Intramolecular reactions involving positions C(2), C(6) and (C2), C(7) in the bicyclo[3.3.1]nonane ring system

Abstract

Reactions likely to involve C(2)–C(6) and C(2)–C(7) intramolecular reactions in bicyclo[3.3.1]nonane derivatives are discussed in terms of the conformations available to the ring system. While endo-6-hydroxybicyclo[3.3.1]-nonan-2-one (11) incorporated three deuterium atoms (excluding the hydroxy-group) on heating with NaOD, the exo-isomer (17) exchanged the six hydrogens adjacent to the oxygenation functions but not the carbinyl proton. Evidence is presented favouring a stereospecific base-induced 2,6-hydride migration, most probably proceeding via a twin-twist boat transition state. Treatment of 6,6-ethylenedioxy-2-methoxymethylenebicyclo-[3.3.1]nonane (36) with aqueous HCl in acetone produced 2-hydroxyprotoadamantan-10-one (38) in high yield. This process resulted from hydrolysis of the oxygenated groups thereby liberating the endo-keto-aldehyde intermediate (37) which underwent subsequent intramolecular aldol condensation between the C(2) aldehyde and C(7).