Carbocyclic Construction: Aquatolide (Hiemstra), Spongiolactone (Romo), Ar-Tenuifolene (Ávila-Zárraga), Antroquinonol (Weng/Chen), (Z)-2β-Hydroxy-14-hydro-β-Santalol (Ishigami), Cortistatin A (Chiu)

The structure of Aquatolide, isolated from the Mediterranean flower Asteriscus aquaticus, was recently corrected to 3. Henk Hiemstra of the University of Amsterdam devised (Org. Lett. 2015, 17, 3892. DOI: 10.1021/acs.orglett.5b01888) a synthesis of 3 based on the elegant photocyclization of 1 to 2.

Spongiolactone (7), isolated from Spongionella gracilis, shows antineoplastic activity. The key step in the synthesis of 7 reported (Chem. Eur. J. 2015, 21, 1425. DOI: 10.1002/chem.201405980) by Daniel Romo of Texas A&M was the diastereoselective cyclization of 4 to lactone 6, mediated by 5.

In the course of a synthesis of Ar-Tenuifolene (10), José Gustavo Ávila-Zárraga of the Universidad Autónoma de México reported (Tetrahedron Lett. 2015, 56, 5321. DOI: 10.1016/j.tetlet.2015.07.087) the remarkable thermal rearrangement of 8 to 9. It would be interesting to explore the generality of this transformation.

Antroquinonol (13), from Antrodia camphorata, is an effective anti-diabetic agent. In the course of a synthesis of 13, Ching-Feng Weng and Chinpiao Chen of the National Dong Hwa University observed (J. Org. Chem. 2015, 80, 6044. DOI: 10.1021/acs.joc.5b00345) significant diastereoselectivity in the radical cyclization of 11 to 12.

The sesquiterpene (Z)-2β-Hydroxy-14-hydro-β-santalol (16) is a potent inhibitor of Helicobacter pylori, a major causitive factor of gastric ulcers and cancer. En route to 16, Ken Ishigami of the University of Tokyo effected (Tetrahedron Lett. 2015, 56, 5816. DOI: 10.1016/j.tetlet.2015.09.011) the cascade radical cyclization of 14 to 15.

Cortistatin A (19), isolated from the marine sponge Corticium simplex, has potent antiangiogenic activity. Pauline Chiu of the University of Hong Kong designed (Chem. Eur. J. 2015, 21, 14287. DOI: 10.1002/chem.201502890) the intramolecular dipolar cycloaddition of the oxallyl cation derived from 17 to prepare 18, that could be carried on to 19.