<i>cis</i>‐ and <i>trans</i>‐Tris‐[2.2.2]‐σ‐Homobenzenes

McMullen, Gabrielle L.; Lutterbeck, Monika; Fritz, Hans; Prinzbach, Horst

doi:10.1002/ijch.198200005

Cited by 11 publications

(2 citation statements)

References 21 publications

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“…Although the interpretations of the individual investigations differ, the final conclusion is that all of these examples, 10 − 13 , are not homoaromatic. The σ-tris-homobenzene analogues of 10 , 11 , and 12 , 10-SAT , 11-SAT , and 12-SAT , respectively, (Figure ) have also been studied, but no evidence for cyclic electron delocalization has been reported. ,− The latter σ-tris-homobenzenes isomerize to the corresponding π-tris-homobenzenes via tris-homoaromatic transition states 10-TS , 11-TS , and 12-TS .…”

Section: Introductionmentioning

confidence: 99%

“…The σ-trishomobenzene analogues of 10, 11, and 12, 10-SAT, 11-SAT, and 12-SAT, respectively, (Figure 2) have also been studied, but no evidence for cyclic electron delocalization has been reported. 19,[68][69][70] The latter σ-tris-homobenzenes isomerize to the corresponding π-tris-homobenzenes via tris-homoaromatic transition states 10-TS, 11-TS, and 12-TS.…”

Section: Introductionmentioning

confidence: 99%

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Resurrection of Neutral Tris-homoaromaticity

et al. 2002

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Neutral in-plane tris-homoaromaticity is evaluated in tris(bismethano)benzene (15) and modifications of this parent structure in which the pi-orbitals might interact in the plane established by the unsaturated carbon atoms (in-plane conjugation). On the basis of magnetic susceptibility exaltation, nucleus-independent shift (NICS), and aromatic stabilization energy (ASE, evaluated via homodesmotic and isodesmic equations using B3LYP/6-311+G + ZPVE energies, as well as by MM3 and MM4 force field computations), we identified triene 17, a triply bridged analogue of 15, as the system where homoaromaticity is most effective. The NICS(total) in the center of 17 is -30.1 ppm and the diatropic pi-contribution is -18.0 ppm. This structure possesses more than one-third of the aromatic stabilization of benzene and is the best candidate for neutral tris-homoaromaticity ever proposed. The previously described tris-(bismethano)-benzene (15) also shows homoaromaticity but to a smaller extent compared to 17. Structure 18, which is closely related to 17, also is significantly homoaromatic but, as evaluated by MM3, strain partially counteracts the stabilizing effects from homoconjugation. Such a counteracting increase in strain largely cancels or even overwhelms the stabilization from homoconjugation in all other species considered in this study.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Resurrection of Neutral Tris-homoaromaticity

et al. 2002

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Unusual Saturated Hydrocarbons: Interaction Between Theoretical and Synthetic Chemistry

Dodziuk¹

1994

Topics in Stereochemistry

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Leichte Hydrierung des zentralen Cyclohexatriens von Tris(benzocyclobutadieno)benzol: Synthese und Struktur sowie thermische und photochemische Isomerisierung von all‐cis‐Tris(benzocyclobuta)cyclohexan

Mohler¹,

Vollhardt²,

Wolff³

1990

Angewandte Chemie

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Wir beschreiben die erste chemische Reaktion des Kohlenwasserstoffs 1 ['I, namlich seine leichte und stereoselektive Hydrierung zu 2, das nach einer Rontgenstrukturanalyse einen ungewohnlichen, bindungsfixierten, planaren Cyclohexanring hat. Durch stereospezifische thermische Retrocyclisierung entsteht aus 2 ausschlieDlich das Hexaen 3. Dieser Befund IaDt, zusammen mit den dazugehorigen kinetischen Daten, auf einen bisher beispiellosen all-disrotatorischen ProzeB schlieDen[21. Demgegeniiber fuhrt die Bestrahlung von 2 uber eine Umlagerung zunachst zum neuen Kohlenwasserstoff 4 und schlieBlich zu Phenanthren und Naphthalin, wohingegen 3 zu 5 photoisomerisiert (Schema 1). Die Ergebnisse enveitern wesentlich die Chemie des Benzocyclobuten-Gerusts und des Tribenzo(CH), ,-Systems.Die Hydrierung von I zu 2 a gelingt unter aukrgewohnlich milden Bedingungenl3], was dem hohen Grad der Bindungslokalisierung und der hohen Spannung in 1 zuzuschreiben ist. Das 2,3,6,7,10,1l-Hexakis(trimethylsilyl)-Derivat von 1 war hingegen sogar bei erhohtem Wasserstoffdruck (80 atm, THF, Pd-C) inert.Die Stereochemie von 2 a wurde zunachst NMR-spektroskopisch ermittelt; dabei waren das Signal fur die Protonen am zentralen Ring (ein Singulett bei 6 = 4.19) im 'H-NMRund die vier Signale im "C-NMR-Spektrum sowie die Analogie im Verhalten der entsprechenden angularen und linearen [3]Phenylenetq1 besonders wichtig. Nach einer Rontgenstrukturuntersuchung (Abb. l)l51 ist der zentrale Cyclohexanring planar, was durch die drei anellierten Benzocyclobuten-Einheiten verursacht wird. Der durchschnittliche Di-

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cis‐ and trans‐Tris‐[2.2.2]‐σ‐Homobenzenes

Cited by 11 publications

References 21 publications

Resurrection of Neutral Tris-homoaromaticity

Resurrection of Neutral Tris-homoaromaticity

Unusual Saturated Hydrocarbons: Interaction Between Theoretical and Synthetic Chemistry

Leichte Hydrierung des zentralen Cyclohexatriens von Tris(benzocyclobutadieno)benzol: Synthese und Struktur sowie thermische und photochemische Isomerisierung von all‐cis‐Tris(benzocyclobuta)cyclohexan

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