Cascade Synthesis of Phenanthrenes under Photoirradiation

Abstract

We report a photoinduced phenanthrene synthesis from aryl iodides and styrenes through an arylation/cyclization cascade. Compared to prior methods, this approach obviates the need for hazardous reagents and provides access to unsymmetrical phenanthrenes with good functional group tolerance. Mechanistic studies revealed that photoexcitation of aryl iodides leads to homolytic C−I bond cleavage. Arylation of styrenes with the formed aryl radical species furnishes stilbene derivatives, which undergo photoinduced cyclization promoted by iodine generated in situ to yield phenanthrene products.

Deaminative ring contraction for the synthesis of polycyclic heteroaromatics: a concise total synthesis of toddaquinoline

“…35 Our interest in pyridylcontaining polycyclic aromatic natural products directed us to further evaluate the impact of system electronics. Electron-rich (17,18) and electron-decient (19-21) benzo[h]quinolines are all accessed in good yields (Fig. 3c).…”

“…Classic approaches 12 to build phenanthrenes from stilbene precursors include the Pschorr, 13 and Mallory reactions, 14,15 which have seen impressive procedural updates. 16,17 Unsurprisingly, the advent of transition metal-catalyzed cross-coupling reactions makes construction of the biaryl bond a natural entry point to these scaffolds. 18 Recent approaches toward polycyclic aromatics have relied on these methods, using transition metal-, 19 oxidation-, 20 Lewis acid-, 21,22 and base-promoted 23 alkene-forming reactions.…”

Visible Light Induced Photocatalyst‐Free C−X (X=B, C, O, P,S, Se) Bond Formation of Aryl Halides

“…Recently, Parasram and co‐workers demonstrated phenanthrenes 95 synthesis from aryl iodides 2 and styrenes 94 using MTBE (methyl‐ tert ‐butyl ether) as a green solvent under 390 nm photoirradiation (Scheme 37). [46b] Aryl iodides as well as styrenes with both electron‐donating and electron‐withdrawing groups yielded phenanthrenes in moderate to good yields. Furthermore, 1,4‐diiodobenzene furnished monofunctionalized product with 30% yield.…”

Light‐Induced Domino and Multicomponent Reactions: How to Reach Molecular Complexity without a Catalyst

“…As shown in Scheme 40, a photo-induced synthesis of nonsymmetrical phenanthrenes 111 was reported in 2023. [84] Overcoming the need for preformed stilbenes precursors, hazardous reagents and harsh conditions leading to low functional group tolerance and by-products formation, Parasram et al simply engaged iodo-arenes 109 and substituted styrenes in an arylation/cyclization cascade mediated by a 390 nm light. Functionalized phenanthrenes 111 were obtained in moderate to good yields up to 5 mmol scale.…”

“…As shown in Scheme 40, a photo‐induced synthesis of non‐symmetrical phenanthrenes 111 was reported in 2023 [84] . Overcoming the need for preformed stilbenes precursors, hazardous reagents and harsh conditions leading to low functional group tolerance and by‐products formation, Parasram et al.…”