Spongiane diterpenoids are bioactive natural products isolated exclusively from sponges
and marine shell-less mollusks (nudibranchs). They are believed to be spongian-derived
metabolites from the sponges which are sequestered by soft corals, hydroids and other sessile
marine invertebrates and used as food resources.
Most of these compounds play a key role as eco-physiological mediators and are of
interest for potential applications as therapeutic agents[1, 2].
Synthesis of spongia-13(14)-en-12,15-dione (1) was accomplished starting from (-)-
sclareol (2), according to the Scheme 1 given below.

Scheme 1. Reagents and conditions: (a) mCPBA, CH2Cl2, r.t., over night, 65%%; (b) (iPrO)3Al, PhMe, reflux,
18 h, 52%; (c) H2SO4-Dioxane, 90oC, 4 h, 37%; (d) Na2CrO4, AcOH, Ac2O, C6H6, 80oC, 24 h, 82%.
Firstly, starting material (2) was transformed into methyl ent-isocopalate (3) in four steps.
Then, the last was involved in a short synthetic sequence of epoxidation with m-CPBA and
aluminium isopropoxide rearrangement [3] to yield the allylic alcohol (5) in 52% overall yield,
which was treated with H2SO4 in dioxan to give a -lactone (6). Sodium chromate oxidation of
compound (6) led to the formation of spongiane ,-unsaturated keto-lactone (1), functionalized
in C-12 position.
References:
1. Keyzers, R. A.; Northcote, P. T.; Davies-Coleman, M. T. Nat. Prod. Rep., 2006, 23, 321–334.
2. González, M. A. Curr. Bioac. Comp., 2007, 3, 1-36.
3. Mischne, M. P.; Sierra, M.; Riiveda, E. A. J. Org. Chem., 1984, 49, 2035-2037.