Dispirocyclobutane und Propellane aus 1,2‐Bisenollactonen

Dispirocyclobutanes and Propellanes from 1,2-Bisenollactones Electronically excited biphthalidylidene (1) and isocoumarino-isocoumarin (5) are trapped by electron-Poor stilbenes and by 1,3-dienes to give the dispirocyclobutanes 3, 8, 9, 11, 12 and the heterocyclic [4.4.2]propellanes 6 and 14 resp. The unusual tetraspirocyclobutane 4 is formed upon photodimerization of 1 as a by-product. The structures of the products have been established primarily by high-field, 1H-NMR spectroscopy and in part by chemical transformations.