Thiazolo 2,3-c l,2,4 triazines

Thiazolo[2,3-c][l,2,4]triazines 658 were prepared (84LA1302) regio-specifically by cyclizing 2-hydrazono-2-thiazoline 659 with glyoxylic acid or ester. They had herbicidal activity. Condensation of 659 with oxamic acid ethyl ester gave hydrazide 660, which was cyclized with sodium... 

Thiazolo[2,3-c][l,2,4]triazines 667 were synthesized by coupling the diazotized thiazole derivative 666 with activated nitriles to give 667 without... 

A fairly substantial amount of preparative work on the title ring systems has been published in the recent years. Some procedures are closely related to earlier elaborated methods reviewed in CHEC-II(1996) <1996CHEC-II(8)445>, but some new approaches have also been recognized. The majority of the available literature relates to one ring system, thiazolo[2,3-c][l,2,4]triazine, whereas synthesis of four others have also been reported. Synthetic routes to these four outstanding ring systems are discussed first and shown in Schemes 46 and 47. 

Dihydro-2iT-thiazolo[2,3-c][l,2,4]triazine-3,4-dione rearranges in dilute base to give an unstable acid which decarboxylates on acidification of the sodium salt to give 5,6-dihydrothiazolo[2,3-c]-s-triazole (equation 68) (81CB1200). Kinetic evidence has been put forward in favor of covalently hydrated intermediates in the acid-catalyzed rearrangement of triazolo[4,3-a]pyrazines to 1H-imidazo[2,1 -c]-s-triazoles. The intermediate triazole has been isolated and characterized (equation 69) (72JCS(P2)4). 

A Pd(PhCN)2Cl2-catalyzed cyclization of 3-propargylthio-1,2,4-triazines affording a mixture of 6-methylene-6,7-dihydro-4//-thiazolo[2,3-c][l,2,4]triazin-4-ones and 3-methylene-2,3-dihydro-7//-thiazolo[3,2-b][l,2,4]triazin-7-ones has also been reported (eq 72). ... 

Thiazolo[2,3-c][l,2,4]triazines [CaNS-CsNg].—Condensation of triazine (76 R = SEt) with chloroacetic acid gives 5,6-diphenyl-5fl -thiazolo[2,3-c][l,2,4]-triazin-3(lff)-one (77), which condenses with benzaldehyde to give the arylidene... 

Benzo[2,l ]thiazolo[2,3-c][l,2,4]triazines [CsNS-CsNs-C ].—Oxidative cyclization of 3-(o-amino-aryl)-2-imino-4-phenyl-AMhiazolines (117) with A -bromo-succinimide gives the corresponding 9/f-benzo[2,l-c]thiazolo[2,3-c][l,2,4]-triazine. ... 

The tautomeric enamine (163) and endocyclic (164) forms of the substituted thiazolo[2,3-c](l,2,4]triazine have been isolated in the solid state. Thus, on stirring (162) in cold methanol containing triethylamine, the... 

The Wittig-type reactions of iminophosphoranes with isocyanates and related compounds have also been extensively used in heterocyclic synthesis. Examples include the preparations of the mesoionic [l,3,4]thiadiazolo[2,3-c][l,2,4]triazines (210) from (209), 0 bicyclic guanidines, e.g. (212), from (211), naphthypyridines (215), (216), and (217) from (213) and (214), 2 pyrido[l,2-f]pyrimido-[4,5-d)pyrimidines (218), 7H-pyrido-[4,3-c]- (219) and 10H-pyrido[3,4-b]- (220) carbazoles, tricyclic fused 2,4-diimino-l,3-diazetidines (222) from the bisiminophosphorane (221), benzotriazepines (225) from (223) and (224), 6 and mesoionic thiazolo-[2,3-b]-1,3,4-thiadiazoles (227) and N,N-bisheteroarylamines from the iminophosphorane (226), derived from 3-amino-4-phenylthiazole-2(3H)-thione. The carbodiimides (229), prepared from the iminophosphorane (228), can be converted into quinolines or a-carboline derivatives depending on the nature of the isocyanate used in the reaction with (228) and the reactions of iminophosphoranes (230) and (231) with aryl and styryl isocyanates provide one-pot syntheses of quinoline, a-carboline, and quinindoline derivatives. 9... 

Oxidation of the partially saturated derivative of the thiazolo[4,3-c][l,2,4]triazine ring system 115 was studied by Stoodley et al. <1999J(P1)1067>. Reaction of 115 with w-chloroperbenzoic acid gave rise to the cyclic sulfone 116 in poor yield (28%). 

Alkylation of 694 with phenacyl bromides, followed by cyclization with acetic anhydride gave (87H2183) thiazolo[2,3-c]pyrido[2,l-/][ 1,2,4]-triazine 695. 

Thiazolo-[3,2-h]- and -[3,2-c]-[l,2,4]triazines [C3NS-C3N3]. Examples of the latter class of compounds are obtained by treatment of H02CC(CH=CHR)=NNHCSNH2 (A) with phenacyl bromide, followed by cyclization of the resulting thiazolylhydrazones to give (132), whilst if (A) is first cyclized to the triazine and subsequently allowed to react with an a-halogenated ketone, the isomeric products (133) are obtained. ... 

The synthesis of 9H-benzo[2,l-e]thiazolo-[2,3-c]-as-triazine (401) was achieved by oxydative cyclization of 2-imino-3-(o-aminophenyl)-4-phenyl-4-thiazoline (718, 719). This latter reacts also with paraformaldehyde in hot toluene yielding 3-phenyl-9H.10H-benzo[l,2-/]thiazolo-[2,3-d][l,3,5]triazepine (402) (720). This heterocyclic sytem is also formed when carboxylic acids replace paraformaldehyde (Scheme 230) (721). 

I, 2,4-triazine nuclei can be affected in two ways represented by thia-zolo[2,3-c]-[l,2,4]-triazin-3(2//)-one (148) and thiazolo[3,2-fe]-[l,2,4]-triazin-3(2//)-one (157). Synthesis of both the systems have been accomplished by building the 1,2,4-triazine nucleus onto the thiazolidinone nucleus or vice-versa. 

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