Diastereo- and Atroposelective Synthesis of Bridged Biaryls Bearing an Eight-Membered Lactone through an Organocatalytic Cascade

We
present herein an unprecedented stereo­selective synthesis
of bridged biaryls with defined axial and central chirality from readily
available starting materials. This N-heterocyclic carbene-catalyzed
method proceeds through propargylic substitution of azolium enolates
followed by two-directional cyclization, as supported by DFT calculation.
A range of benzo­furan/indole-derived bridged biaryls bearing
an eight-membered lactone are accessed with uniformly high stereo­selectivity
(>98:2 dr, mostly >98% ee).