A combined experimental and computational study of ligand-controlled Chan-Lam coupling of sulfenamides.

The unique features of the sulfenamides' S(II)-N bond lead to interesting stereochemical properties and significant industrial functions. Here we present a chemoselective Chan-Lam coupling of sulfenamides to prepare N-arylated sulfenamides. A tridentate pybox ligand governs the chemoselectivity favoring C-N bond formation, and overrides the competitive C-S bond formation by preventing the S,N-bis-chelation of sulfenamides to copper center. The Cu(II)-derived resting state of catalyst is captured by UV-Vis spectra and EPR technique, and the key intermediate is confirmed by the EPR isotope response using 15N-labeled sulfenamide. A computational mechanistic study reveals that N-arylation is both kinetically and thermodynamically favorable, with deprotonation of the sulfenamide nitrogen atom occurring prior to reductive elimination. The origin of ligand-controlled chemoselectivity is explored, with the interaction between the pybox ligand and the sulfenamide substrate controlling the energy of the S-arylation and the corresponding product distribution, in agreement with the EPR studies and kinetic results.

Synthesis of Sulfilimines Enabled by Copper-Catalyzed S-Arylation of Sulfenamides.

Herein, an unprecedented synthetic route to sulfilimines via a copper-catalyzed Chan-Lam-type coupling of sulfenamides is presented. A key to success in this novel transformation is the chemoselective S-arylation of S(II) sulfenamides to form S(IV) sulfilimines, overriding the competitive, and more thermodynamically favored, C-N bond formation that does not require a change in the sulfur oxidation state. Computations reveal that the selectivity arises from a selective transmetallation event where bidentate sulfenamide coordination through the sulfur and oxygen atoms favors the S-arylation pathway. The mild and environmentally benign catalytic conditions enable broad functional group compatibility, allowing a variety of diaryl or alkyl aryl sulfilimines to be efficiently prepared. The Chan-Lam coupling procedure could also tolerate alkenylboronic acids as coupling partners to afford alkenyl aryl sulfilimines, a class of scaffolds that cannot be directly synthesized via conventional imination strategies. The benzoyl-protecting groups could be conveniently removed from the product, which, in turn, could be readily transformed into several S(IV) and S(VI) derivatives.

Palladium-Catalyzed Aryl-Furanylation of Alkenes: Synthesis of Benzofuran-Containing 3,3-Disubstituted Oxindoles.

A novel palladium-catalyzed aryl-furanylation of alkenes is described. This protocol provided a straightforward route to the synthesis of various benzofuran-containing 3,3-disubstitutedoxindole derivatives bearing a quarternary carbon center. In the cascade process, one C(sp2)-O bond, two C(sp2)-C(sp3) bonds, an oxindole, and a furan ring are formed in a single chemical operation.