[Synthesis]
Cyclohexene 1a (0.2 g, 1.26 mmol) was used as raw material and mixed with K2CO3 (0.34 g, 2.53 mmol) in DMF (7 mL) in a two-necked round bottom flask. The reaction mixture was continuously bubbled with air at 80 °C for 20 hours. Upon completion of the reaction, purification was carried out by fast column chromatography (silica gel, petroleum ether/ethyl acetate = 7:3) to afford 3-hydroxy-5-methylbenzaldehyde 2a as a brown solid (melting point 78-80 °C, 0.15 g, 89% yield). Thin layer chromatography (TLC) showed an Rf value of 0.5 (30% ethyl acetate/petroleum ether).1H NMR (200 MHz, CDCl3) data: δ 2.39 (s, 3H), 6.22 (brs, 1H), 6.91-7.00 (m, 1H), 7.15-7.20 (m, 1H), 7.21-7.25 (m, 1H). 9.89 (s, 1H).13C NMR (50MHz, CDCl3+CCl4+DMSO) data: δ20.7,112.3,121.6,122.2,137.2,139.5,157.6,191.8.GC-MS (EI) analysis showed the molecular ion peaks at m/z=136 (M+). |