4-Methoxy-9H-xanthene (3c). 1H NMR (500 MHz, DMSO):
d 7.26–7.19 (m, 2H), 7.10–7.04 (m, 2H), 7.02–6.97 (m, 1H), 6.94–
6.90 (m, 1H), 6.83–6.79 (m, 1H), 4.02 (s, 2H), 3.83 (s, 3H); 13C
NMR (125 MHz, DMSO): 151.2, 147.6, 140.6, 129.1, 127.7, 123.3,
122.9, 121.3, 120.5, 120.4, 116.2, 110.5, 55.6, 27.0; HRMS-(EI)
(m/z): M+ calc. for C14H12O2, 212.083730; found 212.083684.
3H), 7.54–7.43 (m, 3H), 7.40–7.37 (m, 1H), 4.51 (s, 2H); 13C NMR
(125 MHz, CDCl3): 148.70, 145.73, 133.53, 132.23, 130.44, 128.57,
128.41, 127.69, 127.14, 126.85, 126.19, 126.08, 124.35, 124.28,
122.75, 122.53, 121.53, 118.14, 113.61, 111.79, 25.46; HRMS-(EI)
(m/z): M+ calc. for C21H14O, 282.104462; found 282.104546.
2-Methoxy-7H-benzo[c]xanthene (3l). 1H NMR (500 MHz,
DMSO): d 7.84–7.80 (m, 1H), 7.62–7.52 (m, 2H), 7.32–7.26 (m,
3H), 7.21–7.15 (m, 2H), 7.13–7.08 (m, 1H), 4.16 (s, 2H), 3.94
(s, 3H); 13C NMR (125 MHz, DMSO): 157.64, 151.18, 144.83,
129.41, 129.22, 128.32, 127.75, 124.47, 124.30, 123.47, 122.32,
120.43, 118.34, 116.41, 115.21, 99.45, 55.23, 27.24; HRMS-(EI)
(m/z): M+ calc. for C18H14O2, 262.099378; found 262.099142.
9H-Xanthen-2-ol (3d). 1H NMR (500 MHz, DMSO): d 9.18
(s, 1H), 7.25–7.17 (m, 2H), 7.06–6.99 (m, 2H), 6.90–6.89 (m, 1H),
6.64–6.59 (m, 2H), 3.96 (s, 2H); 13C NMR (125 MHz, DMSO):
153.03, 151.74, 144.08, 129.10, 127.61, 122.74, 121.22, 120.24,
116.68, 115.94, 114.64, 114.48, 27.30; HRMS-(EI) (m/z): M+ calc.
for C13H10O2, 198.068079; found 198.067949
2-Methyl-9H-xanthene (3e). 1H NMR (500 MHz, DMSO): d
7.26–7.19 (m, 2H), 7.07–6.99 (m, 4H), 6.97–6.93 (m, 1H), 4,00 (s,
2H), 2.26 (s, 3H); 13C NMR (125 MHz, DMSO): d 151.4, 149.2,
132.1, 129.4, 129.2, 128.2, 127.7, 123.1, 120.5, 120.2, 116.0, 115.8,
26.9, 20.2; HRMS-(EI) (m/z): M+ calc. for C14H12O, 196.088811;
found 196.088659.
13,14-Dihydrochromeno[3,2a]xanthene (5). Isolated as a by-
product in the synthesis of 3d from 1b and 4. 1H NMR (500 MHz,
CDCl3): d 7.22–7.15 (m, 4H), 7.05–6.98 (m, 4H), 6.88 (s, 2H),
3.96 (s, 4H); 13C NMR (125 MHz, CDCl3): 151.61, 147.12, 129.21,
127.98, 122.92, 118.84, 118.69, 116.40, 115.50, 25.6; HRMS-(EI)
(m/z): M+ calc. for C20H14O2, 286.099377, found 286.099179.
2-Chloro-9H-xanthene (3f). 1H NMR (500 MHz, DMSO): d
7.34–7.32 (m, 1H), 7.27–7.21 (m, 3H), 7.09–7.04 (m, 3H), 4.04
(s, 2H); 13C NMR (125 MHz, DMSO): d 150.9, 150.1, 129.1,
128.7, 127.9, 127.6, 126.7, 123.5, 122.8, 119.9, 117.8, 116.1, 26.7;
HRMS-(EI) (m/z): M+ calc. for C13H9OCl1, 216.034193; found
216.034201.
Acknowledgements
We thank Dr Christophe Fare`s and Jo¨rg Rust for help with the
NMR and crystallographic analysis, Dr Nuno Maulide for helpful
discussions, and Prof. Benjamin List and the Max-Planck-Institut
fu¨r Kohlenforschung for support.
1,3-Dimethyl-9H-xanthene (3g). 1H NMR (500 MHz,
DMSO): d 7.26–7.17 (m, 2H), 7.05–6.98 (m, 2H), 6.73 (s, 1H), 6.68
(s, 1H), 3.88 (s, 2H), 2.22 (s, 6H); 13C NMR (125 MHz, DMSO):
150.95, 150.80, 136.88, 136.45, 129.49, 127.71, 125.04, 122.93,
120.06, 115.83, 115.81, 113.94, 24.53, 20.56, 18.64; HRMS-(EI)
(m/z): M+ calc. for C15H14O, 210.104467; found 210.104383.
Notes and references
´
1 A. Pinte´r, A. Sud, D. Sureshkumar and M. Klussmann, Angew. Chem.,
Int. Ed., 2010, 49, 5004.
2 (a) W. Tang, H. Hioki, K. Harada, M. Kubo and Y. Fukuyama, J. Nat.
Prod., 2007, 70, 2010; (b) M. S. T. Gonc¸alves, Chem. Rev., 2008, 109,
190; (c) B. L. Feringa, J. Org. Chem., 2007, 72, 6635; (d) T. Troxler, K.
Hurth, H. Mattes, M. Prashad, P. Schoeffter, D. Langenegger, A. Enz
and D. Hoyer, Bioorg. Med. Chem. Lett., 2009, 19, 1305; (e) K. Chibale,
M. Visser, D. van Schalkwyk, P. J. Smith, A. Saravanamuthu and A. H.
Fairlamb, Tetrahedron, 2003, 59, 2289; (f) R. Pellicciari, G. Costantino,
M. Marinozzi, A. Macchiarulo, L. Amori, P. Josef Flor, F. Gasparini,
R. Kuhn and S. Urwyler, Bioorg. Med. Chem. Lett., 2001, 11, 3179.
3 (a) S. Wawzonek, in Heterocyclic Compounds, ed. R. C. Elderfield, John
Wiley & Sons, New York, 1951, pp. 419–500; (b) M. A. Brimble, J. S.
Gibson and J. Sperry, in Comprehensive Heterocyclic Chemistry III, ed.
R. K. Alan, A. R. Christopher, F. V. S. Eric and J. K. T. Richard, Elsevier,
Oxford, 2008, pp. 419–699.
7-Methoxy-1,3-dimethyl-9H-xanthene
(3h). 1H
NMR
(500 MHz, DMSO): 6.96–6.92 (m, 1H), 6.84–6.81 (m, 1H),
6.79–6.75 (m, 1H), 6.72 (s, 1H), 6.66 (s, 1H), 3.88 (s, 2H), 3.72 (s,
3H), 2.22 (s, 6H); 13C NMR (125 MHz, DMSO): 154.78, 151.07,
144.87, 136.81, 136.39, 124.79, 120.80, 116.59, 115.36, 113.87,
113.59, 55.36, 24.99, 20.58, 18.70; HRMS-(EI) (m/z): M+ calc.
for C16H16O2, 240.115026; found 240.115225.
12H-Benzo[a]xanthene (3i). 1H NMR (500 MHz, DMSO): d
7.97–7.93 (m, 2H), 7.88–7.85 (m, 1H), 7.66–7.61 (m, 1H), 7.52–
7.48 (m, 1H),7.43–7.39 (m, 1H), 7.35–725 (m, 2H), 7.17–7.11 (m,
1H), 4.41 (s, 2H); 13C NMR (125 MHz, DMSO): 150.33, 147.95,
131.57, 129.81, 129.68, 128.35, 128.33, 127.87, 126.90, 124.34,
123.42, 122.49, 119.49, 117.51, 116.06, 111.68, 23.87; HRMS-(EI)
(m/z): M+ calc. for C17H12O, 232.088813; found 232.088790.
4 For recent methods to access 9-substituted xanthenes exclusively, see,
for example: (a) Z. Karimi-Jaberi and M. Keshavarzi, Chin. Chem. Lett.,
2010, 21, 547; (b) X. Huang and T. Zhang, J. Org. Chem., 2010, 75, 506;
(c) M. Hong and C. Cai, J. Fluorine Chem., 2009, 130, 989; (d) H. Sahin,
M. Nieger and S. Bra¨se, Eur. J. Org. Chem., 2009, 5576; (e) H. Yoshida,
M. Watanabe, H. Fukushima, J. Ohshita and A. Kunai, Org. Lett., 2004,
6, 4049.
9-Methyl-7H-benzo[c]xanthene (3j). 1H NMR (500 MHz,
DMSO) d 8.30–8.26 (m, 1H), 7.92–7.88 (m, 1H), 7.62–7.51 (m,
3H), 7.36–7.30 (m, 1H), 7.17–7.12 (m, 1H), 7.10–7.04 (m, 2H), 4.13
(s, 2H), 2.27 (s, 3H); 13C NMR (125 MHz, DMSO): 149.00, 145.64,
132.90, 132.43, 129.43, 128.29, 127.67, 127.00, 126.11, 123.40,
122.29, 120.73, 119.91, 116.07, 114.47, 27.13, 20.27; HRMS-(EI)
(m/z): M+ calc. for C18H14O, 246.104468; found 246.104376.
5 To access xanthenes without 9-substituents, see, for example: (a) R.
Singh and G. Panda, Org. Biomol. Chem., 2010, 8, 1097; (b) X. Xu, X.
Xu, H. Li, X. Xie and Y. Li, Org. Lett., 2010, 12, 100; (c) K. Okuma, A.
Nojima, N. Matsunaga and K. Shioji, Org. Lett., 2008, 11, 169; (d) U. K.
Ohnemu¨ller, C. F. Nising, M. Nieger and S. Bra¨se, Eur. J. Org. Chem.,
2006, 1535; (e) A. Jha and J. Beal, Tetrahedron Lett., 2004, 45, 8999;
(f) H. J. Kabbe and H. Heitzer, Justus Liebigs Ann. Chem., 1976, 1976,
511; (g) F. G. Baddar and M. Gindy, J. Chem. Soc., 1951, 64; (h) W.
Borsche and A. Geyer, Justus Liebigs Ann. Chem., 1912, 393, 29.
6 S. Kobayashi, M. Sugiura, H. Kitagawa and W. W. L. Lam, Chem. Rev.,
2002, 102, 2227.
14H-Dibenzo[a,h]xanthene (3k). 1H NMR (500 MHz,
CDCl3): d 8.46–8.42 (m, 1H), 7.94–7.78 (m, 4H), 7.64–7.56 (m,
7 J. Weigelt and G. Otting, J. Magn. Reson., Ser. A, 1995, 113, 128.
1748 | Org. Biomol. Chem., 2011, 9, 1744–1748
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