THE REACTION OF ISATIN AZOMETHINE YLIDES WITH (Z)-2-OXOINDOLIN-3 YLIDENE AND (E)-2-OXOINDOLIN-3-YLIDENE ACETOPHENONES - CONCERTED VS APPARENT NONCONCERTED 1,3-DIPOLAR CYCLOADDITION

The reaction of 1-benzyl-5-bromoisatin with proline, sarcosine, or gly cine gives azomethine ylides that can be trapped by (Z)- or (E)-2-oxoi ndolin-3-ylidene acetophenones acting as dipolarophiles in a 1,3-dipol ar cycloaddition. The configuration of the adducts was determined by H -1-nmr with nOe experiments. The kinetically controlled adducts always retain the configuration of the reacting dipolarophile but they can r earrange, sometimes under extremely mild conditions. The rearrangement s were demonstrated to involve a 1,3-dipolar cycloreversion/cycloaddit ion sequence since the intermediates were trapped by more reactive dip olarophiles.