Ethylenediamine → Benzyl 4-(t-butyldimethylsilyloxy)indole-1-carboxylate

Participants

Reaction Steps

A stirred, ice-cold mixture of 9 (18.56 g, 75 mmol), tetrabutylammonium bromide (2.42 g, 7.5 mmol) and powdered sodium hydroxide (4.0 g, 75 mmol) in dichloromethane (375 mL) was treated dropwise with benzyl chloroformate (95% purity; 20.20 g, 112.5 mmol). The reaction mixture was stirred at room temperature and the progress of the reaction was followed by TLC [ethyl acetate-hexanes (1:9)]. Further aliquots of benzyl chloroformate (each 20.20 g) were added after 1 h and 2 h, and the mixture was stirred at room temperature for a total of 18 h, diluted with water and extracted with dichloromethane. The combined organic phases were washed with brine, dried and evaporated. The residual oil was dissolved in dry diethyl ether (250 mL), cooled in ice and treated dropwise with a solution of ethylenediamine (47 mL, 355 mmol) in dry diethyl ether (150 mL) and stirred at room temperature for 0.5 h. The mixture was washed with 0.5 M aq. hydrochloric acid and brine and the organic phase was dried and evaporated. After trituration with diethyl ether and cooling in ice, some precipitated N,N-di-(benzyloxycarbonyl)ethylenediamine was removed by filtration and 10 was isolated as a pale oil (28.62 g, 100%) which was used in the next step without further purification; 1H NMR (90 MHz) δ 7.78 (d, J=7.2 Hz, 1H), 7.00-7.56 (m, 7H), 6.58-6.72 (m, 2H), 5.42 (s, 2H), 1.03 (s, 9H), 0.22 (s, 6H).

Provenance & Evidence