Copper‐Catalyzed Double Intramolecular Ullmann Coupling for the Synthesis of Diastereomerically and Enantiomerically Pure 4b,9b‐Dihydrobenzofuro[3,2‐b]benzofurans

Abstract The copper‐catalyzed double intramolecular Ullmann coupling of syn ‐1,2‐bis(2‐bromoaryl)ethane‐1,2‐diols with catalytic amounts of Cu II oxinate as the copper source, K 3 PO 4 as a base, and KI as a reductant in aqueous acetonitrile selectively delivers 4b,9b‐dihydrobenzofuro[3,2‐ b ]benzofurans in diastereomerically and enantiomerically pure form and yields of up to 90 %. The substrates can be obtained in both diastereomerically and enantiomerically pure form by catalytic dihydroxylation of the corresponding ( E )‐stilbenes.