Resolution Origins and Control

Use as chiral auxiliary. Whitcscll1 has reviewed use of this chiral alcohol (1), particularly as compared with that of (-)-menthol and (lR)-(+)-8-phenylmcnthol. One advantage is that both enantiomers of 1 are available by resolution of trans-2-phcnyl-cyclohcxanol by means of enzymatic hydrolysis of the esters and that 2-substitutcd cyclohexanols arc readily available. Although this chiral auxiliary was used originally for control of enc reactions of glyoxylatcs, it is also useful for asymmetric alkylation of enolatcs, and for control of various cycloaddition reactions. 

A-TRISPHAT anion intercalates between two cationic complexes providing a onedimensional supramolecular chain. To our knowledge this example represented the first direct observation of chiral recognition between the A-TRISPHAT and any chiral organometallic species at least in the solid state. We also feel that this resolution originates from supramolecular control. 

One of the approaches described in this paper entails keeping the reaction rate and partial pressure of product gas constant during calcination by changing the tempo ature appropriately by means of a feedback loop. This technique has its origins in Controlled Rate Thermal Analysis (CRTA), which was developed by Rouquraol [4] to provide improved kinetic data and higher resolution in thermal analysis. He showed that constant reaction rate conditions could be of benefit also in preparing materials with specifiable surface areas. 

Owing to the fully reversible equilibrium nature of the aldol addition process, enzymes with low diastereoselectivity will typically lead to a thermodynamically controlled mixture of erythro/threo-isomers that are difficult to separate. The thermodynamic origin of poor threo/erythro selectivity has most recently been turned to an asset by the design of a diastereoselective dynamic kinetic resolution process by coupling of L-ThrA and a diastereoselective L-tyrosine decarboxylase (Figure 10.47)... 

Chirality at surfaces can be manifested in a number of forms including the intrinsic chirality of the surface structure and even the induction of chirality via the adsorption of achiral molecules onto achiral surfaces. The ability of STM to probe surfaces on a local scale with atomic/molecular resolution has revolutionized the understanding of these phenomena. Surfaces that are globally chiral either due to their intrinsic structure or due to the adsorption of chiral molecules have been shown by STM to establish control over the adsorption behavior of prochiral species. This could have profound consequences for the understanding of the origin of homochirality in life on Earth and in the development of new generations of heterogeneous chiral catalysts that may, finally, make a substantial impact on the pharmaceutical industry. 

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