General synthetic method A (products 11–28, 31 and 33). The
trifluoromethyl-substituted arene (1 mmol) was dissolved in C6H6
(2 mL). If the reaction was performed at 0 ◦C, then CHCl3 (1 mL)
was added as a co-solvent. Trifluoromethanesulfonic acid (2 mL)
was then added. The mixture was stirred for at least 4 h, after
which it was poured over several grams of ice. The solution
was extracted twice with chloroform and the organic extracts
washed with water followed by brine (2¥). The solution was dried
over sodium sulfate and the products isolated by removal of the
solvent. In some cases, the major product(s) could be isolated by
column chromatography (hexane : ether). However, some of the
benzophenone/triarylmethanol product mixtures (11/20, 12/21,
13/22) were inseparable by column chromatography.
[M+], 209/207, 181/179, 141/139, 113/111. High resolution mass
spectroscopy (EI): calc. C14H9OF3Cl2 317.98262, found 317.98381.
2¢,4-Dihydroxy-3-(trifluoromethyl)benzophenone (39). mp 77–
79 ◦C (CH2Cl2). 1H NMR (500 MHz, CDCl3): d 10.2 (s, 1H), 8.10
(dd, J = 0.4, 2.0 Hz, 1H), 7.76 (d, J = 1.9 Hz, 1H), 7.69–7.66 (m,
1H), 7.59–7.56 (m, 1H), 7.45–7.40 (m, 2H), 7.07 (d, J = 8.5 Hz, 1H),
7.02 (m, 1H). 13C NMR (125 MHz, CDCl3): d 168.1, 162.3, 147.5,
136.9, 133.1, 130.6, 127.1 (q, JC–F = 4 Hz), 126.4, 124.3, 123.4
(q, JC–F = 31 Hz), 122.8 (q, JC–F = 271 Hz), 119.8, 117.9, 111.3.
Low resolution mass spectroscopy (EI): m/z 282 [M+], 162, 142,
121, 93. High resolution mass spectroscopy (EI): calc. C14H9O3F3
282.05039, found 282.05132.
General synthetic method B (products 35, 37, 40 and 41).
The trifluoromethyl-substituted arene (1 mmol) was dissolved in
CHCl3 (2 mL). Trifluoromethanesulfonic acid (2 mL) was then
added. The mixture was then stirred for at least 4 h, after which it
was poured over several grams of ice. The solution was extracted
twice with chloroform and the organic extracts washed with water
followed by brine (2¥). The solution was dried over sodium sulfate
and the products isolated by removal of the solvent.
Acknowledgements
We gratefully acknowledge the support of the National Science
Foundation (CHE-0749907) and the NIH-National Institute of
General Medical Sciences (GM085736-01A1).
Notes and references
1 (a) B. M. Kraft, R. J. Lachicotte and W. D. Jones, J. Am. Chem. Soc.,
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2 M. Klahn, C. Fischer, A. Spannenberg, U. Rosenthal and I. Krossing,
Tetrahedron Lett., 2007, 48, 8900.
3 H. Schirok, H. Paulsen, W. Kroh, G. Chen and P. Gao, Org. Process
Res. Dev., 2010, 14, 168.
4 Y. Hayakawa, H. Kimoto, L. A. Cohen and K. L. Kirk, J. Org. Chem.,
1998, 63, 9448.
3-Hydroxy-5-(trifluoromethyl)benzophenone (18). mp 77–
79 ◦C (C6H6). 1H NMR (500 MHz, CDCl3): d 7.82 (m, 2H), 7.65
(m, 1H), 7.55 (m, 4H), 7.27 (s, 1H), 6.89 (bs, 1H). 13C NMR
(125 MHz, CDCl3): d 196.1, 156.6, 139.5, 136.5, 133.4, 132.3
(q, JC–F = 33 Hz), 130.2, 128.7, 123.3 (q, JC–F = 271 Hz), 119.9,
119.0 (q, JC–F = 4 Hz), 116.7 (q, JC–F = 3 Hz). Low resolution
mass spectroscopy (EI): m/z 266 [M+], 189, 161, 105, 77. High
resolution mass spectroscopy (EI): calc. C14H9O2F3 266.05547,
found 266.05635.
5 G. A. Olah and G. K. S. Prakash, Carbocation Chemistry, Wiley, New
York, 2004.
6 H. Amii and K. Uneyama, Chem. Rev., 2009, 109, 2119.
7 (a) J.-L. M. Abboud, R. Notario, E. Ballesteros, M. Herreros, O. Mo,
M. Yanez, J. Elguero, G. Boyer and R. Claramunt, J. Am. Chem. Soc.,
1994, 116, 2486; (b) B. A. Hess Jr. and R. Zahradnik, J. Am. Chem. Soc.,
1990, 112, 5731; (c) J. K. Laerdahl, P. U. Civcir, L. Bache-Andreassen
and E. Uggerud, Org. Biomol. Chem., 2006, 4, 135.
8 M. Aschi, B. Chiavarino, M. E. Crestoni and S. Fornarini, J. Phys.
Chem., 1996, 100, 19859.
9 J. Zakzeski, I. S. Fan and A. T. Bell, Appl. Catal., A, 2009, 360, 33.
10 F. Wang and J. Hu, Chin. J. Chem., 2009, 27, 27.
11 The same conversion was reported in ref. 10.
12 G. M. Le Fave, J. Am. Chem. Soc., 1949, 71, 4148.
13 Product 38 is formed with a minor amount of a regioisomer (~95 : 5
ratio). Purification may be undertaken by recrystallization from
benzene.
2¢,4-Dichloro-3-(trifluoromethyl)benzophenone (38)13. mp 138–
◦
1
139 C (hexanes). H NMR (500 MHz, CDCl3): d 8.17 (s, 1H),
7.86 (dd, J = 1.5, 8.0 Hz, 1H), 7.62 (d, J = 8.0 Hz, 1H), 7.51–7.48
(m, 2H), 7.43–7.40 (m, 2H). 13C NMR (125 MHz, CDCl3): d 192.9,
137.9, 137.2, 135.1, 134.0, 132.0, 132.0, 131.4, 130.4, 129.3, 129.2
(q, JC–F = 32 Hz), 129.1 (q, JC–F = 5 Hz), 127.1, 122.3 (q, JC–F
=
271 Hz). Low resolution mass spectroscopy (EI): m/z 320/318
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