Parallel simultaneous kinetic resolution

The resolution of rac-20 represents a less common form of catalytic kinetic resolution (parallel kinetic resolution) [9]. In conventional kinetic resolution, one substrate enantiomer reacts preferably to leave behind the unreacted isomer in high optical purity (e.g., rac-18 (k)-19 in Scheme 4). In this instance, both starting material enantiomers undergo catalytic alkylation to give constitutional isomers. Since both enantiomers are consumed simultaneously, as the reaction proceeds, the amount of slow enantiomer (relative to the unreacted fast enantiomer) does not increase. Therefore, product ee remains high, even at relatively high conversions. 

Parallel kinetic resolution is a developing area of asymmetric synthesis which facilitates the simultaneous conversion of both enantiomers of a racemic mixture into useful products. Pedersen and co-workers have recently reported the first Horner-Wadsworth-Emmons procedure that allows the parallel kinetic resolution of racemic aldehydes. 

Benzyl alcohols have been resolved in parallel kinetic resolutions that use two reagents with selectivities for opposite isomers to make carbonates in simultaneous reactions (10.27).55... 

Recently, a cascade process for the simultaneous preparation of two enantiopure secondary alcohols by the same ADH was investigated [12]. In this work, a kinetic oxidative resolution of different secondary alcohols was coupled with the irreversible asymmetric reduction of selected prochiral activated ketones, that is, a-chloro ketones (Scheme 11.5a). The proposed strategy, named PIKAT (parallel intercoimected kinetic asymmetric transformations), represents an example of redox neutral (or self-sufficient) cascade, with no additional reducing or oxidizing reagents being required. Moreover, the reaction was catalyzed by a single enzyme in the presence of catalytic amounts of the cofactor. As the outcome of the cascade process is a mixture of two different enantioenriched products, substrates were properly selected on the basis of different physical properties. 

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See also in sourсe #XX -- [ ]

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