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Synthesis of Acenaphthenequinone Bis(ethylene ketal): anUnusually Distorted Ketal

 

作者: M. John Plater,  

 

期刊: Journal of Chemical Research, Synopses  (RSC Available online 1997)
卷期: Volume 0, issue 4  

页码: 116-117

 

ISSN:0308-2342

 

年代: 1997

 

DOI:10.1039/a607414f

 

出版商: RSC

 

数据来源: RSC

 

摘要:

O O O O O O O OO 1 2 3 O 116 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 116–117 J. Chem. Research (M), 1997, 0720–0724 Synthesis of Acenaphthenequinone Bis(ethylene ketal): an Unusually Distorted Ketal M. John Plater,* Derek M. Schmidt and R. Alan Howie Department of Chemistry, Aberdeen University, Meston Walk, Aberdeen AB24 3UE, UK The title compound is prepared by the acid catalysed protection of acenaphthenequinone with ethylene glycol and characterised by single crystal X-ray crystallography.In the course of our synthetic studies aimed at the regiospecific functionalisation of polycyclic aromatic hydrocarbons for the synthesis of fragments of the buckminsterfullerene surface,1 we required a protected derivative of acenaphthenequinone. The two electrophilic carbonyl groups were expected to form ketals readily under acid catalysis and not undergo a benzil–benzilic acid ring contraction as this would lead to the formation of a strained fourmembered 1,1-peri-fused naphthalene.It was of interest to see which of the two possible ketals 2 or 3 would predominate as a consequence of molecular strain, anomeric effects and electrostatic repulsion between the electronegative oxygens. Treatment of acenaphthenequinone 1 with ethylene glycol and a catalytic amount of toluene-p-sulfonic acid in refluxing benzene with azeotropic removal of water gave a single colourless crystalline product in 70% yield. The IR spectrum showed the absence of a carbonyl group and the mass spectrum confirmed the molecular structure as the bis ketal 2 or 3.The 13C NMR spectrum confirmed the presence of a single product and showed one sharp resonance for the ethylene bridge carbons. The 1H NMR spectrum was, however, complex and difficult to interpret. A single-crystal X-ray structure determination confirmed ketal 3 to be the correct structure. The molecule adopts a cistetraoxadecalin double chair conformation with C2 symmetry (see Figure).This product is probably thermodynamically more stable than the alternative isomer 2 because the oxygens adopt a pairwise axial–equatorial arrangement which will reduce their electrostatic repulsion compared to the eclipsed oxygens in isomer 2. The complex 1H NMR spectrum is probably a well resolved AApBBp spectrum, owing to a rapid double chair inversion, to which we were unable to assign coupling constants. The spectrum is complex because each pair of chemically equivalent protons on the ethylene bridge (AAp and BBp) has a different J value (JAB8JABp) so that they are magnetically non-equivalent.2 Variable temperature 1H NMR spectroscopy confirmed the molecular flexibility because on heating to 110 °C in deuterated toluene the methylene proton spectrum remained sharp and unchanged, but on cooling between µ36 and µ40 °C the spectrum changed from a 16 to an 8 line spectrum.The geometry of six-membered rings allows for more favourable stabilising ground state anomeric effects than the geometry of five-membered rings.However, although the crystal structure shows some disorder limiting the accuracy to which the bond lengths can be determined, the C–O bond lengths are not consistent for a stabilising anomeric effect. The bonds C(1)–O(1) are in a pseudoaxial position relative to the C(1)–O(2) bonds of the adjacent ring and hence a stabilising anomeric effect would have been expected to lengthen the C(1)–O(1) bond and shorten the C(1)–O(2) bond.3–5 In the crystal structure the opposite variation of bond lengths is observed with the C(1)–O(1) bond (1.315 Å) considerably shorter than the C(1)–O(2) bond (1.488 Å).The expected anomeric effect appears to have been dominated by the influence of the planar p-system. The C(1)–O(1) bond lies approximately in the plane of the aromatic ring, and hence perpendicular to the p-system, while the C(1)–O(2) bond is remarkably close to 90° to the aromatic ring and coplanar with the p-system [(C(2)–C(1)–O(2)i=93.9° and C(1)i–C(1)–O(2)i=102.0°)].The long C(1)–O(2) bond could therefore be explained as a consequence of a ground state stereoelectronic effect owing to the electron push from the aromatic ring. Crystal data for 3. C16H14O4, Mr=170, F(000)=5680, monoclinic, a=11.561(11), b=8.768(5), c=13.092(9) Å, V=1247.6(16) Å3, space group C2/c (no. 15), Z=4, Dr=1.439 g cmµ3, m(MoKa)=0.063 mmµ1. The experimental data were collected at room temperature on a Nicolet P3 diffractometer using a graphite monochromator with MoKa radiation (l=0.71069 Å).The structure was solved by direct methods.6 The final R value was 0.058 (Rw=0.060). The estimated standard deviations for the geometrical parameters involving non-hydrogen atoms lie within the following ranges: bond lengths 0.006–0.021 Å; bond angles 0.3–1.8°. Techniques used: IR, 1H and 13C NMR, X-ray crystallography References: 11 Tables: 2 (atomic coordinates and Ueq values for non-H atoms; interatomic distances and angles) *To receive any correspondence. Figure Crystal structure of 3J. CHEM. RESEARCH (S), 1997 117 Received, 31st October 1996; Accepted, 19th December 1996 Paper E/6/07414F References cited in this synopsis 1 M. J. Plater, M. Praveen and D. M. Schmidt, Fullerene Science and Technology, in press. 2 W. Kemp, NMR in Chemistry: A Multinuclear Introduction, Mac- Millan, London, 1992. 3 P. Deslongchamps, Stereoelectronic Effects in Organic Chemistry, Pergamon Press, Oxford, 1986. 4 B. Fuchs, I. Goldberg and U. Schmueli, J. Chem. Soc., Perkin Trans. 2, 1972, 357. 5 L. Lopez, V. Cal`o and F. Stasi, Synthesis, 1987, 947. 6 G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467.

 



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