Helical Topologies via [4 + 2] Cycloaddition Reactions between Structurally Complex Benzynes and Several Alkenyl Polycyclic Aromatic Compounds

We report here reactions of a number of vinyl-substituted arenes (phenyl, 2-naphthyl, 9-phenanthryl, and 2-triphenylenyl) with benzynes that give rise to structurally complex, polycyclic products having helical topologies. Indene and benzofuran were also explored. The benzynes were formed by heating triyne substrates to effect their cycloisomerization via a hexadehydro-Diels–Alder (HDDA) reaction. The initial [4 + 2], dearomatized adducts showed a variety of unexpected modes of reactivity that are mechanistically intriguing. These include ene reactions, [2 + 2] cycloadditions, and autoxidation events. The complexity-building nature of the processes is notable: in some cases as many as five new rings were formed, and three-component cascades are possible. Notably, some of the overall transformations are fully atom-economical.