(S)-4-(2-Methylbutoxy)Chelidamic acid dimethyl ester (8):

Chelidamic acid dimethyl ester (0.55g, 1.94 mmol, 1 equiv.), (S)-2-methylbutanol (0.48 g, 0.59 mL, 5.45 mmol, 2 equiv.) and triphenylphosphine (2.17 g, 8.26 mmol, 3.05 equiv.) were dissolved in THF (50 mL) and the solution was cooled to 0 °C. After being degassed with a nitrogen stream, DIAD (0.83 mL, 0.86 g, 4.25 mmol, 1.57 equiv.) was added in a dropwise manner. The reaction mixture was left under nitrogen and allowed to warm to rt before being stirred for 3 d, after which time the solvent was removed under reduced pressure and subjected to column chromatography (SiO2, petroleum ether/EtOAc, 6:4) to obtain the title compound as a white solid (0.59 g, 77%): mp 78-80 °C; 1H NMR (300 MHz, CDCl3) δ 7.72 (s, 2H), 4.04-3.89 (m, 8H), 1.98-1.88 (m, 1H), 1.62-1.53 (m, 1H), 1.33 (t, J = 7.3 Hz, 1H), 1.04 (d, J = 6.7 Hz, 3H), 0.96 (t, J = 7.5 Hz, 3H); 13C NMR (400MHz, CDCl3, 298K) δ 166.4, 164.1, 148.6, 113.4, 72.7, 52.0, 33.2, 24.8, 15.2, 10.0; HRMS (ESI) m/z calculated for C14H19NO5+ [M + H+] 282.1342, found 282.1350.