Enantioselective Synthesis of Functionalized β‑Lactones by NHC-Catalyzed Aldol Lactonization of Ketoacids

N-Heterocyclic carbene
(NHC)-catalyzed intramolecular aldol lactonization
of readily available ketoacids leading to the enantioselective synthesis
of cyclopentane-fused β-lactones is presented. The reaction
proceeds via the generation of NHC-bound enolate intermediates formed
from the ketoacids in the presence of the peptide coupling reagent
HATU and NHC generated from the chiral triazolium salt. The functionalized
β-lactones are formed under mild conditions in high yields and
enantioselectivities.