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By temporary immobilization on a quaternary ammonium resin (Amberlyst 26-A, OH− form), the acidic 2,4-pyrrolidinediones (tetramic acids) could be purified immediately after being synthesized by a Dieckmann condensation of amide esters that was catalyzed by this resin [Eq. (a)]. R1 H, alkyl, benzyl; R2 = phenyl, aryl; R3 CN, o-O2NC6H4, P(O)(OEt)2.
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Kulkarni et al. (1997) studied this question.
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