Steric Factors Direct Baylis−Hillman and Aldol Reactions in Titanium Tetrachloride Mediated Coupling between α-Keto Esters and Cyclohex-2-enone Derivatives

The titanium tetrachloride mediated reaction of α-keto esters with 5,5-dimethylcyclohex-2-enone provides the corresponding Baylis−Hillman adducts exclusively whereas a similar reaction of α-keto esters with cyclohex-2-enone furnishes the corresponding aldol adducts (with high syn-diasteroeselectivity) as the major product (along with the Baylis−Hillman adducts as the minor product), thus clearly demonstrating the role of the steric factors in directing the reaction pathway.