Mesoionic thiazol-4-one

Mesoionic thiazol-4-one, see 4-Hydroxy-thiazolium hydroxide inner salts Methanol, action on thiazolium salts, 32 Methine dyes, nonionic, nomenclature of, 27... 

Irradiation of the adduct (178) obtained from benzyne and a mesoionic thiazol-4-one in benzene-methanol solution resulted in extrusion of sulphur and formation of the isoquinolone (179).108 This is in complete contrast with the... 

Lactams. Desulfurization of mesoionic thiazole-4-ones (1) with Raney nickel in CH3OH or THF results in ring contraction to /S-Iactams (2). ... 

A very detailed report on /3-lactams, both synthetic and natural, has been published." An excellent new method for the synthesis of a-amino-/8-lactams has been described." The central feature of the synthesis is the protection of a-amino-acids as an enamine followed by acid chloride formation and annellation of imines (Scheme 86). Yields are in the region 35—45%. An unusual transformation of mesoionic thiazol-4-ones into /8-lactams has been reported. It is... 

Mesoionic 1,3-thiazole-4-ones of type 34 are known as thioisomiinchnones. As one of the mesomeric structures demonstrates, these species contain the structural fragment characteristic of thiocarbonyl ylides (61). A convenient access to thioisomiinchnones involves the reaction of /V-arylthiobenzamides with a-bromo-phenylacetyl chloride (62). 

Besides being useful precursors to pyrroles pyridine-2-ones -4-ones, -4-thiones. and -4-imines 4-alkylidene-dihydropyridines thiophenes 1,2,4-triazoles thiapyrane-2-thiones, isoquinoline-3-ones isoben-zothiophenes and 4-mercaptoimidazolium hydroxide inner salts, mesoionic thiazoles are potentially useful in the construction of molecules with herbicidic (39). central nerve stimulating, and antiinflammatory properties (40,41). Application in dye synthesis has likewise been reported (42). 

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 photochemical rearrangement of the mesoionic thiazole (33) provides an original synthesis of the 4-methylthio-derivatives of the A-4-thiazoline-2-one (34) (Scheme 15) (33). 

In 4- and 5-substituted thiazoles the character of the protomerism is not so sharply defined. IR and lH NMR data indicate that in non-polar solvents, as in the solid state, A2-thiazolin-4-ones exist predominantly in the keto form (15b) but that polar solvents such as DMSO shift the keto-enol equilibrium towards the enol form (15a) in acetone equal amounts of (15 R2 = Ph, Rs = H) enol and keto form were found, whereas in DMSO more than 90% of the enol form exists at equilibrium (65ACS1215). The third form (15c) corresponds to the mesoionic 4-hydroxythiazole and its existence has been suggested from reactivity experiments but it could not be established spectroscopically. 

Reaction of mesoionic thiazoles (40) and (41) with w-chloroperbenzoic acid (MCPBA) affords thiazolidine-4-ones (42) and thiazolidine-4,5-diones (43), respectively, accompanied by several minor products of further degradation (Scheme 5) <80JOC4850>. 

Thiazolo[2.3-bl- and [5.4-dlthiazoles [C NX-C NS]. Glyoxal reacts with thiourea to give the [5,4-d] system (228 X=S, Z=NH) and not (2285X=NH,Z=S) as previously reported. Arylthiazolo [5,4-d]thiazoles (229) can also be prepared by cyclisation of (230) with PhNCS in refluxing acetone or diglyme . Mesoionic 2-substi-tuted thiazolo[2,3 b]thiazol-3-ones (231 R=Ph,Ar, R =H,ROCOalkyl,... 

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