vinyllithium additions. The configuration of the newly created C9 stereocenter was assigned through Rychnovsky's acetonide 13C NMR method. The diastereoselectivity in this particular type of (Z)-vinylmetaladdition reaction appears to be controlled by a subtle balance between the intrinsic stereochemical preference of the β-silyloxyaldehyde (1,3-anti-selective) and that of the chiral lithium (Z)-vinylzincates