Bonding oxidation reactions

Olefins undergo a two-step oxidative process, with the first step leading to an epoxide that, in the presence of excess oxidant, subsequently is cleaved to afford aldehydes or ketones, dependent on the position of the olefinic bond. Oxidative reactions by peroxovanadates tend to be retarded by protic solvents such as water or methanol. For instance, oxidation of norbomene by picolinatooxomonoperoxo-vanadate in acetonitrile affords 22% of the product epoxide in 9 min. After 120 min in methanol solvent, only 1.8% yield was obtained. In dichloromethane, even cyclohexane is oxidized faster than this, giving 4% cyclohexanol and 9% cyclohexanone in 120 min, whereas benzene in acetonitrile yields 56% of phenol [23],... 

Eliminations to Form Carbon-Oxygen Double Bonds Oxidation Reactions... 

ELIMINATIONS TO FORM CARBON-OXYGEN DOUBLE BONDS OXIDATION REACTIONS... 

There are further subtle infiuences of structure on the strength of allylic C—H bonds. Oxidation reactions in which there is initial removal of allylic hydrogen proceed with probabilities governed in part by the relative strength of this bond. Detailed experimental data are beginning to appear, as noted later, on the more subtle effects of olefin structure, including substituent effects, steric effects, and charge effects. Theoretical treatments of such effects are not far advanced indeed, these will... 

A similar type of chiral rhodium porphyrin was found to be effective for the carbene-insertion reaction to olefins, where formation of the carbene complex takes place. Chiral rhodium complexes for catalytic stereoselective-carbene addition to olefins were prepared by condensation of a chiral aldehyde and pyrrole. Formation of the metal-carbene complex and substrate access to the catalytic center are crucial to the production of optically active cyclopropane derivatives. Optically active a-methoxy-a-(trifluoro-methyOphenylacetyl groups are linked witfi the amino groups of a,p,0L,p isomers of tetrakis-(2-aminophenyI)por-phyrin through amide bonds. Oxidation reactions of the... 

Development of an efficient catalyst for selective oxygenation is an important objective in synthetic organic chemistry. However, the asymmetric C—H bond oxidation reactions by metal oxo species are still challenging due to the over oxidation of the newly formed C—O bonds. Metalloenzymes always accomplish highly efficient and selective oxygenation of organic molecules under mild conditions. To mimic these systems, a few artificial catalysts have been developed for this process. 

The search for general and selective C—H bond oxidation reactions never stops due to its importance in synthetic chemistry. A breakthrough in this area has been realized in the realm of Fe-catalyzed oxidation reactions reported by White and co-workers since 2007. They developed an electrophilic iron catalyst C21 with a bulky ligand framework that utilized H2O2, an inexpensive... 

Scheme 1.58 Fe(PDP)-catalyzed selective aliphatic C—H bond oxidation reactions...

In 1997, the same group disclosed an example of highly enantioselective C—H bond oxidation reactions. As shown in Scheme 1.61, conformationally fixed 3-oxa-bicycle[3.3.0]-octane 156 was oxidized at the a position under the catalysis of the Mn catalyst C25 ligated by a BINOL-derived salen ligand. Subsequently, the same group further expanded the scope to a meso-pyrrolidine derivative (up to 76% ee) and a meso-tetrahydrofuran derivative (up to 90% ee). Later,... 

Scheme 1.61 Mn-catal3 ed enantioselective C—H bond oxidation reactions reported by Katsuki and Murahashi.

Out first example is 2-hydroxy-2-methyl-3-octanone. 3-Octanone can be purchased, but it would be difficult to differentiate the two activated methylene groups in alkylation and oxidation reactions. Usual syntheses of acyloins are based upon addition of terminal alkynes to ketones (disconnection 1 see p. 52). For syntheses of unsymmetrical 1,2-difunctional compounds it is often advisable to look also for reactive starting materials, which do already contain the right substitution pattern. In the present case it turns out that 3-hydroxy-3-methyl-2-butanone is an inexpensive commercial product. This molecule dictates disconnection 3. Another practical synthesis starts with acetone cyanohydrin and pentylmagnesium bromide (disconnection 2). Many 1,2-difunctional compounds are accessible via oxidation of C—C multiple bonds. In this case the target molecule may be obtained by simple permanganate oxidation of 2-methyl-2-octene, which may be synthesized by Wittig reaction (disconnection 1). 

Alkynes undergo stoichiometric oxidative reactions with Pd(II). A useful reaction is oxidative carboiiyiation. Two types of the oxidative carbonyla-tion of alkynes are known. The first is a synthesis of the alkynic carbox-ylates 524 by oxidative carbonylation of terminal alkynes using PdCN and CuCh in the presence of a base[469], Dropwise addition of alkynes is recommended as a preparative-scale procedure of this reation in order to minimize the oxidative dimerization of alkynes as a competitive reaction[470]. Also efficient carbonylation of terminal alkynes using PdCU, CuCI and LiCi under CO-O2 (1 I) was reported[471]. The reaction has been applied to the synthesis of the carbapenem intermediate 525[472], The steroidal acetylenic ester 526 formed by this reaction undergoes the hydroarylalion of the triple bond (see Chapter 4, Section 1) with aryl iodide and formic acid to give the lactone 527(473],... 

The oxidative reaction of furan with bromine in methanol solution or an electrochemical process using sodium bromide produces 2,5-dimethoxy-2,5-dihydrofuran (19), which is a cycHc acetal of maleic dialdehyde. The double bond in (19) can be easily hydrogenated to produce the corresponding succindialdehyde derivative. Both products find appHcation in photography and as embalming materials, as well as other uses. 

Oxidation. The oxidation reactions of organoboranes have been reviewed (5,7,215). Hydroboration—oxidation is an anti-Markovnikov cis-hydration of carbon—carbon multiple bonds. The standard oxidation procedure employs 30% hydrogen peroxide and 3 M sodium hydroxide. The reaction proceeds with retention of configuration (216). 

At combustion temperatures, the oxidation of butane [106-97-8] is similar to that of propane (153). This is because most butyl radicals are consumed by carbon—carbon bond scission (reaction 28). 

SuIfona.tlon, Sulfonation is a common reaction with dialkyl sulfates, either by slow decomposition on heating with the release of SO or by attack at the sulfur end of the O—S bond (63). Reaction products are usually the dimethyl ether, methanol, sulfonic acid, and methyl sulfonates, corresponding to both routes. Reactive aromatics are commonly those with higher reactivity to electrophilic substitution at temperatures > 100° C. Tn phenylamine, diphenylmethylamine, anisole, and diphenyl ether exhibit ring sulfonation at 150—160°C, 140°C, 155—160°C, and 180—190°C, respectively, but diphenyl ketone and benzyl methyl ether do not react up to 190°C. Diphenyl amine methylates and then sulfonates. Catalysis of sulfonation of anthraquinone by dimethyl sulfate occurs with thaHium(III) oxide or mercury(II) oxide at 170°C. Alkyl interchange also gives sulfation. 

There appear to be few examples of the formation of azetidin-2-ones by closure of the C(2) —C(3) bond. One reaction which fits into this category involves reaction of the iron carbonyl lactone complexes (144) with an amine to give the allyl complexes (145) which on oxidation are converted in high yield to 3-vinyl-/3-lactams (146) (80CC297). 

A common feature of die interaction of oxides with organic molecules is the breaking of C-H bonds, but rarely C-C bonds. The reaction to form CaHg... 

This synthesis is only one example of a wide range of reactions which involve aryl (or alkyl) radical addition to electron-deficient double bonds resulting in reduction.The corresponding oxidative reaction using aryl radicals is the well known Meerwein reaction, which uses copper(II) salts. 

The proximity of the methyl group to the double bond in natural rubber results in the polymer being more reactive at both the double bond and at the a-methylenic position than polybutadiene, SBR and, particularly, polychlor-oprene. Consequently natural rubber is more subject to oxidation, and as in this case (c.f. polybutadiene and SBR) this leads to chain scission the rubber becomes softer and weaker. As already stated the oxidation reaction is considerably affected by the type of vulcanisation as well as by the use of antioxidants. 

The reaction capability of PS is weak, but the reaction capability can be improved by anchoring the functional group to the aliphatic chain or aromatic ring of PS using chemical or conversion reactions. Aliphatic chain reactions are halogenation reactions, oxidation reactions, or unsaturated acids to bonded aliphatic chain of PS (in the presence of a radical catalysis). 

In the third sequence, the diastereomer with a /i-epoxide at the C2-C3 site was targeted (compound 1, Scheme 6). As we have seen, intermediate 11 is not a viable starting substrate to achieve this objective because it rests comfortably in a conformation that enforces a peripheral attack by an oxidant to give the undesired C2-C3 epoxide (Scheme 4). If, on the other hand, the exocyclic methylene at C-5 was to be introduced before the oxidation reaction, then given the known preference for an s-trans diene conformation, conformer 18a (Scheme 6) would be more populated at equilibrium. The A2 3 olefin diastereoface that is interior and hindered in the context of 18b is exterior and accessible in 18a. Subjection of intermediate 11 to the established three-step olefination sequence gives intermediate 18 in 54% overall yield. On the basis of the rationale put forth above, 18 should exist mainly in conformation 18a. Selective epoxidation of the C2-C3 enone double bond with potassium tm-butylperoxide furnishes a 4 1 mixture of diastereomeric epoxides favoring the desired isomer 19 19 arises from a peripheral attack on the enone double bond by er/-butylper-oxide, and it is easily purified by crystallization. A second peripheral attack on the ketone function of 19 by dimethylsulfonium methylide gives intermediate 20 exclusively, in a yield of 69%. 

When 2-lithio-2-(trimethylsilyl)-l,3-dithiane,9 formed by deprotonation of 9 with an alkyllithium base, is combined with iodide 8, the desired carbon-carbon bond forming reaction takes place smoothly and gives intermediate 7 in 70-80% yield (Scheme 2). Treatment of 7 with lithium diisopropylamide (LDA) results in the formation of a lactam enolate which is subsequently employed in an intermolecular aldol condensation with acetaldehyde (6). The union of intermediates 6 and 7 in this manner provides a 1 1 mixture of diastereomeric trans aldol adducts 16 and 17, epimeric at C-8, in 97 % total yield. Although stereochemical assignments could be made for both aldol isomers, the development of an alternative, more stereoselective route for the synthesis of the desired aldol adduct (16) was pursued. Thus, enolization of /Mactam 7 with LDA, as before, followed by acylation of the lactam enolate carbon atom with A-acetylimidazole, provides intermediate 18 in 82% yield. Alternatively, intermediate 18 could be prepared in 88% yield, through oxidation of the 1 1 mixture of diastereomeric aldol adducts 16 and 17 with trifluoroacetic anhydride (TFAA) in... 

The enol ether double bond contained within the ds-fused dioxa-bicyclo[3.2.0]heptene photoadducts can also be oxidized, in a completely diastereoselective fashion, with mCPBA. Treatment of intermediate XXII, derived in one step from a Patemo-Buchi reaction between 3,4-dimethylfuran and benzaldehyde, with mCPBA results in the formation of intermediate XXIII. Once again, consecutive photocycloaddition and oxidation reactions furnish a highly oxygenated system that possesses five contiguous stereocenters, one of which is quaternary. Intermediate XXIII is particularly interesting because its constitution and its relative stereochemical relationships bear close homology to a portion of a natural product known as asteltoxin. 

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