Herein, we disclosed a highly chemoselective synthesis of quinoline-2-one and quinoline-2-thione derivatives using EtOS 2 K as the C1 source. Quinoline-2-one derivatives were synthesized selectively with NaCl as a catalyst in the solvent DMSO/H 2 O, while quinoline-2-thione derivatives were produced without the need for any catalyst in an environmentally friendly solvent EtOH/H 2 O. The reaction conditions were mild and had good functional group tolerance.