Reaction SMILES: [CH2:1]1[O:5][C:4]2[CH:6]=[C:7]([OH:10])[CH:8]=[CH:9][C:3]=2[O:2]1.C([Mg]Cl)(C)C.[NH:16]1[C:26]2[C:21](=[CH:22][CH:23]=[CH:24][CH:25]=2)[C:19](=[O:20])[C:17]1=[O:18].[Cl-].[NH4+]>O.O1CCCC1>[OH:20][C:19]1([C:8]2[C:7]([OH:10])=[CH:6][C:4]3[O:5][CH2:1][O:2][C:3]=3[CH:9]=2)[C:21]2[C:26](=[CH:25][CH:24]=[CH:23][CH:22]=2)[NH:16][C:17]1=[O:18]
Reactant: Oc1ccc2c(c1)OCO2
Reactant: O=C1Nc2ccccc2C1=O
Agent: CC(C)[Mg]Cl
Agent: [Cl-]
Agent: [NH4+]
Solvent: C1CCOC1
Solvent: O
Product: O=C1Nc2ccccc2C1(O)c1cc2c(cc1O)OCO2
Temperature: 2 °C
Reaction time: 2.75 h
Yield: 103.1 %

Procedure:
A 630 L reactor was charged with sesamol (42.6 kg, 299 mol). Tetrahydrofuran (400 kg) was added and the resultant solution was cooled to 1° C. over 42 minutes. Isopropylmagnesium chloride (2 M solution in tetrahydrofuran, 173 kg, 337 mol) was added over 2 h such that the internal temperature was kept between 0 and 4° C. Once the addition was complete, the internal temperature was lowered to −5° C. and isatin (37.9 kg, 250 mol) was added in four portions. The reaction mixture was stirred for 2.75 h at 1 to 3° C. A 1000 L reactor was charged with ammonium chloride (72 kg), followed by deionized water (356 kg). The mixture was stirred at 15° C. until the solid had completely dissolved and the resultant solution was cooled to 1° C. over 1 h. The contents of the 630 L reactor were transferred to the 1000 L reactor over 1 h such that the internal temperature remained between 3 and 4° C. The 630 L reactor was rinsed with toluene (133 kg) and the rinse solution added to the 1000 L reactor. The contents of the 1000 L reactor were allowed to warm to 20-25° C. over 29 minutes and were stirred for a further 15 minutes. The stirring was stopped and the contents of the reactor held at 25° C. for 15 minutes, allowing the phases to separate. The aqueous phase was removed and a solution of sodium chloride (42 kg) in deionized water (218 kg) was added over 25 minutes at an internal temperature of 22-24° C. The stirring was stopped and the mixture held at 25° C. for 1 h, allowing the phases to separate. The organic phase was degassed for 0.5 h with nitrogen and toluene (89 kg) was added. A 300 mbar vacuum was applied to the reactor and the reactors external temperature was set to 50-60° C. Volatile components of the mixture were removed by distillation over a period of 12 h such that 670 L of distillate were collected. The reactors external temperature was set to 20-25° C. An orange precipitate was deposited upon cooling. Toluene (114 kg) was added and the suspension stirred for 10 minutes. The solid was collected by filtration, washed with tert-butyl methyl ether (171 kg) and heptane (85 kg) and dried at 55-60° C. under a reduced pressure of 170 to 4 mbar over a period of 10.5 h to afford 3-hydroxy-3-(6-hydroxy-1,3-benzodioxol-5-yl)-1,3-dihydro-2H-indol-2-one (73.5 kg, quantitative yield) as a pale pink solid: purity (HPLC-UV at 300 nm) 99.3% a/a; 1H NMR (300 MHz, DMSO-d6) δ 10.18 (s, 1H), 9.08 (s, 1H), 7.21-7.07 (m, 2H), 6.88-6.74 (m, 3H), 6.38 (br s, 1H), 6.23 (s, 1H), 5.92 (s, 2H); 13C NMR (75 MHz, DMSO-d6) δ 178.4, 148.4, 146.6, 143.0, 139.4, 133.2, 128.6, 123.8, 121.1, 120.1, 109.0, 106.8, 100.8, 97.4, 75.1.