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

A base-catalyzed stereoselective intramolecular dearomatizative [4+2] cycloaddition of o-phenylene-linked ethynylnaphthol-benzofuran systems was explored. In this reaction, we presume the involvement of electrophilic vinylidene o-quinone methides (4), which add across the electron-rich furan double bonds (2) to produce elaborate, fused oxa-polyheterocyclic frameworks with consecutive quaternary and tertiary asymmetric carbon atoms as single diastereomers. The catalytic and enantioselective synthesis of these chiral fused polyheterocyclic structures is also feasible with the use of a prevalent cinchonidine or cinchonine chiral base.