(1) Cram-chelate Rule:1b,3,4 If chelation between the carbonyl group and one of the substituents 5 of the R-stereocenter facilitated by a metal cation can occur, the substrate will be locked into the conformation 4 (Scheme 2). This will place the remaining two substituents, here S and M, on different sides of the carbonyl group. A nucleophile will now preferentially