Recyclable iodine-catalyzed oxidative C–H chalcogenation of 1,1-diarylethenes in water: green synthesis of trisubstituted vinyl sulfides and selenides

Abstract

We disclose a metal-free, iodine-catalyzed oxidative C–H sulfenylation and selenation of alkenes, particularly 1,1-diarylethenes with diorganyl dichalcogenides in water for the cost-effective, highly atom-economical, and sustainable synthesis of valuable vinyl sulfides and selenides including some aggregation-induced-emission (AIE) active molecules. The transformation required only 10 mol% iodine as the catalyst and a very small amount of a green oxidant, H₂O₂ (0.3 equiv.), to afford the desired products in moderate to high yields of up to 96% under mild reaction conditions, i.e. 50 °C and an aerobic atmosphere. The products were further synthetically diversified to various novel classes of organic molecules. The notable advantages of this method over the previously developed ones for the C–H chalcogenation of 1,1-diarylalkenes are (a) a metal-free, energy-efficient, cost-effective and sustainable protocol for the synthesis of both vinyl sulfides and selenides, (b) use of inexpensive reagents such as iodine as the catalyst and H₂O₂ as the green oxidant, (c) water as the green reaction medium and water as the only byproduct, (d) a straightforward scale-up process up to the gram scale without any compromise on the reaction outcome, (e) very clean reactions (100% conversion) in multiple cases to afford pure vinyl sulfides/selenides without the requirement of a huge organic-solvent consuming column chromatographic purification technique, and (f) excellent green chemistry metrics such as high atom economy (>96%), atom efficiency (≥87%), carbon efficiency (>88%), and reaction mass efficiency (≥81%), a very low E-factor (≤4.5 g waste per g product), here the byproduct is nothing but water, and a very high EcoScale score (≥82) which revealed that this method is excellent in the context of green chemistry. Moreover, the catalyst iodine could be recovered after the reaction and recycled without any compromise on the reaction outcome which makes the process highly sustainable. Mechanistic studies revealed a radical pathway for this transformation.