Thiazolo triazole synthesis

A novel one-step synthesis of thiazolo[3,2-fc]l,2,4-triazoles 182 was reported from the reaction of chalcones 180 with bis(l,2,4-triazolyl)sulfoxide 181 . 1,2,4-... 

The synthesis of a series of thiazolo[2,3-c][l,2,4]triazole derivative 33 has been approached by base-mediated intramolecular cyclization of bromide 349 or acid-promoted ring closure of alcohol 350, obtained from pyrazinoyl-dithiocarbazate 348 (Scheme 33) <2004PS(179)2519>. 

Triazolo[4,3-7 ]pyridazinc-6(5//)-one-3(2//)-thiones 309 undergo an unprecedented ring transformation on treatment with dimethyl acetylenedicarboxylate in DMF, resulting in a new method for the synthesis of thiazolo[2,3-c][l,2,4]triazole derivatives, which is strongly dependent on the reaction temperature and the... 

Jain and Handa reported [82IJC(B)732] that the mode of ring closure may depend critically on the 5-substituent of the triazole. 3-Mercapto-5-(4 -pyridyl)[l,2,4]triazole 143 was reacted with phenacyl bromides to give 144, which on treatment with PPA resulted in the formation of thiazolo[2,3-c][l,3,4]triazoles 145. The structure of 145 [R = (4-Cl)C6H4] was proved by an independent synthesis starting with isonicotinyl thiosemicarbazide. 

A further synthesis of thiazolo[3,2-6][l,2,4]triazoles starts with 2,3-diaminothiazoles. Treatment of 2-aminothiazole with O-mesitylensulfonyl-hydroxylamine results in the formation of salt 171, which on heating with acetic anhydride (140-150°C) gives a mixture of 172 and 173. 2-Phenylthia-zolo[3,2-h]-5-triazole could be obtained from 171 and benzoylchloride ( 200°C) in 68% yield. When 2-acylamino-3-aminothiazolium salts 174 are heated 20-30°C above their melting point for 1 h the corresponding thiazolo[3,2-h]-5-triazoles were obtained. Much better results were achieved by using PPA (100-110°C, 1.5 h 97% yield) (73JHC947). 

The last step in a stereospecific total synthesis of ( )-biotin consists of the facile reaction of the precursor diamine with phosgene (equation 5) (77JA6754). The reaction of a cyclic amidrazone precursor with phosgeniminium chloride gives thiazolo[3,2-6]-s-triazoles (equation 6) (73AG(E)405). Treatment of 4,5-diaminopyrazoles with thionyl chloride forms pyrazolo[3,4-c][l,2,5]thiadiazoles (equation 7) (68JMC1164). 

The most commonly used method for the preparation of fused thiazoles involves the reaction of a-mercapto N-heterocyclic compounds of type (138) with an a-halocarbonyl compound or ester to give S-alkylated intermediates (139) which can be dehydrated to (140). When R2 is alkoxy, thiazolones (141) are formed (Hantzsch synthesis). Strong dehydrating agents are necessary to cyclize aldehydes and ketones (139) to fused thiazoles. The method has been used to prepare (dihydro) imidazo[2,l-6]thiazoIes and thiazolo[3,2- ]-s-triazoles (80JHC1321, 78JHC401, 82IJC(B)243). 

Triazole-containing compounds exhibit various biological effects, such as antiviral (Moorhouse and Moses, 2008), antibacterial (Hon et al., 2012), antifungal (Agalave et al, 2011), and anticancer (Jordao et al., 2009). Heravia et al. (2006) developed an easy and eco-friendly method for the synthesis of thiazolo[3,2-fc]l,2,4-triazoles using SSA as an efficient catalyst. This method involved the condensation of 3-mercapto-l,2,4-triazoles with allyl bromide. Keivanloo et al. (2013) also reported silica-supported zinc bromide as an efficient heterogeneous catalyst for the one-pot synthesis of 4,5-disubstituted-l,2,3-(NH)-triazoles. The reaction involved the cross-coupling of 1,3-dipolar cycloaddition with various acid chlorides, terminal alkynes, and sodium azide in the presence of silica-supported zinc bromide under aerobic conditions. The reaction is described in Scheme 6.34. 

Thiazolo-[2 c]> and -[3,2-h]>sym-triazoles (C2Nj-CjNS).—3-(2-Furyl)-5-phenylthiazolo[2,3-c]-sym-triazole (126) is obtainable from the appropriate triazole-5-thiol and phenacyl bromide by Hantzsch s synthesis.Members of the isomeric [3,2-b]-ring system (127) have been obtained by annelating... 

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