Cerium(IV) Pyridinium Chloride
· Cerium(IV) Pyridinium Chloride
· (MW 513.06)
(oxidizing reagent for the direct preparation of amides from protected carboxylic acids;1 for the functionalization of methyl-substituted aromatic compounds2)
Alternate Name: dipyridinium hexachlorocerate(IV).
Solubility: sol acetonitrile, methanol, ethanol, and water.
Form Supplied in: yellow powder.
Analysis of Reagent Purity: elemental analysis.
Preparative Methods: by reaction of cerium(IV) hydroxide with anhydrous hydrogen chloride and pyridine.3
Purification: dry at 120 °C under reduced pressure (0.1 mmHg) for 3 h.3
Handling, Storage, and Precautions: hygroscopic, store under nitrogen and protect from exposure to moisture.
Preparation of Amides.1
Various amides are directly prepared from 5-acyl-5,6-dihydrophenanthridine carboxylic acid derivatives by reaction with primary amines in the presence of cerium(IV) pyridinium chloride and copper(II) oxide (eq 1). This reagent is far superior to Cerium(IV) Ammonium Nitrate (CAN) for this purpose. Employment of secondary amines did not give satisfactory results. 5-Acyl-5,6-dihydrophenanthridines with functional groups such as esters, carbonyls, or halogens in the same molecule are also converted to the corresponding amides. The benzoylation of a-amino ester proceeds without racemization.
Oxidation of Aryl Methyl Groups.2
Methyl-substituted aromatic compounds are oxidized to alkoxymethylbenzene derivatives by treatment with cerium pyridinium chloride in alcohol. Oxidation of hexamethylbenzene in ethanol proceeds at reflux temperature to afford the ethyl ether in good yield, while the reaction in methanol gives a 1:1 mixture of methyl ether and chloride (eq 2).
- 1. Narasaka, K.; Hirose, T.; Uchimaru, T.; Mukaiyama, T. CL 1982, 991.
- 2. Maini, S.; Mandolini, L. JOC 1978, 43, 3236.
- 3. Bradley, D. C.; Chatterjee, A. K.; Wardlaw, W. JCS 1956, 2260.
K. Narasaka & H. Kusama
The University of Tokyo, Japan
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