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■ N,N’-Linked Biozoles. Part 5. Synthesis of Pyrazolyl Dimers by the Reaction of 3-Methoxycarbonyl-2-pyrazoline with Lead Tetraacetate

Javier de Mendoza,* M. Rosario González-Muñiz, M. Rosario Martín, and José Elguero

*Departamento de Química Orgánica, Facultad de Ciencias, Universidad Autónoma de Madrid, Cantoblanco, 28049-Madrid, Spain

Abstract

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).