Chapter 16, Problem 14PP

Practice Problem 16.14

Dihydropyran reacts readily with an alcohol in the presence of a trace of anhydrous HCL or $H_{2}S{O}_4$ to form a tetrahydropyranyl (THP) ether:

(a) Write a plausible mechanism for this reaction.

(b) Tetrahydropyranyl ethers are stable in aqueous base but hydrolyze rapidly in aqueous acid to yield the original alcohol and another compound. Explain. (What is the other compound?)

(c) The tetrahydropyranyl group can be used as a protecting group for alcohols and phenols. Show how you might use it in a synthesis of 5-methyl-1,5-hexanediol starting with 4-chloro-1-butanol.