Cyclohexene vinylic oxidation

With higher olefins, allylic and vinyl oxidation products are obtained (31), Thus, cyclohexene yields almost exclusively allylic oxidation product (2). 

By far the largest outlet for benzene (approx. 60%) is styrene (phenyl-ethene), produced by the reaction of benzene with ethylene a variety of liquid and gas phase processes, with mineral or Lewis acid catalysts, are used. The ethylbenzene is then dehydrogenated to styrene at 600-650°C over iron or other metal oxide catalysts in over 90% selectivity. Co-production with propylene oxide (section 12.8.2) also requires ethylbenzene, but a route involving the cyclodimerization of 1,3-butadiene to 4-vinyl-(ethenyl-) cyclohexene, for (oxidative) dehydrogenation to styrene, is being developed by both DSM (in Holland) and Dow. 60-70% of all styrene is used for homopolymers, the remainder for co-polymer resins. Other major uses of benzene are cumene (20%, see phenol), cyclohexane (13%) and nitrobenzene (5%). Major outlets for toluene (over 2 5 Mt per annum) are for solvent use and conversion to dinitrotoluene. 

Several mechanisms for the polymerization of vinyl ether and epoxies have been suggested [20,22,23,25,27,28,33-35]. On irradiation with gamma rays or electrons, pure epoxies polymerize via a cationic mechanism [35]. However, this cationic polymerization is inhibited by just traces of moisture, as shown below for cyclohexene oxide in reaction 5. 

The DIBF OPPI combination has been shown to efficiently cure a wide variety of epoxies including cycloaliphatics. With this photoinitiator it is possible to cure bisphenol A epoxies such as Epon 828 quickly without the need for acrylation of the epoxy. Cycloaliphatic epoxies were of special interest because they were expected to react much faster than bisphenol A type epoxies. Those tested include 3,4-epoxycyclohexylmethyl-3 ,4 -epoxycyclohexyl-carboxylate (UVR 6110), bis(3,4 epoxy-cyclohexylmethyl) adipate (UVR 6128), and 1,2-epoxy-4-vinylcyclohexane (vinyl cyclohexene oxide). It was found that the vinyl cyclohexene oxide reacted rapidly, but work with it was discontinued because it has a fairly high vapor pressure (2 torr at 20 °C), an intense odor, and the photoinitiator does not dissolve in this resin. 

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. 

T. Watabe, T. Sawahata, Metabolism of the Carcinogenic Bifunctional Olefin Oxide, 4-Vinyl-l-cyclohexene, by Hepatic Microsomes , Biochem. Pharmacol. 1976, 25, 601 -602. 

Other recent reports of interesting terpolymerization processes involving cyclohexene oxide and diglycolic anhydride or vinylcyclohexene oxide have appeared in the literature [66-68]. These processes are indicated in (7) and (8), and were carried out in the presence of p-diiminate zinc catalysts. The vinyl functionalized polymer was intramolecularly crosslinked by a metathesis reaction to afford nanoparticles. 

Hsu T, Tan C (2002) Block copolymerization of carbon dioxide with cyclohexene oxide and 4-vinyl-1-cyclohexene-1,2-epoxide in based poly(propylene carbonate) by yttrium-metal... 

Similarly, the oxidation of iodocyclohexane by DMD under a nitrogen-gas atmosphere leads to the iodohydrin and diol as unexpected products (equation 24). The iodohydrin, formed as the major product, clearly reveals that hypoiodous acid (HOI) is generated in situ, which adds to the liberated cyclohexene. Indeed, when methyl iodide (Mel) is oxidized by DMD at subambient temperature in the presence of cyclohexene, the corresponding iodohydrin is obtained in very good yield The latter method may be utilized for the preparation of allylic alcohols with a vinylic iodo functional group from allenes (equation 25) . ... 

Several dyes have been found to sensitize the cationic polymerization of cyclohexene oxide, epichlorohydrin, and 2-chloroethyl vinyl ether initiated by diaryliodonium salts (109,110). Acridinium dyes such as acridine orange and acridine yellow were found to be effective sensitizers. One example of a benzothiazolium dye (setoflavin T) was also reported, but no other class of dye nor any other example of a dye absorbing at longer wavelengths were discovered. Crivello and Lam favored a sensitization mechanism in which direct energy transfer from the dye to the diaryliodonium salt occurred. Pappas (12,106) provided evidence that both energy transfer and electron transfer sensitization were feasible in this system. 

The chiral anisole derivative 37 has been used in the synthesis of several asymmetric functionalized cyclohexenes (Table 9) [22]. In a reaction sequence similar to that employed with racemic anisole complexes, 37 adds an electrophile and a nucleophile across C4 and C3, respectively, to form the cyclohexadiene complex 38. The vinyl ether group of 38 can then be reduced by the tandem addition of a proton and hydride to C2 and Cl, respectively, affording the alkene complex 39. Direct oxidation of 39 liberates cydohexenes 40 and 41, in which the initial asymmetric auxiliary is still intact. Alternatively, the auxiliary may be cleaved under acidic conditions to afford /y3 -allyl complexes, which can be regioselectively attacked by another nucleophile at Cl. Oxidative decomplexation liberates the cyclohexenes 42-44. HPLC analysis revealed high ee values for the organic products isolated both with and without the initial asymmetric group. 

The monomers of styrene oxide, 1,4-cyclohexene oxide, trioxane, and vinyl ether were polymerized at satisfactory rates. However, tetrahydrofuran, e-caprolactone, and cc-methylstyrene could not be polymerized7). 

The evidence in the case of styrene, where both modes of radiation-induced polymerization can be conveniently studied, is quite convincing that reduction of the concentration of water changes the predominating mode of propagation from purely free radical to essentially ionic. Evidence for an ionic propagation initiated by radiation has also been obtained in pure a-methylstyrene (3, 24), isobutylene (12, 32), cyclopenta-diene (5), / -pinene (2), 1,2-cyclohexene oxide (II), isobutyl vinyl ether (6), and nitroethylene (38), although the radical process in these monomers is extremely difficult, if not impossible, to study. 

Similar oxidative additions involving the inner carbon atoms of the butadiene molecules can generate complexes having the formal structures 7.26 and 7.27. These may also be formed from 7.25 through tautomerization. Regeneration of 7.24 from these species involves elimination of vinyl cyclohexene and divinyl cyclobutane, respectively. 

Further examples for electron acceptor monomers are acrylonitrile [37], diethyl fumarate [39], fumaronitrile [29,30, 38], maleonitrile [38], N-carbethoxymaleimide [29], N,N-diethylaminoethyl methacrylate [39], nitroethylene [10] and iV-ethyl-maleimide [40], As electron donor monomem also are used vinyl alkyl ethers [38, 40], alkyl methacrylate [40], JV-vinyl pyrrolidone [40] and cyclohexene oxide [10]. 

Cyclic monomers such as cyclohexene oxide were readily polymerized upon irradiation of the CT complexes of pyridinium salts whereas spontaneous polymerizations were observed upon mixing with strong electron donating monomers such as butyl vinylether and A-vinyl carbazole. These monomers are known to form CT complexes themselves with electron acceptors which may interfere with the rapid polymerization observed. 

Since both oxidative splitting of the double bond and aldol condensation represent reliable and general reactions, their sequence serves as an efficient route for the transformation of readily available cyclohexene systems e.g. formed via the Diels-Alder reaction or Robinson annulation) into functionalized cyclopentene derivatives. This standard operational mode is extensively used in total syntheses. One of the numerous examples, the synthesis of helminthosporal 463, the sesquiterpenoid toxin of fungi, is shown in Scheme 2.150. In the initial phases of the synthesis, commercially available (—)-carvomenthone 464 was transformed into 465 via Michael reaction with methyl vinyl ketone to give 466 and subsequent intramolecular aldol condensation. 

A number of monomers has already been investigated, e.g., cyclo-pentadiene [86], styrene [89, 93], a-methylstyrene [87, 89, 95], formaldehyde [94], alkyl vinyl ethers [85, 89], isobutene [84], nitroethylene [96] and also the cyclic monomer cyclohexene oxide [97]. For most of these reliable quantitative data is now available. Because the number of active centres formed is small all of these systems are particularly susceptible to traces of impurities, especially water and spurious basic materials. Indeed much of the early data [82, 83] from 7-ray initiation was confused because of the use of relatively wet monomers. Furthermore the intrinsic lifetime of a free cation is limited because the... 

Although an unstable triazoline intermediate was a possibility, it was thought that a concerted mechanism involving a species such as 283 was more likely When benzenesulphonyl azide was heated at 100° for 1 hr with maleic anhydride, iV -phenylmaleimide, divinyl sulphone, mesityl oxide, cyclohexene, cyclopentene, styrene, vinyl acetate or / -quinone, no gas evolution was observed, nor was there any change in the concentration of sulphonyl azide (as indicated by infrared measurement)... 

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