Isomerization of tetrahydropyrans

Summary

• 1. The transformations ofα-alkyl-,α-phenyl-, andα-cyclohexyltetrahydropyrans in the vapor phase on a Pt-C catalyst at 340–350° were investigated.

• 2. α-Alkyl- andα-phenyltetrahydropyrans not only isomerize at the C-O bond, but also undergo partial decomposition to formaldehyde and the corresponding olefin (10–20%).

• 3. The isomerization ofα-alkyltetrahydropyrans proceeds 70% at the C-O bond not next to the side substituent, and 20% at the other C-O bond, while that ofα-phenyltetrahydropyran proceeds to an extent of 60% at the bond away from it.

• 4. The cyclohexane ring is dehydrogenated to benzene before isomerization of the tetrahydropyran ring.