Efficient diastereoselective pinacol reaction of aliphatic and aromatic aldehydes by combined use of newly utilized titanium(II) bromide and copper

Newly utilized low-valent titanium reductant, titanium(II) bromide, was con veniently prepared by treating titanium(IV) bromide with hexamethyldisilane . The pinacol reaction of aromatic and aliphatic aldehydes including primar y aldehydes proceeded smoothly in dichloromethane-pivalonitrile at temperat ures ranging from -23 to 0 degrees C by the combined use of soluble titaniu m(II) bromide and copper to give 1,2-diols in good to high yields with good to high dl-selectivities.