Acceleration effect of Lewis acid in allylboration of aldehydes: catalytic,regiospecific, diastereospecific,and enantioselective synthesis of homoallyl alcohols

The addition of pinacol allylboronic esters to aromatic and aliphatic aldehydes smoothly occurred at -78 degrees C in toluene in the presence of a catalytic amount of AlCl3 or Sc(OTf)3 (10 mol %) to give the corresponding homoallyl alcohols in high yields. The reactions proceeded regio- and diastereospecifically, yielding the isomerically pure syn- and anti-homoallyl alcohols from (Z)- and (E)-allylboronic esters, respectively. The protocol was also applied to enantioselective reactions by using a chiral Lewis acid catalyst.