N-Heterocyclic Carbene Catalyzed Synthesis of δ-Sultones via α,β-Unsaturated Sulfonyl Azolium Intermediates

β-Aminosulfonyl Fluorides via Water-Accelerated N-Heterocyclic Carbene Catalysis

Herein, a water-accelerated, N-heterocyclic carbene (NHC)-catalyzed aza-Michael addition reaction was reported to access β-aminosulfonyl fluorides, which are key hubs of the sulfur(VI) fluoride exchange (SuFEx) reaction. As a crucial reaction medium, water considerably enhanced the reaction rate with excellent chemo- and site-selectivity (up to >99 : 1) compared to conventional solvents. In addition, the late-stage ligation of bioactive molecules with the aliphatic β-amino SuFEx hub was demonstrated. Mechanistic studies on experimental, analytical, and computational approaches support noncovalent activation over NHC catalysis "on-water".

Hydrophobic Amplification Enabled High-Turnover Phosphazene Superbase Catalysis

β-Sulfido sulfonyl fluoride and its derivatives have been gaining attention recently in the fields of medicinal chemistry and material science. The conventional method for the synthesis of functionalized alkyl sulfonyl fluorides requires several chemical transformations. Therefore, a direct establishment of such chemical structures remains challenging, and an efficient catalytic approach is highly desired. Herein a significant "on-water" hydrophobic amplification was achieved, enabling a high-turnover catalytic thia-Michael addition to produce unprecedented β-arylated-β-sulfido sulfonyl fluorides. Amounts as low as 100 ppm (0.01 mol %) of the phosphazene superbase were sufficient to successfully catalyze the reaction with excellent chemo-/site-selectivity and with optimal functional group tolerance. Several β-arylated ethene sulfonyl fluorides were converted into thia-Michael adducts up to >99 % yields. The mild conditions, high turnover, neutral pH, and scalability of the sustainable catalytic process benefit the preparation of potential pharmaceuticals (e. g., polyisoprenylated methylated protein methyl esterase inhibitors) and organic materials (e. g., electrolyte additives).

Enantioselective (4+2) Annulation of Donor-Acceptor Cyclobutanes by N-Heterocyclic Carbene Catalysis

Herein we report the enantioselective (4+2) annulation of donor-acceptor cyclobutanes and unsaturated acyl fluorides using N-heterocyclic carbene catalysis. The reaction allows a 3-step synthesis of cyclohexyl β-lactones (25 examples) in excellent chemical yield (most ≥90 %) and stereochemical integrity (all >20:1 d.r., most ≥97:3 e.r.). Mechanistic studies support ester enolate Claisen rearrangement, while derivatizations provide functionalized cyclohexenes and dihydroquinolinones.