Cleavage of ether

These reactions are similar to the reaction of alcohols with strong acids (eq. 7.18). If the alkyl groups R and/or R are primary or secondary, the bond to oxygen can be broken by reaction with a strong nucleophile such as 1 or Br (by an 8 2 process). For 

CH3CH2I + H0CH(CH3)2 ethyl iodide isopropyl alcohol 

If R or R is tertiary, a strong nucleophile is not required since reaction will occur by an 

The net result of these reactions is cleavage of the ether at one of the C—O bonds. Ether cleavage is a useful reaction for determining the structure of a complex, naturally occurring ether because it allows one to break the large molecule into more easily handled, smaller fragments. 

Prior to the 1 840s, pain during surgery was relieved by various methods (asphyxiation, pressure on nerves, and administration of narcotics or alcohol), but on the whole, it was almost worse torture to undergo an operation than to endure the disease. Modern use of anesthesia during surgery has changed all that. Anesthesia stems from the work of several physicians in the mid-nineteenth century. The earliest experiments used nitrous oxide, ether, or chloroform. Perhaps the best known of these experiments was the removal of a tumor from the jaw of a patient anesthetized by ether, performed by Boston dentist William T. C. Morton in 1 846. 

The method has also been used successfully to remove the methoxymethyl (MOM) group (Eq. 23) [48,49], and should be compared once again with the use of BF3 Et20-ethanedithiol (Eq. 24), which was used in a total synthesis of brucean-tin [50]. 

The benzyloxycarbonyl (Cbz) group can be removed from nitrogen by BF3 Et20 in the presence of either a thiol or dimethyl sulfide. The carbamates derived from secondary amines are cleaved more rapidly than those from primary amines by use of the ethanethiol method, even when using BF3 Et20 as solvent. This procedure is reasonably selective, as shown in Eq. (25) [46]. 

Cleavage of the tetrahydrofuran ring gave the diacetate (Eq. 26) with inversion of configuration at C-20 [51]. 

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Cleavage of ethers with hydriodic acid. Aliphatic ethers suflFer fission when boiled with constant boiling point hydriodic acid ... 

The cleavage of ethers is normally earned out under conditions (excess hydrogen halide heat) that convert the alcohol formed as one of the original products to an alkyl halide Thus the reaction typically leads to two alkyl halide molecules... 

FIGURE 16 4 The mechanism for the cleavage of ethers by hydrogen halides using the reac tion of diethyl ether with hydrogen bromide as an example... 

Organosodium compounds are prepared from sodium and other organometaUic compounds or active methylene compounds by reaction with organic haUdes, cleavage of ethers, or addition to unsaturated compounds. Some aromatic vinyl compounds and aHyUc compounds also give sodium derivatives. 

Pyndinium p-toluenesuHonate (PPTS) reagent 1 for protection of alcotwls as the tetrahydropyranyt ethers as well as for cleavage of ethers (in warm ethanol)... 

JUNG OLAH - VORONKOV Etherdeavage Cleavage of ethers or esters, carbamates, phosphorates with trimethylsilyl Iodides. Oeoxygenation of sulfoxides. 

This method is probably the most commonly used method for the cleavage of ethers because it generally gives excellent yields with a variety of structural types. BBr3 will cleave ketals. 

Scheme 5.1-15 The acylative cleavage of ethers in an ionic liquid.

We have studied the thermal decomposition of diaryl ether in detail, since the cleavage of ether linkage must be one of the most responsible reactions for coal liquefaction among the various types of decomposition reaction and we found that the C-0 bond of polynucleus aromatic ethers is cleaved considerably at coal liquefaction temperature. 

Use of graphite-supported methodology has been reported for three types of reaction - the Friedel-Crafts acylation [15, 16, 27, 66], the acylative cleavage of ethers [15, 16], and the ketodecarboxylation of carboxylic diacids [67, 68], either with conventional heating (GS/A) or MW irradiation (GS/MW coupling) these are discussed below. First, however, we describe the analysis of two commercial graphites of different purity which are used for these experiments. 

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