Condensation of beta-diester titanium enolates with carbonyl substrates: a combined DFT and experimental investigation.

The condensation of dialkyl beta-diesters with various aldehydes promoted by TiCl4 has been studied by DFT approaches and experimental methods, including NMR, IR and UV/Vis spectroscopy. Various possible reaction pathways have been investigated and their energy profiles evaluated to find out a plausible mechanism of the reaction. Theoretical results and experimental evidence point to a three-step mechanism: 1) Ti-induced formation of the enolate ion; 2) aldol reaction between the enolate ion and the aldehyde, both coordinated to titanium; and 3) intramolecular elimination that leads to a titanyl complex. The presented mechanistic hypothesis allows one to better understand the pivotal role of titanium(IV) in the reaction.