The hetero-Diels-Alder reactions between methyl pyridinedithiocarboxylates and butadienes have been investigated theoretically using density functional theory at the B3LYP/6-31G(d) level, in which the influences of catalysts, solvents and substituent groups on the mechanisms and activation barriers of these reactions have been involved. The obtained results indicate that all of these hetero-Diels-Alder reactions are concerted but asynchronous, in which the formation of C—S bond is prior to that of C—C bond in most of the reactions. The catalysts or trimethylsilyloxy group may lower the activation barriers by changing energy gaps between FMOs of reactants. Polar solvents have remarkable influences on the reaction with a cation system, such as H^＋, as catalyst. As for the reaction catalyzed by BF₃, the complete regio-selectivity and stereo-selectivity observed experimentally have well been reproduced by theoretical calculations, in which probably the C—H…F interactions in these transition states play a key role.

Key words: pyridinedithiocarboxylate, butadiene, hetero-Diels-Alder reaction, reaction mechanism, density functional theory