Chloranthalactone (Liu), Rumphellaone A (Kuwahara), Lactiflorin (Bach), Echinosporin (Hale), Harveynone (Taylor), (6,7-deoxy)-Yuanhuapin (Wender)
The lindenane sesquiterpenes, exemplified by Chloranthalactone (4), display interesting physiological activity. Bo Liu of Sichaun University assembled (Org. Lett. 2011, 13, 5406. ) 4 by opening the epoxide 1 to the carbene, which cyclized to 3.
Establishment of the relative configuration of sidechain stereogenic centers is a continuing issue in carbocyclic synthesis. Shigefumi Kuwahara of Tohoku University paired (Tetrahedron Lett. 2012, 53, 705. ) Sharpless epoxidation, to prepare 5, with the Stork epoxy nitrile cyclization, leading to (+)-Rumphellaone A (7).
Three competing structures had been put forward for the structure of (+)-Lactiflorin (10). Thorsten Bach of the Technische Universität München settled (Angew. Chem. Int. Ed. 2012, 51, 1261. ) this controversy by preparing the most likely structure, 10, and showing that it was congruent with the natural product. A key step in the synthesis was the tethered 2+2 cycloaddition of 8 to give 9.
The conversion of a carbohydrate to a carbocycle is a powerful strategy for the enantiospecific construction of natural products. En route to (-)-Echinosporin (14), Karl J. Hale of Queen’s University Belfast added (Org. Lett. 2012, 14, 3024. ) the allene 12 to the enone 11, prepared from glucose, to give the cyclopentene 13.
Richard J. K. Taylor of the University of York prepared (Tetrahedron Lett. 2010, 51, 6619. ) the enone 16 by oxidation of m-iodophenol 15 followed by asymmetric epoxidation. Reduction followed by deprotection and Pd-mediated coupling delivered (-)-Harveynone (17).
Some of the daphnane diterpene orthoesters, exemplified by (6,7-deoxy)-Yuanhuapin (20), are single-digit nanomolar inhibitors of protein kinase C. Paul A. Wender of Stanford University, in the course of initial studies to optimize this remarkable activity, prepared (Nature Chem. 2011, 3, 615. ) 20 by way of the thermal cyclization of 18 to 19.