Base-catalyzed Schmittel cycloisomerization of o-phenylenediyne-linked bis(arenol)s to indeno[1,2-c]chromenes

We describe the transition metal-free base-catalyzed Schmittel cycloisomerization reactions of o-phenylene-linked bis(arenol)s to indeno[1,2-c]chromene derivatives through prototropic rearrangement (tautomerization) to a putative vinylidene o-quinone methide intermediate with an enyne-allene system followed by a formal inverse-electron-demand hetero Diels-Alder cycloaddition. The preliminary results on catalytic asymmetric cycloisomerization with chiral bases are also disclosed.