Synfacts 2008(8): 0810-0810  
DOI: 10.1055/s-2008-1077935
Synthesis of Heterocycles
© Georg Thieme Verlag Stuttgart ˙ New York

A Tunable Heteroannulation Route to Fused Pyrazoles

Contributor(s): Victor Snieckus, Toni Rantanen
L. Filák, T. A. Rokob, G. Á. Vaskó, O. Egyed, A. Gömöry, Z. Riedl, G. Hajos*
Hungarian Academy of Sciences, Budapest, Hungary
Further Information

Publication History

Publication Date:
23 July 2008 (online)

Significance

2-Pyrazinyl and 3-pyridazinylketone arylhydrazones have been found to undergo ring-closure reaction under acid-catalyzed and thermal conditions to yield pyrazolo[3,4-b]pyrazines or pyrazolo[4,3-c]pyridazines. The reaction proceeds in adequate to good yields but its substrate scope was poorly studied. More emphasis was placed on the cyclization mechanism which was studied using quantum chemical calculations. The calculations suggest a pericyclic mechanism under thermal conditions and the pericyclicity is still favored under acidic conditions. The cyclization also proceeds under basic conditions for which the calculations suggest a pseudoelectrocyclization mechanism.