[OH:1][CH2:2][C:3]1[CH:4]=[CH:5][C:6]([CH3:13])=[C:7]([CH:12]=1)[C:8]([O:10][CH3:11])=[O:9].C(Cl)(=O)C(Cl)=O.CS(C)=O.CCN(CC)CC>C(Cl)Cl>[CH:2]([C:3]1[CH:4]=[CH:5][C:6]([CH3:13])=[C:7]([CH:12]=1)[C:8]([O:10][CH3:11])=[O:9])=[O:1]A solution of 377 mg of methyl 5-(hydroxymethyl)-2-methylbenzoate and 0.8 mL (9.17 mmol) of oxalyl chloride in 20 mL of CH2Cl2 was cooled to −78° C. To this solution was added 1.1 mL (15.5 mmol) of DMSO dropwise, and after stirring for 10 min., 3.2 mL of Et3N was added and stirring was continued at −78° C. for 10 min. The dry ice-acetone bath was removed, and the mixture was allowed to warm to r.t. and after 2 h, 30 mL of sat. NH4Cl solution was added. The organic layer was washed with 25 mL of brine, dried over Na2SO4, filtered, and concentrated. Purification by flash silica gel chromatography (10% EtOAc/hexanes) provided 268 mg of methyl 5-formyl-2-methylbenzoate as a red liquid in 71% yield with some impurity.
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