Base-catalysed ring contraction of 6,7-dihydro-1-methyl-1H-1,2,5-triazepines to 2,3-dimethyl-1,2,4-triazines

Abstract

6,7-Dihydro-1-methyl-1H-1,2,5-triazepines 3–5 and 8 in ethanolic sodium hydroxide have been converted into one or two compounds of the following types: 1,2,3,6-tetrahydro-6-hydroxy-, 1,2-dihydro- and 2,3-dihydro-2,3-dimethyl-1,2,4-triazines 10–16. In contrast, 1,6-dimethyl analogues are converted into the corresponding 2,3-dihydro-2,3,3-trimethyl-1,2,4-triazines 17–19 under similar conditions. Since alkali hydroxide is essential to the present ring contraction it is likely that it proceeds via a 3-hydroxylated anion formed by hydroxide attack on the 3-position of triazepines 3–9. 1,2,3,6-Tetrahydro-6-hydroxy-2,3-dimethyl-1,2,4-triazines 10–12 are found to be precursors to the 1,2-dihydro-2,3-dimethyl-1,2,4-triazines 13–15.