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Typical procedure: To a solution of 1 (0.168 g, 1 mmol) and appropriate aryl halide (2.1 mmol) in dry DMF (15 mL) were introduced anhyd K2CO3 (0.600 g, ca. 2 mmol), n-Bu4NBr (0.644 g, 2 mmol) and Pd(OAc)2 (10 mg). The reaction mixture was stirred and heated at 80 °C for the time specified (Table
[1]
) under a N2 atmosphere. The reaction mixture was allowed to cool to r.t., poured into H2O, extracted with CH2Cl2 and the organic extract dried over anhyd Na2SO4. The crude material obtained on solvent removal was purified by flash column chromatography on silica gel (hexane-CHCl3- mixtures) to obtain the corresponding diaryl thienothiophenes. 4: Yield 70%; mp 300 °C (dec.); IR (KBr): 2922, 1588, 1512, 1417, 1340, 1106, 932, 850, 750, 737, 694, 524, 485 cm-1; 1H NMR (CDCl3, 300 MHz): δ = 2.60 (s, 6 H, CH3), 7.61 (d, J = 10.5 Hz, 4 H, ArH), 8.31 (d, J = 10.5 Hz, 4 H, ArH); Anal. Calcd for C20H14N2O4S2: C, 58.54; H, 3.41; N, 6.83; S, 15.61. Found: C, 58.34; H, 3.63; N, 6.85; S, 15.49. 10: Yield 65%; mp 293-295 °C; IR (KBr): 3423, 2921, 1722, 1604, 1523, 1433, 1403, 1279, 1180, 1104, 1017, 965, 932, 850, 766, 700 cm-1; 1H NMR (CDCl3, 300 MHz): δ = 2.57 (s, 6 H, -CH3), 2.95 (s, 6 H, -OCH3), 7.54 (d, J = 6 Hz, 4 H, ArH), 8.11 (d, J = 6 Hz, 4 H, ArH); Anal. Calcd for C24H20O4S2: C, 66.05; H, 4.60; S, 14.70. Found: C, 66.10; H, 4.52; S, 14.55. 12: Yield 71%; mp >320 °C; IR (KBr): 3070, 2921, 1655, 1510, 1485, 1432, 1360, 1301, 1269, 1088, 1035, 937, 897, 881, 790, 745, 672, 610, 592, 555, 463 cm-1; 1H NMR (CDCl3, 300 MHz): δ = 2.57 (s, 6 H, CH3), 2.67 (s, 6 H, -COCH3), 7.29 (d, J = 3 Hz, 2 H, thiophene H), 7.60 (d, J = 3 Hz, 2 H, thiophene H); Anal. Calcd for C20H16O2S4: C, 57.69; H, 3.90; S, 31.22. Found: C, 57.54; H, 3.85; S, 31.02. 14: Yield 61%; mp 265-268 °C; IR (KBr): 2958, 2837, 1606, 1570, 1525, 1492, 1461, 1439, 1297, 1275, 1248, 1177, 1110, 1041, 1028, 926, 810, 825, 649, 628, 542, 517 cm-1; 1H NMR (CDCl3, 300 MHz): δ = 2.20 (s, 6 H, -CH3), 3.80 (s, 6 H, -OCH3), 6.90 (d, J = 8.0 Hz, 4 H, ArH), 7.35 (d, J = 8.0 Hz, 4 H, ArH); Anal. Calcd for C22H20O2S2: C, 69.47; H, 5.26; S, 16.84. Found: C, 69.31; H, 5.20; S, 16.64. 18: Yield 47%; mp 308-311 °C; IR (KBr): 3086, 2916, 1440, 1418, 1382, 1216, 1158, 1117, 1045, 1034, 999, 961, 902, 863, 830, 809, 736, 725, 564 cm-1; 1H NMR (CDCl3, 300 MHz): δ = 2.35 (s, 6 H, -CH3), 2.50 (s, 6 H, -CH3), 6.85 (s, 2 H, thienothiophene H), 7.30 (s, 4 H, ArH); Anal. Calcd for C22H18S4: C, 64.40; H, 4.40; S, 31.22. Found: C, 64.28; H, 4.42; S, 31.02.
18 The in situ reduction of Pd2+ to Pd0 is conceivable via DMF and or tributylamine mediated processes. Tributylamine in turn could be generated via the Hoffmann elimination of the quarternary ammonium salt under the reaction conditions.
19 For a related mechanism proposed for Pd catalyzed arylations of 2-furfuraldehyde, see: McClure MS.
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