A vigorously stiffed solution of L-Lys(Z)—OMe (3.31 g, 10 mmol) in acetic acid (20 mL) and dioxane (40 mL) was heated to 75° C., at this temperature 2,5-dimethoxytetrahydrofuran (DMTHF, ee 97%) (3.97 g, 3.90 mL, 30 mmol) was added dropwise to the reaction mixture. After complete addition of DMTHF, the reaction mixture was refluxed at 110° C. for 3 h followed by 5-6 h stiffing at room temperature. The volatiles were removed under reduced pressure to afford a dark brown residue, which was dissolved in dichloromethane (100 mL) and washed with 10% NaHCO3 solution (15 mL), brine (15 mL) and water (15 mL). The organic phase was dried over anhydrous Na2SO4 and evaporated under reduced pressure. The residue was purified by flash chromatography on silica gel (230-400 mesh) using hexane:ethyl acetate (7:3) as eluent to afford (S)-methyl 6-benzyloxycarbonylamino-2-carbazol-9-yl-hexanoate 3 (1.10 g, 25%) as a pale yellow solid.
