Substituent Effects and Complexation Phenomena in the Diastereoselective Protonation of Chiral Enolates

Ethyl salicylate is the best proton source for the cis ‐selective protonation of chiral five‐, six‐, and seven‐membered ring enolates [e.g., Eq. (a)]. This was the conclusion of investigations based on a series of phenols and enolates. The selectivity was found to depend markedly on, for example, the substitution pattern in the proton source.