K₂CO₃-Catalyzed Synthesis of Chromones and 4-Quinolones through the Cleavage of Aromatic C–O Bonds

Phenol-derived electrophiles are favorable substrates because phenols are naturally abundant or can be readily prepared from other aromatic compounds. However, the cleavage of aromatic C–O bonds is a great challenge because of their high energy. K₂CO₃-catalyzed intramolecular cyclization of 1-(2-alkoxyphenyl)-3-akylpropane-1,3-dione and 3-(alkylimino)-1-(2-methoxyphenyl)-2-methylpropan-1-one derivatives via the selective cleavage of aromatic C–O bonds is reported. The corresponding chromone and 4-quinolone derivatives were obtained in reasonable yields

Copper-Catalyzed Decarboxylative C–P Cross-Coupling of Alkynyl Acids with <i>H</i>‑Phosphine Oxides: A Facile and Selective Synthesis of (<i>E</i>)‑1-Alkenylphosphine Oxides

A novel and efficient copper-catalyzed decarboxylative cross-coupling of alkynyl acids for the stereoselective synthesis of <i>E</i>-alkenylphosphine oxides has been developed. In the presence of 10 mol % of CuCl without added ligand, base, and additive, various alkynyl acids reacted with <i>H</i>-phosphine oxides to afford <i>E</i>-alkenylphosphine oxides with operational simplicity, broad substrate scope, and the stereoselectivity for <i>E</i>-isomers

Manganese-Mediated Electrochemical Dearomatization of Indoles To Access 2‑Azido Spirocyclic Indolines

An efficient and environmentally friendly electrochemical protocol for dearomatization of indoles was developed, delivering a series of azido-containing spirocyclic indolines with good functional group tolerance. This dearomatization process is proposed to result from the oxidation of MnII–N3 species, supported by cyclic voltammetry experiments. Moreover, synthetic transformations can provide an alternative approach to a range of functionalized indolines

Computations Offer an Unconventional Route to Metallaphosphabenzene from a Half-Phosphametallocene

Metallaaromatics have attracted continuing interest of both theoretical and experimental chemists since the first metallabenzene was predicted by Hoffmann and isolated by Roper. In sharp contrast to metallabenzenes, metallaphosphabenzene (MPB) is much less developed and has not been synthesized so far. Thus, developing synthetic approaches is urgent. Here we present thorough density functional theory (DFT) calculations on the thermodynamics and kinetics of the rearrangement between MPBs and the corresponding η⁵-phosphacyclopentadiene (η⁵-PCp) complexes. The effects of metal centers, ligands, and substituents on the metallacycles were examined systematically. Our results reveal that the third-row metal osmium has the highest possibility to form MPB in comparison with the first-row metal iron and second-row metal ruthenium. Substituents were found to have a significant effect on the thermodynamics and kinetics of the rearrangement reactions, leading to an interconversion between osmaphosphabenzenes (OsPBs) and the corresponding η⁵-PCp complexes by simply tuning the substituents on the metallacycles. Thus, all of these findings should invite experimentalists to test these unconventional methods to realize the first MPB

An efficient synthesis of 2-Aminoethylidene-1,1-Bisphosphonates derivatives via Michael addition reaction

<p>A facile, rapid and cheap synthetic strategy towards a wide range of novel 2-aminoethylidene-1,1-bisphosphonate derivatives was developed through the Michael addition reaction of various aromatic amines, aromatic amides as well as nucleoside analogues with tetraethyl ethenylidene-1,1-bisphosphonate. All the newly obtained compounds were characterized by ¹H, ³¹P, ¹³C NMR spectroscopy, IR and HR MS.</p

Mechanistic Insight into the Copper-Catalyzed Phosphorylation of Terminal Alkynes: A Combined Theoretical and Experimental Study

The reaction mechanism of copper-catalyzed phosphorylation of terminal alkynes under different conditions has been investigated experimentally and theoretically. The important role of dioxygen has been elucidated, including the formation of η¹-superoxocopper­(II), η²-superoxocopper­(III), μ-η²:η²-peroxodicopper­(II), and bis­(μ-oxo)­dicopper­(III) complexes. More importantly, the proton transfer from the dialkyl phosphonate (in the form of phosphite) to the bridging oxygen atom entails the migration of the deprotonated phosphonate to the terminal alkyne, leading to the formation of a C–P bond with an activation barrier of only 1.8 kcal/mol. In addition, a particularly stable six-centered dicopper­(I) species is formed with the migration of both of the Ph₂P­(O) groups from the copper atoms to the oxygen atoms of the bis­(μ-oxo) bridge, explaining the experimental observation that secondary phosphine oxides can be oxidized to the phosphinic acids. Thus, the diphenylphosphine oxide was added to the reaction mixture dropwise to minimize the concentration during the reaction course. Gratifyingly, the coupling product was generated almost quantitatively when the reaction was completed

Copper-Catalyzed Aerobic Oxidative Intramolecular C–H Amination Leading to Imidazobenzimidazole Derivatives

A highly efficient copper-catalyzed aerobic oxidative intramolecular C–H amination has been developed using substituted 2-(1<i>H</i>-imidazol-1-yl)-<i>N</i>-alkylbenzenamines as the starting materials, and the corresponding imidazobenzimidazole derivatives were obtained in excellent yields. This is an economical and practical method for the construction of <i>N</i>-heterocycles

Copper-Catalyzed Cascade Radical Addition–Cyclization Halogen Atom Transfer between Alkynes and Unsaturated α‑Halogenocarbonyls

A Cu-catalyzed cascade radical addition/cyclization/halogen atom transfer between alkynes and α-halogeno-γ, δ-unsaturated carbonyl compounds for the synthesis of various substituted cyclopentenes is described. Since up to four Csp³–Csp² bonds, two Csp³–Br bonds, and two carbocycles can be established in a single reaction, this 100% atom-efficient reaction exhibits the advantages of wide substrate scope, high functional group tolerance, and step-economics, and it offers an entry of the atom transfer radical addition/cyclization (tandem ATRA-ATRC) process to the synthesis of substituted cyclopentenes

A Cascade Phosphinoylation/Cyclization/Desulfonylation Process for the Synthesis of 3‑Phosphinoylindoles

3-Phosphinoylindole derivatives play important roles as pharmaceutical drugs and ligands. A new method for the synthesis of 3-phosphinoylindole derivatives has been achieved through silver-mediated cycloaddition between N-Ts-2-alkynylaniline derivatives and H-phosphine oxides. This transformation offers a straightforward route to the formation of the C–P bond, indole ring, and desulfonylation in one step

Isolation of a Heavier Cyclobutadiene Analogue: 2,4-Digerma-1,3-diphosphacyclobutadiene

The heavier cyclobutadiene analogue 2,4-digerma-1,3-diphosphacyclobutadiene ([L¹₂Ge₂P₂], <b>4</b>; L¹ = CH­{(CMe)­(2,6-^<i>i</i>Pr₂C₆H₃N)}₂), featuring a planar Ge₂P₂ four-membered ring, has been synthesized via the elimination of carbon monoxide from the corresponding phosphaketenyl germylene [L¹GePCO] (<b>2</b>) under UV irradiation