Lewis surfactant-combined catalysis

Since the seminal contributions in the 1980s of Breslow [la] for the Diels-Alder reaction and Kuntz and Ruhrchemie for hydroformylation reactions [lb], there has been an upsurge in interest in using water as the solvent, not only to enhance the reaction rates, but also to perform organic reactions that would otherwise be impossible, or to elicit new selectivities. Several reviews have been devoted specially to such a use [2], which nevertheless does not exclude the possibility of further catalyzing the reactions with Lewis acids [3] or the use of Lewis acid-surfactant-combined catalysis (LASC) [4],... 

This type of catalyst was named Lewis acid-surfactant combined catalyst (LASC), and was expected to possess the characters of both a Lewis acid and a surfactant. Sc(DS)3 showed quite high activity in aldol reactions in water without using any organic solvents (Scheme 12.63). A kinetic study on the initial rate of this reaction revealed that the reaction in water is about 130 times faster than that in dichloromethane. It was assumed that hydrophobic reaction environments were created by combining Sc(DS)3 and substrates under the conditions, and that they were concentrated in water to realize efficient catalysis. Interestingly, under neat conditions, the reaction proceeded much slower to give the desired adduct in a much lower yield. 

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