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Short Paper | Regular issue | Vol 94, No. 10, 2017, pp.1923-1930
Published online, 25th August, 2017
DOI: 10.3987/COM-17-13772
■ Synthesis of (5,6-Dihydro-4H-pyrrolo[1,2-b]pyrazol-3-yl)-methanamine

Zhong-Gang Bai, Hui Qi, Qun-Zheng Zhang, Yu Ma, Qing Pan, and Xun-Li Zhang*

*College of Chemistry and Chemical Engineering, Xi’an Shiyou University, 18, 2nd Dianzi Road, Xi’an, Shanxi 710065, China

Abstract

This short paper reports the development of a new method for the synthesis of (5,6-dihydro-4H-pyrrolo[1,2-b]pyrazol-3-yl)methanamine. Pyrazole was initially protected with an N-SEM protective group, followed by alkylation at C-5 position with 1-bromo-3-chloropropane. Following SEM deprotection, the intramolecular ring was closed and then a bromine atom (Br) was introduced with N-bromosuccinimide (NBS) by electrophilic aromatic substitution (SEAr), forming 3-bromo-5,6-dihydro-4H-pyrrolo[1,2-b]pyrazole. The Br group was subsequently converted into aldehyde group, then into oxime. The final step of hydrogenation resulted in the desired product. The overall yield through the 8-step reaction process was found to be 29.4%. The intermediates and final product were identified by HPLC-MS and 1H NMR. This development provides a novel synthetic route to the formation of 5,6-dihydro-4H-pyrrolo[1,2-b]pyrazole skeleton.