Design of Fine Acid Base Catalysts and their Utility in Selective Organic Synthesis

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In this research project, we focused our attention on the rational design of truly efficient acid/base catalysts for the development of synthetic processes in order to achieve the high reactivity and selectivity, not observable by ordinary, acid/base catalysts. In the sophisticated Lewis acid chemistry, a new, chiral bidentate Ti(IV) complex was successfully designed and can be utilized for simultaneous coordination to aldehyde carbonyls, thereby allowing the precise enantioface discrimination of such carbonyls for a new catalytic, practical enantioselective allylation of aldehydes with allyltributyltin. This chiral bidentate Ti(IV) complex has been successfully applied to asymmetric 1, 3-dipolar cycloaddition of nitrones or diazoacetates. On the other hand, phase transfer catalysis is a very useful approach that typically involves simple experimental operations, mild reaction conditions, inexpensive and environmentally benign reagents and solvents, and the large-scale reactions. Accordingly, structurally rigid, chiral spiro ammoniurn salts derived from commercially available (S)- or (R)-binaphthol have been designed as new C_2-symmetric chiral phase transfer catalysts and successfully applied to the highly efficient, catalytic enantioselective synthesis under mild phase transfer conditions. Quite recently, we have successfully designed simplified, yet very active chiral phase transfer catalysts for practical asymmetric synthesis of α-alkyl- and α,α-dialkylamino acids. In addition, chiral, helical-type phase transfer catalysts were newly designed for effecting asymmetric Strecker reaction for large-scale production of sterically hindered α-alkylamino acids. A bowl-shaped organometallic host, tris(2, 6-diphenylbenzyl)-silyl, -germyl, and -tin compounds can be prepared, and applied to selective organic transformations.