Alkanes chiral

Constitutional Isomerism and the Physical Properties of Alkanes Chiral Molecules and Optical Isomerism Alkenes Alkynes... 

In the earlier, longer approach to (Z)-and (E)-alkenes, ThxR BH was used iastead of IpcR BH. It is also possible to prepare a-chiral acetylenes and alkanes by this method (76,520). In a shorter synthesis of a-chiral alkynes, a prochiral disubstituted (Z)-a1kene is hydroborated with... 

When there are many carbon atoms which might be asymmetrical, the solution is more complicated. Nevertheless, by methods that basically rely on Polya s Theorem, enumeration of compounds taking chirality into account can be carried out. For alkanes and mono-substituted alkanes see the paper [BalA76] for the chiral alkanes with some restrictions see [QuiL77,79]. See also [HarF75], [PalE77], and [WorNSl] for other problems in which chirality appears. 

Chirality center, 292 detection of, 292-293 Eischer projections and, 975-978 R,S configuration of, 297-300 Chitin, structure of, 1002 Chloral hydrate, structure of, 707 Chloramphenicol, structure of, 304 Chlorine, reaction with alkanes, 91-92,335-338 reaction with alkenes, 215-218 reaction with alkynes, 262-263 reaction with aromatic compounds, 550 Chloro group, directing effect of, 567-568... 

The a-lithiated sulfides 33 are another class of chiral organometallic reagent, readily available by deprotonation of the parent l-(phcnylthio)alkanes 32 with butyllithium in tetrahydrofuran at - 78 °C. 

A bromoalkane is formed from an alkane when a bromine atom replaces a hydrogen atom. Decide whether the bromoalkanes (a) CH3CH,CHBrCH3 and (b) CH3CHBrCH are chiral. 

Alkanes undergo substitution of hydrogen atoms when treated with halogens. Bromination of which of the following compounds could give rise to chiral monosubstituted products ... 

Scheme 7 summarizes the synthesis of (7JR,llS)-7,ll-dimethylheptadecane (1), the female sex pheromone of the spring hemlock looper (Lambdina athasaria) by Mori [ 18]. Enantiopure alkanes are usually synthesized by coupling enantio-pure building blocks derived from natural products or compounds prepared by asymmetric synthesis. Even among hydrocarbons, chirality is very important for pheromone activity, and in this particular case meso-1 was bioactive, while neither (7R,11R)-1 nor (7S,11S)-1 showed bio activity. 

Chemical catalysts for transfer hydrogenation have been known for many decades [2e]. The most commonly used are heterogeneous catalysts such as Pd/C, or Raney Ni, which are able to mediate for example the reduction of alkenes by dehydrogenation of an alkane present in high concentration. Cyclohexene, cyclo-hexadiene and dihydronaphthalene are commonly used as hydrogen donors since the byproducts are aromatic and therefore more difficult to reduce. The heterogeneous reaction is useful for simple non-chiral reductions, but attempts at the enantioselective reaction have failed because the mechanism seems to occur via a radical (two-proton and two-electron) mechanism that makes it unsuitable for enantioselective reactions [2 c]. 

Various catalytic or stoichiometric asymmetric syntheses and resolutions offer excellent approaches to the chiral co-side chain. Among these methods, kinetic resolution by Sharpless epoxidation,14 amino alcohol-catalyzed organozinc alkylation of a vinylic aldehyde,15 lithium acetylide addition to an alkanal,16 reduction of the corresponding prochiral ketones,17 and BINAL-H reduction18 are all worth mentioning. 

Chiral active pharmaceutical ingredients, 18 725-726. See also Enantio- entries Chiral additives, 6 75—79 Chiral alcohols, synthesis of, 13 667-668 P-Chiral alcohols, synthesis of, 13 669 Chiral alkanes, synthesis of, 13 668-669 Chiral alkenes, synthesis of, 13 668—669 Chiral alkoxides, 26 929 Chiral alkynes, synthesis of, 13 668-669 Chiral ammonium ions, enantiomer recognition properties for, 16 790 Chiral ansa-metallocenes, 16 90 Chiral auxiliaries, in oxazolidinone formation, 17 738—739... 

Hydrogen atom transfer implies the transfer of hydrogen atoms from the chain carrier, which is the stereo-determining step in enantioselective hydrogen atom transfer reactions. These reactions are often employed as a functional group interconversion step in the synthesis of many natural products wherein an alkyl iodide or alkyl bromide is converted into an alkane, which, in simple terms, is defined as reduction [ 19,20 ]. Most of these reactions can be classified as diastereoselective in that the selectivity arises from the substrate. Enantioselective H-atom transfer reactions can be performed in two distinct ways (1) by H-atom transfer from an achiral reductant to a radical complexed to a chiral source or alternatively (2) by H-atom transfer from a chiral reductant to a radical. 

Ruthenium complexes are capable of catalyzing halogen atom transfer reactions to olefins. This has been illustrated in the enantioselective atom transfer reactions of alkane and arene-sulfonyl chlorides and bro-motrichloromethanes to olefins using chiral ruthenium complexes. Moderate ee s up to 40% can be achieved for these transformations [74-77]. These specific reactions are believed to follow a radical redox transfer chain process. 

J. Prud homme I think here the same situation arises as with hydrogenated 1,4-polydimethylbutadiene. It would appear that when two methylene units separate two chiral carbons, each methylene unit shows little sensitivity to the meso and racemic configurations of the two adjacent chiral carbons. Carman et al. have reported spectra measured on alkanes which show that when two tertiary chiral carbons are separated by two methylene units, the difference in the chemical shifts of the methylene units in the meso and racemic configurations is close to 0.3 ppm. It was not possible to observe this kind of resolution in the spectra of the present polymers. Only a broadening effect occurred. 

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