The preparation and the cascade reactions of <i>N</i>-butadienyl-<i>N</i>-alkylketene<i>N,O</i>-<i>tert</i>-butyldimethylsilyl acetals

The preparation of <i>N</i>-butadienyl-<i>N</i>-alkylketene <i>N,O</i>-<i>tert</i>-butyldimethylsilyl acetals (<b>11a - d</b>) from readily available starting materials is described. The cascade <i>Diels-Alder</i> reaction followed by acylation of these ketene acetals yields bicyclic and tricyclic products <b>7.13a,b</b> and <b>14c,d</b> with high diastereoselectivity.