Quantum chemical insights into the mechanism of the TADDOL-TiCl2 catalyzed Diels-Alder reactions

Quantum chemical calculations have been carried out for the first time on model compounds of TADDOL-TiCl2 (1,4-butanediol-TiCl2) complexed with an N-alkenoyl-1,3-oxazolidin-2-one. The results of these calculations have shown that the intermediate in which the carbonyl oxygen atom of the enoate moiety is in trans-position with respect to a chlorine atom experience a higher degree of Lewis acid activation, and therefore it is the most reactive, although it is not the most stable. These results are in agreement with the experimental observations, as well as with a previous hypothesis based on the mechanism of the Diels-Alder reactions of this kind of complex.