Thiadiazol-2-enes

4-Thiadiazol-2-enes (Anhydro-2-alkyl-l,3,4-thiadiazolium Hydroxides) (261) 

A-Thioacylhydrazines (232) and either 3,3-dichloroacrylonitriles (262, Y = Cl), 3,3-bis(methylthio)acrylonitriles (262, Y = SMe), or cyano-methoxycarbonylthioketene prepared in situ from the dithietanone form meso-ionic 1,3,4-thiadiazol-2-enes (261).114 

The orange-yellow meso-ionic thiadiazol-2-enes (261) are reasonably stable, but the isomerization (261, R1 = Me, R2 = Ph, Z = CN) - 263 occurs at 250°.114 

The reaction between JV-thiobenzoyl-JV-methylhydrazine (232, R1 = Me, R2 = Ph), and phenylthioacetylthioglycolic acid, Ph-CH2-CS—S— CH2—C02H, did not yield the expected product. A deep red substance, m.p. 238°-239°, has been isolated, and its X-ray crystallographic examination has shown that it has the meso-ionic structure 264.173 This 

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Chemical Name (6R-trans)-3-([(5-methyl-1,3,4-thiadiazol-2-yl)thio] methyl)-8-oxo-7-([(1-H-tetrazol-1 -yl)acetyl] amino)-5-thia-1-azabicyclo[4.2.0] oct-2-ene-2-carboxylic acid sodium salt... 

Other Carboxylic Esters. Selective 2-0-acylation of sucrose has been achieved by way of the 2-oxyanion compound. Treatment of sucrose in DMF with 3-lauryl-, 3-stearyl-, 3-hydrocinnamoyl-, and 3-(4-phenylbutyryl)-thiazolidine-2-thione derivatives and sodium hydride produced the corresponding 2-0-acyl derivatives in good yield (69). Syntheses of 6-O-acylsucroses were also achieved by acylation with 3-acylthiazolidine-2-thione and 3-acyl-5-methyl-1,3,4-thiadiazole-2(3ff)-thione derivatives in the presence of sodium hydride in DMF, followed by acyl migration using l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) or aqueous triethyl amine. 6-0-Acylsucroses were obtained directly when onlyDBU was used (70). 

A solution of 1 eq. of sodium salt of 3-acetoxymethyl-8-oxo-7-(2-tetrazol-l-acetylamino)-5-thia-l-aza-bicyclo[4.2.0]oct-2-ene-2-carboxylic acid (it may be prepared with equivalent of sodium bicarbonate and above named acid) and 1 eq. of [1.3.4]-thiadiazole-2-thiol in 20 ml of phosphate buffer (pH 6.4) was stirred for 5.5 hours at 60°C. The reaction mixture was adjusted to pH 2.0 with 5% hydrochloric acid and treated with ethyl acetate to form a title compound - ceftezole. 

The A-sulfonyl protection in general,PI and more recently the 2-nitrophenylsulfonyl (oNps, 106), the l,3-benzothiazol-2-ylsulfonyl (Bts, 104), and the 5-methyl-l,3,4-thiadiazol-2-ylsulfonyl (105) groups have been used for terminal N-alkylation (Scheme 50), e.g. for the synthesis of polyamines.In fact, as the sulfonamide N—H bond is very acidic, deprotonation with 7-methyl-l,5,7-triazabicyclo[4.4.0]dec-5-ene and alkylation is possible... 

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