Proline-catalyzed asymmetric aldol reactions between ketones and α-unsubstituted aldehydes

[GRAPHICS] With this communication we extend the methodology of proline-catalyzed direct asymmetric aldol reactions to include a unsubstituted aldehydes as accepters. This important aldehyde class gives the corresponding aldols in 22-77% yield and up to 95% ee when the reactions are performed in pure acetone or in ketone/chloroform mixtures. On the basis of these results we have developed a concise new synthesis of (S)-ipsenol.