Reactivity of alicyclic 1,5,9-triketones toward five-, six-, and seven-membered rings in acidic medium. Stereochemistry of intramolecular cyclization products

Among nine alicyclic 1,5,9-triketones with differently fused 5-, 6-, and 7-membered rings in the molecule, existing as mixtures of 3–6 diastereomers, only those containing at least two 6-membered rings were capable of intramolecular cyclization in acidic medium (HCl, EtOH). The diastereomer mixture underwent stereoselective transformation, giving one major cyclization product. The relative configuration of chiral centers in cyclization products obtained under acidic or basic conditions was compared by X-ray crystallography. The differences were caused by divergent stereochemical outcome at the first stage of cyclization.