Helvetica Chimica Acta Vol. 85 (2002)
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MeCN (2Â). The residue was suspended in 500 ml of dry MeCN, and 1 g (5 mmol) of TSOH was added. The
mixture was refluxed for 1 h, cooled, filtered, and the solvent was removed under reduced pressure. The residue
(containing the presumed l-threonolactone [12]) was dissolved in 200 ml of pyridine, cooled to 08, and 50 g (358
mmol) of BzCl was added dropwise. The mixture was allowed to warm to r.t., stirred for 10 h, and diluted with
400 ml of CH2Cl2. The resulting mixture was washed sequentially with 3 Â 250 ml of ice-cold aq. 1m HCl soln.,
200 ml of H2O, 200 ml of sat. aq. NaHCO3 soln., and 200 ml of sat. aq. NaCl soln. The org. phase was dried
(MgSO4) and evaporated to dryness. The residue was crystallized from hexane/AcOEt 6 :1 to yield 52 g (60%)
of 3. Colorless needles. 1H-NMR (300 MHz, CDCl3): 4.37 (m, HÀC(4)); 5.02 (m, HÀC(4)); 5.80 (m, HÀC(2);
HÀC(3)); 7.43 8.12 (m, 10 arom. H).
2,3-Di-O-benzoyl-l-threofuranose (4). A soln. of 40 g (120 mmol) of 3 in 500 ml of THF was cooled to
À788. Under Ar, 150 ml of a 1.5m (225 mmol) of DIBAL-H soln. in toluene was added dropwise. The mixture
was stirred at À788, and, as soon as the starting material was completely consumed (TLC, 4 10 h), 20 ml of
MeOH was added over a period of 5 min to quench the reaction. The cooling bath was removed, the mixture
was diluted with AcOEt, 400 ml of a sat. aq. sodium potassium tartrate soln. was added, and the mixture was
stirred vigorously for 3 h. The org. phase was separated, washed with sat. aq. NaCl soln., and dried (MgSO4).
Evaporation of the solvent in vacuo, followed by CC (silica gel; hexane/AcOEt 2 :1), gave a colorless oil (21 g
(53%)) consisting of the two diastereoisomers 4a,b30).
Data of 4a,b: TLC (hexane/AcOEt 2 :1): Rf 0.38. 1H-NMR (600 MHz, CDCl3): 3.97 (dd, J 7.5, 3.1,
HÀC(4) of isomer b); 4.28 (dd, J 10.4, 4.1, HÀC(4) of isomer a); 4.60 (dd, J 10.4, 6.1, HÀC(4) of isomer a);
4.63 (dd, J 7.9, 4.4, HÀC(4) of isomer b); 5.48 (dd, J 4.3, 4.3, HÀC(2) of isomer b); 5.55 (m, HÀC(2),
HÀC(3) of isomer a); 5.61 (s, HÀC(1) of isomer a); 5.78 (ddd, J 4.3, 4.3, 3.3, HÀC(3) of isomer b); 5.89 (d,
J 4.4, HÀC(1) of isomer b); 7.43 7.46 (m, 8 arom. H); 7.56 7.57 (m, 4 arom. H); 8.05 8.28 (m, 8 arom. H).
13C-NMR (150 MHz, CDCl3): 69.2 (q, C(4) of isomer b); 71.7 (q, C(4) of isomer a); 76.6 (2d, C(3) of both
isomers); 77.9 (d, C(2) of isomer a); 81.7 (d, C(2) of isomer b); 95.3 (d, C(1) of isomer a); 100.8 (d, C(1) of
isomer b); 128.4 (d, arom. C); 129.7 (d, arom. C); 129.8 (2d, arom. C); 133.4 (d, arom. C); 133.5 (d, arom. C);
165.5, 165.8, 165.9, 166.1(4s). MALDI/TOF-MS (pos., DHB): 351 (100, [M Na] ).
1-O-Acetyl-2,3-di-O-benzoyl-l-threofuranose (5). To a soln. of 19.7 g (60 mmol) of 4 in 200 ml of CH2Cl2/
pyridine 1:1, 6.8 ml of (62 mmol) of Ac2O and 50 mg (0.4 mmol) of DMAP were added, and the mixture was
stirred at r.t. for 18 h. The mixture was then poured into a stirred, ice-cold mixture of sat. aq. NaHCO3/CH2Cl2
and stirred for 1 h. The org. layer was separated, washed sequentially with sat. aq. NaHCO3 soln., H2O, and sat.
aq. NaCl soln., dried (MgSO4), and filtered. The solvent was removed under reduced pressure, and the residue
was purified by CC (silica gel; hexane/AcOEt 2 :1) to afford 21 g (93%) of a mixture of the two diastereoisomers
5a,b as colorless oil.
1
Data of 5a,b: TLC (hexane/AcOEt 2 :1): Rf 0.32. H-NMR (600 MHz, CDCl3): 2.03 (s, MeCO); 2.16 (s,
MeCO); 4.06 (dd, J 10.5, 3.5, HÀC(4) of isomer b); 4.22 (dd, J 10.5, 3.7, HÀC(4) of isomer a); 4.62 (dd, J
10.5, 6.4, HÀC(4) of isomer b); 4.68 (dd, J 10.5, 6.1, HÀC(4) of isomer a); 5.58 (m, HÀC(3) of isomer b); 5.66
(s, HÀC(2) of isomer b); 5.71 (dd, J 4.7, 4.7, HÀC(2) of isomer a); 5.76 (ddd, J 6.3, 4.7, 3.7, HÀC(3) of
isomer a); 6.39 (s, HÀC(1) of isomer b); 6.66 (d, J 4.6, HÀC(1) of isomer a); 7.23 7.50 (m, 4 H, arom. H);
7.59 7.62 (m, 2 H, arom. H); 8.05 8.11 (m, 4 H, arom. H). 13C-NMR (150 MHz, CDCl3): 20.8 21.0 (2q,
MeCO); 70.8 (s, C(4) of isomer b); 73.2 (s, C(4) of isomer a); 75.9 (2t, C(3) of both isomers); 76.6 (t, C(2) of
isomer a); 80.3 (t, C(2) of isomer b); 94.1 (t, C(1) of isomer b); 99.2 (t, C(1) of isomer a); 128.4 (d); 128.5 (d);
129.7 (d); 129.7 (d); 129.8 (d); 133.5 (d); 133.7 (d), 166.1, 165.0, 165.5, 165.3, 169.3 (2s, MeCO). MALDI/TOF-
MS (pos., DHB): 393 (100, [M Na] ).
1,2,3-Tri-O-benzoyl-l-threofuranose (6) [18]. To a soln. of 5 g (15 mmol) of 4 in 50 ml of CH2Cl2/pyridine
1:1; 2 ml (17 mmol) of BzCl was added at 08. The cooling bath was removed, and the mixture was stirred at r.t.
for 18 h. The mixture was cooled to 08, and 20 ml of 0.1m aq. HCl soln. was added. The org. layer was separated,
washed with sat. aq. NaHCO3 soln., H2O, and sat. NaCl soln., dried (MgSO4), and filtered. The solvent was
removed under reduced pressure, and the residue was recrystallized from EtOH to afford a single isomer. The
ethanolic mother liquor was filtered over silica gel (washed with hexane/AcOEt 2 :1 to give the other isomer, for
a combined yield of 4.57 g (70%).
Data of a-Isomer: 1H-NMR (300 MHz, CDCl3): 4.13 (dd, J 11.6, 3.0, HÀC(4)); 4.71 (dd, J 11.8, 6.0,
HÀC(4)); 5.86 (m, HÀC(2), HÀC(3)); 6.88 (d, J 4.3, HÀC(1)); 7.35 7.75 (m, 9 H, arom. H); 7.98 8.22 (m, 6
arom. H).
30
)
The two diastereoisomers can be obtained as crystals [16].