Thiazolo thiadiazin-6 -ones

Disubstituted 2-thioxo-pyrido[2,3-d]pyrimidinones condensed with aldehydes in the presence of chloroacetic acid to yield thiazolo[2,3-a]pyrido[2,3-. One-pot alkoxylation at the 7-position of 6-arylpyrazino[2,3-c][l,2,6]thiadiazine 2,2-dioxides with NBS or NCS in the appropriate alcohol has been studied <02EJ02109>. 

The practical utility of the facile addition of mercaptoacetic acid across the double bond of an azomethine has been used in the synthesis of thiazolo-triazolothiadiazin-6(7//)-one (328). Thus, 7//-3-methyl-5-triazolo[3,4-f>]thiadiazine hydrochloride (327), obtained by reacting l-amino-2-methyl-j-triazolyl-2-thione (326) with chloroacetaldehyde di-ethylacetal, reacts with mercaptoacetic acid in the presence of p-toluenesulfonic acid in boiling anhydrous benzene for 40 hr using a Dean-Stark water separator followed by basification with sodium bicarbonate to furnish 8a//,9//-3-methylthiazolo[3,2-u]-[l,3,4]triazolo(3,4-f>](1,3,4]-thiadiazin-6(7//)-one (328) (74IJC287) (Scheme 77). The absorption at 1725 cm (lactam carbonyl) in product 328 supports the cyclic structure in preference to the open-chain acid structure. 

The electrochemical oxidation of catechols in the presence of 6-methyl-l,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-fi][l,2,4]triazin-7-one and l,2,4-triazino[3,4- ]l,3,4-thiadiazine derivatives respectively <06TL1713> <06TL8553>. 

Substituted 2 f-l,2,4-benzothiadiazin-3(4//)-one 1,1-dioxides are available by a one-pot intramolecular Friedel-Crafts reaction involving the action of chlorosulfonyl isocyanate on a secondary aromatic amine in the presence of aluminum chloride <85IJC(B)1295>. Chlorosulfonyl isocyanate is also employed in the synthesis of oxazolo- and thiazolo[2,3-z(][l,2,4]-thiadiazin-3(2//)-ones (196 X = O and S) from 2-ethyloxazolines (195 X = O) and 2-ethylthiazolines (195 X = S) respectively (Scheme 33) <93SC121>. 

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