Benoxazolone-based ionic liquid catalyzed C–S bond construction for synthesis of benzothiazoles from 2-aminothiophenols and CO2 under ambient conditions

Abstract

The green synthesis of sulfur-containing compounds via the use of CO₂ as a C1 feedstock to build C–S bonds is an attractive topic. Although a few implementations for this route have been reported, the transformation of CO₂ at ambient conditions remains a great challenge. In this work, a novel benoxazolone-based ionic liquid (i.e., tetrabutylphosphonium benoxazolone, [P₄₄₄₄][Benoxa]) was discovered, which could efficiently catalyze the synthesis of benzothiazoles via the cyclization of 2-aminothiophenols with CO₂ in the presence of hydrosilanes at atmospheric pressure and room temperature (e.g., 30 °C, 0.1 MPa). The catalytic protocol was applicable to various 2-aminothiophenols bearing electron-withdrawing or electron-donating substituents, affording the corresponding benzothiazoles in good-to-excellent yields. To the best of our knowledge, this is the first example of the synthesis of benzothiazoles using CO₂ under solvent-free and ambient conditions.