Olefinic addition reactions

It should be noted here again that the catalytic reaction does not involve a change of valence of the metal. In general, catalytic olefin addition reactions that involve a hydride transfer do not require change of valence in the metal catalyst. On the other hand, carbon-carbon bond formation by coupling reactions which involve electron shifts, such as in Wilke s Ni°-catalyzed butadiene oligomerization reaction [Eq. (1)], requires a valence change on the metal. 

An alternative LIS scheme is one in which a vibrationally excited molecule reacts preferentially with another species. An example is the hydrogen halide/olefin addition reaction, DX + RiR2C = CH2 RiR2CXCH2D. The scheme involves sequential absorption of several quanta from a C02 laser near 5 p,m to selectively excite DX to a vibrational quantum number of 3 or more. Successful implementation would be expensive because of the highly corrosive nature of halogen acids. 

Synthetic applications of the asymmetric Birch reduction and reduction-alkylation are reported. Synthetically useful chiral Intermediates have been obtained from chiral 2-alkoxy-, 2-alkyl-, 2-aryl- and 2-trialkylsllyl-benzamides I and the pyrrolobenzodlazeplne-5,ll-diones II. The availability of a wide range of substituents on the precursor benzoic acid derivative, the uniformly high degree of dlastereoselection in the chiral enolate alkylation step, and the opportunity for further development of stereogenic centers by way of olefin addition reactions make this method unusually versatile for the asymmetric synthesis of natural products and related materials. 

The conversion of alkenes to 1,2-diols by osmium tetroxide is also an olefin addition reaction. In this case a hydroxy group is added to each carbon of the olefin group, and the addition is termed an oxidative addition since the diol product is at a higher oxidation level than the alkene reactant. Oxidation of the carbon atoms of the alkene takes place in the first step, which is the reaction with 0s04 to produce the intermediate osmate ester. 

A typical example of a stereospecific olefin addition reaction is the addition of bromine to olefins. If d.v-2-pentene is used as the substrate, only the 2R,3R and 2S,3S pair will be produced (they are enantiomers). 

These experiments provide further proof of the radical nature of the N204-olefin addition reaction. 

Rhodium-olefin complexes have been identified as intermediate species in rhodium-catalyzed olefin-to-olefin addition reactions (5a, 150a, 151) and olefin hydrogenation reactions (450). Although the ethylene-Rh(I) complexes are not in themselves catalysts for dimerization of ethylene, both [(C2H4)2RhCl]2 and (C2H4)2Rh( Cac) react with... 

Demonstration of cis addition with acetylene is unequivocal, in that the stereochemistry of the resulting bis(dihaloboryl)ethylene has been shown directly by spectroscopic evidence (90) and by conversion of the initially produced cis isomer to the trans compound by photochemical isomerization (27). Stereochemical inferences in the olefin addition reactions are based on the assumption that hydrolysis and oxidation of the bis(boryl) compounds to the corresponding diols occurs with retention of configuration, as is the case in closely related systems 19). The NMR spectrum of the addition product of B2CI4 with 1,3-cyclohexadiene is also consistent with cis addition (120). 

Rhodium chloride also catalyzes a number of other olefin-to-olefin addition reactions, including the addition of ethylene to dienes (i, 25),... 

Selected scaled ks results have been presented in Table VII. A more extensive listing follows in Appendix B. Many thermal hydrogen abstraction and olefinic addition reactions have been tabulated that are too fast to be characterized using the available direct measurement methods. Based on comparisons with the scaled MNR data, the HF chemiluminescence (52), electron spin resonance (53,66), and laser pulse decay (54,67), absolute teclmiques apparently involve large systematic errors. 

Table VII. Absolute Rate Constants for Selected Thermal Hydrogen Abstraction and Olefinic Addition Reactions by Atomic Fluorine"...

A comprehensive listing of absolute thermal rate coefficients for hydrogen abstraction and olefinic addition reactions by atomic fluorine has been given in Table X. 

Conceivably, in an olefin addition reaction, if the more substituted end of the ethylenic linkage is sterically shielded such that the approach of the nucleophile or the radical is essentially blocked, the product cannot be expected to be the result of a simple addition reaction, but would always be complicated by the intervention of other pathways, such as elimination/rearran ment. To illustrate this point, the reaction of chlorine-free hypochlorous acid with u/wym-dineopentylethylene (110) and 2,4,4-trimethyl-l-pentene (112) may be cited (110) gives a complex reaction product in which (111) predominates (48%) and no oxygen-containing material was detected in the total product, while (112) which is less hindered furnishes 34% of the normal product (113) and 46% of elimination product (114) (65). 

ABSTRACT. Aldehydes, ketones and a,p-unsaturated aldehydes and ketones undergo a wide variety of reactions with unactivated alkenes in the presence of alkylaluminum halide catalysts. Ene reactions, Diels-Alder reactions, Prins reactions and cation-olefin addition reactions occur depending on the choice of substrate and Lewis acid. 

TrialkyIboranes or alkyl 9-borabicyclo[3,3,1]nonanes, obtained by appropriate olefin addition reactions, may be used in Sjj2 displacement reactions upon a-halo esters, i r s 2 a-haloketones, or a-halonitriles to effect alkylation of these substrates in high yield. In many cases 2,6-di-t-butylphenoxide, a base of very high steric requirement, is essential. 

I. Four-Electron Hiickel Systems. The literature abounds with examples of photochemical olefin addition reactions which proceed through transition states that are analogous to Hiickel cyclobutadiene e.g.. 

Partially because of last minute cancellations, several important topics have not been included in the present work. Papers on fluorine atom chemical lasers, high-energy fluorine atom reactions, and classical trajectory simulations of hydrogen transfer reactions by atomic fluorine are conspicuously absent. Other more speciahzed topics not included were olefin addition reactions by fluorine-rich carbenes, H2/F2 explosions, unimolecular reaction d3mamics of fluorine-containing aliphatic radicals, and high-power fluorine atom lasers in energy research. 

Rydrogen Abstraction and Olefin Addition Reactions By Atomic Fluorine. ... 

The COC mechanism was originally proposed to explain the negative activation energies observed for carbene-olefin addition reactions." " Later, Liu and Tomioka used this mechanism to explain the curved correlations between the ratio of trapping products to rearrangement product and concentration of carbene trap. > > They proposed that the second intermediate was a COC in equihbrium with the initially generated carbene intermediate (Scheme 4). 

There are also important differences in the nature of the polymer backbone formed by these processes. Olefin addition reactions lead to polymer chains containing aliphatic carbon as the backbone. Most step-growth reactions instead form polymer chains or rings containing heteroatoms (noncarbon atoms) in addition to aliphatic carbon in the backbone. The presence of heteratoms can provide remarkable enhancements in polymer performance and often leads to polymers with higher glass transition temperatures and thermal stability leading to such properties as conductivity or electroluminescence. 

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