Iron‐Catalyzed Oxidative Radical Cross‐Coupling/Cyclization between Phenols and Olefins

Abstract

Direkt gekuppelt: Die Titelreaktion führt hoch effizient und selektiv unter milden Bedingungen zu Dihydrobenzofuranen. Mechanistische Untersuchungen deuten auf einen radikalischen Reaktionspfad hin; für die hohe Selektivität sorgt die Lewis‐Säure.

External oxidant-free electrooxidative [3 + 2] annulation between phenol and indole derivatives

“…Based on the experimental results and previous reports 10 , 48 , a plausible reaction mechanism between 1a and 2a is presented in Fig. 8 .…”

Oxidative Catalytic Coupling Reactions: Selective Formation of CC and CX Bonds Using Radical Processes

“…In this respect, Lei and coworkers reported a novel iron-catalyzed radical oxidative coupling reaction of phenols and olefins (Scheme 5). [12] When simple phenols are employed in oxidative coupling reactions, the generation of the desired product usually occurs with concomitant formation of homocoupled by-products as well as higher-molecular-weight polymers or C À O connected phenol portions, such as quinol ethers. In contrast, when FeCl 3 was utilized as the catalyst in the presence of 2,3dichloro-5,6-dicyano-1,4-benzoqinone (DDQ) as the oxidant, a highly selective oxidative coupling/cyclization reaction occurred at room temperature.…”

Synthesis of Divergent Benzo[b]fluorenones through Cycloaromatization Reactions of 1,5-Enynols and 1,5-Diynols

“…We proposed the following mechanism for the cycloaromatization of 1,5-endiynol 1 as shown in Scheme 5 for this cascade cycloaromatization reactions. Under heating conditions, the loss of H 2 O in Meyer−Schuster rearrangement of a formal 1,3-OH shift of 1,5-enynol 1 to produce allenol species A can be envisioned first.5Radical oxidation of A by DDQ followed by deprotonation would generate the allenol radical B, 24 which would then undergo C2−C6 5-exo-trig ring closure to give the indenone radical C. At this stage, the following radical attack at the pendant phenyl group by the alkyl radical to give the benzo [b]fluorenone radical D is unlikely, because alkyl radicals are not reactive enough to attack at the pendant phenyl moiety or similar systems. 25 Alternatively, single-electron oxidation of the alkyl radical by DDQH• radical species would give rise to a resonancestabilized cation E, which then would undergo Friedel−Crafts alkylation into the phenyl group to form the benzo [b]fluorenone framework F. Finally, deprotonation of F followed by rearomatization would yield the product 2.…”