A mixture of 48 mL (0.4 mol) of o-xylene with 50 g of 3-chloropropionyl chloride was slowly added dropwise to a suspension containing 116 g (0.87 mol) of aluminum chloride and 200 mL of nitromethane under ice bath conditions. After the dropwise addition, the reaction system was slowly warmed to room temperature and stirring was continued for 5 hours. Subsequently, the reaction mixture was poured into a pre-cooled mixture of 1 N hydrochloric acid and ice water and stirred thoroughly. The organic phase was separated and washed sequentially with 1N hydrochloric acid, water and saturated brine and finally dried with anhydrous magnesium sulfate. The solvent was removed by distillation under reduced pressure to give the intermediate solid. The solid was added to 300 mL of concentrated sulfuric acid in batches and heated and stirred in an oil bath at 100 °C for 4 h. About 40% of the cyclic isomer by-product was generated in this process. Upon completion of the reaction, the reaction solution was quenched by pouring it into ice water and extracted with diethyl ether. The organic phase was washed sequentially with water and saturated saline, and then dried with anhydrous magnesium sulfate. After evaporating the solvent under reduced pressure, the resulting solid was purified by recrystallization from hot hexane to remove the cyclic isomer. Finally 25.5 g of 5,6-dimethyl-2,3-dihydro-1H-inden-1-one was obtained in 40% yield.
