title: Synthesis of chiral building blocks for oxygenated terpenoids through a simultaneous and stereocontrolled construction of contiguous quaternary stereocenters by an Ireland-Claisen rearrangement.
abstract: Methods for highly stereocontrolled syntheses of chiral building blocks with a triad of contiguous stereocenters, including two quaternary ones, have been developed. Ireland-Claisen rearrangement of the (Z)-silyl ketene acetal generated stereoselectively from the (R)-3-methylcyclohex-2-enyl ester derived from an acyclic carboxylic acid proceeded through a chairlike transition state to give the rearranged product with an S configuration at the position α to the carboxyl group. Introduction of a cyclic conformational constraint in the acid component completely switched the transition state of the rearrangement to a boatlike one, leading to the predominant formation of a product with an R configuration, from which pseudodiastereomeric α-hydroxy esters were obtained in a four-step sequence. The enyne obtained through a base-mediated double eliminative ring-opening reaction was successfully converted into advanced intermediates for the synthesis of 9-oxygenated labdane diterpenoids through a Heck reaction and a regioselective transformation of the resultant diene.
authors.affiliation: Graduate School of Pharmaceutical Sciences, Nagoya City University , 3-1 Tanabe-dori, Mizuho-ku, Nagoya 467-8603, Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Akahori
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Yamakoshi
authors.forename: Yuki
authors.initials: Y
authors.lastname: Sawayama
authors.forename: Shunichi
authors.initials: S
authors.lastname: Hashimoto
authors.forename: Seiichi
authors.initials: S
authors.lastname: Nakamura
mesh_terms: D004224:Diterpenes / Q000138:chemical synthesis* / Q000737:chemistry; D008968:Molecular Conformation; D010100:Oxygen / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D004224:Diterpenes; D010100:Oxygen