Reaction of 6‐Methyl‐2‐Thiouracil and 6‐Phenyl‐2‐Thiouracil with Chloro‐β‐Dicarbonyl and Bromo‐β‐Dicarbonyl Compounds and Their Nitrile Analogs

Derivatives of 2‐methylidene‐1,3‐dihydropyrimidin‐4‐ones 2a , 2b , 2c , 2d , 2e , 2f , 2g were synthesized by interaction of 6‐methyl‐2‐thiouracil and 6‐phenyl‐2‐thiouracil 1a , 1b with some activated halogenides: diethyl bromomalonate, ethyl 2‐chloro‐3‐oxobutanoate, ethyl 2‐bromocyanoacetate, 2‐bromo‐5,5‐dimethylcyclohexan‐1,3‐dione, and bromomalononitrile. The boiling of 1a with ethyl 2‐bromocyanoacetate in mixture of ethanol and EtONa results in intramolecular cyclization and formation of thiazolo[3,2‐ a ]pyrimidin‐5‐one 3 . Interaction of 1a with 3‐chloropentane‐2,4‐dione and 2‐bromo‐1,3‐diphenylpropane‐1,3‐dione yielded corresponding S‐substituted thiopyrimidines 4a , 4b . In general, the products of 1b S‐alkylation are less prone to sulfur extrusion . Reaction of 1b with diethyl bromomalonate in the absence of EtONa stops at the S‐alkylation step, while in the presence of EtONa in ethanol or PPh 3 in dioxane 2‐(ethoxycarbonylmethyl)thio‐6‐phenyl‐1,3‐dihydropyrimidin‐4(1H)‐one 6 is formed exclusively. Molecular structure and crystal structure of 2‐(1,1‐diethoxycarbonylmethyliden)‐6‐methyl‐1,3‐dihydropyrimidin‐4(1H)‐one 2a are discussed.