Nucleophilic Cleavage of Carbon-Oxygen Bonds in Ethers and Esters

The cleavage of carbon-oxygen bonds in ethers or esters by nucleophilic substitution is frequently a useful synthetic transformation. 

SECTION 3.3. NUCLEOPHILIC CLEAVAGE OF CARBON-OXYGEN BONDS IN ETHERS AND ESTERS 

Generally, good yields are observed, especially for methyl ethers. The combination of boron tribromide with dimethyl sulfide has been found to be particularly effective for cleaving aryl methyl ethers.  

Trimethylsilyl iodide cleaves methyl ethers in a period of a few hours at room temperature. Benzyl and r-butyl systems are cleaved very rapidly, whereas secondary systems require longer times. The reaction presumably proceeds via an initially formed silyl oxonium ion. 

The direction of cleavage in unsymmetrical ethers is determined by the relative ease of O—R bond breaking by either Sn2 (methyl, benzyl) or SnI (t-butyl) processes. 

Nucleophilic Cleavage of Carbon-Oxygen Bonds in Ethers and Esters 

CHAPTER 3 FUNCTIONAL GROUP INTERCONVERSION BY NUCLEOPHILIC SUBSTITUTION 

The mechanism for ether cleavage with boron tribromide involves attack of bromide ion on an adduct formed from the ether and the electrophilic boron reagent. The cleavage step can occur by either an Sn2- or Swl-type process, 

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