[O:1]([C:8]1[CH:12]=[CH:11][S:10][CH:9]=1)[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.C([Li])CCC.[CH3:18][Si:19](Cl)([CH3:21])[CH3:20].CN([CH:26]=[O:27])C>CCOCC.O>[O:1]([C:8]1[CH:12]=[C:11]([CH:26]=[O:27])[S:10][C:9]=1[Si:19]([CH3:21])([CH3:20])[CH3:18])[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=1
To a 0° C. solution of 3-phenoxythiophene (9.5 g, 53.9 mMol) in ether (200 mL) was added n-butyllithium (24 mL, 60 mMol, 2.5M in hexanes). The reaction was stirred for 15 min and trimethylsilyl chloride (6.45 g, 59.4 mMol) was added via syringe. The reaction was stirred 15 min and additional n-butyllithium (24 mL, 60 mMol, 2.5M in hexanes) was added and the reaction stirred 15 min. To the cold reaction mixture is added DMF (14 mL) and the reaction allowed to warm to room temperature over night. Water (5 mL) was added cautiously while stirring. The reaction mixture was diluted with ether and washed with water. The aqueous layer was washed with ether and the organic layer combined, washed with brine, dried (MgSO4), and concentrated. Purification by flash chromatography (SiO2, eluted with 5% ether/hexanes) afforded 4-phenoxy-5-trimethylsilylthiophene-2-carboxaldehyde (12.1 g, 83%) as a slightly yellow oil.
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