REACTIONS OF CYCLIC OXALYL COMPOUNDS .37. SUBSTITUENT EFFECTS ON THE SITE OF NUCLEOPHILIC-ATTACK AT 1H-PYRROLE-2,3-DIONES

Reactions of 1H-pyrrole-2,3-diones 2a-i with N- and O-nucleophiles pro ceed by initial attack at C-2 or/and C-5. Consequently, earlier result s suggesting structures of type A (attack at C-3) have to be revised ( 5, 13, 17, 18b). In general, electron-withdrawing substituents at C-4 favor attack at C-5 with formation of 2-pyrrolones 5, 6, 10, 13, 17, a nd 20. Alternatively, attack at C-2 leads to alpha-oxobutenoic acid de rivatives 3, 7, 11, 12, 15, and 18. IR and C-13-NMR spectroscopic tech niques were employed to differentiate between the possible isomeric ad dition products formed. The structure of methyl alpha-oxobutenoate 15 was established by an X-ray crystallographic analysis.