Abstract Treatment of diethyl fumarate and triethoxycarbonylethylene with Bu 2 CuLi· AlCl 3 led to 1, 4-addition to give butylated products in high yields. In sharp contrast, diethyl maleate and tetraethoxycarbonylethylene predominantly gave the respective reduction products. The first evidence for a presumed dianionic intermediate by trapping with some electrophiles was also presented.
