On the formation of uncommon pyrazoloazepines from 5-aminopyrazoles as by-products in the Clauson-Kaas reaction

Abstract

An unexpected generation of a 5,7-bicyclic framework from 5-aminopyrazoles and 2,5-dimethoxytetrahydrofuran was detected in the synthesis of originally desired 5-pyrrol-1-ylpyrazoles. To gain insight about the structure and behavior of the novel studied compounds, heteronuclear 2D NMR (including 1H15N, 19F13C and 19F15N correlations), single-crystal X-Ray diffraction structural analysis and HR-MS were exploited. Four other syntheses were designed to obtain the pyrazoloazepines by independent reaction pathways which never yielded the desired bicyclic products obtained before. The reaction conditions of the original Clauson-Kaas synthesis were optimized to yield the pyrazoloazepines in reasonable yields.