Potassium Hydroxide → Diethyl (2-phenylpropan-2-yl)propanedioate

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Diethyl (α, α -dimethylbenzyl)malonate was prepared by the conjugate addition of phenyl magnesium bromide to diethyl isopropylidenemalonate as described by C. Holmberg [Liebigs Ann. Chem., 748 (1981)]. A solution of this diester (42.1 g, 0.15 mol) in ethanol (100 ml) was treated by dropwise addition with a solution of potassium hydroxide (8.48 g, 0.13 mol) in 100 ml of ethanol. After heating at 90° C. for 1 h and at 50° C. for 20 h, the reaction mixture was evaporated on the rotary evaporator to a residue. The residue was diluted with water and extracted with ether to remove unreacted starting material. The aqueous phase was cooled to 5° C., acidified to pH 3 with 6N HCl, and extracted with methylene chloride. The organic layer was washed with brine solution and dried over magnesium sulfate. Evaporation of the solvent gave 27.3 g (84%) of liquid product. NMR (CDCl3): 1.05 (3H,t), 1.6 (6H,s), 3.78 (1H,s), 3.96 (2H,m), 7.2-7.4 (5H,m).

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