CHEM01200604012 Dibakar Goswami - Homi Bhabha National ...

pyridine (12 mL) was stirred overnight at room temperature. Ice-cold water was added to
the mixture, the mixture stirred for 1 h and extracted with CHCl 3 (40 mL). The organic
layer was washed with dilute HCl, water and brine, and dried. Removal of solvent and
chromatographic purification (silica gel, 5-20% EtOAc/Hexane) afforded pure 149. Yield
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0.291 g (91%); white solid; [α] D -2.3 (c 1.4, CHCl 3 ); 1 H NMR: δ 1.05 (s, 9H), 1.4-1.6
(m, 10H), 1.96 and 2.04 (2s, 3H), 2.1-2.3 (m, 2H, H-2), 2.6 (m, 1H, H-3), 3.6-3.8 (m,
2H), 3.9-4.1 (m, 4H), 6.24 (m, 1H, H-1), 7.40 (m, 6H), 7.65 (m, 4H). Anal. Calcd. For
C 31 H 42 O 6 Si : C, 69.11; H, 7.86. Found, C, 69. 29; H, 8.04.
5R,6-Cyclohexylidenedioxy-1-thymine-3-C-(tert)-butyldiphenylsilyloxy-2,3-dideoxy-
D-ribofuranose 150. To a well stirred suspension of 149 (0.250 g, 0.451 mmol) and
thymine (0.085 g, 0.678 mmol) uhder Ar in dry CH 3 CN (40 mL) at room temperature was
drop-wise added bis(trimethylsilylacetamide (0.189 g). This reaction mixture was stirred
for 3 h, cooled to -30 o C, and treated with trifluromethanesulphonate (1 mL). After stirring
for 7 days at room temperature, the mixture was diluted with CH 2 Cl 2 and water. The
organic layer was separated and aqueous layer washed with CHCl 3 . The organic extract
were washed with aqueous saturated NaHCO 3 , water and brine, and dried. Removal of
solvent in vacuo followed by preparative TLC (silica gel, 25% EtOAc/hexane) afforded
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150. Yield: 0.153 g (63%); [α] D -15.03 (c 1.4, CHCl 3 ); 1 H NMR: δ 1.05 (s, 9H), 1.4-1.7
(m, 10H, overlapped with a s at δ 1.7, 3H), 1.9-2.6 (m, 3H, H-2', H-3'), 3.6-4.0 (m, 3H),
4.1-4.3 (m, 2H), 4.45 (m, 1H, H-4), 6.38 (m, 1H, H-1), 7.3-7.5 (m, 6H), 7.6-7.7 (m, 4H,
overlapped with a m, 1H, H-6), 8.1 (broad s, 1H, NH); Anal. Calcd. For C 31 H 42 O 6 N 2 Si: C,
70.79; H, 7.68%. Found, C, 70. 55; H, 7.44%.
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