Carbon-isotope chirality

Carbon-isotope chirality is experimentally difficult to discriminate because the chirality originates from the very small difference between the carbon-12 and carbon-13. Therefore, it has been a question whether isotopically substituted carbon chiral compounds can induce chirality in some enantioselective reactions. To address this problem, we performed asymmetric autocatalysis triggered by a chiral compound arising solely from carbon-isotope substitution. 

This is the first example of the chiral effect, that is, asymmetric induction by carbon isotopically chiral compounds. The neglected carbon-isotope chirality of... 

Scheme 14 Asymmetric autocatalysis triggered by carbon isotopically chiral diphenylmethanol...

Phosphate esters, particularly AMP, ADP and ATP, have vital biological functions and this fact has generated intense interest in their reaction mechanisms. Subtle stereochemical experiments, such as the use of isotopically chiral compounds, have been important and, since all biological phosphorylation reactions appear to involve metal ion catalysis, the stereochemistry of phosphate ion coordination has also been subject to much attention.229,230 Apart from its biological significance, this work has revealed some interesting contrasts with the stereochemistry of ligand systems in which saturated carbon units link the donor atoms. 

Discrimination of Chiral Compound Arising from Carbon-Isotope Substitution.. 273... 

Kawasaki T, Matsumura Y, Tsutsumi T, Suzuki K, Ito M, SoaM K (2009) Asymmetric autocatalysis triggered by carbon isotope ( C/ Q chirality. Science 324 492-495. doi 10.1126/science. 1170322... 

Even isotopes qualify as different substituents at a chirality center The stereo chemistry of biological oxidation of a derivative of ethane that is chiral because of deu terium (D = H) and tritium (T = H) atoms at carbon has been studied and shown to... 

Isopropyl group (Section 2 13) The group (CH3)2CH— Isotactic polymer (Section 7 15) A stereoregular polymer in which the substituent at each successive chirality center is on the same side of the zigzag carbon chain Isotopic cluster (Section 13 22) In mass spectrometry a group of peaks that differ in m/z because they incorporate differ ent isotopes of their component elements lUPAC nomenclature (Section 2 11) The most widely used method of naming organic compounds It uses a set of rules proposed and periodically revised by the International Union of Pure and Applied Chemistry... 

The stereospecific conversion of menthyl arenesulphinates into chiral aryl methyl sulphoxides may also be achieved by means of methyllithium . The reaction of methyllithium with diastereoisomerically or enantiomerically pure arenesulph-inamides 283 was found to give optically active aryl methyl sulphoxides 284 (equation 156). The preparation of optically active sulphoxides 285 and 286, which are chiral by virtue of isotopic substitution (H - D and - respectively), involves the reaction of the appropriate non-labelled menthyl sulphinates with fully deuteriated methyl magnesium iodide (equation 157) and with benzylmagnesium chloride prepared from benzyl chloride labelled with carbon (equation 158). 

Initially, it was thought more likely that the electron poor metal atom would be involved in the electrophilic attack at the alkene and also the metal-carbon bond would bring the alkene closer to the chiral metal-ligand environment. This mechanism is analogous to alkene metathesis in which a metallacyclobutane is formed. Later work, though, has shown that for osmium the actual mechanism is the 3+2 addition. Molecular modelling lends support to the 3+2 mechanism, but also kinetic isotope effects support this (KIEs for 13C in substrate at high conversion). Oxetane formation should lead to a different KIE for the two alkene carbon atoms involved. Both experimentally and theoretically an equal KIE was found for both carbon atoms and thus it was concluded that an effectively symmetric addition, such as the 3+2 addition, is the actual mechanism [22] for osmium. 

A different experimental approach to the relative importance of one-center and two-center epimerizations in cyclopropane itself was based on the isomeric l-13C-l,2,3-d3-cyclopropanes165"169. Here each carbon has the same substituents, one hydrogen and one deuterium, and should be equally involved in stereomutation events secondary carbon-13 kinetic isotope effects or diastereotopically distinct secondary deuterium kinetic isotope effects may be safely presumed to be inconsequential. Unlike the isomeric 1,2,3-d3-cyclo-propanes (two isomers, only one phenomenological rate constant, for approach to syn, anti equilibrium), the l-13C-l,2,3-d3-cyclopropanes provide four isomers and two distinct observables since there are two chiral forms as well as two meso structures (Scheme 4). Both chiral isomers were synthesized, and the phenomenological rate constants at 407 °C were found to be k, = (4 l2 + 8, ) = (4.63 0.19)x 10 5s l and ka = (4kl2 + 4, ) = (3.10 0.07) x 10 5 s 1. The ratio of rate constants k, kl2 is thus 1.0 0.2 both one-center and two-center... 

The four different groups attached to a chiral carbon can be different elements, isotopes, or functional groups, and chiral centers can be present in bodi open-chain molecules or cyclic compounds. The recognition of chirality and chiral centers in molecules is an important step in determining the numbers of stereoisomers that are possible for a given compound. 

The resulting isotope effects determined relative to the para carbon are summarized in Figure 13. Independently of used catalyst similar 13C isotope effects were observed for olefinic carbons. This fact suggests that in the presence of the bulky chiral catalyst as Rh2(S-DOSP)4 the geometry of the cyclopropana-tion transition state was not change. 

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