Studies for a Diastereoselective Synthesis of the Tetracyclic Diterpenic Diol Stemarin. A Model Work for the Preparation, from an 8( 9)-Podocarpen-14-one, of a Key Intermediate by the Wiesner Photochemical Method.-The preparation of the alcohol (VIII) from the octalenone (I) serves as a model approach for the synthesis of the diterpene stemarin (IX). Key step in the sequence is the photochemical addition of allene (II) to the octalenone (I). -(BARTOLETTI, A.; BERETTONI, M.; CATTERUCCIA, F.; DE CHIARA, G.; BETTOLO, R. M.; MASTRANGELI, C.; SCARPELLI, R.; TOZZI, C.; LAMBA, D.; Gazz.

Dedicated to Prof. Alessandro Ballio on the occasion of his 75th birthday (14.VI.96)A novel preparation of methyl~(l3S)-l>hydroxyisoatisiren-18-oate (4), a key-intermediate in a synthesis of (+)-methyl trachyloban-18-oate ((+)-1), from (-)-abietic acid, is described. Since (-)-1 has been previously converted into (-)-methyl l6-oxo-17-norkauran-l8-oate ((-)-16), our preparation of 4 constitutes also a formal total synthesis, from (-)-ahietic acid, of (+)-16. Key steps in this approach were the allene photoaddition to podocarp-8(14)-en-13-one (5) and the conversion of the endo-toluene-4-sulfonate 11 into the ex0 -benzoate 12b.

A Formal Total Synthesis of (+)-Methyl Trachyloban-18-oate and (+)-Methyl 16-Oxo-17-norkauran-18-oate: Regio-and Diastereoselective Preparation of Methyl (13S)-13-Hydroxyisoatisiren-18-oate from (-)-Abietic Acid.-The key steps in the novel synthesis of the hydroxyisoatisirenoate (X), a precursor of (+)-methyl trachylobanoate and (+)-methyl 16-oxo-17-norkauranoate, are regio-and diastereoselective allene photoaddition to the enone (II) and conversion of the sulfonate (VII) to the benzoate (IX). -(BERETTONI, M.; DE CHIARA, G.; IACOANGELI, T.; LO SURDO, P.; MARINI BETTOLO, R.; MONTAGNINI DI MIRABELLO, L.; NICOLINI, L.; SCARPELLI, R.; Helv.