Synthesis of haloconduritols from an endo-cycloadduct of furan and vinylene carbonate

Article abstract of DOI:10.1016/S0040-4020(03)00510-6

A method for preparing haloconduritols having a conduritol-A construction is described. A mixture of endo- and exo-cycloadduct derivatives prepared from the Diels-Alder reaction of furan and vinylene carbonate was converted into diacetate derivatives by hydrolysis (K₂CO₃/MeOH) followed by acetylation (Ac₂O/pyridine). Boron trihalide (BBr₃ or BCl₃)-assisted ring-opening of the endo-diacetate in CH₂Cl₂ at -78°C gave (1α,2α,3β,6β)-6-halogeno-4-cyclohexene-1,2,3-triol 1,2-diacetate from which the corresponding triacetate was prepared by acetylation (AcCl). trans-Esterification of the triacetate (MeOH/HCl) afforded (1α,2α,3β,6β)-6-halogeno-4-cyclohexene-1,2,3-triol (X=Br or Cl). BF₃-Assisted ring-opening of the endo-diacetate in CH₂Cl₂ gave (1α,2α,3β,6β)-6-chloro-4-cyclohexene-1,2,3-triol 1,2-diacetate by means of halogen exchange.

Full text of DOI:10.1016/S0040-4020(03)00510-6

Tetrahedron 59 (2003) 3643–3648
Synthesis of haloconduritols from an endo-cycloadduct of furan
and vinylene carbonate
*
Arif Baran, Cavit Kazaz, Hasan Sec¸en and Yas¸ar Su¨tbeyaz
*
¨
Department of Chemistry, Faculty of Arts and Sciences, Ataturk University, 25240 Erzurum, Turkey
Received 7 October 2002; revised 6 March 2003; accepted 27 March 2003
Abstract—A method for preparing haloconduritols having a conduritol-A construction is described. A mixture of endo- and exo-cycloadduct
derivatives prepared from the Diels–Alder reaction of furan and vinylene carbonate was converted into diacetate derivatives by hydrolysis
(K2CO3/MeOH) followed by acetylation (Ac2O/pyridine). Boron trihalide (BBr3 or BCl3)-assisted ring-opening of the endo-diacetate in
CH2Cl2 at 2788C gave (1a,2a,3b,6b)-6-halogeno-4-cyclohexene-1,2,3-triol 1,2-diacetate from which the corresponding triacetate was
prepared by acetylation (AcCl). trans-Esterification of the triacetate (MeOH/HCl) afforded (1a,2a,3b,6b)-6-halogeno-4-cyclohexene-1,2,3-
triol (X¼Br or Cl). BF3-Assisted ring-opening of the endo-diacetate in CH2Cl2 gave (1a,2a,3b,6b)-6-chloro-4-cyclohexene-1,2,3-triol 1,2-
diacetate by means of halogen exchange. q 2003 Elsevier Science Ltd. All rights reserved.
1. Introduction
present a method for the stereoselective preparation of a
new bromoconduritol and chloroconduritol having the
conduritol-A construction.
Bromoconduritol is a covalent, irreversible, active-site
directed glucosidase inhibitor. It inhibits mammalian
a-glucosidase II (but not a-glucosidase I), yeast a-gluco-
sidase and some b-glucosidases.1 Bromoconduritol is a
diastereomeric mixture of (1a,2b,3a,6b)-6-bromo-4-cyclo-
hexene-1,2,3-triol (in the construction of conduritol-B) and
(1a,2b,3a,6a)-6-bromo-4-cyclohexene-1,2,3-triol (in the
construction of conduritol-F) prepared from conduritol-B
by treatment with HBr.1d Apart from this method, however,
only a small number of procedures are reported in the
literature for the preparation of the other bromoconduritols.
Guo2 et al. described a method for the preparation of
dihalogenoconduritols having a conduritol-A and B con-
struction by the reaction of dilithium tetrachlorocuprate and
dilithium tetrabromonickelate with unsaturated epoxides. In
addition, they reported an improved procedure for the
preparation of conduritol-B, from which they prepared
mono and dibromoconduritol and chloroconduritol deriva-
tives having a conduritol-B, E, and F construction.3 Haines4
and co-workers have reported the formation of some
bromoconduritol derivatives in the synthesis of
(1a,2a,4b)-5-cyclohexene-1,2,4-triol. Hudlicky5 and
co-workers showed the preparation of chloro and fluoro-
conduritol derivatives having conduritol-F and conduritol-E
construction by the substitution of an epoxide derived from
3-chloro-cyclohexa-3,5-diene-cis-1,2-diol. In this paper, we
2. Results and discussion
Our synthesis was inspired by the conduritol-C synthesis
described by Zefirov6 et al. They prepared conduritol-C by
acidic hydrolysis of furan–vinylene carbonate cycloadducts
(3 and 4) followed by neutralization. In this reaction, the
etheric bond is cleaved stereospecifically to give conduritol-
C (5) (Scheme 1).
Keywords: haloconduritol; furan; vinylene carbonate; cycloaddition; ring-
opening; boron trihalides; neighboring group participation; trans-
esterification.
*
Corresponding authors. Tel.: þ90-442-2314409; fax: þ90-442-2360948;
e-mail: hsecen@atauni.edu.tr (H. Sec¸en).
Scheme 1. (i) Heating at 123–1278C; (ii) H2SO4, H2O; (iii) Ba(OH)2.
0040–4020/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4020(03)00510-6

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A. Baran et al. / Tetrahedron 59 (2003) 3643–3648
derivative 8b, reacting with acetyl chloride in quantitative
yield for further characterization and safe storage. HCl-
catalyzed trans-esterification of triacetate 8b in MeOH gave
bromoconduritol 8c in quantitative yield. In the same
manner, the reaction of endo-diacetate 6 with BCl3 gave
chloroconduritol diacetate 9a in a yield of 96%. Acetylation
of 9a with acetyl chloride for further characterization
afforded chloroconduritol triacetate 9b, from which chloro-
conduritol 9c was prepared by trans-esterification in
quantitative yield (Scheme 3). An important point is that
if the temperature of the reaction with BBr3 or BCl3 rises
above 2788C, many reaction products are formed. The
trans-esterification procedure is also very important for the
Scheme 2. (i) Heating at 123–1278C in pressure tube, 21 h; (ii) K2CO3, Me
OH; (iii) Ac2O, pyridine.
Scheme 3. (i) BX3, CH2Cl2, 2788C, then H2O (BX3¼BBr3 or BCl3); (ii) CH3COCl, CH2Cl2; (iii) MeOH, HCl, 08C.
Boron tribromide and boron trichloride have been success-
fully used to cleave ethers for 40 years.7 Vogel8 et al.
Table 1. Proton coupling constants for 8a–c and 9a–c (J, Hz)
showed stereospecific cleavage of the etheric bond of the
Diels–Alder adducts of maleic anhydride to furfuryl esters
using BBr3. We assumed that the cleavage of the etheric
bond in furan–vinylenecarbonate cycloadducts (3 and 4)
with boron trihalides would result in the formation of
halogenoconduritols.
In the first step of our synthesis, we prepared cycloadducts 3
and 4 by heating furan (1) and vinylene carbonate (2) in a
sealed tube according to the literature procedure.9 In this
reaction, endo-cycloadduct 3 is formed as the main product
(ratio of 3/4 is 4:1). Attempts to direct the BBr3 assisted
ring-opening of 3 failed due to insolubility in the solvent
(CH2Cl2) at the reaction temperature (2788C). Considering
the high polarities and solubility problem in CH2Cl2, we
directly converted the mixture of cycloadducts 3 and 4 into
acetate derivatives 6 and 7 by basic hydrolysis followed by
acetylation with acetyl chloride (Scheme 2). Acetate
derivatives 6 and 7 were easily separated by column
chromatography.
J1,2
J2,3
J3,4
J4,5
J5,6
J1,6
J3,5
8a
8b
8c
9a
9b
9c
2.4
2.1
2.3
2.1
2.0
2.3
7.0
a
2.2
2.6
2.6
2.2
10.1
10.0
9.9
10.3
10.0
10.0
3.3
3.8
3.6
2.7
4.3
4.4
4.0
5.2
5.2
4.8
–
–
1.4
–
–
–
7.0
6.0
a
2.0
b
3.1
b
6.2
a
Undetermined from spectrum.
In the 1H NMR spectrum of 9c H4 and H5 resonate as an AB system due to
Treatment of endo-diacetate 6 with BBr3 at 2788C gave
bromoconduritol diacetate 8a as the sole product in a yield
of 94%. Diacetate 8a was converted into triacetate
b
broadening of the peaks. The same broadening is observed with H3 and
H6.

A. Baran et al. / Tetrahedron 59 (2003) 3643–3648
3645
hydrolysis of triacetates 8b and 9b. Due to halides being in
an allylic position, they are very reactive to substitution.
Thus, experiments performed under basic conditions for the
hydrolysis of 8b and 9b failed to give halogenoconduritols
8c and 9c.
Complete peak assignments of the NMR spectra of 8a–c
and 9a–c were carried out. Taking into consideration the
coupling constants we easily elucidated the relative
stereochemistry of H1, H2, and H3 (Table 1).
Looking at J1,2 values ranging from 2.0 to 2.4 Hz we easily
determined that H1 and H2 are cis. J2,3 values between 6.0
and 7.0 Hz are consistent with a trans-construction. The
mechanistic considerations also support the idea that H2 and
H3 are trans. Here, the most difficult problem was to
determine the relative stereochemistry of H6. Based on J1,6
values ranging from 4.0 to 5.2 Hz indicates that H1 and H6
could be trans or cis. Vogel10 et al. have reported cis
coupling constants J1,2¼2 Hz and J2,3¼1.5 Hz, and a trans
coupling constant J3,4¼8 Hz in conduritol-C (5). Compar-
ing the literature value of J1,2 (2 Hz, cis) in conduritol-C
with J1,6 (4.0–5.2 Hz) in 8 and 9 suggest differences in these
structures. A comparison of our spectral data established
that they were different to the reported stereoisomers 104
and 11† having a conduritol-C construction. In halogen-
substituted conduritol-A type cyclohexenyl systems12 trans
coupling constants (J1,6 and J2,3 according to our numbering
in Table 1) vary from 4.3 to 7.3 Hz while cis coupling
constants J2,3 are 2.1–2.6 Hz. These values are consistent
with those in Table 1. In particular, a comparison of
coupling constants 8a–c and 9a–c with those of A-type
dihalogenoconduritols 122 and 132 supplied us with results
in good agreement with those of the dihalogenoconduritols
(Fig. 1).13
Figure 1.
of the reaction, BX3 may be bonded to carbonyl oxygen of
the acetate, which is presumably more basic. Probably, this
is not productive to afford any product.
As outlined in Scheme 1, without any neighboring group
participation 3 and 4 would give conduritol-C. As chemical
evidence for the mechanism in Scheme 4, we propose that 6
should give conduritol-A tetraacetate (17) by acetolysis
with acetic anhydride under acidic conditions. Indeed, this
reaction afforded conduritol-A tetraacetate (17) and
The configurations of the halogens at C6 of 8c and 9c were
also confirmed by the observation of NOE effects. In 8c, the
irradiation of H–C6(Br) at d 4.61 caused signal enhance-
ment of the resonances at the adjacent double bond proton
(H5), and in particular at H3. In a similar way, in 9c,
irradiation of H–C6(Cl) at d 4.49 caused signal enhance-
ment of the resonances at the adjacent double bond proton
(H5), and in particular at H3.
In the light of structures 8a and 9a, we outline the BBr3 or
BCl3 assisted ring-opening mechanism of 6 in Scheme 4.
Vogel14 et al. have reported the neighboring group
participation of benzoate in BBr3-assisted ring-opening of
furan cycloadducts. Moreover, neighboring group partici-
pation of acetates was observed in many conduritol
syntheses.15 Based on these literature reports we propose a
similar neighboring group participation. As seen in Scheme
4, first BX3 is bound to 6 using the etheric oxygen to form
intermediate 14. Then, cleavage by attack of the carbonyl
oxygen of the neighboring acetate affords intermediate 15
and a free halide (X2). An attack of free halide at the allylic
carbon by an SN2 mechanism gives intermediate 16, which
forms 8a or 9a by hydrolysis. Alternatively, in the first step
Scheme 4. Suggested mechanism for BX3 assisted ring opeining of 6.
†
We thank Professor W. B. Motherwell for providing unpublished data on
this compound.11
Scheme 5. (i) Ac2O, H2SO4, room temperature.

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A. Baran et al. / Tetrahedron 59 (2003) 3643–3648
conduritol-F tetraacetate (18) in a ratio of 2:1 (Scheme 5).
We easily characterized conduritol-A tetraacetate 1716 and
conduritol-F tetraacetate 1815b by comparing their NMR
spectroscopic data with those of authentic samples.
The acetolysis reaction of 6 with neighboring group
participation probably proceeds through a 19-like inter-
mediate. While an SN2 attack of acetate at C1 gives
conduritol-A tetraacetate 17 through 20, an SN20 attack at C5
gives conduritol-F tetraacetate 18 through 21 (Scheme 6).
Scheme 8. (i) BF3, CH2Cl2, 2788C then H2O.
derivative, which was a surprising result (Scheme 8).
Repeated experiments gave the same result. This reaction
probably occurs via in situ halogen exchange17 between
CH2Cl2 and BF3 to form BCl3 (or BClF2 etc.). There was no
reaction when the reaction was performed in Et2O, THF,
benzene or EtOAc.
We submitted 8b and 9b to substitution with KOAc. Both
reactions also resulted in the formation of conduritol-A
tetraacetate 17 (Scheme 7). The formation of conduritol-A
tetraacetate 17 in both reactions shows that they proceed via
neighboring group participation, probably through a 19-like
intermediate.
We expected fluoroconduritol formation by the BF3-assisted
ring opening of 6. The reaction performed in CH2Cl2 gave
chloroconduritol derivative 9a instead of a fluoroconduritol
3. Conclusion
In conclusion, we have described an efficient method for the
preparation of bromoconduritol and chloroconduritol
having a conduritol-A construction via endo-cycloadduct
of furan and vinylene carbonate. Our studies on the ring-
opening of exo-cycloadducts are currently in progress.
4. Experimental
4.1. General information
Solvents were purified and dried by standard procedures
before use. Melting points were determined on a Thomas-
Hoover capillary melting apparatus. Infrared spectra were
obtained from KBr pellets on a Mattson 1000 FT-IR
spectrophotometer. The 1H and 13C NMR spectra were
recorded on a 200 (50) MHz Varian spectrometer. The mass
spectra were recorded on VG Zabspec GC–MS instruments.
Elemental analyses were carried out on a Carlo Erba 1106
model CHNS-O analyser. Column chromatography was
performed on silica gel 60 (70–230 mesh ASTM). Thin
layer chromatography was carried out on Merck 0.2 mm
silica gel, 60 F254 analytical aluminum plates.
4.1.1. Vinylene carbonate (2). The reported procedure9
was used for the synthesis of vinylene carbonate 2. Bp 528C/
25 mm Hg (lit.9 bp 73–748C/32 mm Hg). 1H NMR
(200 MHz, CDCl3) d 6.34 (s, 2H). 13C NMR (50 MHz,
CDCl3) d 151.6, 92.3.
4.1.2. Diels–Alder reaction of furan (1) and vinylene
carbonate (2). The cycloaddition procedure described in
the literature9 was used to afford cycloadducts 3 and 4 in a
ratio of 4:1 (Yield: 42% based on furan). Recrystallization
of the mixture of 3 and 4 from hexane–ethyl acetate (1:1)
gave two types of crystal, which were separated based on
appearance.
Scheme 6. Suggested mechanism for the formation of 17 and 18 from 6.
endo-Cycloadduct 3. Salt-like colorless crystal, mp 144–
1
1468C, lit.18 144–1488C. H NMR (200 MHz, CDCl3) d
6.51 (br s, 2H) 5.16 (m, AA0 part of AA0BB0 system, 2H),
4.94 (m, BB0 part of AA0BB0 system, 2H). 13C NMR
(50 MHz, CDCl3) d 156.3, 136.1, 81.2, 76.3.
Scheme 7. (i) KOAc, Ac2O, AcOH, reflux.

A. Baran et al. / Tetrahedron 59 (2003) 3643–3648
3647
exo-Cycloadduct 4. Colorless needless, mp 130–1328C,
1
171.5, 132.6, 129.3, 74.6, 73.7, 68.8, 45.2, 22.9, 22.7. IR
(KBr) 3463, 3004, 1769, 1429, 1361, 1240, 1057,
922 cm21
.
lit.18 137–1398C. H NMR (200 MHz, CDCl3) d 6.38 (s,
2H) 5.05 (s, 2H), 4.65 (s, 2H). 13C NMR (50 MHz, CDCl3) d
156.7, 136.7, 82.6, 78.4.
4.1.5. (1a,2a,3b,6b)-6-Chloro-4-cyclohexene-1,2,3-triol
1,2-diacetate (9a). The procedure described above for
BBr3 was applied to 6 using BCl3 to give 9a (colorless oil,
4.1.3. endo-Diacetate 6 and exo-diacetate 7. A 4:1
isomeric mixture of cycloadducts 3 and 4 (4.62 g,
30 mmol) was dissolved in 100 mL of MeOH–H2O (20:1)
and then K2CO3 (1.00 g) was added. The resulting mixture
was magnetically stirred at room temperature for 10 h. The
mixture was neutralized with AcOH and the solvent was
evaporated. To the residue were added Ac2O (7.35 g,
72 mmol) and 10 mL of pyridine. The mixture was stirred at
room temperature for 6 h. The mixture was cooled to 08C
and 70 mL of 10% HCl solution was added, followed by
extraction with ethyl acetate (3£50 mL). The combined
organic extracts were washed with saturated NaHCO3
solution (3£10 mL) and then dried (Na2SO4). Removal of
the solvent under reduced pressure gave a mixture of
diacetates 6 and 7 (5.09 g, overall yield of crude acetate
mixture: 80%). Chromatography of the diacetates on a
silicagel column (40 g) eluting with hexane–ethyl acetate
(2:1) gave endo-diacetate 6 as the first fraction and exo-
diacetate 7 as the second.
1
96%). H NMR (200 MHz, CDCl3) d 5.79 (dd, 1H, H4,
J4,5¼10.3 Hz, J3,4¼2.2 Hz), 5.73 (dd, 1H, H5, J4,5¼10.3 Hz,
J5,6¼2.7 Hz), 5.27 (dd, 1H, H1, J1,6¼5.2 Hz, J1,2¼2.1 Hz),
5.15 (dd, 1H, H2, J2,3¼6.0 Hz, J1,2¼2.1 Hz), 4.42 (dd, 1H,
H6, J1,6¼5.2 Hz, J5,6¼2.7 Hz), 4.24 (br d, 1H, H3,
J2,3¼6.0 Hz), 3.62 (br s, OH), 2.00 (s, 6H). 13C NMR
(50 MHz, CDCl3) d 172.3, 171.7, 132.4, 129.1, 74.2, 73.8,
68.5, 55.5, 22.8, 22.7. IR 3448, 2941, 1749, 1437, 1379,
1240, 1055, 951 cm21
.
4.1.6. (1a,2a,3b,6b)-6-Bromo-4-cyclohexene-1,2,3-triol
triacetate (8b). To a solution of 8a (1.00 g, 3.4 mmol) in
20 mL of CH2Cl2 was added acetyl chloride (0.32 g,
4.1 mmol). The resulting mixture was stirred for 12 h.
Removal of the solvent, HCl, and excess acetyl chloride
under reduced pressure (308C, 25 mm Hg) gave triacetate
8b (colorless oil, 1.14 g, quantitative). 1H NMR (200 MHz,
CDCl3) d 5.95 (dd, 1H, H5, J4,5¼10.0 Hz, J5,6¼3.8 Hz),
5.68 (dd, 1H, H4, J4,5¼10.0 Hz, J3,4¼2.6 Hz), 5.53–5.42
(m, 2H, H2 and H3), 5.38 (dd, 1H, H1, J1,6¼4.4 Hz,
J1,2¼2.1 Hz), 4.51 (dd, 1H, H6, J1,6¼4.4 Hz, J5,6¼3.8 Hz),
2.07 (s, 6H), 2.02 (s, 3H). 13C NMR (50 MHz, CDCl3) d
171.5, 171.0 (two carbon), 131.2, 128.7, 74.4, 70.4, 70.2,
44.1, 22.7, 22.6 (two carbon). IR (KBr) 3061, 2995, 2961,
1757, 1437, 1379, 1233, 1055, 963.
First fraction endo-cis-7-oxabicyclo[2.2.1]hept-5-ene-2,3-
diol diacetate (6). Rf¼0.35, (4.10 g, 64%). Colorless
crystals. Mp 81–838C (lit.19 75–768C, from Et2O). 1H
NMR (200 MHz, CDCl3) d 6.42 (br s, 2H), 5.07–5.03
(AA0BB0 system, 4H), 1.96 (s, 6H). 13C NMR (50 MHz,
CDCl3) d 171.6, 136.8, 80.6, 70.7, 22.4. IR (KBr) 3185,
2978, 1754, 1439, 1388, 1244, 1105, 1076, 1037, 944 cm21
.
Anal. calcd for C10H12O5 (212.20): C, 56.60; H, 5.70;
Found: C, 56.56; H, 5.69.
4.1.7. (1a,2a,3b,6b)-6-Chloro-4-cyclohexene-1,2,3-triol
triacetate (9b). The procedure described above for 8a
was applied to 9a to give triacetate 9b (colorless oil, 100%).
1H NMR (200 MHz, CDCl3) d 5.85 (dd, 1H, H5,
J4,5¼10.0 Hz, J5,6¼3.1 Hz), 5.68 (dd, 1H, H4,
J4,5¼10.0 Hz, J3,4¼2.0 Hz), 5.34–5.25 (m, 2H, H2 and
H3), 5.22 (dd, 1H, H1, J1,6¼5.2 Hz, J1,2¼2.0 Hz), 4.42 (dd,
1H, H6, J1,6¼5.2 Hz, J5,6¼3.1 Hz), 2.03 (s, 6H), 1.99 (s,
3H). 13C NMR (50 MHz, CDCl3) d 171.5, 171.1, 171.0,
131.1, 128.6, 74.1, 70.4, 70.2, 54.7, 22.7, 22.5 (two carbon).
IR (KBr) 2978, 2876, 1753, 1446, 1395, 1242, 1063,
Second fraction exo-cis-7-oxabicyclo[2.2.1]hept-5-ene-2,3-
diol diacetate (7). Rf¼0.19 (0.52 g, 8%). Colorless crystal.
Mp 91–928C. 1H NMR (200 MHz, CDCl3) d 6.45–6.43 (m,
2H), 4.89–4.87 (m, 2H), 4.81 (br s, 2H), 2.09 (s, 6H). 13C
NMR (50 MHz, CDCl3) d 172.1, 137.9, 83.5, 72.0, 22.6. IR
(KBr) 3104, 3012, 2950, 1758, 1727, 1430, 1380, 1292,
1257, 1052, 944 cm21. Anal. calcd for C10H12O5 (212.20):
C, 56.60; H, 5.70. Found: C, 56.61; H, 5.66
4.1.4. (1a,2a,3b,6,b)-6-Bromo-4-cyclohexene-1,2,3-triol
1,2-diacetate (8a). Under nitrogen atmosphere, to a stirred
solution of endo-diacetate 6 (1.00 g, 4.7 mmol) in 20 mL of
CH2Cl2 was added dropwise a solution of BBr3 (0.5 mL,
1.30 g, 5.2 mmol) in 20 mL of CH2Cl2 at 2788C over
10 min. After addition was completed, the mixture was
stirred at 08C for 1 h, and then at room temperature for 4 h
under air atmosphere. To the reaction mixture was added
5 mL of saturated NaHCO3 solution. The organic phase was
separated. The aqueous phase was additionally extracted
with CH2Cl2 (3£30 mL). The combined organic phases
were dried over Na2SO4. Evaporation of the solvent gave 8a
(colorless oil, 1.30 g, 94%). 1H NMR (200 MHz, CDCl3) d
5.90 (br dd, 1H, H5, J4,5¼10.1 Hz, J5,6¼3.3 Hz), 5.80 (dd,
1H, H4, J4,5¼10.1 Hz, J3,4¼2.2 Hz), 5.42 (dd, 1H, H1,
J1,6¼4.3 Hz, J1,2¼2.4 Hz), 5.31 (dd, 1H, H2, J2,3¼7.0 Hz,
J1,2¼2.4 Hz), 4.53 (dd, 1H, H6, J1,6¼4.3 Hz, J5,6¼3.3 Hz),
4.46 (br d, 1H, H3, J2,3¼7.0 Hz), 3.78 (br s, OH), 2.11 (s,
3H), 2.10 (s, 3H). 13C NMR (50 MHz, CDCl3) d 172.4,
961 cm21
.
4.1.8. (1a,2a,3b,6b)-6-Bromo-4-cyclohexene-1,2,3-triol
(8c). A stirred solution of 8b (1.00 g, 3.0 mmol) in 20 mL
of methanol was cooled to 08C. At the given temperature,
HCl gas was passed through the solution over 20 min. The
reaction flask was closed with a stopper and stirred at room
temperature for 12 h. Removal of the solvent, methyl
acetate and HCl under reduced pressure (308C, 25 mm Hg)
gave bromoconduritol 8c (0.63 g, quantitative). Colorless
crystals, mp 129–1308C (from EtOAc). 1H NMR
(200 MHz, CD3OD) d 5.84 (ddd, 1H, H5, J4,5¼9.9 Hz,
J5,6¼3.6 Hz, J3,5¼1.4 Hz), 5.71 (dd, 1H, H4, J4,5¼9.9 Hz,
J3,4¼2.6 Hz), 4.61 (dd, 1H, H6, J1,6¼4.0 Hz, J5,6¼3.6 Hz),
4.30 (dm, 1H, H3, J2,3¼7.0 Hz). 4.16 (dd, 1H, H1,
J1,6¼4.0 Hz, J1,2¼2.3 Hz), 3.96 (dd, 1H, H2, J2,3¼7.0 Hz,
J1,2¼2.3 Hz). 13C NMR (50 MHz, CD3OD) d 134.3, 130.2,
76.9, 74.4, 71.9, 52.1. IR (KBr) 3387, 3182, 2953, 2876,
1472, 1421, 1370, 1319, 1268, 1242, 1217, 1165, 1114,

3648
A. Baran et al. / Tetrahedron 59 (2003) 3643–3648
1063, 1038, 1012, 987. EIMS m/z (%): 192.0 [Mþ2H2O]
(5),190.0 [Mþ2H2O] (5), 149.9 (98), 147.9 (100), 111.0
(85), 99.0 (80), 83.0 (100) 65.1 (51), 60.1 (37). Anal. calcd
for C6H9BrO3 (209.04) C, 34.47; H, 4.34. Found: C, 34.81;
H, 4.45.
References
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9b to give chloroconduritol 9c in a quantitative yield.
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We are grateful to Atatu¨rk University for supporting this
work (Project number: 1998/55). We wish to thank
Professor Dr Metin Balci and Dr Ahmet Ceyhan Goren
for helpful discussions.