Thiazol-4-ones

3-Thiazol-5-ones (Anhydro-5-hydroxy-lJ-thiazolium Hydroxides) (105) 

TV-Alkyl- and iV-aryl-JV-thiobenzoylglycines (106) and hot acid anhydrides or acid chlorides in pyridine yield28,64 meso-ionic 4-acyl-1,3-thiazol-5-ones (105, R3 = R-CO), but at room temperature 4-acylation is avoided.65 

A second route to meso-ionic l,3-thiazol-5-ones (105) is provided by 

3- dipolar cycloaddition. Thus, the meso-ionic l,3-oxazol-5-one(66, R1 = R3 = Ph, R2 - Me), and carbon oxysulfide yields the corresponding 

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Analogously, the mesoionic jV-methyl thiazol-5-ones and l,3-dithiol-4-ones afforded A-methyl-4-pyridones and thiapyran-4-ones when reacting with diphenyl cyclopropenone and its thione261. Benzonitrile oxide apparently gives a 1,3-dipolar cycloaddition to the C=0 group of diphenyl cyclopropenone rationalizing the formation of triphenyl-l,3-oxazin-6-one 41626i ... 

The endothiopeptide amides have been converted into the corresponding 4H-l,3-thiazol-5-ones or 4/f-l,3-thiazol-5-imines in the presence of ( )- 10-cam-phorsulfonic acid (CSA) (Scheme 22).44 46... 

Meso-ionic l,3-diazole-4-thiones (103, R = Ph) have been prepared by 1,3-dipolar cycloaddition of phenylisothiocyanate to meso-ionic 1,3-oxazol-5-ones (66) and l,3-thiazol-5-ones (105). Another route to l,3-diazole-4-thiones is exemplified by the formation of the derivative (103, R = R = Me, R = R = Ph) from the methiodide (104) and methylamine. ... 

The pyrolysis of lead salts of dicarboxylic acids gives ketones, as exemplified by the formation of 2-methyl-2-cyclopentano[4,3-d]thiazol-5-one (equation 16) (63JPR(292)285). 

The usual precursor to the thiazolo-fused systems is a cyclic thioamide or its tautomeric form . A convenient approach to the synthesis of bicyclic [5-5] systems, e.g., the tricyclic thiazolium salt 46 and 2,3-dihydroimidazo[2,l-A]thiazol-5-one 48, involves the N,S-dialkylation of appropriate precursors 45 and 47 with 1,2-dihaloalkanes (Scheme 31) <1999JMC2828, 2002EJC777>. 

The primary cycloadduct 145 from the mesoionic l,3-thiazol-5-one (144) and benzyne (generated from 9) was isolated in 78% yield. Thermal decomposition of 145 (in boiling xylene) gave l,3-diphenylbenzo[c]thiophen (143) and phenyl isocyanate, but in striking contrast UV irradiation of 145 yielded... 

Interconversion of thiono- and dithio-esters has been considered earlier (p. 179). The reaction of these compounds with amines has remained one of the most important and widely applied methods for the preparation of thioamides and related substances. This is especially true for carboxymethyl dithio-benzoates, - but other alkyl dithiocarboxylates > > - or RC(S)SSR work as well in many cases. For example, MeCSaMe reacted with amino-acids, free peptides, and peptides which were fixed to a polystyrene matrix, and the terminal A-thioacetyl amino-acid was split off by CF3CO2H to give 2-substituted thiazol-5-ones, which served to identify the -terminal amino-... 

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