Thiazolo triazin-3-ones

The reaction of 6-amino[l,2,4]triazin-5(2//)-ones or its thione derivatives 680 with acetic anhydride gave the 6-acetamido derivatives 681 and 682, respectively. Treatment with phosphorus pentasulfide in pyridine gave thiazolo[5,4-e][l,2,4]triazines 683 (84LA283 87AJC491) (Scheme 142). 

Cyclocondensation of 632 with dibromoethane in the presence of sodium ethoxide gave 2,3-dihydro-6-benzyl-7//-thiazolo[3,2-h][l, 2,4]triazin-7-one, whose structure was confirmed by X-ray analysis (91MI7). 

Propargylmercapto-6-methyl-l,2,4-triazin-5(2fl)-one 85 cyclises to the thiazolo[3,2-6] [l,2,4]triazin-7-one 86 which can be brominated, and subsequently aminated, yielding the products 87 <95MI06 96CA(124)176024>. 

The electrochemical oxidation of catechols in the presence of 6-methyl-1,2,4-triazin-3-thion-5-one and 4-amino-6-methyl-l,2,4-triazin-3-thion-5-one as nucleophiles in aqueous solutions provided an efficient electrosynthesis of thiazolo[3,2-6][l,2,4]triazin-7-one and l,2,4-triazino[3,4-/)J 1,3,4-thiadiazinc derivatives respectively <06TL1713> <06TL8553>. 

Research on only one ring system, thiazolo[3,2- ][l,3,5]triazine, was published in recent years. Although in CHEC-11(1996) <1996CHEC-II(8)445> ring closures to this skeleton ring were already discussed, some new approaches also appeared. These are shown in Scheme 36. 

Yadav and Kapoor <2003TL8951> reported on a microwave-assisted ring closure leading to novel thiazolo[l,3,5]-triazines, as shown in Scheme 36. This three-component one-pot procedure started from the thiazolyl Schiff base 230, to which ammonium acetate and an aldehyde was added. In the first step, the azomethine moiety of the Schiff base reacted with ammonia to give the zwitterionic first intermediate 231, which underwent deprotonation to the amine 232, and, finally, reaction of this second intermediate with the aldehyde involving the ring-closure step afforded the product 233. It is important to emphasize that the MW-assisted technique ensured high yields (76-88%)... 

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. 

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. 

Aminomethylation of 2-amino-5,5-bis(hydroxymethyl)-l,3-thiazol-4(5//)-one and its spiro analogs gave the corresponding [l,3]thiazolo[3,2-a][l,3,5]triazine derivatives <06CHE1086>. 

Naphtho[l,2-rf]thiazole (244) cyclocondensates with glyoxilic acid derivatives to give naphtho-[l, 2 4,5]thiazolo[3,2-i>][l,2,4]triazin-9-ones (245) (Equation (39)) <93JHC1331>. 

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