Molecular rearrangements of 4‐iminomethyl‐1,2,3‐triazoles. Replacement of 1‐aryl substituents in 1H‐1,2,3‐triazole‐4‐carbaldehydes

The two structural isomers, 4 and 5, of 1‐substituted‐4‐iminomethyl‐1,2,3‐triazoles are interconvertible when heated in dimethyl sulfoxide at 80°. The equilibrium position depends on the electronic properties of the R‐substituent, favoring 5 for R = alkyl, benzyl and anisyl, and 4 for p‐chlorophenyl and p‐nitrophenyl. An interesting application is the synthesis of 1‐alkyl‐1,2,3‐triazole‐4‐carbaldehydes from 1‐phenyl‐1,2,3‐triazole‐4‐carbaldehyde by Scheme I. The hydrazones 4ij and the oxime 4k do not rearrange due to an unfavorable Z‐configuration around the C  N bond, whereas the acyloximino derivative 4m is converted into the nitrile 11. The structures of the products have been fully characterized by 13C nmr spectroscopy and the mechanistic details of the rearrangement are discussed.