| Sumario: | This article focuses on the mechanism of titanium-crossed-claisen condensation between carboxylic esters and acid chlorides. This chemical reaction is suggested to be a highly selective and general method for the preparation of various β-keto esters. The Claisen condensation is recognized as a fundamental and useful c-c bond-forming reaction in organic syntheses. Generally, strong basic reagents are used to conduct this reaction. The said titanium-crossed-claisen condensation method is claimed to possess powerful reactivity compared with that of the conventional method using strong bases. The major problem of the Claisen condensation lies in the difficulty in directing the reaction, that is, a general crossed condensation between different esters or between esters and acid chlorides, all of which possess α-protons, have never been documented. to solve this problem, N-methylimidazoles were employed as the key cocatalyst, because acid chlorides condense with N-methylimidazole to form an activated electrophilic acylammonium interrnediate.
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