Chapter 16: Ethers, Epoxides and Sulfides Ch 16 contents

Using Halohydrins to Synthesise Epoxides
(review of Chapter 6 and 8)

preparation of a 1,2-halohydrin
intramolecular SN2 to give an epoxide
Reaction type: Electrophilic Addition then Nucleophilic Substitution

Summary

Questions:
What named reaction is the ring closure step most like ? Williamson ether synthesis
If the ring closure is an SN2 reaction then what should be the arrangement of the -O-C-C-X system ?180 degrees = anti (recall SN2 backside attack, see Ch8)
What is the stereochemistry of the halohydrin formation ?anti : water opens the halonium ion (review Ch6 on halohydrins)

Related reactions

MECHANISM OF HALOHYDRIN TO EPOXIDE
Step 1:
An acid/base reaction.  The base deprotonates the alcohol forming an alkoxide intermediate that has enhanced nucleophilicity.
Friedel-Crafts alkylation of benzene
Step 2:
An intramolecular SN2 reaction where the alkoxide nucleophile attacks the electrophilic C displacing the leaving group, the halide ion. The nucleophile has to attack anti to the C-X bond.

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