Three-Component Synthesis of Pyrano[2,3-c]pyrazoles
A. Shaabani, A. Sarvary, A. H. Rezayan, S. Keshipour
Shahid Beheshti University, Tehran, Iran
25. Mai 2009 (online)
A three-component reaction of isocyanides, symmetrical dialkylacetylene dicarboxylates, and 1-phenyl-1H-pyrazol-5(4H)-one to give substituted pyrano[2,3-c]pyrazoles is described. A mechanism is proposed, whereby the alkyne is sequentially attacked through Michael addition of the isocyanide and pyrazolone to give a keteneimine, which is then further attacked by the pyrazolone to give the observed products. Although this mechanism is plausible, no evidence for it was presented by the authors.