Two-Step Electrochemical Annulation for the Assembly of Polycyclic Systems

Abstract

[reaction: see text] A two-step electrochemical annulation has been developed for the preparation of fused furans. The process involves an initial conjugate addition of a furyethyl cuprate and trapping of the enolate as the corresponding silyl enolether. The second step of the annulation involves the anodic coupling of the furan and the silyl enol ether to form a six-membered ring.

Electrochemical strategies for C–H functionalization and C–N bond formation

“…Here, electron transfer confers umpolung reactivity of a functional group, thus enabling alternative retrosynthetic disconnections of complex structures through previously challenging bond disconnections. 63,81 The Moeller [793][794][795] and Wright 796 groups have exploited the intramolecular anodic coupling of enol ethers or vinyl sulfides and electronrich aromatic systems to deliver the fused, bicyclic or tricyclic ring skeletons in moderate to high yields (Schemes 93 and 94).…”

“…797 Heteroaromatic rings are also compatible coupling partners in these intramolecular anodic olefin coupling reactions. Here, different tethers can be employed to afford, for example, six-(Scheme 96) 794,796,798,799 or seven-membered 800 (Scheme 97) annulated furan systems, which can be readily transformed into various carbo-and oxacyclic motifs. [801][802][803][804][805][806][807] These electrochemical annulations are presumed to involve initial oxidation of the silyl enol ether moiety rather than the furyl group.…”

Electrifying green synthesis: recent advances in electrochemical annulation reactions

“…An example of this was proposed by Wright and co-workers, who developed a two-stage electrochemical annulation for fused furan products 124 (Scheme 33). 131 After the conjugated addition of a furyethyl cuprate and the capture of the enolate as the corresponding silyl enol ether, the annulation step involves the anodic coupling of furan and silyl enol ether (123), providing the six-membered ring. High current densities may promote the formation of oligomers by providing other electroactive species.…”

Five‐Membered Heterocycles: Furan

“…This pathway involves an initial conjugate addition of a furylethyl cuprate to cyclopentenone (95) and trapping of the enolate as the corresponding silyl enol ether 96. The second step involves anodic coupling of the furan and the silyl enol ether to form the cis-fused six-membered ring 97 with high stereoselectivity (Scheme 6.38) [88]. The reaction can be extended to the formation of seven-membered ring fused furan 98 [89].…”