Bidentate Lewis acid catalysts in asymmetric synthesis*
Keiji Maruoka
Department of Chemistry, Graduate School of Science,
Kyoto University, Kyoto 606-8502, Japan
Abstract: The chemistry of bidentate Lewis acids belongs to
an unexplored field of science, and so far has been only poorly studied.
This paper illustrates the design of several bidentate Al and Ti Lewis
acids, and their successful application to selective organic synthesis,
particularly to asymmetric synthesis. For example, a new, chiral bidentate
Ti(IV) complex is successfully designed by adding commercially available
Ti(OPri)4 and (S)-binaphthol sequentially to 2,2'-bis(tritylamino)-4,4'-dichlorobenzophenone
in CH2Cl2, 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) catalyst
exhibits 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.
*Lecture presented at the 11th IUPAC International
Symposium on Organometallic Chemistry Directed Towards Organic Synthesis
(OMCOS-11), Taipei, Taiwan, 22-26 July 2001. Other presentations are
presented in this issue, pp.1-186.
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