Four-membered ring cleavage of perfluorinated benzocyclobutene and 1-methylbenzocyclobutene under the action of I2-SbF5

摘要

Mendeleev Communications Electronic Version, Issue 2. 1997 (pp. 47ndash;86) Four-membered ring cleavage of perfluorinated benzocyclobutene and 1-methylbenzocyclobutene under the action of I2ndash;SbF5 Victor M. Karpov,* Tatyana V. Mezhenkova and Vyacheslav E. Platonov Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk,Russian Federation. Fax: +7 383 235 4752; e-mail: root@orchem.nsk.su Interaction of perfluorobenzocyclobutene with I2 in an SbF5 medium leads to the formation of 2-iodoperfluoroethylbenzene and perfluoro-o-xylene; perfluoro-1-methylbenzocyclobutene in the I2ndash;SbF5 system is transformed into perfluoro-2-ethyltoluene.Previously, we have found that benzocyclobutene 1 and perfluoro-1-methylbenzocyclobutene 2 under the action of Br2 or HF in an SbF5 medium undergo cleavage of the fourmembered ring to give the corresponding 2-bromo- or 2-Hperfluoroalkylbenzenes. 1ndash;3 Here we report a substantially different route to the ring opening of benzocyclobutenes 1 and 2 in the I2ndash;SbF5 system (about the I2ndash;SbF5 system4).We have found that compound 1 under the action of I2 in an SbF5 medium gives not only the cleavage product of the CArndash;C1 bond of the four-membered ring (as in the case of Br2 or HF1,2), but the product of C1ndash;C2 bond cleavage as well.At the same time, compound 2 undergoes only of the C1ndash;C2 bond cleavage. Thus, when heated with I2 in an SbF5 medium, compound 2 is transformed to perfluoro-2-ethyltoluene 3dagger; (Scheme 1). Under the same conditions compound 1 gives perfluoro-o-xylene 4 together with 2-iodoperfluoroethylbenzene 5.In addition to these products, the reaction mixture contained perfluoro- 2-(1-benzocyclobutenyl)ethylbenzene 6, perfluoro-2-(1-hydroxy- 1-benzocyclobutenyl)ethylbenzene 7, perfluoro-2-ethyl- 2'-methyldiphenylmethane 8 and perfluoro-2-ethyl-2'-methylbenzophenone 9Dagger; (Scheme 2). Compound 6 is formed as a result of dimerisation of benzocyclobutene 1 in an SbF5 medium.1 Compound 8 seems to be the product of further transformations of dimer 6 under the reaction conditions (these transformations did not proceed under the action of SbF5 at 90 deg;C in the absence of I2). It may be suggested that oxygen-containing compounds 7 and 9 are the hydrolysis products of cation salts, which seems to be formed from precursors 6 and 8 in an SbF5 medium (cf.refs.5,6). dagger; Compound 3 was described by us earlier.1 Formation of compound 5 from benzocyclobutene 1 under the action of I2 in an SbF5 medium may be represented by a scheme similar to that for reactions of polyfluorobenzocyclobutenes with Br2 or HF in an SbF5 medium.1ndash;3 One of the possible routes of transformation of compound 1 to xylene 4 in the I2ndash;SbF5 system includes intermediate formation of cation 10 (Scheme 3).The latter may be considered as a heteroatomic analogue of perfluorobenzocyclobutenylalkyl cations for which a similar mechanism of four-membered ring cleavage was discussed.7 We gratefully thank the Russian Foundation for Basic Research (project no.95-03-08374a) for financial support.References 1 V. M. Karpov, T. V. Mezhenkova, V. E. Platonov and G. G. Yakobson, Bull. Soc. Chim. Fr., 1986, 980. 2 V. M. Karpov, T. V. Mezhenkova, V. E. Platonov and L. N. Shchegoleva, Izv. Akad. Nauk SSSR, Ser. Khim., 1991, 2618 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1991, 40, 2292). 3 V. M. Karpov, T. V. Mezhenkova and V. E. Platonov, J. Fluorine Chem., 1996, 77, 133. Dagger; Typical experimental procedure.Benzocyclobutene 1 (5.07 g, 20.4 mmol) was added to a stirred solution of 5.18 g (20.4 mmol) I2 in 31.0 g (143 mmol) of SbF5. The mixture was stirred for 5 h 45 min at 90 deg;C, then cooled to ndash;10 deg;C, treated with 6 ml of anhydrous HF and poured on to ice cooled with liquid N2. The mixture was then extracted with CH2Cl2 and the combined extracts dried over MgSO4.The solvent was distilled off to give 4.08 g of a mixture containing (GLC, 19F NMR spectrum) 20 of ethylbenzene 5, 28 of xylene 4, 6 of dimer 6, 4 of product 7, 17 of diphenylmethane 8 and 22 of benzophenone 9. Individual compounds 4ndash;9 were isolated by preparative GLC. The 19F NMR spectra of compounds 4 and 6 are in agreement with those reported in literature.8,1 New compounds 5, 7ndash;9 exibited sutisfactory analytical data. 19F NMR spectra, (d/ppm downfield from C6F6 as internal standard). 5 (in CCl4, 56.4 MHz): 78.2 (CF3), 58.3 (F-3), 55.5 (CF2), 32.2 (F-6), 16.7 (F-4), 11.2 (F-5), JF-6, CF2 40 Hz (cf. ref. 1). 7 (in CDCl3, 188.3 MHz): 81.4 (CF3), 62.5 (FA) and 51.2 (FB, CF2CF3), JAB 285 Hz, 68.5 (FA) and 56.8 (FB, CF2), JAB 220 Hz, 33.4 (1F), 27.7 (1F), 26.1 (1F), 24.6 (1F), 18.9 (1F), 16.1 (2F), 13.2 (1F). 8 (in CHCl3, 188.3 MHz): 108.7 (CF3), 92.3 (CF2), 80.7 (CF2CF3), 62.5 (FA) and 59.4 (FB, CF2CF3), JAB 280 Hz, 35.0 (1F), 30.6 (1F), 30.1 (1F), 29.3 (1F), 17.0 (1F), 15.8 (2F), 15.3 (1F). 9 (in Me2CO, 56.4 MHz): 109.6 (CF3), 80.9 (CF2CF3), 59.7 (CF2CF3), 17.9ndash;15.2 (4F), 32.0 (1F), 29.1 (1F), 27.1 (1F), 25.9 (1F). X = H, Br 2 3 Scheme 1 CF(CF3) 2 X CF3 CF2CF3 CF3 F F F F HFndash;SbF5 or Br2 ndash;SbF5 I2 ndash;SbF5 90deg;C + + + + + CF2CF3 C F3C O F F CF2CF3 CF2 F3C F F CF2CF3 OH F F F CF2CF3 F F F F F CF3 CF3 F CF2CF3 I F i, I2ndash;SbF5, 90 deg;C ii, HF iii, H2O 1 4 5 6 7 8 9 Scheme 2 + + + ...F F F F I2 F F F CFI2 CF2 F CF3 CF3 Fndash; SbF5 SbF5 I2 1 10 4 Scheme 3Mendeleev Communications Electronic Version, Issue 2. 1997 (pp. 47ndash;86) 4 (a) R.D. W. Kemmitt, M. Murray, V. M. McRae, R. D. Peacock, M. C. R. Symons and T. A. Orsquo;Donnell, J. Chem. Soc. A, 1968, 862; (b) C. G. Davies, R. J. Gillespie, P. R. Ireland and J. M. Sowa, Can. J. Chem., 1974, 52, 2048. 5 V. M. Karpov, T. V. Mezhenkova, V. E. Platonov and G. G. Yakobson, J. Fluorine Chem., 1985, 28, 121. 6 Yu. V. Pozdnyakovich and V. D. Shteingarts, J. Fluorine Chem., 1974, 4, 317. 7 V. M. Karpov, T. V. Mezhenkova, V. E. Platonov and G. G. Yakobson, Izv. Akad. Nauk SSSR, Ser. Khim., 1990, 1114 (Bull. Acad. Sci. USSR, Div. Chem. Sci., 1990, 39, 1000). 8 F. A. M. Ayanbadejo, Spectrochim. Acta, 1969, 25A, 1009. Received: Moscow, 15th August 1996 Cambridge, 11th November 1996; Com. 6/05864G