considered as promising scaffolds in the field of organic
electronics and materials chemistry.5 In addition, diben-
zothiophene-S-oxides6 are recognized as triplet oxygen
precursors by their photochemical deoxygenation.7 Re-
cently triplet oxygen-mediated cleavage of DNA was
demonstrated which raises the interesting potential of
triplet oxygen precursors in biological systems.8 Several
straightforward methods to access dibenzothiophenes
have been reported, but they often require multistep
synthesis.9 Thus the development of a new strategy to
access dibenzothiophene and dibenzothiophene-S-oxide
scaffolds would be of great interest. Recently Antonchick
reported, for the first time, a palladium-catalyzed double
CÀH activation directed by sulfoxides. The key step of
this transformation involved sulfoxide-directed cyclo-
metalation of the aromatic ring, followed by the second,
intramolecular CÀH bond activation and a Pummerer
rearrangement which gave access to dibenzothiophene
scaffolds.10 Taking into account our experience in the use
of sulfoxides as chiral auxiliaries in diastereoselective
SuzukiÀMiyaura cross-coupling reactions,11 we report
herein our results on a new palladium-catalyzed direct
arylation, via CÀH bond activation of easily accessible
2-bromo-diaryl sulfoxides, and its application in the direct
synthesis of differently substituted dibenzothiophene-S-
oxides. The latter can be easily reduced to the correspond-
ing dibenzothiophenes using standard methodologies for
the reduction of sulfoxides to thioethers (Scheme 1).12
Our preliminary attempts at implementing Scheme 1
were conducted with Pd(OAc)2 (5 mol %) and Ag2CO3
(1 equiv) on 1-bromo-2-p-tolylsulfinylbenzene 1a13 in
1,3,5-trifluorobenzene at 125 °C under microwave irradiation.
Scheme 1. Synthesis of Complex Biarylmolecules from
Heteroatom-Tethered 2-Halo-diaryl Substrates
A complex reaction mixture was obtained in 30%
yield, and we identified the hydrodehalogenated starting
material (p-tolylsulfinyl benzene), dibenzothiophene, and
the expected product, the dibenzothiophene-S-oxide 2a, in
the reaction mixture. Rewardingly, replacing apolar 1,3,5-
trifluorobenzene with polar DMAc, substituting the silver
base with KOAc, and using 3 mol % Pd(OAc)2 led, in 8 h,
to the desired product 2a in 70% yield, together with traces
of the hydrodehalogenated starting material.14 Note-
worthily, reduction of the starting material could be pre-
vented when using a preheated oil bath whereupon 2a was
isolated in an 85% yield (Scheme 2).
Scheme 2. Synthesis of Dibenzothiophene-S-oxide 2a from
1-Bromo-2-p-tolylsulfinylbenzene 1a
(6) Thiemann, T.; Walton, D. J.; Brett, A. O.; Iniesta, J.; Marken, F.;
Li, Y.-G. ARKIVOC 2008, 9, 96.
(7) Korang, J.; Grither, W. R.; McCulla, R. D. J. Am. Chem. Soc.
2010, 132, 4466 and references cited herein.
(8) Wauchope, O. R.; Shakya, S.; Sawwan, N.; Liebman, J. F.; Greer,
A. J. Sulfur Chem. 2007, 28, 11.
(9) (a) Tengho Toguem, S.-M.; Malik, I.; Hussain, M.; Iqbal, J.;
Villinger, A.; Langer, P. Tetrahedron 2013, 69, 160. (b) Hashmi, A. S. K.;
Yang, W.; Rominger, F. Chem.;Eur. J. 2012, 18, 6576. (c) Pandya,
V. B.; Jain, M. R.; Chaugule, B. V.; Patel, J. S.; Parmar, B. M.; Joshi,
J. K.; Patel, P. R. Synth. Commun. 2012, 42, 497. (d) Xu, X.; Li, X.;
Wang, A.; Sun, Y.; Schweizer, W. B.; Prins, R. Helv. Chem. Acta 2011,
94, 1754. (e) Rodriguez-Aristegui, S.; Clapham, K. M.; Barrett, L.;
Cano, C.; Desage-El Murr, M.; Griffin, R. J.; Hardcastle, I. R.; Payne,
S. L.; Rennison, T.; Richardson, C.; Golding, B. T. Org. Biomol. Chem.
2011, 9, 6066. (f) Jepsen, T. H.; Larsen, M.; Jørgensen, M.; Solanko,
K. A.; Bond, A. D.; Kadziola, A.; Nielsen, M. B. Eur. J. Org. Chem.
2011, 53. (g) Kienle, M.; Unsinn, A.; Knochel, P. Angew. Chem., Int. Ed.
2010, 49, 4751. (h) Black, M.; Cadogan, J. I. G.; McNab, H. Org. Biomol.
Chem. 2010, 8, 2961. (i) Hussain, M.; Malik, I.; Villinger, A.; Langer, P.
Under these optimized reaction conditions, the scope
of the reaction was investigated. R-Bromo-diarylsulfoxides
1bÀl bearing different substituents on the aryl moieties
were synthesized through two known methodologies:13
(1) SNAr reaction on 2-fluoro-1-bromoaryls followed by
oxidation and (2) by condensation of 2-bromoaryl Grignard
reagents on an aryl menthyl sulfinate (Scheme 3).
The 2-bromo-diaryl sulfoxides 1bÀl were subjected to
the palladium-catalyzed cyclization conditions, and the
corresponding dibenzothiophene-S-oxides 2bÀl were ob-
tained in excellent yields (Table 1). Compound 2b, bearing
only an acetyl group on the dibenzothiophene scaffold,
was obtained in an excellent yield of 86%. In addition,
various electron-withdrawing and -donating groups in the
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Synlett 2009, 16, 2691. (j) Sanz, R.; Fernandez, Y.; Castroviejo, M. P.;
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(10) Samanta, R.; Antonchick, A. P. Angew. Chem., Int. Ed. 2011, 50,
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(11) (a) Broutin, P.-E.; Colobert, F. Org. Lett. 2003, 5, 3281. (b)
Broutin, P.-E.; Colobert, F. Org. Lett. 2005, 7, 3737. (c) Broutin, P.-E.;
Colobert, F. Eur. J. Org. Chem. 2005, 1113. (d) Colobert, F.; Valdivia,
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V.; Choppin, S.; Leroux, F. R.; Fernandez, I.; Alvarez, E.; Khiar, N.
Org. lett. 2009, 11, 5130. Synfacts 2010, 1, 64–64. (e) Leermann, T.;
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(12) Grossert, J. S. In The Chemistry of Sulfones and Sulfoxides; Patai,
S., Rappoport, Z., Eds.; John Wiley and Sons: NewYork, 1998; Chapter 20,
pp 925À968.
(13) The syntheses of biarylsulfoxides 2aÀl are detailed in the
Supporting Information.
(14) Bheeter, C. B.; Bera, J. K.; Doucet, H. J. Org. Chem. 2011, 76,
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