Direct-Excitation-Enabled Radical Hydrosilylation via a Silyl Radical Precursor

Area of Science:

• Organic Chemistry
• Photochemistry
• Catalysis

Background:

• Radical hydrosilylation of alkenes is a crucial synthetic transformation.
• Traditional methods often rely on transition metal catalysts or photoredox catalysis, posing limitations.
• Developing photocatalyst-free methods for radical generation is highly desirable.

Purpose of the Study:

• To develop a novel photocatalyst-free radical hydrosilylation of alkenes.
• To achieve this using direct visible-light excitation of tailored silyl radical precursors.
• To explore the versatility of this method in various organic transformations.

Main Methods:

• Synthesis of chromophore-modified silyl radical precursors (naphthalene-conjugated 2-silyldihydroquinazolinone).
• Visible-light irradiation to directly excite the precursor.
• Hydrosilylation of electron-deficient alkenes and subsequent radical reactions (cyclization, Smiles rearrangement).

Main Results:

• Efficient generation of silyl radicals upon visible-light irradiation without photocatalysts or transition metals.
• Successful hydrosilylation of various electron-deficient alkenes, yielding silylated products in moderate to good yields.
• Demonstration of radical cyclization and Smiles rearrangement reactions, showcasing the method's versatility.

Conclusions:

• Direct visible-light excitation of chromophore-modified silyl radical precursors offers a photocatalyst-free route to radical hydrosilylation.
• The developed method is efficient and versatile, applicable to various alkene substrates and subsequent radical transformations.
• Mechanistic studies suggest a nonchain radical pathway initiated by triplet excited state homolytic C-Si bond cleavage.