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A highly, stereo- and regioselective Meerwein-Ponndorf-Verley-Aldol etherification process of enolizable aldehydes is described. This new transformation is catalyzed by trifluoroacetic acid. The method also allows cross-aldol reactions with alpha-branched enolizable aldehydes and thus provides access to defined configured quaternary stereogenic centers.

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Asymmetric Acid-Catalyzed Meerwein-Ponndorf-Verley-Aldol Reactions of Enolizable Aldehydes. -The asymmetric version of the reaction is carried out under neat conditions using an alcohol, catalytic amount of TFA and dry LiClO4 as an additive and methyl silyl ether as a chiral hydrogen source. The reaction proceeds using only one or two different enolizable aldehydes. Intramolecular version of the reaction is demonstrated [cf. (XVIII)]. -(SEIFERT, A.; SCHEFFLER, U.; MARKERT, M.; MAHRWALD*, R.; Org.