CN(C)CCN(C)C.[Li]CCCC.[CH3:14][C:15]1[CH:20]=[CH:19][C:18]([SH:21])=[CH:17][CH:16]=1.CN([CH:25]=[O:26])C.Cl>C1CCCCC1>[CH3:14][C:15]1[CH:16]=[CH:17][C:18]([SH:21])=[C:19]([CH:20]=1)[CH:25]=[O:26]Tetramethylethylenediamine (TMEDA)(12.6 mL, 83.5 mmol) was added via syringe to n-BuLi (33 mL of 1.6 M in hexanes, 82.5 mmol) and the solution was chilled to 0° C. A solution of p-thiocresol (4.53 g, 36.5 mmol) in cyclohexane (40 mL) was added with stirring over 5 minutes. The resulting tan slurry was stirred overnight at room temperature, chilled to 0° C., and DMF (4.0 mL, 3.77 g, 51.6 mmol) was added via syringe over 2 minutes. The resulting gummy slurry was stirred at room temperature for 1.3 hours. The reaction mixture was added to 3 N HCl (150 mL). This mixture was extracted with ethyl acetate. The combined organic layers were washed with brine, dried over MgSO4, filtered and concentrated in vacuo yielding a brown oil. This oil was purified by flash chromatography over silica gel, eluting with 10% ethyl acetate-hexanes to afford 5-methyl-2-mercaptobenzaldehyde (4.47 g, 69%) as an intensely yellow solid suitable for use without further purification.
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