Cyclohexene oxide, basicity

It appears that oxiranes known to give predominantly a-deprotonation in basic media (cyclopentene, cyclooctene and exo-norbomene oxide) are also the more strained (Table 1 entries 3, 6, 7). On the other hand, oxiranes that give mainly -deprotonation (butene, cyclohexene oxide) have lower strain energies and higher a-anion stabilities (Table 1 ... 

Japanese authors have made comprehensive investigations of the rearrangements of oxiranes in the presence of solid acids, bases, and salts.The model compounds employed were cyclohexene oxide and 1-methylcyclohexene oxide. The effects of the acidic and basic properties of the catalysts on the selectivity were interpreted on the basis of the products obtained. The main products are carbonyl compounds and allyl alcohol isomers. Rearrangements of limonene oxide over acids and bases were studied on five different types of Al203 similar research has been carried out on 2- and 3-carene oxides, cis- and trans-carvomenthene oxides and a-pinene oxide. ... 

The reaction of S,S,S-(136) with tris-dimethylaminophosphine/PCl3 in CH3CN at 0°C gave the chiral azaphosphatrane (137) in overall 56% yield. Unfortunately (137) did not induce asymmetry in mandelonitrile formed from the catalyzed reaction of Me3SiCN with PhCHO. It was also inefficient in catalyzing the addition of alkyl cyanide to benzaldehyde, and was not sufficiently basic to effect rearrangement of cyclohexene oxide to 2-cyclohexenol. Further experiments with analogues of (137) are promised for future publications. 

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... 

When an alkene reacts with BH3 in THF solution, rapid addition to the double bond occurs three times and a tricilkylborcme, R3B, is formed. For example, 1 molar equivalent of BH3 adds to 3 molar equivalents of cyclohexene to yield tricyclohexylborane. When tricvclohexylborane is then treated with aqueous hydrogen peroxide (H2C>2) in basic solution, an oxidation takes place. The three C-B bonds are broken, -OH groups bond to the three carbons, and 3 equivalents of cyclohexanol are produced. The net effect of the... 

A similar reaction carried out with cyclohexene led to the formation of 3-methoxycyclohexene When this reaction sequence is carried out with internal olefins, the methoxyalkyl phenyl tellurium oxides are not stable and decompose to methoxyalkenes in the basic medium required for the hydrolysis of the methoxyalkyl phenyl tellurium dibromides(see p. 583). Aqueous solutions of sodium hydrogen carbonate cause the same transformations at a slower rate". Thus, 5-hydroxy and 5-methoxy-4-hexyl phenyl tellurium dibromide were converted to the corresponding 5-substituted 3-hexenes. 3-Hydroxy- and 3-methoxy-l-cycloheptene were similarly obtained. ... 

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. 

Thermolysis of 24 at 180-190°C for 6 days gave a 35% yield of the desired endo product 35a contaminated with the exo isomer 35b. The ratio of these adducts was quite acceptable (4 1 endo exo. With the basic cytochalasin ring system in hand, what remained was the introduction of the required unsaturation adjacent to the lactone and oxidation of the cyclohexene ring. The former was achieved in 70-76% yield by selenylation followed by oxidative elimination to afford solely the ( )-olefin 36. Hydroxylation was initiated by nitrogen acylation followed by stereo- and regioselective epoxidation of the A olefin. Deacylation and desilylation then afforded cytochalasin F (37) in 51% yield. Cytochalasin B (20) was obtained in a similar way by isomerization of the intermediate epoxide to the allylic alcohol with aluminum isopropoxide, followed by deacylation and desilylation. 

Samples with particulate matter may present quite serious problems, and it may be desirable to remove particles, for example, by centrifugation, and examine this fraction by procedures applicable to solid phases which are discussed in Section 2.2.5. Tangential-flow high-volume filtration systems have been used for analysis of particulate fractions (>0.45 jum) where the analytes occur in only low concentration (Broman et al. 1991). Attention has already been drawn to artifacts resulting from reactions with cyclohexene added as an inhibitor to dichloromethane. It has also been suggested that under basic conditions, Mn2+ in water samples may be oxidized to Mn(III or IV) which in turn oxidized phenolic constituents to quinones (Chen et al. 1991). Serious problems may arise if mercuric chloride is added as a preservative after collection of the samples (Foreman et al. 1992) since this has appreciable solubility in many organic solvents, and its use should therefore be avoided. 

Bcrkani ct al. [222] proposed the transformation of an alcohol (cyclopenianol) in the presence of a ketone (cyclohexanone) as a model reaction to characterize the acidity and the basicity of oxide catalysts (Figure 3). Actually, it is a Meerwein-Ponndorf-Verley (MPV) reduction which will be discussed in section 5. The authors found a good correlation between basicity of NaCsX zeolites or K impregnated alumina and their activities for hydrogen transfer (monitored by cyclohexanol or cyclohexene production). On the other hand, the more acidic the catalyst, the higher the dehydration extent. 

Basic metal oxides are active in diene hydrogenation to mono-olefins. MgO prepared from Mg(0H)2 by calcination at 1373K is highly selective in butadiene hydrogenation to cis-2-butene. A-isopropenyl-methyl-cyclohexene in the... 

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