Reaction Steps
(8R)-6-(tert-Butoxycarbonyl)-8-(tert-butyldimethylsilyloxy)-3-(2′-cyanoethyl)-3,6,7,8-tetrahydroimidazo[4,5-d][1,3]diazepine 10 (0.76 g, 1.81 mmol) was dissolved in dry THF (15 mL) and potassium tert-butoxide (1.0 M in THF, 3.6 mL) was added at RT. The mixture turned brown immediately and was quenched by addition of glacial acetic acid (206 μL, 3.6 mmol) and coevaporated with toluene (30 mL). The residue was suspended in chloroform/ethyl acetate (5 mL, 1:2 v/v) by ultrasonification and applied on a chromatography column (50 g silica, chloroform/ethyl acetate=1:2 v/v, then ethyl acetate), which gave (8R)-6-(tert-butoxycarbonyl)-8-(tert-butyldimethylsilyloxy)-3,6,7,8-tetrahydro-imidazo[4,5-d][1,3]diazepine 11 as an amorph yellow solid (0.51 g, 1.39 mmol, 77%). 11 was dissolved in dry acetonitrile (10 mL) and evaporated in vacuo, flushed with Argon and redissolved again in dry acetonitrile (15 mL). Addition of sodium hydride (60% in mineral oil, 72 mg) gave a visible gas formation. After 30 min 2-deoxy-3,5-di-O-(p-toluoyl)-D-erythro-pentofuranosyl chloride 9 (made according to Chem. Ber. 1960, 93, 2777-2781) (0.70 g, 1.81 mmol) was added to the reaction mixture, a thick heterogeneous slurry was formed. After further 40 min the reaction mixture was filtered through flux calcined diatomaceous earth and rinsed thoroughly with ethyl acetate. The filtrate was evaporated to dryness in vacuo. Purification of the residue by chromatography (60 g silica, petroleum ether/ethyl acetate=2:1 v/v) gave 12 as yellowish oil (0.85 g, 1.18 mmol, 85% calcd. from 11). Rf=0.31 (petrol ether/EtOAc=3:2 v/v), [α]D20=−17.4 (c 11.8, chloroform), 1H-NMR: (CDCl3) δ 0.05 (s, 3H, SiMe), 0.19 (s, 3H, SiMe), 0.88 (s, 9H, SitBu), 1.54 (s, 9H, OtBu), 2.40 (s, 3H, ArMe), 2.43 (s, 3H, ArMe), 2.70 (ddd, J=2.2, 5.9, 14.2 Hz, 1H, H-2′), 2.84 (ddd, J=6.4, 8.4, 14.2 Hz, 1H, H-2′), 3.08 (br d, J=13.6 Hz, 1H, H-7), 4.50 (dd, J=4.4, 13.6 Hz, 1H, H-7), 4.55-4.60 (m, 1H, H-4′), 4.61-4.65 (m, 2H, H-5′), 5.13 (br d, J=4.4 Hz, H-8), 5.70 (ddd, J=2.2, 2.3, 6.0 Hz, 1H, H-3′), 6.42 (dd, J=5.9, 8.4 Hz, 1H, H-1′), 7.19-7.30 (m, 4H, Ar), 7.57 (s, 1H, H-2), 7.85-7.99 (m, 5H, 4×Ar and H-5), 13C-NMR: (CDCl3) δ −4.6 (SiMe), −4.2 (SiMe), 18.6 (SiC(CH3)3), 22.0 (ArCH3), 26.2 (SiC(CH3)3), 28.5 (OC(CH3)3), 38.9 (C-2′), 47.2 (C-7), 64.6 (C-5′), 67.6 (C-8), 75.6 (C-3′), 82.7 (C-4′), 83.7 (OC(CH3)3), 84.4 (C-1′), 127.0, 127.2, 129.6, 130.1, 130.2, 132.3 (C-2), 133.1, 134.8, 142.7 (C-5), 144.4, 144.7, 152.8, 166.3, 166.6, HRMS: (MH+) calcd. for C38H51N4O8Si+: 719.3476. found: 719.3492.
