Acyclic olefins, oxidation

The same authors later on presented their results of the epoxidation of various cyclic and acyclic olefins employing a heterogeneous catalyst with an oxovanadium(IV) ion incorporated on a sulfonic acid ion-exchange resin and TBHP as oxidant . Selectivities... 

The literature on liquid-phase olefin oxidation has been well reviewed (1, 2, 3, 5, 6, 8,12,14,15, 16,17, 18,19,20). Recent attention has been focused on the effects of structure and reaction conditions on the proportions of alkenyl hydroperoxy radical reaction by the abstraction and addition mechanisms at lower temperatures and conversions. The lower molecular weight cyclic and acyclic olefins have been extensively studied by Van Sickle and co-workers (17, 18, 19, 20). These studies have recently been extended to include higher molecular weight alkenes (16). 

Allylic hydroperoxides are primary products in the autoxidation of - olefins, and lack of definite information on their reactivity and chemical behavior has hampered efforts to understand olefin oxidation mechanisms (2). This deficiency is most strongly felt in determining the relative rates of addition and abstraction mechanisms for acyclic olefins since assignment of secondary reaction products to the correct primary source is required. Whereas generalizations about the effect of structure on the course of hydroperoxide decompositions are helpful, most questions can be answered better by directly isolating the hydroperoxides involved and observing the products formed by decomposition of the pure compounds. 

Herisson and coworkers 79> studied the reactions of acyclic olefins catalyzed by homogeneous and heterogeneous tungsten catalysts. They concluded that the presence of a Lewis-type acid appears to be indispensable, the degree of oxidation of the tungsten plays only a secondary role, and the homogeneous or heterogeneous nature does not appear to influence the course of the reaction. 

AUylic oxidation. Cyclohexene is oxidized to cyclohex-2-enyl acetate in 75% yield by the reagent at 70° when catalyzed by potassium bromidefea. 8 hr.). The reaction is slow in the absence of a catalyst. Norbomene is unreactive, but bicyclo[3.2.noclene-2 is oxidized rapidly to about an equal mixture of endo- and cxo-bicycIo[3.2.1]oct-3-ene-2-yl acetates. Acyclic olefins or cyclic olefins prone to allylic rearrangement give a complex mixture of allylic acetates. 

Acyclic olefins are stereoselectively and sometimes stereospecifically dimethoxylated [301,303]. Anodic oxidation of 1,5- and 1,6-dienes in methanol provides the corresponding 1,4-dimethoxylated six- and seven-membered rings, and the trans-isomers are predominantly formed in both cases, as in Eq. (45) [304]. 

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). 

A strategically similar approach has been used for the synthesis of tetrasubstituted acyclic olefins [201] (Scheme 91). The initial addition of a Grignard reagent to 658 followed by Swem oxidation of the intermediate mixture of alcohols affords enone 664. Chelation-controlled addition of methyl Grignard to 664 gives the anti tertiary alcohol 665 as a single diastereomer. 

Although the asymmetric Kharasch-Sosnovsky reaction of cyclic olefins has been developed with high enantioselectivity, the results for acyclic olefins are unsatisfied in terms of the enantioselectivity and regioselectivity. For examples, in the recent work of the oxidation of allylbenzene reported by Ginotra and Singh (Scheme 5.69), only 60% yield of a mixture of benzoates (b l = 47 53) was obtained. The enantiomerie excess of branched product was only 40%. 1-Octene also gave a poor yield of branched and linear products in a ratio of 3 2 and low enantioselectivity (27% ee). ... 

There are genuine examples where co-ordination-sphere dioxygen transfer is likely, but here again these involve heavier metal complexes such as those of Rh(I). Three typical examples are shown in which different mechanisms may be operating. For cyclic olefins (Scheme 4), an oxygen atom inserts into the conveniently positioned allylic carbon-hydrogen bond (37). For acyclic olefins (38, 39) oxidation initially occurs via a sigma complex, followed by reduction with triphenyl-... 

Fragmentation reactions of cyclic substrates containing silicon or tin provide a useful route into functionalized acyclic olefins. Wilson has developed the Ce" -mediated oxidative fragmentation of... 

The oxidation obeyed the same rate expression (Eq. 1) as ethene and other acyclic olefins under Wacker conditions. This indicates aUyl alcohol is oxidized by the same mechanism as other acyclic olefins. ... 

Smdies of the oxidation of deuteriated 2-cyclohexenol provided some surprises. First, the rate expression for oxidation was not the rate expression for Wacker oxidation of acyclic olefins. Rather, it was the same form (Eq. 2) as that observed for isomerization of deuteriated aUyl alcohol at high [Cl ]. Second, as shown in Scheme 16, the deuterium distributions from the two deuteriated isomers, 14a and 14b, are consistent only with anti addition if the hydroxyl group is directing the Pd(ll) to the same side of the ring as the hydroxyl group. 

Cu(OTf)2 in the presence of the ligand ( )-N-((naphthalen-7-yl)methylene) benzenamine and C6H5NHNH2 catalyses selective oxidation of benzylic C(sp )-H bonds to C(sp )-0 bonds with t-butyl perbenzoate (TBPB) in acetone. Cu(MeCN)4PF5 catalyses asymmetric allylic oxidation of acyclic olefins by TBPB in acetone in the presence of spiro bisoxazoline ligands (8) the product allyl esters are formed with excellent regioselectivity (>20 1 in most cases) and up to 67% ee. °°... 

A method for the synthesis of chiral binol-based [1 -1- l]-macrocyclic Schiff bases in high yields is described. Chiral dialdehydes afforded [1 + l]-macrocycles in higher yields with chiral diamines. The catalyst structure was tuned by incorporating lengthy spacers and bulkier groups, which displayed increased catalytic activity and enantioselectivity forming epoxides in good yields and over 94% ee. Cyclic olefins were found to be better substrates than acyclic olefins with NaOCl as the oxidant of choice. ... 

Three-membereil Ring Nitrogen Heterocycles.—The preparation of epoxides by peracid oxidation is an established procedure, and well known to proceed stereospecifically. Sadly there is no nitrogen equivalent that is so impeccably well behaved. Nitrene additions to acyclic olefins frequently cause scrambling,... 

The general catalytic cycle for the Heck-Matsuda reaction using acyclic olefins starts with the oxidative addition of the Pd(0) catalyst A to the aryldiazonium salt and sequential elimination of nitrogen to produce the cationic palladium species C. This intermediate is very electrophilic and it promptly... 

Dlsubstltuted alkynes are oxidized to a-diketones by NaOCl (or NaI04) with a catalytic amount of Ru04. Symmetrically dlsubstltuted acyclic olefins or large ring allcyclic olefins are directly converted to a-dlketones by KMn04 Ac20 In the cold. 

In the presence of a suitably disposed /i-hydrogen—as in alkyl-substituted thiirane oxides such as 16c—an alternative, more facile pathway for thermal fragmentation is available . In such cases the thiirene oxides are thermally rearranged to the allylic sulfenic acid, 37, similarly to the thermolysis of larger cyclic and acyclic sulfoxides (see equation 9). In sharp contrast to this type of thiirane oxide, mono- and cis-disubstituted ones have no available hydrogen for abstraction and afford on thermolysis only olefins and sulfur monoxide . However, rapid thermolysis of thiirane oxides of type 16c at high temperatures (200-340 °C), rather than at room temperature or lower, afforded mixtures of cis- and trans-olefins with the concomitant extrusion of sulfur monoxide . The rationale proposed for all these observations is that thiirane oxides may thermally... 

The thermolysis of acyclic- and/or six- and larger ring sulfoxides to yield olefins and sulfenic acids is well documented . The formation of allylic sulfenic acids and thiosulfinates in the thermolysis of thiirane oxides containing hydrogen on the a-carbon of the ring substituent (which is syn to the S—O bond) has been discussed previously in terms of /i-elimination of hydrogen, which is facilitated by relief of strain in the three-membered ring (Section llI.C.l). 

The one-electron oxidation of enol silyl ether donor (as described above) generates a paramagnetic cation radical of greatly enhanced homolytic and electrophilic reactivity. It is the unique dual reactivity of enol silyl ether cation radicals that provides the rich chemistry exploitable for organic synthesis. For example, Snider and coworkers42 showed the facile homolytic capture of the cation radical moiety by a tethered olefinic group in a citronellal derivative to a novel multicyclic derivative from an acyclic precursor (Scheme 8). 

Similar oxidative cyclization reactions involving the direct oxidation of acyclic 1,3-dicarbonyl compounds have not been reported. However, the generation of radical intermediates by the direct oxidation of cyclic 1,3-dicarbonyl compounds at an anode surface has been reported. Yoshida and coworkers have shown that the anodic oxidation of cyclic 1,3-dicarbonyl compounds in the presence of olefin trapping groups gives rise to a net cycloaddition reaction (Scheme 10) [23]. These cycloaddition reactions proceeded by initial oxidation of the 1,3-dicarbonyl compound at the anode followed by a radical addition to the second olefin. Following a second oxidation reaction, the material then... 

An extension of this methodology was used In another approach (16) to the octosyl acids and ezomyclns (Figure 10). In this sequence, D-galactose was transformed Into the 2-0-acetyl derivative 57. Transformation to the acyclic nucleoside derivative and selective oxidation then gave sulfoxide 58. Elimination afforded the trans olefin 59 whereupon solvolysis followed by epoxldatlon and acid-catalyzed cycllzatlon produced and In a 1 2 ratio respectively. The H-NMR spectra showed each to contain a l, 2 -trans configuration, and that the minor Isomer was the required 6-D-nucleoslde, while the major product was the a-D-nucleoslde. 

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