Epoxides and Ethers

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Chapter 18

• Epoxides and Ethers

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Structure of Ethers and Epoxides
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Acid-Catalyzed Dehydration

• Limited to symmetrical ethers
• Works with only 1o alcohols
• 2o and 3o alcohols give elimination pdts

Synthetically Useless
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Williamson Ether Synthesis

• Reaction of an alkoxide base with an alkyl halide
  or tosylate.
• SN2 chemistry (see Ch. 11)
• Primary substrate (R-X)
• Alkoxide is a good base
• Need good leaving groups like iodide or tosyl

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Synthetic Strategy for Preparing Unsymmetrical
Ethers

• Use your knowledge of SN2 chemistry

Good LG ? iodide or tosyl
The more substituted portion
Primary or at most secondary
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Silver (I) Oxide Variant

• A free substituted alcohol, Ag2O and a 1o alkyl
  halide/tosylate

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Oxymercuration (CHEM 210)
Review!!
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Cleavage of Ethers

• Ethers are very stable to a variety of media.
• They will react with HI (or HBr) to give cleavage
  products under SN2-type conditions.

Why this outcome?
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Ether Cleavage, continued

• Allylic, benzylic, and 3o ethers cleave via
  E1/SN1 mechamisms

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Claisen Rearrangement

• Allylic aromatic ethers rearrange to give allylic
  phenols

• 3,3 Sigmatropic rearrangement

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