Synthetic applications in radical/radical cationic cascade reactions

Area of Science:

• Organic Chemistry
• Photochemistry
• Reaction Mechanisms

Background:

• Cyclic silyl ethers are versatile substrates in organic synthesis.
• Photoinduced electron transfer (PET) offers a unique pathway for radical generation and subsequent transformations.
• Controlling stereoselectivity in complex cyclizations remains a significant challenge.

Purpose of the Study:

• To investigate oxidative photoinduced electron transfer (PET) reactions of cyclic cyclopropyl(vinyl) silyl ethers.
• To explore the formation of complex polycyclic ring systems through fragmentation-radical/radical cationic addition.
• To understand the factors influencing cyclization selectivity (endo/exo) and the mechanistic details of the final saturation step.

Main Methods:

• Performed oxidative photoinduced electron transfer (PET) reactions on various cyclic cyclopropyl(vinyl) silyl ethers.
• Utilized nucleophilic additives to influence reaction pathways and control cyclization modes.
• Employed quantum chemical calculations to study cyclization transition states.
• Conducted mechanistic studies to elucidate the final radical saturation process.

Main Results:

• Successfully synthesized bi- to tetracyclic ring systems via a fragmentation-radical/radical cationic addition pathway.
• Demonstrated partial control over endo/exo cyclization selectivity through the addition of nucleophiles, suppressing radical cationic pathways.
• Quantum chemical calculations corroborated the experimentally observed selectivities.
• Identified solvent and trace water as primary sources for the final radical saturation.

Conclusions:

• Oxidative PET reactions provide an efficient route to complex polycyclic structures from silyl ethers.
• Nucleophile-mediated control offers a strategy for directing stereochemical outcomes in these cyclizations.
• Computational studies are valuable for understanding and predicting selectivity in these radical-mediated processes.