The photochemical ring expansion of dispiro substituted cyclobutane-1, 3-diones in methanol has been investigated. The formation of ring expansion product was strongly dependent on the spiro ring size of dispiro substituent. The ring expanded acetal was obtained in a low yield when the spiro ring of dispiro substituted cyclobutane-1, 3-diones was a five-or seven-membered ring. This is the first example of photochemical ring ...
[Muedas, Cesar A.; Ferguson, Richard R.; Brown, Stephen H.; Crabtree, Robert H. Journal of the American Chemical Society, 1991 , vol. 113, # 6 p. 2233 - 2242]