Upon cooling by a dry ice-acetone bath, a solution of 6-bromo-1-ethyl-indan 41b (2.52 g, 11.2 mmol) in 15 mL of tetrahydrofuran was added dropwise to a solution of t-butyllithium in cyclohexane (18.1 mL, 1.3 N) under argon atmosphere. Upon completion of the addition, the mixture was stirred for 2 hours in the dry ice-acetone bath. A solution of di-tert-butyl azodicarboxylate in 15 mL of tetrahydrofuran was added dropwise to the above mixture at the same temperature. Upon completion of the addition, the reaction mixture was stirred for another 1.5 hours in the dry ice-acetone bath. Then the dry ice-ethanol bath was removed. The mixture was warmed up to room temperature and stirred for 18 hours. The reaction was monitored by TLC until the disappearance of the starting materials and quenched by addition of 25 mL of saturated ammonium chloride. The mixture was extracted with ethyl acetate (30 mL×3). The combined organic extracts were dried over anhydrous sodium sulfate, filtered to remove the drying agent and concentrated under reduced pressure. The residue was purified by silica gel column chromatography to obtain the title compound di-tert-butyl 1-(3-ethyl-2,3-dihydro-1H-inden-5-yl)hydrazine-1,2-dicarboxylate 41c (3.43 g, 81.5%) as a brown oil.
