title: Application of chiral cationic catalysts to several classical syntheses of racemic natural products transforms them into highly enantioselective pathways.
abstract: This paper describes the application of chiral oxazaborolidinium cations of type 2 to various enantioselective Diels-Alder reactions that have served as early key steps for the syntheses of complex natural products. In the original syntheses these Diels-Alder reactions produced racemic adducts and led to racemic target molecules unless a separation of enantiomers by classical resolution was employed. By use of chiral catalysts of type 2, chiral products were obtained directly from Diels-Alder reactions of achiral components in excellent yield and enantioselectivity and with the mechanistically predicted absolute configuration. As a result, a number of classical syntheses could be converted to enantioselective versions, including (1) cortisone/cortisol (Merck/Sarett), (2) dendrobine (Kende), (3) vitamin B(12) (Eschenmoser), (4) myrocin C (Chu-Moyer/Danishefsky), (5) coriolin and hirsutene (Mehta), (6) dendrobatid 251F (Aube), (7) silphinene (Ito), and (8) nicandrenone core (Stoltz/Corey).
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Qi-Ying
authors.initials: QY
authors.lastname: Hu
authors.forename: Gang
authors.initials: G
authors.lastname: Zhou
authors.forename: E J
authors.initials: EJ
authors.lastname: Corey
mesh_terms: D000470:Alkaloids / Q000138:chemical synthesis; D001688:Biological Products / Q000138:chemical synthesis*; D001896:Boron Compounds / Q000737:chemistry*; D002384:Catalysis; D003348:Cortisone / Q000138:chemical synthesis; D004224:Diterpenes / Q000138:chemical synthesis; D010777:Photochemistry; D000081223:Polycyclic Sesquiterpenes; D012717:Sesquiterpenes / Q000138:chemical synthesis; D013237:Stereoisomerism; D014805:Vitamin B 12 / Q000138:chemical synthesis
chemical_list: D000470:Alkaloids; D001688:Biological Products; D001896:Boron Compounds; D004224:Diterpenes; D000081223:Polycyclic Sesquiterpenes; D012717:Sesquiterpenes; C058997:myrocin C; C002077:dendrobine; C007127:coriolin; C486985:hirsutene; D014805:Vitamin B 12; D003348:Cortisone