アミン-N-オキシドを触媒とする新規不斉合成反応の開発

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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-induced organic reactions. (1) Bipyridine N,N'-dioxide was found to be a felicitous ligand for methyltrioxorhenium-catalyzed epoxidation of olefins with hydrogen peroxide. (2) A new catalytic, enantioselective allylation of aldehydes with allyltrichlorosilanes exploiting (S)-3,3'-dimethyl-2,2'-biquinoline N,N'-dioxide as a catalyst affords homoallylic alcohols in virtually complete diastereoselectivities and high enantioselectivities of up to 92% ee, wherein the use of diisopropylethylamine as an additive has proven to be crucial for the acceleration of the catalytic cycle. It is also noteworthy that the above finding represents the first successful example of asymmetric reactions utilizing amine N-oxide as a chiral catalyst. A one-pot, convenient method for the preparation of optically active homoallylic alcohols from allyl halides was developed based on the above allylation. Allyltrichlorosilanes were generated in situ from allyl halides and trichlorosilane in the presence of cuprous chloride and tertiary amine. Without isolation of the allyltrichlorosilanes, benzaldehyde and chiral biquinoline N,N'-dioxide were introduced into the same flask, producing the corresponding homoallylic alcohols in good to high enantioselectivities. (3) (S)-3,3'-dimethyl-2,2'-biquinoline N,N'-dioxide-cadmium chloride complex was proven to be a good catalyst for the asymmetric conjugate addition of thiols to enones with enantioselectivit of up to 79% ee.