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A New Route for the Preparation of Fluorene Derivativesusing Friedel–Crafts IntramolecularCyclobenzylation

 

作者: Takehiko Yamato,  

 

期刊: Journal of Chemical Research, Synopses  (RSC Available online 1997)
卷期: Volume 0, issue 3  

页码: 82-83

 

ISSN:0308-2342

 

年代: 1997

 

DOI:10.1039/a605730f

 

出版商: RSC

 

数据来源: RSC

 

摘要:

82 J. CHEM. RESEARCH (S), 1997 J. Chem. Research (S), 1997, 82–83 J. Chem. Research (M), 1997, 0584–0596 A New Route for the Preparation of Fluorene Derivatives using Friedel–Crafts Intramolecular Cyclobenzylation Takehiko Yamato,* Masayasu Komine and Koji Matsuo Department of Applied Chemistry, Faculty of Science and Engineering, Saga University, Honjo-machi 1, Saga-shi, Saga 840, Japan A convenient preparation of fluorene derivatives based on a novel Friedel–Crafts intramolecular cyclobenzylation, involving the action of Cl2CHOMe and TiCl4 on a variety of biphenyls (constructed such that electrophilic substitution occurs ortho to the biphenyl linkage), is described.Although there are numerous reports on the synthesis of fluorenes from 2-mono- and 2,2p-di-substituted biphenyls using cyclization reactions,3–5 there has not been any report concerning Friedel–Crafts intramolecular benzylation of 2-halomethylbiphenyls to give fluorenes. Recently we reported6 that the chloromethylation of 4,4p-dimethoxy- 3,3p,5,5p-tetramethylbiphenyl 1b affords the Friedel–Crafts intramolecular benzylation products, 2,7-dimethoxy- 1,3,6,8-tetramethylfluorene derivatives in 20–40% yield.However, the selective preparation of substituted fluorenes using Friedel–Crafts intramolecular cyclobenzylation by the action with chloromethyl methyl ether was very difficult because of low yields as well as their separation from the reaction mixture. On the other hand, Meth-Cohn and coworkers have reported7 that Lewis acid catalysed formylation of diarylmethanes with dichloromethyl methyl ether affords anthracenes by a direct Bradsher reaction. However, this is limited to the preparation of benzothiophene derivatives.This strategy is proposed to be employed for the preparation of fluorene derivatives. Here we report the first success in the formation of a fluorene skeleton via a Friedel–Crafts intramolecular benzylation during the action of Cl2CHOMe and TiCl4 on 4,4p-di-tert-butylbiphenyl 1a and 4,4p-dimethoxy- 3,3p5,5p-tetramethylbiphenyl 1b, which are constructed such that electrophilic substitution occurs ortho to the biphenyl linkage.A series of biphenyls 1a–d was prepared according to previous reports.6,9 On treatment of 1a with Cl2CHOMe (7 equiv.) in the presence of TiCl4 at 0 °C for 5 h, the expected 2,7-di-tert-butyl-9-chloro-4-formylfluorene 5a was obtained in 78% yield along with 2,7-di-tert-butyl-4-formylfluoren- 9-one 6a in 5% yield.The same result was obtained in the case of compound 1b. The reaction was again carried out under the same conditions and the expected 9-chloro-4-formyl-2,7-dimethoxy-1,3,6,8- tetramethylfluorene 5b was obtained in 87% yield. It was also found that treatment of 2,2p,3,3p-tetramethoxybiphenyl 1c with TiCl4 for 24 h under the same conditions as described above resulted only in a quantitative recovery of starting compound. This result indicates that two methoxy groups at the ortho position of compound 1c might disturb the electrophilic substitution at both the 2- and 2p-positions of the biphenyl.Similar treatment of 4,4p-di-tert-butyl-2,2p-dimethylbiphenyl 1d with Cl2CHOMe in the presence of TiCl4 afforded 4,4p-di-tert-butyl-6-formyl-2,2p-dimethylbiphenyl 7 in 70% yield. The present novel intramolecular benzylation reaction is strongly affected by the methyl groups at the 2- and 2p-positions of the biphenyls which are forced to arrange in a conformation appropriate for the subsequent further intramolecular benzylation reaction.However, from consideration of molecular models, 2,2p-dimethylbiphenyl 1d is unlikely to form an intermediate suitable for undergoing intramolecular cyclobenzylation, because a chloromethoxymethyl group at the 6-position would be pushed away from the 6p-position of the other benzene ring in order to avoid crowding between the two methyl groups at the 2- and 2p-positions.The reduction of 5a with chlorohydroalane in diethyl ether afforded the 4-hydroxymethyl derivative 10 in 64% yield. Successive conversion of the hydroxymethyl group to a methyl group was achieved via the chloromethyl derivative. Recently, we have found that Nafion-H, a perfluorinated resin sulfonic acid,10 catalyses Friedel–Crafts benzylations of *To receive any correspondence. Table 1 Formylation of substituted biphenyls 1 with Cl2CHOMe to give fluorenes 5 Run Biphenyl 1 t/h Product 5 (%)a 123 a bc 55 24 a (78)b b (87) d (0)c aIsolated yields.b2,7-Di-tert-butyl-4-formylfluoren-9-one 6a was obtained in 5% yield. cStarting compound 1c was recovered in almost quantitative yield.J. CHEM. RESEARCH (S), 1997 83 benzene and substituted benzenes with benzyl alcohols under relatively mild conditions. The Nafion-H-catalysed transalkylation of 12 in toluene afforded the desired 4-methyl- fluorene 13 in 65% yield together with formation of tertbutyltoluene 14.Trans-alkylation of 12 with Nafion-H catalyst gave a better yield than that achieved with AlCl3–MeNO2 catalyst (30%).12 Although 4-methylfluorene 13 has been prepared by passing 2,2p-dimethylbiphenyl over Pd–charcoal at 450 °C,13 the preparative conditions are very severe as an experimental laboratory procedure in comparison with our method. Furthermore, Kajigaeshi et al.12 have reported the construction of the fluorene skeleton using an Ullmann coupling reaction of 4,4p-di-tert-butyl-2,2p-diiododiphenylmethane.However, the introduction of iodine groups at the 2,2p-positions of 4,4p-di-tert-butyldiphenylmethane seems quite difficult and leads to low product yield and difficult product separation. Utilizing the present novel Friedel–Crafts intramolecular cyclobenzylation reaction we have developed a much more convenient procedure to convert 4,4p-di-tert-butylbiphenyl 1a directly to 4-methylfluorene 13. Consequently, the preparative route to compound 13 can be accomplished in six steps starting from biphenyl.Techniques used: 1H NMR, IR, MS, VPC analysis References: 13 Schemes: 2 Equations: 4 Received, 16th August 1996; Accepted, 9th December 1996 Paper E/6/05730F References cited in this synopsis 3 E. C. Taylor and E. J. Strojny, J. Am. Chem. Soc., 1960, 82, 5198. 4 F. G. Baddar, S. Sherif, L. Ekladios and A. E. Azab, J. Chem. Soc., 1967, 506. 5 W. Reid and D. Freitag, Angew. Chem., Int. Ed. Engl., 1968, 7, 835. 6 T. Yamato, M. Komine, N. Sakaue, T. Matsuda, Y. Nagano and M. Tashiro, J. Chem. Res. (S), 1993, 146. 7 (b) M. Ahmed. J. Ashby, M. Ayad and O. Meth-Cohn, J. Chem. Soc., Perkin Trans. 1, 1973, 1099. 9 (b) T. Yamato, C. Hideshima, K. Suehiro, M. Tashiro, G. K. S. Prakash and G. A. Olah, J. Org. Chem., 1991, 56, 6248. 10 (b) T. Yamato, J. Synth. Org. Chem. Jpn., 1995, 53, 487 and references cited therein. 12 S. Kajigaeshi, T. Kadowaki, A. Nishida and S. Fujisaki, Bull. Chem. Soc. Jpn., 1986, 59, 97. 13 M. Orchin and E. O. Woolfolk, J. Am. Chem. Soc., 1945, 67, 122. Scheme 2

 



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