Simple olefins

The addition is stereospecific for example the adducts of the symmetrical cis olefins 199 and 201 have the three structure (equation 94) and symmetrical trans olefins (200, 202, 203) give adducts with the erythro structure (equation 95). Both forms undergo trans elimination 

Cases exist where steric factors counteract these general polar directive effects (Table 8, compounds 214-219). For example, whereas polar effects direct the addition in compounds 214 and 215, for 3,3-dimethylbut-l-ene (216) adverse steric interactions between the approaching azide ion and the i-butyl group preclude the electronically controlled ring opening of the iodonium ion. Instead, anti-Markownikoff addition occurs with the formation of l-azido-2- 

With solvents such as methanol, acetone, acetic acid and acetonitrile, however, solvent pairticipation can occur . The intermediate bromonium ion is more reactive than the larger iodonium ion and therefore more susceptible to solvolysis, which affords products other than those of Br—Ng addition. 

In a recent extension of this work, Hassner and Boerwinkle have indicated that chlorine azide is predominantly an azide radical source 

The alternative explanation, that iodine azide additions to afi-un-saturated carbonyl compounds are of the Ad, type (equation 96) is. 

Both recent computational studies agree that the most feasible pathway for the hydrogenation of simple olefins is Ir /Ir migratory insertion mechanism with migratory insertion as the rate-determining and stereoregulating step. °  

energy of adduct, kcal mol Rel. energy ofTSu, kcal mol  

If the ligand has a backbone chirality like in 16, computations are required to determine, whether the stereo-discriminating substituent on the oxazoline ring lies below or above the ligand plane.  

This approach has been proved applicable for other types of ligands and trisubstituted olefins containing various functional groups as one of the substituents including cyclic sulfones.  

A large variety of methods is applicable to the formation of isolated double bonds. This permits selection of reagents compatible with other functionality present. Alcohol dehydration, ester elimination and other nonreductive p eliminations are the most common methods. Reductive elimination of halo-hydrins, vic-dihalides, etc., and of a variety of ketone derivatives has also been used. 

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Simple olefins do not usually add well to ketenes except to ketoketenes and halogenated ketenes. Mild Lewis acids as well as bases often increase the rate of the cyclo addition. The cycloaddition of ketenes to acetylenes yields cyclobutenones. The cycloaddition of ketenes to aldehydes and ketones yields oxetanones. The reaction can also be base-cataly2ed if the reactant contains electron-poor carbonyl bonds. Optically active bases lead to chiral lactones (41—43). The dimerization of the ketene itself is the main competing reaction. This process precludes the parent compound ketene from many [2 + 2] cyclo additions. Intramolecular cycloaddition reactions of ketenes are known and have been reviewed (7). 

LB Films of Polymerizable Amphiphiles. Stxidies of LB films of polymerizable amphiphiles include simple olefinic amphiphiles, conjugated double bonds, dienes, and diacetylenes (4). In general, a monomeric ampbipbile can be spread and polymerization can be induced either at tbe air—water interface or after transfer to a soHd substrate. Tbe former polymerization results in a rigid layer tbat is difficult to transfer. 

The 0X0 process is not limited to simple olefins. The terrninal-to-branched ratio of products can be controlled by ligand addition (130). Butanol is produced from propylene and CO using a similar process (see Butyl alcohols). The catalyst in this case is Fe(CO) (131). 

Whereas simple olefins are not usually made by elimination from halides, conjugated systems are frequently obtained in this way. The cases of a- and j5-halo ketones and their vinylogues have already been covered. Allylic halides may also be eliminated to form dienes, for example, the 2,4-diene (109)... 

The over-all transformation covered in this section is that of conversion of a ketone into a simple olefin by the use of carbonyl derivatives ... 

The photochemical addition of simple olefins to a,j -unsaturated ketones is a reaction of great current interest. The steroidal A -20-ketone system is especially prone to cycloaddition under mild conditions. Sunder-Plassmann et irradiated 3j5-acetoxypregna-5,16-dien-20-one (67) in the presence... 

Enamines derived from 1-azabicycloalkanes, readily accessible by mercuric acetate oxidation of saturated bases (112), have been extensively studied recently (113-115). Since an immonium salt is formed during dehydrogenation, the composition of the liberated enamine mixture shows the relative stability of the various possible isomers. The study of infrared and NMR spectra has shown that the position of the enamine double bond is determined by factors similar to those determining the relative stability of simple olefins. 

Selectivity depends importantly on the catalytic metal. A number of selectivity series have been determined for simple olefins, and the presumption is that the sequence holds for more complex polyenes as well. Selectivity for the reduction of allene to propylene declined with metal in the order palladium... 

Ziegler-Natta polymerization is used extensively for the polymerization of simple olefins (such as ethylene, propene, and 1-butene) and is the focus of much academic attention, as even small improvements to a commercial process operated on... 

One problem associated with the peroxotungstate-catalyzed epoxidation system described above is the separation of the catalyst after the completed reaction. To overcome this obstacle, efforts to prepare heterogeneous tungstate catalysts have been conducted. De Vos and coworkers employed W catalysts derived from sodium tungstate and layered double hydroxides (LDH - coprecipitated MgCU, AICI3, and NaOH) for the epoxidation of simple olefins and allyl alcohols with... 

The observation that addition of imidazoles and carboxylic acids significantly improved the epoxidation reaction resulted in the development of Mn-porphyrin complexes containing these groups covalently linked to the porphyrin platform as attached pendant arms (11) [63]. When these catalysts were employed in the epoxidation of simple olefins with hydrogen peroxide, enhanced oxidation rates were obtained in combination with perfect product selectivity (Table 6.6, Entry 3). In contrast with epoxidations catalyzed by other metals, the Mn-porphyrin system yields products with scrambled stereochemistry the epoxidation of cis-stilbene with Mn(TPP)Cl (TPP = tetraphenylporphyrin) and iodosylbenzene, for example, generated cis- and trans-stilbene oxide in a ratio of 35 65. The low stereospecificity was improved by use of heterocyclic additives such as pyridines or imidazoles. The epoxidation system, with hydrogen peroxide as terminal oxidant, was reported to be stereospecific for ris-olefins, whereas trans-olefins are poor substrates with these catalysts. 

High-valent ruthenium oxides (e. g., Ru04) are powerful oxidants and react readily with olefins, mostly resulting in cleavage of the double bond [132]. If reactions are performed with very short reaction times (0.5 min.) at 0 °C it is possible to control the reactivity better and thereby to obtain ds-diols. On the other hand, the use of less reactive, low-valent ruthenium complexes in combination with various terminal oxidants for the preparation of epoxides from simple olefins has been described [133]. In the more successful earlier cases, ruthenium porphyrins were used as catalysts, especially in combination with N-oxides as terminal oxidants [134, 135, 136]. Two examples are shown in Scheme 6.20, terminal olefins being oxidized in the presence of catalytic amounts of Ru-porphyrins 25 and 26 with the sterically hindered 2,6-dichloropyridine N-oxide (2,6-DCPNO) as oxidant. The use... 

Asymmetric epoxidation of olefins with ruthenium catalysts based either on chiral porphyrins or on pyridine-2,6-bisoxazoline (pybox) ligands has been reported (Scheme 6.21). Berkessel et al. reported that catalysts 27 and 28 were efficient catalysts for the enantioselective epoxidation of aryl-substituted olefins (Table 6.10) [139]. Enantioselectivities of up to 83% were obtained in the epoxidation of 1,2-dihydronaphthalene with catalyst 28 and 2,6-DCPNO. Simple olefins such as oct-l-ene reacted poorly and gave epoxides with low enantioselectivity. The use of pybox ligands in ruthenium-catalyzed asymmetric epoxidations was first reported by Nishiyama et al., who used catalyst 30 in combination with iodosyl benzene, bisacetoxyiodo benzene [PhI(OAc)2], or TBHP for the oxidation of trons-stilbene [140], In their best result, with PhI(OAc)2 as oxidant, they obtained trons-stilbene oxide in 80% yield and with 63% ee. More recently, Beller and coworkers have reexamined this catalytic system, finding that asymmetric epoxidations could be perfonned with ruthenium catalysts 29 and 30 and 30% aqueous hydrogen peroxide (Table 6.11) [141]. Development of the pybox ligand provided ruthenium complex 31, which turned out to be the most efficient catalyst for asymmetric... 

Products from Oxidation op Simple Olefins with TP /aq. 

Examination of the reactions of a wide variety of olefins with TTN in methanol (92) has revealed that in the majority of cases oxidative rearrangement is the predominant reaction course (cf. cyclohexene, Scheme 9). Further examples are shown in Scheme 18, and the scope and limitations of this procedure for the oxidative rearrangement of various classes of simple olefins to aldehydes and ketones have been defined. From the experimental point of view these reactions are extremely simple, and most of them are... 

Ester disconnection gives easily made alcohol (39) and yclopropane acid (40), Disconnection of dlazoacetic trster leaves simple olefin (41),... 

A study concerning the lowermost particle size necessary for admitting a reaction to occur is provided by Amiridis et al. [55] in their investigations of propene hydrogenation. For metal particle sizes greater than 2nm, hydrogenation of simple olefins is considered to be structure insensitive... 

By analogy to simple olefins, we propose that 0(3P) initially adds to the 1,4 or 1,2 double bonds in polybutadienes at ambient temperature. Since the rate constants for 0(3P) addition to cis-2-butene and 1-butene (as models for 1,4 and 1,2 double bonds, respectively) are in the ratio 4.2 1 at 298 K ( 6), preferential addition to the 1,4 double bonds is assumed to persist to very high vinyl contents (-8011). The biradical adducts then rearrange to epoxides and carbonyl compounds or give rise to chain rupture and/or crosslinking as a consequence of PIF, according to the scheme ... 

Cationic polymerization of alkenes and alkene derivatives has been carried out frequently in aqueous media.107 On the other hand, the reaction of simple olefins with aldehydes in the presence of an acid catalyst is referred to as the Prins reaction.108 The reaction can be carried out by using an aqueous solution of the aldehyde, often resulting in a mixture of carbon-carbon bond formation products.109 Recently, Li and co-workers reported a direct formation of tetrahydropyranol derivatives in water using a cerium-salt catalyzed cyclization in aqueous ionic liquids (Eq. 3.24).110... 

The addition of perfluoroalkyl iodides to simple olefins has been quite successful under aqueous conditions to synthesize fluorinated hydrocarbons.119 In addition to carbon-based radicals, other radicals such as sulfur-based radicals, generated from RSH-type precursors (R = alkyl, acyl) with AIBN, also smoothly add to a-allylglycines protected at none, one, or both of the amino acid functions (NH2 and/or CO2H). Optimal results were obtained when both the unsaturated amino... 

Benzene undergoes photocycloaddition with simple olefins to produce 1,3, 1,2 and 1,4 adducts as shown below for tetramethylethylene ... 

The resulting material is active for the gas phase epoxidation of simple olefins. Addition of cyclohexene resulted in the formation of cyclohexene oxide as the sole volatile product, detected by GC/MS. 

The presence of V does not diminish the activity of a grafted Ti-Si02 catalyst for olefin epoxidation. However, activity towards simple olefins such as cyclohexene is not enhanced. Since homogeneous V catalysts are known to catalyze the epoxidation of functionalized olefins (e.g., allylic alcohols), the ability of a mixed V-Ti/Si02 catalyst to achieve such transformations will be the next focus of our investigations. 

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