Isothiocyanates 1,2,3,4-thiatriazoles, 5-amino

As shown by Oliveri-Mandalli,and by Lieber et al., 5-sub-stituted-amino-l,2,3,4-thiatriazoles are also formed by reaction of isothiocyanates with hydrazoic acid. When sodium azide is used instead of the free acid the isomeric mercaptotetrazoles are formed. 

Treatment of 5-substituted amino-1,2,3,4-thiatriazoles (283) with aqueous base results in competitive rearrangement to 5-thiotetrazoles (284) and fragmentation to isothiocyanates (285) and... 

It has been shown that thioketenes, isothiocyanates, and carbon disulfide can react with hydrazoic acid to form 5-alkyl-, 5-amino-, and 5-thiosubstituted-l,2,3,4-thiatriazoles <1996CHEC-II(4)691>. Most probably these reactions proceed via [3+2] cycloaddition of azide anion to C=S bond. 

The procedure is essentially similar to that described for the preparation of 5-amino-l,2,3,4-thiatriazole. Freund and Hempel6,7 have reported observing that the initial diazotization products of 4-aryl-substituted thiosemicarba-zides lead to the formation of tetrazoles, while the corresponding 4-alkyl-substituted thiosemicarbazides were considered by Freund and Schwarz8 to be thiatriazoles. However, Oliveri-Mandala,9 on the basis of his study of the reaction of alkyl and aryl isothiocyanates with hydrazoic acid, concluded that the initial diazotization product of either 4-aryl or 4-alkyl thiosemicarbazides were open-chain thiocarbamyl azides, RNHC( S)N3. Lieber, Pillai, and Hites10 have recently clarified this situation and have shown... 

It appears quite probable that this reaction occurs by the same mechanism as the reaction of nitrous acid with thiosemicarbazides and of sodium azide with isothiocyanates. The primary reaction product is a thiocarbamoyl azide (CCXIII) to which, however, the cyclic structure of a 5-amino-l,2,3,4-thiatriazole (CCXIV) is attributed. In alkaline medium these compounds rearrange to the corresponding 1 -substituted-Zla-tetrazoline-5-thiones (CCXII) 236, 237). A survey of these compounds, prepared from the dithiocarbamic acid esters, is given in Table 33. 

The reactivity of electrophilic isothiocyanates towards inorganic and organic azides is well known. The conversion of hydrazoic acid with aryl isothiocyanates 175 provides 5-amino-substituted 1,2,3,4-thiatriazoles 177 by addition of hydrazoic acid to the C=S bond of the isothiocyanate moiety, probably via unstable thiocarbamoyl azides 176 [132]. Benzoyl isothiocyanate (179, R = CeHs), for example, reacts with hydrazoic acid to benzoylcyanamide (180, R = CeHs). hi contrast, the reaction of sodium azide with isothiocyanates 175 occurs at the C=N bond of the isothiocyanate moiety and gives l-substituted-A -tetrazoHne-5-thiones, also known as l-substituted-5-mercaptotetrazoles 178 (Scheme 35) [133-135]. 

Similar dipoles are obtained by heating 1,2,3,4-thiatriazoles and their reaction with isothiocyanates with or without catalysts affords [3+2] cycloadducts. For example, reaction of 5-amino-l,2,3,4-thiatriazole 101 ° or 5-alkyl(aryl)-1,2,3,4-thiatriazoles with isothiocyanates proceeds with loss of nitrogen to form 102 which reacts with two equivalents of isothiocyanate to give [3+2] cycloadducts 103. 

Miscellaneous Ring Systems.— The chemistry of 1,2,3,4-thiatriazoles has been reviewed. The thiatriazole derivatives (730) and (731) exist in the tautomeric forms shownThe formation of amino-thiatriazoles (731) from isothiocyanates is more rapid with trimethylsilyl azide than with hydrazoic acid. ... 

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