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).