Acid- and Base-Promoted Rearrangements of Cycloalkane-Fused Heterocycles

Certain cycloalkane-anellated heterocycles undergo rearrangement under basic or acidic conditions via ring-contraction, ringexpansion or ring-opening pathways to afford new or unusual compounds. The reactivities and properties of cycloalkane-fused heterocycles differ significantly from those of heteroaromatic ring systems. Possible mechanisms are also discussed.