trans,cis,cis,cis-Cyclononatetraenyl Anion, a New Aromatic 10 π System

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<ul><li><p>IS] a) V. V. Perekalin et al., Usp. Chim. 24, 613 (1955) [re- view]; Doklady Akad. Nauk SSSR II2, 441 (1957); A . S. Polyanskaja, Uch. Zap. Leningr. Gos. Ped. Inst. I60, Pt. 1, 53 (1959); Chem. Abstr. 50, 159 (1959); SI, 13866 (1960); 57, 16590 (1962); H. Feuer and R. Miller, J. org. Chemistry 26,1349 (1961); E. B. Hodge, US-Pat. 3024232 (1962); Chem. Abstr. 57, 11046 (1962); b) E. P. Kohler and J . F. Stone, J. Amer. chem. SOC. 52, 761 (1930); G. D. Buckley and E. Ellery, J. chem. SOC. (London) 1947, 1494, 1497; Brit. Pat. 571804 (1945); Chem. Abstr. 41, P 4508; J . MicheI and E. Henry-Basch, C. R. hebd. Seances Acad. Sci. C262,1274 (1966); c) P. Buck and G. Kobrich, Tetrahedron Letters 1967, 1563. </p><p>trans,cis,cis,cis-Cyclononatetraenyl Anion, a New Aromatic 10 n System </p><p>By G. Boche, D . Martens, and W. Danzer[*l </p><p>Woodward and Hoflmann predicted that thermal ring opening of the cyclopropyl anion to the ally1 anion would proceed in a conrotatory fashion. Huisgen et al. [21 have been able to detect the expected thermal conrotation and photo- chemical disrotation in the isoelectronic aziridine/azomethine ylide system. </p><p>Katz and Garratt [3J have prepared potassium cis,cis,cis,cis- cyclononatetraenide (3) in essentially quantitative yield [41 by reaction of anti-9-methoxy-cis-bicyclo[6.1.0]nona-2,4,6- triene (I) with potassium in tetrahydrofuran. Orbital sym- metry considerations 11751 would, however, suggest that the cyclopropyl anion (2) undergoes conrotatory ring opening to give potassium trans,cis,cis,cis-cyclononatetraenide (4). </p><p>H H H </p><p>H HwcH3 - HH 2K_ </p><p>(3) (4) </p><p>We have, therefore, reinvestigated the course of the reaction in [D&amp;THF at 4 O o C by N M R spectroscopy and, after complete consumption of ( I ) [61, a spectrum was obtained that indicates the presence of only 4 5 2% of (3) (sharp signal at 'F = 2.87). The chemical shifts observed clearly indicate that the remaining signals cannot be assigned to the potassium cyclopropanide compound (2) but to the aromatic potassium trans,cis,cis,cis-cyclononatetraenide (4): The six protons H3-Hs absorb between T = 3.0 and 3.6; the signal due to H2 and H9 appears as a broadened doublet (J = 15 Hz) centered at T = 2.73, and HI absorbs as a triplet at T = 13.52 </p><p>As, for example, in the case of the aromatic annulenes [71, the delocalization of the x electrons in ( 4 ) in an external magnetic field gives rise to a ring current which shifts the NMR signals of the protons situated outside the ring (HLH9) downfield, and that of the inner proton HI upfield [81. If (2) were present, six olefinic protons (H2'-H7') and three cyclopropyl-anion protons~91 (HI', HS', H9') would be observed. The ring opening (2) +(4) [IOJ, which is fast even a t -40 O C , profits from formation of the l o x aromatic compound (4) . On the other hand, ring opening does not occur at a measurable rate in the aziridine/azomethine ylide system until the tem- </p><p>(J = 15 Hz). </p><p>perature has been raised to 100 "C fzal. None of the isolable cyclopropyl anions is known to undergo ring opening f * 9 5991. Potassium frns,cis,cis,cis-cyclononiltetraenide (4) can be stored for days at - 4 O O C in a closed vessel. However, con- version to the all-cis compound ( 3 ) takes place when the reaction mixture is stirred at room temperature. </p><p>Received: September 19, 1969 [Z 102 !El German version: Angew. Chem. 81, 1003 (1969) </p><p>[*I Dr. G. Boche, D. Martens, arid W. Danzer Institut fur Organische Chemie der Universitat 8 Munchen 2, Karlstrasse 23 (Germany) </p><p>[l] R. B. Woodward and R. Hoffmann, J. Amer. chem. SOC. 87, 395 (1965). [2] a) R. Huisgeii, W. Scheer, G. Szeimies, and H. Huber, Tetra- hedron Letters 1966, 397; b) R . Huisgen, W. Scheer, and H. Hu- ber, J. Amer. chem. SOC. 89, 1753 (1967); c) R. Huisgen, W . Scheer, and H. Mader, Angew. Chem. 8 I , 619 (1969); Angew. Chem. internat. Edit. 8, 602 (1969); d) R . Huisgen, W.Scheer, H. Mader, and E. Brunn, Angew. Chem. 81, 621 (1969); Angew. Chem. internat. Edit. 8, 604 (1969); e ) R . Huisgen and H.Mader, Angew. Chem. 81, 621 (1969); Angew. Chem. internat. Edit. 8, 604 (1969). [3] T. J . Katz and P . J . Garratt, J. Amer. chem. SOC. 85, 2852 (1963); 86, 5194 (1964). 141 After allowing the temperature of the reaction mixture to rise from -78 to +25 "C within 12 h, Katz and Garrat observed only the sharp absorption signal of the all-cis compound (3) at T = 2.96 (alongside the signals due to the solvent) in the NMR spectrum. 151 H. C. Longuet-Higgins and E. W. Abrahamson, J. Amer. chem. SOC. 87, 2045 (1965). [6] The reaction time, which depends on the rate of stirring, is 3-6 h at -40 "C [7] For a review, see: F. Sondheimer, I . C. Calder, J . A . Elix, Y. Gaoni, P. J . Garratt, K . Grohmann, G. di Maio, J. Mayer, M . V . Sargent, and R. Wolowsky, Spec. Publ. No. 21 (Chem. SOC., London),p. 75. [8] J. A . Popre and K. G. Untch, J. Amer. chern. SOC. 88, 4811 (1966). [9] For the NMR spectrum of cyclopropyllithium see: D. Sey- </p><p>ferth and H. M. Cohen, J. organometallic Chem. I, 15 (1963/64). [lo] (2) could not be detected by NMR spectroscopy. </p><p>C-N Fission of O-Alkylated FormamidesI***I </p><p>By H . G. Nordmann and F. Krohnke[*] </p><p>We have prepared the O-alkylated formamides ethoxy-N- (methy1anilino)- ( 4 ) and ethoxy-N,N-(dipheny1amino)-meth- ylium tetrafluoroborate (5) by alkylation of N-methylform- anilide ( I ) and diphenylformamide (21, respectively, with triethyloxonium tetrafluoroborate (3) 13 r 4 l . </p><p>(4),R' = CH, (5), R' = C,HS </p><p>These products ( 4 ) and (5 ) are crystalline substances that are relatively insensitive to atmospheric moisture and can be re- crystallized from acetonitrileether. Their structure has been proved by analyses and N M R spectra. A characteristic feature is that introduction of the positive charge shifts the formyl-H signals from 8.27 to 8.48 ppm [(I) +(4)] and from 8.55 to 8.82 ppm [ ( 2 ) +5) ] (6 values; in CDCl3; TMS as internal standard). </p><p>(4) reacts with an excess of water at room temperature to give N-methylaniline (6) and ethyl formate (7) almost quantitatively; but, in this reaction, (5 ) gives diphenylamine (8) (90%), diphenylformamide (2) (10 %), and ethyl formate </p><p>984 Angew. Chem. internat. Edit. 1 Vol. 8 (1969) No. I2 </p></li></ul>