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2-Imino-1,3-thiazines or 2-thioxopyrimidines: That is the question

Authors: Hanusek Jiří | Hladíková Veronika

Year: 2014

Type of publication: ostatní - přednáška nebo poster

Page from-to: nestránkováno

Titles:

Language	Name	Abstract	Keywords
eng	2-Imino-1,3-thiazines or 2-thioxopyrimidines: That is the question	We decided to start our synthesis from original isothiuronium salts (1a-d) prepared from easily available dimethyl (2-chloromethylidene)malonate and substituted thioureas. These isothiuronium salts were submitted to the reaction with various bases (TEA, aqueous ammonia, sodium methoxide, sodium carbonate) in water, methanol or in biphasic system (chloroform/water) and reaction products were investigated. It was found that strong bases in excess (and sometimes also in equimolar ratio) caused complete decomposition of individual salts to many different product. When equimolar amount or slight excess of weaker base (ammonia) was used then the formation of cyclic product was observed (Scheme 2). In the case of unsubstituted isothiuronium salt corresponding methyl-2-imino-4-oxo-3,4-dihydro-2H-1,3-thiazine-5-carboxylate (2a) was isolated whereas N,N’-dimethyl (1b), N-phenyl (1c) and N-phenyl-N’-methyl (1d) isothiuronium salts possessed corresponding 4-oxo-2-thioxo-1,2,3,4-tetrahydropyrimidine-5-carboxylates (3b-d). On the basis of careful NMR measurements it was found that corresponding 2-imino-1,3-thiazines are always formed first which subsequently undergo nucleophile-assisted Dimroth rearrangement to give 2-thioxopyrimidines (3b-d).	2-Imino-1,3-thiazine; 2-thioxopyrimidine;