Attempted generation of substituted 1,2,3-triazolium-1-methanides: a new ring expansion to 2,3-dihydro-1,2,4-triazines: ab initio calculations on 1,2,3-triazolium-1-oxide, -1-imide, and -1-methanide 1,3-dipoles and a striking illustration of the Hammond principle in the cyclisation of hetero-1,3,5-trienes

Abstract

Treatment of 1-methyl-1,2,3-triazolium salts with ethoxide gave 2,3-dihydro-1,2,4-triazines via 1,2,5-triazahexa-1,3,5-trienes but the expected 1,2,3-triazolium-1-methanide 1,3-dipoles were not detected and ab initio calculations suggest that they are thermodynamically unfavoured; the X-ray crystal structure of (6a), a dihydro-1,2,4-triazine, is reported.