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N,N'-LINKED BIAZOLES. PART 5. SYNTHESIS OF PYRAZOLYL DIMERS BY THE REACTION OF 3-METHOXYCARBONYL-2-PYRAZOLINE WITH LEAD TETRAACETATE
Mendoza, Javier de,Gonzales-Muniz, M. Rosario,Martin, M. Rosario,Elguero, Jose
, p. 2619 - 2628 (2007/10/02)
Contrary to a previous report by Akhrem et. al. (Tetrahedron Lett. 1973, 2655), the reaction of 3-methoxycarbonyl-2-pyrazoline with lead tetraacetate affords not only 3-methoxycarbonyl-1-(3-methoxycarbonyl-2-pyrazolin-1-yl)pyrazole (8) and 3-methoxycarbonyl-1-(1-methoxycarbonyl-1-cyclopropyl)pyrazole (9), but a complex mixture of pyrazoles and pyrazolines depending on the reaction conditions (LTA/pyrazoline ratio and temperature).The structures of all compounds have been established, and a new mechanism is proposed for the reaction.The oxidation of 8 with N-bromosuccinimide gave the symmetrical 3,3'-dimethoxycarbonyl-1,1'-bipyrazole (17).
