Copper-Catalyzed Base-Controlled Diastereoselective Synthesis of Tetraarylethanes from 2-Benzylpyridines

A highly efficient and base-controlled diastereoselective synthesis of tetraarylethanes through copper-catalyzed dehydrogenative homocoupling of readily available 2-benzylpyridines is reported. Various dl- and meso-tetraarylethanes were diastereoseletively synthesized by this new protocol, where base plays the role of the principle modulator: Grignard reagents selectively provide the C2 isomers, whereas KOt-Bu promotes the formation of the meso-tetraarylethanes. Interestingly, the presence of excess KOt-Bu generates the (E)-tetraarylethenes as the only product.