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2004
Pyrrole derivatives
R 0120
Singlet Oxygen Reactions of 3-Methoxy-2-pyrrole Carboxylic Acid tert-Butyl
A Route to 5-Substituted Pyrrole Precursors of Prodigiosin and Ana50- 069 Esters.
logues. — The title ester (I) is transformed by singlet oxygen in the presence of nucleophiles to 5-substituted pyrroles via a peroxidic intermediate, which reacts with the
nucleophiles with loss of H2O2. A different outcome concerning the reaction of (I) with
β-diketones is observed. Whereas open-chain diketones afford monoaddition products
like (VIe), cyclic diketones (VII) give double addition products (VIII). The increased
acidity of the cyclic diketones will enhance the nucleophilic character of the initially
formed 5-substituted adduct, favoring a second-stage reaction. The title method is
applied to the synthesis of the prodigiosin analogue (XI). — (WASSERMAN*, H. H.;
XIA, M.; WANG, J.; PETERSEN, A. K.; JORGENSEN, M.; POWER, P.; PARR, J.;
Tetrahedron 60 (2004) 34, 7419-7425; Dep. Chem., Yale Univ., New Haven,
CT 06520, USA; Eng.) — Klein
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