Dimethyl Carbonate → Benzoic acid, 4-(allyloxy)-3,5-dimethyl-

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To a solution of 2-allyloxy-5-bromo-1,3-dimethyl-benzene (23.6 g, 98.0 mmol) in THF (150 mL) is added at −75° C. a solution of n-BuLi (90 mL, 1.5 M in diethyl ether). The temperature remains at −75° C. The mixture is stirred for 30 min and then transferred via double-tip canula into a cooled (0° C.) solution of dimethylcarbonate (21.4 g, 238 mmol) in THF (90 mL). The mixture is stirred for 2 h at 0° C., then warmed to rt during 15 h. The solvent of the mixture is evaporated and re-evaporated from EtOH (200 mL) to remove most of the butylacetate side product. The mixture is taken up in 2 N aq. LiOH (150 mL) and EtOH (200 mL) and stirred at rt for 2 h, then at 60° C. for 1 h. The EtOH is evaporated and the remaining mixture is diluted with 0.5 N aq. NaOH and extracted with diethyl ether (200 mL). The org. extract is washed with 1M aq. NaOH (5×50 mL) and the combined aq. washings are re-extracted with ether (100 mL). The aq. phase is acidified with 25% aq. HCl and extracted with DCM (5×50 mL). The combined org. extracts are dried over Na2SO4, filtered, evaporated and dried in vacuo at 60° C. for 15 h to give 4-allyloxy-3,5-dimethyl-benzoic acid (8.0) as yellow-brown solid. LC-MS: tR=0.90 min.

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