摘要:

R = H X = Br benzene Lewis acids room temp. for 1 h 5 7 10 13 15 R CH2 R CH2X XCH2 R = But X = Cl 1a b R R R = H R = But 2a b 7 Na2Cr2O7 8 (25%) in HOAc + O 10 (11%) reflux for 7 days Na2Cr2O7 in HOAc reflux for 7 days 9 (5%) + O O O H OAc O O O 11 O O O 440 J. CHEM. RESEARCH (S) 1997 J. Chem. Research (S) 1997 440–441 J. Chem. Research (M) 1997 2615–2646 Medium-sized Cyclophanes. Part 45.1 Synthesis Oxidation Electrophilic Substitution and Conformational Properties of 10,15-Dihydro-5H-tribenzo[a,d,g]cyclononenes and Their Analogues Takehiko Yamato* and Naozumi Sakaue Department of Applied Chemistry Faculty of Science and Engineering Saga University Honjo-machi 1 Saga-shi Saga 840 Japan The synthesis oxidation and electrophilic substitution of the title compounds 2 and the conformational properties of some of the product ketones were studied.Sato et al. have reported11b the concentrated sulfuric acid catalysed cycloalkylation of 2,2p-bis(hydroxymethyl)diphenylmethane with benzene under high dilution conditions to construct a large-membered ring compound viz. 10,15-dihydro-5H-tribenzo[a,d,g]cyclononene 2a. However their experimental procedures seem to be too tedious for practical purposes and it has been very difficult to obtain sufficient amounts of the above compound to investigate its chemical behaviour. We report here the first successful Lewis acid-catalysed cyclobenzylation of 2,2p-bis(halomethyl)diphenylmethanes 1 with benzene to give 10,15-dihydro-5H-tribenzo[a,d,g]cyclononenes under relatively mild conditions. We also describe the oxidation of these products to 10,15-dihydro-5H-tribenzo[ a,d,g]cyclononen-5-one 7 and the corresponding 5,10-dione 8.Conformational studies have been conducted on these latter compounds. The attempted cyclobenzylation reaction of 2,2p-bis- (bromomethyl)diphenylmethane 1a with benzene was performed in the presence of TiCl4 and AlCl3–MeNO2 at room temperature for 1 h and led to the desired cyclobenzylation reaction giving 2a in 68% yield. However AlCl3-catalysed cyclobenzylation under the same conditions failed affording only the cleavage reaction product diphenylmethane. Similar results affording 2b were obtained when 4,4p-di-tert-butyl- 2,2p-bis(chloromethyl)diphenylmethane 1b was treated with benzene in the presence of a Lewis acid. The AlCl3–MeNO2- catalysed trans-tert-butylation14c of 2b in benzene at room temperature afforded after 24 h the desired de-tert-butylated product 2a in 60% yield along with a small amount of recovered starting compound and the formation of incompletely de-tert-butylated products.However use of toluene as an acceptor for the tert-butyl group failed only ring-cleavage reactions due to the transbenzylation occurring. Thus the ring-cleavage reactions due to the transbenzylation rather than trans-tert-butylation were favourable under the conditions used. It was also found that an attempted AlCl3– MeNO2-catalysed cyclobenzylation and trans-tert-butylation of 1b in benzene in situ under the same conditions as above in an attempt to afford 2a failed only a low yield (20%) of the desired product 2a along with an intractable mixture of products being obtained.Friedel–Crafts formylation and nitration of 2a occurred selectively at the 2 position to afford the corresponding mono-formyl and mono-nitro derivatives whereas in the case of nitration of the tert-butyl derivative 2b with copper(II) nitrate this selectivity was not observed even under relatively mild reaction conditions only a ring-cleavage product was obtained. Oxidation of 2a with sodium dichromate following a reported procedure11b,19a afforded the mono-ketone 7 in 66% yield. Interestingly further oxidation of 7 furnished the diketones 8 in 25% yield along with a lactone 10 in 11% yield having a 10-benzoyloxy-9-anthrone unit formed possibly as a result of a transannular rearrangement of the triketone 11 due to the release of strain on changing the tribenzocyclononene skeleton to an anthrone one.Furthermore compound 9 was also isolated albeit in only 5% yield. *To receive any correspondence (e-mail yamatot@cc.saga-u.ac.jp). Scheme 1 Scheme 4 saddle conformation crown conformation R R H H H H H H H H O O J. CHEM. RESEARCH (S) 1997 441 One of the most interesting properties of 10,15-dihydro- 5H-tribenzo[a,d,g]cyclononene and its congeners is their stable crown conformation.10 Destabilization of the crown may arise from steric hindrance created either by geminal substitution of one methylene gorup19a or by the presence of bulky substituents22c such as a bromine atom or an allyl group (but not a methoxy group23) at the aromatic positions ortho to the nine-membered ring. Both the mono- 7 and di- 8 ketones showed in a variety of solvents a singlet for the methylene protons.On lowering the temperature the singlet for 7 began to broaden and at µ110 °C it separated into two broad peaks at d 3.15 and 4.00 (CDCl3–CS2 1:3). Although the chemical shifts are typical of those of crown compounds (two doublets at d 3.76 and 4.91 for crown 2a) the mono-ketone 7 might be frozen in the saddle form but not the crown form. At higher temperature 7 undergoes rapid inversion between two saddle forms The ketone 7 is expected to be less rigid since it contains a trigonal carbon with a formal C·C·C angle of 120 °C. In fact Tc for the methylene protons is lower than µ90 °C. Thus Sato et al. could not record the frozen spectrum owing to experimental limitations such as low solubility and slow molecular tumbling. Two possibilities are open averaging occurs either between the two crown forms or only among the saddle forms.A twisted saddle form was assigned as a mean conformation to account for the IR spectrum and UV data which indicate conjugation. The slightly low frequency in the IR spectrum for 7 (1640 cmµ1) in comparison with that for the reference compound benzophenone (1651 cmµ1) presumably reflects conjugation between the carbonyl group and the benzene rings. This finding is different from those for the strained paracyclophane analogue for which absorption is toward wavelengths characteristic of unconjugated ketones owing to the expanded C·C·C bond angles.26a The UV spectrum of the flexible molecule 7 showed a similar absorption curve to that of the model acyclic compound benzophenone which implies conjugation between the two aryl rings.The conjugation energy of the Ar-CO-Ar group must also be considered in the case of ketone 7 where such an interaction is possible. From the crystal structure of 7 it is clear that the molecule adopts the saddle conformation in which one benzene is present between two aromatic rings which are forced towards each other (as predicted from the 1H NMR data). The angle inside the carbonyl group is 124.5° which is a slightly larger value than that expected in an acyclic diaryl ketone. A similar phenomenon was observed for the diketone 8. The methylene protons are observed at d 3.96 at room temperature but at µ115 °C this singlet separates into two broad peaks at d 3.72 and 4.22 (CDCl3–CS2 1:3). A lower coalescence temperature was observed compared to that of the mono-ketone 7 implying a more flexible structure.Interestingly two different carbonyl stretching vibrations were observed at 1687 and 1650 cmµ1. Comparison of the IR spectrum with that of the corresponding acyclic system benzophenone revealed that one of the conjugations between the two aryl rings is considerably reduced in the diketone 8. Consequently introduction of a trigonal carbon leads to a more flexible structure and the mono-ketone 7 and diketone 8 both display flexible ‘saddle’ conformations. We conclude that the Lewis acid catalysed cyclobenzylation reaction of 2,2p-bis(halomethyl)diphenylmethanes 1 with benzene to give cyclobenzylated products 2a and 2b appears to be a useful and convenient method for the preparation of 10,15-dihydro-5H-tribenzo[a,d,g]cyclononenes. Interesting findings were obtained in the electrophilic aromatic substitutions and oxidation of 10,15-dihydro-5H-tribenzo[a,d,g]- cyclononenes 2.We have synthesized the diketone 8 for the first time and deduced its conformation. However an attempted synthesis of the triketone 11 failed; instead a lactone having a 10-benzoyloxy-9-anthrone unit which might be formed as a result of a transannular rearrangement of the triketone 11 was obtained. Further studies on the chemical properties of the monoketone 7 and diketone 8 are now in progress. Techniques used 1H NMR IR mass spectrometry VPC X-ray crystallography References 26 Table 1; Lewis acid catalysed reaction of 2,2p-bis(halomethyl) diphenylmethanes 1 in benzene Table 2 Crystallographic data and data-collection details for 7 Fig. 2 Dynamic 1H NMR spectra of 7 at 270 MHz Fig.3 UV absorption spectra of 7 and benzophenone 13 in cyclohexane Fig. 4 ORTEP diagram of 7 Appendix Tables of torsional or conformational angles bond angles and distances atomic coordinates and isotropic equivalent displacement parmaeters and U values for 7 Received 12th May 1997; Accepted 27th August 1997 Paper E/7/03256K References cited in this synopsis 1 Part 44 T. Yamato M. Shigekuni H. Kunugida and Y. Nagano J. Chem. Res. 1997 (S) 192; (M) 1323. 10 A. Collet Tetrahedron 1987 43 5725. 11 (b) T. Sato and K. Uno J. Chem. Soc. Perkin Trans. 1 1973 895. 14 (c) T. Yamato A. Miyazawa and M. Tashiro J. Chem. Soc. Perkin Trans. 1 1993 3127. 19 (a) R. C. Cookson B. Halton and I. D. R. Stevens J. Chem. Soc. Perkin Trans. 1 1968 767; (b) J. E. Baldwin and D. P. Kelly J. Chem. Soc. Chem. Commun. 1968 1664. 22 (c) G. Combaut J.-M. Chantraine J. Teste J. Soulier and K.-W. Glombitza Tetrahedron Lett. 1978 1699. 23 (a) J. Bosch J. Canals and R. Granados Anal. Quim. 1976 72 709; (b) T. Yamato N. Sakaue L. K. Doamekpor and M. Tashiro J. Chem. Res. (S) 1994 176. 26 (a) R. E. Singer and D. J. Cram J. Am. Chem. Soc. 1971 93 4443. Fig. 1

ISSN:0308-2342    

DOI:10.1039/a703256k

出版商:RSC    

年代:1997

数据来源: RSC