Thiazole-2,4-dione

The dioxo tautomer is the major form of thiazole-2,4-dione 221, whereas thiazole-4,5-diones exist in solution as mixtures of monooxo-monohydroxy tautomers 222a,b (Scheme 74) [76AHC(S1), p. 453]. 

The thiazole-2,4-dione 105a has been obtained optically active, demonstrating the existence of the dioxo form. Rhodanines are usually written in the carbonyl form (106, R, R = H or alkyl) (cf, reference 117), and this formulation is supported by infrared, ultraviolet, ... 

Pyrrolo[3,4-d]thiazole-4,6-dione, 5-ethyl-2-phenylazo-synthesis, 6, 1005 Pyrrolof 1,2-c]thiazoles reactions, 6, 1040 synthesis, 6, 988, 1047 Pyrrolo[2,1 - ijthiazoles synthesis, 6, 293, 992 1 /7,3/7-pyrrolo[l,2-c]thiazoles synthesis, 6, 1006 Pyrrolo[3,2-d]thiazoles synthesis, 6, 1009... 

Hydroxy group of 8-hyd oxy-2-cycloalkyl-2,3,4,6,ll,lla-hexahydro-l//-pyrazino[l,2-i]isoquinoline-l,4-diones was alkylated with allyl bromide, 2-(bromodifluoromethyl)pyridines, l-(bromodifluoromethyl)- and l-(bro-momethyl)benzenes, halomethyl derivatives of different heterocycles (pyridine, pyrazine, pyrazole, pyrrole, thiazole, thiophene) in the presence of CS2CO3 or K2CO3 (98MIP7). Hydroxy group of 8-hydroxy-2-cyclopentyl-... 

In the case of a diketone (e.g., 3-tosyloxypentane-2,4-dione), the formation of 5-acetyl-4-methyl-2-aryl-l,3-thiazole derivatives can be realized in very good yields (86-89%) (Scheme 7). All these experiments where performed in a Sears Kenmore unmodified household microwave oven (990 W) equipped with a turntable. The average bulk temperature was estimated by inserting a thermometer in the alumina bath housing the reaction vessel. 

As compounds exhibiting enhancing effects on CL reactions, a variety of phenols, e.g., firefly luciferin and 6-hydroxybenzothiazole derivatives [12,13], 4-iodophe-nol [14], 4-(4-hydroxyphenyl)thiazole [15], 2-(4,-hydroxy-3 -methoxy-benzyli-dene)-4-cyclopentene-l,3-dione (KIH-201) [16], and 2-(4-hydroxyphenyl)-4,5-diphenylimidazole (HDI) and 2-(4-hydroxyphenyl)-4,5-di(2-pyridyl)imidazole (HPI)[17] (Fig. 6A), and phenylboronic acid derivatives, e.g., 4-phenylylboronic acid [18], 4-iodophenylboronic acid [19], and4-[4,5-di(2-pyridyl)-l //-imidazol-2-yl]phenylboronic acid (DPPA) [20] (Fig. 6B), in the luminol/hydrogen peroxide/peroxidase system are well known. Rhodamine B and quinine are used as sensitizers in the CL-emitting reaction between cerium (IV) and thiol compounds. This CL reaction was successfully applied to the sensitive determination of various thiol drugs [21-32],... 

Reaction of the thia-amino acid 392 with trifluoroacetic anhydride gave the 2,2,2-trifluoro-l-[7-(trifluoromethyl)-l//-pyrrolo[l,2-c]-[l,3]thiazol-6-yl] ethanone pyrrole 395. The formation of the pyrrole can be rationalized by a sequence involving trifluoroacetylation of the enamine 392 affording dione 393 followed by loss of water and carbon dioxide to give the aromatic product 395. These decarboxylations afford fluorinated derivatives of heterocyclic skeletons known to exhibit interesting biological activity (Scheme 58) <2000T7267>. 

More recently, 2-thioxo-4-thiazolidinones 415 were reported to undergo facile thiophilic addition of a-phosphonyl carbanions and subsequent lactamization to generate bicyclic thiazolo [2,3-A thiazole-3,5-diones 416 (Equation 189) <2004PS1307>. 

The reaction of the biacetyl-trimethyl phosphite adduct (65) with acyl isocyanates has been extended to the isocyanates ROCONCO and PhCS-NCO.46 With the thiazolin-4,5-diones (66), (65) gave the thiazol-4-ones (67). 

Numerous applications of IR spectral data have been reported for derivatives of (5,5)-fused ring systems, especially in connection with the problem of tautomeric equilibria. For example, the IR spectra of 5,6,7,8-tetrahydro-l//,3H-pyrrolo[l,2-c][l,3]oxazole-1,3-diones (24 X=0) and corresponding thiazole-l,3-diones (24 X = S) show no carbonyl absorption, but broad bands at 3300 cm-1 due to the associated OH group, indicating that the fused structures (24) exist in the enolic forms rather than their diketonic tautomers (81BJC1844). 

The lactamization of A-(5,5-diphenyl-4-oxo-2-imidazolyl)glycine 41 to 6,6-diphenyl-l,6-dihydroimidazo[l,2-tf] imidazole-3,5-dione 42 (Scheme 28) and the conversion of 2-thioacetic acid derivative 43 into the respective imidazo[2,l-A thiazole-3,5-dione 44 can be induced by treatment with DCG or acetic anhydride (Schemes 28 and 29) C1997AP85, 2000PHA429, 2001JST(597)73, CHEC-III(11.04.9.1.4)159>. 

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