Direct vicinal difunctionalization of alkynes through trifluoromethylation and aminosulfonylation via insertion of sulfur dioxide under catalyst-free conditions

Direct vicinal difunctionalization of alkynes through a catalyst-free four-component reaction of Togni's reagent, alkynes, sulfur dioxide, and hydrazines at room temperature is developed, which generates (E)-3,3,3-trifluoroprop-1-ene-1-sulfonohydrazides in good yields. This one-pot transformation works efficiently under extremely mild conditions without any catalysts and additives. The reaction process proceeds through trifluoromethylation of alkynes and aminosulfonylation via insertion of sulfur dioxide with excellent stereoselectivity and regioselectivity. Additionally, this reaction shows a broad substrate scope with good functional group tolerance. A plausible mechanism is proposed, supported by DFT calculations.