Abstract
The palladium-catalyzed Friedel-Crafts-type alkylation of indoles in water has been achieved using amphiphilic polystyrene-poly(ethylene glycol) (PS-PEG) resin-supported phenanthroline-palladium complexes in water under aerobic conditions, affording the corresponding products with good-to-high yield. The polymeric catalyst was also found to promote the C3-alkylation reaction to give a thermodynamic alkylation product with high selectivity. The polymeric catalyst was recovered and reused several times without any loss of catalytic activity.
Highlights
The Friedel-Crafts reaction is one of the considerably important carbon–carbon bond forming reactions to employ Lewis acids as promoters since the pioneering study by Friedel and Crafts [1,2].Recently, the original procedure has been replaced by catalytic Friedel-Crafts-type reactions for the alkylation and acylation of aromatic and heteroarene compounds [3,4]
If the Friedel-Crafts reactions were performed in water with recyclable palladium catalysts, where neither aqueous-organic solvent wastes nor metal-contaminated wastes were yielded, this would go a long way to meeting green chemical requirements
We aimed for the Friedel-Crafts reaction of π-allylic palladium intermediates with indoles in water under aerobic conditions in the presence of amphiphilic polystyrene-poly(ethylene glycol) (PS-PEG) resin-bound pyridine skeleton ligand-palladium complexes 1a–c (Scheme 1)
Summary
The original procedure (for which stoichiometric amounts of a Lewis acid were required) has been replaced by catalytic Friedel-Crafts-type reactions for the alkylation and acylation of aromatic and heteroarene compounds [3,4]. Friedel-Crafts reactions of allyl compounds with electron-rich aromatics, research on the catalytic. Resin-supported terpyridine-palladium complexes that promote varied catalytic transformations [18,19,20,21,22,23,24,25,26,27,28]. We aimed for the Friedel-Crafts reaction of π-allylic palladium intermediates with indoles in water under aerobic conditions in the presence of amphiphilic PS-PEG resin-bound pyridine skeleton ligand-palladium complexes 1a–c (Scheme 1)
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