Reaction Steps
To a suspension of 33 (3.35 g, 6.75 mmol, 1 equiv), triethylamine (4.71 mL, 33.8 mmol, 5.0 equiv), and crushed, activated 3 Å molecular sieves (~15 g) in toluene (50 mL) was added diphenylphosphoryl azide (2.90 mL, 13.5 mmol, 2.0 equiv), and the resulting suspension was heated at 70° C. for 2 h. Benzyl alcohol (1.40 mL, 13.5 mmol, 2.0 equiv) then was added to the reaction mixture, and the suspension was stirred at 70° C. for 1 h. The reaction was filtered, washing well with ethyl acetate (100 mL), and the filtrate was concentrated. The residue was purified by flash column chromatography (10% ethyl acetate in hexane) to afford 34 as a pale yellow oil (3.62 g, 89%). Rf 0.53 (25% ethyl acetate in hexane); 1H NMR (500 MHz, CDCl3) d 7.34 (m, 5H, Cbz ArH), 7.18 (s, 1H, ArCH), 6.77 (s, 2H, ArH), 6.14 (s (br), 1H, NH), 5.13 (s, 2H, Cbz CH2), 3.81 (s (br), 3H, OCH3), 3.75 (s, 3H, OCH3), 1.00 (s, 18H, t-butyl), 0.16 (s, 12H, SiCH3), Z configuration verified by 11.6% NOE of ArH's upon irradiation of NH; 13C NMR (100 MHz, CDCl3) d 165.8, 149.8, 144.4, 135.8, 132.5, 130.0, 128.5, 128.4, 128.2, 126.1, 123.4, 120.2, 116.4, 67.6, 60.0, 52.5, 25.7, 18.3, -4.7; IR (neat film) 3500 (w, br), 2951 (m), 1723 (s), 1567 (m), 1493 (s), 1424 (m), 1289 (s), 1259 (s), 1122 (s), 1006 (w), 829 (s) cm-1 ; HRMS (FAB+) m/z: Calcd for C31H48NO7 Si2 (MH+) 602.2969, found 602.2993.
