1. Depending on the nature of the catalyst and the temperature, the hydrosilylation of 2-ethoxyacrolein with diethylsilane in the presence of H2PtCl6 or colloidal nickel leads to the formation of the 1,2- and 1,4-addition products, and specifically 1-(diethylsiloxy)-2-ethoxy-2-propene and 1-(diethylsiloxy)-2-ethoxy-1-propene, respectively, and also 2-ethoxy-3-diethylsiloxypropyl-(2-ethoxy-1-propenoxy)diethylsilane. Depending on the nature of the catalyst, isomerization of the 1,2-adduct to the 1,4-addition product, and the reverse, occurs. 2. The intramolecular hydrosilylation product of 1-(diethylsiloxy)-2-ethoxy-2-propene in the presence of H2PtCl6 is 2,2-diethyl-4-ethoxyoxasilolane; the latter is also formed by the direct hydrosilylation of 2-ethoxyacrolein with diethylsilane under certain conditions.