N. T. Hoai et al. / Carbohydrate Research 346 (2011) 1747–1751
1751
D2O with acetone as the internal standard (d = 2.22 ppm for 1H
NMR, and 30.89 ppm for 13C NMR) using a JEOL JNM-EX270
instrument (270 MHz for 1H NMR and 67 MHz for 13C NMR). Gas
chromatography was carried out using a GC-17A (Shimadzu)
instrument equipped with an FID detector (a glass-capillary col-
NMR (D2O, 270 MHz): d 5.24 (d, J1,2 4.5 Hz, H-1), 4.30 (dd, J2,3
9.5 Hz, H-2), 4.53 (dd, J3,4 6.7 Hz, H-3), 4.38 (m, J4,5 2.2 Hz, H-4),
3.84 (br s, J5,6endo 2.8 Hz, H-5), 4.43 (dd, J6endo,6exo 12.8 Hz, H-6endo),
3.72 (dd, J5,6exo 1.1 Hz, H-6exo); 13C NMR (D2O, 67 MHz): d 97.93 (C-
1), 80.00 (C-4), 68.47 (C-2), 66.77 (C-6), 65.78 (C-3), 64.37 (C-5).
Anal. Calcd for C6H10O5: C, 44.45; H, 6.22. Found: C, 44.20; H, 6.09.
umn, Shimadzu, CBP-10, 0.32 mm ꢀ 25 m ꢀ 0.5
lm; injector temp
250 °C; detector temp 270 °C; carrier gas He; flow rate 1.6 mL min
ꢁ1; split ratio 1: 40). The temperature of the column oven was pro-
grammed at 7.5 °C minꢁ1 from 110 to 260 °C, then maintained at
260 °C for 20 min.20 The microwave-assisted heating was carried
out using a Green Motif-I apparatus (IDX Co, Ltd; single mode; out-
put power 30–300 W) at 2.45 GHz.
4. Conclusion
The dehydration of
methyl- -mannopyranoside (M
anoside (M MF) were performed using microwave-assisted heat-
ing in ordinary or dry sulfolane without any catalyst. The
dehydration of -mannose in the ordinary sulfolane gave 1,6-anhy-
dro-b- -mannopyranose (AMP) and 1,6-anhydro-b- -mannofura-
nose (AMF) in high yields with a moderate selectivity for the
AMP. The demethanolization of M MP in the ordinary or dry sul-
folane was found to proceed with a high selectivity for AMP. The
demethanolization of M MF in dry sulfolane exhibited a high
D-mannose and the demethanolization of
a-
D
a
MP) or methyl- -mannofur-
a-D
a
3.3. Microwave-assisted heating
D
D
D
To the starting material (100 mg of
D-mannose, MaMP, or
MaMF) in a 20-ml test tube was added the ordinary or dry sulfo-
a
lane (5 mL). A K-type thermocouple through a capillary tube sealed
with Bond SU adhesive (Konishi; #04592) and a parallel side arm
adapter (Claisen adapter) was placed in the center of the mixture.
The test tube was placed on a Green Motif-I mounted with an ar-
gon gas bubbler on the side arm. The mixture was heated to a pre-
set temperature with magnetic stirring for 3 min using microwave
irradiation. It took about 25 and 31 s to reach 200 and 260 °C,
respectively.
a
selectivity for AMF, while the selectivity of AMF versus AMP was
drastically reduced with the increasing temperature in the ordin-
ary sulfolane.
References
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The conversions and yields of AMP or AMF in the reaction mix-
tures after the microwave-assisted heating were determined as the
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a
a
a
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anhydro-b- -mannopyranose (AMP)
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(a) A reaction mixture of mannose (100 mg) in ordinary sulfo-
lane (5 mL) at 200 °C (see Table 1, entry 5) was directly chromato-
graphed on the silica gel column to give a crude mixture of AMP
and AMF (64 mg, AMF:AMP = 24:76). The crude mixture was iso-
lated by a reported procedure19 on a Dowex AG 50Wx2 (Ca2+) resin
column to afford AMF (14 mg, 16%) and AMP (44 mg, 49%). The GC
retention time and the 1H NMR and 13C NMR spectra of the ob-
tained AMP were identical to those of the commercially available
one.
(b) The microwave-assisted heating of MaMF (100 mg) in dry
sulfolane (5 mL) was repeated 10 times at 240 °C for a 3-min
irradiation time (see Table 3, entry 13). The combined reaction
mixtures were then directly purified by SiO2 column chromatogra-
phy eluted with ethyl acetate (Rf = 0.21) to give a colorless solid
(450 mg, 54%), which was crystallized from methanol/ethyl acetate
(1:4, v/v) to afford the analytical sample of 1,6-anhydro-b-D-
18. Takagaki, A.; Ebitani, K. Chem. Lett. 2009, 38, 650–651.
19. Angyal, J. S.; Beveridge, J. R. Aust. J. Chem. 1978, 31, 1151–1155.
20. Angyal, J. S.; Bodkin, L. C.; Parrish, W. F. Aust. J. Chem 1975, 28, 1541–1549.
mannofuranose (AMF) (405 mg, 49%), mp 185–188 °C, lit.19 188–
190 °C; ½a 2D5
ꢂ
+7.5 (c 1.00, water), lit.19
½
a 2D2 +2.5, c 1.00, water; 1H
ꢂ