Thianthrene/TfOH-catalyzed electrophilic halogenations using N-halosuccinimides as the halogen source

Area of Science:

• Organic Chemistry
• Catalysis
• Synthetic Methodology

Background:

• Organohalides are essential in organic synthesis, but direct halogenation of unreactive substrates is challenging.
• Existing halogenation methods often require specialized reagents or substrate activation, limiting broad applicability.
• A versatile catalytic system for diverse halogenation remains an underexplored area in synthetic chemistry.

Purpose of the Study:

• To develop a novel catalytic system for the efficient halogenation of a wide range of organic substrates.
• To activate common halogenating reagents using a catalytic approach for broader substrate scope and reaction types.
• To investigate the mechanism of the proposed catalytic halogenation system.

Main Methods:

• Utilized thianthrene as a catalyst in combination with trifluoromethanesulfonic acid (TfOH).
• Employed regular halogenating reagents (NXS) activated by the thianthrene/TfOH catalytic system.
• Applied the protocol to various organic substrates including aromatics, olefins, alkynes, and ketones.

Main Results:

• Established an effective catalytic system comprising thianthrene and TfOH for activating NXS.
• Successfully achieved multiple types of halogenation (aromatics, olefins, alkynes, ketones) with broad substrate applicability.
• Mechanism studies revealed the in situ formation of a reactive electrophilic halogen thianthrenium species.

Conclusions:

• The thianthrene/TfOH system provides a versatile catalytic approach for activating conventional halogenating reagents.
• This methodology significantly expands the scope and efficiency of halogenation reactions for diverse organic compounds.
• The identified electrophilic thianthrenium intermediate is key to the catalytic cycle and efficient halogenation.