Regioselective and Stereoselective Pd-Catalyzed Intramolecular Arylation of Furans: Access to Spirooxindoles and 5H-Furo[2,3-c]quinolin-4-ones

Accessing Furan-Linked Methylene Oxindoles/Benzofurans via Stereoselective Palladium-Catalyzed Domino Cyclization/Cycloisomerization

A palladium-catalyzed domino cyclization/cycloisomerization reaction of alkyne-tethered carbamoyl chlorides with (E)-β-chloroenones is reported. This reaction proceeds via a syn-carbopalladation of the alkyne, followed by a vinyl-PdII-catalyzed cycloisomerization of the (E)-β-chloroenone cascade, which provides an efficient method to synthesize furan-linked methylene oxindoles. The reaction features stereodefined vinyl-PdII species, high to excellent 5-exo/6-endo selectivity, excellent Z/E selectivity, and the sequential formation of three bonds and bis-heterocycles. The strategy for the synthesis of furan-containing benzofurans has also been demonstrated.

Palladium-Catalyzed Intermolecular Dearomatization Annulation Cascade Reaction of Furans for Stereoselective Access to 2,5-Dihydrofurans

A novel palladium-catalyzed intermolecular dearomatization of furans with alkynes via a three-component formal [3 + 2] spiroannulation/allylic substitution cascade reaction has been successfully developed for the stereoselective assembly of spiro 2,5-dihydrofuran frameworks. High step economy and efficacy as well as excellent stereoselectivity were achieved for a broad substrate scope. Two new C-C bonds and one new C-O bond were generated sequentially in a one-pot manipulation. The yielded spiro 2,5-dihydrofuran skeleton bearing a tetrasubstituted carbon center constitutes the core structure for plenty of useful natural products or corresponding analogues. This work represents a significant advancement in the dearomatization strategy for furan heterocycles and provides a practical methodology for expedited access to complex spiro dihydrofuran scaffolds.

Synthesis, Characterization, and Cytotoxicity of New Spirooxindoles Engrafted Furan Structural Motif as a Potential Anticancer Agent

A new series of spirooxindoles based on ethylene derivatives having furan aryl moiety are reported. The new hybrids were achieved via [3 + 2] cycloaddition reaction as an economic one-step efficient approach. The final constructed spirooxindoles have four contiguous asymmetric carbon centers. The structure of 3a is exclusively confirmed using X-ray single crystal diffraction. The supramolecular structure of 3a is controlled by O···H, H···H, and C···C intermolecular contacts. It includes layered molecules interconnected weak C-H···O (2.675 Å), H···H (2.269 Å), and relatively short Cl···Br interhalogen interactions [3.4500(11)Å]. Using Hirshfeld analysis, the percentages of these intermolecular contacts are 10.6, 25.7, 6.4, and 6.2%, respectively. The spirooxindoles along with ethylene derivatives having furan aryl moiety were assessed against breast (MCF7) and liver (HepG2) cancer cell lines. The results indicated that the new chalcone 3b showed excellent activity in both cell lines (MCF7 and HepG2) with IC₅₀ = 4.1 ± 0.10 μM/mL (MCF7) and 3.5 ± 0.07 μM/mL (HepG2) compared to staurosporine with 4.3 and 2.92 folds. Spirooxindoles 6d (IC₅₀ = 4.3 ± 0.18 μM/mL), 6f (IC₅₀ = 10.3 ± 0.40 μM/mL), 6i (IC₅₀ = 10.7 ± 0.38 μM/mL), and 6j (IC₅₀ = 4.7 ± 0.18 μM/mL) exhibited potential activity against breast adenocarcinoma, while compounds 6d (IC₅₀ = 6.9 ± 0.23 μM/mL) and 6f (IC₅₀ = 3.5 ± 0.11 μM/mL) were the most active hybrids against human liver cancer cell line (HepG2) compared to staurosporine [IC₅₀ = 17.8 ± 0.50 μM/mL (MCF7) and 10.3 ± 0.23 μM/mL (HepG2)]. Molecular docking study exhibited the virtual mechanism of binding of compound 3b as a dual inhibitor of EGFR/CDK-2 proteins, and this may highlight the molecular targets for its cytotoxic activity.

LiCl-Mediated and Palladium-Catalyzed Oxidative Cyclization of Furan-Ynes via Dearomatizing Alkoxyalkenylation of Furan

A LiCl-mediated and palladium(II)-catalyzed oxidative cyclization of furan-ynes via dearomatizing alkoxyalkenylation of furan is reported to afford polyfunctionalized spiro-dihydrofurans with diastereospecification and high Z/E selectivity. This protocol is likely to involve chloropalladation of alkynes, subsequent intramolecular dearomatizing alkenylation of furan, and final O-allylation. The density functional theory (DFT) calculations demonstrated that the coordination of furan with dissolved Li⁺ weakens its nucleophilicity and promoted the Heck insertion, and dissolved Cl^- promoted chloropalladation of alkynes.

Transition metal-catalyzed synthesis of spirooxindoles

Spirooxindole is a principal bioactive agent and is observed in several natural products including alkaloids. They are broadly studied in the pharmaceutical field and have a significant role in the evolution of drugs such as anti-viral, anti-cancer, anti-microbial etc. In organic chemistry, an indispensable role is presented by transition metal catalysts. An effective synthetic perspective to spirooxindoles is the use of transition metals as the catalyst. This review discusses the synthesis of spirooxindoles catalyzed by transition metals and covers literature up to 2020.

Catalytic C-H Functionalization of Unreactive Furan Cores in Bio-Derived Platform Chemicals

C-H functionalization is one of the most convenient and powerful tools in the arsenal of modern chemistry, deservedly nominated as the "Holy Grail" of organic synthesis. A frequent disadvantage of this method is the need for harsh reaction conditions to carry out transformations of inert C-H bonds, which limits the possibility of its use for modifying less stable substrates. Biomass-derived furan platform chemicals, which have a relatively unstable aromatic furan core and highly reactive side chain substituents, are extremely promising and valuable organic molecules that are currently widely used in a variety of research and industrial fields. The high sensitivity of furan derivatives to acids, strong oxidants, and high temperatures significantly limits the use of classical methods of C-H functionalization for their modification. New methods of catalytic functionalization of non-reactive furan cores are urgently required to obtain a new generation of materials with controlled properties and potentially bioactive substances.

Intramolecular iron-catalyzed transannulation of furans with O-acetyl oximes: synthesis of functionalized pyrroles

Intramolecular iron(iii)-catalyzed reaction of furyl-tethered O-acetyl oximes yields substituted pyrroles through electrophilic 5-exo-trig ipso-addition of nitrogen to the furan ring.

Palladium-Catalyzed Amination/Dearomatization Reaction of Indoles and Benzofurans

This report describes a palladium-catalyzed dearomatization and amination tandem reaction of 2,3-disubstituted indoles and benzofurans via the Catellani strategy. This reaction provides a new method for the construction of amino-substituted indoline-fused cyclic and benzofuran spiro compounds in good yields. The reaction has broad functional group compatibility and substrate scope.

Umpolung Strategy for the Synthesis of Chiral Dispiro[2-amino-4,5-dihydrofuran-3-carbonitrile]bisoxindoles

Based on a novel umpolung strategy, an efficient and highly enantioselective cascade aldol/cyclization/tautomerization of the 2-(2-oxoindolin-3-yl)malononitrile to active carbonyl compounds with excellent diastereo- and enantioselectivity has been developed. Also, various enantio-enriched multifunctional dispiro[2-amino-4,5-dihydrofuran-3-carbonitrile]bisoxindoles with adjacent spiro-stereocenters were conveniently obtained by this novel methodology. Also, the dispiro[2-amino-4,5-dihydrofuran-3-carbonitrile]bisoxindoles were easily transformed into structurally complex molecules without any effect on the diastereo- and enantioselectivity.

A Pd-catalyzed domino Larock annulation/dearomative Heck reaction

A highly efficient synthesis of indolines from N-bromobenzoyl o-iodoanilines and alkynes is developed via a domino Larock annulation/dearomative Heck reaction.

Synthesis of six-membered spirooxindolesviaa chiral Brønsted acid-catalyzed asymmetric intramolecular Friedel–Crafts reaction

By means of the direct condensation of N-aminoethylpyrroles and isatins, followed by a chiral phosphoric acid-catalyzed asymmetric intramolecular Friedel-Crafts reaction, a new class of valuable chiral 3′,4′-dihydro-2′H-spiro[indoline-3,1′-pyrrolo[1,2-a]pyrazin]-2-ones bearing a quaternary carbon stereocenter were successfully synthesized in good to excellent yields and with moderate to good enantioselectivities under mild reaction conditions.

A chiral phosphoric acid-catalyzed asymmetric intramolecular Friedel–Crafts reaction for the synthesis of 3′,4′-dihydro-2′H-spiro[indoline-3,1′-pyrrolo[1,2-a]pyrazin]-2-ones.

Pd(0)-Catalyzed intramolecular arylative dearomatization of β-naphthols

An efficient Pd(0)-catalyzed intramolecular arylative dearomatization of β-naphthols was developed to afford a series of structurally diverse spirocarbocycles.

Pd-catalyzed regioselective intramolecular direct arylation of 3-indolecarboxamides: access to spiro-indoline-3,3′-oxindoles and 5,11-dihydro-6H-indolo[3,2-c]quinolin-6-ones

We report regioselective intramolecular direct C-3 and C-2 arylations of the indole rings of 3-indolecarboxamides for diastereospecific production of spiro-indoline-3,3′-oxindoles and 5,11-dihydro-6H-indolo[3,2-c]quinolin-6-ones, respectively, under different reaction conditions.

Aerobic oxidative α-arylation of furans with boronic acids via Pd(ii)-catalyzed C–C bond cleavage of primary furfuryl alcohols: sustainable access to arylfurans

Aerobic oxidative α-arylation of furans with boronic acids via Pd(ii)-catalyzed C–C bond cleavage of primary furfuryl alcohol provides sustainable access to arylfurans.

Transition metal-catalyzed site- and regio-divergent C–H bond functionalization

The regioselectivity of C–H functionalization reactions can be redirected to obtain regioisomeric products form the same starting materials.