Utilizing a chiral bicyclic imidazole organocatalyst and adopting a continuous injection process, an alternative route has been developed for the efficient synthesis of chiral phthalidyl ester prodrugs via dynamic kinetic resolution of 3hydroxyphthalides through enantioselective acylation (up to 99 % ee). The computational studies suggest a general base catalytic mechanism differing from the widely accepted nucleophilic catalytic mechanism. The structure analysis of the key transition states shows that the CH-p interactions and not the previously considered cation/p-p interactions between the catalyst and substrate is the dominant factor giving rise to the observed stereocontrol. Figure 1. Representative ester-based prodrugs.
A stereodivergent Pd/Cu catalyst system for asymmetric desymmetric alkylation of allylic geminal dicarboxylates has been developed, which was successfully applied to the asymmetric synthesis of βhydroxycarbonyl motifs bearing a versatile carbon-carbon double bond in an enantio-and diastereodivergent manner. A wide scope of substrates including challenging alkyl-substituted, 2-substituted, and 3,3'disubstituted allylic species are compatible with this catalytic system, delivering the substituted products in high to excellent yields and with excellent diastereoselectivities (up to >20:1 dr) and enantioselectivities (up to >99% ee). Furthermore, the mechanism of this dual Pd/Cu catalytic system including: a) the desymmetrization process of geminal dicarboxylates; b) the origin of regioselectivity (branched or linear); c) the enantio-and diastereoselectivity observed by changing the combinations of two chiral metal catalysts, have been carefully investigated by theoretical calculation.
Using maximum extraction of carbon-containing components the content of amorphous silicon dioxide was increased in the rice husk solid residue. In accordance with the hypothesis about the mechanism of extracting carbon-containing components from rice husk by liquid extractants, proper extractants were selected. The effect of main technological factors including a process temperature, time and concentration of the extractants was determined.
Utilizing a chiral bicyclic imidazole organocatalyst and adopting a continuous injection process, an alternative route has been developed for the efficient synthesis of chiral phthalidyl ester prodrugs via dynamic kinetic resolution of 3hydroxyphthalides through enantioselective acylation (up to 99 % ee). The computational studies suggest a general base catalytic mechanism differing from the widely accepted nucleophilic catalytic mechanism. The structure analysis of the key transition states shows that the CH-p interactions and not the previously considered cation/p-p interactions between the catalyst and substrate is the dominant factor giving rise to the observed stereocontrol. Figure 1. Representative ester-based prodrugs.
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