Abstract: Four hetero-Diels-Alder reactions between phosphonodithioformate and 1-acetoxybutadiene have been studied theoretically with density functional theory at B3LYP/6-31G(d) level.The results show that all of these reactions proceed in a concerted way.In two reactions the formation of C—S bond is prior to that of C—C bond while the formation of C—S and C—C bond is synchronous in other two reactions.The regioselectivity observed experimentally is predicted correctly by theoretical calculation and is determined ki...