Yttrium Compounds: New Catalysts for the Regioselective Acylative Cleavage of Epoxides
摘要:
The use of Cp2YCl and YCl3 as effective catalysts for the regioselective acylative cleavage of epoxides, especially for the conversion of alpha,beta-epoxy-ketones to alpha-chloroenones is described.
We describe here the first example in which glycerol has been transformed into chlorohydrin esters using an ionic liquid and hydrated aluminium chloride. The method avoids using Crown-18 ether, which was needed to obtain a similar yield when KCl was used. Alkyl and aryl acids can be used, although yields are very dependent on the carboxylic acid used.
Esterification-chlorination of glycerol provides chlorohydrin esters in high yields. A ratio of reagents close to equivalence can be used, so that atom economy of the reaction is optimized. The reaction can be carried out using either classical or microwave heating, and no solvent is required. 2-Chloro-1-(chloromethyl)ethyl esters can be obtained in high regioisomeric relationship when either low or moderate temperature is used. In contrast, microwave irradiation allows the use of higher reaction temperatures that render mixtures of both regioisomers in variable relationships. Kinetic control of the process is proposed for classical heating, and experimental results are analyzed with the aid of ab initio calculated values. Non-thermal phenomena can be used to explain the high efficiency of microwave irradiation at low temperature. (C) 2009 Elsevier Ltd. All rights reserved.
A tandem Finkelstein-rearrangement–elimination reaction: a straightforward synthetic route to allyl esters
Finkelstein-rearrangement–elimination reaction of 2-chloro-1-(chloromethyl)ethyl esters induced by NaI. Sodium iodide can be used below equivalence using a reductive agent as sodium thiosulfate. High yields are obtained with most of the diverse esters studied. The method described avoids the use of allyl alcohol as a reagent. 2-Chloro-1-(chloromethyl)ethyl esters are prepared from glycerol, the main by-product
Yttrium Compounds: New Catalysts for the Regioselective Acylative Cleavage of Epoxides
作者:Changtao Qian、Dunming Zhu
DOI:10.1080/00397919408010236
日期:1994.8
The use of Cp2YCl and YCl3 as effective catalysts for the regioselective acylative cleavage of epoxides, especially for the conversion of alpha,beta-epoxy-ketones to alpha-chloroenones is described.