Stereoselective construction of azepine-containing bridged scaffolds via organocata-lytic bicyclization of yne-allenone esters with nitrones

A new organocatalytic double annulation cascade involving scission/recombination of N-O bonds of nitrones is reported for the first time, and used to produce a range of hitherto unprecedented tricyclic bridged-fused benzo[d]azepines bearing three stereogenic centers with moderate to good yields and complete diastereoselectivity. A quinine-catalyzed reaction of yne?allenone esters with nitrones worked well and provided a convergent and regioselective pathway to access these three-dimensional scaffolds from the planar conjugated system. Density functional theory (DFT) calculations have been applied to understand the key process for forming diradical intermediates.