Tricyclic challenges: synthetic approaches toward dodecahydrocyclopenta[a]indenes

Tetrahydrospiro[1,3-dioxolane-2,1′-pentalen]-4′-ones were stereoselectively converted to either (cis,anti,cis)- or (cis,syn)-linear dodecahydrocyclopenta[a]indene isomers employing a 1,4- or 1,2-conjugate addition of organometallic reagents and an intramolecular aldol reaction as the key steps. The relative configuration of the products was determined by X-ray crystal structure analysis and 1D NOE spectroscopy.