Azines and Azoles: CXXV.~1 New Regioselective Synthesis of 1-Amino-6-methyluracils

摘要

Readily accessible 5-acetyl-4-hydroxy-3,6-dihydro-2H-1,3-thiazine-2,6-dione reacts with substituted hydrazines and carboxylic acid hydrazides under mild conditions to give the corresponding hy-drazones.Under severe conditions (heating in boiling dimethylformamide) the reaction is accompanied by extrusion of COS with formation of substituted 1-amino-6-methyluracils.Reactions of 5-acetyl-4-hydroxy-3,6-dihydro-2H-1,3-thiazine-2,6-dione with monosubstituted alkyl- and arylhydrazines take different pathways,depending on the conditions.Heating of equimolar mixtures of the reactants in ethanol or propan-1-ol leads to the formation of 2-substituted 5-methyl-3-oxo-2,3-dihydro-lH-pyrazole-4-carboxamides rather than 1-amino-6-methyluracil derivatives.