Palladium-Catalyzed α-Arylation of Aryloxyketones for the Synthesis of 2,3-Disubstituted Benzofurans

Abstract

A highly efficient palladium-catalyzed α-arylation of aryloxyketones has been developed, allowing for facile installation of various (hetero)aryl groups at C2 position in good to excellent yields. Subsequent cyclodehydration of the resulting α-arylated aryloxyketones provided rapid access to diverse 2,3-disubstitured benzofurans.

Total Synthesis of the Resveratrol Oligomers (±)‐Ampelopsin B and (±)‐ϵ‐Viniferin

“…A model experiment was first executed to investigate whether the epimerization of C2 was feasible. After investigating several options9 cis ‐dihydrobenzofuran 6 was prepared10 in five steps using methods inspired by Kim's synthesis of pentamethylated viniferifuran 11. By treating compound 6 with the moderately strong acid trifluoroacetic acid (TFA) in CH 2 Cl 2 , trans epimer 7 was obtained in excellent yields (Scheme 2).…”

Synthesis of benzofurans from the cyclodehydration of α-phenoxy ketones mediated by Eaton’s reagent

“…It can be accessed by refluxing 1a in ethanol in the presence of a base (Path 1) such as KOH with subsequent acidification 29,30 or in the presence of acid (Path 2), for example, Lewis acids such as TiCl 4 , 31 Bi(OTf) 3 , 32 BCl 3 , 33,34 and Al 2 O 3 35 or Brønsted acids such as triflic acid, 36 methanesulfonic acid (MeSO 3 H), 37–40 and p -toluenesulfonic acid. 41,42 In addition, a few transition-metal catalysts (path 3) such as Ir or Pd have been used to facilitate cyclodehydration reaction. 43–45 These protocols usually require long reaction times even in refluxing solvents, which encouraged us to find an alternative method to prepare benzofurans under moderate conditions.…”

Trifluoroacetic Acid Catalyzed Cascade Reactions of 2,3‐Diketoesters with Cyclohexane‐1,3‐diones: Strategy Towards 4‐Hydroxybenzofuran Derivatives

“…Generally, methods for the synthesis of 4‐hydroxybenzofurans rely on [3+2] annulation reactions (Scheme ). The phenol ring of the 4‐hydroxybenzofurans can be constructed 1) from appropriate phenol or phenolic ether,, and 2) by a two‐step process using cyclohexane‐1,3‐dione as the starting material and an extra oxidant for the subsequent dehydroaromatization . Although much work has been done in this area, the existing methods suffer from some obvious limitations.…”