Of pyrazoles condensed to heteroaromatic

Chemistry of Pyrazoles Condensed to Heteroaromatic Five- and Six-Membered Rings... 

Elnagdi, M. H., Elmoghayer, M. R. H., Sadek, K. U., Chemistry of Pyrazoles Condensed to Heteroaromatic Five- and Six-Membered Rings, 48, 223. 

Pyrazoles condensed to heteroaromatic five-and six-membered rings, 48, 223 Pyrazolopyridines, 36, 343 Pyrazolopyrimidines, chemistry of, 41, 319 Pyridazine chemistry, advances in, 49, 385 Pyridazines, 9, 211 24, 363 49, 385 Pyridine(s)... 

Dimerizations of p-Rich N-Heteroaromatic Compounds and Xanthine Derivatives. Sekine, Toshikazu Higuchi, Yoshihiro Yamada, Tomoko Murakoshi, Isamu (Fac. Pharm. Sci., Chiba Univ., Chiba, Japan 260). Chem. Pharm. BuU. 1989, 37 (8) 1987-9 (Eng.). N-Methylimidazole, benzimidazole, and N-methylbenzimidazole condensed dehydrogenatively to afford the corresponding sym. dimers when heated in the presence of Pd-Pt/C catalyst and pyridine N-oxide. Imidazole, pyrazole, and N-methylpyrazole did not dimerize under the same conditions. The same reactions using caffeine and 1,7-dimethylhypoxanthine gave the eorresponding dimers. 

Hydrogen borrowing and dehydrogenative condensations provide new opportunities for the preparation of both saturated and aromatic heterocycles respectively. The ability to directly access azacycles from stable species such as alcohols and amines allows chemists to circumvent the preparation and use of relatively unstable carbonyls and alkyl halides that conventional methods require. Pyridines, pyrazines, pyrroles, as well as fused bicyclic heteroaromatics, may all be prepared by dehydrogenative condensation this reactivity will likely be extended to pyrimidines, imidazoles, pyrazoles, and triazoles in the near future. Continuous advances in scope and scalability will expand the role of hydrogen transfer in the discovery and production of small molecule therapeutics. 

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