Construction of pyrazolo[1,5-a]pyrimidines and pyrimido[1,2-b]indazoles with calcium carbide as an alkyne source
Xinjie You1, Botao Wang1, Fei Wen2
1College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu, 730070, P. R. China. lizheng@nwnu.edu.cn.
Abstract:
An efficient method for the construction of 5-arylpyrazolo[1,5-a]pyrimidines using calcium carbide as a solid alkyne source instead of flammable and explosive gaseous acetylene, pyrazole-3-amine and (hetero)aromatic aldehydes as starting materials in the presence of a copper mediator is described. Meanwhile, 2-arylpyrimido[1,2-b]indazoles are also synthesized under similar conditions using indazole-3-amine as a substitute for pyrazole-3-amine as a starting material. The method has salient features such as the use of an inexpensive and easy-to-handle alkyne source, commercially available substrates, wide functional group tolerance, a low-cost mediator, and simple workup procedures. This protocol can also be extended to gram-scale synthesis.
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