text: According to Reetz, the Cram-chelate model for 1,2-inductions can be extended to predict the chelated complex of a β-alkoxy aldehyde and metal.  The nucleophile is seen to attack from the less sterically hindered side and anti- to the substituent R, leading to the anti-adduct as the major product.
  To make such chelates, the metal center must have at least two free coordination sites and the protecting ligands should form a bidentate complex with the Lewis acid.