Methyl trachyloban-19-oate

The asymmetric syntheses of (-)-methyl kaur-16-en-19-oate and (-)-methyl trachyloban-19-oate was achieved by M. lhara and co-workers. One of the last transformations was the deoxygenation of the ketone carbonyl group of the tetracyclic intermediate, which was effected by the Wolff-Kishner reduction. Under the strongly basic conditions the ester functionality was hydrolyzed, so an esterification using diazomethane was necessary as the final step. The major deoxygenated product was (-)-methyl kaur-16-en-19-oate (59%). The minor product was identified as (-)-methyl trachyloban-19-oate (16%). 

Methyl kaur-16-en-19-oate (-)-Methyl trachyloban-19-oate... 

In Bettolo and co-workers approach to (+)-methyl trachyloban-18-oate (16), enone 13 was subjected to a photocycloaddition with 1,2-propadiene (1) to afford the [2 + 2]-cycloadduct 14 as a single product in 67% yield (Scheme 19.3) [5]. The addition proceeded exclusively from the /3-face. The resulting exocyclic olefin was eventually converted to a ketone using osmium tetroxide and NaI04 and taken on to 15, constituting a formal total synthesis of 16. 

Scheme 19.3 A formal total synthesis of (+)-methyl trachyloban-18-oate.

Ferguson, G., McCrindle, R., Murphy, S. T., and Parvez, M. 1982. Further diterpenoid constituents of Helianthus annuus I. Crystal and molecular-structure of methyl-er7M5-beta-hydroxy-trachyloban-19-oate. J. Chem. Res.-S.t 8, 200-201... 

---