Syntheses, Structures, and Reactions of Highly Strained Dihydro- and Tetrahydroacepentalene Derivatives

The highly strained 4,7-disubstituted dihydroacepentalene derivatives 1, which are obtained in good yields from the stable acepentalenediide 2 with bulky electrophiles, are structurally interesting molecules in their own right. Some of them may even serve as precursors to the intriguing and long elusive acepentalene. The protonation of 2 leads to the highly reactive 4,7-dihydroacepentalene 3, which undergoes rapid Diels–Alder reactions.