Efficient diastereoselective pinacol coupling reaction of aliphatic and aromatic aldehydes by using newly utilized low valent titanium bromide and iodide species

Reductive coupling reaction of aromatic and aliphatic aldehydes proceeded under mild conditions to give the corresponding pinacols in moderate to high yields and dl-diastereoselectivities by using combinations of either low valent titanium(II) bromide and copper or titanium(IV) iodide and copper in a mixed solvent of dichloromethane and pivalonitrile. In the case of using titanium(IV) iodide and copper, pinacols were obtained in good to high yields with moderate to high diastereoselectivities irrespective of the number of substitutuents at α-position of aliphatic aldehydes.