title: New syntheses of E7389 C14-C35 and halichondrin C14-C38 building blocks: reductive cyclization and oxy-Michael cyclization approaches.
abstract: Cr-mediated coupling reactions are usually achieved with a slight excess of a given nucleophile. To develop a cost-effective use of this process, two different approaches have been studied. The first approach depends on two consecutive catalytic asymmetric Cr-mediated couplings, with use of coupling partners purposely being of unbalanced molecular size and complexity. The second approach rests on the success in identifying the nucleophile, which allows us to achieve the coupling satisfactorily with a 1:1 molar ratio of the coupling partners. The C23-O bond is stereospecifically constructed via reductive cyclization of the oxonium ion, or oxy-Michael cyclization. Both syntheses have a high overall efficiency: E7389 C14-C35 and halichondrin C14-C38 building blocks have been synthesized from the corresponding C27-C35 and C27-C38 aldehydes, respectively, in high overall yields with an excellent stereoselectivity. Because of operational simplicity, the synthesis outlined herein appears to be well suited for scaling.
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, 12 Oxford Street, Cambridge, Massachusetts 02138, USA.
authors.forename: Cheng-Guo
authors.initials: CG
authors.lastname: Dong
authors.forename: James A
authors.initials: JA
authors.lastname: Henderson
authors.forename: Yosuke
authors.initials: Y
authors.lastname: Kaburagi
authors.forename: Takeo
authors.initials: T
authors.lastname: Sasaki
authors.forename: Dae-Shik
authors.initials: DS
authors.lastname: Kim
authors.forename: Joseph T
authors.initials: JT
authors.lastname: Kim
authors.forename: Daisuke
authors.initials: D
authors.lastname: Urabe
authors.forename: Haibing
authors.initials: H
authors.lastname: Guo
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Kishi
mesh_terms: D002384:Catalysis; D003500:Cyclization; D004988:Ethers, Cyclic / Q000138:chemical synthesis* / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D013237:Stereoisomerism
chemical_list: D004988:Ethers, Cyclic