N-tert-butoxycarbonyl-3-methoxy-2-methylaniline → 1-[2-(Tert-butoxycarbonylamino)-6-methoxyphenyl]-2-butanone

Participants

Reaction Conditions

Reaction Steps

A solution of 140 mL (0.18 mol) of 1.3 M sec-butyl lithium in cyclohexane is added slowly to N-tert-butoxycarbonyl-3-methoxy-2-methylaniline (21.3 g, 0.09 mol) in 250 mL of THF keeping the temperature below −40° C. with a dry ice-ethanol bath. The bath is removed and the temperature allowed to rise to 0° C. and then the bath replaced. After the temperature is cooled to −60° C., 18.5 g (0.18 mol) of N-methoxy-N-methylpropanamide in an equal volume of THF is added dropwise. The reaction mixture is stirred 5 minutes, the cooling bath removed and stirred an additional 18 hours. It is then poured into a mixture of 300 mL of ether and 400 mL of 0.5N HCl. The organic layer is separated, washed with water, brine, dried over MgSO4, and concentrated at reduced pressure to give 25.5 g of a crude of 1-[2-(tert-butoxycarbonylamino)-6-methoxyphenyl]-2-butanone. This material is dissolved in 250 mL of methylene chloride and 50 mL of trifluoroacetic acid and stirred for a total of 17 hours. The mixture is concentrated at reduced pressure and ethyl acetate and water added to the remaining oil. The ethyl acetate is separated, washed with brine, dried (MgSO4) and concentrated. The residue is chromatographed three times on silica eluting with 20% EtOAc/hexane to give 13.9 g of 2-ethyl-4-methoxy-1H-indole.

Provenance & Evidence