Enolate anions simple diastereoselection

For lithium enolate anions, the tendency is for the enolate to occupy the concave face of the transition structure cf. Figure 6.4d and 6.5c) and therefore to prefer transition structures such as those illustrated in Figure 6.6b and c. Table 6.2 lists several examples of simple acyclic diastereoselection, which show a tendency for E -> syn and Z —> anti selectivity, in contrast to the tendency observed for hydrocarbon substituted carbanions (Table 6.1). Entries 1 and 2 involve dianions of crotyloxy acetates, and show E -> syn and Z —> anti selectivity. A more complex example involving extension of a steroid side chain (similar to Scheme 6.6a), is 100% anti selective from an -alkene, however [53]. 

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