Résumé The methylene-de-oxo-bisubstitution reaction between dimethyl isopropylidene malonate and the C-15 β-methylenealdehyde 1 which could serve as substitute for E β- ionylideneacetaldehyde 2, produces stereoselectively the E, E olefin. Hence, new stereoselective syntheses of 13 E and 13 Z retinoic acids were described.