C([Li])CCC.[CH3:6][C:7]1[CH:8]=[CH:9][C:10]2[O:14][CH:13]=[CH:12][C:11]=2[CH:15]=1.[CH3:16][Sn:17](Cl)([CH3:19])[CH3:18]>C1COCC1>[CH3:16][Sn:17]([CH3:19])([CH3:18])[C:13]1[O:14][C:10]2[CH:9]=[CH:8][C:7]([CH3:6])=[CH:15][C:11]=2[CH:12]=1n-Butyl lithium (1.57M in hexane, 75 ml) was added dropwise to a stirred solution of 5-methylbenzofuran (14 g) in dry THF (150 ml) at -70° under nitrogen over 45 min. The solution was then allowed to warm to -55° before a solution of trimethyltin chloride (23 g) in THF (70 ml) was added dropwise. The solution temperature rose to -32°. The cooling bath was removed and the solution was stirred at room temperature for 2 h. The solution was diluted with ethyl acetate (250 ml) and washed with water (200 ml). The organic layer was dried and concentrated in vacuo to afford a yellow liquid (32 g). Kugelrohr distillation of this liquid gave the title compound (23.3 g) as a colourless liquid, b.p. 115° at 7 mbar.
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