Enantio- and Diastereoselective Desymmetrization of 1,1'-Biaryl-2,6-dicarbaldehydes by Copper-Catalyzed 1,2-Addition of Silicon Nucleophiles.

A desymmetrizing 1,2-addition of silicon nucleophiles to biaryl derivatives containing an 2,6-dicarbaldehyde-1-yl unit is reported. The reaction is catalyzed by copper with a triazolium-derived N-heterocyclic carbene as the chiral ligand and an Si-B reagent as the silicon pronucleophile. The practical methodology furnishes axially chiral aromatic carbaldehydes decorated with a centrally chiral α-hydroxysilane moiety in moderate to high yields and with high enantio- as well as excellent diastereoselectivities. The silicon nucleophile always attacks at either carbonyl group away from the ortho substituent on the phenyl ring at C1 of the 2,6-dicarbaldehyde-1-yl fragment. The resulting axially and centrally chiral products can be further converted into valuable biaryl compounds with hardly any erosion of the enantiomeric excess.