Synthesis of Ethers Alcohols and Mineral Acids

In contrast, the IS,2R) isomer contains the same functions on the same side of the five-membered ring. To proceed to (the same) product, a frontside displacement is needed, which is much more difficult. Thus, the alkoxide derived from the l/ ,2ff-diastereomer reacts faster than that generated from the 15, 2/J-isomer. 

Bromoalcohol A transforms rapidly in the presence of sodium hydroxide to give the corresponding oxacyclopropane, whereas its diastereomer B does not. Why [Caution Unlike the previous problem, both substrates are frans-bromoalcohols. Hint Draw the most stable cyclohexane chair conformers of both isomers (Section 4-4) and picture the respective transition states for the intramolecular Williamson ether synthesis.] 

In Summary Ethers are prepared by the Williamson synthesis, an Sn2 reaction of an alkoxide with a haloaUcane. This reaction works best with primary halides or sulfonates that do not undergo ready elimination. Cychc ethers are formed by the intramolecular version of this method. The relative rates of ring closure in this case are highest for three- and five-membered rings. 

We have learned that treating primary alcohols with HBr or HI furnishes the corresponding haloalkanes through intermediate alkyloxonium ions (Section 9-2). However, when strong nonnucleophilic acids—such as sulfuric acid—are used at elevated temperatures, the main products are ethers. 

Symmetrical Ether Synthesis from a Primary Alcohol with Strong Acid 

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Synthesis of Ethers Alcohols and Mineral Acids CHAPTER 9... 

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