substituted / Cyanohydrins, 0-(trimethylsily1)-/ Hydrogen fluoridephosphorus oxychloridepyridine, elimination of trimethylsilanol by / Phenyl cuprate reagent, conjugate addition of / Phase-transfer catalysis I Chlorination by hexachloroethanesodium hydroxide I Cyclization by dehydrochlorination I Endoperoxides by triplet oxygen I 2H-Pyran, derivative of I Thermochromism Synthesis of Dicyanodiphenylsemibullvalene 4The synthesis of 4 parallels the straightforward route which recently has led from the unsaturated diketone 5 to the dicyanodiphenylbarbaralane 6L7].
2,6‐Dicyano‐4,8‐diphenylbarbaralane[1] Conjugate addition of the phenylcuprate reagent, obtained from phenyllithium, copper(I) cyanide, and boron trifluoride–diethylether, to the bicyclo[3.3.1]nonadienedione 3 affords the diphenylbicyclo[3.3.1]nonanedione 4 in high yield. Catalyzed by the potassium cyanide/18‐crown‐6 complex, addition of trimethylsilyl cyanide produces a mixture of the diastereomeric bis[O‐(trimethylsilyl)cyanohydrins] exo,exo‐, exo,endo‐ and endo,endo‐5. The hydrogen fluoride – pyridine complex in phosphorus oxychloride as solvent and, subsequently, an excess of pyridine convert the diastereomers 5 into the unsaturated γ,γ′1‐diphenyldinirile 6. This is brominated by N1‐bromosuccinimide to yield the γ,γ′1‐dibromodinitriles exo‐ and endo‐ 7 (6:1). The predominant diastereomer exo‐7 is debrominated by the zinc‐copper couple to afford the orange‐red title compound 2 in 78% yield. More conveniently, the unsaturated dinitrile 6 is converted to 2 in a single step by treatment with hexachloroethane and concentrated aqueous sodium hydroxide in the presence of tetrabutylammonium hydroxide as phase‐transfer catalyst. Surprisingly, low yields of 2 are also obtained when the bis[O‐(trimethylsilyl)cyanohydrins] 5 or the unsaturated dinitrile 6 are treated with phosphorus oxychloride in boiling pyridine. – The structures of the new compounds are based on spectroscopic evidence and X‐ray diffraction analyses of 2, 4, and endo,endo‐5. The conformations of 4 and endo,endo‐5 in solution are inferred on the basis of vicinal proton coupling constants and a comparison with coupling constants calculated with the aid of the Karplus equation and torsional angles obtained by X‐ray diffraction analyses. – While the barbaralane 2 exists as a pair of very rapidly rearranging degenerate valence tautomers in solution, the degeneracy is lifted in the crystal lattice. As a result, the crystal consists of two rapidly rearranging but non‐equivalent valence tautomers in a ratio of 9:1 as estimated from the apparent atomic distance C2–C8 of 2 and the C2–C8 bond length of non‐rearranging barbaralanes. – The colour of 2 in the crystal and in solution results from a maximum at 436 nm which increases on heating of the solution to 450 K. Cooling to 77 K results in reversible fading and the disappearance of the maximum. Thus, 2 is a barbaralane like 1 which exhibits colour though it is lacking a classical long‐wavelength chromophore.
Stereochemistry of the Addition of Phenylmetal Reagents toConjugate addition of dilithium diphenylcyanocuprate is observed only on one side of the dienedione 4b, affording the enedione 5 b, but on both sides in the presence of boron trifluoride yielding the diphenyldione 6b. Likewise, the latter reagent gives rise to the formation of 6a from 4a. Phenylcerium(II1) dichloride is much superior to phenyllithium and phenylmagnesium bromide in the 1,2 addition reaction to encumbered, enolizeable bicyclo[3.3.0]octanediones. Thus, a mixture of the diols exo,exo-8, exo,endo-8, and endo,endo-8 is formed in almost quantitative yield from the 3,Tdione 7. Furthermore, the diphenyldione 6a is transformed into the tetraphenyldiol 14 in this way and in high yield. The 2,6-dione l l b adds phenylcerium(II1) dichloride affording a mixture of the hydroxyketone endo-16, which is inert towards an excess of the reagent, and the diol exo,endo-12 b. The inertness of endo-16 is attributed to the formation of the cyclic hemiacetal20 which eventually is trapped quantitatively by 0-silylation with chlorotrimethylsilane in the presence of pyridine. The hydroxyketone endo-16 is dehydrated to give the enone 17 which subsequently is treated with phenylcerium(II1) dichloride to form exo-and endo-19. A solution of sulfuric acid in acetic acid dehydrates the tertiary benzyl alcohols 8 (+ 9 + lo), endo,endo-l2a (+ 13a), exo,endo-l2b (--13b), 14 (-+ 15), endo-16 (-+ l?), and 19 (+ 13b) in high yields. The same results are achieved even more conveniently with a solution of chlorotrimethylsilane in dichloromethane in the absence of a base. The oxanortwistane 18 is obtained as a byproduct in the dehydration of exo,endo-l2b with both reagents. The gross structures of all compounds are based on spectroscopic evidence, in particular NMR spectra. Concentration-independent IR and low-field NMR absorptions of two equivalent hydroxy groups are indicative of intramolecular hydrogen bonds and hence the endo,endo configuration of the diols endo,endo-8, endo,endo-l2a, and 14. Eventually, the configurations of 5 b, 6b, endo,endo-8, endo,endo-l2a, exo,endo-l2b, 14, 15, endo-16, and the structure of 18 as well, are established by X-ray diffraction analyses. In the solid state, the bicyclo[3.3.0]-octanols endo,endo-l2a, exo,endo-12 b, 14, and endo-16 adopt conformations that allow the phenyl groups the occupation of quasi equatorial positions.
Photooxygenierung des Gcmiscbs derEine Synthese der theoretisch interessanten2) cyansubstituierten Semibullvalene 3, von denen 3a bereits dargestellt 3,4) und untersucht 3,5) wurde, besitzt als Schlusselschritt den RingschluD zwischen C-2 und C-8 oder C-4 und C-6 der Bicyclo[3. Ein aussichtsreicher Weg zu ungesattigten 1,3-Dinitrilen wie lb,c und 2b,c mit der bei cyclischen Systemen noch unbekannten Teilstruktur 9') besteht in der 1,CHydrocyanicrung a$-ungeslttigter Ketone 6 zu P-Cyanketonen 7, Addition von Trimethylsilylcyanid zu 8 und formaler Eliminierung von Trimethylsilanol. a$-Ungeslttigte Ketone 6 erhllt man aus 4 durch 1,2-Carbonylverschiebung (4+ 5)4,6) und anschlieoende (5+ 6) oder gleichzeitige (4+ 6)637) Dehydrierung. Grund fur die Wahl des 4 entsprcchenden 3,7-Diketons 10 als Ausgangsmaterial ist der besonders einfache Zugang durch Weiss-Reaktion' -I1) von 2,3-Butandion und Acetondicarbonsaure-dimethylester "I. Allerdings besitzt das 3,7-Diketon 10 wie alle anderen C,,-symmetrischen Bicyclo-[3.3.0]octane den Nachteil, daD bei der Aufhebung der C,-Symmetric beider Cyclopentanringc durch gleichartige Modifikation der Funktionalitlt 4~10~12,13) stets lhnliche Mengen C,-und C,-symmetrischer Regioisomerer entstehen. Ferner gelang es bisher nicht, nur einen Cyclopentanonring 1,5-substituierter Bicyclo[3.3.0]octan-3,7-dione zu modifizieren, ohne daJ3 die Reaktion in mehr oder wenigcr groDem Umfang auch an der gegenuberliegenden Molekiilhllfte ablauft 1",12,14). Aus diesen Grunden muBte die Umpolung von 10 durch 1,2-Carbonylverschiebung unter Dehydrierung moglichst efizient und auch in groljerem MaRstab durchzufuhren sein.Die bisherigen Methoden zur 1,2-Carbonylverschiebung 4-5 und 4 + 6 sind wegen der Zahl der Schritte aufwendig und wenig ergiebig, wenn diese obendrein auch noch auf zwei Seiten des Molekuls durchgefuhrt werden mussen. Das gilt erst recht, wenn noch eine Dchydrierung zum a,p-ungeslttigten Keton folgt (4-+5+6). So fiihrte die doppelte Liebigs Ann. Chem. 1987, [965][966][967][968][969][970]
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