Total synthesis of (+)-chinensiolide B via tandem allylboration/lactonization.
The chinensiolides are a family of guaiane type alpha-methylene gamma-lactone natural products recently isolated from Ixeris chinensis Nakai, a plant used in Chinese folk medicine. The first enantioselective total synthesis of (+)-chinensiolide B was accomplished in 15 steps for the longest linear sequence with an overall yield of 6.7% starting from inexpensive and readily available (R)-carvone. A highly stereoselective and E/Z-selective tandem allylboration/lactonization reaction between two highly functionalized partners was exploited as a key step. The synthesis also highlights several solutions to chemoselectivity issues arising from the reactive alpha-methylene gamma-lactone. For instance, a ring-closing metathesis formed the requisite seven-membered ring in a chemoselective fashion while avoiding the reactivity of the conjugated alpha-methylene unit.
Elford
Tim G
TG
Department of Chemistry, University of Alberta, Edmonton, AB, T6G 2G2, Canada.
Hall
Dennis G
DG
D019659:Asteraceae / Q000737:chemistry*; D001688:Biological Products / Q000138:chemical synthesis; D007783:Lactones / Q000138:chemical synthesis*; D015394:Molecular Structure; D012717:Sesquiterpenes / Q000138:chemical synthesis*; D013237:Stereoisomerism
D001688:Biological Products; D007783:Lactones; D012717:Sesquiterpenes; C473438:chinensiolide A