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.