Alkoxycarbene Complexes Research Articles

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.

Formation and Selective Trapping of 2,5-Dihydropyridine and Its Isopropylidene Derivative by Tungsten(0) Alkylidene Complexes. X-ray Structure of the 5-Isopropylidene-2,5-dihydropyridine Adduct

A mixture of 1,2- and 2,5-dihydropyridines and 5-isopropylidene-2,5-dihydropyridine, obtained from 1-(methoxycarbonyl)-1,2-dihydropyridine and methyllithium followed by protonation, reacts with a series of pentacarbonyl tungsten(0) alkoxycarbene complexes to afford, besides the expected pyridinium ylide complexes 7, the 2,5-dihydropyridinium ylide complexes 6 together with the 5-isopropylidene-2,5-dihydropyridinium ylide complexes 5, which could be separated and fully characterized by X-ray analysis.

Reactions of m- and p-Divinylbenzene−Diiron Hexacarbonyl with Aryllithium Reagents. Crystal Structures of [(CO)3Fe(m-C10H10)(CO)2FeC(OC2H5)C6H4CH3-o] and [(CO)3Fe(p-C10H10)(CO)2FeC(OC2H5)C6H4CF3-p

The reactions of m-divinylbenzene−diiron hexacarbonyl (1) with aryllithium reagents, ArLi (Ar = C6H5, o-, m-, p-CH3C6H4, p-CH3OC6H4, p-CF3C6H4, m-ClC6H4), in ether at low temperature gave acylmetalate intermediates followed by alkylation with Et3OBF4 in aqueous solution at 0 °C to afford the isomerized divinylbenzene-coordinated alkoxycarbene complexes [(CO)3Fe(m-C10H10)(CO)2FeC(OC2H5)Ar] (3, Ar = C6H5; 4, Ar = o-CH3C6H4; 5, Ar = m-CH3C6H4; 6, Ar = p-CH3C6H4; 7, Ar = p-CH3OC6H4; 8, Ar = p-CF3C6H4; 9, Ar = m-ClC6H4) with two types of structures. The p-divinylbenzene-diiron hexacarbonyl (2) also reacted with the aryllithium reagents under the same conditions to give the corresponding isomerized alkoxycarbene complexes [(CO)3Fe(p-C10H10)(CO)2FeC(OC2H5)Ar] (10, Ar = C6H5; 11, Ar = o-CH3C6H4; 12, Ar = m-CH3C6H4; 13, Ar = p-CH3C6H4; 14, Ar = p-CH3OC6H4; 15, Ar = p-CF3C6H4; 16, Ar = m-ClC6H4). The structures of complexes 4 and 15 have been determined by single-crystal X-ray diffraction studies.

Half-sandwich rhenium(III) acyl complexes: synthesis, structure and conversion to rhenium(I) and rhenium(III) isonitrile complexes

The synthesis, structure and reactions of rhenium(III)η 1-acyl complexes bearing a cyclopentadienyl (Cp) or a pentamethylcyclopentadienyl (Cp *) ligand are described. Oxidation of the rhenium(I) acyl complexLi[CpRe(CO) 2(η 1-PhCO)] ( 1) with one equivalent of PhICl 2 affords the rhenium(III) acyl complex trans-CpRe(CO) 2(η 1-PhCO)Cl ( trans- 2a). The diphenylcarbene complex Cp(CO) 2Re CPh 2 ( 3) is also formed in this reaction. Similarly, oxidation of 1 with Br 2 givescis/trans-CpRe(CO) 2(η 1-PhCO)Br(cis/trans- 2b), which can also be obtained from the alkoxycarbene complex Cp(CO) 2Re C(OEt)Ph ( 4) with one equivalent of Br 2. Oxidation ofLi[Cp *Re(CO) 2(η 1-PhCO)] ( 5) with one equivalent of PhlCl 2, Br 2 or I 2 affords selectively the rhenium(III) acyl complexescis/trans-Cp *Re(CO) 2(η 1-PhCO)X(X Cl I) [ cis/trans-( 6a–6c)]. Cleavage of the Re C acyl bond of trans- 2a with PhICl 2 and of cis/trans- 2b with Br 2 offers a convenient way to the rhenium(III) dihalo complexes cis/trans-CpRe(CO) 2Cl 2 ( cis/trans- 7a) and cis/trans-CpRe(CO) 2Br 2 ( cis/trans- 7b) respectively. Reduction of cis/trans- 7a with sodium/amalgam gives in the presence of RNC, the rhenium(I) isonitrile complexes CpRe(CO) 2(CNR) ( 8:R Et; 9:R 10:R 1Bu). Oxidation of 8–10 with one equivalent of bromine leads selectively to the rhenium(III) isonitrile complexes [ trans-CpRe(CO) 2(CNR)Br]Br ( 11:R = Et; 12:R - iPr; 13:R = tBu). The crystal structure of the acyl complex trans- 2b and the carbonyl complex [Cp 2 *Re 2(CO) 4(μ-Br)][Re 2(μ-Br) 3(CO) 6] ( 14) are described, complex 14 being formed by the thermal decomposition of cis/trans- 6b.

Multiple Re−C Bonds at the [{MeC(CH2PPh2)3}Re(CO)2]+Auxiliary

After displacement of the η2-H2 ligand from [(triphos)Re(CO)2(η2-H2)]BF4 (2), ethyne and various 1-alkynes, HC≡CR, are tautomerized at the Re(I) center to vinylidene ligands (R = H, Ph, p-tolyl, COOEt, n-C6H13, SiMe3). A kinetic π-alkyne adduct is intercepted at low temperature during the reaction between 2 and ethyne. The primary vinylidene complex [(triphos)Re(CO)2(CCH2)]BF4 (7-BF4) can also be obtained by reaction of the (trimethylsilyl)vinylidene complex [(triphos)Re(CO)2{CC(H)SiMe3}]BF4 with stoichiometric water. Unprecedented examples of addition of either water or alcohols to Re−vinylidene moieties to give hydroxycarbene or alkoxycarbene complexes are presented. In particular, an excess of water transforms 7-BF4 into the secondary hydroxycarbene complex [(triphos)Re(CO)2{C(OH)CH3}]BF4 (11), which can be isolated in the solid state. Upon thermolysis in refluxing tetrahydrofuran, 11 selectively converts to the tricarbonyl complex [(triphos)Re(CO)3]BF4 and methane. Deprotonation of 11 by mild bases gi...

Ruthenium Alkoxycarbene Complexes from an Acetal Function by C−O Bond Cleavage and Alcohol Elimination

Heating solutions of acetal complexes {CpRu(CH3CN)2[η1-P-2-(Ph2P)[CH(OR)2]C6H4]}OTf (3; R = Me, Et) at 60−95 °C results in loss of one CH3CN ligand and the alcohol ROH, with concomitant formation of carbene complexes CpRu(CH3CN)[η2-C,P-2-(Ph2P)[C(OR)]C6H4]}OTf (4) in high yield. Kinetic and reactivity studies suggest that the rate-determining step of the conversion of 3 to 4 is oxidative addition of an acetal C−O bond to the ruthenium center, which occurs under neutral, mild conditions.

Characterization of chromium-carbene complexes by high-performance liquid chromatography-mass spectrometry with particle beam interface

High-performance liquid chromatography (HPLC) coupled with mass spectrometric (MS) detection was used to separate and characterize a series of chromium -aminocarbene and alkoxycarbene complexes of the Fischer type, some of which were synthesized as new compounds. Chromium-carbene complexes are known to have interesting photochemical properties. The separation of all the compounds examined was performed under normal-phase conditions and a particle beam LC-MS interface was used. The acquisition of positive-ion and negative-ion chemical ionization mass spectra of the eluates was performed. The use of the LC-PB-MS system demonstrated the potential role of this technique in the elucidation of the structure of polar organometallic compounds, such as the carbene complexes of chromium examined.

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.

Group 6 Pyrrolocarbene Complexes as Alkoxycarbene Complex Analogs

Group 6 Pyrrolocarbene Complexes as Alkoxycarbene Complex Analogs

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.

Neue Organometall-Derivate des 1,6-Methanol[10]annulens

Fischer-type amine-carbene complexes of 1,6-methano[16]annulenes 4a-e were prepared in high yields by the aminolyses of 1,6-methano[10]annulenyl substituted alkoxy-carbene complexes 1 with various amines 2a-e. The benzylamino complex 4c was selectively transformed into the benzylamide 5 by oxidation or to the acylamino chelate carbene complex 6 by acylation catalyzed by dimethylaminopyridine.

Synthesis and Metal Complexation Reactions of Bis-Dioxocyclams from Photochemical Reaction of Bis-Chromium Alkoxycarbene Complexes with Imidazolines

Synthesis and Metal Complexation Reactions of Bis-Dioxocyclams from Photochemical Reaction of Bis-Chromium Alkoxycarbene Complexes with Imidazolines

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.

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

Abstract Alkylation of tetramethylammonium acylate complexes of chromium, molybdenum, and tungsten with alkyldiphenylsulfonium salts readily proceeds under mild conditions to afford alkoxycarbene complexes containing a variety of functional groups in good yields.

Synthesis of .beta.-Lactones by the Photochemical Reactions of Chromium Alkoxycarbene Complexes with Aldehydes

Photolysis of chromium alkoxycarbene complexes with aldehydes in the presence of Lewis acids produced β-lactones in low yield. Incorporation of the aldehyde into either side chain of the carbene complex resulted in intramolecular processes which were considerably more efficient

Synthesis of optically active butenolides via chromium alkoxycarbene complexes: total synthesis of (+)-tetrahydrocerulenin and two butenolides from the marine sponge Plakortis lita

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSynthesis of optically active butenolides via chromium alkoxycarbene complexes: total synthesis of (+)-tetrahydrocerulenin and two butenolides from the marine sponge Plakortis litaMichael Miller and Louis S. HegedusCite this: J. Org. Chem. 1993, 58, 24, 6779–6785Publication Date (Print):November 1, 1993Publication History Published online1 May 2002Published inissue 1 November 1993https://doi.org/10.1021/jo00076a044RIGHTS & PERMISSIONSArticle Views589Altmetric-Citations38LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1020 KB) Get e-Alerts Get e-Alerts

Organische Synthesen mit Übergangsmetall‐Komplexen, 63. (β1‐Aminovinyl)carben‐Komplexe und (Alkinyl)aminocarben‐Komplexe von Chrom und Wolfram. — Stereochemie und Isomerisierung

Organic Syntheses via Transition Metal Complexes, 63[1]. — (β1‐Aminovinyl)carbene complexes and (Alkinyl)aminocarbene Complexes of Chromium and Tungsten. — Stereochemistry and Isomerization(Alkinyl)alkoxycarbene complexes LnMC(OEt)–CCR 3 [LnMCr(CO)5, W(CO)5; RPh, nBu, SiMe3] react with primary amines H2NR1 4 (R1Me, iPr, allyl, CH2Ph, CHMePh) to give (β1‐aminovinyl)carbene complexes LnMC(OEt)–CHCR‐NHR1 (Z)‐5 (by a Michael‐type 3‐addition) together with (alkinyl)aminocarbene complexes anti‐6 (by a 1‐aminolysis). The product ratio (Z)‐5/anti‐6 is strongly influenced by the reaction temperature: at 20°C (Z)‐5 is obtained as the main product, while at –78°C mainly anti‐6 is formed. Both reactions are stereospecifical; they yield 5 in the (Z), and 6 in the anti configuration only. An anti/syn isomerization is achieved by acidic treatment of anti‐6i. The (alkinyl)aminocarbene complex 6a adds EtOH/EtO– albeit much slower than the (alkinyl)alkoxycarbene complex 3a. A NH21‐Enamino carbene complexes (CO)5CrC(OEt)–CHC(NH2)Ph [(Z)‐8a] is obtained on addition of ammonia to 3a at 90°C.