[Efficient Synthesis of Polyaromatic Hydrocarbon via a Formal [2+2] Cycloaddition].

A potassium base-promoted formal [2+2] cycloaddition of 2-acyl-2'-vinyl-1,1'-biaryls was developed to afford benzo-fused polycyclic cyclobutanols in a highly stereoselective manner. We demonstrated synthesis of substituted polycyclic aromatic hydrocarbons and these heterocyclic derivatives via this cyclization, followed by an acid-promoted rearrangement. Furthermore, asymmetric total synthesis of phenanthroindolizidine alkaloid (-)-tylophorine was achieved using our methodology and late-stage asymmetric hydrogenation of a cyclic imine.