2-(Triisopropylsilyloxy) acrolein is easily prepared by the reaction of triisopropylsilyl triflate and 2-methoxy-2-methyl-[1, 3] dioxan-5-one in the presence of triethylamine. This dienophile reacts with selected dienes in the presence of catalytic amounts of scandium triflate to afford products that are formally 4+ 3 cycloadducts. An exception is seen in the case of butadiene, where only a 4+ 2 cycloadduct is observed.