A DFT examination of the role of proximal boron functionalities in the S-alkylation of sulfenic acid anions.
Org Biomol Chem
; 20(3): 649-657, 2022 01 19.
Article
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| MEDLINE
| ID: mdl-34942637
ABSTRACT
Sulfenic acid anions represent an emerging nucleophile for the preparation of sulfoxides. Their S-functionalization chemistry can often be influenced by a nearby group that interacts with the component atoms of the sulfenate through non-bonding interactions. This study uses DFT methods to assess the importance of proximal boron-containing functional groups to direct S-alkylation chemistry of selected sulfenate anions. Several structural variations were modelled at the B3LYP/6-311++G(d,p) level, with the boron species positioned 3 to 5 carbons away from the alkylation site. Transition state free energies of S-alkylation transition states were located with and without sulfenate oxygen precomplexing to the nearby boron atom. The outcomes suggest that an ortho-substituted boronate ester on benzyl bromide can direct and accelerate an alkylation reaction principally due to a reduction of the entropic barrier. It was also determined that an intermolecular precomplex imparts too much stabilization to the sulfenate, thereby reducing its reactivity. The modelling suggests a possible aryl migration of the boronate/sulfenate complex is not competitive with S-alkylation.
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MEDLINE
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En
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2022
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Article