Imidazol 1,2-6 1,2,4 triazole-2-thiones

Thione groups can often be eliminated by oxidation probably the sulfinic acid is the intermediate. Sometimes the sulfinic acid can be isolated (e.g., 740 741), but more often it spontaneously loses SO2. In this way, thiazoline-2-thiones give thiazoles, l,2-dithiole-3-thiones 742 are converted into 1,2-dithiolylium salts 743, l,3-dithiole-2-thiones 744 into 1,3-dithiolylium salts 745, 1,5-disubstituted imidazole-2-thiones into imidazoles <2003JHC229>, and 3-mercapto-l,2,4-triazoles into the parent triazole <2006S156>. In the pyrazole series, 746 also loses an A-methyl group to yield 747. 

The first isolated NHC was reported by Arduengo et al. in 1991 [12]. The synthetic protocol leading to this isolation followed a methodology developed to deprotonate the precursor imidazohiun salt with sodium or potassium hydride in the presence of KO Bu in DMSO [20]. Herrmann subsequently developed a method based on deprotonation of the corresponding salts in hquid ammonia [21]. These methods tolerate a large variety of functional groups and can be scaled up. Other synthetic approaches include reaction of imidazol-2-thiones with potassium metal [22], thermal ehmination of methanol from adducts to form triazol-2-yhdene [23], and ehmination of phenoxides. 

Dihydro-3-( 1,10-phenanthrolin-2-yl)-5-(2-pyridinyl)-1,2,4-triazole, D-00465, 4-Dihydro-1 (2//)-phenazinone, D-00466, 3-Dihydro-4-phenyl-2/f-imidazole-2-thione, see P-00140... 

Reaction of 232 with 4-substituted l,3-oxazol-5(4/7)-one 247 led to diacylhydrazines 248 or to imidazole derivatives 249 depending on the reaction temperature (Scheme 24). l,2,4-Triazole-3-thione 250 was obtained by a two-step sequence from 232 with phenyl isothiocyanate and subsequent base-catalyzed cyclization of thiosemicarbazide 251. The effects of hydrazones 241-246 on inhibition of photosynthetic electron transport in spinach chloroplasts and chlorophyll content in the antialgal suspensions of Chlorella vulgaris were investigated <2005CEC622>. 

Different synthetic routes have been used to prepare these carbenes (Scheme 8.6). The most common procedure is the deprotonation of the conjugate acid. In early experiments, sodium or potassium hydride, in the presence of catalytic amounts of either f-BuOK or the DMSO anion were used. ° Then, Herrmann et al. showed that the deprotonation occurs much more quickly in liquid ammonia as solvent (homogeneous phase), and many carbenes of type IV have been prepared following this procedure. In 1993, Kuhn and Kratz" developed a new and versatile approach to the alkyl-substituted N-heterocyclic carbenes IV. This original synthetic strategy relied on the reduction of imidazol-2(3//)-thiones with potassium in boiling tetrahydrofuran (THF). Lastly, Enders et al." reported in 1995 that the 1,2,4-triazol-5-ylidene (Vila) could be obtained in quantitative yield from the corresponding 5-methoxy-l,3,4-triphenyl-4,5-dihydro-l//-l,2,4-triazole by thermal elimination (80 °C) of methanol in vacuo (0.1 mbar). 

Numerous structures containing the thiocarbonyl ylide dipole are conceivable. Incorporation of the thiocarbonyl ylide dipole into a bicyclic heterocyclic system is possible by the conversion of the cyclic thione (203) into the ring-fused mesoionic system (204). The thiocarbonyl ylide dipole (205) undergoes cycloaddition with both alkenic and alkynic electron-poor dipolarophiles in refluxing benzene or xylene so that, after extrusion of hydrogen sulfide or sulfur, respectively, from the initial 1 1 cycloadducts (206) and (207), a ring-fused pyridinone is formed. The method has been used for the annelation of pyridinones to the imidazole, 1,2,4-triazole, thiazole and 1,3,4-thiadiazole systems... 

With nucleophilic bases 3,7,7a-trimethyl-2,3,5,6,7,7a-hexahydro-17f-imidazo[l,5-Zi][l,2,4]-triazole-2,5-dione (130) and -2,5-dithione (129) the [3 -H 2] cycloelimination of the heterocumulene moiety from the triazole ring is followed by nucleophilic addition of the base to give 4-substituted 4,5,5-trimethyl-2,3,4,5-tetrahydro-l/7-imidazol-2-ones (135) and -2-thiones (136), respectively (Scheme 7) <93TH 805-01, 95FES379). 

The reaction of l-arylamino-4,4-dimethyl-5-methylene-2,3,4,5-tetrahydro-l//-imidazol-2-one (338 Y = O) and -2-thione (338 Y = S) with protic heterocumulenes affords 7,7,7a-trimethyl-3-aryl-2,3,5,6,7,7a-hexahydro-l/7-imidazo[l,5-fe][l,2,4]triazol-2,5-diones (339 X = Y = 0), and N-and 5-derivatives of these functions in 2- and 5-positions (Equation (104)) <93TH 805-oi, 95FES379>. 

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