Aromatic 4-Tetrahydropyranyl and 4-Quinuclidinyl Cations. Linking Prins with Cope and Grob

The chair 4-tetrahydropyranyl cation and the 4-quinuclidinyl cation are shown to be energy minima and to be delocalized, with exceptionally long CH₂CH₂ bonds, according to B3LYP/6-31G* calculations; the implications for Prins cyclizations, Cope rearrangements, and Grob fragmentations are discussed.