Chromium Alkoxycarbene Complexes Research Articles

Negishi Cross-Coupling Reaction as a Simple and Efficient Route to Functionalized Amino and Alkoxy Carbene Complexes of Chromium, Molybdenum, and Tungsten

Synthesis of functionalized phenyl, 2-thienyl, and N-methyl-pyrrol-2-yl Fischer carbene complexes of chromium and tungsten was achieved via a Negishi cross-coupling reaction of metalated aminocarbenes in the presence of a palladium catalyst. The reverse approach, i.e., coupling bromocarbenes with organozinc reagents, is also feasible and is particularly useful with alkoxycarbene complexes, metalation of which is not possible. Both these procedures are also suitable for the cross-coupling of molybdenum amino- and alkoxycarbene complexes. The presented methodology enables an access to the new amino and alkoxy carbene complexes bearing aldehyde, ketone, nitrile, and ester functionality.

Electrochemistry of Fischer alkoxycarbene complexes of chromium: The use of density functional theory to predict and understand oxidation and reduction potentials

The electrochemical behaviour of a series of Fischer ethoxycarbene complexes of the type [(CO)5CrC(OEt)R] with R = 2-thienyl (1), 2-furyl (2), 2-(N-methylpyrrolyl) (3), N-methyl-2-(2′-thienyl)pyrrole) (4) and 2,2′-thienylfuran (5), is investigated by means of cyclic voltammetry. Results show that the first one electron reduction process is sensitive to the energy, shape and distribution of the LUMO orbital, leading to a linear relationship between the formal reduction potential and the LUMO energy: E0′(Ccarbene) = –0.70 ELUMO–3.44 (R2 = 1.00) which is valid over a large potential range. The dimeric heteroarene substituents of 4 and 5 lead to enhanced stabilization of the reduced complexes 4 and 5, making another one electron reduction possible. The formal reduction potential, E0′(Cr) of the first oxidation process of 1–5 lays within a narrow potential range of 0.43–0.50 V vs. Fc/Fc+, is Cr-based and is mainly sensitive to the electrophilic character of the heteroarene ring directly attached to the carbene carbon.

ChemInform Abstract: Photochemical Reactions of Chromium-Alkoxycarbene Complexes with Stabilized Ylides to Produce “Push-Pull” Captodative Allenes.

Photolysis of chromium alkoxycarbene complexes in the presence of stabilized ylides produced allenes having effect withdrawing groups on C-1 and electron donating groups on C-3. These highly reactive captodative allenes rearranged to 1,3-substituted-1,3-dienes under mildly acidic conditions and hydrolyzed to γ-ket-α,β-unsaturated esters, both in excellent yield

ChemInform Abstract: Optically Active Quaternary Carbon Centers from the Photoaddition of Chromium-Alkoxycarbene Complexes and Optically Active Thiazolines.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Reaction of substituted alkynols with alkoxycarbene complexes of chromium: a facile synthesis of substituted α,β-unsaturated-γ-butyrolactones

Substituted α,β-unsaturated-γ-butyrolactones, were synthesized from Fischer chromium carbenes and substituted alkynols in a two-step sequence. This method demonstrates a novel and mild route for the synthesis of this class of molecules.

Reaction of Nucleophiles with Alkoxycarbene Complexes of Chromium: A General Access to Polycyclic Substituted Butenolides.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Reaction of nucleophiles with alkoxycarbene complexes of chromium: a general access to polycyclic substituted butenolides

A series of new substituted butenolides has been obtained either by reacting alkynylalkoxycarbene complexes 3 with simple nucleophiles such as metal hydrides, metal alkoxides and metal alkyls, or by reacting simple alkoxycarbene complexes 6 with more elaborate nucleophiles such as metal alkynolates or metal alkynyls.

ChemInform Abstract: Enantioselective Approach to Butenolides upon Reduction of Alkoxycarbene Complexes of Chromium with Chiral Dihydropyridines.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Functionalized dihydropyridines do reduce alkoxycarbene complexes of chromium and give access to polycyclic butenolides

Abstract The dihydropyridine-induced reduction of alkoxycarbene complexes of chromium has been generalized to differently substituted dihydropyridines, e.g. N -benzyl dihydropyridine and N -methyl- N’N’ -diethyldihydronicotinamide. In all the cases examined, alkoxyalkynyl carbene complexes lead, upon cascade insertions, to butenolides, the diastereomeric excesses being dependent on the structure of the dihydropyridines.

Enantioselective approach to butenolides upon reduction of alkoxycarbene complexes of chromium with chiral dihydropyridines

Chromium alkoxycarbene complexes tethered to a triple bond react with a series of chiral dihydropyridines, among which is N-methyl-1,2-dihydronicotine, to give enantioselectively, upon cascade insertion reactions, polycyclic butenolides.

A Major Breakthrough in the Use of Alkoxycarbene Complexes of Chromium and Tungsten for the Synthesis of Elaborate Organic Compounds: Dihydropyridine Induced Reductions and Cascade Insertion Reactions

Alkoxy (alkyl)carbene complexes of tungsten and chromium react with dihydropyridine and N-methyldihydropyridine to give respectively pyridinium ylid complexes and N-methylpyridinium tungstates and chromates. These two types of complexes can be used, for the former, as cyclopropanation reagents, for the latter, as unprecedented initiators of cascade multiinsertions of olefins, alkynes and CO. These insertions lead to elaborate polycyclic compounds.

ChemInform Abstract: Reaction of N‐Methyldihydropyridines with Alkoxycarbene Complexes of Chromium and Tungsten: Sequential Use of Three Carbonyl Ligands of Cr(CO)6 for the Formation of Polyoxygenated Compounds.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Reaction of N-methyldihydropyridines with alkoxycarbene complexes of chromium and tungsten: sequential use of three carbonyl ligands of Cr(CO)6 for the formation of polyoxygenated compounds

N-methylpyridinium ylide complexes obtained from alkoxycarbene complexes of chromium and N-methyldihydropyridines easily insert successively a CO ligand to give α-alkoxy chromium acyl complexes, then a tethered triple bond and two additional CO groups to yield bicyclic butenolides.

Synthesis of Functionalized Chiral (Racemic) Cyclobutanones

Chiral (racemic) cyclobutanones, produced by the photochemical reaction between chiral ene carbamates and chromium alkoxycarbene complexes, were functionalized in several ways. Enolization/O-alkylation produced enol ethers and esters that underwent facile ring opening to produce electron-rich dienes. Epoxidation of the silyl enol ether followed by epoxide opening produced α-(silyloxy)cyclobutanones. α-Bromination (NBS) of the cyclobutanones followed by Baeyer−Villiger oxidation led to α-bromobutyrolactones that could be converted to butenolides. By using α-stannyl ene carbamates as substrates for the photochemical cycloaddition, β-stannyl cyclobutanones were produced.

Friedel−Crafts Acylation of Chromium-Carbene-Complex-Derived Ketenes

Photolysis of chromium alkoxycarbene complexes containing electron-rich aromatic systems on either the oxygen or carbon group of the carbene carbon resulted in intramolecular Friedel−Crafts acylation of the arene.

Synthesis and Reactivity of Optically Active Spiroketals by Ring-Expansion of Chromium Carbene Complex-Derived Cyclobutanones.

Photolysis of cyclic chromium alkoxycarbene complexes with an optically active ene-carbamate gave spirofused, optically active cyclobutanones. Baeyer-Villiger ring expansion followed by further functionalization gave optically active spiroketals. Photochemical ring expansion of these spirofused cyclobutanones in the presence of acetic acid or thiophenol gave 2-acetoxy- or 2-(thiophenoxy)-4-spirofused tetrahydrofurans. Elimination of the thiophenoxy group gave a 3,4-dihydrofuran that underwent Heck arylation and photochemical cycloaddition with chromium carbene complexes to give cyclobutanones.

Dihydropyridines in Organometallic Synthesis. Formation of Pyridine and Dihydropyridine-Stabilized Alkylidene Complexes of Tungsten(0) and Chromium(0) from Fischer Carbene Complexes: Structure and Reactivity

1,2- and 1,4-dihydropyridines react with alkoxycarbene complexes of chromium and tungsten to give, upon an unprecedented hydride transfer, alcohol elimination, and pyridine fixation on the carbene carbon, a new class of air-stable pyridinium ylide complexes. These pyridine-protected alkylidene complexes of chromium(0) and tungsten(0) were fully characterized by X-ray crystallography. In the case of (CO)5WC(CH3)(OEt) (5a), besides the pyridinium ylide complex (CO)5W-−C(H)(CH3)(pyridine)+ (7a), the dihydropyridinium complex (CO)5W-−C(H)(CH3)(2,5-dihydropyridine)+ (8a) was also isolated. The intermediate tungstate (CO)5W-−C(H)(CH3)(OEt)(CH3NC5H5)+ could be easily obtained and characterized by using, as reducing agent, N-methyldihydropyridine. Whereas phenyl-substituted pyridinium complexes easily transferred the benzylidene moiety to alkenes, alkyl-substituted complexes appeared more reluctant to such a transfer: satisfactory results were observed in the case of nucleophilic olefins such as enol ethers. However, straightforward transfer of the tungsten(0) alkylidene group took place, even at room temperature, in the case of alkoxycarbene complexes tethered to alkenes, giving access, upon intramolecular cyclopropanation reactions, to polycyclic systems.

Synthesis of 4-Alkyl-4-alkoxybutenolides Having Unsaturated Side Chains via Chromium Carbene Complex Photochemistry: (+)-Cerulenin.

The photochemical reaction between optically active ene carbamates and chromium alkoxycarbene complexes containing unsaturated aliphatic side chains was further developed. Although remote olefinic groups, including conjugated dienes, were tolerated, a homoallylic side chain underwent intramolecular reaction to give a strained cyclobutanone. (+)-Cerulenin was synthesized utilizing the photochemical reaction of an alkynylcarbene complex with an optically active ene carbamate and the bis(pi-crotyl)nickel halide alkylation of a vinyl bromide as key steps.

ChemInform Abstract: Synthesis of β‐Lactones by the Photochemical Reactions of Chromium Alkoxycarbene Complexes with Aldehydes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: New Method for the Preparation of Alkoxycarbene Complexes of Chromium, Molybdenum and Tungsten Using Sulfonium Salts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.