Olefin additive effects

The quantitative treatment of the electron-transfer paradigm in Scheme l by FERET (equation (104)) is restricted to the comparative study of a series of structurally related donors (or acceptors). Under these conditions, the reactivity differences due to electronic properties inherent to the donor (or acceptor) are the dominant factors in the charge-transfer assessment, and any differences due to steric effects are considered minor. Such a situation is sufficient to demonstrate the viability of the electron-transfer paradigm to a specific type of donor acceptor behavior (e.g. aromatic substitution, olefin addition, etc.). However, a more general consideration requires that any steric effect be directly addressed. 

Arcus, C. L., and D. G. Smyth Olefinic additions with asymmetric reactants. Part. III. The resolution and addition reactions of 3-ethylhept-3-en-2-ol. A partial asymmetric synthesis effected by hydrogenation. J. chem. Soc. [London] 1955, 34. 

In unsymmetrical olefins there is a pronounced orientating effect in addition. Both la and lb are not formed in reaction (13) but predominantly (and sometimes perhaps exclusively) the biradical in which the oxygen atom is attached to the less substituted carbon atom of the double bond. Thus in terminal olefins addition is almost exclusively terminal as evidenced by the fact that the carbonyl product consists almost entirely of the corresponding aldehyde. 

Hydroboration is widely employed to obtain an anti-Markovnikov alcohol from an olefin. Addition of diborane to the double bond produces an organoborane intermediate. Three equivalents of the olefin are needed to consume the BH3 and a trialkylborane is produced. Reaction with basic H202 converts the carbon-boron bond to a carbon oxygen bond. This process is effective and widely used. 

The slight enhancement observed for cyclization of radical 20 is consistent with the slight electrophilicity of such radicals which was demonstrated earlier in the studies of their bimolecular olefin addition reactivity [70], The similar reactivities of 20 and hydrocarbon parent are consistent with the similarity of the ESR parameters for these two types of radicals [169]. That is they are both effectively planar rr-radicals. 

Re has recently come to the forefront in liquid phase oxidation catalysis, mainly as a result of the discovery of the catalytic properties of the alkyl compound CH3Re03 [methyltrioxorhenium (MTO)]. MTO forms mono-and diperoxo adducts with H2O2 these species are capable of transferring an oxygen atom to almost any nucleophile, including olefins, allylic alcohols, sulfur compounds, amides, and halide ions (9). Moreover, MTO catalysis can be accelerated by coordination of N ligands such as pyridine (379-381). An additional effect of such bases is that they buffer the strong Lewis acidity of MTO in aqueous solutions and therefore protect epoxides, for example. 

Highly propylene selective catalysts have been developed to meet this challenge. These catalysts, referred to as FCC olefin additives , are generally used in admixture with more traditional FCC catalysts. These additives are based on the MFI (H-ZSM-5) zeolite and the effect of the additive level, which, combined with higher temperatures increases C3 (Figure 5.21) and C4 (Figure 5.22) olefinicity. For instance, at a temperature of 566 °C and 32% Olefin additive, the propylene yield can reach 15% of the feed. 

The catalyst (PPh3)3RuCl in the presence of DPPB is an efficient reagent for the hydrophosphorylation of olefins. The reaction is highly sensitive to olefin substitution and monosubstituted olefins can be reliably converted to their aliphatic phosphonates in the presence of other olefins. Additionally, a trimethyl-silyl group is an effective acetylene protecting functionality that reverses the normal preference for alkyne hydrophosphorylation over a terminal olefin (Scheme 54). 

The effect of the last monomeric unit of the growing polymer chain on the stereospecificity of the olefin addition has been confirmed by the calculation of the energy of non-bonded interactions and by quantum-chemical calculations (see section 5.2). Corradini et al. have analyzed the possibility of the it-complex formation on the octahedral titanium ions located on different faces of a- andy-TiCla. The possibility of the coordination by both faces of the propylene molecule was studied. It was shown that active centers on the lateral faces of a-TiCls and y-TiClj may be regioselective (primary insertion of propylene) ruther than stereospecific (no predominant CjHs coordination by one face). In the case of active centers located on the edges of the layered modifications of TiClj, CsHg is coordinated with the more accessible (outward) coordination sites of the titanium ions predominantly the polymer chain is then located on the less accessible (inward) octahedral site. This position of the polymer chain results in a fixed orientation of the first carbon-carbon bond of the polymer chain due to its non-bonded interaction with the TiClj surface. This may explain the predominant coordination of propylene molecules by one face and the stereospecificity of such type of active centers. 

The necessity of a vacant coordination site for the addition of an olefin to AIR3 is confirmed by the data on the effect of donor-type compounds (e.g. ether) on the reaction kinetics . It has been found that in olefin addition only a monomeric... 

Thus, recent experimental data and calculationsshow the important role of the end of the growing polymer chain on the stereospecificity of the olefin addition. This role is due to the influence of the carbon atom (Cp, C ) of the main chain on the isospecificity of the olefin addition and not to the effect of the substituent of the last monomeric unit as in the case of the syndiospecific addition. The growing polymer chain is one of,the ligand which, together with other ligands of titanium ions, determines the chirality of the active center. 

When chloride was added to the system either as sodium chloride (Table I, lines 3a and b) or as palladium chloride (lines 4r-6) a drastic change in the reaction path occurred. The source of the halide is unimportant apparently a rapid scrambling of anionic ligands occurs during the preparation of the solutions prior to olefin addition (c/., Table I, lines 3a and 4a). However, in the presence of chloride, temperature effects become pronounced. In all cases, the higher reaction temperatures greatly favor I-substitution, so much so that it was possible to reverse completely... 

Olefin addition. Addition of iodine and A -cholestene to a solution of silver trifluoroacetate in methylene chloride generates iodine trifluoroacetate which adds to the olefin to give 3a-iodo-2 -trifluoroacetatoxycholestane in 72% yield. Lithium aluminum hydride effects reduction and deacetylation to cholestane-2/3-ol. D. E. Janssen and C. V. Wilson, Org. Syn., Coll. Vol., 4,547 (1963)... 

R. Mas-Balleste, M. Fujita, C. Hemmila, L. Que, Jr., Bio-inspired iron-catalyzed olefin oxidation. Additive effects on the cis-diol/epoxide ratio, /. Mol. Catal. A Chem. 251 (2006) 49. 

One of the problems encountered in the development of the AD reaction was a second cycle.23 The first cycle is the same as the cycle we saw in the Upjohn procedure with one modification. It is possible for the osmium in the osmate (VI) ester to become oxidised before hydrolysis to form an osmate (VIII) ester. If this species simply hydrolyses to diol and 0s04 then there is no problem but otherwise this is where the trouble starts. In the second cycle the osmate (VIII) ester reacts with another olefin instead of being hydrolysed. It does so with low enantioselectivity (and sometimes in the opposite sense to the first cycle) which results in the poorer enantiopurity of the product (step D rather than step C below). One way round this is to keep the olefin concentration as low as possible which can be done by adding the olefin slowly.22,23 Although slow olefin addition resulted in a profound improvement in enantiomeric excess, it was inconvenient and no way near as effective as the alternative which was to alter the conditions. The use of two phases makes it impossible for the second cycle to occur.19,24... 

In short, the experimental results presented above collectively form a more coherent understanding of the [Mn(salen)] -catalyzed epoxidation of unfunctionalized olefins. Side-on approach of the substrate at the metal-oxo species leading to stepwise C-0 bond formation offers a straightforward explanation for product selectivity and additive effects. The degree of C-0 bond formation reflects the position of the transition state along the reaction coordinate, and it is this position that is critical to the level of asymmetric induction in the [Mn(salen)]-catalyzed epoxidation. 

Effect of Stracture of the Olefins. One may regard the Oxo reaction as consisting of the addition of H and CHO to the carbon atoms joined by the double bond of the olefin, th a straight-chain unsymmetrical olefin, addition can lead to one or the other of two compounds or to a mixture ai both, depending on where the formyl group is added ... 

Addition of bromine to olefins was effected using tetrabutylammonium tribromide in chloroform solution (Eq. 21).126 The expected z ic-dibromides are formed quantitatively in all the cases tested and the reactions are extremely rapid. The short reaction times can explain the absence of decomposition of the dibromides. The conventional addition normally proceeds via an electrophilic attack of the double bond, but the sonochemical mechanism was not studied. 

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