2094
K. Sivapriya et al. / Tetrahedron Letters 48 (2007) 2091–2095
Table 1. 77Se NMR Chemical shifts (76 MHz, CDCl3)
ethyl acetate 7:3). Compound 5a was obtained as pale
25
77Se NMR (d ppm)
orange crystals (0.17 g, 0.25 mmol, 73%); ½aꢀD 10 (c 1,
Tetraselenide
1
CHCl3), mp: 185 ꢁC; H NMR (300 MHz, CDCl3): d 5.78
5a
5b
6
720.2, 635.9, 472.8, 468.4
715.6, 633.8, 469.7, 468.8
719.6, 634.1, 470.9, 466.8
714.0, 638.1, 472.4, 462.2
(s, 1H), 5.52–5.35 (m, 3H), 4.13 (m, 1H), 3.15 (d,
J = 10.3 Hz, 2H), 2.18 (s, 3H), 2.12 (s, 3H), 2.02 (s, 3H);
13C NMR (75 MHz, CDCl3): d 170.6, 170.4, 169.9, 78.2,
73.8, 72.7, 70.3, 67.3, 61.3, 25.6, 20.7, 20.6; 77Se NMR
(76 MHz, CDCl3): d 720.2, 635.9, 472.8, 468.4; HR-MS
(m/z): calculated for C12H16O7Se4 (M+Na+): 613.7376,
observed (M+Na+): 613.7427.
12
10. Tetraselenides 5a, 5b, 6 and 12 are stable at low temper-
ature (4 ꢁC). In solution over a period of time they gave
rise to elemental selenium as one of the products. It is
reported that polyselenide compounds decompose readily
to give elemental selenium due to the lower bond energy of
a Se–Se bond compared to a S–S bond.6 In the present
case where the polyselenide chain forms the backbone of a
sugar it was found to be stable at low temperatures.
11. Crystal structure data for 5a: C18H20O8Se4, MW = 613.7,
crystal dimensions 0.25 · 0.24 · 0.17 mm3, T = 293(2) K,
Orthorhombic, space group P 21 21 21, a = 8.057(5),
(Et4N)2WSe4 1,
1 equiv, CH3CN
OTs
4 h, 74%
OBz
O
BzO
BzO
Complex mixture
4c
Se
)
2
Li2Se2/ THF
16
t-BuOH, 1 h,
72%
Scheme 5.
˚
b = 8.640(5), c = 26.858(16) A, a = b = c = 90.00ꢁ, Z = 4,
V = 1869.6(19) cm3, qcalcd = 1.855 g/cm3, Mo Ka radia-
tion (kvꢁ = 0.71073 A), l = 4.001 mmꢁ1
,
2h = 1.52ꢁ–
˚
26.37ꢁ; of 14,756 reflections collected, 3716 were indepen-
dent (R(int) = 0.0328); GOF = 0.781, R1 = 0.0350,
These tetraselenides are the first of their kind where all
four selenium atoms are arranged in a cyclic manner
as the backbone of mannose. The utility of these tetra-
selenides in carbohydrate chemistry is currently under
investigation.
wR2 = 0.0875 (r > 2r(I)), absolute structure parameꢁte3r
˚
0.00(7), residual electron density 0.574/ꢁ0.487 e A
.
CCDC Number 282452. Crystal structure data for 5b:
C21H34O7Se4, MW = 740.9, crystal dimensions 0.38 ·
0.27 · 0.22 mm3, T = 293(2) K, trigonal, space group P
˚
31, a = 12.9677(14), b = 12.9677(14), c = 29.728(6) A,
a = b = 90.00ꢁ, c = 120ꢁ, Z = 8, V = 4329.4(11) cm3,
Acknowledgements
q
calcd = 2.192 g/cm3, Mo Ka radiation (k = 0.71073 A),
˚
l = 6.824 mmꢁ1, 2h = 1.81–25.97ꢁ; of 33,534 reflections
collected, 11,066 were independent (R(int) = 0.0480);
GOF = 0.968, R1 = 0.0519, wR2 = 0.1074 (r >2r(I)),
absolute structure parameter ꢁ0.010(12), residual electron
The authors thank the DST, New Delhi, for CCD X-ray
facilities, Mr. Vijay Thiruvenkatam for his help in solv-
ing the molecular structures and Mr. V. Ganesh for his
help and discussions on B3LYP calculations.
density 0.661/ꢁ0.362 e Aꢁ3. CCDC number 287584. Crys-
˚
tallographic data (excluding structure factors) for the
structures in this paper have been deposited with the
Cambridge Crystallographic Data Centre as supplemen-
tary publications. Copies of these data can be obtained,
free of charge, on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44(1223)336033 or
References and notes
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9. General experimental procedure for compound 5a: To a
stirred solution of anomeric bromide 4a (0.28 g,
0.395 mmol) in CH3CN (3 ml), tetraethylammonium tetra-
selenotungstate 1 (2 equiv) was added and the reaction
mixture was stirred for 8 h at 28 ꢁC. After the disappear-
ance of the starting material (TLC), the solvent was
removed in vacuo and the resulting black residue was
extracted with CH2Cl2–Et2O (1:9, 5 · 20 ml) and filtered
through a Celite pad. The filtrate was concentrated and
the crude product was purified by flash column chroma-
tography on silica gel (230–400 mesh, eluting with hexane–