A new cycloaddition profile for ortho-quinone methides: photoredox-catalyzed [6+4] cycloadditions for synthesis of benzo[b]cyclopenta[e]oxepines

Abstract

Visible-light-induced [6+4] cycloaddition reactions of ortho-quinone methides have been developed. The reaction of ortho-quinone methides with pentafulvenes in the presence of a thioxanthylium photoredox catalyst afforded benzo[b]cyclopenta[e]oxepines. The present reaction...

The synthesis of seven- and eight-membered rings by radical strategies

“…In 2022, Tanaka, Hoshino, and co-workers developed the synthesis of benzo[ b ]cyclopenta[ e ]oxepines by photoredox-catalyzed [6 + 4] cyclization (Scheme 33). 62 Unlike most photocatalytic reactions, green LED worked best in this reaction. Although less exploration was carried out for different o -QMs and pentafulvenes, the results suggested that the substrate scope was broad, allowing access to various functional groups.…”

Progress in Electrochemically Empowered C−O Bond Formation: Unveiling the Pathway of Efficient Green Synthesis

“…In very recent time, transition metal catalysed reaction (condensation) or other oxidant promoted direct condensation of sulphonamide and formamide are reported in literature. Likewise, several methods including a) Oxidative annulations between hydrazide and ketone using isocyanides, [12] b) Cleavage of bond through oxidation of methyl ketone or unsaturated compounds and direct condensation of DMF via oxidation, [14,15] are developed for the synthesis of 1,3,4oxadiazoles motif. But the major disadvantages of abovementioned procedures are the use of excess amount of transition metals, hazardous chemicals and oxidizing agents.…”

“…[13] However, recent advanced protocols for oxipin synthesis are Au-catalyed cyclization of (oalkynyl)phenoxyacrylates in mild conditions, green visible-lightinduced [6 + 4] cycloaddition reactions of ortho-quinone methides with pentafulvenes. [14] Rhodium-catalyzed diastereoselective [5 + 2] annulation between indoles with cyclohexadienone is another fruitful approach for the oxepine ring synthesis 15 . Nucleophilic substitution followed by Knovenagel condensation between 2-methyl-3-nitrophenol and 2-fluorobenzaldehyde were used (in one step) to produce Bauhinoxepin C natural product.…”

“…The six membered saturated cyclic analogues of ether is known as pyran which has been recently synthesized by various traditional pathways by the modification of different synthetic strategies such as NHC‐catalyzed [2+ 4] cyclization of alkynyl ester with α,β‐unsaturated ketone, [10] Prins‐type cyclization of cyclopropane carbaldehydes in the presence of 3‐buten‐1‐ol [11] and Lewis‐acid promoted bicyclization between cyclopropane carbaldehydes with quinone methides/esters etc [12] Oxepine is the one carbon homologated analogue can be synthesized via intramolecular C−O bond formation using Ullmann‐ether reaction or cyclodehydration process from aliphatic or aromatic alcohol under harsh conditions [13] . However, recent advanced protocols for oxipin synthesis are Au‐catalyed cyclization of ( o ‐alkynyl)phenoxyacrylates in mild conditions, green visible‐light‐induced [6+4] cycloaddition reactions of ortho‐quinone methides with pentafulvenes [14] . Rhodium‐catalyzed diastereoselective [5+2] annulation between indoles with cyclohexadienone is another fruitful approach for the oxepine ring synthesis 15 .…”