Condensed cyclic and bridged-ring system. Part 9. Stereocontrolled synthesis and X-ray structural analyses of cis-3,4,4a,9,10,10a-hexahydro-1,4a-ethanophenanthrene-2(1H),12-dione and trans-3,4,4a,9,10,10a-hexahydro-3,4a-ethanophenanthrene-2(1H), 12-dione

Abstract

The isomeric bridged diketones cis-3,4,4a,9,10,10a-hexahydro-1,4a-ethanophenanthren-2(1H), 12-dione (5) and trans-3,4,4a,9,10,10a-hexahydro-3,4a-ethanophenanthren-2(1H),12-dione (6) have been synthesised by highly regioselective intramolecular aldol condensations through the stereochemically defined cis- and trans-2,2-ethylenedioxy-1,2,3,4,4a,9,10,10a-octahydrophenanthren-4a-ylacetaldehydes (3f) and (4f) and their structures have been established by X-ray analysis. The isomeric diketones (5) and (6) undergo cleavage with toluene-p-sulphonic acid in boiling benzene leading finally to the known keto-ester (3a) and a new spiro-keto acid (14). Carbon-13 n.m.r. spectra of these and the other compounds reported in this paper have been measured and assigned.