A Copper-Catalyzed Formal [3 + 2]-Cycloaddition for the Synthesis of All Different Aryl-Substituted Furans and Thiophenes

Abstract

A highly efficient formal [3 + 2]-cycloaddition was established using a copper catalyst. The resulting dihydrofurans were subjected to oxidation followed by arylations to produce tetraarylfurans. In addition, the dihydrofuran can be converted to diaryldihydrothiophene by using Lawesson's reagent. This protocol will facilitate the synthesis of all different aryl-substituted furans and thiophenes.

Recent developments in copper-catalyzed radical alkylations of electron-rich π-systems

“…When the alkyl bromide coupling partner was changed to an α-bromo keto ester, the radical addition is followed by a tautomerization/cyclization event that provides dihydrofurans in excellent yields [ 38 ]. The radical formation/addition events proceed largely in the same manner as the aforementioned alkenylation reactions.…”

Domino Radical Addition/Oxidation Sequence with Photocatalysis: One‐Pot Synthesis of Polysubstituted Furans from α‐Chloro‐Alkyl Ketones and Styrenes

“…Based on the above experimental results and previous reports, [9,22] ar adicala ddition/oxidation pathway is proposed in Scheme 2. AS ET from the excited photocatalyst to 1a generates an electron-deficient a-carbonyl carbon radical A along with Ir IV (ppy) 3 .I ntermolecular p-addition of the radical A to 2a produces benzylic radical B.AfurtherS ET from radical B (E ox 1=2 = 0.73 V, vs. SCE) [20] to Ir IV (ppy) 3 (E red 1=2 = 0.77 V, vs. SCE) [23] gives carbocation C and regenerates the photocatalyst.S ubsequently, cyclization and deprotonation of C facilitated by the base results in dihydrofuran derivative E.F inally,o xidationo fi ntermediate E by the excited photocatalyst or K 2 S 2 O 8 provides the desired product 3a.…”

Copper-catalyzed formylation of alkenyl C–H bonds using BrCHCl2 as a stoichiometric formylating reagent

“…After a simple work-up without purification and further dehydration with T3P, 2a was finally furnished in 80% yield (entry 8). Considering the key role that PMDTA played in this transformation, 10 other bases were also screened instead of PMDTA, but they did not give the desired product 2a ( Table 1 , entries 11–13). Notably, by the replacement of KI with NaI, the yield of 2a was further improved to 90% after this two-step formylation of 4-methoxystyrene (entry 15).…”