Thio-sugars. IV. Synthesis of carbohydrate 1,3-glycol (six-membered) thionocarbonates and their attempted O-S rearrangement)

Article abstract of DOI:10.1248/cpb.49.1210

Four six-membered cyclic thionocarbonates (two sec-sec and two prim-sec) were prepared and their radical-promoted O-S rearrangement reaction was examined. The results revealed that the reaction in six-membered rings is difficult compared with the simple r

Full text of DOI:10.1248/cpb.49.1210

1210
Notes
Chem. Pharm. Bull. 49(9) 1210—1213 (2001)
Vol. 49, No. 9
Thio-Sugars. IV. Synthesis of Carbohydrate 1,3-Glycol (Six-Membered)
Thionocarbonates and Their Attempted O–S Rearrangement1)
a
,b
Yoshisuke TSUDA,a,2) Shinsuke NOGUCHI, and Hideki NIINO
*
Faculty of Pharmaceutical Sciences,a Kanazawa University, 13–1 Takara-machi, Kanazawa 920–0923, Japan and R & D
Research Center,b Permachem Asia Ltd., 14–29 Torihama-cho, Yokohama, 236-0002, Japan.
Received March 21, 2001; accepted May 30, 2001
Four six-membered cyclic thionocarbonates (two sec–sec and two prim–sec) were prepared and their radi-
cal-promoted O–S rearrangement reaction was examined. The results revealed that the reaction in six-membered
rings is difficult compared with the simple rearrangement in five-membered rings. In the course of syntheses of
the substrates, interesting acyl migration during the stannylation process occurred.
Key words six-membered cyclic thionocarbonate; thiocarbonylation; acyl migration; spiro-orthocarbonate; O–S rearrangement
In previous papers,1—3) we showed that when five-mem-
75% yield.
bered cyclic thionocarbonates formed from 1,2-glycols were
treated with a catalytic amount of appropriate radical genera-
tors, they underwent O–S rearrangement to give thiolcarbon-
ates in acceptable yields. Although the regioselectivity of the
reaction is not always high, the sterereochemistry of the
product is exclusively cis. The method was successfully ap-
plied to the synthesis of thio-sugars carrying a thiol group at
the secondary positions in carbohydrate molecules, while
ionic reaction4) of the same substrate gave no reaction. The
present study was undertaken to determine whether a similar
rearrangement occurs in six-membered analogues formed
from 1,3-glycols. During synthesis of these substrates, inter-
esting acyl migration reactions were observed.
Thiocarbonylation of the 6-O-tosylate 6 using method (1)
gave the 3,6-ether 7,3,8) indicating that the activated 3-OH at-
tacked the 6-position in an SN2 manner. Treatment of 6 with
Im2CS gave a solid in 75% yield, which contained one imida-
zole group and m/z of 312. The 1H-NMR data were compati-
ble with the structure 8 (the probable mechanism is indicated
in brackets [J→K]).
Thiocarbonylation of the 6-deoxy derivative 9 using
method (1) gave two products, 10 (57%) and 11 (36%), while
Im2CS gave only 10 in 83% yield, which was the expected
3,5-O-thionocarbonate. Compound 11 lacked a thiocarbonyl
group and had the MS peak at m/z 401, which corresponded
to (MϪMe)+ originating from the dimeric spiro-orthocarbon-
ate structure 11 formed by the route O→P. Formation of
such spiro-orthocarbonates by the reaction of thionocarbon-
ates and tin-activated glycols has a precedent.9) The stereo-
chemistry of the central carbon is uncertain.
Thionocarbonates 14a and 14b were best prepared by thio-
carbonylation of 12a and 12b using method (1), followed by
treatment of the resulting 6-O-thiocarbonyl chlorides (13a, b)
with N,N-dimethylaminopyridine (DMAP) in refluxing diox-
ane. The other method gave poor results.
Attempted O–S Rearrangement The prim–sec thiono-
carbonate 14a is known to give the primary-S product 15a in
ionic rearrangement (KI in MeCN).4) The b-anomer 14b
similarly gave 15b in good yield.
Results and Discussion
Synthesis of Six-membered Cyclic Thionocarbonates
For the 1,3-glycols, three derivatives of 1,2-O-isopropyli-
dene-a-D-glucofuranose (6-O-benzoate 2,5) 6-O-tosylate 6,5)
and 6-deoxy compound 96)) and two derivatives of pryano-
sides [methyl 2,3-di-O-methyl-a- and -b-D-glucopyranosides
(12a, b)]7) were chosen. Thiocarbonylation of these glycols
was carried out by one of the following methods: (1) stanny-
lation with Bu2SnO, then treatment with thiophosgene
(CSCl2); or (2) direct treatment with thiocarbonyldiimidazole
(Im2CS).
When the 6-O-benzoate 2 was thiocarbonylated using
method (1), the product was not the expected 3,5-O-thiono-
cabonate 5, but 3-O-benzoyl-5,6-O-thionocarbonate 33)
(67%), indicating that an acyl migration took place during
the reaction. To determine which process (activation by stan-
nylation or the reaction with thiophosgene) is responsible for
this migration, 2 was treated with Bu2SnO. The product was
the 3-O-benzoate 4 (92%), revealing that the benzoyl migra-
tion from O-6 to O-3 occurred during the stannylation
process through D→E→F. This compound 4 was previously
reported as an intermediate in the alkaline hydrolysis of 3-O-
benzoyl-5,6-O-thionocarbonate 3 to the triol 1.8) Detailed
comparison of the spectral data of 2 and 4 revealed that the
previously reported intermediate was not the 3-O-benzoate 4,
but instead was the 6-O-benzoate 2, indicating that acyl mi-
gration from O-3 to O-6 had taken place during alkaline hy-
drolysis (as G→H). Thiocarbonylation of 2 with Im2CS
(method 2) gave the expected 3,5-O-thionocarbonate 5 in
For attempted radical-promoted O–S rearrangement, the
following three methods, all of which gave good results for
five-membered thionocarbonates,1,3) were tested: (A) heat-
ing with a catalytic amount of Bu3SnH in the presence of
a,a-azobis(isobutyronitrile) (AIBN); (B) photolysis with
(Bu3Sn)2 in benzene; and (C) heating with dimethyl phos-
phonate and benzoyl peroxide.
The reaction of the prim–sec thionocarbonate 14b using
method A gave a mixture in which the rearrangement prod-
Chart 1
To whom correspondence should be addressed. e-mail: ZVN11235@nifty.ne.jp
© 2001 Pharmaceutical Society of Japan

September 2001
1211
Chart 2
Chart 3
uct 17 was not found judging from the absence of the thiol- 20 (24%). Although the minor presence of an O–S rearrange-
carbonate peak (ca. d 160) in the 13C-NMR. Method C gave ment product 19 was suggested from the 13C-NMR signal at
similar results. The reaction of sec–sec thionocarbonate 10 d 171, it could not be isolated. Reactions of the 6-O-ben-
was again fruitless. Using method A, the recovery of the zoate 5 were again fruitless: method A was of low efficacy
products was low with major formation of oxo derivative 18. and method C gave a complex mixture. In neither case was
The major product using method C was a dideoxy derivative the formation of a rearrangement product indicated.

1212
Vol. 49, No. 9
Table 1. 13C-NMR Data for New Compounds Reported in This Paper (in
CDCl3)a)
Imidazole Derivative (8) A mixture of 6 (561 mg) and Im2CS (1.1 eq) in
toluene (100 ml) was heated under reflux for 2 h. The solvent was removed
under reduced pressure and the residue was chromatographed to give, from
the benzene–AcOEt (1 : 1) eluate, compound 8 (350 mg, 75%) as colorless
plates from AcOEt–hexane, mp 128—130 °C. IR (KBr): 1377, 1296, 1237,
Comp. C-1
C-2
C-3
C-4
C-5
C-6
Othersb)
1
1040. H-NMR: 6.04 (1H, d, Jϭ3.6 Hz, H-1), 5.21 (1H, br d, Jϭ6.8 Hz, H-
2
4
8
9
10
11
12a
12b
13a
13b
14a
14b
15a
15b
105.0
104.9
105.5
104.8
104.6
106.4
97.6
104.6
97.4
104.3
98.6
85.2
83.0
83.3
85.2
82.7
83.6
81.9
83.6
81.6
83.2
80.8
83.1
80.5
82.6
82.9
81.7
75.8
79.6
77.6
75.3
80.3
83.3
82.9
85.8
82.7
85.5
80.3
81.4
82.2
82.8
82.1
31.0
79.4
77.2
74.2
81.9
73.3
71.2
70.2
69.8
69.5
69.2
78.4
79.8
79.5
81.6
79.0
80.5
69.8
68.2
78.5
67.0
76.1
76.8
70.8
75.0
68.2
72.2
61.1
62.6
61.9
65.3
62.9
66.2
66.7 166.7 (CϭO)
64.2 166.5 (CϭO)
35.3
5), 4.38 (1H, d, Jϭ2.8 Hz, H-3), 4.76 (1H, d, Jϭ3.6 Hz, H-2), 4.08 (1H, t,
Jϭ2.0 Hz, H-4), 3.72 (1H, dd, Jϭ10.3, 6.8 Hz, H-6), 3.27 (1H, d, Jϭ10.3
Hz, H-6), 1.52, 1.35 (each 3H, s, Me2CϽ). 13C-NMR: 135.0, 129.4, 116.8
(imidazole), 116.3 (C-7), 112.3, 28.8, 26.1 (Me2CϽ). MS: 312 (Mϩ, 47),
297 (MϩϪMe, 55), 279 (100), 95 (90). Anal. Calcd for C13H18O5N2S: C,
49.99; H, 5.16; N, 8.97. Found: C, 49.91; H, 5.13; N, 8.88.
6-Deoxy-1,2-O-isopropylidene-a-D-glucofuranose (9) This was pre-
pared from the 6-O-tosylate 6 by LiAlH4 reduction in 85% yield. mp 90—
92 °C (lit.6) 90—91 °C).
Thiocarbonylation of 9 (1) With Bu2SnO–CSCl2: A mixture of 9 (200
mg) and Bu2SnO (274 mg, 1.1 mol eq) in dry toluene (80 ml) was heated
under reflux for 2 h. After cooling the mixture to room temperature, CSCl2
(84 ml, 1.1 mol eq) was added drop by drop, and the mixture was stirred for
2.5 h at room temperature. The mixture was poured onto a silica gel column,
and the column was washed thoroughly with benzene to remove excess
reagents. Elution of the column with benzene–AcOEt (5 : 1) gave the 3,5-O-
thionocarbonate 10 (137 mg, 57%) and the spiro-orthocarbonate 11 (81 mg
36%).
(2) With Im2CS: A mixture of 9 (600 mg) and Im2CS (1.1 eq) in toluene
(40 ml) was heated under reflux for 3 h. The cooled reaction mixture was
poured onto a silica gel column and the column was washed with benzene.
Elution of the column with benzene–AcOEt (5 : 1) gave 6-deoxy-1,2-O-iso-
18.6
18.0 187.0 (CϭS)
19.0
62.2
62.1
75.8 186.4 (CϭS)
75.8 186.4 (CϭS)
71.5 188.1 (CϭS)
71.2 187.9 (CϭS)
30.6 163.8 (CϭO)
30.2 163.8 (CϭO)
69.2 147.2 (CϭO)
17.9
104.7
97.9
103.9
16bc) 104.8
20
105.3
a) Assignments were confirmed by the C–H COSY spectra. b) The other carbons
not included here are indicated in the Experimental section. c) Prepared by the action
of Bu2SnO on 14b (cf. Tsuda Y., Sato Y., Kakimoto K., Kanemitsu K., Chem. Pharm.
Bull., 40, 1033—1036 [1992]).
In conclusion, radical-promoted O–S rearrangement in
six-membered cyclic 1,3-thionocarbonates is difficult com- propylidene-3,5-O-thiocarbonyl-a-D-glucofuranose (10) (613 mg, 83%) as
colorless prisms from CHCl3–hexane, mp 171 °C. IR (KBr): 1296, 1274,
pared with the reaction in five-membered cyclic 1,2-thiono-
1
1249, 1199. H-NMR: 6.02 (1H, d, Jϭ3.7 Hz, H-1), 4.89 (1H, d, Jϭ3.1 Hz,
carbonates. This difficulty must occur in the cyclization step
H-3), 4.85 (1H, d, Jϭ3.7 Hz, H-2), 4.82 (1H, qd, Jϭ7.0, 1.7 Hz, H-5), 4.08
of the intermediary radical. Although intermediary radical
(1H, dd, Jϭ3.0, 1.7 Hz, H-4), 1.56 (3H, d, Jϭ7.0 Hz, H-6), 1.52, 1.35 (each
3H, s, Me2CϽ). MS: 246 (Mϩ, 100), 231 (MϩϪMe, 28). Anal. Calcd for
C10H14O5S: C, 48.77; H, 5.73. Found: C, 48.73; H, 5.70.
formation is indicated, the reaction does not proceed to re-
arrangement but to hydride abstraction. This is parallel with
the fact that the intramolecular radical cyclization to a double
bond usually preferentially produces 5-membered rings
rather than 6-membered rings.
Spiro-orthocarbonate (11) Pale yellow oil. IR: 1164, 1097, 1073,
1
1030. H-NMR: 6.02 (1Hϫ2, d, Jϭ4.0 Hz, H-1), 4.68 (1Hϫ2, d, Jϭ4.0 Hz,
H-2), 4.40 (1Hϫ2, d, Jϭ4.0 Hz, H-3), 4.26 (1Hϫ2, m, H-4), 3.89 (1Hϫ2,
m, H-5), 1.4 (3Hϫ2, d, Jϭ7.0 Hz, H-6), 1.52, 1.35 (each 3Hϫ2, s, Me2CϽ).
13C-NMR: 119.0 (central C), 112.4, 27.3, 26.7 (Me2CϽ). MS: 401 (MϩϪ
Me, 19), 231 (100), 113 (92).
Experimental
Methyl 3-O-methyl-4,6-O-thiocarbonyl-a-D-glucopyranoside 14a (1)
Thiocarbonylation of 12a with Bu2SnO and CSCl2: A mixture of 12a (1.0 g)
and Bu2SnO (1.12 g, 1.0 mol eq) in toluene (20 ml) was heated under reflux
for 2 h, then cooled to 0 °C. CSCl2 (0.38 ml, 1.1 eq) was added drop by drop,
and the mixture stirred for 30 min at room temperature, then poured onto a
silica gel column. After washing the column with benzene, elution with
AcOEt–hexane (1 : 1) gave methyl 6-O-chlorothiocarbonyl-2,3-di-O-methyl-
General The same as in ref. 3.
6-O-Benzoyl-1,2-O-isopropylidene-3,5-O-thiocarbonyl-a-D-glucofura-
nose (5) A mixture of the 6-O-benzoate 25) (200 mg) and Im2CS (121 mg,
1.1 eq) in toluene (100 ml) was heated under reflux for 3 h. The solvent was
evaporated and the residue was chromatographed. The CHCl3–EtOAc eluate
gave the 3,5-O-thionocarbonate 5 (169 mg, 75%) as colorless plates from
benzene–hexane, mp 160—161 °C. IR: 1731, 1255. 1H-NMR: 7.98 (2H, dd,
Jϭ8.4, 0.9 Hz, o-Ph-H), 7.61 (1H, br t, Jϭ8.4 Hz, p-Ph-H), 7.48 (2H, br t,
Jϭ8.4 Hz, m-Ph-H), 6.04 (1H, d, Jϭ3.7 Hz, H-1), 5.04 (1H, m, H-5), 4.92
(1H, d, Jϭ3.0 Hz, H-3), 4.89 (1H, d, Jϭ3.7 Hz, H-2), 4.71 (1H, dd, Jϭ12.5,
3.9 Hz, H-6), 4.67 (1H, dd, Jϭ3.0, 1.7 Hz, H-4), 4.65 (1H, dd, Jϭ12.5, 2.8
Hz, H-6), 1.50, 1.34 (each 3H, s, Me2CϽ). Anal. Calcd for C17H18O7S: C,
55.73; H, 4.95. Found: C, 55.50; H, 4.90.
1
a-D-glucopyranoside (13a) (1.3 g, 98%) as a syrup. H-NMR: 4.87 (1H, d,
Jϭ3.7 Hz, H-1), 4.79 (1H, dd, Jϭ11.7, 2.0 Hz, H-6), 4.71 (1H, dd, Jϭ11.7,
5.6 Hz, H-6), 3.93 (1H, ddd, Jϭ8.2, 5.6, 2.0 Hz, H-5), 3.65, 3.51, 3.46 (each
3H, s, OMe), 3.49—3.47 (2H, m, H-3, 4), 3.27 (1H, dd, Jϭ9.3, 3.7 Hz, H-2),
2.48 (1H, d, Jϭ2.0 Hz, 4-OH).
A mixture of 13a (1.25 g) and DMAP (508 mg, 1.0 mol eq) in toluene (5
ml) was stirred for 10 min at room temperature. Chromatography of the re-
Acyl Migration in 2 from O-6 to O-3 A mixture of 6-O-benzoate 2
(100 mg) and Bu2SnO (85 mg, 1.0 eq) in toluene (50 ml) was heated under
reflux for 5 h. Chromatography and crystallization of the mixture gave the 3-
O-benzoate 4 (92 mg, 92%) as colorless prisms from CHCl3–hexane, mp
194—198 °C. It was not separable from 2 on thin-layer chromatography
1
action mixture gave the 4,6-O-thionocarbonate 14a (1.3 g) as a syrup. H-
NMR: 4.90 (1H, d, Jϭ3.7 Hz, H-1), 4.59 (1H, dd, Jϭ10.0, 6.0 Hz, H-6),
4.27 (1H, t, Jϭ10.2 Hz, H-6), 4.14 (1H, td, Jϭ10.3, 6.0 Hz, H-5), 4.02 (1H,
t, Jϭ9.8 Hz, H-4), 3.70 (1H, t, Jϭ9.3 Hz, H-3), 3.67, 3.56, 3.48 (each 3H, s,
OMe), 3.29 (1H, dd, Jϭ9.4, 3.7 Hz, H-2).
1
(TLC). H-NMR: 8.10—7.40 (5H, m, Ph-H), 5.99 (1H, d, Jϭ3.4 Hz, H-1),
(2) The Colidine-CSCl2 method10) gave 14a in Ͻ5% yield.
5.53 (1H, d, Jϭ2.0 Hz, H-3), 4.71 (1H, d, Jϭ3.4 Hz, H-2), 4.30 (1H, dd,
Jϭ8.5, 2.0 Hz, H-4), 3.87 (1H, br d, Jϭ9.5 Hz, H-6), 3.79—3.72 (2H, m, H-
5, 6), 1.55, 1.34 (each 3H, s, Me2CϽ).
Thiocarbonylation of 2 with Bu2SnO and CSCl2 Compound 2 was
treated with Bu2SnO as described above, then thioacylated with CSCl2 (1.0
eq) at room temperature for 30 min to give the 3-O-benzoyl-5,6-O-thiono-
carbonate 3, mp 205—206 °C, identical with the authentic specimen3) in
67% yield.
3,6-Ether (7) A mixture of the 6-O-tosylate 6 (150 mg) and Bu2SnO
(120 mg, 1.2 eq) in toluene (40 ml) was heated under reflux for 4 h. Removal
of the solvent and chromatography of the residue gave the 3,6-ether 7 (83
mg, 100%) from the benzene–hexane eluate as a colorless oil (lit.3) mp 53—
55 °C). The NMR and IR spectra were identical with those of the authentic
specimen.3,8)
(3) The Im2CS method gave 14a in 15% yield.
Methyl 3-O-methyl-4,6-O-thiocarbonyl-b-D-glucopyranoside 14b (1)
Thiocarbonylation of 12b with Bu2SnO and CSCl2: Compound 12b (1.43 g)
was stannylated with Bu2SnO (1.6 g, 1.0 mol eq) and treated with CSCl2
(0.54 ml, 1.1 mol eq), then worked up as described for the a-anomer to give
the 6-O-chlorothiocarbonyl derivative 13b (1.9 g, 100%), as a syrup. 1H-
NMR: 4.83 (1H, dd, Jϭ11.9, 2.0 Hz, H-6), 4.68 (1H, dd, Jϭ11.9, 6.0 Hz, H-
6), 4.25 (1H, d, Jϭ7.6 Hz, H-1), 3.64, 3.57, 3.55 (each 3H, s, OMe), 3.63
(1H, m, H-5), 3.46 (1H, t, Jϭ9.2 Hz, H-4), 3.14 (1H, t, Jϭ8.8 Hz, H-3), 3.04
(1H, dd, Jϭ9.1, 7.6 Hz, H-2).
Treatment of 13b (1.9 g) in dioxane (5 ml) with DMAP (100 mg) for 30
min as described for the a-anomer gave the cyclic 4,6-O-thionocarbonate
14b (800 mg, 48%), as colorless prisms from CHCl3–hexane, mp 173—

September 2001
1213
175 °C. IR (KBr): 1298, 1278, 1119. 1H-NMR: 4.64 (1H, dd, Jϭ10.3, 6.0 ddd, Jϭ9.8, 6.6, 3.4 Hz, H-5), 1.96 (1H, dd, Jϭ13.5, 3.9 Hz, H-3), 1.89 (1H,
Hz, H-6), 4.38 (1H, d, Jϭ7.8 Hz, H-1), 4.29 (1H, t, Jϭ10.4 Hz, H-6), 4.06 ddd, Jϭ13.5, 10.4, 4.5 Hz, H-3), 1.52, 1.33 (each 3H, s, Me2CϽ), 1.14 (3H,
(1H, t, Jϭ9.7 Hz, H-4), 3.78 (1H, td, Jϭ10.1, 6.0 Hz, H-5), 3.67, 3.59, 3.55 d, Jϭ6.6 Hz, H-6).
(each 3H, s, OMe), 3.42 (1H, t, Jϭ8.2 Hz, H-3), 3.09 (1H, t, Jϭ8.2 Hz, H-
2). MS: 264 (Mϩ, 24), 232 (5), 203 (10), 145 (33), 88 (100). Anal. Calcd for References and Notes
C10H16O5S: C, 45.45; H, 6.10. Found: C, 45.29; H, 5.70.
(2) The Im2CS method gave 14b in only 7% yield.
1) Part XXXIV of Utilization of Sugars in Organic Synthesis. Part
XXXIII (Thio-Sugars III) Tsuda Y., Noguchi S., Kanemitsu K., Sato
Y., Kakimoto K., Iwakura Y., Hosoi S., Chem. Pharm. Bull., 45, 971—
980 (1997).
2) Present address: H. E. J. Research Institute of Chemistry, University of
Karachi, Karachi-75270, Pakistan.
3) Tsuda Y., Sato Y., Kanemitsu K., Hosoi S., Shibayama K., Nakao K.,
Ishikawa Y., Chem. Pharm. Bull., 44, 1465—1475 (1996).
4) Trimnell D., Doane W. M., “Methods in Carbohydrate Chemistry,” Vol.
VII, ed. by Whistler R. L., BeMiller J. N., Academic Press, New York,
1976, pp. 42—43.
Rearrangement of 14b under Ionic Conditions A mixture of 14b
(100 mg) and KI (600 mg) in MeCN (4 ml) was heated in a sealed tube at
70 °C for 24 h. The cooled mixture was filtered and the filtrate was chro-
matographed on a short silica gel column to give the methyl 4,6-O,S-car-
bonyl-3-O-methyl-6-thio-b-D-glucopyranoside 15b as a syrup (slightly cont-
aminated with 14b). 1H-NMR: 4.30 (1H, d, Jϭ7.8 Hz, H-1), 4.13 (1H, t,
Jϭ9.2 Hz, H-4), 3.77 (1H, td, Jϭ10.0, 5.7 Hz, H-5), 3.37 (1H, t, Jϭ9.0 Hz,
H-3), 3.23 (1H, t, Jϭ10.3 Hz, H-6), 3.17 (1H, dd, Jϭ11.2, 5.7 Hz, H-6), 3.05
(1H, dd, Jϭ9.0, 7.8 Hz, H-2), 3.64, 3.59, 3.55 (each 3H, s, OMe).
Attempted Radical Rearrangement Each 50 mg was treated using
methods A, B, and C (see text), respectively. The result was judged from the
peak at d 160—170 (thiolcarbonate), ca. 140 (carbonate) in the 13C-NMR of
the product.
5) Tsuda Y., Nishimura M., Kobayashi T., Sato Y., Kanemitsu K., Chem.
Pharm. Bull., 39, 2883—2887 (1991).
6) Valverde S., Hernandez A., Herradon B., Rabanal R. M., Martin-
Lomas M., Tetrahedron, 43, 3499—3504 (1987).
Reaction of 10 by Method C Benzoyl peroxide (101 mg, 1.0 eq) was
added every 30 min to a heated mixture of the deoxy derivative 10 (100 mg)
and dimethyl phosphonate (153 ml, 4.0 eq) in dioxane (5 ml) in a sealed tube
at 120 °C, and heating was continued for 1 h. The mixture was diluted with
CHCl3, washed with NaHCO3, dried, and concentrated. Chromatography of
the residue with benzene–AcOEt (10 : 1 to 0 : 1) gave 3,6-dideoxy-a-D-glu-
7) “Carbohydrates,” ed. by Collins P. M., Chapman and Hall, London
1987, D-00262.
8) Tsuda Y., Shibayama K., Chem. Pharm. Bull., 44, 1476—1479 (1996).
9) Sakai S., Kiyohara Y., Itoh K., Ishii Y., J. Org. Chem., 35, 2347—2350
(1970).
10) Trimnell D., Doane W. M., “Methods in Carbohydrate Chemistry,” Vol.
VII, ed. by Whistler R. L., BeMiller J. N., Academic Press, New York,
1976, pp. 277—279.
1
cofuranose (20) (18 mg, 24%). H-NMR: 5.82 (1H, d, Jϭ3.7 Hz, H-1), 4.75
(1H, t, Jϭ4.0 Hz, H-2), 4.17 (1H, ddd, Jϭ10.5, 4.9, 3.4 Hz, H-4), 4.11 (1H,