Abstract
The ability of CeCl3 ·nH2 O/NaI system to work as an useful water tolerant promoter and/or reagent in many organic transformations is reviewed. They include Michael additions of 1,3-dicarbonyl compounds, amines and indoles to α,β-unsaturated ketones, and related systems, the cleavage of carbon-oxygen and carbon-silicon bonds, the conversion of alcohols into the corresponding iodides, as well as the stereospecific dehydration of β-hydroxy carbonyl compounds and the hydroxacyclization of unsaturated 3-hydroxy esters. Generally the reactions are carried out at reflux in wet CH3 CN, however, in some case, it is possible to work under solvent free conditions and/or in the presence of the catalyst supported on SiO2 . In the last case the simple experimental procedures allow the complete recovery of the catalyst and its recycling without loss of activity. Many of these protocols found wide application in organic synthesis and are now methods of common choice, since they are competitive and in some cases superior to the pre-existing procedures. The reasons for this success can be ascribed to the fact that this reagent allows the reaction to be carried out in close to neutral conditions and thus allows the survival of a large variety of functionalities sensitive to acidic hydrolysis. In addition, CeCl3 ·7H2 O and NaI are cheap, non toxic, and stable compounds, and therefore the protocols based on their use represent an environmentally benign alternative to current chemical processes using water intolerant Lewis acids.
1 Introduction
2 Michael Additions
3 Cleavage of Carbon-Oxygen and Silicon-Oxygen Bonds
3.1 General Protocol for the Deprotection of PMB Ethers
3.2 Cleavage of Trityl, Trialkylsilyl, and Allyl Ethers
3.3 Cleavage of tert -Butyl and Prenyl Esters
3.4 Deprotection of Dioxolanes, Oxathiolanes, and Dithiolanes
4 Reactions Involving the Hydroxyl Group
4.1 Conversion of Alcohols into Iodides
4.2 Dehydration of β-Hydroxy Carbonylic Compounds to the
4.3 Synthesis of E- Alkylidene Cycloalkanones
4.4 Hydroxacyclization of Unsaturated 3-Hydroxy Esters
5 The Origin of the High Lewis Acid Activity of 3 ·nH2 O/NaI Combination
6 Conclusions
Key words
cerium(III) chloride - Lewis acids - sodium iodide - Michael additions - cleavage of ethers - hydroxyl group transformation
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