achiral 1-silyloxybutadiene 1a with the chiral acyinitroso dienophile 2a gave cycloadduct 4 in high diastereomeric excess (d.e. > 98 %), a result which is undoubtedly due to the C-2 symmetrical chiral dimethylpyrrolidine inductor. Excellent d.e. was also observed when the (R)-prolinol dienophile 2d was reacted with the chiral diene 1b (d.e. = 96 %), whereas cycloaddition of the (S) enantiomer 2e with 1b gave