Alkenes catalytic

R =H, R =alkyl for terminal alkynes R =alkyl, R =H for terminal alkenes Catalytic Cycle for Addition to Alkenes and Alkynes... 

Some of the most exciting reactions in organic chemistry are based on transition metals. How about these two for example The first is the Heck reaction, which allows nucleophilic addition to an unactivated alkene. Catalytic palladium (Pd) is needed to make the reaction go. The second, the Pauson-Khand reaction, is a special method of making five-membered rings from three components an alkene, an alkyne, and carbon monoxide (CO). It requires cobalt (Co). Neither of these reactions is possible without the metal. 

The aziridination of alkenes, catalytic in porphyrinatoiron and -manganese salts, has been developed where the nitrene moiety is supplied by A -(4-methylphenylsulfonyl)iminophenyl-iodinane (C6H5I = NTs) and the reaction intermediate is a high-valent tosylimidometal species (Table 9)98-10°. This intermediate may undergo addition to an alkene double bond by a free radical mechanism or via a four-membered metallocycle. 

The formation of the linear carbon-carbon skeletons of lipids and carotenes usually depends on the reaction of the electropositive carbonyl carbon atoms of aldehydes or ketones with carbanions. Most popular is the Wittig reaction between a phosphorus ylene as obtained from alkylbromides and an aldehyde to form alkenes. Catalytic hydrogenation then converts alkenes to alkanes. The reaction has been adjusted to all kinds of functional groups, which can be connected to both educts, namely aldehydes and bromides (Scheme 1.3.1). 

Several examples of intermolecular C-H bond functionalization have appeared during the past decade. In addition to the oxidations reported above in Shilov-type systems, and the dehydrogenation of alkanes to make alkenes, catalytic systems have been developed to introduce functional groups into hydrocarbons. 

Yawalkar et al. (2001) has developed a model for a three-phase reactor based on the use of a dense polymeric composite membrane containing discrete cubic zeolite particles (Fig. 4.5) for the epoxidation reaction of alkene. Catalytic particles of the same size are assumed vdth a cubic shape and uniformly dispersed across the polymer membrane cross-section. Effects of various parameters, such as peroxide and alkene concentration in liquid phase, sorption coefficient of the membrane for peroxide and alkene, membrane-catalyst distribution coefficient for peroxide and alkene and catalyst loading, have been studied. The results have been discussed in terms of a peroxide effidency defined as the ratio of flux of peroxide through the membrane utilized for alkene oxidation to the total flux of organic peroxide through the membrane. The paper aimed to show that, by using an organophilic dense membrane and the catalysts confined in the polymeric matrix, the oxidant concentration (in that reaction peroxides) can be controlled on the active site with an improvement of the peroxide efficiency and selectivity to desired products. 

Alkynes can be reduced to either a cis or trans alkene. Catalytic hydrogenation of an alkyne using a poisoned catalyst (H2, Lindlar catalyst) results in the syn addition of one equivalent of H2 to give a cis alkene product. Dissolving metal reduction (Li, NH3) of an alkyne produces the corresponding trans alkene. This strategy is well suited for synthesizing monosubstituted alkenes and disubstituted alkenes with a specific stereochemistry. 

HAYASHI-UOZUMI Asymmetric Functionalization ggymmetric synthesis of optically active alcohols via hydrosilylation of alkenes Catalytic nfionophosphine-palladium. 

The Heck reaction is carried out by heating the R-X, the alkene, catalytic amounts of Pd(ll)acetate, and an excess of a tertiary amine. The mechanism given below is well accepted. Oxidative addition of R-X to Pd(0) occurs (step 1). The alkene coordinates (step 2), and alkyl group migration svibsequently ensues (step 3). 

Scheme 20 General reaction of the catalytic oxidation of alkenes catalytic oxidation of alkenes...

Apart from hydrosilylation of alkenes/ " catalytic transformations involving organosilicon compounds have been extensively studied, mainly by Marciniec and co-workers.Iridium complexes have shown to be active catalysts for these processes incorporation of CO and silanes into organic substrates has been reported via silylcarbo-... 

The reaction of furans with ethyl 2,2-difluoro-l-diethylamino-carboxyacrylate generates fluorinated 7-oxanorbomenes [163]. These cycloadducts undergo alkene catalytic hydrogenation (or other reactions) into the corresponding 7-oxabicyclo[2.2.1]heptanes. Examples have been presented with the synthesis of norcantharidin, 5, with the synthesis of the 2-epimer of rac-3, 6 -epoxyauraptene, 32 (Scheme 3), and with the synthesis of thromboxane mimetics (Scheme 8). In 1929, Diels and Alder first reported the reaction of furan with maleic anhydride that produces at room temperature the exo-adduct 132 [164]. In 1962, Anet found that at low temperature, the reaction produces first the ew fo-adduct 133 in agreement with the endo Alder rule [165]. At 25 °C and in MeCN, the exo-adduct 132 is more stable by 1.9 kcal/mol compared with 133 [166] (Scheme 20). 

Alkynes can be treated with organometallic reagents to get c/s-carbometalated alkenes in the presence of suitable catalysts. Subsequently, the metal can be substituted by a proton during aqueous workup. Alternatively, the metalated alkene can be treated with an electrophile to introduce a second substituent to the alkene. Catalytic amounts of tris(acetylacetonato)iron allow the reaction of 3-pentynyl ethers with butyllithium at -20 °C in toluene to give 4-methyl-octen-3-yl ethers in high yields (Scheme 4—268). Addition of an electrophile other than before aqueous workup leads in a stereoselective reaction to the products of a syn carbometalation with subsequent displacement of the metal by the electrophile under retention of the configuration. ... 

---