Synthesis of Bicyclo[n,3,0]alkanes and Aza-Bicyclo[n,3,0]alkanes by Phosphine-Mediated Domino Reaction of Enones with Morita–Baylis–Hillman (MBH) Carbonates

Herein, we developed a domino reaction of designed enones with MBH carbonates. The reaction proceeded either with stoichiometric PBu₃ or was catalyzed by R₃P═O via P^III/P^V═O redox cycling by using silane as a reductant. This metal-free and step-economic method allowed for the <i>de novo</i> synthesis of a wide range of bicyclic compounds, including aza-bicyclo[3,3,0]octanes, bicyclo[3,3,0]octanes (diquinanes), aza-bicyclo[4,3,0]nonanes, and bicyclo[4,3,0]nonanes (hydrindanes), bearing one bridgehead all-carbon quaternary stereocenter in moderate to excellent yields. Furthermore, this domino reaction forged four new C-C and C-X bonds while simultaneously assembling two rings.