title: Brønsted acid-catalyzed allylboration: short and stereodivergent synthesis of all four eupomatilone diastereomers with crystallographic assignments.
abstract: This study describes a novel Brønsted acid-catalyzed allylboration method suitable for the most difficult, electronically deactivated allylboronate and aldehyde substrates. This method circumvents the use of metal ions, and rather employs a simple and cheap catalyst, triflic acid. Its usefulness as a complementary allylboration variant was demonstrated with a four-step, stereodivergent synthesis of all four diastereomers of eupomatilone-6 from a single allylboronate. A thorough proof of stereochemistry supported by as many as five X-ray crystallographic structures brings an end to the ambiguity of the original stereochemical assignments. Further to the TfOH-catalyzed allylboration, the synthetic route featured a number of remarkable observations: the surprising reactivity of 2-bromo-3,4,5-trimethoxybenzaldehyde, the subtle reagent control observed in the hydrogenation of an alpha-exo-methylene lactone intermediate, and the success of a difficult case of Suzuki biaryl coupling using Buchwald's conditions.
authors.affiliation: Department of Chemistry, University of Alberta, Edmonton, AB, T6G 2G2, Canada.
authors.forename: Siu Hong
authors.initials: SH
authors.lastname: Yu
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Ferguson
authors.forename: Robert
authors.initials: R
authors.lastname: McDonald
authors.forename: Dennis G
authors.initials: DG
authors.lastname: Hall
mesh_terms: D000143:Acids / Q000737:chemistry*; D001572:Benzofurans / Q000138:chemical synthesis* / Q000737:chemistry; D001896:Boron Compounds / Q000138:chemical synthesis*; D002384:Catalysis; D018360:Crystallography, X-Ray; D008968:Molecular Conformation; D013237:Stereoisomerism
chemical_list: D000143:Acids; D001572:Benzofurans; D001896:Boron Compounds; C485126:eupomatilone-6