Direct Enantio- and Diastereoselective Oxidative Homocoupling of Aldehydes.

A novel strategy for the direct enantioselective oxidative homocoupling of α-branched aldehydes is presented. The methodology employs open-shell intermediates for the construction of chiral 1,4-dialdehydes by forming a carbon-carbon bond connecting two quaternary stereogenic centers in good yields and excellent stereoselectivities for electron-rich aromatic aldehydes. The 1,4-dialdehydes were transformed into synthetically valuable chiral pyrrolidines. Experimental mechanistic investigations based on competition experiments combined with computational studies indicate that the reaction proceeds through a radical cation intermediate and that reactivity and stereoselectivity follow different trends.