SINGLE AND DOUBLE ASYMMETRIC INDUCTION IN DIELS-ALDER CYCLOADDITIONS WITH CHIRAL ACYLNITROSO DIENOPHILES

Diels-Alder reaction of the achiral 1-silyloxybutadiene 1a with the chiral acylnitroso 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 only poor asymmetric induction (d.e. = 4%). These two latter examples nicely illustrate the influence of ''matched pair'' (1b/2d) versus ''mismatched pair'' (1b/2e) upon double asymmetric induction. All herein reported Diels-Alder cycloadditions were regiospecific.