Cascade enantiopure -alcohols

With this new methodology in hands, Hu et al. [166] explored the trapping of the 1,4-addition intermediate with a different electrophile for the development of a new MCR. RhjCOAc) was again the most active catalyst in the 1,4-addition/aldol-type intramolecular cascade reaction. Under the optimized reaction conditions, this three-component reaction worked well with a broad family of bifunctional substrates 135 bearing different substituents on the aryl group next to the enone moiety and a variety of alcohols 136 (Scheme 3.63). In all cases, 1-indanols 137 were obtained in 60-83% yield and with complete diastereoselectivity. Enantiopure 1-indanol was obtained employing a L-menthol-derived diazo compound. The intermolecular four-component version was also attempted, but the formation of the desired product was not observed. 

Table 4.2 Selected results of the redox-neutral oxidation-transamination cascade using enantiopure and racemic secondary alcohols as substrate (Scheme 4.5).

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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