Access to Densely Functionalized Chalcone Derivatives with a 2-Pyridone Subunit via Pd/Cu-Catalyzed Oxidative Furan–Yne Cyclization of N-(2-Furanylmethyl) Alkynamides under Air

Interrupted Furan-Yne Cyclization: Access to Unsaturated Dicarbonyl Compounds and Their Subsequent Transformation into Functionalized Pyridazines

The key carbenoid intermediate of transition-metal-catalyzed furan-yne cyclization in Hashmi phenol synthesis could be efficiently intercepted with water under the developed reaction conditions in order to provide access to functionalized unsaturated dicarbonyl compounds that might serve as convenient precursors for the straightforward synthesis of annulated pyridazines.

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.

Fe(III)-Catalyzed Tandem Cyclization of Phenylpropiolamides with 3-Formylchromones for the Construction of 2-Pyridones

A highly efficient and atom-economic iron(III)-catalyzed three-component heteroannulation reaction between phenylpropiolamides, 3-formylchromones, and water is described for the construction of diversely multifunctionalized 2-pyridones. This protocol allows rapid access to a variety of 2-pyridones bearing an ortho-hydroxybenzoyl and a benzoyl scaffold under operationally simple conditions. The synthetic utility of the synthesized 2-pyridone scaffolds is demonstrated by transformation into biologically interesting complex heterocycles.

The construction of phosphonate triazolyl by copper(II)-catalyzed furan dearomatized [3 + 2] cycloaddition

Triazole phosphonates are valuable structural motifs in chemical biology and the subject of growing recent interest. A novel methodology to synthesize triazolyl phosphonates starting from furfuryl phosphonate alcohols and organo-azides was developed. This method involved an intermolecular copper-catalyzed dearomatized [3 + 2] cycloaddition/furan ring-opening cascade reaction. A strategy involving a three-component reaction was realized for quick access to triazole phosphonates.

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.

Synthesis of alkynamides through reaction of alkyl- or aryl-substituted alkynylaluminums with isocyanates

An efficient and facile method for the preparation of alkynamides through Et₃N-catalyzed alumination of alkyl- or aryl-substituted terminal alkynes with AlMe₃ and sequential nucleophilic addition of in situ generated alkynylaluminums to isocyanates is described. This method has the merits of using readily available isocyanates and monosubstituted alkynes, easy access to organoaluminums, short reaction times, and high efficiency. A gram-scale synthesis of the desired alkynamide and its application to the formation of α-methylene-β-lactams demonstrates the synthetic utility of this method.

Synthesis of Highly Conjugated Functionalized 2-Pyridones by Palladium-Catalyzed Aerobic Oxidative Dicarbonation Reactions of N-(Furan-2-ylmethyl) Alkyne Amides and Alkenes as Coupling Partners

A mild, step-economical method for the synthesis of highly conjugated functionalized 2-pyridones from N-(furan-2-ylmethyl) alkyne amides is reported. This method involves Pd-catalyzed aerobic oxidative dicarbonation reactions of alkynes with carbon nucleophiles of a furan ring and an acrylate or styrene as coupling partners. The UV-vis absorption spectra of some of the 2-pyridones indicated that they absorbed shortwave radiation, suggesting their potential utility for filtration of such radiation.

Regioselective synthesis of tetrahydroquinolines via syn- and anti-nucleopalladation-initiated cascade processes

Regioselective synthesis of tetrahydroquinolines via nucleopalladation-initiated cascade sequences was established.

Substituent-controlled chemoselective synthesis of multi-substituted pyridones via a one-pot three-component cascade reaction

A substituent-controlled chemoselective cycloaddition reaction which afforded a variety of 2-pyridones and 4-pyridones in good to excellent yields, respectively, has been developed.

Intramolecular azavinyl carbene-triggered rearrangement of furans

An intramolecular rhodium-catalyzed reaction of 1-tosyl-1,2,3-triazoles with furans has been explored. The tosylimino functionality was found to play a significant chemical role participating in the subsequent domino-transformations of a key reaction intermediate. One of the reaction pathways leads to valuable 2-formyl- and 2-acetylpyridine building blocks, which could be obtained in one-pot starting from easily accessible (furan-2-ylmethyl)propargyl amines. An original method for the synthesis of highly functionalized indolizines from the obtained pyridines has been proposed.