Accessing chiral sulfones bearing quaternary carbon stereocenters via photoinduced radical sulfur dioxide insertion and Truce-Smiles rearrangement.

From the viewpoint of synthetic accessibility and functional group compatibility, photoredox-catalyzed sulfur dioxide insertion strategy enables in situ generation of functionalized sulfonyl radicals from easily accessible starting materials under mild conditions, thereby conferring broader application potential. Here we present two complementary photoinduced sulfur dioxide insertion systems to trigger radical asymmetric Truce-Smiles rearrangements for preparing a variety of chiral sulfones that bear a quaternary carbon stereocenter. This protocol features broad substrate scope and excellent stereospecificity. Aside from scalability, the introduction of a quaternary carbon stereocenter at position ß to bioactive molecule-derived sulfones further demonstrates the practicality and potential of this methodology.

Regioselective Radical-Relay Sulfonylation/Cyclization Protocol to Sulfonylated Pyrrolidones under Transition-Metal-Free Conditions.

A simple and low-cost tandem sulfonylation/cyclization of 1,5-diene, aryldiazonium salt, and DABCO·(SO2)2 is disclosed. This base-promoted multicomponent reaction can provide a "green" and economic synthesis of sulfonylated pyrrolidones under transition-metal-free and moisture/oxygen-insensitive reaction conditions, thus delivering a wide range of sulfonylated pyrrolidones in moderate to high yields with excellent functional group compatibility. A plausible mechanism involving a radical process is proposed, which demonstrates highly chemoselective trapping of the aryl radical with "SO2" species, and a regioselective sulfonylation/cyclization protocol in this reaction.

A metal-free reaction of sulfur dioxide, cyclopropanols and electron-deficient olefins.

The importance of γ-keto sulfones in medicinal chemistry and organic synthesis is known. An efficient route to γ-keto sulfones via a metal-free reaction of cyclopropanols, sulfur dioxide and electron-deficient olefins is achieved. This reaction proceeds smoothly under mild conditions without the need of catalyst, oxidant or additive. A plausible mechanism is proposed, which occurs through a γ-keto sulfinate intermediate generated in situ from the reaction of cyclopropanol with sulfur dioxide. The γ-keto sulfinate intermediate would be trapped by the electron-deficient olefin, resulting in the formation of γ-keto sulfones. Various functional groups in the cyclopropanols and electron-deficient olefins are compatible in this transformation.

Microwave-Assisted Cp*CoIII-Catalyzed C-H Activation/Double C-N Bond Formation Reactions to Thiadiazine 1-Oxides.

A microwave-assisted, Cp*CoIII-catalyzed direct C-H activation/double C-N bond formation reaction of simple NH-sulfoximines with 1,4,2-dioxazol-5-ones to produce diverse thiadiazine-1-oxides is reported. The reaction tolerates a broad range of functional groups under external oxidant-free conditions and only releases CO2 and H2O as the sole byproducts. The preliminary mechanistic studies revealed an electrophilic metalation pathway is likely involved in the reaction.

Transition-Metal-Catalyzed Hydrosulfoximination and Oxidation Reaction for the Synthesis of Sulfoximine Derivatives.

We report herein a Au/Ag-cocatalyzed chemoselective hydrosulfoximination reaction of simple ynamides with free NH-sulfoximines, which produces the N-alkenylated sulfoximidoyl derivatives with quantitative atom efficiency and good to excellent yields. Further elaborations of the enamine isomers under Ru-catalyzed oxidative conditions to cleave the C═C double bonds can selectively afford urea-type sulfoximines. The aforementioned catalytic reactions provide new opportunities for the convergent and straightforward access to sulfoximine derivatives.

Platinum-Catalyzed Cascade Rearrangement Reaction of 1,5-Diynyl Esters: Unusual Regioselective 1,5-Hydride Migration.

A highly regioselective sequential 1,3-acyloxy migration/pentannulation/1,5-hydride migration reaction is disclosed which provides an efficient access to (E)-2-vinyl-3-oxo-1-methyleneindenes under neutral and mild reaction conditions. The migrated hydrogen atom was derived from an unactivated alkyl group, and the long-range 1,5-H shift was confirmed through related deuterium experiments.

Platinum-catalyzed tandem cycloisomerization reaction of benzoendiynyl esters: regioselective long-range 1,5-acyl migration.

A Pt(II)-catalyzed intramolecular chemo- and regioselective pentannulation/long-range 1,5-acyl migration reaction is described. This cascade cycloisomerization protocol produces a wide variety of benzofulvene diketones in good to excellent yields with exclusively the Z configuration of the exocyclic double bond of the final product. The (18)O isotope experiment together with (13)C NMR, HRMS, and HMBC analyses confirmed an interesting long-range acyl rearrangement process in this transformation.