Acid-catalyzed additions of acetic acid, formic acid and water to endo- dihydrodicyclopentadiene (I) lead to products 111 which almost complete ring isomerizations (to 111, or its analogs) has occurred On the other hand, addition of methanol (or of water in methanol solvent) to I or to dicyclopentadiene (11), followed by hydrogenation, gives a mixture containing about 1 part of endo skeleton unrearranged ...