Synthesis of 2,3-dihydro-1,3-thiazin-4(1 H)-ones and their remarkably facile recyclization to 2,3-dihydropyrimidin-4(1 H)-ones

Article abstract of DOI:10.1002/hc.20129

Functionalized 2,3-dihydro-1,3-thiazin-4(1 H)-one derivatives have been synthesized by cyclocondensation of 3-alkyl(aryl)amino-2-cyano-3- mercaptoacrylamides with aldehydes and ketones under acidic catalysis. 6-Alkyl(aryl)amino-5-cyano-2,3-dihydro-1,3-thiazin-4(1 H)-ones, when treated with a dilute solution of potassium hydroxide, are converted into the potassium salts of isomeric compounds, 1-alkyl-(aryl)-5-cyano-6-mercapto-2,3- dihydropyrimidin-4(1 H)-ones. Alkylation of the latter with dimethyl sulfate in situ furnishes 1-alkyl(aryl)-6-alkylthio-5-cyano-2,3-dihydropyrimidin-4(1 H)-ones, whereas boiling them in ethanol with an excess of hydrochloric acid leads to starting 2,3-dihydro-1,3-thiazin-4(1 H)-ones.