Development of new function of N-oxide based on the electron-donating property of oxide oxygen

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Although it is well documented that amine N-oxides act as powerful electron-pair donors to form complexes with a variety of acceptor molecules, synthetic utility of amine N-oxides as ligands or catalysts still remains to be developed. We have developed the following N-oxide-mediated organic reactions. 1.Optically active allenic and homopropargylic alcohols were selectively obtained by a chiral N-oxide-catalyzed reaction of aldehydes with propargyltrichlorosilane and allenyltrichlorosilane, prepared in situ from propargyl chloride. 2.An enantioselective ring opening of meso-epoxides with tetrachlorosilane in the presence of diisopropylethylamine exploiting chiral bipyridine N,N'-dioxides as catalysts affords the corresponding chlorohydrins in high enantioselectivities of up to 90% ee. 3.Chiral N,N'-dioxides and monodentate N-oxides were employed as catalysts in catalytic, enantioselective aldol reactions of trichlorosilyl enol ethers. The reactions of acyclic enol etheis using N,N'-dioxides resulted in the anti-adducts from (E)-enol ethers and the syn-adducts from (Z)-enol ethers. The reactions of cyclic (E)-enol ethers using N,N'-dioxides gave the anti-adducts, whereas monodentate N-oxides predominantly gave the syn-adducts. 4.Chiral N,N'-dioxide-cadmium iodide complex has been shown to catalyze enantioselective conjugate additions of thiols to cyclic enones and enals. The sulfides are generated in high yields and in good enantioselctivities up to 78% ee using 1 mol % of the chiral catalyst. The present reaction provides the first example of utilizing a cadmium complex as a catalyst in enantioselective reaction. 5.A catalytic, enantioselective Michael addition of β-keto esters to α,β-unsaturated carbonyl compounds was achieved by using a chiral biquinolme N,N'-dioxide-scandium trifluoromethanesulfonate complex as a catalyst. The corresponding Michael adducts were obtained in high yields and with enantioselectivities up to 84% ee.