accomplished without addition of phosphine (see STable 1
of the Supporting Information for details). Simply heating
the DMF (5 mL) solution of 1a (0.5 mmol), 2a (1.5 mmol),
Pd(OAc)2 (10 mol %), and Na2CO3 (1.0 mmol) at 120 °C
resulted in the formation of the dibenzothiophene 3a in a
76% yield (Table 1, entry 1). With this optimized catalytic
system in hand, the scope of the substrates was evaluated
with a variety of substituted benzothiophenes and al-
kynes (Table 1). The electronic densities of Ar (entries
1À4) and Ar1 groups (entries 5À7) did not affect the
yields of the reaction to a significant extent, allowing for
dibenzothiophenes 3aÀg to be isolated in 54À76% yields.
The crystal structure of 3g (Figure 1) clearly shows that the
C(Br)ÀS bond of the thiophene moiety was cleaved regio-
selectively and a new CÀS bond was formed with neigh-
boring Ar1 group (entry 7, R1 = F).
Encouraged by the above selective cleavage of the CÀS
bond and the consequent intramolecular CÀS coupling
process, we conducted further experiments with simple
bromothiophenes 4a and 4b. Interestingly, these reactions
provided thiopyran derivatives 5a and 5b, respectively
(Scheme 3). Product 5b was confirmed by X-ray crystal
analysis (Figure 2). Notably, the formation of thiopyran
ring occurred regioselectively, and only the C(Br)ÀS bond
of thiophene was cleaved. The sulfur-containing species
were trapped by an intermolecular carbothiolation of
alkyne. These results highlighted that this regioselective
CÀS cleavage reaction of bromothiophene has a wide
reaction spectrum.
Scheme 2
(HDS), a very important industrial heterogeneous process
to produce sulfur-free petroleum products.4 Significantly,
the reactions of thiophene with transition-metal complexes
have usually led to the cleavage of the CÀS bond and thus
to the formation of various new transition-metal com-
plexes, which contain metalÀsulfur and metalÀcarbon
bonds.5À8 However, there is no application of these
CÀS bond cleavage reactions catalytically in organic
synthesis.9,10 We hypothesized the formation of 3a occurs
through the catalytic cleavage of CÀS bond and the
rearrangement of benzothiophene 1a with alkyne 2a. A
new CÀS bond is formed between the sulfur fragment and
the neighboring phenyl group through CÀH bond activa-
tion, which give the dibenzothiophene moiety, while the
reactive carbon part is trapped by alkynes to form the
fulvene moiety.
A brief screening of various reaction conditions revealed
that this reaction did not proceed in the absence of Pd-
(OAc)2 or Na2CO3. Moreover, this transformation can be
(5) Ates-in, T. A.; Oster, S. S.; Skugrud, K.; Jones, W. D. Inorg. Chim.
Acta 2006, 359, 2798.
ꢀ
ꢀ
(6) (a) Nova, A.; Novio, F.; Gonzalez-Duarte, P.; Lledos, A.; Mas-
ꢀ
Balleste, R. Eur. J. Inorg. Chem. 2007, 5707. (b) Ates-in, T. A.; Ates-in, A.
Table 1. Reactions of Bromobenzothiophenes with Alkynes
C-.; Skugrud, K.; Jones, W. D. Inorg. Chem. 2008, 47, 4596. (c) Tan,
R. Y.; Song, D. T. Organometallics 2011, 30, 1637.
(7) (a) Paz-Sandoval, M. A.; Cervantes-Vasquez, M.; Young, V. G.,
Jr.; Guzei, I. A.; Angelici, R. J. Organometallics 2004, 23, 1274. (b)
Shibue, M.; Hirotsu, M.; Nishioka, T.; Kinoshita, I. Organometallics
2008, 27, 4475. (c) Ates-in, T. A.; Jones, W. D. Inorg. Chem. 2008, 47,
10889. (d) Grochowski, M. R.; Li, T.; Brennessel, W. W.; Jones, W. D.
J. Am. Chem. Soc. 2010, 132, 12412.
(8) (a) Kim, Y.-J.; Lee, S.-C.; Cho, M. H.; Lee, S.-W. J. Organomet.
Chem. 1999, 588, 268. (b) Torres-Nieto, J.; Brennessel, W. W.; Jones,
W. D.; Garcıa, J. J. J. Am. Chem. Soc. 2009, 131, 4120. (c) Oster, S. S.;
´
Grochowski, M. R.; Lachicotte, R. J.; Brennessel, W. W.; Jones, W. D.
Organometallics 2010, 29, 4923.
(9) For RLi-mediated and similar reactions: (a) Dickinson, R. P.;
Iddon, B. J. Chem. Soc. C 1971, 3447. (b) Iddon, B. Heterocycles 1983,
20, 1127. (c) Kawase, T.; Fujino, S.; Ode, M. Tetrahedron Lett. 1991, 32,
3499. (d) Fuller, L. S.; Iddon, B.; Smith, K. A. J. Chem. Soc., Perkin
Trans. 1 1999, 1273. (e) Chen, Z.; Mocharla, V. P.; Farmer, J. M.; Pettit,
G. R.; Hamel, E.; Pinney, K. G. J. Org. Chem. 2000, 65, 8811. (f) Belley,
M.; Douida, Z.; Mancuso, J.; Vleeschauwer, M. D. Synlett 2005, 247.
(g) Wu, W.; Xu, L.; Shi, J. W.; Qin, X. L.; Wang, H. Organometallics
2009, 28, 1961.
(10) For catalytic CÀS bond breaking, see: (a) Kondo, T.; Mitsudo,
T. A. Chem. Rev. 2000, 100, 3205. (b) Nakamura, I.; Sato, T.; Yamamoto,
Y. Angew. Chem., Int. Ed. 2006, 45, 4473. (c) Minami, Y.; Kuniyasu, H.;
Sanagawa, A.; Kambe, N. Org. Lett. 2010, 12, 3744. (d) Beletskaya, I. P.;
Ananikov, V. P. Chem. Rev. 2011, 111, 1596. (e) Ke, F.; Qu, Y. Y.; Jiang,
Z. Q.; Li, Z. K.; Wu, D.; Zhou, X. G. Org. Lett. 2011, 13, 454. (f) Prasad,
D. J. C.; Sekar, G. Org. Lett. 2011, 13, 1008. (g) Inami, T.; Baba, Y.;
Kurahashi, T.; Matsubara, S. Org. Lett. 2011, 13, 1912. (h) Samanta, R.;
Antonchick, A. P. Angew. Chem., Int. Ed. 2011, 50, 5217. (i) Henke, A.;
Srogl, J. Chem. Commun. 2011, 47, 4282. (j) Park, N.; Park, K.; Jang, M.;
Lee, S. J. Org. Chem. 2011, 76, 4371. (k) Zhang, Z. H.; Lindale, M. G.;
Liebeskind, L. S. J. Am. Chem. Soc. 2011, 133, 6403. (l) Rao, H. H.;
Yang, L.; Shuai, Q.; Li., C. J. Adv. Synth. Catal. 2011, 353, 1701.
isolated
entry
1
4
2
time (h)
13
product
yield (%)
1a (Ar1 = 2a (Ar = Ph)
p-H-Ph)
3a (R1 = H)
76
2
3
4
5
6
7
1a
1a
1a
2b (Ar =
p-Me-Ph)
2c (Ar =
p-OMe-Ph)
2d (Ar =
p-F-Ph)
10
14
14
17
17
18
3b (R1 = H)
3c (R1 = H)
3d (R1 = H)
3e (R1 = Me)
3f (R1 = OMe)
3g (R1 = F)
54
75
58
57
76
72
1b (Ar1 = 2a
p-Me-Ph)
1c (Ar1 = 2a
p-OMe-Ph)
1d (Ar1 = 2a
p-F-Ph)
Org. Lett., Vol. 13, No. 19, 2011
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