PPh3-Triggered Tandem Synthesis of 2,3-Disubstituted Benzofuran Derivatives from o-Quinone Methides with Acyl Chlorides

A PPh₃-triggered tandem strategy for the efficient synthesis of valuable 2,3-disubstituted benzofuran derivatives in generally good to high yields from aryl or alkyl acyl chlorides and o-quinone methides has been developed. This method features mild reaction conditions, simple operation, and a broad substrate scope.

Recent Achievement in the Synthesis of Benzo[b]furans

BACKGROUND

Benzo[b]furan derivatives are oxygen-containing heterocyclic compounds consisting of fused benzene and furan rings and are present in a large number of natural and non-natural compounds. This class of compounds has a wide spectrum of biological activities, such as antiarrhythmic, anticancer, inflammatory, antioxidant, antimicrobial, and antiviral. Furthermore, benzo[b]furan derivatives have also been applied in various areas, such as organic electroluminescence device materials and organic dyes, photosensitizing material, organic synthesis as building blocks or intermediates. Because of a broad range of applicability, the synthesis of benzo[b]furan derivative has drawn great attention of chemists and many studies on the synthesis of this class of compounds have been reported recently. This review will give an overview of benzo[b]furan preparation based on studies dating back to the year 2012.

OBJECTIVE

In this review, recent development in the synthesis of benzo[b]furans are discussed. There has been increasingly new methodologies for the construction of benzo[b]furans skeleton to improve efficiency or develop environmentally friendly procedures. In some studies, reaction mechanisms were also outlined.

CONCLUSION

Many methods for the synthesis of benzo[b]furans have been reported recently. Most of them involve cyclization or cycloisomerization processes. Unquestionably, more imaginative strategies for the construction of benzo[b]furan skeleton will be established in the near future. Application of known methods to natural products or drug synthesis, on industrial scale for the synthesis of economically or medicinally important benzo[ b]furans will probably be paid attention to.

Palladium-catalyzed enantioselective [5 + 4] annulation of ortho-quinone methides and vinylethylene carbonates

Highly enantioselective [5 + 4] annulations of ortho-quinone methides with vinylethylene carbonates are enabled by asymmetric palladium catalysis for the synthesis of chiral nine-membered benzo-heterocycles.

One-Pot Allylation-Intramolecular Vinylogous Michael Addition-Isomerization Cascade of o-Hydroxycinnamates and Congeners: Synthesis of Substituted Benzofuran Derivatives

A unique intramolecular vinylogous Michael addition leading to the synthesis of heterocycles has been disclosed. Base-promoted one-pot sequential O-allylation of o-hydroxy-cinnamates or -cinnamonitrile or -chalcones with γ-bromocrotonates followed by an intramolecular conjugate addition of vinylogous Michael donors resulted in the formation of highly substituted benzofuran derivatives in good to excellent yields. The intramolecular event followed by two [1,3]-H shifts leading to aromatization appears to be the key to the success of this unprecedented transformation.

Divergent synthesis of 3,4-dihydrodibenzo[b,d]furan-1(2H)-ones and isocoumarins via additive-controlled chemoselective C–C or C–N bond cleavage

Rh(iii)-Catalyzed C–C/C–O bond formation between cyclic 2-diazo-1,3-diketones and salicylamides with additive-controlled chemoselectivity.

A new dehydrogenative [4 + 1] annulation between para-quinone methides (p-QMs) and iodonium ylides for the synthesis of 2,3-dihydrobenzofurans

A new dehydrogenative [4 + 1] annulation of para-quinone methides (p-QMs) with acyclic and cyclic iodonium ylides has been established, delivering a variety of functionalized 2,3-dihydrobenzofurans with the retention of the quinone methide unit in generally good yields.

Synthesis of Functionalized Benzo[b]furans via Oxidative Cyclization of o-Cinnamyl Phenols

Disclosed herein is an efficient synthetic route for the synthesis of functionalized 2-benzyl benzo[b]furans via a regioselective 5-exo-trig intramolecular oxidative cyclization of ortho-cinnamyl phenols using [PdCl₂(CH₃CN)₂] as catalyst and benzoquinone as an oxidant. Further, a sequential ortho-cinnamylation of phenols using cinnamyl alcohols catalyzed by Re₂O₇, followed by an oxidative cyclization using the above Pd catalyst, is performed. The reaction showed broad substrate scope with good to excellent yields.

BF3·OEt2 Mediated Regioselective Reaction of Electron-Rich Arenes with 3-Ylidene Oxindoles

A BF₃·OEt₂ mediated novel and regioselective protocol for the construction of a C-C bond between 3-ylidene oxindoles and electron-rich arenes has been successfully accomplished. The reaction was compatible with a wide variety of electron-rich arenes. A cascade reaction of 3-ylidene oxindoles with phenols and β-naphthol resulted in 2,3-difunctionalized benzofuran and lactone bearing indoline-2-one scaffolds under same conditions.