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■ 1,3-Dipolar Cycloaddition of Pyrazolo[1,2-a]indazoles with Domethyl Acetylenedicarboxylate

Yasuo Fujimura,* Yoshiharu Nawata, and Masatomo Hamana

*Central Research Laboratories, Chugai Pharmaceutical Company, Ltd., Takada 3-41-8, Toshima-ku, Tokyo 171, Japan

Abstract

Pyrazolo[1,2-a]indazoles (3a and 3b) obtained from 9H-pyrazolo[1,2-a]indazolium bromides (2a and 2b) and sodium hydride readily react with dimethyl acetylenedicarboxylate to give 1,3-dipolar cycloadducts (4 and 8). Products 4 and 8 are hydrogenated to the 3,4-dihydro derivatives (6 and 10) and converted into their 4-alkoxy derivatives (5,7 and 9) with alcohols under acidic conditions.