"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.

Rigid NN/NN (diazene/diazene) systems (F) consisting of more or less alkylated DBH and DBO chromophoric units (1, 2, X‐ray structures), with very short π,π distances [d = 2.849 (1a, av.), 2.822 Å (2)] and almost perfect syn‐periplanar π,π alignments [ω = 168.6 (1a), 174.2° (2)] as well as the more flexible, less “proximate” metathesis isomers (3a,c, 27a,c, d >4.6 Å, ω = 90‐100°) have been synthesized. Homoconjugate π,π interaction (in 1, 2, not in 3, 27) is deduced from UV spectroscopic measurements [π → π* maxima at 239 (234) nm (sh, 260)], while PE analyses furnished only small interaction parameters (1a: <0.3 eV). The potential of the novel syn‐periplanar NN/NN motif in 1 and 2 for the synthesis of somewhat exotic polyheterocycles has been explored by calculation (B3LYP) as well as experimentally: i.a. kinetically stabilized, all‐cis‐peralkylated tetrazolidines (38, 44) and perhydro‐1,2,4,5‐tetrazines (41, 47) have become accessible (i.a. via novel azomethine/diazene and azomethine/azomethine cycloadditions). In 1a with its unreactive DBO chromophoric subunits, in the “buttressed” derivatives 1b‐d, as well as in the DBH/DBO combination 2, and likewise in more ‘distant’ 27 (differently from the analogous CC/CC and NN/CC systems), irrespective of the excitation conditions employed (light of λ ≥≥ 280, 254 nm, low temperature matrix irradiation, acetone sensitization) no [2+2]photocycloaddition was observed. Instead exclusively N2‐elimination took place. It is argued that unproductive NN/NN photocycloaddition would have become observable through metathesis isomerization of the respective tetrazetidines.

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Die Synthese des 7.8 ; 9.10-Dibenzo-sesquifulvalens (2) und des 7.8.9.10-Tetraphenyl-sesquifulvalens (3) sowie Versuche zur Darstellung des 7.8.9.10-Tetrachlor-sesquifulvalens (34) werden beschrieben. Die stabilen Derivate 2 und 3 des sehr unbestandigen Grundkorpers 1 sind durch groRe Reaktionsbereitschaft sowohl gegeniiber elektrophilen als auch nucleophilen Reaktionspartnern ausgezeichnet. Mit Tetracyanathylen bildet 2 ein 1.8-Addukt, 3 hingegen ein 1.4-Addukt. Die physikalischen Daten (UV, NMR) werden im Hinblick auf die x-Elektronendichteverteilung im Grundzustand des cyclischen gekreuzt-konjugierten Bindungssystems 1 diskutiert.Sesquifulvalen (1) ist sehr instabil und nur in hochverdunnter Losung existenzfahig3). Die Identifizierung dieses Kohlenwasserstoffs gelang erst, nachdem wir substi-

Der Substituenteneinfluo auf die einzelnen Schritte der 30-3x-Route zu 1 H-Azepinen wird an Hand mehrerer neu synthetisierter Edukte niiher definiert: Das C-unsubstituierte 7-Azanorbornadien 2a, das 2,3-Dichlorderivat 2 b, der 5,6-Dichlor-2,3-dicarbonester 2c und die an C-l/N-7 mit einem dipolarophilen Rest versehenen 2,3-Dicarbonester 26, e lassen sich durch sensibilisierte/direkte Lichtanregung mehr oder weniger einheitlich in die zum Teil hochlabilen Azaquadricyclane 29 ae isomerisieren. Fur die thermische Umwandlung des Grundgeriistes (N-Tos) 29a werden die kinetischen Parameter bestimmt (Benzol): E, =28.0 f 0.2 kcal/mol, lg A = 15.7; AH* = 27.3 f 0.2 kcal/mol, AS* = 11.1 f 0.7 e.u.Diese Barriere wird durch die Halogenreste in 29b(c) noch starker als durch die Esterreste (290 herabgesetztwobei die +M-im Gegensatz zu den ---Resten ausschlieBlich die Spaltung der gegeniiberliegenden Cyclopropanbindungen bewirken. Die intermediaren Azomethinylide konnen je nach Substitution mit dipolarophilen Reagentien unterschiedlich gut abgefangen werden. Im Fall von 29d (28d) ist die intramolekulare Addition der nichtaktivierten In-Seitenkette (37) bei -30°C so rasch, daB Azepinbildung fast vollstandig unterdriickt wird (Cn2 + 02 + 02], 36?). Das Azepin/Benzolimin-Gleichgewichtsgemisch 31c P 32c (ca. 90: 10) kristallisiert als 31 c (Rontgenstrukturanalyse). Photochemical Transformations, 65 ') The 3a-+fx-Route to lH-Azepines/Benzene IminesWith several newly prepared substrates the influence of substituents upon the individual steps in the 30+3x-route to Iff-azepines is more precisely defined: The C-unsubstituted 7-azanorbornadiene 2a, its 2,3-dichloro derivative 2 b, the dimethyl 5,6-dichloro-2,3-dicarboxylate 2c, and the diesters 2d,e with dipolarophilic groups at C-1/N-7 are selectively isomerized by sensitized/direct photoexcitation into the azaquadricyclanes 29a -e, some of which are highly unstable. For the thermal conversion of the basic skeleton (N-Tos)29a the kinetic parameters have been determined (benzene): E, = 28.0 f 0.2 kcal/mol, Ig A = 15.7; AH* = 27.3 f 0.2 kcal/mol, AS* = 11.1 f 0.7 e. u. This barrier is lowered more efficiently by the chloro (29b,c) than by the methoxycarbonyl substituents (290, with the former (latter) causing exclusive scission of the opposite (neighbouring) cyclopropane bonds. The intermediate azomethine ylides are captured with dipolarophilic reagents more or less efficiently 0 VCH Verlagsgesellschaft mbH, D-

The chances for intramolecular imine/ene (→ azetidines), diazene/ene (→ 1,2‐diazetidines), diazeneoxy/ene (→ 1,2‐diazetidine oxides) and diazenedioxiene (→ 1,2‐diazetidine dioxides) [2+2]photocycloadditions and for the isolation of the respective photoproducts, have been probed with specifically designed substrates. Upon direct or sensitized excitation, [2+2]cycloaddition was found to be the exclusive or at least dominant chemical process for the CN/CC, NN/CC and ONN(O)/CC systems featuring very small π,π‐distances of 2.8‐3.0 Å and large π,π‐interorbital angles of 160‐170° (7 → 51, 17 → 55, 33 → 58 (competing N2 elimination), 22 → 62). This is not the case, however, in ONNO/CC (23, where electron transfer is a possibility), or in the more flexible, less “proximate” CN/CN (57) and CNO/CN (63) systems (π,π‐distances of >3.8 Å). While the corseted 1,2‐diazetidine photoadducts (55, 58) proved to be thermally stable, their N‐oxides (62, 65) were thermally too labile to be directly observable above ‐65 °C. For the latter's only fleeting existence, electronic rather than strain effects are held responsible (B3LYP/6‐31G* calculations). Very facile CNO/CC (12 → 13) and NNO/CC (22 → 24) [3+2]cycloadditions, homoconjugate addition of H2 and of dienophiles ([2+2+2]) to the diazene/ene 17 (→ 39, 41, 45) are manifestations of “proximity” in these bichromophoric skeletons.

As part of a study to achieve selective oligo(poly)bromination-ultimately perbromination-of the dodecahedral C(20) skeleton, the extent and direction of the ionic bromination of dodecahedrene and 1,16-dodecahedradiene were explored. Along sequences of Br(+) additions/deprotonations and allylic rearrangements, up to ten hydrogen atoms were substituted (traces of C(20)H(x)Br(10)). Tetrabromododecahedrenes obtained under defined conditions in up to 50 % total yield with three and four allylic bromine substituents protecting the extremely bent C==C bonds, proved highly unreactive even towards oxygen but reacted rapidly with CH(2)N(2). Upon electron impact ionization (MS) of the newly secured oligo(poly)bromododecahedra(e)nes, sequential loss of the substituents ended generally in polyunsaturated dodecahedranes (in the extreme C(20)H(4), "tetrahydro-C(20) fullerenes"). Only subsequently did skeletal fragmentations occur. From X-ray crystal-structure analyses, more information was obtained on the structural response of the dodecahedral skeleton to the strain induced by the voluminous substituents. As Appendix, the forcing radical bromination of 1,6-dibromododecahedrane and exploratory cis-beta-HBr/cis-beta-Br(2) eliminations in bromododecahedranes with [Fe(2)(CO)(9)], P(2)F/[FeCp(2)] and [Fe(tmeda)Cp*Cl] (in situ protection) are presented.