Design of novel functional oxide and its application to catalytic reactions

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Organocatalysis has been one of the current hot topics in the field of synthetic chemistry because of its environmentally benign nature. Recently, asymmetric organocatalyses utilizing neutral Lewis bases attracted much attention because it led to the emergence of new types of chiral ligands based on functional oxide compounds. Phosphine oxide has high polarity and relatively low Bronsted basicity, whose reactivity is expected to be similar to those of such Lewis bases. Moreover, various types of chiral phosphine oxides can be easily obtained by the simple oxidation of commercially available chiral phosphines. However, the examples of the application of chiral phosphine oxides to asymmetric organocatalyses are still limited. We investigated the catalytic activity of BINAPO, which is easily prepared from the most common chiral phosphine ligand BINAP. We found that BINAPO was an effective catalyst for the enantioselective allylation of aldehyde with allyltrichlorosilane and the enantiosel … More ective aldol reaction of trichlorosilyl enol, wherein the allylated adducts or aldol adducts were obtained in high diastereo- and enantioselectivities (up tp 96% ee). BINAPO was found to be effective in the enantioselective ring opening of meso-epoxides with tetrachlorosilane in the presence of diisopropylethylamine, affording the corresponding chlorohydrins in high enantioselectivities of up to 90% ee. An aldol reaction of trimethoxysilyl enol ether catalyzed by lithium binaphthoxide was also developed. The aldol reaction of trimethoxysilyl enol ether derived from cyclohexanone under anhydrous conditions predominantly afforded the anti-aldol adduct with moderate enantioselectivity, whereas the reaction under hydrous conditions predominantly resulted in the syn-adduct and the enantioselectivity of the syn-adduct was considerably improved. The best enantioselectivity was obtained in the reaction of trimethoxysilyl enol ether derived from 1-indanone with cyclohexanecarboxaldehyde (97% ee (syn)). This is the first example of an aldol reaction of trimethoxysilyl enol ether catalyzed by a chiral base. Less