The established route to the [1.1.1.1]/[2.2.1.1]pagodanes (1, 2) has been applied to the construction of the homologous [2.2.2.2] and [2.1.1.1] skeletons (3, 7). Application of this synthetic scheme to the iso[1.1.1.1]/iso[2.2.1.1]/iso[2.2.2.2] structures (4−6) failed though; the crucial [6+6]benzo/benzo photocycloaddition step in the face-to-face benzo/benzo intermediates (26a and b) − in contrast to the corresponding clean [6+2]benzo/ene-photocycloaddition (27a Ǟ 36) − did not take place. A bypass involving a stereoelectronically less demanding [2+2]ene/ene-photocycloaddition proved rewarding when double Birch reduction was achieved with the benzo/benzo substrates (26a and b), giving 28a and b. Domino-type [4+2]/[4+2] cycloadditions to the thermally rather labile "benzene-cyclodimers" [33a and b, E a (33a) = 23.9 ± 1.5 kcal mol −1 ] allowed the subsequent completion of the isopagodane skeletons in standard manner. The attempts to convert the highly strained, yet thermally highly persistent, (iso)pagodanes (3−7) into one of the derived (iso)pagodadienes [A(AЈ), B(BЈ)] − the calculated energies (MMP2) are also
Edgar Heilbronner in alter Verbundenheit (H. P.; H.-D. M.) zum 80. Geburtstag Secodecahedradiene 2a, featuring very proximate, perfectly syn-periplanar and significantly pyramidalized CC bonds, was synthesized as testing object for in-plane(s)-homoconjugational electron delocalization, starting from the available pagodane 15b. The response of 2a (and in part its diester 2b) ± in p,p-distance (average 3.08 ), olefinic pyramidalization (average 26.98), and p,p-split (PE, 1.15 eV) intermediate between disecododecahedradiene 1a and 1,16-dodecahedradiene 3a ± to selected 4p-reagents, electrophiles, and radicals was explored experimentally and by calculations. Intriguing multistep reaction sequences attest to the ease of competing stabilization pathways for the 3C/2e in-plane homoconjugated cationic intermediates. PE, CV, and ESR measurements and calculations (DFT) characterize the radical cation generated from 2a as in-plane homoconjugated 4C/3e-species 2a. , persistent in a Freon matrix, but only very shortly existent in solution (CIDNP). Consequently, NMR control of the two-electron oxidation in SbF 5 /SO 2 ClF did not disclose the s-bishomoaromatic dication 4C/2e (see 2a 2 ), but a bis-allylic dication 75 as persistent species. In support of 2a 2 as intermediate, evidence is presented for very limited kinetic protection offered by the secododecahedral framework to through H-cage s-homoconjugated cations.
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