Chiral allylating reagents, readily generated in situ from 2 lambda(2)
-1,3,2-benzodioxastannole [Sn-II(O2C6H4)], allyl halides, chiral dialk
yl tartrates and 1,8-diazabicyclo[5.4.0]-7-undecene (DBU) smoothly rea
ct with aromatic aldehydes at -78 degrees C in the presence of a catal
ytic amount of copper salts to afford the corresponding homoallylic al
cohols in high yields with high enantioselectivities.