen from a l.ff-triazole can be written as an imino-carbene, as a zwitterion, or as a diradical. Subsequent reactions of the intermediate which have been observed (Scheme 57) include (a) photochemical WoUf rearrangement (suggesting that the intermediate may have a singlet carbene structure) ... 

After treatment with alkyllithium reagents, dihalocyclopropanes bearing vicinal vinyl or imino groups can undergo carbene-carbene rearrangements. This quality was utilized, for instance, for generation of 1,5-dihydropentalene and synthesis of pyrroles (equation I22)2 26i... 

Initiation involves coordination of the double bond of monomer with the transition metal (imino and OR ligands not shown), cleavage of the 7t-bond with formation of a 4-membered metallocyclobutane intermediate, followed by rearrangement to form a metal-carbene propagating center ... 

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