Date of this Version
Org Lett. 2012 February 17; 14(4): 968–971. doi:10.1021/ol203088g.
A streamlined entry into the sesquiterpene lactones (SQL) cores of linearifolin and zaluzanin A is described. Stereochemistry is controlled through transformations uncovered by ISES (In-Situ- Enzymatic-Screening). Absolute stereochemistry derives from kinetic resolution of 5- benzyloxypentene-1,2-oxide, utilizing a β-pinene-derived-Co(III)-salen. Relative stereochemistry (1,3-cis-fusion)is set via formal halometalation/carbocyclization, mediated by [Rh(O2CC3F7)2]2/ LiBr. Subsequent ring-closing metathesis (RCM-Grubbs II) yields the title exomethylene-δ- lactone SQL-cores. In complementary fashion, RCM with Grubbs-I catalyst provides the oxabicyclo[3.3.1]nonyl-core of xerophilusin R and zinagrandinolide.