Directing Influence of Proximal Boron Functionalities on the S‑Alkylation of Sulfenic Acid Anions: An Experimental and Computational Study

The S-functionalization chemistry of sulfenic acid anions, also known as sulfenate anions, represents an emerging method for the preparation of sulfoxides. Nearby functional groups can often influence the S-functionalization chemistry of sulfenate anions through nonbonding interactions. Recently, several reports have illustrated the combination of the Lewis acidity of trivalent boron and Lewis basicity of sulfinyl groups to perform valuable chemistry, but limited experimental investigations into the Lewis acid/Lewis base complex between sulfenate anions and trivalent boron functionalities have been conducted. In this paper, the interaction between sulfenate anions and trivalent boron functionalities is investigated using sulfenate S-functionalization competition reactions between ortho-borylated and nonborylated benzyl electrophiles. In 22 competition experiments with varied sulfenate anions and electrophilic boron species, sulfenate anion S-functionalization reactions were up to 100% selective for an ortho-borylated benzyl bromide electrophile. DFT computational modeling experiments, 11B NMR tracking experiments, Hammett correlation analysis, and control experiments were conducted to investigate the origin of the observed selectivities, and these provided evidence that the formation of a Lewis acid/Lewis base complex between the sulfenate oxygen and the trivalent boron prior to intramolecular sulfenate S-functionalization is a major factor in establishing the selectivity.