Stereoselective Intramolecular Dearomatizative [4+2] Cycloaddition of Linked Ethynylnaphthol–Benzofuran Systems

The novel base-catalyzed stereoselective intramolecular dearomatizative [4+2] cycloaddition of o-phenylene-linked ethynylnaphthol-benzofuran systems is described. In this reaction, we presume the involvement of electrophilic vinylidene o-quinone methides (4π), which adds across the electron-rich furan double bonds (2π), producing elaborate fused oxa-polyheterocyclic frameworks with consecutive quaternary and tertiary asymmetric carbon atoms as single diastereomers. The catalytic and enantioselective synthesis of this chiral fused polyheterocyclic structure is also feasible using a prevalent chiral base: cinchonidine and cinchonine.