Synthesis of Phenol-Pyridinium Salts Enabled by Tandem Electron Donor-Acceptor Complexation and Iridium Photocatalysis.

Herein, we describe a dual photocatalytic system to synthesize phenol-pyridinium salts using visible light. Utilizing both electron donor-acceptor (EDA) complex and iridium(III) photocatalytic cycles, the C-N cross-coupling of unprotected phenols and pyridines proceeds in the presence of oxygen to furnish pyridinium salts. Photocatalytic generation of phenoxyl radical cations also enabled a nucleophilic aromatic substitution (SNAr) of a fluorophenol with an electron-poor pyridine. Spectroscopic experiments were conducted to probe the mechanism and reaction selectivity. The unique reactivity of these phenol-pyridinium salts were displayed in several derivatization reactions, providing rapid access to a diverse chemical space.

Recent advances in oxidative phenol coupling for the total synthesis of natural products.

Covering: 2008 to 2023This review will describe oxidative phenol coupling as applied in the total synthesis of natural products. This review covers catalytic and electrochemical methods with a brief comparison to stoichiometric and enzymatic systems assessing their practicality, atom economy, and other measures. Natural products forged by C-C and C-O oxidative phenol couplings as well as from alkenyl phenol couplings will be addressed. Additionally, exploration into catalytic oxidative coupling of phenols and other related species (carbazoles, indoles, aryl ethers, etc.) will be surveyed. Future directions of this particular area of research will also be assessed.

Photocatalytic Synthesis of para-Peroxyquinols: Total Synthesis of (±)-Stemenone B and (±)-Parvistilbine B.

A photocatalytic method to selectively synthesize 4-hydroperoxy-2,5-cyclohexadienones from para-alkyl phenols is disclosed. This photosensitized singlet oxygen approach functionalized a variety of electronically diverse para-alkyl phenols in 27-99% isolated yields. Utilizing this dearomative oxidation, (±)-stemenone B and (±)-parvistilbine B were synthesized in 9 and 11 steps, respectively, from commercially available starting materials. Additional experiments revealed the dramatic influence of base and solvent on the selectivity while providing insight into the mechanism of this transformation.