title: Enantioselective (4+2) Annulation of Donor-Acceptor Cyclobutanes by N-Heterocyclic Carbene Catalysis.
abstract: Herein we report the enantioselective (4+2) annulation of donor-acceptor cyclobutanes and unsaturated acyl fluorides using N-heterocyclic carbene catalysis. The reaction allows a 3-step synthesis of cyclohexyl β-lactones (25 examples) in excellent chemical yield (most ≥90 %) and stereochemical integrity (all >20:1 d.r., most ≥97:3 e.r.). Mechanistic studies support ester enolate Claisen rearrangement, while derivatizations provide functionalized cyclohexenes and dihydroquinolinones.
authors.affiliation: School of Chemistry, Monash University, Clayton, 3800, Victoria, Australia.
authors.forename: Alison
authors.initials: A
authors.lastname: Levens
authors.affiliation: School of Chemistry, Monash University, Clayton, 3800, Victoria, Australia.
authors.forename: Adam
authors.initials: A
authors.lastname: Ametovski
authors.affiliation: School of Chemistry, Monash University, Clayton, 3800, Victoria, Australia.
authors.forename: David W
authors.initials: DW
authors.lastname: Lupton
keywords: N-heterocyclic carbenes; cyclohexanes; donor-acceptor cyclobutanes; enantioselective catalysis; organocatalysis