p-Toluenesulfonic acid → Isocoumarin

Participants

Reaction Steps

To a stirred solution of the isocaumarin from step 3 above (9.4 mg, 0.4 mmol) in 8 ml of toluene was added dropwise a solution of DIBAL-H (1M, 0.50 ml, 0.50 mmol) at -78° C. under argon. The resulting mixture was stirred at -78° C. for 1.5 hour before Na2SO4 10 H2O (100 mg, 0.31 mmol). After the reaction was warmed to room temperature, it was filtered to remove the solids, and washed with acetone. The filtrate was evaporated to give an oily residue which contained the corresponding lactol. Without further purification, the residue was treated with 5 ml of CH3OH, 1 ml of CH(OMe)3, and PTSA (30 mg, 0.16 mmol) at room temperature for 10 minutes. The solvents were removed by rotavapor and the residue was purified by flash chromatography with hexane and ethyl acetate (7:3) to give pure title isocoumarin (65 mg, 0.26 mmol) in 65% overall yield. 1H NMR (CDCl3) δ:2.47 (1H, dd, J=17.2, 12.0 Hz), 2.85 (1H, dd, J=17.2, 3.6 Hz), 3.56 (3H, s), 3.78 (3H, s), 3.82 (3H, s), 4.63 (1H, m), 5.24 (1H, dt, J=10.6, 1.4 Hz), 5.43 (1H, dt, J=17.3, 1.4 Hz), 5.63 (1H, s), 6.05 (1H, m), 6.70 (1H, d, J=8.9 Hz), 6.76 (1H, d, J=8.9 Hz).

Provenance & Evidence