Diastereomeric Enols and Enol Derivatives of 8-Fluoro-5,11-dihydro-10H-dibenzo[a,d]cyclohepten-10-one with a Chiral 11-Substituent

Aldol condensation of 8-fluoro-5,11-dihydro-10H-dibenzo[a,d]cyclohepten-10-one and (4S)-2,2-dimethyl-1,3-dioxolane-4-carbaldehyde provides access to the corresponding (E,Z)-α,β-unsaturated ketones with a (4R)-chiral 11-substituent. Subsequent hydrogenation affords a mixture of (11R)/(11S)-epimeric ketones, which undergoes base-catalysed equilibration resulting in selective crystallisation of the (11R) epimer. The enol intermediate and acyclic enol derivatives are shown to exist as two slowly interconverting conformers with a high inversion barrier of the 10,11-disubstituted ring. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)