1.3- Thiazetidines, formation from thioureas

Foerster15 reported that 2-phenylimino-3-phenyl-l,3-thiazetidine was formed by reaction of l,3-diphenyl-2-thiourea with methylene iodide. Underwood and Dains16 repeated this reaction and obtained only a gummy product however, they obtained crystalline 1,3-thiazeti-dines from l,3-di- )-tolyl-2-thiourea and also from l,5-diphenyl-2-methyl-2,4-dithiopseudobiuret. Recently, Ried et a/.17 observed the formation in low yields of 1,3-thiazetidines from unsymmetrically disubstituted thioureas in the presence of triethylamine. They reported that l-(4-quinazolyl)-2-thioureas (7), which have an intramolecular hydrogen bond, react rapidly with methylene iodide in the presence of triethylamine to give the 1,3-thiazetidines (8) in high yields.17... 

A new synthesis of 6-arylamino-2-heteroarylimino-l,2-dihydro-l,3,5-triazines from 2,4-bis-(heteroarylimino)-l,3-diazetidines and amidines has been developed by Molina et al. The formation of the triazines was explained as an initial addition of the imino nitrogen of the amidine to the exocyclic C=N bond, followed by formation of an open chain intermediate. This intermediate cyclized, followed by elimination of 4-amino-6-methyl-3-methylthio-l,2,4-triazin-5(47/)-one to give the triazine product (Scheme 62) <87S150>. 1,3,5-Triazines (207) and (208) have been prepared from 2-acylimino-l,3-thiazetidines (204) by treatment with iso thioureas or guanidines respectively (Scheme 63) <91JHC177>. 

Good yields of 1,3-thiazetidmes (202) are obtained by treatment of the unsynunetrically substituted thioureas (201) (in which hydrogen-bonding appears necessary for success) with di-iodomethane. " The formation and properties of some other 1,3-thiazetidines have been surveyed. Photolysis of a mixture of a thioketone and a nitrile yields N-thioacylketimines, possibly via a thiazete. Another thiazete was discarded as a possible intermediate in the acyl migration from sulphur to nitrogen observed in S-benzoylisothiouronium salts. ... 

---