4-Phosphonated or 4-Free 1,2,3-Triazoles: What Controls the Dimroth Reaction of Arylazides with 2-Oxopropylphosphonates?

The influence of base-solvent systems and substituents on the reaction of aryl azides with dimethyl 2-oxopropylphosphonate was studied. It was shown that azides with electron-withdrawing substituents in K2CO3/DMSO medium (mild conditions) afford 5-methyl-1-aryl-1H-1,2,3-triazole-4-ylphosphonates as major products. In contrast, azides with electron-donating substituents produce 1-aryl-5-methyl-1H-1,2,3-triazoles. Based on the obtained results the plausible mechanisms of the reactions were discussed and key points of selectivity control were indicated.