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

Aldol condensation of 8‐fluoro‐5,11‐dihydro‐10 H ‐dibenzo[ a , d ]cyclohepten‐10‐one and (4 S )‐2,2‐dimethyl‐1,3‐dioxolane‐4‐carbaldehyde provides access to the corresponding ( E , Z )‐α,β‐unsaturated ketones with a (4 R )‐chiral 11‐substituent. Subsequent hydrogenation affords a mixture of (11 R )/(11 S )‐epimeric ketones, which undergoes base‐catalysed equilibration resulting in selective crystallisation of the (11 R ) 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)