5- Arylamino-l ,2,3-triazole

Very early in the history of heteroeyelic chemistry it was diseovered by Dimroth (09LA183) that l-aryl-5-amino-l,2,3-triazole (1, R = H) undergoes a faeile, reversible isomerization to 5-(arylamino)-l,2,3-triazole (2, R = H) (Scheme IV.4). 

Another synthetic pathway recently used is the cyclization of linear triazenes, like (224), which in aprotic media with Lewis base catal) is yield 5-amino-1-ary 1-1,2,3-triazoles (225). However, in protic media Dimroth rearrangement affords the isomeric 5-(arylamino)-l,2,3-triazoles (226) (70JOC2215, 81JOC856). The 2-tetrazene (227) gives methyl l-benzyl-1,2,3-triazolecarboxylate (228) by photochemically induced homol) is of a single N—N bond (81TL227). 

By contrast, 3-hydrazino-l,2,4-thiadiazoles (163), which are prepared by ring closure methods, are very sensitive to acids and undergo elimination of sulfur with formation of 5-arylamino-l,2,4-triazoles (164) as indicated in Scheme 61 (63JCS4566). The mechanism of this conversion is not known but presumably involves the attack of a hard nucleophile at the 5-position followed by ring opening, loss of sulfur and recyclization as has been observed with the quaternary salts (77JCS(P1)1791) (see Schemes 22, 23, and 24). Hydrazine (163) reacts with aldehydes to produce hydrazones (165) and with dimethyl malonate to yield pyrazoles (166). Diazonium salts of type (153) have been prepared by the methods... 

The reaction of l-arylamino-4,4-dimethyl-5-methylene-2,3,4,5-tetrahydro-l//-imidazol-2-one (338 Y = O) and -2-thione (338 Y = S) with protic heterocumulenes affords 7,7,7a-trimethyl-3-aryl-2,3,5,6,7,7a-hexahydro-l/7-imidazo[l,5-fe][l,2,4]triazol-2,5-diones (339 X = Y = 0), and N-and 5-derivatives of these functions in 2- and 5-positions (Equation (104)) <93TH 805-oi, 95FES379>. 

Aryl-6-phenyl-2-methylthio/secondary amino substituted-4(3//)-pyrimidinones were derived from a reaction of N-arylamino substituted 1,3-diaza-1,3-butadienes with substituted ketenes that was analyzed by computational methods <97T13829>. 1,3-Diazines related to 6-amino-4-chloro-5-cyano-2-(dimethylamino)pyrimidine were prepared in one-pot fashion from 1,1-diamino-2,2-dicyanoethylene and phosgeniminium chloride <97SC1223>. Pyrazolo[3,4- /]pyrimidines were derived from 4-substituted 5-aminopyrazole-l-carbothioamides <97JCR(S)352>. Amino-5-(trifluoromethyl)-l,2,4-triazole gave polysubstituted 2-... 

V,iV -Diarylguanidino)-3,5-bis(methylthio)[l,2,4]triazoles 60 undergo base-induced cyclization to give 7-aryl-6-arylamino-3-methylthio-77/-[l,2,4]triazolo[4,3-7][l,2,4]triazoles 61 (Equation 10) <1988H(27)161>. Similarly, the cyclization of the iV-substituted 4-ureido and 4-thioureido derivatives of 3-phenyl-4,5-di hydro-1//-[ 1,2,4] triazole-5-thiones 62 affords 7-substituted. 5//-[l,2,4]triazolo[4,3- ][l,2,4]triazol-6(7//)-one and -triazole-6(7//)-thiones 63, respectively (Equation 11) <1991RRC619>. 

A(,Ai -Diarylguanidino)-3,5-bis(methylthio)[l,2,4]triazoles (63) undergo base-induced cycli-zation to give 7-aryl-6-arylamino-3-methylthio-7/f-[l,2,4]triazolo[4,3-()][l,2,4]triazoles (64) (Equation (14)) <88H(27)161>. 

Adducts of thiocarbonohydrazides and carbodi-imides are also suitable precursors of 1,3,4-thiadiazoles. l-AW -Diarylamidino-S-phenylthiocar-bonohydrazides (86), arising from 1-phenylthiocarbonohydrazide (85) and diarylcarbodi-imides, are cyclized to the expected substituted 1,2,4-triazoles (87) by aqueous alkali, but yield 2-arylamino-5-phenylazo-l,3,4-thiadiazoles (89) on treatment with ethanolic potassium hydroxide. The observed formation of a 1,3,4-thiadiazole (89) in an alkaline medium conflicts with the general experience that linear compounds of general type (86) are cyclized to 1,2,4-triazoles in alkaline, and to 1,3,4-thiadiazoles in acidic media accordingly, the production of (91) could reasonably have been expected. 

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