Diels-Alder Reactions between Silabenzenes and Dienophiles

The mechanism, potential energy surface, substituent effect and salvation effect of two types of Diels-Alder reactions between silabenzenes and some dienophiles were investigated using density functional theory (DFT) at B3LYP/6-311G(d,p) level. All the studied reactions proceeded in a concerted way. The influence of phenyl at the C atom of dienophiles on the asynchronicity in the bond-formation process and the activation barrier of the reaction were determined by the relative position of phenyl in products. The CCl3 group at the Si atom of the silabenzene molecule favors the hetero-Diels-Alder reactions. The hetero-Diels-Alder reactions associated with the C-Si forming bond proceed much more easily than traditional Diels-Alder reactions both thermodynamically and kinetically. The complete regioselectivity observed experimentally in hetero-Diels-Alder reactions were reproduced well by theoretical calculations and are controlled by kinetic factors. Reactions between silabenzene and olefins proceed more easily than those between silabenzene and corresponding alkynes kinetically, but thermodynamically, this is reversed. Benzene as a solvent only has a trivial influence on the potential energy surface of the studied reactions.