5380-80-3Relevant academic research and scientific papers
Earth-Abundant Mixed-Metal Catalysts for Hydrocarbon Oxygenation
Pankhurst, James R.,Curcio, Massimiliano,Sproules, Stephen,Lloyd-Jones, Guy C.,Love, Jason B.
supporting information, p. 5915 - 5928 (2018/05/28)
The oxygenation of aliphatic and aromatic hydrocarbons using earth-abundant Fe and Cu catalysts and "green" oxidants such as hydrogen peroxide is becoming increasingly important to atom-economical chemical processing. In light of this, we describe that dinuclear CuII complexes of pyrrolic Schiff-base macrocycles, in combination with ferric chloride (FeCl3), catalyze the oxygenation of π-activated benzylic substrates with hydroperoxide oxidants at room temperature and low loadings, representing a novel design in oxidation catalysis. Mass spectrometry and extended X-ray absorption fine structure analysis indicate that a cooperative action between CuII and FeIII occurs, most likely because of the interaction of FeCl3 or FeCl4- with the dinuclear CuII macrocycle. Voltammetric measurements highlight a modulation of both CuII and FeIII redox potentials in this adduct, but electron paramagnetic resonance spectroscopy indicates that any Cu-Fe intermetallic interaction is weak. High ketone/alcohol product ratios, a small reaction constant (Hammett analysis), and small kinetic isotope effect for H-atom abstraction point toward a free-radical reaction. However, the lack of reactivity with cyclohexane, oxidation of 9,10-dihydroanthracene, oxygenation by the hydroperoxide MPPH (radical mechanistic probe), and oxygenation in dinitrogen-purge experiments indicate a metal-based reaction. Through detailed reaction monitoring and associated kinetic modeling, a network of oxidation pathways is proposed that includes "well-disguised" radical chemistry via the formation of metal-associated radical intermediates.
Intramolecular hydroxycarbene C-H-insertion: The curious case of (o-methoxyphenyl)hydroxycarbene
Gerbig, Dennis,Ley, David,Reisenauer, Hans Peter,Schreiner, Peter R.
, p. 1061 - 1069 (2011/03/22)
The first C-H insertion of a hydroxycarbene species in the gas phase has been observed experimentally by means of high vacuum flash pyrolysis (HVFP) and subsequent matrix isolation: (o-Methoxyphenyl)glyoxylic acid gives non-isolable (o-methoxyphenyl)hydroxycarbene upon pyrolysis at 600 °C, which rapidly inserts into the methyl C-H bond. The insertion product, 2,3-dihydrobenzofuran- 3-ol, was trapped in an excess of Ar at 11 K and characterized by infrared spectroscopy. The insertion process kinetically outruns the alternative [1,2]H-tunneling reaction to o-anisaldehyde, a type of reaction observed for other hydroxycarbenes. Traces of the dehydration product, benzo[b]furan, were also detected. The potential energy hypersurface including the insertion and hydrogen migration processes was computed at the all-electron coupled-cluster level of theory encompassing single and double substitutions and perturbatively included triple excitations [AE-CCSD(T)] in conjunction with a correlation-consistent double-ζ basis set (cc-pVDZ) by utilizing density functional theory (DFT) optimized geometries (M06-2X/ccpVDZ) with zero-point vibrational energy (ZPVE) corrections. Exchange of the methoxy for a trifluoromethoxy group successfully prevents insertion and (o-trifluoromethoxy) benzaldehyde is produced instead; however, the carbene cannot be observed under these conditions. Thermal decomposition of (o-methoxyphenyl)glyoxylic acid in refluxing xylenes does not give the insertion product but yields o-anisaldehyde. This unanticipated outcome can be rationalized by protonation of the hydroxycarbene intermediate leading to the tautomeric formyl group. Thermochemical computations at M06-2X/cc-pVDZ in conjunction with a self-consistent solvent reaction field model support this suggested reaction pathway.
ACID-CATALYSED DEHYDRATION OF HETEROCYCLIC RING HYDRATES OF BENZOFURAN, BENZOTHIOPHENE, CHROMENE AND THIOCHROMENE
Kelly, Sandra C.,McDonnell, Claire A.,O'Ferrall, Rory A. More,Rao, S. Nagaraja,Boyd, Derek R.,et al.
, p. 747 - 754 (2007/10/03)
Rate constants and equilibrium constants have been measured for acid-catalysed dehydration of benzo-fused five- and six-membered heterocyclic and carbocyclic rings.Substrates studied include 2- and 3-hydroxy-2,3-dihydrobenzofuran, 3-hydroxy-2,3-dihydrobenzothiophene, 1-indanol, 4-chromanol, 4-thiochromanol and 1-tetralol.For the benzofuran-3-hydrate (3-hydroxy-2,3-dihydrobenzofuran), 1-indanol and 1-tetralol rate constants have also been measured for the acid-catalysed racemisation of optically active substrates.These are believed to represent carbocation formation, and this supposition is confirmed by measurements of product partitioning between benzofuran and benzofuran hydrate products from solvolysis of the chloroacetate ester of the 3-hydrate.A surprising observation is that, in the five-membered ring series, heterocyclic oxygen and sulphur atoms have very small accelerating effects on rates of carbocation formation (1.3 and 2.5-fold, respectively, relative to indanol) despite the possibility of direct resonance between the heteroatom and carbocation centre.For dehydration of the corresponding six-membered rings indeed the heteroatoms slow the reaction: in the case of oxygen (4-chromanol) by 100-fold.The possibility that this behavior arises from adverse inductive or stereoelectronic effects is discussed.
