Thiazolo pyridine-5-carboxylates

A microwave-assisted variant of the Rosenmund von Braun reaction has also been developed (Scheme 73) [83]. DMF at 200 °C proved not very useful for the cyanodehalogenation of methyl (3R)-6-bromo-5-oxo-2,3-dihydro-5ff-[l,3]thiazolo[3,2-a]pyridine-3-carboxylates since only low yields of the corresponding nitrile were obtained, and there were substantial amoimts of unconverted starting material. Extending the reaction time from 10 to 20 min gave more desired reaction product but also significant amoimts of... 

A number of syntheses of substituted 2,3 -bipyridines are worthy of note. Tetracyclone heated at 215°C with nicotinonitrile affords 3,4,5,6-tetraphenyl-2,3 -bipyridine, whereas 3,4-di(2-pyridyl)pyridine is obtained by an oxidative degradation of the corresponding 6,7-disubstituted thiazolo[3,2-a]-pyridinium salt. Nicotinic acid on UV irradiation in aqueous solution at pH 4-6 gives 2,3 -bipyridine-5-carboxylic acid, whereas irradiation of picolinic acid in the same pH range in the absence of metal ions gives some 2,3 -bipyridine. 6,6 -Diphenyl-2,3 -bipyridine is thought to be formed from... 

S, 8aS )-6-[(terf-Butoxycarbonyl)aminol-5-oxohexahydro-5H-thiazolo[3,2-a]pyridine-3-carboxylic Add (31) [77]... 

In an attempt to synthesize fused aromatic systems of a pentalene-like structure, Boekelheid and Fedoruk (332) submitted the dicyanomethyl ylide of thiazole (77) to the addition reaction with dimethyl acetylenedi-carboxylate (DMA). They unexpectedly observed the formation of a fused six-membered (80) rather than a five-membered-ring (78). This ylide (77) was readily afforded by the reaction of thiazole (73) with tetracyanoethylene oxide and then put into reaction with DMA. The initially formed thiazolopyrrole derivative (78) is strongly polarized by the gcm-dicyano group, and its pyrrole ring is spontaneously cleaved with proton elimination. The ring dosure of the intermediate (79) leads to the final stable derivative of 5-FT-thiazolo[3,2-a]pyridine (80). More recently. 

Thiazolo-[4,5-d]- and -[5,4-d]-pyrimidines [C3NS-C4N2]. The reaction of the A" -thiazoline (139) with NaSH or with H2S and pyridine gives the thiazolo-[4,5-i/]pyrimidine-7-thione (140 R = Ac, R = H, X = S), and with acetic anhydride and PPA yields (140 R = H, R = Me,X = O), whilst the readily available ethyl 2-methylmercapto-5-aminothiazole-4-carboxylate will react with formamide to give the thiazolo[5,4- f]pyrimidin-4-one (141). ... 

At room temperature, 120 mg CuCN (1.3 mmol) was added to a stirred solution of 150 mg (3/ )-6-bromo-7-naphthalen-l-ylmethyl-5-oxo-8-phenyl-2,3-dihydro-57/-thiazolo[3,2-Q ]pyridine-3-carboxylic acid methyl ester (0.30 mmol) in 1.0 mL NMR The mixture was heated at 220°C for 20 min under microwave irradiation, and the solvent was then removed by lyophilization from deionized water. The residue was thoroughly extracted with CH2CI2, dried, and concentrated. Silica gel column chromatography using heptane/EtOAc (1 1) as the eluent afforded 110 mg (3R)-6-cyano-7-naphthalen-l-ylmethyl-5-oxo-8-phenyl-2,3-dihydro-5i/-thiazolo[3,2-o ]pyridine-3-carboxylic acid methyl ester as a white foam, in a yield of 82%. 

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