General procedure for the synthesis of 4-methyl-2-nitrobenzaldehyde from (4-methyl-2-nitrophenyl)methanol: (4-methyl-2-nitrophenyl)methanol (1.028 g, 6.15 mmol), pyridinium dichromate (3.47 g, 9.22 mmol), and molecular sieves (7 g, 6.15 mmol) were dissolved in anhydrous dichloromethane (14 mL) under argon protection and stirred at room temperature overnight. The reaction mixture was filtered through a silica/diatomaceous earth (1:1) column and subsequently extracted with water and dichloromethane. The organic layers were combined and the solvents were evaporated to give a light yellow solid product (0.665 g, 65.5% yield), which could be used in subsequent reactions without further purification. The product was characterized by 1H-NMR (CDCl3): δ 2.54 (s, 3H), 7.57-7.60 (m, 1H), 7.86-7.90 (m, 2H), 10.49 (s, 1H). the LC/MS analysis showed a retention time of 3.01 min (100% purity, no ionization peaks observed).
