Double Annulation Route to Fused Bicyclic Compounds with Three Contiguous Quaternary Centers

Fused bicyclic and tricyclic compounds featuring two or three new CC σ bonds, two new rings, two or three new stereocenters, and three new contiguous quaternary centers can be prepared stereoselectively, atom-economically, and in one synthetic operation via a cascade reaction of two nonstereogenic, readily available starting materials:  a tethered bis(malononitrile) and an internal alkynone. The course of the “double annulation” changes drastically with the structure of the starting materials, alternately affording trans-decalins or cis-fused unsaturated lactones.