Addition of olefins

The basis of the high normal to isoaldehyde selectivity obtained ia the LP Oxo reaction is thought to be the anti-Markovnikov addition of olefin to HRhCOL2 to give the linear alkyl, Rh(CO)L2CH2CH2CH2CH2, the precursor of straight-chain aldehyde. Anti-Markovnikov addition is preferred ia this... 

Two possible reasons may be noted by which just the coordinatively insufficient ions of the low oxidation state are necessary to provide the catalytic activity in olefin polymerization. First, the formation of the transition metal-carbon bond in the case of one-component catalysts seems to be realized through the oxidative addition of olefin to the transition metal ion that should possess the ability for a concurrent increase of degree of oxidation and coordination number (177). Second, a strong enough interaction of the monomer with the propagation center resulting in monomer activation is possible by 7r-back-donation of electrons into the antibonding orbitals of olefin that may take place only with the participation of low-valency ions of the transition metal in the formation of intermediate 71-complexes. 

Sulfur trioxide reacts with MesSiCl 14 to give the trimethylsilyl ester of chloro-sulfonic acid 1334 [96], which on treatment vvdth iodosobenzene forms iodosoben-zenedichloride 1335, HMDSO 7, and regenerated SO3 [97]. Addition of olefins such as cyclohexene leads to the formation of sulfones such as 1336 [97]. With... 

Figure 1. Diastereomeric catalyst-substrate adducts produced upon addition of olefin to solvated catalyst with chelating diphosphine ligand.

Instead of having the olefin insertion reactions, the calculations indicate that M2b and M2c can only proceed uphill with the reductive elimination of HB(OH)2, leading to the formation of M3, an olefin complex which could be in principle obtained directly from the addition of olefin to the catalyst Rh (PH3)2C1. The olefin complex M3 then could undergo a-bond metathesis processes with HB(OH)2, giving two isomeric products M4 and M5 depending on the orientation of the HB(OH)2 borane. The a-bond metathesis processes are however found to be unfavorable because of the very high reaction barriers (Figure 4). 

A further improvement resulted when potassium hexacyanoferrate(III) was used as secondary oxidant (Table 10.4, entries 5 and 6), in which case the slow addition of olefin was not necessary. O Chemical yields of 85-90% and ee of 89% were obtained by adding at room temperature 0.0025 equiv. of OSO4 to a mixture of 1 equiv. of ( )-3-hexene, 0.25 eq of 4a or 4b, 3 equiv. of K3Fe(CN)6 and 3 equiv. of K2CO3 in rert-butyl alcohol-water (1/1, v/v), followed by reductive working-up with N32S03. 

Having established the validity of the Huckel analysis of these molecules, it is useful to extend the method to the study of the cycloaddition reaction of the RjPSjNj molecules with norbomadiene. Thus the additidn of a 2e-olefin to the R PS Nj system can be regarded as a novel example of a thermally allowed 8 + 2 reaction. As in the addition of olefins to the preference for S,S-addition over... 

Methods have been studied to inhibit this reversal process. Some have involved the addition of olefins such as limonene, myrcene, and cyclopentadiene to the ends to inhibit the depolymerization. Such stabilized polysulfur has been incorporated into concrete and asphalt mixes to strengthen them. Concrete blocks, posts, and parking tire restrainers containing polysulfur... 

The addition of olefins to aldehydes can take place via an ene reaction. As shown in Figure 9.34, reaction of methylenecyclohexene 98 with ethyl glyoxylate 99 forms the ene product 100. Evans and co-workers showed that such an ene reaction can be carried out enantioselectively by utilizing bis(oxazoline)-metal complexes. Examples of ene products with yields up to 99% and ee up to 97% are summarized in Table 9.16 (Fig. 9.34). ... 

As recently reported, cobalt-catalyzed addition of olefins to butadiene is probably an example of the addition of cobalt alkyls to butadiene (106). The catalyst was the type prepared by reaction of cobalt chloride with an aluminum alkyl in the presence of a diene. A bis-7r-allylcobalt derivative is probably formed. The unstable 7r-allylcobalt compounds probably decompose (reversibly) into cobalt hydride. The hydride would add to the olefin present to form a dialkyl, which could then add again to the diene. 

When disubstituted acetylenes are employed, the >/2-acetylene complex, [Co(i/5-C5H5)(PPh3)(RC=CR)], can be isolated. In such cases, one can construct a cobaltacyclopentadiene with two different acetylene units by addition of other acetylenes, or one can synthesize cobaltacyclopentene complexes6 by addition of olefins. 

The proposed mechanisms may also be used to explain the formation of paraffins having both lower and higher molecular weights than would be expected from simple addition of olefin molecules to isobutane molecules. A typical example is the formation of heptanes and nonanes when isobutane is alkylated with butene. The first step consists of... 

Hydration of Olefins. The earliest and still the largest production of chemicals from petroleum hydrocarbons was based on the hydration of olefins to produce alcohols by the employment of sulfuric acid. The addition of olefins to sulfuric acid to form alkyl sulfates and dialkyl sulfates takes place on simple contact of the hydrocarbons with the acid. To keep down polymerization and isomerization of the hydrocarbons, the temperature is kept relatively low, usually below 40° C. and commonly considerably lower than that (18). The strength of the sulfuric acid used depends on the olefin to be absorbed. Absorption of ethylene requires an acid concentration higher than 90%, whereas propylene and butylenes are readily absorbed in 85% acid or less. The alkyl and dialkyl sulfate solutions, on dilution and heating, are hydrolyzed to the alcohols plus small amounts of by-product ethers. After distilling off the organic products, the dilute sulfuric acid is reconcentrated and re-used. 

The addition of olefins to olefins426 can also be accomplished by bases427 as well as by the use of catalyst systems428 consisting of nickel complexes and alkylaluminum compounds (known as Ziegler catalysts), 29 catalysts derived from rhodium chloride,430 and other transition metal catalysts. These and similar catalysts also catalyze the 1,4-addition of olefins to conjugated dienes,431 e.g.,... 

Cycloaddition of diphenyl ketene with benzoquinone diimides (44) gives quinoxalinones of type 45.45 Analogous additions of olefins lead to tetrahydroquinoxalines these reactions are classified as Diels-Alder additions with inverse electronic demand. 

Figure 29. A schematic illustration of the face preference for addition of olefins to a steroidal enone in solution and on silica surface. In solution the less-hindered a face is preferred. On silica surface the molecule adsorbs from the less-hindered face exposing the more-hindered face for attack by an olefin.

According to Shaipless, two cycles operate in the catalytic reaction (Scheme 39) (88c, 9CF). The first cycle is highly enantioselective, whereas the second is poorly enantioselective. Hydrolysis of the key intermediate formed from B and oxidant is not very fast. The second osmylation of olefinic substrate occurs as the intermediate enters the undesired catalytic cycle. Therefore, slow addition of olefinic substrates to minimize the second cycle is essential for obtaining high ee. Use of potassium hexacyanoferrate(III) as oxidant in a 1 1 tert-butyl alcohol-water two-layer system can suppress the second cycle and lead to high enantioselectivity (91). This procedure allows the convenient synthesis of 3-lactams from 2-octenoate. 

The formation of the tra/w-fused 4/ ,5a-ethylene adduct (262) has analogies in the addition of olefins to simple a,/ -unsaturated ketones. The possibility is that this compound derives in a concerted antara-antarcfi cial process from an excited state of the dienone (260) in which the a,j8-bond is nonplanar. Alternatively, it has been argued that upon a stepwise addition of the olefin to the excited (di)enone system a diradical is formed (e.g., through the formation of a single bond to the /2-carbon in the first step), and that part of the excess energy of this intermediate is absorbed in the formation of the strained trans-fused system. A two-step reaction is consistent with the result that the addition of either cis- or traws-dichloroethylene to enone (267) affords the same 1 1 mixture of 16a,17a-adducts [(269) and (270)]. 

High Octane Fuels Without Hydrogenation, The Addition of Olefins to Isoparaffins in the Presence of Sulfuric Acid, J. Petrol. Technol. (1938) 303. 

Equation 12.15 illustrates another variation of the 2 + 2 reaction, the rr2 + o2 addition of olefins activated by electron-withdrawing groups to highly strained single bonds. (The wavy lines indicate a mixture of stereoisomers.) The lack of stereospecificity shows that these are stepwise reactions.33... 

The addition of olefinic compounds to the three component system, BAIB/TMSNCS/PhSeSePh (2.5 1 5), or its KSCN variant, results in stereo- and regioselective (trans, Markovnikov) phenylselenenyl-thiocyanation (or -isothio-cyanation) of the C,C-double bond (Scheme 13) [36]. Whether C-S or C-N bond formation occurs when the SCN group is introduced seems to depend on the capacity of the alkene to stabilize carbocation-like intermediates. For example, C-S bond formation occurred with cyclohexene, while C-N bond formation... 

Pandarus and Zargarian developed propane-1,3-diol-based diphosphinite pincer nickel(III) complex 135 as a catalyst for Kharasch additions of olefins with CCI4 [154,155]. Only 0.1 mol% of the complex catalyzed the reaction of several olefins, such as styrene, methyl (meth)acrylate, acrolein, or acrylonitrile, in 65-97% yield. 

Metallacyclobutanes, fomed upon addition of olefin to the metal carbene, were proposed as intermediates or transition states for olefin metathesis. Metal-acyclobutanes are also known to undergo reductive and p-hydride elimination [27] to produce cyclopropanes, Eq. (8 a), and olefins, Eq. (8 b), respectively. These reactions are termination reactions for olefin metathesis. 

As with cytochrome P-450 oxidations of alkanes, the mechanism of P-450-catalyzed formation of oxiranes has been extensively studied, but certain details remain in dispute272. Examples of mechanistic schemes include formation of a transient [FeIV—0]+2-olefin complex followed by collapse to an [Fe—Oj-olefin adduct that collapses further to the epoxide and other products264. An alternative mechanism involves a 2a + 2s addition of olefin to the Fe=0 double bond to give an intermediate metallocene, followed by rearrangement to products273-275. 

Addition of Olefinic and Aliphatic C-H Bonds to C-C Multiple Bonds. 65... 

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