A2-1,3,4-Thiadiazolines

A general synthesis of 4-amidino-A2-thiadiazolines consists in the reaction of 1-chloro-2,3-diazabutadiene with thiourea at room temperature (Scheme 22b). The characteristic spectroscopic features of A2-1,3,4-thiadiazolines are associated with the sp3-hybridized C-5 atom and its methine proton. The C-5 atom resonates in the 13C NMR spectrum at about 570.5, the signal appearing as a doublet in the off-resonance spectrum, while the methine proton resonates in the H spectrum at about 57, displaying a strongly deshielded environment (8UCS. 

The mesoionic tetrazole dehydrodithizone is transformed by iron penta-carbonyl into 4-phenyl-2-phenylazo-A2-l,3,4-thiadiazolin-5-one, presumably by a mechanism of ring opening, complexation, carbonyl insertion and subsequent ring closure (Scheme 128).193 Unfortunately, analogous processes do not occur on other mesoionic compounds in the 1,2,3-oxadiazole, s-triazole or tetrazole series, and the scope of this unusual carbonylation is probably limited. 

The mass spectra of a series of 3-amino-4-aryl-5-aryl(or alkyl)imino-A2-1,2,4-thiadiazolines (366) have been interpreted in terms of fragmentation patterns, that are the result of fission of the molecules by routes a-c.257 (see also Ref. 49). In an extension of this study to variously substituted 3,5-... 

Synonyms Ciba-Geigy CS 13005 5 -(2-Dihydro-5-methoxy-2-oxo-l,3,4-thiadiazol-3-methyl)dimethyl phosphorothiolothionate 5 -2-Dihydro-5-methoxy-2-oxo-l,3,4-thiadia-zol-3-ylmethyl 0,0-dimethyl phosphorodithionate 0,0-Dimethyl S -(5-methoxy-1,3,4-thiadiazoliny 1-3-methyl) dithiophosphate O,(9-Dimethyl 5 -(2-methoxy-l,3,4-thiadiazol-5(4 -ony 1-4-methyl) phosphorodithioate DMTP ENT 27193 Fisons NC 2964 Geigy 13005 Geigy GS-13005 GS 13005 Methidathion 50S 5 -((5-Methoxy-2-oxo-l,3,4-thia-diazol-3(2//)-yl)methyl) (9,(9-dimethyl phosphorodithioate Phosphorodithioic acid 0,0-dimethyl ester, S-ester with 4-(mercaptomethyl)-2-methoxy-A2-l,3,4-thiadiazolin-5-one Somonil Surpracide Ultracide. 

X-Ray crystallographic studies on 1,2,4-thiadiazoles (see Table 1) show the 1,2,4-thiadiazole ring to be essentially planar. The X-ray structure of 4-phenyl-5-(/>-nitrophenyl)-3-(/>-methoxyphenyl)-A2-l,2,4-thiadiazoline 3 shows that the 1,2,4-thiadiazoline ring has a 30° fold around the S(l)-N(4) vector atoms S-l, N-2, C-3, and N-4 are nearly coplanar <1986JCM156>. 

The numbering of the 1,3,4-thiadiazole ring is given below. The present chapter is intended to update the previous work on the aromatic 1,3,4-thiadiazole 1, the nonaromatic A2-thiadiazolines 2, A3-thiadiazolines 3, the thiadiazoli-dines 4, the tautomeric forms 5 and 6, and the mesoionic systems 7. Reference is made to earlier chapters of CHEC(1984) and CHEC-II(1996) where appropriate. 

Alkyl-5-imino-3-methyl-A2-l,2,4-thiadiazolines react exothermally at 0°C with dibenzoyl or dimethoxy carbonylacetylenes in tetrahydrofuran to give the 2-aIkylaminothiazoles in high yields (1564). The cyclo addition reaction of 2-pyridyl isothiocyanates with 1-azirines results in the formation of 2-pyridylaminothiazoles (1565). 

H2NCMe2CN SOCl2 or so2ci2 3-Chloro-4,4-dimethyl-A2-1,2,5-thiadiazoline 1-oxide or 1,1-dioxide 75MI42600... 

The condensation of N-acyl-S-chloroisothiocarbamoyl chlorides (188) and amidines (189) yields 5-benzoylimino-3-phenyl-2-aryl-A3-l, 2,4-thiadiazolines (190) as major, and the isomeric A2-l,2,4-thiadiazolines (191) as minor products. Analogs (193) of the latter are formed exclusively from N-aryl-S-chloroisothiocarbamoyl chlorides (192). The divergent course of the reaction is ascribed to the different reactivity of the chlorine atoms in the two reagents (188,192). It is plausible that the initial nucleophilic attack of the base occurs at the imido carbon of 188, but at the sulfenyl sulfur of 192.166 The condensation of N-phenyl-S-chloroisothiocarbamoyl chloride (194) and isothioureas (195) similarly yields the 1,2,4-thiadiazolines (196).167... 

The replacement of 5-chloro substituents by oxygen functions has been effected by the use of ethylene glycol and its homologs,125 126 glyddol (2-hydroxymethyloxiran),308 and sodium phenoxide.309 Prolonged treatment of 3-substituted 5-chloro-1,2,4-thiadiazoles with boiling acetic add yields the corresponding A2-l,2,4-thiadiazolin-5-ones.310... 

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