Chirality intermolecular transfer

In modem terminology, the core of Marckwald s definition is the conversion of an achiral substance into a chiral, nonracemic one by the action of a chiral reagent. By this criterion, the chiron approach falls outside the realm of asymmetric synthesis. Marckwald s point of reference of course, was biochemical processes, so it follows that modern enzymatic processes [30-32] are included by this definition. Marckwald also asserted that the nature of the reaction was irrelevant, so a self-immolative reaction or sequence such as an intermolecular chirality transfer in a Meerwein-Pondorf-Verley reaction would also be included ... 

With a four-level concept of chirality, the question of how chirality can be transferred from one level to an adjacent level is of fundamental interest. In particular, the mapping of the chirality of a molecule (second level) onto the liquid crystal phase (third level) or vice versa—the intermolecular chirality transfer—will be discussed within the scope of this chapter. But what does chirality transfer really mean The questions of how much chirality a molecule possesses or how much chirality can be transferred to an adjacent level are not allowed in the sense of transport of an amount of chirality from one level to another. Chirality is an information which can be transferred from one level to the other without being lost in the level from which it is originated. There are two possible statements [10] ... 

Enamines derived from ketones are allylated[79]. The intramolecular asymmetric allylation (chirality transfer) of cyclohexanone via its 5-proline ally ester enamine 120 proceeds to give o-allylcyclohexanone (121) with 98% ee[80,8l]. Low ee was observed in intermolecular allylation. Similarly, the asymmetric allylation of imines and hydrazones of aldehydes and ketones has been carried out[82]. 

An intermolecular example of this process was also shown to proceed with a high degree of chirality transfer (equation 341).426 The chirality transfer process can also function with oxygen nucleophiles as shown in equations (342) and (343).427... 

Ramamurthy and coworkers reported the photochemical electron-transfer-initiated intermolecular hydrogen transfer reaction [80,81] of phenyl cyclohexyl ketone 25 in chiral amine-immobilized zeolk cavities. 

Racemization by this mechanism seems to be a general problem for allyl esters and phosphates since, as the following discussion shows, successful chirality transfer in intermolecular reactions is observed only for 1,3-disubstituted 7i-allyl complexes, which cannot racemize via this pathway. 

Atom transfer reactions have proven to be particularly useful in radical transformations, and these reactions have been used to examine the efficacy of chiral auxiliaries. Atom transfer addition, sometimes called the Kharasch-Curran reaction, has been the focus of extensive investigation in recent years [6]. This transformation results in the addition of R-X to a carbon-carbon double bond. Although respectable yields are possible with certain R-X/alkene combinations, recent studies have provided insight into some of the limitations of intermolecular atom transfer... 

An intermolecular Claisen rearrangement of 137 gives 138 with a chirality transfer of at least 98%. Attempted dehalogenation of 138 affords butyrolactone 139. 

VCD Chirality Transfer A New Insight into the Intermolecular Interactions... 

Abstract The Vibrational Circular Dichroism (VCD) spectroscopy has been developing rapidly in both experimental and theoretical aspects. Currently, the VCD has become one of the most effective and reliable spectroscopic technique to determine the absolute configuration of chiral molecules. Its success is related to the availability of instrumentation and software for quantum-chemical calculation of the spectra. Nowadays, large parts of the VCD spectra can be trustfully predicted by theory and critically verified by confiding experiment, and vice versa. In the last decade, several theoretical and experimental VCD studies reported on VCD chirality transfer phenomenon occurring when an achiral molecule becomes VCD active as a result of intermolecular interactions with a chiral one. There are still some theoretical and experimental uncertainties about the VCD chirality transfer, however, benefits from an comprehensive use of the phenomenon can push our ability to diversify the intermolecular complexes and deepen our understanding of intermolecular interactions. This chapter is a review of the computational studies on VCD chirality transfer phenomenon supported by the experimental references, and ended by perspectives. 

The main purpose of this review is to explain how the VCD spectra can potentially be used to better characterize the intermolecular interactions and to document the advance of this aspect of VCD spectroscopy to the present data. We overview recent theoretical predictions and the innovative VCD observations of chirality transfer (Sect. 15.2.2) from a chiral molecule to an achiral one as a result of hydrogen bond interactions between them. Of particular interest is the hydrogen bonding interaction between chiral molecules with water. Throughout... 

We say that the chirality transfer occurs from a chiral to an achiral molecule if, in presence of the chiral molecule, the achiral one gains a property observable by a chirality-sensitive-method (CSM). The origin of this phenomenon is a symmetry breaking incident induced by intermoleculecular interactions between the two individua which shifts the achiral molecule from the achiral point symmetry group to the chiral one. This means that achiral molecule possessing either a symmetry plane, or symmetry center, or 2/t-fold inversion axis looses one or more such symmetry elements as a result of intermolecular interactions, and thus it falls into a chiral point symmetry group. 

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