4-(Methylthio)phenylboronic Acid

Technical Specifications

Product Description & Scientific Applications

4-(Methylthio)phenylboronic acid (4-thioanisoleboronic acid; 4-(methylsulfanyl)phenylboronic acid) is a para-substituted arylboronic acid carrying a methylthio thioether group. The substituent is close to electronically neutral at the para position (σp ≈ 0.00), as sulfur resonance donation and inductive withdrawal largely offset one another, so the reagent sits between the electron-rich 4-alkoxy arylboronic acids and the electron-poor 4-cyano and 4-trifluoromethyl members of the family. Consistent with this near-neutral effect, its boronic acid acidity is expected to remain close to that of unsubstituted phenylboronic acid rather than shifting toward the electron-rich or electron-poor extremes. The methylthio group is a useful chemical handle: a soft donor that can influence transition-metal coordination in sensitive systems, and a sulfide that can be oxidised after coupling, most directly to the corresponding sulfoxide and, under stronger oxidation conditions, to the sulfone. It is useful wherever a para-methylthioaryl unit, an oxidisable sulfide handle, or a thioether-bearing arylboronic acid coupling partner is required.

May contain small amounts of the cyclic anhydride 4-(methylthio)phenylboroxine. Under aqueous or basic coupling conditions the two forms re-equilibrate and the impact on yield is minor.

Applications and Reactions

• Suzuki–Miyaura coupling: installs the 4-(methylthio)phenyl group into aryl, alkenyl, and alkynyl frameworks; reported examples include cross-coupling with 2-aryl-1-bromo-1-nitroethenes and with alkynyl bromides. The thioether is generally compatible with coupling chemistry but may influence catalyst choice through sulfur coordination in sensitive systems.
• Methylthio as an oxidisable handle: the aryl sulfide undergoes sulfoxidation to the corresponding sulfoxide, allowing the electronic character and polarity of the coupled aryl group to be modified after installation.
• Addition to naphthyridine N-oxides: addition reactions with naphthyridine N-oxides provide access to arylated N-heterocyclic scaffolds.
• Oxyarylation of Heck intermediates: oxyarylation of Heck-reaction intermediates provides access to tetrahydrofuran (THF) derivatives.
• Copper-catalysed halogenation: reported copper-catalysed halogenation chemistry provides access to halogenated para-methylthioarene derivatives from the boronic acid handle.

Further Reading

For boronic acids, boronic esters, protodeboronation, boroxine content, and Suzuki–Miyaura reagent selection, see NorrChemica's Lab Journal guide: Choosing Your Boron Source for Suzuki–Miyaura Coupling.

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