Chlorine being a relatively weak electron acceptor assumes the role of L; however, as the size of M
increases, the stereoelectronic effect of the acceptor is counteracted by the steric effect, resulting in a loss of selectivity (Scheme 9, Table 1, entries 62-68). When the acceptor substituent becomes stronger, e.g., OTBS, even highly sterically demanding substituents such as cyclohexyl are seemingly unable to override the stereoelectronic control (Table 1, entries 69-71). However, if chelation is not effectively precluded or more than one possibility for chelation exists, diastereomeric
mixtures of 2 and 3 are usually obtained (Table 1, entries 74, 79).