Unsaturated hydrocarbons stereochemistry

The discussion of the activation of bonds containing a group 15 element is continued in chapter five. D.K. Wicht and D.S. Glueck discuss the addition of phosphines, R2P-H, phosphites, (R0)2P(=0)H, and phosphine oxides R2P(=0)H to unsaturated substrates. Although the addition of P-H bonds can be sometimes achieved directly, the transition metal-catalyzed reaction is usually faster and may proceed with a different stereochemistry. As in hydrosilylations, palladium and platinum complexes are frequently employed as catalyst precursors for P-H additions to unsaturated hydrocarbons, but (chiral) lanthanide complexes were used with great success for the (enantioselective) addition to heteropolar double bond systems, such as aldehydes and imines whereby pharmaceutically valuable a-hydroxy or a-amino phosphonates were obtained efficiently. 

Although reference is made to other kinds of information pertinent to the mechanistic problems which are considered, the discussion emphasizes the stereochemical contributions to mechanism. The recent review of the Mechanism of the Hydrogenation of Unsaturated Hydrocarbons on Transition Metal Catalysts by Bond and Wells (5) may be consulted for a more detailed analysis of the kinetic and exchange data which are available as well as a briefer, and in some respects different, evaluation of the stereochemistry of these reactions. 

The concept that the stereochemistry of reduction of an unsaturated hydrocarbon is determined at the adsorption stage of the reaction is evident in each of the above accounts, and others could be cited. However, the development of techniques which permit the identification of different product-controlling reactions directs one to consider the stereochemical consequences of various postulated reaction sequences and this will be discussed in Section IV. 

Stereochemistry and the Mechanism of Hydrogenation of Unsaturated Hydrocarbons Samuel Siegel... 

Some interesting stereoselective anodic reactions of unsaturated hydrocarbons have been known, although the stereoselectivity is not always high [367-369]. The reaction seems to proceed via radical cations of the diene. Ando and coworkers [368] investigated in detail the stereochemical consequence of anodic (probably EGA) catalyzed oxygenation of stereoisomeric syn and anti) di-/-butyl(bicyclo[3,3,l]non-9-ylidenes) compared with the stereochemistry of the photosensitized oxygenation. 

All the currently known indolizidine and quinolizidine alkaloids isolated from ants are illustrated in Fig. 6. (+ )-Monomorine I (427), the well-studied trail pheromone constituent of the Pharaoh ant Monomorium pharaonis), and the analogs 428-431 were described in the earlier volumes in this series. These five compounds are 3,5-disubstituted indolizidines bearing short saturated or mono-unsaturated hydrocarbon chains. The relative stereochemistry in monomorine VI (430) still remains unknown, while that of 431 was atypical for the class at the time of its isolation 380). The structural resemblance of fiiis group of alkaloids to the... 

Stereochemistry, of unsaturated hydrocarbon hydrogenation, 16, 123 Structure, of cracking catalysts, 4, 87 Surface area measurements, for studying contact catalysts, 1, 66 Surface barrier effects, in adsorption, 7, 269... 

Oxidation of Alkenes and Other Unsaturated Hydrocarbons. The epoxidation of double bonds has been the major area for the application of DDO methodology and a wide range of alkenes are effectively converted to epoxides by solutions of DDO. Epoxidation is stereospecific with retention of afkene stereochemistry, as shown by the reactions of geometrical isomers for example, ( -1-phenylpropene gives the cw-epoxide cleanly (eq 2), whereas the (E) isomer yields the corresponding trans-epoxide. Rate studies indicate that this reagent is electrophilic in nature and that alkyl substitution on the double bond enhances reactivity Interestingly, cw-disubstituted alkenes react 7-9 times faster than the trans isomers, an observation that has been interpreted in terms of a spiro transition state. ... 

Unsaturated hydrocarbons are converted by atomic carbon into dienes, in addition to the allenes reported previously a singlet precursor is assigned to this insertion reaction, in which the stereochemistry of the original olefinic site is essentially retained (Scheme 6). 

Hydrocarbon 136 subsequently cyclizes to a bismethylencyclobutene again, 137, in which the triple bonds of the substituent are so close that they can engage in a [2+ 2] cycloaddition, leading to the doubly annelated hydrocarbon 138. For less highly unsaturated bisallenes, a similar behavior is observed and they allowed the determination of the stereochemistry of the first ring-closure step [51]. 

The first naturally occurring tricyclo[6.3.0.0 ]undecane to be synthesized was isocomene (757), a colorless oily sesquiterpene hydrocarbon isolated from several plant sources. In 1979, Paquette and Han reported an efficient, stereospecific approach starting with a preformed bicyclic enone, to which the third five-membered ring was appended with proper attention to stereochemistry and position of unsaturation (Scheme LXXX) The pivotal steps are seen to be the stannic chloride-induced cyclization of aldehyde 732 and the conjugate addition of lithium dimethylcuprate to 733 which sets the stereochemistry of the last methyl group. 

Reaction with unsaturated bicyclic hydrocarbons. From a study of the chlorination of unsaturated bicyclic compounds, Masson and Thuillier1 conclude that the reaction follows, a radical addition mechanism when initiated thermally or photo-chemically. The stereochemistry of the addition is markedly influenced by steric effects. No Wagner-Meerwein rearrangements are observed under these conditions. An ionic mechanism is involved without initiation or in the presence of trifluoroacetic acid in this case the usual carbonium ion rearrangements are observed. 

Fatty acids are carboxylic acids containing variable lengths of hydrocarbon chains. The length can vary from 4 to 36 carbons or more depending on the mammalian species. Fatty acids can be further defined by the degree of unsaturation (double and triple bonds), and the number and position, as well as the stereochemistry cis or trans) of the double bonds with respect to the carboxyl terminus. The systematic name of oleic acid is... 

A fatty acid that occurs in a living system normally contains an even number of carbon atoms, and the hydrocarbon chain is usually unbranched (Figure 8.1). If there are carbon-carbon double bonds in the chain, the fatty acid is unsaturated if there are only single bonds, the fatty acid is saturated. Tables 8.1 and 8.2 list a few examples of the two classes. In unsaturated fatty acids, the stereochemistry at the double bond is usually as rather than trans. The difference between as and trans fatty acids is very important to their overall shape. A as double bond puts a kink in the long-chain hydrocarbon tail, whereas the shape of a trans fatty acid is like that of a saturated fatty acid in its fully extended conformation. Note that the double bonds are isolated from one another by... 

The organization is fairly classical, with some exceptions. After an introductory chapter on bonding, isomerism, and an overview of the subject (Chapter 1), the next three chapters treat saturated, unsaturated, and aromatic hydrocarbons in sequence. The concept of reaction mechanism is presented early, and examples are included in virtually all subsequent chapters. Stereoisomerism is also introduced early, briefly in Chapters 2 and 3, and then given separate attention in a fuU chapter (Chapter 5). Halogenated compounds are used in Chapter 6 as a vehicle for introducing aliphatic substitution and elimination mechanisms and dynamic stereochemistry. 

Abstract. The methods are discussed for the synthesis of optically active polymers with a hydrocarbon backbone starting with unsaturated monomers. Emphasis is given to the stereochemistry of the polymerization process and the cases are considered yielding directly an optically active polymer or a polymer separable in samples having detectable optical activity. 

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