The pivotal role of chelation as a stereochemical control element in non-Evans anti aldol product formation.

The origin of stereoselective formation of Evans syn and non-Evans anti aldol products in the reaction between titanium enolate derived from N-succinyloxazolidinone and benzaldehyde is established by using transition-state modeling. The chelated transition-state model is found to hold the key to otherwise less likely non-Evans anti aldol product, whereas the nonchelated model offers a convincing rationalization toward Evans syn aldol product. The computed results are in agreement with the reported experimental observations.