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Synthesis 2002(14): 1956-1958
DOI: 10.1055/s-2002-34366
PAPER
© Georg Thieme Verlag Stuttgart · New York

Enhancement of Lewis Acidity by Ligand-Defined Metal Geometry: A Catalytic Allylation of Aldehydes with Allyltrimethylsilane

Motomu Kanaia,b, Akiyoshi Kuramochia, Masakastu Shibasaki*a
a Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo 113-0033, Japan
Fax: +81(3)56845206; e-Mail: mshibasa@mol.f.u-tokyo.ac.jp;
b PRESTO, The Japan Science and Technology Corporation (JST)
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Publication History

Received 9 July 2002
Publication Date:
26 September 2002 (online)

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Abstract

A highly Lewis acidic aluminum complex was produced using a tridentate ligand 1. The enhanced Lewis acidity of 1-Al was attributed to the combination of a stereoelectronic effect and an electrostatic effect. Comparison with an unstrained complex 4-Al indicated that the ligand-defined sp3 geometry of the aluminum in 1-Al led to the lower LUMO level and the larger LUMO coefficient on the aluminum. 1-Al promotes a catalytic allylation of aromatic aldehydes using allyltrimethylsilane. A catalytic amount of excess ligand added to the aluminum was important for high chemical yield. The excess ligand might act as a proton source to facilitate ligand exchange on the highly Lewis acidic aluminum.

Key words

Lewis acid - metal - ligand - allylation - aluminum

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