SPONGIAN PENTACYCLIC DITERPENES - STEREOSELECTIVE SYNTHESIS OF APLYROSEOL-1, APLYROSEOL-2 AND DEACETYLAPLYROSEOL-2

Natural spongian pentacyclic diterpenes aplyroseol-1 19, aplyroseol-2 18 and deacetylaplyroseol-2 17 have been synthesized in enantiomerical ly pure form from (+)-podacarp-8(14)-en-13-one 3. Key intermediate in these syntheses is a suitably substituted acid-dialdehyde 2, which is prepared from enone 3 by a sequence of transformations involving stere oselective introduction of a C-7 oxygen functionality, photoaddition o f acetylene to the C(8)-C(14) double bond to form a cyclobutene ring s ystem, reductive cyanation of the C-13 carbonyl group, hydrolysis of t he resulting nitrile group, and ozonolysis of the cyclobutene moiety. An intramolecular participation of the 7alpha-hydroxy group in the hyd rolysis of the 13alpha-nitrile 8 is set in focus.