A metal-free route to alkynyl sulfones under photoinduced conditions with the insertion of sulfur dioxide
A metal-free route to alkynyl sulfones under photoinduced conditions is accomplished, starting from 4-alkyl Hantzsch esters, sulfur dioxide, and alkynyl bromides under visible light irradiation at room temperature. This transformation proceeds smoothly, affording the corresponding alkylalkynyl sulfones in moderate to good yields by using sodium metabisulfite as the sulfur dioxide surrogate. A plausible mechanism is proposed, showing that alkyl radical generated in situ from 4-alkyl Hantzsch esters in the presence of photocatalyst initiates the reaction. Subsequent sulfonylation, addition to alkynyl bromide, and release of bromide give rise to the corresponding alkylalkynyl sulfone.