Phanes with three- and four-membered rings as building elements

The systematic integration of the small 2π- and 4π-electron systems cyclopropenylium ion, cyclopropenone, oxocyclobutenylium ion, and cyclobutadiene into phane chemistry was initiated only a few years ago. [n2]Cyclopropenyliophanes, [n2]cyclopropenonophanes, metal-capped [n4]cyclobutadienosuperphanes, and other new families of double-decker phane species became available from cycloalkydiynes through special methods of double [2+l]cycloaddi-tion with carbenes and metal complex induced dimerization by double [2 + 2]-cycloaddition. Phane-specific structural features were elucidated by X-ray structural analyses. Cyclic voltammetry and PE spectroscopy as well as MO calculations revealed considerable interactions between closely spaced π-electron systems. Decapping cyclobutadienosuperphanes formally extended the synthetic principle to threefold [2 + 2]cycloadditions resulting in [n4-bridged tricyclo-[4.2.0.03, 5]octa-3,7-dienes, which represent a new type of cage compounds. Moreover, completion to fourfold [2 + 2]addition was achieved with the photoinduced transformation of [34]-bridged tricyclo[4.2.0.03, 5]octa-3,7-diene into propella[34]cubane. © WILEY-VCH Verlag GmbH, D-69451 Weinheim, 1997.