Copper oxidative olefination

Tertiary bismuthines appear to have a number of uses in synthetic organic chemistry (32), eg, they promote the formation of 1,1,2-trisubstituted cyclopropanes by the iateraction of electron-deficient olefins and dialkyl dibromomalonates (100). They have also been employed for the preparation of thin films (qv) of superconducting bismuth strontium calcium copper oxide (101), as cocatalysts for the polymerization of alkynes (102), as inhibitors of the flammabihty of epoxy resins (103), and for a number of other industrial purposes. 

In addition to a-additions to isocyanides, copper oxide-cyclohexyl isocyanide mixtures are catalysts for other reactions including olefin dimerization and oligomerization 121, 125, 126). They also catalyze pyrroline and oxazoline formation from isocyanides with a protonic a-hydrogen (e.g., PhCH2NC or EtOCOCHjNC) and olefins or ketones 130), and the formation of cyclopropanes from olefins and substituted chloromethanes 131). The same catalyst systems also catalyze Michael addition reactions 119a). 

NO reduction by CO, 28 162 olefin oxidation, 27 241,242 water-gas shift, 28 118,119 coordination number, 30 265 -copper alloy, 26 75 -copper alloy films thermodynamic properties of, 22 118 -copper oxide, 27 90,91 -manganese oxide, 27 91,92... 

The linear polymerization of Scheme 7.15 represents an unusual case of diazoacetophenone oxidation. For instance, on the action of copper oxide, diazoacetophenone gives ketocarbene, which is involved in typical carbene reactions such as dimerization, addition to olefins, and insertion in the 0-H bonds of alcohols. If the amine cation-radical is used as an oxidant instead of copper oxide, only the polymer is formed. The ketocarbene was not observed despite careful searches (Jones 1981). 

Infrared spectra of propene and isobutene on different catalysts were measured by Gorokhovatskii [143]. Copper oxide, which converts olefins to butadiene and aldehydes, shows adsorption complexes different from structures on a V2Os—P2Os catalyst which produces maleic acid anhydride. Differences also exist between selective oxidation catalysts and total oxidation catalysts. The latter show carbonate and formate bands, in contrast to selective oxides for which 7r-allylic species are indicated. A difficulty in this type of work is that only a few data are available under catalytic conditions most of them refer to a pre-catalysis situation. Therefore it is not certain that complexes observed are relevant for the catalytic action. 

Intramolecular cyclopropanation of diazoketones to furnish [3.1.0] and [4.1.0] bicyclic systems are the most common and effective reactions in this category. Two recent examples are shown in equations 48 and 49. The bicyclic ketone 34 has been used in the synthesis of polycyclic cyclobutane derivatives77, whereas ketone 35 is the key intermediate in the total synthesis of ( )-cyclolaurene78. When the olefinic double bond is attached to, or is part of, a ring system, the cyclopropanation process also works well. Copper oxide catalysed decomposition of diazoketone 36 produces the strained tricyclic ketone 37 in 86% yield (equation 50)79. In another case, in which the cyclopropanation of diazoketone 38 gave stereospecifically the cyclopropyl ketone 39, copper sulphate catalysis was used. The cyclopropyl ketone 39 is the key intermediate in the total synthesis of ( )-albene 40 (equation 51). ... 

The mechanistic picture for addition of organocuprates to a,P-unsaturated carbonyl compounds is no less complex than that for substitution reactions. On the basis of current information, conjugate addition of lithiocuprates to a, P-unsaturated ketones and esters may proceed via a initial reversible copper(I)-olefin-lithium association, which then undergoes oxidative addition followed by reductive elimination. ... 

Tp CuL complexes catalyze both reactions shown in Scheme 17. The aziridination reaction with such catalysts was discovered using Tp CulCjH ) and Phi=NTs as the nitrene source (Scheme 18). The influence of the hapticity of the Tp ligand and the oxidation state of the copper center were later studied demonstrating that tricoordination of the ligand and +1 as the copper oxidation state were the best choices. The use of the fluorinated version of the above catalyst, that is Tp< u(C2H ) also proved effective. Moreover, the already mentioned Tp Cu(NCMe) complex induced the aziridination reaction not only with the frequently employed olefins (styrene, 1-hexene, cyclooctene) but also with aaylates and using a stoichiometric mixture of olefin and PhI=NTs. ... 

Several copper-exchanged and CuCl2-supported solids, together with copper oxide, have been tested as catalysts in the benchmark cyclopropanation reaction of styrene with ethyl diazoacetate. The catalytic activity does not depend on the amount of copper but on the structure and pretreatment of the catalyst. The trans/cis selectivity also depends on the nature of the solid and with KlO-montmorillonite the cis-cyclopropane is predominantly obtained, so that the selectivity is reversed with regard to that observed with copper homogeneous catalysts. The use of several olefins confirms this tendency to reverse the selectivity obtained in solution and the electrophilic character of the reaction. The effect of the reaction conditions and the influence of the solvent are also analyzed. 

Kinetics of oxidation of isobutene to methacrolein have been studied by Popova and Mil man 103) in a conventional flow reactor. The rates were found to be first order in oxygen and zero order in olefin for formation of both methacrolein and COg. The same orders were reported by Mann and Rouleau lOi) for the over-all oxidation in a static system. Mann and Rouleau 104a) also published data on the kinetics of oxidation of isobutene to methacrolein and COg over a copper oxide on pumice catalyst in a flow system. Selectivities up to about 50 % were observed at C4H8/Og = 0.25-4 and 350-450°. The rate of isobutene oxidation was correlated by the equation... 

On the development of copper-catalysed olefin aziridination, Evans et al. [36] reported oxidative amidine formation. Treatment of cyclohexene, a less reactive substrate towards... 

Indazoles were prepared by many different methods. Indazoles 41 were synthesized from nitroaromatics 39 and N-tosylhydrazones 40 with bases (14CC5061). A rhodium(III)-catalyzed oxidative olefination of 1,2-di-substi-tuted arylhydrazines with alkenes via sp C-H bond aaivation followed by an intramolecular aza-Michael reaction yielded indazoles (140L2494). Copper-catalyzed C-H amidation with aromatic imines 42 with tosyl azide provided a route to 3-substituted indazoles 43 (14OL4702). 4,5,6,7-Tetrahydro-lH-inda-zol-3-(2fJ)-one derivatives were prepared in two-step one-pot process (14SC1076). A regioselective synthesis of 2H-indazoles 45 was achieved using... 

On the large scale, oxidation (dehydrogenation) of secondary alcohols to ketones is usually achieved using air and a catalyst - copper oxide is an established one. Aldehydes are often prepared by hydroformylation of olefins rather than from the corresponding alcohol. However, on the smaller scale, a large and diverse number of carbonyl compounds are... 

The oxidation of copper(i)-olefin complexes by O2 has been reported. The copper complexes were prepared pulse-radiolytically by rapid reduction of Cu in the presence of ethylene or allyl alcohol. The irradiated solution was then mixed with oxygenated water in a stopped-flow apparatus. For the two complexes described the rate laws differ only slightly. In the reaction with the ethylene (L) species the rate law obtained is... 

It is only very recently that rhodium-based catalytic systems have been described in efficient oxidative olefination reactions. Inspired by the work of Satoh and Miura on rhodium/copper-catalyzed aerobic oxidative coupling of benzoic acids with internal allqmes or acrylates (Scheme 9.11), Glorius and co-workers described, in 2012, a rhodium-catalyzed directing group assisted olefination of 2-aryloxazolines under air. This method, which necessitated rhodium, silver and copper metal sources, afforded the desired olefin-oxazoline products in moderate-to-good yields (Scheme 9.12). 

Another attractive commercial route to MEK is via direct oxidation of / -butenes (34—39) in a reaction analogous to the Wacker-Hoechst process for acetaldehyde production via ethylene oxidation. In the Wacker-Hoechst process the oxidation of olefins is conducted in an aqueous solution containing palladium and copper chlorides. However, unlike acetaldehyde production, / -butene oxidation has not proved commercially successflil because chlorinated butanones and butyraldehyde by-products form which both reduce yields and compHcate product purification, and also because titanium-lined equipment is required to withstand chloride corrosion. 

Finally, selective hydrogenation of the olefinic bond in mesityl oxide is conducted over a fixed-bed catalyst in either the Hquid or vapor phase. In the hquid phase the reaction takes place at 150°C and 0.69 MPa, in the vapor phase the reaction can be conducted at atmospheric pressure and temperatures of 150—170°C. The reaction is highly exothermic and yields 8.37 kJ/mol (65). To prevent temperature mnaways and obtain high selectivity, the conversion per pass is limited in the Hquid phase, and in the vapor phase inert gases often are used to dilute the reactants. The catalysts employed in both vapor- and Hquid-phase processes include nickel (66—76), palladium (77—79), copper (80,81), and rhodium hydride complexes (82). Complete conversion of mesityl oxide can be obtained at selectivities of 95—98%. 

Apparently the alkoxy radical, R O , abstracts a hydrogen from the substrate, H, and the resulting radical, R" , is oxidized by Cu " (one-electron transfer) to form a carbonium ion that reacts with the carboxylate ion, RCO - The overall process is a chain reaction in which copper ion cycles between + 1 and +2 oxidation states. Suitable substrates include olefins, alcohols, mercaptans, ethers, dienes, sulfides, amines, amides, and various active methylene compounds (44). This reaction can also be used with tert-huty peroxycarbamates to introduce carbamoyloxy groups to these substrates (243). 

The reactive species that iaitiate free-radical oxidatioa are preseat ia trace amouats. Exteasive studies (11) of the autoxidatioa mechanism have clearly estabUshed that the most reactive materials are thiols and disulfides, heterocycHc nitrogen compounds, diolefins, furans, and certain aromatic-olefin compounds. Because free-radical formation is accelerated by metal ions of copper, cobalt, and even iron (12), the presence of metals further compHcates the control of oxidation. It is difficult to avoid some metals, particularly iron, ia fuel systems. 

A cursory inspection of key intermediate 8 (see Scheme 1) reveals that it possesses both vicinal and remote stereochemical relationships. To cope with the stereochemical challenge posed by this intermediate and to enhance overall efficiency, a convergent approach featuring the union of optically active intermediates 18 and 19 was adopted. Scheme 5a illustrates the synthesis of intermediate 18. Thus, oxidative cleavage of the trisubstituted olefin of (/ )-citronellic acid benzyl ester (28) with ozone, followed by oxidative workup with Jones reagent, affords a carboxylic acid which can be oxidatively decarboxylated to 29 with lead tetraacetate and copper(n) acetate. Saponification of the benzyl ester in 29 with potassium hydroxide provides an unsaturated carboxylic acid which undergoes smooth conversion to trans iodolactone 30 on treatment with iodine in acetonitrile at -15 °C (89% yield from 29).24 The diastereoselectivity of the thermodynamically controlled iodolacto-nization reaction is approximately 20 1 in favor of the more stable trans iodolactone 30. 

Although beyond the scope of the present discussion, another key realization that has shaped the definition of click chemistry in recent years was that while olefins, through their selective oxidative functionalization, provide convenient access to reactive modules, the assembly of these energetic blocks into the final structures is best achieved through cydoaddition reactions involving carbon-het-eroatom bond formation, such as [l,3]-dipolar cydoadditions and hetero-Diels-Al-der reactions. The copper(i)-catalyzed cydoaddition of azides and terminal alkynes [5] is arguably the most powerful and reliable way to date to stitch a broad variety... 

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