The general procedure for the synthesis of 4,7-dimethyl-1H-indene from cyclopentadiene and 2,5-hexanedione was as follows: sodium filaments (426 mmol, 9.8 g) were pressed into a three-necked flask under argon protection, and about 100 mL of dry methanol was added slowly until the sodium filaments were completely dissolved. Subsequently, freshly distilled cyclopentadiene (260 mmol, 21.2 mL) and 2,5-hexanedione (170 mmol, 26.5 mL) were added, and the reaction mixture was stirred for 24 h, during which time bubbles were observed. Upon completion of the reaction, 50 mL of water was added to quench the reaction. After removal of the methanol solvent by steam distillation, the pH of the reaction solution was adjusted to neutral with dilute hydrochloric acid. The aqueous phase was extracted three times with 200 mL of petroleum ether, and the organic phases were combined, dried over anhydrous magnesium sulfate and filtered. The solvent was removed by rotary evaporation to give a dark brown liquid. The liquid was distilled under reduced pressure and the 76-80 °C fraction was collected at a pressure of 4 mmHg to give a final 21.5 g of yellow oily liquid product.
