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saturated NH4Cl water solution as an additive. The
organic phase was washed with water, saturated
NaHCO3 solution, and brine. After drying
(MgSO4), the ®ltrate was concentrated under reduced
pressure, and the residue was puri®ed by silica gel
column chromatography (hexane±acetone, 95:5) to
give 5 in 77% yield. 1H NMR (CDCl3) 5a d: 1Á89±
2Á10 (6H, s, CH3), 3Á56 (2H, bs, H-5a, H-5b), 4Á52
(2H, s, CH2), 4Á78 (1H, bs, H-4), 5Á18 (1H, s, CH),
5Á22 (1H, s, CH), 5Á59 (1H, d, H-2), 6Á45 (1H, d,
J 4Á47, H-1), 7Á26 (5H, bs, Harom); 5b d: 1Á89±2Á10
(6H, s, CH3), 3Á56 (2H, bs, H-5a, H-5b), 4Á55 (2H, s,
CH2), 4Á88 (1H, bs, H-4), 5Á35 (1H, s, CH), 5Á43 (1H,
s, CH), 5Á56 (1H, d, H-2), 6Á15 (1H, s, H-1), 7Á26 (5H,
bs, Harom); 13C NMR (CDCl3) 5a d: 21Á00±20Á43
(2C, CH3), 72Á05 (1C, C-5), 72Á98 (1C, CH2), 73Á28
(1C, C-2), 79Á31 (1C, C-4), 93Á86 (1C, C-1), 109Á06
(1C, CH2), 127Á55, 127Á60, 128Á31 (5C, Carom),
137Á85 (1C, Cipso), 142Á08 (1C, C-3), 169Á17 (1C,
CO); 5b d: 21Á00±20Á43 (2C, CH3), 72Á55 (1C, C-5),
73Á29 (1C, CH2), 77Á74 (1C, C-2), 80Á68 (1C, C-4),
98Á95 (1C, C-1), 115Á45 (1C, CH2), 127Á55, 127Á60,
128Á31(5C, Carom), 137Á85(1C, Cipso), 142Á08(1C, C-
3), 169Á17 (1C, CO). Calculated for C17H20O6: C,
63Á74; H, 6Á29. Found: C, 63Á73; H, 6Á31.
Figure 1. 1-(5-O-Benzyl-3-C-methylidene-2-oxo-3-deoxy-b-
D-glycero-pentofuranosyl) thymine (8) as precursor of 20,30-di-
C-nucleoside 9 and 20-C-30-C-methylidene 10.
(CDCl3) d: 1Á42 (3H, s, CH3), 1Á46 (3H, s, CH3),
3Á53 (1H, dd, J 10Á35 and 3Á69, H-5a), 3Á65 (1H,
dd, J 4Á95, H-5b), 4Á42 (1H, d, H-2), 4Á56 (2H, s,
CH2), 4Á57 (1H, bs, H-4), 6Á16 (1H, d, J 4Á43, H-
1), 7Á26 (5H, bs, Harom); 13C NMR (CDCl3) d:
27Á10 (1C, CH3), 27Á32 (1C, CH3), 70Á02 (1C, C-
5), 73Á03 (1C, CH2), 76Á73 (1C, C-4), 79Á83 (1C, C-
2), 103Á50 (1C, C-1), 114Á05 (1C, Ciso), 127Á44,
127Á78, 128Á40 (5C, Carom), 137Á30 (1C, Cipso),
209Á86 (1C, C-3). Calculated for C15H18O5: C,
64Á74; H, 6Á52. Found: C, 64Á71; H, 6Á53.
5-O-Benzyl-1,2-O-isopropylidene-3-C-methyli-
dene-3-deoxy-a-D-xylofuranose (4). Lithium n-
butyl (1Á6 M in hexane, 13Á5 mL, 21Á56 mmol) was
added dropwise to a solution of methyltriphenyl-
phosphonium bromide (7Á7 g, 21Á56 mmol) in dry
THF (20 mL) under N2. After the solution became
red, compound 3 (3Á3 g, 10Á78 mmol) in dry THF
(20 mL) was added at 0ꢀC. The mixture was stirred
for 1 h at room temperature then poured into water
(10 mL) and extracted twice with diethyl ether. The
extract was worked up and the crude product was
puri®ed by silica gel column chromatography
(hexane±acetone, 97:3) to give 4 in 50% yield.
1H NMR (CDCl3) d: 1Á35 (3H, s, CH3), 1Á48 (3H, s,
CH3), 3Á53 (1H, dd, J 10Á35 and 3Á69, H-5a),
3Á65 (1H, dd, J 4Á95, H-5b), 4Á86 (1H, d, H-4),
4Á56 (2H, s, CH2), 4Á88 (1H, d, H-2), 5Á16 (1H, s,
CH), 5Á39 (1H, s, CH), 5Á85 (1H, d, J 3Á95, H-1),
7Á26 (5H, bs, Harom); 13C NMR (CDCl3) d: 27Á12
(1C, CH3), 27Á38 (1C, CH3), 71Á55 (1C, C-5), 73Á41
(1C, CH2), 78Á58 (1C, C-4), 81Á76 (1C, C-2), 104Á57
(1C, C-1), 111Á73 (1C, CH2), 112Á37 (1C, Ciso),
127Á51, 127Á59, 128Á31 (5C, Carom), 137Á90 (1C,
Cipso), 146Á70 (1C, C-3). Calculated for C16H20O4:
C, 69Á55; H, 7Á30. Found: C, 69Á58; H, 7Á31.
1-(2-O-Acetyl-5-O-benzyl-3-C-methylidene-3-
deoxy-b-D-glycero-pentofuranosyl) thymine (6). A
suspension of thymine (236 mg, 1Á87 mmol) and a
small crystal of ammonium sulphate in a mixture of
1,1,1,3,3,3-hexamethyldisilazane (4 mL) and tri-
methylchlorosilane (0Á5 mL) was re¯uxed until a
clear solution was obtained. Volatile matter was
evaporated and the residue was repeatedly coeva-
porated with toluene. In the resulting syrup com-
pound 5 (500 mg, 1Á56 mmol) in dry CH3CN
(10 mL) was dissolved under N2 and the mixture
was cooled to 15ꢀC. tert-Butyldimethylsilyl-tri-
¯uoromethanesulphonate (430 mL, 1Á87 mmol) was
added and the mixture left to warm slowly. After
2 h, the reaction was quenched by the addition of
saturated aqueous NaHCO3, stirred for 30 min and
extracted with CH2Cl2. The organic phase was
dried with MgSO4 and evaporated. The crude
product was puri®ed over silica gel column chro-
matography (hexane±ethyl acetate, 1:1) to give 6
1
in 55% yield. H NMR (CDCl3) d: 1Á59 (3H, s,
CH3), 2Á10 (3H, s, CH3), 3Á60 (1H, dd, J 10Á10
and 2Á27 H-5a), 3Á85 (1H, bd, H-5b), 4Á56 (1H, s,
CH2), 4Á76 (1H, d, H-4), 5Á21 (1H, s, CH), 5Á33
(1H, s, CH), 5Á83 (1H, d, H-2), 6Á05 (1H, d,
J 5Á64, H-1), 7Á29 (5H, bs, Harom), 7Á49 (1H, d,
H-6), 8Á37 (1H, s, NH); 13C NMR (CDCl3) d: 12Á13
(1C, CH3), 20Á74 (1C, CH3), 71Á79 (1C, C-5), 73Á65
(1C, CH2), 75Á81 (1C, C-4), 80Á07 (1C, C-1), 86Á44
(1C, C-2), 111Á28 (1C, CH2), 111Á54 (1C, C-5),
1,2-Di-O-acetyl-5-O-benzyl-3-C-methylidene-3-
deoxy-D-xylofuranose (5). A mixture of 4 (1Á45 g,
5Á07 mmol), anhydride acetic acid (5 mL), and
concentrated H2SO4 (43 mL) in acetic acid
(46 mL) was stirred for 2Á5 h at room temperature.
The mixture was poured into ice-cooled water, stirred
for 30 min, and extracted twice with CHCl3, using