Development of New Molecular Recognition Chemistry using Organoaluminums

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Exceptionally bulky, oxygenophilic methylaluminum bis(2,6-di-tert-butyl-4-methylphenoxide) (MAD) can be utilized as a Lewis acidic receptor for complexation with a series of carbonyl compounds, ether, and epoxides. By using low-temperature ^<13>C NMR spectroscopy, MAD was found to coordinate strongly to oxygen-containing substrates in the order of amides, aldehydes, ketones or esters, epoxides, and ethers. Even structurally very similar carbonyl compounds can be easily separated by MAD. This observation enabled the highly regio- and stereocontrolled Diels-Alder reaction of unsymmetrical fumarates based on the discrimination of two different fumarate carbonyls with MAD. The high recognition ability of MAD is successfully applied to the clean separation of structurally very similar ethers by complexation chromatography using MAD-type, polymeric organoaluminum reagents. This polymeric organoaluminum column is also employable as solid-state reactor for catalytic rearrangement of epoxides to carbonyl compounds. Based on the molecular recognition chemistry with MAD, a new type of chiral organoaluminum reagents have been developed which are prepared from trimethylaluminum and optically active 3,3'-bis(triarylsilyl)binaphthols. These chiral organoaluminum reagents are highly useful for asymmetric Claisen rearrangement of allylic vinyl ethers and asymmetric Diels-Alder reaction of dienes and unsaturated esters.