DEVELOPMENT OF MODIFIED CYCLODEXTRINS FOR SELECTIVE ORGANIC SYNTHESIS

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Development of new method for the selective synthesis of valuable chemicals in industry is quite important from the viewpoints of ecology, resource, energy, and so on. Previously we reported that cyclodextrins, cyclic oligomers of glucose, are highly effective for the selective organic synthesis. Various fine chemicals were synthesized in almost 100 % selectivities and in high yields. However, the reactions catalyzed by cyclodextrins are rather limited, since the hydroxyl residues are only the catalytic ones available. Still better catalysts should be obtained if appropriate functional residues are introduced to cyclodextrins by chemical modification.Here we succeeded in the selective synthesis of 4-(hydroxymethyl)phenol from phenol and formaldehyde and of 4-(hydroxyethyl)phenol from phenol and acetaldehyde, by use of various modified cyclodextrins. The structures of the molecular complexes, formed in these reaction mixtures, are determined by NMR spectroscopy. The hydroxyl residue introduced by the chemical modification to the primary hydroxyl side of the cavity form hydrogen bond with the formaldehyde, resulting in the activation of the formaldehyde for the reaction. In addition, the formaldehyde is fixed in the vicinity of the papa-carbon of the phenol by the hydrogen bonding, and thus the electrophilic attack by the formaldehyde selectively proceeds at the para-carbon. Potentialities of the modified cyclodextrins as practical catalysts are strongly indicated.