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A solution of dimethyl 4,5-dichlorophthalate A5 (98.86 g, 375.78 mmol) in tetrahydrofuran (150 mL) is added dropwise over 1 h to a mechanically stirred suspension of LAH (20.8 g, 548.1 mmol) in tetrahydrofuran (1.5 L). During the addition, the reaction is cooled in an ice-water bath. When the addition is completed, the reaction is stirred overnight at RT. The excess LAH is decomposed by cautious addition of water (20 mL), 10% aqueous NaOH (40 mL) and water (20 mL). The solids are removed by filtration through a celite pad and washed with tetrahydrofuran. The combined filtrate and wash is concentrated in vacuo on a rotary evaporator to afford crude 251 as white solid that is purified by crystallization from acetone (150 mL)-heptane (150 mL). The crystals are collected by filtration, washed with heptane and dried to give 4,5-dichloro-1,2-bis(hydroxymethyl)benzene (37.2 g). The combined filtrate and wash afforded a second crop of 251 (18.8 g, 24.1%). [L. A. Levy, Synth. Commun., 13, 639-648 (1983); O. Farooq, Synthesis, 1035-1036 (1994)]

1. additionDuring the addition
2. temperaturethe reaction is cooled in an ice-water bath
3. additionWhen the addition
4. customThe solids are removed by filtration through a celite pad
5. washwashed with tetrahydrofuran
6. washThe combined filtrate and wash
7. concentrationis concentrated in vacuo on a rotary evaporator