"One-pot" substitution of the twenty hydrogen atoms in pentagonal dodecahedrane (C(20)H(20)) by OH, F, Cl, and Br atoms is explored. Electrophilic insertion of oxygen atoms with DMDO and TFMDO as oxidizing reagents ended, far off the desired C(20)(OH)(20), in complex polyol mixtures (up to C(20)H(10)(OH)(10) decols, a trace of C(20)H(OH)(19)?). Perfluorination was successful in a NaF matrix but (nearly pure) C(20)F(20) could be secured only in very low yield. "Brute-force" photochlorination (heat, light, pressure, time) provided a mixture of hydrogen-free, barely soluble C(20)Cl(16) dienes in high yield and C(20)Cl(20) as a trace component. Upon electron-impact ionization of the C(20)Cl(16) material sequential loss of the chlorine atoms was the major fragmentation pathway furnishing, however, only minor amounts of chlorine-free C(20) (+) ions. "Brute-force" photobrominations delivered an extremely complex mixture of polybromides with C(20)HBr(13) trienes as the highest masses. The MS spectra exhibited exclusive loss of the Br substituents ending in rather intense singly, doubly, and triply charged C(20)H(4-0) (+(2+)(3+)) ions. The insoluble approximately C(20)HBr(13) fraction (C(20)Br(14) trienes as highest masses) obtained along a modified bromination protocol, ultimately allowed the neat mass selection of C(20) (-) ions. The C(20)Cl(16) dienes and C(20)H(0-3)Br(14-12) tri-/tetraenes, in spite of their very high olefinic pyramidalization, proved resistant to oxygen and dimerization (polymerization) but added CH(2)N(2) smoothly. Dehalogenation of the respective cycloaddition products through electron-impact ionization resulted in C(22-24)H(4-8) (+(2+)) ions possibly constituting bis-/tris-/tetrakis-methano-C(20) fullerenes or partly hydrogenated C(22), C(23), and C(24) cages.

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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).

The [1.1.1.1]pagodane (A, m = n = 1) and functionalized derivatives have received considerable attention as intermediates in the various synthetic routes to pentagonal dodecahedranes. 1 An important theoretical aspect is linked to the central, planar, peralkylated cyclobutane ring: Two-electron oxidations had allowed the experimental verification of shomoaromaticity in form of the respective 4C/2e dications. 2,3 In order to gain more insight into the limiting structural and energetic prerequisites of this intriguing phenomenon-and into the intermediate 'tight' and 'extended' radical cations 4 -structural variations of the pagodane skeleton have been made by homologation 5 and 90° rotation of the two molecular 'halves' to give the isopagodanes B. 6The [1.1.1.1]-and [2.2.1.1]-isopagodanes 1 and 6 had shown rather differing behaviour upon one-electron oxidation: the radical cation of 1 (Scheme 1) was only observable in a Freon matrix (2196 °C) and was identified as a tight species (3, a = 1.768 Å), 7 that from 6 was persistent in fluid solution (240°C, CH 2 Cl 2 ) and existed, also in the Freon matrix, in an extended configuration (9, a = 2.512 Å). Under cyclic voltammetry (CV) conditions only for the latter a (reversible) two-electron oxidation wave (ECE) had been recorded. 8 Apparently the iso[1.1.1.1] skeleton does not allow the expansion of tight 3 into extended 4. Here the question is addressed whether the sbishomoaromatic stabilization potentially arising from twoelectron oxidation of 1 and 6 would be sufficient to enforce the skeletal changes which are necessary to make the respective cyclically delocalized 4C/2e dications observable.Upon dissolution of 1 in SbF 5 -SO 2 ClF at 278 °C (dry iceacetone bath) the initial dark green-blue color of the paramagnetic solution ( 3 7 (Fig. 1), 4 establish the C 2v symmetrical s-bishomoaromatic structure 5 and exclude a rapid equilibration with degenerate 5A. The lowering of the symmetry from D 2d of 1 to C 2v of 5 reflects distortion of the central carbon core from square to rectangular. Quenching the ion solution with cold MeOH (at 278 °C) induced two-electron reduction back to pagodane 1 (70% isolated) rather than to the much less stable diene 2 [DE rel (1-2) = 14.68 kcal mol 21 , Fig. 2]. Particularly 1,4-bisaddition to give the bismethoxy ether was not observed ( < 5%); in case of reference 15 the corresponding bisether had been the sole product. 2 Exposure of 6 (Scheme 2) to similar oxidation conditions (278 °C) produced the deep blue colour of the highly persistent extended radical cation 9. Only after repeated vortex mixing at higher temperature (0 °C) the colour changed into pale yellow. (Fig. 1) provided additional confirmation. After quenching with MeOH (278 °C) from a complex product mixture the dichlorodimethoxy-and chlorotrimethoxydienes 13 (two isomers) and 14 in the ratio ~1 : 2 were separated. Two-electron reduction to either 6 or 7 was not detected. A plausible explanation implies reduced anti-Bredt-

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