Photocatalyzed syntheses of phenanthrenes and their aza-analogues. A review

Abstract

Phenanthrenes and their aza-analogues have important applications in materials science and in medicine. Aim of this review is to collect recent reports describing their synthesis, which make use of radical cyclizations promoted by a visible light-triggered photocatalytic process.

Recent Progress in Cyclic Aryliodonium Chemistry: Syntheses and Applications

“…In 2015, the Wen group disclosed palladium-catalyzed insertion of internal alkynes into cyclic diaryliodoniums via [4 + 2] benzannulation to generate various phenanthrenes, 90 one of the vital molecular structural features in functional materials. 257 Recently, a new synthetic approach to dibenzopleiadieneembedded PAHs 68 through a palladium-catalyzed cascade intermolecular decarbonylation and intramolecular decarboxylative annulation between commercially available naphthalene anhydride 66 and cyclic diaryliodoniums 67 has been described by Leowanawat et al (Scheme 21). 258 The protocol also works well with HCIs and provides heterocycle-containing PAHs, for example, 68g, smoothly.…”

“…Polycyclic aromatic hydrocarbons (PAHs) have attracted much attention due to their novel optoelectronic, self-assembly, and charge-transport properties resulting from their unique π-conjugated scaffold. − Therefore, synthetic strategies to produce PAHs have been extensively explored. In 2015, the Wen group disclosed palladium-catalyzed insertion of internal alkynes into cyclic diaryliodoniums via [4 + 2] benzannulation to generate various phenanthrenes, one of the vital molecular structural features in functional materials . Recently, a new synthetic approach to dibenzopleiadiene-embedded PAHs 68 through a palladium-catalyzed cascade intermolecular decarbonylation and intramolecular decarboxylative annulation between commercially available naphthalene anhydride 66 and cyclic diaryliodoniums 67 has been described by Leowanawat et al.…”

Visible-Light-Mediated Synthesis of Phenanthrenes through Successive Photosensitization and Photoredox by a Single Organocatalyst

“…As an advancement, visible-light-mediated photoredox catalysis was employed to circumvent the aforementioned issues . The interest in photoredox catalysis has experienced a resurgence, and there has been speculation that the process can be considered as an advantageous alternative to the traditional methods due to its operational simplicity and eco-friendly nature .…”

Iodine-Catalyzed Methylthiolative Annulation of 2-Alkynyl Biaryls with DMSO: A Metal-Free Approach to 9-Sulfenylphenanthrenes

“…Moreover, phenanthrene derivatives also exhibit interesting electronic and optical properties and are utilized in various useful materials, such as organic field-effect transistors and solar cells . Consequently, several synthetic strategies have been developed so far for the synthesis of phenanthrenes. , Among them, two synthetic strategies, i.e., transition-metal (TM) (Pd, Ir, Rh, and Fe)-catalyzed or visible-light photocatalyzed [4 + 2]-benzannulation of 2-functionalized 1,1′-biaryls with alkynes and transition-metal (Pt, Au, Ga, Ir, Ru, Fe, and Sn)-catalyzed/mediated intramolecular carbocyclization or electrophilic annulation of 2-alkynyl biaryls (6- endo - dig cyclization) are widely employed, perhaps because of their high atom-economical feature and the requirement of relatively less prefunctionalized starting materials . Despite significant advancement, the above-mentioned synthetic methods suffer from at least one of the following severe limitations, such as the requirement of (a) expensive and toxic transition-metal salts or complexes in catalytic or (sub)­stoichiometric amounts, (b) expensive and hazardous ligand and reagents, (c) harsh or critical reaction conditions, and (d) limited substrate scope.…”