Olefins aerobic oxidation

There are several available terminal oxidants for the transition metal-catalyzed epoxidation of olefins (Table 6.1). Typical oxidants compatible with most metal-based epoxidation systems are various alkyl hydroperoxides, hypochlorite, or iodo-sylbenzene. A problem associated with these oxidants is their low active oxygen content (Table 6.1), while there are further drawbacks with these oxidants from the point of view of the nature of the waste produced. Thus, from an environmental and economical perspective, molecular oxygen should be the preferred oxidant, because of its high active oxygen content and since no waste (or only water) is formed as a byproduct. One of the major limitations of the use of molecular oxygen as terminal oxidant for the formation of epoxides, however, is the poor product selectivity obtained in these processes [6]. Aerobic oxidations are often difficult to control and can sometimes result in combustion or in substrate overoxidation. In... 

Ishii and coworkers have demonstrated that V-hydroxyphtalimide (NHPI) is an effective mediator for the oxidation of inactive hydrocarbons, alcohols, olefins and aromatic compounds by molecular oxygen, since the corresponding V-oxyl (PINO) generated from NHPI is an active species for their oxidation" . Before the aerobic oxidation by Ishii... 

Textbook chemistry (297,298) teaches that palladium is the preferred catalyst for aerobic oxidation of olefins. When water is the solvent, nucleophilic water addition to coordinated olefins is the key step in the so-called Wacker cycle. Wacker oxidation occurs regiospecifically because a carbonyl group is formed at that carbon atom of the double bond where the nucleophile in a Markovnikov-like addition would enter. The Wacker reaction thus yields methylketones from primary alkenes ... 

However, all these systems suffer from high concentrations of chloride ion, so that substantial amounts of chlorinated by-products are formed. For these reasons there is a definite need for chloride- and copper-free systems for Wacker oxidations. One such system has been recently described, viz., the aerobic oxidation of terminal olefins in an aqueous biphasic system (no additional solvent)... 

In the present work zeoUte-encapsulated Fe-phthalocyanine (FePc) and Co- salophen (CoSp) catalysts, synthesized by different methods, were used as oxygen activating catalysts for the aerobic oxidation of olefins in a triple catalytic system. 

J.K. Cha et al. developed a stereocontrolled synthesis of bicyclo[5.3.0]decan-3-ones from readily available acyclic substrates. Acyclic olefin-tethered amides were first subjected to the intramolecular Kulinkovich reaction to prepare bicyclic aminocyclopropanes. This was followed by a tandem ring-expansion-cyclization sequence triggered by aerobic oxidation. The reactive intermediates in this tandem process were aminium radicals (radical cations). The p-anisidine group was chosen to lower the amine oxidation potential. This substituent was crucial for the generation of the aminium radical (if Ar = phenyl, the ring aerobic oxidation is not feasible). 

The group of Masui first attempted the direct epoxidation of olefins by using oxygen and NHPI with metalloporphyrins, but they obtained poor results [15]. Ishii and coworkers proposed two different methods. In the first protocol [16,17], the epoxidizing agent is obtained in situ by the aerobic oxidation of a suitable alcoholic (benzhydrol) compound in the presence of catalytic amounts of NHPI. The resulting oxidant, which is not able to promote the epoxidation by itself, is then activated in the presence of an olefin by catalytic amounts of hexafluoroacetone (HFA) (Scheme 6.1). 

TABLE 6.3 Epoxidation of olefins by aerobic oxidation of acetaldehyde, catalyzed by NHPI... 

The synthesis of N phthaloyl enamides has been reported by a remarkably general method for aerobic oxidative amination of unactivated alkyl olefins as shown in Scheme 9.6 [12]. From a practical synthesis point of view, the phthalimide can not only serve as a directing group for asymmetric hydrogenation but can also be removed under mild conditions. 

Several metal macrocycles, like iron phthalocyanine and cobalt salophen were tested in these palladium-catalyzed aerobic oxidation of olefins and dienes. These tnacrocycles were able to activate the molecular oxygen, but in the homogeneous system several problems have arised, such as poor solubility, self-degradation and the difficulty to reuse theses complexes. A... 

Scheme 16 Pd-catalyzed aerobic oxidative animation of cyclic olefins...

Groves, J. T. Quinn, R. Aerobic oxidation of olefins with ruthenium porphyrin catalysts. j. Am. Chem. Soc. 1985, 107, 5790-5792. 

Unsaturated compounds are also susceptible to chemiluminescent reactions. The liquid olefin shown in Fig. 7 undergoes spontaneous aerobic oxidation, presumably via the cyclic peroxy-intermediate also shown in the figure. This reaction is accompanied by the emission of green light. 

Vapor-phase aerobic oxidations of lower olefins, e. g. propylene to acrolein or acrylic acid and isobutene to methacrolein or methacrylic acid, are well-established bulk chemical processes [1,2], They are usually performed over oxidic catalysts, such as bismuth molybdate or heteropoly compounds, although the scope of these allylic oxidations is limited to olefins that cannot form 1,3-dienes via oxidative dehydrogenation. Thus 1- and 2-butene are converted to butadiene, and methylbutenes to isoprene, and with higher olefins complex mixtures result from further oxidation. Hence, such methodologies are not relevant in the context of fine chemicals. 

In the well-known Wacker process ethylene is converted to acetaldehyde by aerobic oxidation in an aqueous medium in the presence of PdCl2 as catalyst and CuCl2 as cocatalyst [7], Terminal olefins afford the corresponding methyl ketones. Oxidative acetoxylation of olefins with Pd(II) salts as catalysts in acetic acid was first reported by Moiseev and coworkers [8], The addition of an alkali metal acetate, e. g. NaOAc, was necessary for the reaction to proceed. Palladium black was also found to be an active catalyst under mild conditions (40-70 °C, 1 bar) in the liquid phase, if NaOAc was added to the solution before reducing Pd(II) to Pd black, but not afterwards [9,10]. These results suggested that catalytic activity... 

Isoxazolidines 92 were converted into 3-nitro-4-hydroxymethyl tetrahydrofurans 94 by treatment with TBAF. The process is believed to occur through the formation of nitroso intermediates 93, that undergo a spontaneous aerobic oxidation. The two-step sequence of intramolecular silylnitronate olefin cycloaddition (ISOC) followed by oxidative ring cleavage was diastereoselective and allowed complete control of the relative configuration of the newly created stereocenters <040L2027>. 

Iron phthalocyanine encapsulated in zeolites was used as oxygen activating catalysts in the triple catalytic aerobic oxidation of hydroquinone to benzoquinone, in the allylic oxidation of olefins and in the selective oxidation of terminal olefins to ketones. The catalyst proved active in the above reactions. It is stable towards self-oxidation and can be recovered and reused. 

Interestingly, dinuclear Pt systems have long been known to allow for catalytic aerobic oxidation of olefins leading to the corresponding olefin oxides and carbonyl compounds [38], Formation of epoxides, in particular, was thought to be a result of an intramolecular C(sp )-0 attack similar to the one in Fig. 13 where the oxygen atom of a p-hydroxoaUcyl intermediate attacks the metal(III)-bound carbon atom (Fig. 14). No studies of C-O reductive elimination have been performed for these systems. 

Khusnutdinova JR, Newman L, Zavalij PY et al (2008) Direct C(ip )-0 reductive elimination of olefin oxides from Pt" -oxetanes prepared by aerobic oxidation of Pt olefin derivatives (Olefin = cw-Cyclooctene, Norbomene). J Am Chem Soc 130 2174—2175... 

Aerobic oxidative Heck reactions also proceed between olefins and other aryl nucleophiles such as aryl tin and aryl boron reagents (Eq. (8.22)). This field started by utilizing aryl tin reagents and electron-deficient alkenes with stoichiometric base additives such as NaOAc [100], but has been significantly improved by... 

Some aerobic oxidation reactions progress effectively in SCCO2 without a catalyst. Aerobic oxidation of olefins (e.g. cw-cyclooctene and (/f)-(-F)-limonene) in the presence of aldehydes (e.g. 2-methyl-propionaldehyde) in SCCO2 (d = 0.75 g/mL) gave the corresponding epoxides without a catalyst. It is speculated that the stainless steel from autoclave walls triggered the formation of acylperoxy radicals from the aldehyde and oxygen, and the reaction proceeded via a non-catalytic radical... 

It is increasing interested in the utilization of heteropoly compounds as catalysts for the oxidation of various organic compounds. Recently, we have found that the mixed addenda heteropolyoxometallates such as (NH4)5H4PV0Mo0O4o 6H2O (PV0MO0) was efficient catalysts for the aerobic oxidation of olefinic compounds in the presence of isobutyraldehyde. We now present here the direct oxidation of amines and hydrocarbons with molecular oxygen by PV0MO0 catalyst. 

In catalytic reactions involving Pd(II) salts, carboxypalladation yields an alkylpal-ladium species that can often undergo (3-H elimination instead of protonolysis. Subsequently, Stoltz and coworkers demonstrated that Wacker-type processes can also afford lactones under oxidative conditions (Scheme 2.35). The proposed mechanism involves Pd(II) coordination to the alkene, followed by oxypalladation and (3-H elimination. After elimination of HX to form Pd(0), aerobic oxidation is required to regenerate a Pd(II) species. The net result is olefin transposition to an adjacent position [80]. 

The mechanism of this aerobic oxidation involves the oxidation of bromide to bromine. The procedure may therefore be limited to sulfides that lack olefinic functionality. 

Figure 7.13 Palladium-catalyzed aerobic oxidation of terminal olefins in water.

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