Acid-catalyzed Grob fragmentation reactions of acetonides derived from terpenes.

[reaction: see text] Acetonides derived from different terpenes undergo Grob fragmentation by treatment with a catalytic amount of acid, triflic acid, or boron trifluoride, giving aldehydes containing a cyclopropane or cyclobutane ring with good yields and complete diastereoselectivity. The structure and the stereochemistry of the starting acetonide have a crucial influence on the reaction course.