Chirality molecular designation

T. Ooi, M Kameda, K Maruoka, Molecular Design of a C2-Symmetric Chiral Phase-Transfer Catalyst for Practical Asymmetric Synthesis of a-Amino Acids , J. Am Chem Soc, 1999,121, 6519-6520. 

Okamoto, Y, Yashima, E, Chiral recognition by optically active polymers, in Molecular Design of Polymeric Materials (Hatada K, Kitayama T, Vogl O, Eds.), Marcel Dekker, New York, pp. 731-746 (1997). 

This unique phenomenon provides a powerful strategy in the molecular design of chiral catalysts that is, the requisite chirality can be served by the simple binaphthyl moiety, while an additional structural requirement for fine-tuning of reactivity and selectivity can be fulfilled by an easily modifiable achiral biphenyl structure. This certainly obviates the use of two chiral units, and should be appreciated in the synthesis of a variety of chiral catalysts with different steric and/or electronic properties. Actually, quaternary ammonium bromide possessing a sterically demanding substituent such as (S)-12b can be easily prepared, and benzylation with (S)-12b as catalyst gave 9 in 95% yield with 92% ee. Further, theenantioselectivity was enhanced to 95% ee with (S)-12c as a catalyst [12]. 

Maruoka and coworkers designed a new and highly efficient chiral N-spiro-type quaternary ammonium salt (S)-70 with dual functions for the asymmetric epoxidation of various enone substrates (Scheme 5.44) [45]. The exceedingly high asymmetric induction is ascribable to the molecular recognition ability of the catalyst toward enone substrates by virtue of the appropriately aligned hydroxy functionality, as well as the chiral molecular cavity. Indeed, the observed enantioselectivity depends heavily... 

The development of various types of chiral phase-transfer catalyst relies largely on the molecular design of both natural product-derived and purely synthetic chiral quaternary ammonium salts. This approach often delivers not only higher reactivity... 

Currently, it is fair to say that asymmetric synthesis using chiral quaternary ammonium fluorides remains an underdeveloped field, and the various useful stereoselective carbon-carbon bond-forming processes described in this chapter are only the start of an exploration of the vast synthetic potential of this process, particularly when combined with current knowledge of organosilicon chemistry. It seems that the key issue to be addressed is the rational molecular design of chiral quaternary ammonium cations with appropriate steric and electronic properties. These are expected to be readily tunable to impart not only a sufficient reactivity but also an ideal chiral environment to the requisite nucleophile involved in a desired chemical transformation. Clearly, the continuous accumulation of information related to the structure of fluoride salts and their reactivity and selectivity should create a solid basis for this field, offering - in time - a unique yet reliable tool for sophisticated bond construction events with rigorous stereocontrol, under mild conditions. 

Photochemical polarization flip was immediately extended to antiferroelectric LCs (AFLCs), and it was found that in azobenzene guest/AFLC host systems, polarization flip could be induced photochemically and effectively, as shown in Figure 3.1331 Novel photochromic molecules to induce polarization flip effectively have been explored, and molecular design on the basis of large Ps resulting from chiral cyclic carbonates has been found to be quite effective. An azobenzene dopant containing a... 

Ooi T, Kameda M, Maruoka K (1999) Molecular design of a C2-symmetric chiral phase-transfer catalyst for practical synthesis of a-amino acids. J Am Chem Soc 121 6519... 

The use of well-designed chemical processes, aided hy chiral molecular catalysts, can provide truly practical and efficient synthetic methods for the production of hioactive substances and functional materials. In particular, the growing awareness of the importance of chirality to the function of chemical substances has led to the development of many new chiral molecular catalysts for use in large-scale production. Chiral molecular catalysts consisting of a metal atom or ion and a chiral organic ligand(s), under the appropriate conditions, can not only repeatedly accelerate organic reactions, but also simultaneously control the absolute stereochemical outcome [1]. 

Chemoinformatics is characterized by the use of large amounts of information. Specific ways to represent the molecules, and to organize and analyze the data have been and continue to be developed. There are different ways to represent the molecules, and they can be classified according to the information that they encode. The most basic level corresponds to representations that depend on or are associated with one dimensional (ID) representation, such as molecular weight. The next level corresponds to the 2D representations associated with the connectivity of the molecules without the consideration of the stereochemistry. In 3D methods the incorporation of stereochemistry conveys not only the specification of the chirality of stereogenic centers but also the possible conformation or conformations. In this regard, the research fields dedicated to conformational analysis have an important impact in reactivity prediction, molecular design, and stability. Examples of ID, 2D, and... 

The foregoing approach to the aza-Henry reaction can be also classified as an example of chiral phase transfer catalysis. A more recent example of chiral phase transfer catalysis in water was made possible by a careful molecular design aiming at incorporating into the same species both a water soluble frame in the form of a long PEG chain and two catalytically active quininium salt moieties. The synthetic plan is shown in Figure 13 The... 

Fig. 9.2 Design of a chiral molecular tool, CSDP and CSP acids containing the 2,10-camphorsultam moiety.

Morihara K., Kurokawa M., Kamata Y. and Shimada T. (1992) Enzymelike enantioselective catalysis over chiral Molecular Footprint cavities on a silica (alumina) gel surface, J. Chem. Soc., Chem. Comm., 358-360. Davis M E., Katz A. and Ahmad W.R. (1996) Rational catalysts design via imprinted nanostructured materials, Chem. Mater., 8,1820-1839. 

Much attention has been paid to molecular design of effective guest molecules to induce the photochemical flip of polarization in ferroelectric LC systems. An azobenzene derivative with a chiral cyclic carbonate group (13) was designed to induce a large value of polarization and examined as a chiral dopant to induce a... 

Once the starting point of the synthesis is established using CHIRON then another program, REACCS, from Molecular Design Limited (MDL), can be used to fill in the details of the synthetic pathway that leads to the chiral product. 

Y. Dobashi, A. Dobashi, H. Ochiai and S. Kara, New, rational molecular design for chiral recognition involving application of dual hydrogen bond association,/. Am. Chem. Soc., 1990,112, 6121-6123. 

Stage. However, molecules which are optically-resolved must crystallise in a non-centrosymmetric space group, and so in passing from the molecular design to the generation of the crystal, incorporation of a chiral centre or centres could be advantageous. Alternatively, one can rely on luck and nature to produce the desired crystal form ... 

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