Enantioselective Access to Triaryl-2-pyrones with Monoaxial or Contiguous C–C Diaxes via Oxidative NHC Catalysis

We present herein an unprecedented stereoselective synthesis
of
triaryl-2-pyrones with monoaxial or contiguous diaxes from readily
available starting materials. This N-heterocyclic carbene catalysis
method adopts an atroposelective annulation of 2-aryketones with ynals
under oxidative conditions. The annulation includes the construction
of one or two axes in a single operation, achieves step economy, and
affords axially chiral triaryl-2-pyrones in moderate to good yields,
with high to excellent enantioselectivities. DFT calculations of the
relative energies of stereoisomers and rotational barriers were performed.