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Paper | Regular issue | Vol 63, No. 11, 2004, pp.2475-2494
Published online, 7th September, 2004
DOI: 10.3987/COM-04-10144
■ Mononuclear Heterocyclic Rearrangement: Synthesis of [5:5] Bicyclic [c]-Fused 3-Aminopyrazoles via the N-N Bond Formation Strategy

David A. Berry, Tun-Cheng Chien, and Leroy B. Townsend*

*Department of Medical Chemistry, College of Pharmacy, University of Michigan, 930 North University, Ann Arbor, MI 48109-1055, U.S.A.

Abstract

The formation of [5:5] bicyclic heterocyclic ring systems containing [c]pyrazoles, i.e. imidazo[4,5-c]pyrazole, pyrazolo[3,4-c]pyrazole, pyrrolo- [2,3-c]pyrazole, and pyrazolo[3,4-d][1,2,3]triazole, was accomplished by mononuclear heterocyclic rearrangement (MHR). The core pyrazole ring was formed based on a N-N bond formation strategy. The ring transformation of 5-substituted 3-(2-aminoaryl)-1,2,4-oxadiazoles (14, 15a-b, 16b and 33) under thermal conditions to the corresponding [5:5] bicyclic [c]-fused 3-aminopyrazole ring systems (17a, 18a-b, 20 and 34 respectively) was promoted by sodium hydride in DMF or DMSO. The ring transformation by MHR has provided a practical and general synthetic method for the derivatives of 3-aminoimidazo- [4,5-c]pyrazole (4), 3-aminopyrazolo[3,4-c]pyrazole (5), 3-aminopyrrolo[2,3-c]- pyrazole (6) and 6-aminopyrazolo[3,4-d][1,2,3]triazole (7).