Design of Metal Artificial Enzymes and the Application to Fine Organic Synthesis

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In this research project, we focused our attention on the bidentate Lewis acid chemistry. (2,7-Dimethyl-1, 8-biphenylenedioxy)bis(dimethylaluminum) can be successfully prepared as a bidentate Lewis acid for the simultaneous coordination to carbonyl substrates. The high, simultaneous coordination ability of the bidentate organoaluminum reagent toward carbonyls is emphasized in comparison with the corresponding monodentate reagent, and characterized by evaluating the double electrophilic activation of ketonic substrates in the reduction and Mukaiyama aldol reaction. Another interesting feature of the bidentate Lewis acid in organic synthesis is the regio- and stereocontrolled Michael addition of a silyl ketene acetal to benzalacetone, where bidentate aluminum Lewis acid exhibits the totally opposite E selectivity to a monodentate counterpart.(Anthraquinone-1, 8-dioxy)bis(triisopropoxytitanium) was also successfully developed as a bidentate Lewis acid catalyst for the simultaneous coordin … More ation to carbonyl substrates. The high double-activation ability of the bidentate Ti catalyst toward carbonyls is emphasized using several synthetic examples (i.e., ketone reduction and aldehyde allylation) in comparison with the corresponding monodentate Ti catalyst The simultaneous coordination complex formation of these bidentate aluminum and titanium reagents with DMF as a carbonyl substrate is characterized by 13C NMR spectroscopy.A new, chiral bidentate Ti(LV) 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. The requisite chiral bidentate Ti(IV) catalysts can be readily prepared by adding commercially available titanium tetraisopropoxide and (S)-binaphthol sequentially to 2,2'-bis(tritylamino)benzophenone derivatives. These chiral bidentate Ti catalysts exhibit uniformly high asymmetric induction as well as high chemical yields for various aldehydes. The present enantioselective allylation is highly chemoselective in the presence of other carbonyl moieties such as ketone, ester, and amide functionalities as exemplified by the allylation of 4-acetoxy-3-acetylbenzaldehyde with excellent chemo- and enantioselectivity. Less