Oxidation of cyclic alkenes

Although the catalytic reactions described above involve mononuclear Rh and Rh complexes, dinuclear Rh compoimds have also been studied as catalyst precursors in oxygenation reactions. The system [Rh2(p.-OAc)4]/ f-BuOOH is effective in the oxidation of cyclic alkenes such as cyclopentene, cyclohexene and cycloheptene, mainly to o, /i-unsaturated ketones and allylic acetates, but with poor yields (Eq. 4) [30,31]. 

The oxidation of simple internal alkenes is very slow. The clean selective oxidation of a terminal double bond in 40, even in the presence of an internal double bond, is possible under normal conditions[89,90]. The oxidation of cyclic alkenes is difficult, but can be carried out under selected conditions. Addition of strong mineral acids such as HC104, H2S04 and HBF4 accelerates the oxidation of cyclohexene and cyclopentene[48,91). A catalyst system of PdS04-H3PMo6W604o [92] or PdCT-CuCh in EtOH is used for the oxidation of cyclopentene and cyclohexene[93]. 

Van Sickle DE, Mayo F, Arluck RM. Liquid-phase oxidation of cyclic alkenes. J Am Chem Soc 1965 87 4824 4832. 

Salts of [Cu(bpy)3] have been used as catalysts for aldol condensations (419) or the tert-butyl hydroperoxide oxidation of cyclic alkenes (54, 55). The oxidation of water by [Rulbpyls] in the presence of [Cu(bpy)3] + catalysts has been investigated in alkaline and slightly acidic solutions the active catalysts were probably [Cu(bpy)2] complexes (223). The autoxidation of EtCHO in MeC02H is catalyzed by [Culbpyla] salts (776). The complex [Cu(bpy)3]Cl2 is reported to add HCl reversibly the product is not characterized, but could be [Cu-(bpy)2(bpyH)Cl] (873). The binding of [Culbpyls] to hectorite (913) and Dowex SOW (923) has been described. 

Reddy, M. M. Punniyamurthy, T. Iqbal, J., Cobalt Catalyzed Oxidation of Cyclic Alkenes with Molecular Oxygen Allylic Oxidation Versus Double BondAttack. Tetrahedron Lett. 1995, 36,159. 

By rule (2) above, oxidation of cyclic alkenes usually occurs in the ring. 

The direct oxidation of unfunctionahsed alkanes in an asymmetric fashion is a formidable challenge. However, oxidation of C—H bonds adjacent to suitable functional groups gives a handle on which to operate. In particular, the aUyKc oxidation of cyclic alkenes utilising asymmetric variants of the Kharasch—Sosnovsky reaction has received considerable attention. The reaction is catalysed by copper salts and requires a perester to give the allylic ester as product. 

The Zhou group synthesized a series of C2-symmetric chiral bisoxazo-line ligands (SpiroBOX) featuring a spirobiindane scaffold and tested these ligands in the enantioselective Cu-catalyzed allylic oxidation of cyclic alkenes with tert-butyl perbenzoate as the oxidant. The desired allylic benzoate was obtained in 58% yield and 70% ee with (7 ,S, S )-L35 as the ligand. 

The oxidation of cyclic alkenes by Cr(VI) reagents can be a useful method for formation of dicarboxylic acids. The initial oxidation step appears to yield an epoxide, which then undergoes solvolytic ring opening to a glycol or glycol monoester, which is... 

It was also possible to set up a photocatalytic reaction where singlet oxygen oxidation of cyclic alkenes was controlled by the capsule via interaction with water-soluble Rose Bengal (RB) or insoluble dimethylbenzil (DMB) as sensitizers. All the alkenes provided quaternary 2 2 capsular self-assembled structures with the oxidation product distribution related to the position assumed in the cavity. The same reaction in acetonitrile without host led to a complex mixture of hydroperoxides (Figure 25). 

Cyclic diketones can be the predecessors of quinoxaline macrocycles, obtained in one stage with the oxidation of cyclic alkenes with potassium permanganate (1971JA3303) or in two stages by the cyclotrimerization of cyclic alkynes and subsequent ozonolysis of compounds 18 (1986JOC3257). Along with the formation of diketone 4 the latter reaaion leads, to the unstable hexaketone 19. The reaction of the mixture of compounds 4 and 19 with the DAB leads to macrocycles 20 and 21 with one or three quinoxaline fr pients, respectively, with 10% and 3% yields, calculated in two st es.The synthesis of the macrocycle 20a from the analytically pure diketone 4a was in quantitative yield. 

Cyclic diketones can be the predecessors of quinoxaline macrocycles, obtained in one stage with the oxidation of cyclic alkenes with potassium permanganate... 

The Pd/MOP combination has proved active for the asymmetric hydrosilylation of cyclic alkenes and dienes. Thus treatment of norbornene with HSiCl3 at 0 °C for 24 h in the presence of 0.01 mol.% of M eO-MOIV[Pd(// -C3H5)Cl]2 gave quantitative yield of evo-2-(trichlorosilyl)norbornane oxidation produced the corresponding alcohol in 93% ee (Equation (12)). Lowering the temperature (to — 20 °C) increased this to a 96% ee. Both mono- and difunctionalization of nbd has proved possible, depending upon the quantity of trichlorosilane used (Scheme 22). In both reactions, extremely good enantioselectivities are observed 113... 

Ring contraction ofglycals.1 The oxidative ring contraction of cyclic alkenes (4,492-493) can be applied to protected glycals. Thus oxidation of the D-glucal 1 with TTN in CH3CN provides the 2,5-anhydro-D-manose 2, whose structure was established by conversion to the 2,5-anhydro-D-mannitol derivative (3). 

Anodic regioselective acetamidosulfeny-lation of alkenes is similarly achieved by oxidation of diphenyldisulfide in acetonitrile [81]. Cyclic enamines, which are intermediates in the oxidation of cyclic N-methoxycarbonyl amines, react in aqueous acetonitrile that contains chloride ions to a-hydroxy- 8-chloro compounds via intermediate chloronium ions [82]. Enolethers undergo a regioselective azidomethoxyla-tion to yield acetals of a-azido carbonyl compounds upon electrolysis in methanol containing sodium azide [83]. The reaction proceeds possibly via addition of an anodicaUy generated azide radical. 

Most of the work reported with these complexes has been concerned with kinetic measurements and suggestions of possible mechanisms. The [Ru(HjO)(EDTA)] / aq. HjOj/ascorbate/dioxane system was used for the oxidation of cyclohexanol to cw-l,3-cyclohexanediol and regarded as a model for peroxidase systems kinetic data and rate laws were derived [773], Kinetic data were recorded for the following systems [Ru(Hj0)(EDTA)]702/aq. ascorbate/dioxane/30°C (an analogue of the Udenfriend system cyclohexanol oxidation) [731] [Ru(H20)(EDTA)]70j/water (alkanes and epoxidation of cyclic alkenes - [Ru (0)(EDTA)] may be involved) [774] [Ru(HjO)(EDTA)]702/water-dioxane (epoxidation of styrenes - a metallo-oxetane intermediate was postulated) [775] [Ru(HjO)(EDTA)]7aq. H O /dioxane (ascorbic acid to dehydroascorbic acid and of cyclohexanol to cyclohexanone)... 

SCHEME 78. Solvent-free oxidation of cyclic and acyclic cis- and trans-alkenes using (NHqlsPMonOqo on fluorapatite... 

These multicomponent catalyst systems have been employed in a variety of aerobic oxidation reactions [27]. For example, use of the Co(salophen) cocatalyst, 1, enables selective allylic acetoxylation of cyclic alkenes (Eq. 6). Cyclo-hexadiene undergoes diacetoxylation under mild conditions with Co(TPP), 2 (Eq. 7), and terminal alkenes are oxidized to the corresponding methyl ketones with Fe(Pc), 3, as the cocatalyst (Eq. 8). 

Since the first synthesis of TS-1 in 1983 [1], considerable efforts have been devoted to the synthesis of titanium-containing zeolites [2, 3]. Recently, Ti-beta, a large-pore molecular sieve, has been extensively studied [4, 5]. Owing to its unique large-pore channel system, Ti-beta seems to be more active than the medium-pore TS-1 catalyst for the oxidation of cyclic and branched alkenes with aqueous hydrogen peroxide. Under the usual synthesis conditions, however, Ti-beta crystallizes with some Al as a framework constituent [4], This leads to the presence of acid centers, which may have a detrimental effect on the activity or selectivity of this type of catalyst. Since 1992, the discovery of a new family of mesoporous molecular sieves has received much attention [6,7], Because of their mesoporous nature (20-100A), the Ti-MCM-41 zeolites may be useful as oxidation catalysts for larger molecules [8], In this... 

Allylic oxidation of a variety of cyclic alkenes with copper complexes of different pybox ligands (8) and with various peresters shows high enantioselectivity (80-96% ee). Use of phenylhydrazine as an additive and acetone as solvent accelerates the reaction. It has been suggested that the phenylhydrazone is responsible for the observed acceleration. Using EPR spectra, it has been shown that the Cu(II) species is reduced to Cu(I) by phenylhydrazine and phenylhydrazone. It has been found that the presence of a gem-diphenyl group at C(5) and a secondary or tertiary alkyl substituent at the chiral centre at C(4) of the oxazoline rings is crucial for high enantioselectivity. 

Homometathesis of cyclic alkenes affords larger rings. For example, cyclohex-adecadiene (57) was prepared by liquid-phase metathesis of cyclooctene (56) using WCl5/Et3Al [21], or in the gas phase by short-time contact of cyclooctene to a supported catalyst of Re207 activated with Me4Sn [22], Cyclohexadecenone (58), a muscone-type perfume, is produced commercially from 57 by selective oxidation. 

The dicarboxylation of cyclic alkenes is a useful reaction. Only cxo-methyl-7-oxabicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylate (121) was prepared from the cyclic alkene 120 using Pd on carbon and CuCl in MeOH at room temperature with high diastereoselectivity [89]. Methyl nitrite 37 is used for efficient oxidative carbonylation of alkenes to produce the succinate derivatives 122 [la,90]. It was claimed that the... 

Oxidation of l-alkene-4-ols. These substrates are oxidized by PdCl2 (catalytic) and p-benzoquinone (3 equiv.) or by CuCl/O, at 40° to y-butyrolactols (cyclic hemiacetals), precursors to y-butyrolactones.1... 

The oxidative reanangement of cyclic alkenes and ketones often leads to ring expansion or ring contraction reactions. The reagents generally used for this purpose are hypervalent main group oxidants such as thallium(III), lead(lV), iodine(III) and selenium(IV), aldiough palladium(II) has been used as well. 

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