J. Chem. Research (S), 1997, 48–49 J. Chem. Research (M), 1997, 0437–0452 Conformational Analysis of Spirocyclopropane- and Spirooxirane-annelated Dibenzobicyclo[4.4.1]undecanes by 1H NMR Spectroscopy and X-Ray Crystallography Shuntaro Mataka,*a Masahiko Taniguchi,b Yoshiharu Mitroma,b Tsuyoshi Sawadaa and Masahi Tashiroa aInstitute of Advanced Material Study, Kyushu University, 6-1, Kasuga-koh-en, Kasuga-shi, Fukuoka 816, Japan bDepartment of Molecular Science and Technology, Graduate School of Engineering Sciences, Kyushu University, 6-1, Kasuga-koh-en, Kasuga-shi, Fukuoka 816, Japan Conformational behaviour of dibenzo[c,h]bicyclo[4.4.1]undecanes having a dichloro- and a dibromo-cyclopropane ring, together with an oxirane ring on the methylene bridge, has been studied by 1H NMR spectroscopy and X-ray crystallography.Of the possible conformations of bicyclo[4.4.1]undecane, the twin-boat type usually is the most unstable and the twin-chair the most stable.The twin-chair conformer is unstable in the case of dibenzobicyclo[4.4.1]undecane 1, owing to electronic repulsion between the p-electrons of the two layered benzounit, and thus 1 exists as an equilibrium mixture of the chairboat and boat-chair conformers.1 A twin-chair conformation with layered benzo-units is seen in the acetal and the alcohol 2 (Scheme 1),4,5 which have substituents on the methylene bridge of a dibenzobicyclo[4.4.1]undecane system. The present article reports on the conformational behaviour of dibenzobicyclo[4.4.1]undecanes having a spiroannelated three-membered ring on the methylene bridge.The methylene derivative 3 was prepared by dehydration of the alcohol 2 and converted into the spirocyclopropanes 4 and 5 by [2+1] cycloaddition with dihalocarbenes.6,7 Reductive removal of the halogen substituents of 4 with LiAlH4 8 gave 6. In contrast, the dichloro derivative 5 gave a mixture of 6 and the monochloro derivative 7. The desired 6 was more conveniently prepared by a Simmons–Smith reaction.9 Oxirane 8 was obtained by epoxygenation10 with m-chloroperbenzoic acid (m-CPBA) (Scheme 2).The flexible 6 exists at room temperature as an equilibrium of a mixture of the two indistinguishable chair-boat (C-B) and boat-chair (B-C) conformers. In the 1H NMR spectrum of 6 at µ60 °C, one of the two methylene groups of the spirocyclopropane moiety shows an up-field shift, since the methylene protons are shielded by the ring current of the benzene ring of the boat-like benzocycloheptene unit. Introduction of halogen atoms does not fix the conformation of 4, 5 or 7, while oxirane 8 is also flexible (Scheme 3).The conformer ratios for 4, 5 and 8 are given in Table 1. The ratio of 7 could not be determined because of overlapping of the signals. The parameters DH°, DS°, and DG° for 4, 5 and 8 were determined from the signals for the methylene protons of the spirocyclopropane rings and the oxirane ring in variable temperature 1H NMR spectra in CDCl3 run over a temperature range from µ60 to 0 °C (Fig. 1 and Table 2). The predominant conformation of 4 and 5 in solution is the C-B type, although it could be expected that the C-B conformation, in which the dihalogenomethylene group is positioned above the boat-like benzocycloheptene ring, might be sterically less preferable. On the other hand, 4 takes the B-C conformation in the solid state, as revealed by X-ray crystallographic analysis (Fig. 2). The conformer ratio of 5 is dependent on the ET-30 value of the solvent. With an increase in ET-30, the proportion of C-B conformer tends to increase. The solvent effect is less clear in 4. These facts seem to be in agreement with PM3 calculations of the dipole moment: the calculated dipole 48 J. CHEM. RESEARCH (S), 1997 *To receive any correspondence (e-mail: mataka@cm.kyushu-u. ac.jp). Scheme 1 Scheme 2 Scheme 3J. CHEM. RESEARCH (S), 1996 49 Fig. 1 van’t Hoff plot for 4, 5 and 8 Fig. 2 ORTEP drawing of 4 Table 1 Conformer ratiosa and calculated dipole moments of 4, 5 and 8 Ratio of B-C/C-B conformers in solvent (ET-30) Dipole momentb [2H6]Acetone CD2Cl2 CDCl3 [2H8]THF [2H8]Toluene Compd. (B-C/C-B) (42.2) (41.1) (39.1) (37.4) (33.9) 458 1.21 D/1.35 D 1.07 D/1.61 D 1.38 D/2.06 D 40/60 28/72 90/10 37/63 29/71 71/29 37/63 31/69 68/32 47/53 40/60 100/0 43/57 43/57 100/0 aAt µ60 °C. bPM 3 calculation. Table 2 Parameters DH°, DS° and DG° for the B-C and C-B equilibriaa,b Compd.DH° (kJ molµ1) DS° (J molµ1 Kµ1) DG° (kJ molµ1)c 458 3.49 5.15 4.91 11.9 17.4 28.6 µ0.06 µ0.04 µ3.61 aIn CDCl3. bK\[B-C]/[C-B]. cAt 25 °C. moment of the C-B conformer is larger than that of the B-C conformer and the difference between the values is larger in 5 than in 4. The oxirane 8 prefers the B-C conformation in order to avoid the electronic repulsion between the lone-pair electrons of the oxygen atom and the p-electrons of the benzene ring.The ratio for 8 is more temperature-dependent than those for 4 or 5 (Fig. 1); it is estimated that in chloroform at 25 °C, more than 99% of 8 exists as the B-C conformer, having a smaller calculated dipole moment. The large difference in DS° for 8 may reflect tight solvation on the oxygen atom in the B-C conformer as compared to the C-B conformer. Crystal Data for 4.·C21H20Br2, Mr=432.19, orthorhombic, a=24.926(6), b=17.125(1), c=8.253(2) Å, V=3522.9(12) Å3, Dc=1.630 g cmµ3, space group Pbca, Z=8, F(000)=1728, m(CuKa)=5.791 cmµ1.Data were collected on an Enraf Nonius CAD-4 diffractometer using a graphite monochromator with CuKa radiation (l=1.54184 Å). The structure was solved by direct methods (SIR 92).11 The final R value was 0.033 (Rw=0.0886). The estimated standard deviations for the geometrical parameters involving non-hydrogen atoms lie within the following ranges: bond lengths, 0.004– 0.006 Å; bond angles 0.2–0.4°. We are indebted to Dr T.Thiemann (University of Coimbra) for helpful discussions. Techniques used: IR, 1H NMR, mass spectrometry References: 11 Schemes: 3 Figures: 2 Tables 3–6: Bond lengths and angles, fractional atomic coordinates and equivalent isotropic thermal parameters, and anisotropic thermal parameters for 4 Received, 15th July 1996; Accepted, 5th November 1996 Paper E/6/04939G References 1 S. Mataka, K. Takahashi, T. Hirota, K. Takuma, H. Kobayashi, M. Tashiro, K. Imada and M. Kuniyoshi, J. Org. Chem., 1986, 51, 4618. 4 S. Mataka, K. Takahashi, T. Hirota, K. Takuma, H. Kobayashi and M. Tashiro, J. Chem. Soc., Chem. Commun., 1985, 973. 5 S. Mataka, K. Takahashi, T. Hirota, K. Takuma, H. Kobayashi, M. Tashiro, K. Imada and M. Kuniyoshi, J. Org. Chem., 1985, 52, 2653. 6 G. W. Gokel, J. P. Shepherd, W. 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