A new activated cross-conjugated triene, 3-(methoxymethylene)-2, 4-bis (trimethylsilyloxy)-1, 4-pentadiene, was prepared. Its reactions with acetylenic dienophiles resulted in the exclusive formation of mono-cycloadducts, while in the reactions with cyclic olefinic dienophiles such as maleimides and maleic anhydride the mono-and bis-adducts were obtained depending upon the amounts of dienophiles.