With the prerequisite of L being orthogonal to the carbonyl group, the two conformations 9and 10
remain possible.9, leading to the preferred Cram or Felkin-Anh product2, is apparently favored accord-ing to this model. When calculations by Bu ¨ rgi/Dunitz10 and Anh/Eisenstein 11,12
showed that theattack of the nucleophile onto the carbonyl group does not occur in a 90° but rather in a 103° angle with
respect to the carbonyl group, a conclusive argument had been found pointing toward9as the decisive
reactive conformation. This way the nucleophile attacks from the side of the small substituent S, i.e., it is experiencing the least steric repulsion by the chiral center.