Enantioselective synthesis of the fragrance trans-magnolione under asymmetric phase transfer catalysis

The stereoselective synthesis of the fragrance trans-magnolione (1) through conjugate Michael addition of alkyl acetoacetates to 2-pentyl-2-cyclopentenone (2) under solid/liquid phase transfer catalysis (PTC) is reported. Under optimized conditions, the 1,4-addition of tert-butyl acetoacetate to enone 2 catalyzed by N-9-anthracenylmethylquininium chloride (4) affords, after hydrolysis and decarboxylation, trans-(2S,3S)-1 with 85/15 d.r. and 74% ee. The use of the pseudo-enantiomeric catalyst N-9-anthracenymethylquinidinium chloride (5) allows obtaining the enantiomer trans-(2R,3R)-1 with comparable enantio- and diastereoselectivity. © 2005 Published by Elsevier SAS on behalf of Académie des sciences.