Aldol Condensation: A Stereoselective Approach to Tetrahydrophenanthrene Derivatives and 3-Oxa-bicyclo[3.3.1]nonan-6-ones

Aldol condensation of the lithium enolate of 2 with m-methoxyphenylacetaldehyde afforded 3a and 3b with good erythro steroselectivity (5:95). Acid catalyzed cyclization of 3a gave the tetrahydrophenanthrene 5 while 3b yielded the 3-oxobicyclononanones 6. A mechanism is discussed to account for the derived products and a detailed H-1 NMR structural analysis of the [3.3.1] bicyclic systems is utilized to indirectly characterize the threo and erythro alcohols 3a and 3b.