27436-93-7Relevant academic research and scientific papers
A four-step route to synthetic equivalents of ortho-xylylenes: D?tz benzannulation, desilylation, bromo-dehydroxylation, and sultine formation. A concise approach to oxygenated linearly fused polycyclic aromatics
Kotha, Sambasivarao,Aswar, Vikas R.,Manchoju, Amarender
, p. 2306 - 2315 (2016)
A new route has been reported for the synthesis of densely oxygenated polycyclic aromatic compounds via cycloaddition approach. This strategy involves the D?tz benzannulation and Diels-Alder reaction as key steps. Naphthalene synthons required here were g
Physical organic chemistry of transition metal carbene complexes. 4. Kinetics and equilibria of methoxide ion addition to [methoxy(phenyl)carbene]pentacarbonylchromium(0) and [methoxy(phenyl)carbene]pentacarbonyltungsten(0)
Bernasconi, Claude F.,Flores, Francis X.,Gandler, Joseph R.,Leyes, Aquiles E.
, p. 2186 - 2193 (1994)
A stopped-flow kinetic study of the reversible addition of methoxide ion to [methoxy(phenyl)-carbene]pentacarbonylchromium(0) (2-Cr) and [methoxy(phenyl)carbene]pentacarbonyltungsten-(0) (2-W) in methanol at 25°C is reported. The reaction was investigated by approaching the equilibrium (eq 1) from either side; due to the rapid decomposition of the adduct, the reaction in the reverse direction had to be measured in a sequential stopped-flow apparatus a few milliseconds after the adduct had been generated. Evidence that the observed reaction refers to the formation of (CO)5M--C(Ph)(OCH3)2 (M = Cr, W) includes a comparison of the absorption spectrum of (CO)5W--C(Ph)(OCH3)2 with that of the ylide derived from 2-W and DABCO, low-temperature IR of the adducts, and demonstration of CH3O/CD3O exchange on the same time scale as the kinetic experiments. The following rate and equilibrium constants were obtained: k1 = 77.1 M-1 s-1, k-1 = 1.10 s-1, and K1 = 70.1 M-1 for 2-Cr and k1 = 186 M-1 s-1, k-1 = 1.68 s-1, and K1 = 111 M-1 for 2-W. Approximate intrinsic rate constants (k0 = k1 = k-1 when K1 = 1) were calculated from the experimental rate constants. The k0 values are substantially lower than those estimated for the addition of methoxide ion to methyl benzoate. This is consistent with significant charge delocalization in the methoxide ion adducts of the metal carbene complexes. Rate constants, k-1BH, for general acid catalyzed methoxide ion loss from the adducts by phenol and 3,5-dichlorophenol were also determined. They allow an estimate of a Br?nsted α value on the order of 0.9, suggesting a transition state in which proton transfer from the catalyst to the incipient methoxide ion is well advanced. The near-independence of K1 on the metal contrasts with the strong metal dependence (Cr vs W) of the pKa values of (η5-C5H5)M(CO)3H-type hydrido complexes and supports Norton's view that the acidity of these hydrido complexes is not governed by the stabilization of the negative charge in the respective anions.
Coupling of Cyclobutenediones with Fischer Carbene Complexes: A One-Step Synthesis of Cyclopentenediones and/or 5-Alkylidenefuranones via Net Insertion of the Carbene Unit into a C - C Bond
Zora, Metin,Li, Yuhui,Herndon, James W.
, p. 4429 - 4436 (1999)
The reaction of Fischer carbene - chromium complexes with 3-cyclobutene-1,2-diones has been investigated. In most cases, the major product of the reaction is the C - C bond insertion product, a 2-alkoxy-4-cyclopentene-1,3-dione, accompanied by a minor amount of the partial deoxygenation product, a 4-cyclopentene-1,3-dione. In some cases, 5-alkylidenefuranones are also formed. A mechanism involving oxidative addition of the coordinatively unsaturated Fischer carbene complex followed by acyl migration and reductive elimination was proposed to account for cyclopentenedione formation. Furanone formation was thought to arise via demetalation of the acyl migration product, followed by O-acylation. An electronic dependence was noted for cyclopentenedione/alkylidene - furanone ratio, which was evaluated using the Hammett equation.
Abstraction of methyl from neutral Fischer-type carbene complexes: A new site for nucleophilic attack
Toomey, Laurence M.,Atwood, Jim D.
, p. 490 - 493 (1997)
Reactions of Fischer-type carbene complexes, M(CO)5(C(OMe)Ph) (M = Cr, W), with metal carbonyl anions (M′- = CpFe(CO)2-, Re(CO)5-, Mn(CO)4PPh3-, Co(CO)3PPh3-, Cp*Cr(CO)3-, CpMo(CO)3-) result in demethylation of the carbene complexes. The products are M(CO)5C(O)Ph- and M′-Me, characterized by infrared and NMR spectroscopy. A slower rate for reaction with W(CO)5(C(OEt)Ph) in comparison to the methyl analogue is consistent with nucleophilic attack of the metal carbonyl anion on the methyl of the methoxy group of the carbene. This is a new type of nucleophilic attack on a Fischer-type carbene.
Preparation of Fischer carbene complexes by alkylation of acylmetalates with alkyl iodides
Hoye, Thomas R.,Chen, Kejian,Vyvyan, James R.
, p. 2806 - 2809 (1993)
Neutral Fischer carbene complexes bearing alkoxy groups as the donor substituents on the carbene carbon atom have been synthesized by direct alkylation of the lithium acylmetalates (formed by classical addition of organolithium compounds to metal hexacarbonyl) by alkyl iodides. It was shown that the reaction proceeds under normal phase-transfer conditions (CH2-Cl2/H2O) or, preferably, in aqueous medium alone. However, in both cases the presence of a catalytic amount of a tetraalkylammonium salt (n-Bu4NBr) was required. Attractive features of this methodology are (i) the economy of using alkyl iodides in place of the usual alkylating agents (like Me3O+BF4-, magic methyl, or methyl triflate), (ii) the procedural ease of one-pot preparation of the carbene complexes, and (iii) the greater variety of alkyl moieties that can be incorporated as part of the alkoxy substituent using the more readily available alkyl iodides containing nontrivial alkyl groups. The procedure is preparatively useful for accessing chromium-containing carbenes, but yields of the analogous molybdenum- and tungsten-containing species are only ≤10%. Mechanistic considerations suggest that products are formed by competing pathways involving direct SN2 displacement vs electron-transfer-initiated SRN1 processes.
Physical organic chemistry of transition metal carbene complexes. 19. Kinetics of reversible alkoxide ion addition to substituted (methoxyphenylcarbene)pentacarbonylchromium(0) and (methoxyphenylcarbene)pentacarbonyltungsten(0) in methanol and aqueous ace
Bernasconi, Claude F.,Garcia-Rio, Luis
, p. 3821 - 3829 (2007/10/03)
Rate and equilibrium constants for the nucleophilic addition of MeO- in methanol and in 90% MeCN-10% MeOH, of HC≡CCH2O- and CF3CH2O- in 50% MeCN-50% water, and of OH- in 50% MeCN
Total synthesis of parvaquone and the serendipitous discovery of a novel chromium-mediated method for β-lactone formation
Harrity, Joseph P. A.,Kerr, William J.,Middlemiss, David,Scott, James S.
, p. 219 - 227 (2007/10/03)
During attempts to synthesise the 2-hydroxy-1,4-naphthoquinone, parvaquone, 1, a novel chromium-mediated method for the synthesis of functionalised β-lactones from propargyl alcohols has been discovered. Additionally, using both dry state and ultrasound conditions, the total synthesis of parvaquone (1) has been achieved; the most efficient techniques deliver this target compound in up to 46% overall yield over, as low as, two synthetic processes.
New synthesis of functionalized chromium carbene complexes using zinc organometallics
Stadtmüller, Heinz,Knochel, Paul
, p. 3163 - 3166 (2008/10/09)
The reaction of functionalized dialkylzincs with photochemically generated Cr(CO5·THF affords, after carbonylation and methylation using Meerwein's reagent, polyfunctional chromium carbene complexes in 35%-45% overall yield. The hydroboration of the unsaturated chromium carbene complex 4e followed by a boron-zinc exchange mediated by diethylzinc provides the dialkylzinc 6 bearing a chromium carbene functionality. This was reacted with deuterium oxide and iodine, affording the expected chromium carbene complexes in 67% and 43% yields, respectively.
New Method for the Preparation of Alkoxycarbene Complexes of Chromium, Molybdenum, and Tungsten Using Sulfonium Salts
Nakamura, Takako,Matsuyama, Haruo,Iyoda, Masahiko
, p. 1537 - 1540 (2007/10/02)
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.
Low-temperature infrared spectral study of the photochemical reaction of (CO)5Cr=C(OMe)Ph with solvent and alkynes
Knorr, Joseph R.,Brown, Theodore L.
, p. 2178 - 2185 (2008/10/08)
The photochemical behavior of the Fisher carbene (CO)5Cr=C(OMe)Ph (1) under a variety of low-temperature conditions is studied. Photolysis of 1 with low-pressure mercury lamps at 95 K in a 3-methylpentane (3MP) glass is followed by FTIR observation during programmed warmup in the range from 95 K to 295 K. Photolysis of 1 in 3MP glass results in loss of CO with low quantum yield and formation of a cis-solvento species. Recombination with CO occurs in the temperature range to 140 K. When THF is present in low concentration, photolysis results in formation of cis-(CO)4(THF)Cr=C(OMe)Ph. In the temperature interval 95-160 K this species undergoes changes of uncertain origins, before reverting to 1 upon THF loss and recombination with CO, at temperatures above 165 K. In the presence of dilute p-CF3C6H4-CCH, photolysis at 95 K results in formation of a single intermediate which remains unchanged upon warming until, in the temperature range 200-235 K, it converts to the final phenol annulation product. When THF is present in addition to the alkyne, the cis-THF complex is formed at low temperature and then converts to the same alkyne intermediate as THF dissociates from the complex. The results of these experiments are discussed in terms of the various intermediates previously proposed for the reactions of 1 with alkynes.
