1056
E. M. Beccalli et al.
LETTER
6a
1/2 H2O + 2 H+
H2O
– HCl
H
5a
2 Cu+
PdClL2
H
2 Cu2+
PdCl2L2
Me
Cl
S
N
Cl PdL2
CO2Et
H
Pd 0
PdL2
Me
N
S
Me
Cl
CO2Et
S
N
Cl
C
CO2Et
PdL2
H
+
– HCl
HPdClL2
Me
Me
S
N
CO2Et
S
N
CO2Et
E
D
Scheme 6 Catalytic cycle for intramolecular oxidative coupling exemplified on carbamate 5a
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(20 mg, 0.15 mmol) in DMF (13 mL) was stirred at r.t. for
30 min under oxygen atmosphere. After addition of a
solution of 5a (225 mg, 1 mmol) in DMF (13 mL), the
mixture was heated at 100 °C for 2 h under an O2
atmosphere. The mixture was washed with brine and
extracted with Et2O (2 × 20 mL). The organic layer was
dried over Na2SO4 and the solvent removed under reduced
pressure. The residue was chromatographed on a silica gel
column with light PE–EtOAc (10:1) as eluent to give 6a.
Data for 6-Carbethoxy-2,4-dimethyl-6H-thieno[2,3-
b]pyrrole (6a)
Oil. IR (nujol): 1635 cm–1. 1H NMR (400 MHz, CDCl3): d =
1.45 (3 H, t, J = 7.2 Hz), 2.20 (3 H, s), 2.53 (3 H, s), 4.45 (2
H, q, J = 7.2 Hz), 6.65 (1 H, s), 7.11 (1 H, s). 13C NMR (100
MHz, CDCl3): d = 11.4 (q), 14.7 (q), 16.3 (q), 63.8 (t), 114.7
(d), 117.7 (s), 120.3 (d), 133 (s), 136.6 (s), 150.1 (s), 162.9
(s). MS: m/z 223 [M+]. Anal. Calcd for C11H13NO2S: C,
59.17; H, 5.87; N, 6.27. Found C, 59.01; H, 6.06; N, 6.41.
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(7) Experimental Procedure
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Leung, W.-P.; Ling, P.; Thurmond, R. L. WO 2004021999,
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A mixture of PdCl2(MeCN)2 (39 mg, 0.15 mmol) and CuCl2
Synlett 2008, No. 7, 1053–1057 © Thieme Stuttgart · New York