Ethers, 4-methoxytetrahydropyranyl oligonucleotide synthesis

An inherent disadvantage of the TPIP and acetaldehyde acetals is that they contain a new chiral center, giving rise to mixtures of diastereomers if chiral alcohols are involved. This can be overcome by the use of 4-methoxytetrahydropyranyl ethers (Scheme 29). They are extensively applied in oligonucleotide synthesis. The analogous thiopyranyl compounds are hydrolyzed five times more quickly, but their S -dioxides 2(XX) times more slowly, than the corresponding oxygen compounds. 

---