Sulfuric Acid → 1,1,3,3-Tetramethyl-2,3-dihydro-1H-indene

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Reaction Steps

Methyl magnesium bromide (3M solution in diethyl ether, 22.2 mL, 66.6 mmol) was added slowly to a solution of 4-methyl-4-phenyl-pentan-2-one (Compound 40, 7.8 g, 44.3 mmol) in 50 mL of tetrahydrofuran (THF) at 0° C. After stirring and warming to room temperature for 2 h, the mixture was quenched with water at 0° C., extracted with ethyl acetate (3×10 mL), washed with brine (1×10 mL), dried (MgSO4) and concentrated at reduced pressure to give a light yellow oil. The crude oil was then added slowly to 80% concentrated sulfuric acid at 0° C. and the resulting brown mixture was stirred at 0° C. for 1 h. The mixture was then slowly diluted with ice water, extracted with pentane (3×15 mL) and washed with brine (1×15 mL). After the extract was dried (MgSO4) and concentrated at reduced pressure, high-vacuum distillation of the residue afforded indan the title compound (3.3 g, 43% yield) as a colorless oil:

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