A mixture of zinc dust (6.0 g, 91.7 mmol), 2,2-dimethyl-3,4-dihydro-2H-benzo[h]chromene-5,6-dione (6.0 g, 24.8 mmol), Na2S2O4 (17.26 g, 99.1 mmol), N-(tert-butoxycarbonyl)glycine (8.77 g, 49.6 mmol), triethylamine (3.1 mL, 22.3 mmol), HBTU (18.79 g, 49.6 mmol) and DMF (100 mL) is stirred for 16 hours at room temperature. To the reaction mixture is then added EtOAc (300 mL). The reaction is filtered and the filtrate washed with H2O (4×200 mL). The organic extract is dried with Na2SO4 and concentrated under reduced pressure. The residue is dissolved in acetic anhydride (30 mL) followed by the addition of zinc dust (3.0 g, 45.9 mmol) and thriethylamine (3.35 mL, 24.0 mmol). The reaction is heated at 90° C. with vigorous stirring and held for 2 hours. The reaction is allowed to cool and the solvent removed under reduced pressure. The residue is dissolved in EtOAc (200 mL) and washed with water (2×100 mL). The organic extract is dried with Na2SO4 and concentrated under reduced pressure. The crude product is purified by flash column chromatography (SiO2, 2% EtOAc in dichloromethane) to afford about 60% pure final product. Crystallization of the partly pure solid from EtOAc/Hexane gives the desired product as pure white solid (3.2 g, 31%). M.p.=177° C.; 400 MHz 1H NMR (CDCl3) δ: 8.21 (d, J=8.4 Hz, 1H), 7.67 (d, J=8.4 Hz, 1H), 7.46 (m, 2H), 5.13 (br. s, 1H), 4.30 (d, J=5.6 Hz, 2H), 2.68 (t, J=6.6 Hz, 2H), 2.38 (s, 3H), 1.87 (t, J=6.6 Hz, 2H), 1.48 (s, 9H), 1.42 (s, 6H); LCMS: 444 [M+H]; Calc. for C24H29NO7: C, 64.94; H, 6.59; N, 3.16; Found C 64.98, H 6.51, N 3.15.
