On the regioselectivity in the Hurd-Mori reaction

Various α-substituted (Y) acetone hydrazones were subjected to the Hurd-Mori reaction to give the 4-methyl-5-Y-substituted 1,2,3-thiadiazoles and/or 4-Y-CH 2 derivatives. The ratio of the two products changed drastically depending on the kind of the substituent Y and was parallel to the relative rate of enolization of the two α-carbons in the parent ketones