Ether cleavage reaction

Substitution Reactions on Side Chains. Because the benzyl carbon is the most reactive site on the propanoid side chain, many substitution reactions occur at this position. Typically, substitution reactions occur by attack of a nucleophilic reagent on a benzyl carbon present in the form of a carbonium ion or a methine group in a quinonemethide stmeture. In a reversal of the ether cleavage reactions described, benzyl alcohols and ethers may be transformed to alkyl or aryl ethers by acid-catalyzed etherifications or transetherifications with alcohol or phenol. The conversion of a benzyl alcohol or ether to a sulfonic acid group is among the most important side chain modification reactions because it is essential to the solubilization of lignin in the sulfite pulping process (17). 

Unlike the acid-catalyzed ether cleavage reaction discussed in the previous section, which is general to all ethers, the Claisen rearrangement is specific to allyl aryl ethers, Ar—O—CH2CH = CH2. Treatment of a phenoxide ion with 3-bromopropene (allyl bromide) results in a Williamson ether synthesis and formation of an allyl aryl ether. Heating the allyl aryl ether to 200 to 250 °C then effects Claisen rearrangement, leading to an o-allylphenol. The net result is alkylation of the phenol in an ortho position. 

Predict the products of the following ether cleavage reactions ... 

It was not possible to obtain LisP by metallation of LiPHj with LiBu due to an ether cleavage reaction. Its formation succeeded through the reaction of PHj with an excess of LiBu in a solution of hexane/toluene and through the repeated action of LiBu on the lithium phosphide obtained initially (34). 

In a reversal of the ether cleavage reactions described above, benzyl alcohols and ethers may be transformed to alkyl or aryl ethers via acid-catalyzed etherification or transetherification, respectively, by reaction with the appropriate alcohol or phenol (reaction R, Fig. 1.5). 

Unlike the add-catalyaed ether cleavage reaction discussed in the section, which is general to all ethars, the Claisen rearrangement is pe>) ctAc to allyl aryl ethers, Ar-Ch< HaCH=CH2. Treatment of a pbenexMle ten... 

The analogous ether cleavage reaction of the crown-5 analog of 40 rendered its synthesis from the aryl bromide and magnesium next to impossible isolation of crystalline 2-bromomagnesio-I,3-xylyl-18-crown-5 (41), formed in 16% yield, from the crude reaction mixture was not feasible. Therefore, pure 41 had to be obtained by treatment of the aryl bromide with /j-butyllithium, followed by the addition of 1 equiv magnesium bromide. The crystal structure of 41 contained two independent residues (41a and 41b) and proved to be very irregular the conformation of its crown... 

A total synthesis of ( )-codeine also utilized the aziridinium salt 94 as a key intermediate, which was converted to 100 via epidihydrothebainone methyl ether (98) according to Evans s procedure. Specific ether cleavage reaction of 100 with NaSEt afforded dihy othebainone (101) in 100% yield. Since dihydrothebainone (101) had already been transformed into codeine (102), this synthesis constitutes a formal synthesis of 102 (Scheme 19). 

Izumi, Y, Matsuo, K., and Urabe, K. 1983. Efficient homogeneous acid catalysis of heteropoly acid and its characterization through ether cleavage reactions. /. Mol. Catal. 18 299-314. 

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