Exploiting the Pd- and Ru-catalyzed cycloisomerizations: enantioselective total synthesis of (+)-allocyathin B2.
Pd- and Ru-catalyzed cycloisomerizations of 1,6-enynes are compared and contrasted. Such considerations led to the enantioselective synthesis of a cyathin terpenoid, (+)-allocyathin B(2) (1). The synthesis features a Pd-catalyzed asymmetric allylic alkylation (AAA) to install the initial quaternary center, a Ru-catalyzed diastereoselective cycloisomerization to construct the six-membered ring, and a diastereoselective hydroxylative Knoevenagel reaction to introduce the final hydroxyl group. We demonstrate for the first time a mechanism-based stereochemical divergence in Pd- and Ru-catalyzed cycloisomerization reactions as well as in creation of alkene geometry with alkynes bearing a carboalkoxy group. Mechanistic rationalization is proposed for these observations.
Trost
Barry M
BM
Department of Chemistry, Stanford University, Stanford, California 94301-5080, USA. bmtrost@stanford.edu
Dong
Li
L
Schroeder
Gretchen M
GM
D002384:Catalysis; D018360:Crystallography, X-Ray; D003500:Cyclization; D004224:Diterpenes / Q000138:chemical synthesis* / Q000737:chemistry; D010165:Palladium / Q000737:chemistry; D011083:Polycyclic Compounds / Q000138:chemical synthesis / Q000737:chemistry; D012428:Ruthenium / Q000737:chemistry; D013237:Stereoisomerism
D004224:Diterpenes; D011083:Polycyclic Compounds; C430643:allocyathin B2; D010165:Palladium; D012428:Ruthenium