Divergent Synthesis of 2-Aminofurans via Palladium-Catalyzed Acetoxylative, Alkoxylative, and Hydroxylative Cycloisomerization of Homoallenyl Amides

Ynamides in Radical Reactions: A Route to Original Persubstituted 2-Aminofurans

Mn(OAc)₃/Cu(OAc)₂-mediated reaction between ynamides, derived from oxazolidone or 3-methylindole carboxylate, and cyclic α-dicarbonyl radicals led to the one-pot synthesis of 2-aminofurans. The transformation involves addition of the α-dicarbonyl radical to ynamide, oxidation to ketene-iminium, and polar cyclization steps to provide original persubstituted 2-aminofurans in good to excellent yields. This work represents the first radical route for the synthesis of furans from ynamides.

Synthesis of 2-Aminofurans and 2-Aminothiophenes through Elemental Sulfur-Promoted Switchable Redox Condensation Reaction of Enaminones with Methylene Nitriles

Herein, we report an elemental sulfur-promoted switchable redox condensation reaction that can selectively prepare 2-aminofurans and 2-aminothiophenes from the corresponding enaminones and methylene nitriles, respectively. Mechanistic studies demonstrated that the enaminones, as dual nucleophiles, reacted with nitrile acetate to produce 2-aminofurans via 3,5-annulation under promotion by elemental sulfur. These reactions used readily available starting materials, transition metal-free, eco-friendly procedures, gram-scale syntheses, and wide functional group tolerance. The methodology may be useful for the construction of 2-aminofuran and 2-aminothiophene derivatives with potential biological activity.

Palladium-Catalyzed Organic Reactions Involving Hypervalent Iodine Reagents

The chemistry of polyvalent iodine compounds has piqued the interest of researchers due to their role as important and flexible reagents in synthetic organic chemistry, resulting in a broad variety of useful organic molecules. These chemicals have potential uses in various functionalization procedures due to their non-toxic and environmentally friendly properties. As they are also strong electrophiles and potent oxidizing agents, the use of hypervalent iodine reagents in palladium-catalyzed transformations has received a lot of attention in recent years. Extensive research has been conducted on the subject of C—H bond functionalization by Pd catalysis with hypervalent iodine reagents as oxidants. Furthermore, the iodine(III) reagent is now often used as an arylating agent in Pd-catalyzed C—H arylation or Heck-type cross-coupling processes. In this article, the recent advances in palladium-catalyzed oxidative cross-coupling reactions employing hypervalent iodine reagents are reviewed in detail.

Hypervalent Iodine Reagents in Palladium-Catalyzed Oxidative Cross-Coupling Reactions

Hypervalent iodine compounds are valuable and versatile reagents in synthetic organic chemistry, generating a diverse array of useful organic molecules. Owing to their non-toxic and environmentally friendly features, these reagents find potential applications in various oxidative functionalization reactions. In recent years, the use of hypervalent iodine reagents in palladium-catalyzed transformations has been widely studied as they are strong electrophiles and powerful oxidizing agents. For instance, extensive work has been carried out in the field of C–H bond functionalization via Pd-catalysis using hypervalent iodine reagents as oxidants. In addition, nowadays, iodine(III) reagents have been frequently employed as arylating agents in Pd-catalyzed C–H arylation or Heck-type cross-coupling reactions. In this review, recent advancements in the area of palladium-catalyzed oxidative cross-coupling reactions using hypervalent iodine reagents are summarized in detail.

Atom-Economical and Metal-Free Synthesis of Multisubstituted Furans from Intramolecular Aziridine Ring Opening

Multisubstituted furans were prepared from dialkyl 2-(aziridin-2-ylmethylene)malonate and/or 1,3-dione through aziridine ring opening by the internal carbonyl oxygen with the assistance of BF3·OEt2, followed by aromatization. This synthetic method is free from any metal and is atom-economical with all of the atoms in the starting material retained in the final product.

Preparation of 2-Amino-5-homoallylfurans via Palladium-Catalyzed Tandem Cycloisomerization/Heck-Type Coupling of Homoallenyl Amides with Allyltrialkylsilanes

The direct access to 2-amino-5-homoallylfurans has been realized by a palladium-catalyzed tandem cycloisomerization/Heck-type coupling between homoallenyl amides and allyltrialkylsilanes, using a novel DDQ/MnO₂ combination as the efficient oxidant. The reaction exclusively affords γ-allylation products in good to excellent yields with broad substrate scope under exceptionally mild reaction conditions. It represents one of the rare examples of the Pd-catalyzed intermolecular Heck-type coupling of allytrialkylsilanes terminated by β-silyl elimination, thus complementing traditional allylation methods because of the excellent γ-selectivity.

Palladium-catalyzed tandem cyclization/sulfonylation of homoallenyl amides with sodium sulfinates

A palladium-catalyzed cyclizative sulfonylation of homoallenyl amides has been developed using sodium sulfinates as the sulfonylation reagent and PhI(O₂CCF₃)₂ as the oxidant, providing a facile access to 2-amino-5-sulfonylmethylfurans in good to excellent yields.

Directing group assisted meta-hydroxylation by C-H activation

meta-Hydroxylated cores are ubiquitous in natural products. Herein, we disclose the first template assisted meta-hydroxylation reaction. Experimental and in silico studies helped us to gain valuable mechanistic insights, including the role of the hexafluoroisopropanol (HFIP) solvent, during C-H hydroxylation. The reactive intermediates, prior to the C-H activation, have been detected by spectroscopic techniques. Additionally, the C-O bond formation has been extended to meta-acetoxylation. The preparation of a phase II quinone reductase activity inducer and a resveratrol precursor illustrated the synthetic significance of the present strategy.

Synthesis of α-haloenamides via zinc halide mediated direct addition of benzhydryl halides to ynamides

A regio- and stereoselective synthesis of highly substituted α-haloenamides was described via the zinc halide mediated direct addition of benzhydryl halides to ynamides under mild conditions. The products α-haloenamides were further transformed into multisubstituted enamides via Suzuki and Sonogashira cross-coupling reactions.

Synthesis of 2,3-allenylamides utilizing [1,2]-phospha-Brook rearrangement and their application to gold-catalyzed cycloisomerization providing 2-aminofuran derivatives

An efficient synthetic method for 2,3-allenylamides having an oxygen functionality at the 2-position was newly developed by utilizing the [1,2]-phospha-Brook rearrangement under Brønsted base catalysis.

Direct access to 2-amino-5-azidomethylfurans through palladium-catalyzed azidative cycloisomerization of homoallenyl amides

A room temperature Pd-catalyzed azidative cycloisomerization of homoallenyl amides using TMSN₃ as the azidation reagent and PhI(O₂CCF₃)₂ as the oxidant is described, producing various 2-amino-5-azidomethylfurans in moderate to excellent yields.

Insights into the unexpected chemoselectivity in Brønsted acid catalyzed cyclization of isatins with enaminones: convenient synthesis of pyrrolo[3,4-c]quinolin-1-ones and spirooxindoles

Chemoselective [1+2+3] vs. cascade cyclization has been developed by switching Brønsted acid, offering a divergent synthesis of pyrrolo[3,4-c]quinolin-1-ones and spirooxindoles.

Pd-Catalyzed oxidative isomerization of propargylic acetates: highly efficient access to α-acetoxyenones via alkenyl Csp2–O bond-forming reductive elimination from PdIV

A Pd(ii)/(iv)-catalyzed oxidative isomerization of propargylic acetates developed for the synthesis of polysubstituted alkenyl acetates is described.