Di-tert-butyl dicarbonate → propyl [(7R)-7-(methylamino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl]acetate

Participants

Reaction Steps

Propyl [(7R)-7-amino-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl]acetate (2.5 g) and TEA (1.4 mL) were dissolved in 87 mL MeOH. Boc2O (2.1 g) was added in 10 mL MeOH, and the mixture was stirred for 2 h. The solvent was removed and propyl {(7R)-7-[(tert-butoxycarbonyl)amino]-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl}acetate was purified on silica gel (ethyl acetate/hexanes). Propyl {(7R)-7-[(tert-butoxycarbonyl)amino]-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl}acetate (3.15 g) was dissolved in DMF (81 mL). The mixture was cooled in an ice bath and MeI (3.47 g) was added followed by NaH (342 mg, 60% w/w in mineral oil). The ice bath was removed after 0.5 h, and the mixture was stirred for 1 h at RT. The reaction was quenched with ½ (sat.) aqueous ammonium chloride. Work up consisted of extraction of the aqueous layer with ether (2×). The combined organic fractions were washed with water and brine, then dried (MgSO4). The solvent was evaporated under reduced pressure and propyl {(7R)-7-[(tert-butoxycarbonyl)(methyl)amino]-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl}acetate was purified on silica gel (ethyl acetate/hexanes). {(7R)-7-[(tert-butoxycarbonyl)-(methyl)amino]-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl}acetate and anisole (2.2 g) were dissolved in 66 mL DCM. 66 mL of TFA was added and the mixture was stirred for 1 h. The mixture was then stripped several times with toluene. Work up consisted of extraction with dichloromethane (3×) from aqueous sodium carbonate. The combined organic fractions were washed with brine and dried (MgSO4). The solvent was evaporated under reduced pressure and propyl [(7R)-7-(methylamino)-6,7,8,9-tetrahydropyrido[1,2-a]indol-10-yl]acetate was obtained after purification on silica gel. (MeOH/DCM).

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