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

The copper‐catalyzed double intramolecular Ullmann coupling of syn‐1,2‐bis(2‐bromoaryl)ethane‐1,2‐diols with catalytic amounts of CuII oxinate as the copper source, K3PO4 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.