Tetrahydropyranyl THP and Related Ethers

THP ethers are labile to mild acid such as HOAC-H2O (4 1) at 45 C - conditions that cleave TBS ethers but not PMB, SEM, MEM, or MOM ethers 

Most Lewis acids will cleave THP ethers and conditions are mild enough to allow retention of protecting groups that would otherwise be labile in aqueous or alcoholic acid. For example, three equivalents of magnesium bromide in ether have been used to cleave THP ethers of primary and secondary alcohols and these conditions are compatible with TBS and MEM ethers however, MOM ethers cleave slowly. A further limitation is that tertiary and 

In many instances the reaction of an alcohol with dihydropyran (or ethyl vinyl ether or 2-methoxypropene) does not go to completion despite the addition of a large excess of the enol ether as much as 20% of the starting material will be present at equilibrium. The equilibrium, once reached, can be shifted toward product by adding excess finely powdered anhydrous potassium carbonate and stirring the reaction mixture at room temperature. As the acid concentration gradually diminishes, the reaction goes to completion. 

---