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Three conceptual routes (A, B, C) from [l.l.l.l]pagodane (1) to pentagonal dodecahedrane (2) are evaluated by MM2 (MM3) calculations. After limited experimental success with a catalytic one-pot route (A), a more selective transformation along one of two stepwise routes (B/C) is explored. An expeditious entry into route C is achieved by hydrogenolytic cyclobutane opening in 1; secopagodane 7 (loo%), however, resists both progression along route C (dehydrogenative C -C bond formation to isododecahedrane 8) and crossover into route B (hydrogenolysis to bissecododecahedrane 5). The first transformation along route B, the 2o-t2n-isomerization of the highly strained 1 to bissedodecahedra-l,lO(ll)-diene 3, is not attainable by metal catalysis and cannot productively be brought about by thermal activation: The necessarily very high reaction temperatures ( > 700°C) enforce instead a mechanistically interesting fragmentation into two CloHlo halves to give ultimately naphthalene. The very rapid pagodane opening occurring after one-electron oxidation, too, is not a preparatively useful alternative. Highly efficient, on the other hand, is a two-step process affording a high yield of the product and consisting of regiospecific, photochemically induced bromine addition to the central four-membered ring (+ dibromosecopagodane 37) followed by reductive bromine elimination (+ diene 3). In spite of the necessarily rather severe reaction conditions in both steps, this procedure is applicable to the preparation of various 3,8-difunctionalized bissecodienes (dienedione 11, diene diesters 43, 50, 52, dichlorodiene 56). Limitations of this procedure are met with the 4,4,9,9-tetrachloropagodane 60 (inert) and the [2.2.l.l]pagodane 80 (bridgehead bromination). The lateral half-cages of the (seco)-pagodane structures are explored for preparatively (dis)advantageous steric effects, that might be later exploited on the way towards functionalized dodecahedrane derivatives.The pentagonal dodecahedrane 2, the organic chemist's molecular transliteration of Plato's Universe into hydrocarbon reality, has a colorful history"]. Out of numerous attempts towards the construction of this fascinating spherical network of saturated carbon-carbon bonds ['], to date only two have been successfully completed: The synthesis reported by the Paquette group[51 is based on a linear approach, starting ultimately from cyclopentadiene and an acetylene derivative and reaching the target after a series of as elegant as demanding bond forming procedures.The strategy towards dodecahedranes as devised in our laboratory implies the construction of (substituted) pagodanes as precursor molecules and their subsequent structural re~rganization[~,'~. Thus, for the parent hydrocarbons 1 and 2, full advantage is taken of the formidable Zh symmetry of the target molecule. The progress of this project made headway, once it was demonstrated, that the isomeric C20H20 hydrocarbon 1 as well as 4,9-difunctionalized derivatives thereof (e.g. diketone 9 and syn,syn-diester 42) could be ...

Homo-and bishomododecahedral cage molecules with one and two 0 -C O (0-CH2) linkers installed into the parent pentagonal framework and featuring diverse functionalization patterns have been made available from pagodane precursors via highly expeditious synthetic sequences. The enforced geometrical changes with respect to molecular curvature, olefinic pyramidalization, transannular n,n-distance as well as to the chemical reactivity particularly of the unsaturated homododecahedranes are generally in good agreement with expectations based on calculations (MM2). In the appreciably pyramidalized monohomododecahedradjene skeleton 40 the non-parallel n-bonds are ca. 2.9 (3.1) A [(D = ca. 20 (32) O , MM21, in the bishomododecahedradiene skeleton 55 the perfectly syn-periplanar n-bonds 2.81 A apart (@ = 18.2", X-ray crystal structure).