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 w ith an N-alkenoyl-1,3-oxazolidin-2-one. The results of these calculati ons 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 therefor e it is the most reactive, although it is not the most stable. These r esults 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.