Table
arylzinc bromides
3
Formation of 2-arylbenzo[b]thiazole from various
The coupling yields were generally better with aryl iodides
except in the case of iodobenzonitrile. In fact, more homo-
coupling product from iodobenzonitrile was obtained,
decreasing the cross-coupling yield.
Entry FG-C6H4Br FG Reaction time/h Product No. Yield %a
1
2
3
4
5
p-OMe
o-OMe
p-EtOCO
p-CF3
12
72
6
4c
4d
4e
4f
60
0
57
50
45
In conclusion, we have devised an expedient route to cobalt-
catalyzed activation of the C–SMe bond of various
methylthio-substituted N-heterocycles. This catalytic process
involves a simple, inexpensive and environmentally friendly
cobalt halide without ligand and allows the cross-coupling of
these compounds with various aryl or benzylzinc halides.
This activation of C–SMe also leads to the synthesis of the
corresponding organozinc species in good yields.
4
p-CN
6
4g
a
Isolated yields.
reaction involving benzyl chloride derivatives requires longer
reaction times than the coupling with aryl bromides.
As we just observed in the case of coupling, it was also
possible to activate the C–SMe bond of 2-methylthiobenzo-
[b]thiazole or 2-methylthiothiazole to form the corresponding
zinc compound by activation of zinc dust by trifluoroacetic
acid in the presence of CoBr2. The resulting organozinc
compounds were converted into iodide species by addition
of iodine for GC titration using an internal standard (alkane).
Then, the cross-coupling reaction between the organozinc
species from 2-methylthiobenzo[b]thiazole or 2-methylthiothiazole
with an aryl bromide was also possible using palladium catalyst
PdCl2(PPh3)2.
Notes and references
1 (a) Transition Metals for Organic Synthesis, ed. M. Beller and
C. Bolm, VCH, Weinheim, 2nd edn, 2004; Metal-catalyzed
Cross-coupling Reactions, ed. A. de Meijere and F. Diederich,
Wiley-VCH, Weinheim, 2nd edn, 2004, vol.
1
and 2;
(b) S. P. Stanforth, Tetrahedron, 1998, 54, 263–303; (c) J. Hassan,
M. Sevignon, C. Gozzi, E. Schultz and M. Lemaire, Chem. Rev.,
2002, 102, 1359–1469.
2 J. P. Corbet and G. Mignani, Chem. Rev., 2006, 106, 2651–2710.
3 J. Roncali, Chem. Rev., 1992, 92, 711–738.
4 (a) H. Okamura, M. Miura and H. Takei, Tetrahedron Lett., 1979,
20, 43–46; (b) H. Takei, M. Miura, H. Sugimura and H. Okamura,
Chem. Lett., 1979, 1447–1450; (c) E. Wenkert, T. W. Ferreira and
E. L. Michelotti, J. Chem. Soc., Chem. Commun., 1979, 637–638.
5 L. N. Pridgen, L. B. Killmer and R. L. Webb, J. Org. Chem., 1982,
47, 1985–1989.
6 (a) C. Savarin, J. Srogl and L. S. Liebeskind, Org. Lett., 2001, 3,
91–93; (b) C. Savarin and L. S. Liebeskind, Org. Lett., 2001, 3,
2149–2152; (c) F. A. Alphonse, F. Suzenet, A. Keromnes,
B. Lebret and G. Guillaumet, Synlett, 2002, 447–450;
(d) L. S. Liebeskind and J. Srogl, Org. Lett., 2002, 4, 979–981.
7 (a) M. Egi and L. S. Liebeskind, Org. Lett., 2003, 5, 801–802;
(b) F. A. Alphonse, F. Suzenet, A. Keromnes, B. Lebret and
G. Guillaumet, Org. Lett., 2003, 5, 803–805.
However, these corresponding well-known Negishi couplings
proceeded in good yields exclusively if another solvent such as
DMF was added to the solution to improve solubility
(Scheme 6). The replacement of DMF by THF decreased the
yields. This coupling process was conducted at 35 1C since the
organozinc species from 2-methylthiothiazole was not stable at
50 1C. Then, results are correct and reported in Table 4. To
our knowledge, this is the first reported synthesis of organozinc
species from the C–SMe bond.
8 (a) M. E. Angiolelli, A. L. Casalnuovo and T. P. Selby, Synlett,
2000, 905–907; (b) K. Lee, C. M. Counceller and J. P. Stambuli,
Org. Lett., 2009, 11, 1457–1459; (c) A. Metzger, L. Melzig,
C. Despotopoulou and P. Knochel, Org. Lett., 2009, 11,
4228–4231.
These organozinc species were obtained in good yields of
90% but the cross-coupling with various aryl iodides or
bromides should be improved with different palladium
complexes in order to increase the yield of cross-coupling.
9 The world market prices of palladium (2010) 420 USD per ounce
and nickel 8USD per pound.
10 (a) C. Melber and I. Mangelsdorf, Palladium Emissions in the
Environment, ed. F. Zereini and F. Alt, Springer, Berlin,
Heidelberg, 2006, pp. 575–596; (b) K. S. Kasprzak, B. A. Diwan,
J. M. Rice, M. Misra, C. W. Riggs, R. Olinski and M. Dizdaroglu,
Chem. Res. Toxicol., 1992, 5, 809–815.
11 (a) T. Hatakeyama and M. Nakamura, J. Am. Chem. Soc., 2007,
129, 9844–9845; (b) I. Sapountzis, W. Lin, C. C. Kofink,
C. Despotopoulou and P. Knochel, Angew. Chem., Int. Ed.,
2005, 44, 1654–1657; (c) W. M. Czaplik, M. Mayer, J. Cvengros
and A. Jacobi von Wangelin, ChemSusChem, 2009, 2, 396–417;
Scheme 6 Pd-catalyzed cross-coupling of organozinc species from
2-methylthiobenzo[b]thiazole or 2-methylthiothiazole with aryl
halides.
´
(d) A. Furstner, A. Leitner, M. Mendez and H. Krause, J. Am.
Chem. Soc., 2002, 124, 13856–13863.
¨
Table 4 Formation of 2-arylbenzo[b]thiazole or 2-arylthiazole
12 (a) C. Gosmini, J. M. Begouin and A. Moncomble, Chem.
´
Commun., 2008, 3221–3233; (b) G. Cahiez and A. Moyeux, Chem.
Rev., 2010, 110, 1435; (c) T. J. Korn and P. Knochel, Angew.
Chem., Int. Ed., 2005, 44, 2947; (d) T. Kobayashi, H. Ohmiya,
H. Yorimitsu and K. Oshima, J. Am. Chem. Soc., 2008, 130, 11276;
(e) P.-S. Lin, M. Jeganmohan and C.-H. Cheng, Chem.–Eur. J.,
2008, 14, 11296; (f) A. Moncomble, P. Le Floch and C. Gosmini,
Chem.–Eur. J., 2009, 15, 4770; (g) J. M. Begouin, S. Claudel and
C. Gosmini, Synlett, 2009, 3192; (h) M. Amatore and C. Gosmini,
Chem. Commun., 2008, 5019.
Entry HetArZnSMe
FG-C6H4X FG Product No. Yield (%)
1
2
3
4
5
6
7
8
p-OMe
p-EtOCO
p-CN
4c
4e
4g
4f
5a
5b
5c
5d
70a
65a
50a (55)b
55a
p-CF3
p-OMe
p-EtOCO
p-CN
55a(0)b
29a
34a(49)b
0a
13 J. M. Begouin and C. Gosmini, J. Org. Chem., 2009, 74, 3221.
14 Z.-B. Dong, G. Manolikakes, L. Shi, P. Knochel and H. Mayr,
Chem.–Eur. J., 2010, 16, 248.
p-CF3
a
b
Isolated yield from the corresponding ArI. Isolated yield from the
corresponding ArBr.
15 V. J. Majo, J. Prabhakaran, J. J. Mann and J. S. D. Kumar,
Tetrahedron Lett., 2003, 44, 8535.
ꢀc
This journal is The Royal Society of Chemistry 2010
5974 | Chem. Commun., 2010, 46, 5972–5974