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Paper | Special issue | Vol 101, No. 2, 2020, pp.496-511
Published online, 12th September, 2019
DOI: 10.3987/COM-19-S(F)32
Synthetic Challenges in the Construction of 8- to 10-Membered Pyrazole-Fused Rings via Ring-Closing Metathesis

Yoshihide Usami,* Yasuyuki Tsujiuchi, Yudai Machiya, Akihiro Chiba, Tomomi Ikawa, Hiroki Yoneyama, and Shinya Harusawa

*Department of Pharmaceutical Organic Chemistry, Osaka University of Pharmaceutical Sciences, 4-20-1 Nasahara, Takatsuki, Osaka 569-1094, Japan.

Abstract

Novel pyrazole-fused heterobicyclic systems, i.e., trihydrooxocino[3,2-c]pyrazoles, tetrahydrooxonino[3,2-c]pyrazoles, and pentahydrooxecino[3,2-c]pyrazoles, were synthesized starting from 3- or 5-allyl-4-hydroxy-1H-pyrazoles via ring-closing metathesis (RCM) as the key step for the construction of the medium-sized rings (8- to 10-membered rings). The RCM reactions at room temperature required longer times and gave lower yields than those in our previous studies on the preparation of normal RCM products with 6- or 7-membered rings. The microwave-assisted RCM generally afforded double-bond migrated products or ring-contracted products along with normal RCM products.