2-CARBOMETHOXY-1,3-BUTADIENE - AN ELECTRONICALLY ACTIVATED DIENE IN [4+2] CYCLOADDITIONS WITH ELECTRON-DEFICIENT DIENOPHILES

Cross Diels-Alder reactions between 2-carbomethoxy-1,3-butadiene 1 and electron-rich dienes were carried out. It was found that diene 1 had a higher reactivity than even the well-known Danishefsky diene in its Diels-Alder cycloaddition with electron-deficient dienophiles. In addition, (Z)-1-methylthio-3-carbomethoxy-1,3-butadiene 11 was found to have a higher reactivity than (Z)-1-methylthio-1,3-butadiene and (Z)-2-carbomethoxy-1,3-hexadiene, while both (E)- and (Z)-1,2-(bis)-carbomethoxy-1,3-butadiene 14 reacted efficiently with maleic anhydride to give the corresponding cycloadduct 15.