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.

本文报道了一种前所未有的立体选择性合成方法，可通过易得的起始原料制备带有单轴或连续双轴结构的三芳基-2-吡喃酮（triaryl-2-pyrones）。该氮杂环卡宾（N-heterocyclic carbene）催化方法，以2-芳基酮与炔醛为底物，在氧化条件下实现阻转选择性环化反应。该环化过程可一步构建一个或两个轴单元，兼具步骤经济性，能够以中等至良好的产率得到轴手性三芳基-2-吡喃酮产物，且产物具有高至优异的对映选择性。本研究还对立体异构体的相对能量及旋转能垒进行了密度泛函理论（DFT）计算。