title: Ligand- and Brønsted acid/base-switchable reaction pathways in gold(I)-catalyzed cycloisomerizations of allenoic acids.
abstract: Gold-promoted cyclizations of 2,2-diaryl substituted γ-allenoic acids were found to give three isomeric lactone products, each of which could be obtained selectively by exploiting Brønsted acid/base and ligand effects. Simple 5-exo-trig cyclization products were favored by strong donor ligands or base additives, whereas weak donor ligands and a Brønsted acid additive gave isomeric enelactones resulting from double bond migration. Further optimization afforded a class of medicinally relevant bridged tricyclic lactones via a tandem hydroacyloxylation/hydroarylation process. Kinetic studies and control experiments indicated that the initial 5-exo-trig cyclization product serves as a branch point for further isomerization to the other lactone products via cooperative gold(I)/Brønsted acid catalysis.
authors.affiliation: Department of Chemistry, Oklahoma State University, Stillwater, Oklahoma 74078, USA.
authors.forename: Sachin
authors.initials: S
authors.lastname: Handa
authors.forename: Sri S
authors.initials: SS
authors.lastname: Subramanium
authors.forename: Aaron A
authors.initials: AA
authors.lastname: Ruch
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Tanski
authors.forename: LeGrande M
authors.initials: LM
authors.lastname: Slaughter