Sustainable synthesis of pyrazoles using alcohols as the primary feedstock by an iron catalyzed tandem C–C and C–N coupling approach

Abstract

We report two new efficient iron-catalyzed synthetic strategies for multicomponent synthesis of tri-substituted pyrazoles using biomass-derived alcohols as the primary feedstock. A well-defined, bench stable, and easy to prepare Fe(II)-catalyst (1) bearing a tridentate pincer 2-(phenyldiazenyl)-1,10-phenanthroline (L¹) was used as the catalyst. A wide variety of tri-substituted pyrazoles were prepared via dehydrogenative coupling of alcohols, and aryl hydrazines with secondary alcohols and alkynes, respectively. These methods eliminate the potential use of any pre-functionalized starting materials, noble metal catalysts, oxidants, or additives producing various substituted pyrazoles in moderate to good isolated yields via sequential C–C and C–N bond formation. A series of control experiments and spectroscopic studies were performed to understand the plausible mechanism of these multicomponent reactions.