Olefins cyclohexene

The results of the olefin oxidation catalyzed by 19, 57, and 59-62 are summarized in Tables VI-VIII. Table VI shows that linear terminal olefins are selectively oxidized to 2-ketones, whereas cyclic olefins (cyclohexene and norbomene) are selectively oxidized to epoxides. Cyclopentene shows exceptional behavior, it is oxidized exclusively to cyclopentanone without any production of epoxypentane. This exception would be brought about by the more restrained and planar pen-tene ring, compared with other larger cyclic nonplanar olefins in Table VI, but the exact reason is not yet known. Linear inner olefin, 2-octene, is oxidized to both 2- and 3-octanones. 2-Methyl-2-butene is oxidized to 3-methyl-2-butanone, while ethyl vinyl ether is oxidized to acetaldehyde and ethyl alcohol. These products were identified by NMR, but could not be quantitatively determined because of the existence of overlapping small peaks in the GC chart. The last reaction corresponds to oxidative hydrolysis of ethyl vinyl ether. Those olefins having bulky (a-methylstyrene, j8-methylstyrene, and allylbenzene) or electon-withdrawing substituents (1-bromo-l-propene, 1-chloro-l-pro-pene, fumalonitrile, acrylonitrile, and methylacrylate) are not oxidized. 

On the other hand, kinetic evidence, notably the inverse dependence of the rate on the partial pressure of CO, has led to the formulation by Natta (46) and Martin (47) of an alternative type of mechanism which involves reaction of dicobalt octacarbonyl with olefin (cyclohexene) rather than with hydrogen ... 

A mixture of 0.2 mmol Pd(OAc)2 (2 mol%), 10 mmol benzoquinone, and 1 mL perchloric acid (72%) in 50 mL acetonitrile-H20 (7 1) is stirred under Ar at r.t. until complete dissolution. The olefin (10 mmol) is added and the reaction mixture stirred at r.t. (aliphatic olefins, cyclohexene) or 60 °C (styrene, cycloheptene, internal olefins) until completion of the reaction (from 10 min to 90 min), as judged by TLC. The mixture is poured into diethyl ether and washed with aqueous NaOH (30 %). The aqueous layer is extracted with ether. The combined organic layers are dried over MgS04, filtered, and the solvent is evaporated. The crude product is purified by chromatography. 

The results of the olefin oxidation catalyzed by 1 to 6 are summarized in Tables 1-3. Table 1 shows that linear terminal olefins are selectively oxidized to 2-ketones, whereas cyclic olefins (cyclohexene and norbornene) are selectively oxidized to epoxides. Cyclopentene shows an exceptional behavior it is oxidized exclusively to cyclopentanone without any produc-... 

The oxidation of cyclohexene has been the subject of considerable discussion, and it is now apparent that it behaves differently from the straight-chain olefins. Cyclohexene was originally reported to yield both cyclohex-2-en-l-yl acetate, structure (VII), and cyclohex-3-en-l-yl acetate, structure (VIII), in chloride-containing acetic acid (76) and only the allylic isomer with Pd(OAc)a in chloride-free acetic acid (6). However, it has now been demonstrated that if no oxidants are present to regenerate the Pd(0) to Pd(II) in neutral or basic HOAc, the Pd(0) formed will disproportionate the cyclohexene to give benzene (22, 295). In acetic acid containing perchloric acid, cyclohexanone (structure VIII) and cyclohex-1-en-l-yl acetate are formed (22). If Pd(0) is prevented from precipitating by use of oxidants in neutral or basic acetic acid, the allylic and homoallylic acetates are formed. 

The rate of hydroformylation depends on the structure of the olefin, the order being as follows straight-chain terminal olefins > straight-chain internal olefins > branched-chain olefins. Cyclohexene reacts more slowly than cyclopentene, cycloheptene, or cyclooctene. 

Reactants other than olefins were tested using flow type reactor, however, no silylated product was obtained, cyclic olefin cyclohexene... 

Experimental information on the energetics of silver-olefin bonds comes from a 1973 study by Partenheimer and Johnson26. Using titration calorimetry with the inert dichloromethane as solvent, these authors measured the enthalpies of reaction 14 for several olefin complexes (hfacac = 1, 1, 1, 5, 5, 5-hexafluoro-2,4-pentanedionate) whose structure (1) is illustrated below for olefin = cyclohexene. 

Selective photochemical epoxidation of olefins cyclohexene, 2-hexene) with dioxygen (irradiation with a 500 W tungsten lamp) is catalyzed by oxoethoxo(tetra-p-tolylporphinato)molybdenum(V) and niobium(V) [73,74]. 

It is important to mention the pivotal role of the alcohol component in the typical Birch reduction. On one hand, the relatively acidic alcohol rapidly protonates the intermediate IV (Scheme 13.2) to give the 1,4 diene in the absence of alcohol, an isomerization of this intermediate to the most stable 1,3-diene anion XIII takes place, and its final protonation affords the corresponding 1,3-diene (17), which is susceptible to reduction by the reaction media to give the final olefin cyclohexene (18) (Scheme 13.8). It is well known that 1,3-dienes are reduced by dissolving metals to the corresponding olefins in quantitative yields [11]. 

A major difficulty with the Diels-Alder reaction is its sensitivity to sterical hindrance. Tri- and tetrasubstituted olefins or dienes with bulky substituents at the terminal carbons react only very slowly. Therefore bicyclic compounds with polar reactions are more suitable for such target molecules, e.g. steroids. There exist, however, several exceptions, e. g. a reaction of a tetrasubstituted alkene with a 1,1-disubstituted diene to produce a cyclohexene intermediate containing three contiguous quaternary carbon atoms (S. Danishefsky, 1979). This reaction was assisted by large polarity differences between the electron rich diene and the electron deficient ene component. 

Oxidation of olefins and dienes provides the classic means for syntheses of 1,2- and 1,4-difunctional carbon compounds. The related cleavage of cyclohexene rings to produce 1,6-dioxo compounds has already been discussed in section 1.14. Many regio- and stereoselective oxidations have been developed within the enormously productive field of steroid syntheses. Our examples for regio- and stereoselective C C double bond oxidations as well as the examples for C C double bond cleavages (see p. 87f.) are largely selected from this area. 

The mixture can be separated by distillation. The primary phosphine is recycled for use ia the subsequent autoclave batch, the secondary phosphine is further derivatized to the corresponding phosphinic acid which is widely employed ia the iadustry for the separation of cobalt from nickel by solvent extraction. With even more hindered olefins, such as cyclohexene [110-83-8] the formation of tertiary phosphines is almost nondetectable. 

Wilkinson Hyd.rogena.tion, One of the best understood catalytic cycles is that for olefin hydrogenation in the presence of phosphine complexes of rhodium, the Wilkinson hydrogenation (14,15). The reactions of a number of olefins, eg, cyclohexene and styrene, are rapid, taking place even at room temperature and atmospheric pressure but the reaction of ethylene is extremely slow. Complexes of a number of transition metals in addition to rhodium are active for the reaction. 

RhCl(P(C3H3)3)2(solv) +H2 Rh(H)2Cl(P(C3H3)3)2(solv) where solvis solvent. An olefin, R, such as cyclohexene, substitutes for the solvent on the dihydride. 

Olefins can be aminomethylated with carbon monoxide [630-08-0] (CO) and amines in the presence of rhodium-based catalysts. Eor example, pipera2ine reacts with cyclohexene [110-83-8] to form W,Af-di-(l-cyclohexylmethyl)-pipera2ine [79952-94-6] (55). 

It is important to exclude air in all hydrazone-type reductions involving olefins (otherwise, over-reduction occurs due to diimide formation) in the above example, as an added precaution cyclohexene was used as a solvent. 

Direct evidence for the existence of dichlorocarbene, by trapping with a suitable substrate, was obtained by Doering and Hoffmann in 1954. Dichlorocarbene was shown to add in a characteristic manner to the double bond of cyclohexene to give dichloronorcarane (1) in 59% yield similar adducts were obtained with other olefins. Bromo-form imderwent an analogous reaction in the presence of olefins to give... 

Thermal decomposition gives olefins, probably by rearrangement of intermediate carbenes. For example, the decomposition of 3,3-penta-methylenediazirine (68) in nitrobenzene above 160°C gives cyclohexene [Eq, (58)]. The yield as determined by bromine titration... 

Stirring. The succinimide is removed by suction filtration and washed twice with 10-mI portions of carbon tetrachloride. The combined filtrate and washings are fractionally distilled at atmospheric pressure to remove the carbon tetrachloride and excess olefin (steam bath). The residue is distilled under vacuum, giving about 60 % yield of 3-bromo-cyclohexene, bp 68715 mm or 4472 mm. 

In a 200-ml three-necked flask fitted with a dropping funnel (drying tube) is placed a solution of 13.4 g (0.12 mole) of 1-octene in 35 ml of THF. The flask is flushed with nitrogen and 3.7 ml of a 0.5 M solution of diborane (0.012 mole of hydride) in THF is added to carry out the hydroboration. (See Chapter 4, Section I regarding preparation of diborane in THF.) After 1 hour, 1.8 ml (0.1 mole) of water is added, followed by 4.4 g (0.06 mole) of methyl vinyl ketone, and the mixture is stirred for 1 hour at room temperature. The solvent is removed, and the residue is dissolved in ether, dried, and distilled. 2-Dodecanone has bp 119710 mm, 24571 atm. (The product contains 15 % of 5-methyl-2-undecane.) The reaction sequence can be applied successfully to a variety of olefins including cyclopentene, cyclohexene, and norbornene. 

A dry 5(X)-mI flask equipped with a thermometer, pressure-equalizing dropping funnel, and magnetic stirrer is flushed with nitrogen and then maintained under a static pressure of the gas. The flask is charged with 50 ml of tetrahydrofuran and 13.3 ml (0.15 mole) of cyclopentene, and then is cooled in an ice bath. Conversion to tricyclo-pentylborane is achieved by dropwise addition of 25 ml of a 1 M solution of diborane (0.15 mole of hydride see Chapter 4, Section 1 for preparation) in tetrahydrofuran. The solution is stirred for 1 hour at 25° and again cooled in an ice bath, and 25 ml of dry t-butyl alcohol is added, followed by 5.5 ml (0.05 mole) of ethyl bromoacetate. Potassium t-butoxide in /-butyl alcohol (50 ml of a 1 M solution) is added over a period of 10 minutes. There is an immediate precipitation of potassium bromide. The reaction mixture is filtered from the potassium bromide and distilled. Ethyl cyclopentylacetate, bp 101730 mm, 1.4398, is obtained in about 75% yield. Similarly, the reaction can be applied to a variety of olefins including 2-butene, cyclohexene, and norbornene. 

In some cases, no cycloalky ladon is observed by the reacdon of uittomethane v/ith electron-deficient olefins v/ilh cyano and methoxycarbonyl groups The reacdon affords new, highly fiincdonalLzed cyclohexenes in the presence of catidydc amount of piperidine under solvent- free conchdons v/ith focused microwave irradiadon fEq 7 41 ... 

Once cyclization has occurred, the formed carbocation can lose a proton, and a cyclohexene derivative is obtained. This reaction is aided by the presence of an olefin in the vicinity (R-CH=CH2). 

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