Green synthesis of 2-trifluoromethyl quinoline derivatives under metal-free conditions and their antifungal properties

The skeleton of 2-trifluoromethyl quinoline is the core structure of many natural products and pharmaceutical molecules. The synthesis of this scaffold is limited by metal catalysis, harsh conditions, toxic or hazardous reagents and solvents, and lower atom-economy. Herein, a novel method for the synthesis of 2-trifluoromethyl quinolines via the [4 + 2] cyclization of β-keto esters or 1,3-diketones with various substituted o-aminobenzaldehydes using the metal free catalyst in EtOH is reported. This atom- and step-economical protocol features simple operation, broad substrate scope, and good functional-group compatibility. The synthetic utility of this methodology was highlighted by easy gram-scale synthesis and late-stage functionalization, which would promote the vigorous development of quinoline chemistry. Moreover, the in vitro antifungal activities of the 2-trifluoromethyl quinolines against F. graminearum (from wheat), F. graminearum (from corn), F. moniliforme, F. oxysporum, and R. solani were investigated to further potential utility of these compounds.