Reaction of methyl-4-methylene-2,3-O-isopropylidene-β-D-ribofuranoside with N-bromosuccinimide in aqueous tetrahydrofurane

Article abstract of DOI:10.1134/S1070428007050168

Methyl-4-methylene-2,3-O-isopropylidene-β-D-ribofuranoside prepared from D-ribose reacted in a system NBS-THF-H₂O to give a mixture of stereoisomeric products of regioselective bromohydroxylation of a double bond. The reaction involved a hydrolysis of the glycoside bond, but the acetonide protective group was retained. The mechanism of the selective hydrolysis originating from the ring-chain tautomerism of bromohydrins obtained was proved by the ¹H NMR spectra of the steroisomeric methyl-5-deoxy-5-bromo-4- hydroxy-2,3-O-isopropylidene-β-D-ribofuranosides. By crotonic cyclization of the formed masked 1,4-dicarbonyl compounds at heating in benzene in the presence of neutral Al₂O₃ a new chiral cyclopentenone block, 2-bromo-4,5-isopropylideneoxycyclopent-2-en-1-one, was obtained in a low yield. Nauka/Interperiodica 2007.

Full text of DOI:10.1134/S1070428007050168

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2007, Vol. 43, No. 5, pp. 742−746. © Pleiades Publishing, Ltd., 2007.
Original Russian Text © N.A. Ivanova, Z.R. Valiullina, O.V. Shitikova, M.S. Miftakhov, 2007, published in Zhurnal Organicheskoi Khimii, 2007, Vol. 43,
No. 5, pp. 745−749.
Reaction
of Methyl-4-methylene-2,3-O-isopropylidene-β-D-ribofuranoside
with N-Bromosuccinimide in Aqueous Tetrahydrofurane
N. A. Ivanova, Z. R. Valiullina, O. V. Shitikova, and M. S. Miftakhov
Institute of Organic Chemistry, Ufa Scientific Center, Russian Academy of Sciences, Ufa, 450054 Russia
e-mail: bioreg@anrb.ru
Received May 27, 2006
Abstract—Methyl-4-methylene-2,3-O-isopropylidene-β-D-ribofuranoside prepared from D-ribose reacted in a system
NBS–THF–H2O to give a mixture of stereoisomeric products of regioselective bromohydroxylation of a double bond.
The reaction involved a hydrolysis of the glycoside bond, but the acetonide protective group was retained. The
mechanism of the selective hydrolysis originating from the ring-chain tautomerism of bromohydrins obtained
1
was proved by the H NMR spectra of the stereoisomeric methyl-5-deoxy-5-bromo-4-hydroxy-2,3-O-
isopropylidene-β-D-ribofuranosides. By crotonic cyclization of the formed masked 1,4-dicarbonyl compounds
at heating in benzene in the presence of neutral Al2O3 a new chiral cyclopentenone block, 2-bromo-4,5-
isopropylideneoxycyclopent-2-en-1-one, was obtained in a low yield.
DOI: 10.1134/S1070428007050168
Here we report on an approach tested for a hypo-
thetical 1,4-ketoaldehyde II (X = Br). Taking into account
that activated 1,4-α-hydroxy(halo)carbonyl compounds
similar to substances II are prone to hydration, oligo-
merization, furanization, (and epimerization!) it seemed
feasible to generate them prior to cyclization from enol
ether IV available from methoxy derivative I [8]. For
preparation of compound IV from alcohol I the latter
was converted by known methods into bromide V and
iodide VI [9], and also into tosylate VII. However at
heating with DBU (80°C, benzene) bromide V did not
changed, whereas under the same conditions iodide VI
was converted enol ether IV. Regretfully, the Rf values
of iodide VI and enol ether IV were too close hampering
the reaction progress monitoring by TLC and chromato-
graphic purification of the product from residual iodide
VI. We avoided these difficulties by reacting tosylate
VII with t-BuOK to obtain enol ether IV in 65–70%
yield.
Chiral cyclopentenones prepared from sugars are used
in the synthesis of cyclopentanoids (prostanoids, carbo-
nucleosides etc) [1–5]. In extension of studies in this
field we planned to prepare from an available D-ribose
derivative I [6] chiral cyclopentenones III (X is an
electron-acceptor group). As seen from the scheme, the
key reaction stage is based on Knoevenagel intra-
molecular cyclization of compounds II containing an
activated methylene group into bicyclic cyclopentenones
III (iodine derivative III is mentioned in [7]).
X
O
OMe
O
CHO
O
HO
O
O
O
I
II
X
We regarded enol ethers as highly reactive latent
equivalents of oxo functions convenient for regiodirect-
ed introduction of an electrophilic moiety X+ into the
α-position with respect to a carbonyl, and thus we studied
a reaction of enol ether IV with N-bromosuccinimide.
The bromohydroxylation in the presence of NBS in
a mixture THF–H2O (3:1) proceeded rapidly (10–15 min)
O
O
O
III
742

REACTION OF METHYL-4-METHYLENE-2,3-O-ISOPROPYLIDENE-β-D-RIBOFURANOSIDE
743
O
O
lysis of acetonide in compound X was ascribed to an
anchimeric assistance to the hydrolysis of the oxygen
atom of the cis-oriented glycoside methoxy group. Other
examples of chemo- and regioselective deblocking of the
acetonide protective group were described for poly-
hydroxy compounds at the use of heterogeneous catalyst
OMe
OMe
R
а, b or c
d or e
I
O
O
O
O
_
V VII
IV
.
.
NaHSO3 SiO2 [11], of BiCl3 [12], La(NO3)3 6 H2O [13],
etc. [12].
O
O
OMe
OH
Br
Br
f
HO
HO
The selective hydrolysis of the C1-glycoside bond we
observed was likely to originate from the ring-chain
tautomerism of bromohydrin VIII. As seen from the
scheme, acyclic form XII is easily converted into
aldehyde XIII whose hydrate gives bromohydrin IX.
+
O
O
O
O
VIII
IX
R = Br (V), I (VI), OTs (VII). Reagents and conditions:
(a) 4.0 equiv CBr4, 1.1 equiv PPh3, MeCN, 20°C, 30 min
(95%); (b) 2.0 equiv I2, 1.25 equiv PPh3, 1.5 equiv Im,
PhMe, MeCN, 70°C, 20 min (76%); (c) 1.5 equiv TsCl,
Py, 20°C, 20 h (80%); (d) 1.1 equiv DBU, 90°C, 30 min
(68%); (e) 1.2 equiv t-BuOK, THT, 0ꢀ20°C, 1.5 h (67%);
(f) 1.1 equiv NBS, THT–H2O, 3:1, 20°C, 10 min (98%).
This suggestion is supported by the data of 1H NMR
spectroscopy that has revealed the presence of four
stereoisomeric methoxybromohydrins VIII which were
isolated in pairs by column chromatography on SiO2.
The comprehensive analysis of the spectra of methoxy-
bromohydrins VIII will be published elsewhere. We
failed to isolate individual oxybromohydrins IX.
and yielded quantitatively isomeric mixtures of bromo-
hydrins VIII and IX in a ratio 2:1. A striking feature of
this reaction was the formation of deblocked acetal IX
in considerable amounts within this short time. Methoxy-
bromohydrin VIII was converted completely into the
corresponding oxybromohydrin IX within 12 h at the
use of 10 equiv of NBS.
Br
HO
OMe
VIII
O
O
O
XII
Al2O3
The selective hydrolysis of the glycoside bond with
the retention of the isopropylidene protection is obviously
of a synthetic interest. The synthetic blocks of sugars
containing in the structure both acetonide and methyl-
acetal combination of protective groups, like in com-
pounds I, IV–VII, are known to be most common among
the hydrocarbon synthons. Usually under typical
stringent conditions of water-acid hydrolysis an exhaus-
tive hydrolysis occurs of both protective groups. We
found in the literature only examples of selective
hydrolysis of acetonide groups with retention of the other
protection. In [10] α-D-ribofuranoside (X) was success-
fully converted into diol XI by a selective hydrolysis of
the acetonide group in a mixture CF3CO2H–CH2Cl2
without affecting the glycoside. In the β-anomer the
acetonide group proved to be stable. The selective hydro-
O
Br
Br
_ MeOH
O
O
O
H
O
O
O
O
XIV
XIII
The intramolecular cyclization of compounds VIII
and IX by aldol-crotonic route at heating in benzene in
the presence of neutral Al2O3 [14] (under optimum
conditions for 1,4-dioxo compounds like diol XI) led to
the formation in low yields (10–20%) of target enone
XIV. We plan to carry on the search for cyclization
conditions of isomeric tetrahydrofurans IX by catalysis
with protonic and Lewis acids.
OMe
O
OMe
R
CF3CO2H
CH2Cl2
R
EXPERIMENTAL
O
O
HO
OH
IR spectra were recorded on spectrophotometers UR-
20 and Specord M-80 from films or mulls in mineral oil.
X
XI
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 5 2007

IVANOVA et al.
744
3
2
NMR spectra were registered on a spectrometer Bruker
AM-300 at operating frequencies 300.13 (1H) and
75.47 MHz (13C)from solutions in CDCl3 using solvent
signals as internal reference (δH 7.27, δC 77.00 ppm).
The reaction progress was monitored by TLC (Silufol,
petroleum ether–ethyl acetate, CH2Cl2–MeOH), spots
were visualized by 10% solution of anise aldehyde in
ethanol with sulfuric acid added. The optical rotation
was measur-ed on a polarimeter Perkin Elmer Polarimetre
241-M.
(3H, OMe), 3.44 d.d (1H, H5B, J5B,4 5.9, J5B,5A 10.0),
4.49 d.d (1H, H4, 3J4,5B 5.9, 3J4,5A 10.0), 4.62 d (1H, H2,
3J2,3 6.0), 4.77 d (1H, H3, J3,2 6.0), 5.0 c (1H, H1).
13C NMR spectrum, δ, ppm: 24.90 (Me), 26.43 (Me),
32.48 (C5), 55.13 (OMe), 82.59 (C2), 85.13 (C3), 86.63
(C4), 109.53 (C1), 112.71 (Ci-Pr). Found, %: C 40.39;
H 5.54; Br 29.79. C9H15BrO4. Calculated, %: C 40.47;
H 5.66; Br 29.91.
3
Methyl-5-deoxy-5-iodo-2,3-O-isopropylidene-β-D-
ribofuranoside (VI). To a stirred mixture of 1.00 g (4.89
mmol) of compound I, 1.60 g (6.11 mmol)of Ph3P, and
0.49 g (7.33 mmol) of imidazole dissolved in a mixture
of 15 ml of toluene and 2.5 ml of acetonitrile at 70°C
was added by portions 1.56 g (9.75 mmol) of fine
crystalline iodine. The reaction mixture was stirred for
20 min, diluted with ethyl acetate, washed with
a saturated solution of Na2S2O3 and with H2O, and dried
with Na2SO4. On evaporating the solvent in a vacuum
the residue was subjected to chromatography on
a column packed with SiO2 (petroleum ether). Yield
1.18 g (76%), colorless oily substance, Rf 0.22 (petroleum
ether–ethyl acetate, 9:1), [α]D20 –79.8° (c 1, CHCl3). IR
Methyl-2,3-O-isopropylidene-β-D-ribofuranoside
(I). To a mixture of 12.40 g of CuSO4, 5.85 g
(38.90 mmol) of D-ribose, 110 ml of anhydrous acetone,
and 32 ml of anhydrous MeOH was added dropwise
0.2 ml of concn. H2SO4. The reaction mixture was stirred
at 40°C for 48 h (TLC monitoring); CuSO4 was filtered
off, the precipitate was washed with a mixture acetone–
MeOH, 1:1 v/v. The filtrate was neutralized with
a saturated NaHCO3 solution and evaporated. The residue
was extracted with ethyl acetate, the extract was washed
with H2O, saturated solution of NaCl, dried with Na2SO4,
and the solvent was evaporated in a vacuum. On distilling
the residue we obtained 7.95 g (75%) of compound I,
bp 110°C (2 mm Hg), Rf 0.44 (CH2Cl2–MeOH, 9:1),
[α]D20 –75° (c 1, CHCl3). IR spectrum, ν, cm–1: 1020,
1056, 3485. 1H NMR spectrum, δ, ppm (J, Hz): 1.32 s
spectrum, ν, cm–1: 1020, 1065, 1080, 1095. H NMR
1
spectrum, δ, ppm (J, Hz): 1.32 s (3H, Me), 1.47 s (3H,
Me), 3.15 t (1H, H5A, J5A,5B 10.0), 3.27 d.d (1H, H5B,
2
3J5B,4 6.0, 2J5B,5A 10.0), 3.36 s (3H, OMe), 4.42 d.d (1H,
3
H4, J4,5B 6.0, J4,5A 10.0), 4.62 d (1H, H2, J2,3 6.0),
3
3
3
(3H, Me), 1.50 s (3H, Me), 3.25 d.d (1H, OH, JOH,5B
2.8, 3JOH,5A 10.0), 3.36 s (3H, OMe), 3.62 t.d (1H, H5A,
3J5A,4 3.5, 2J5A,5B = 3J5A,OH = 10.0), 3.70 d.d.d (1H, H5B,
3J5B,OH 2.8, 3J5B,4 2.8, 2J5B,5A 10.0), 4.45 d.d (1H, H4, 3J4,5B
2.8, 3J4,5A 3.5), 4.60 d (1H, H2, 3J2,3 6.0), 4.83 d (1H, H3,
3J3,2 6.0), 4.9 C (1H, H1). 13C NMR spectrum, δ, ppm:
24.60 (Me), 26.25 (Me), 55.35 (OMε), 63.64 (C5), 81.40
(C2), 85.65 (C3), 88.16 (C4), 109.79 (C1), 112.00 (Ci-Pr).
Found, %: C 52.79; H 7.88. C9H16O5. Calculated, %:
C 52.93; H 7.90.
4.74 d (1H, H3, J3,2 6.0), 5.05 s (1H, H1). 13C NMR
3
spectrum, δ, ppm: 6.64 (C5), 24.82 (Me), 26.22 (Me),
54.98 (OMe), 82.77 (C2), 85.10 (C3), 87.15 (C4), 109.40
(C1), 112.30 (Ci-Pr). Found, %: C 34.58; H 4.95; I 40.23.
C9H15IO4. Calculated, %: C 34.41; H 4.81; I 40.40.
Methyl-2,3-O-isopropylidene-5-O-tosyl-β-D-
ribofuranoside (VII). To a stirred solution of 2.0 g
(9.79 mmol) of alcohol I in 15 ml of pyridine was added
at 0°C by portions 2.8 g (14.69 mmol) of TsCl. The
reaction mixture was stirred at room temperature for
20 h (TLC monitoring), then it was poured into cold
water, the reaction product was extracted into chloroform,
the extract was dried with Na2SO4, and evaporated. The
residue was purified by column chromatography on SiO2
(CH2Cl2) or by recrystallization from petroleum ether–
ethyl acetate, 1:1, to obtain 2.8 g (80%) of tosylate VII
as colorless crystals, mp 80–81°C, Rf 0.18 (petroleum
ether–ethyl acetate, 8:2), [α]D20 –48.7° (c 1, CHCl3). IR
spectrum, ν, cm–1: 814, 838, 1090, 1180, 1354, 1594.
1H NMR spectrum, δ, ppm (J, Hz): 1.21 s (3H, Me),
1.43 s (3H, Me), 2.44 s (3H, Mearom), 3.22 s (3H, OMe),
3.97 d.d (1H, H5A, 3J5A,4 7.2, 2J5A,5B 10.2), 4.03 d.d (1H,
Methyl-5-deoxy-5-bromo-2,3-O-isopropylidene-β-
D-ribofuranoside (V). To a mixture of 0.50 g
(2.45 mmol) of compound I and 0.97 g (3.70 mmol) of
Ph3P in anhydrous acetonitrile was added at room
temperature 1.23 g (9.70 mmol) of CBr4, and the mixture
was stirred for 30 min (TLC monitoring). The precipitate
was filtered off, the solution was evaporated, and the
residue was subjected to chromatography on SiO2
(CH2Cl2). Yield 0.62 g (95%), colorless oily substance,
Rf 0.30 (petroleum ether–ethyl acetate, 9:1), [α]D20 –74.2°
(c 1, CHCl3). IR spectrum, ν, cm–1: 1040, 1070, 1080,
1105. 1H NMR spectrum, δ, ppm (J, Hz): 1.33 s (3H, Me),
2
1.49 s (3H, Me), 3.32 t (1H, H5A, J5A,5B 10.0), 3.35 s
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 5 2007

REACTION OF METHYL-4-METHYLENE-2,3-O-ISOPROPYLIDENE-β-D-RIBOFURANOSIDE
745
3
2
3
H5B, J5B,4 7.2, J5B,5A 10.2), 4.3 t (1H, H4, J4,5 7.2),
(4S)-Methyl-5-bromo-4-hydroxy-5-deoxy-2,3-O-
isopropylidene-β-D-ribofuranoside (4S,β-VIII). Rf 0.3
(petroleum ether–ethyl acetate, 8:2, 2 runs). IR spectrum,
4.52 d (1H, H3, 3J3,2 5.9), 4.59 d (1H, H2, 3J2,3 5.9), 4.92
s (1H, H1), 7.35 d (2H, HO Jo,m 8.3), 7.79 d (2H, Hm,
3
,
1
ν, cm–1: 682, 2986, 3420. H NMR spectrum, δ, ppm
3Jm,o 8.3). 13C NMR spectrum, δ, ppm: 21.67 (Mearom),
24.85 (Me), 26.32 (Me), 55.03 (OMe), 69.24 (C5), 81.35
(C3), 83.57 (C4), 84.87 (C2), 109.45 (C1), 112.69 (Ci-Pr),
127.99 (CO), 129.96 (Cm), 132.70 (Cθ), 145.12 (Cθ).
Found, %: C 53.55; H 6.12; S 8.83. C16H22O7S.
Calculated, %: C 53.62; H 6.19; S 8.95.
(J, Hz): 1.38 s (3H, Me), 1.56 s (3H, Me), 3.38 s (3H,
OMe), 3.40 s (1H, OH), 3.64 d (1H, H5A, 2J5A,5B 10.6),
3.69 d (1H, H5B, 2J5B,5A 10.6), 4.63 d (1H, H3, 3J3,2 5.9),
3
4.70 d (1H, H2, J2,3 5.9), 4.95 s (1H, H1). 13C NMR
spectrum, δ, ppm: 24.64 (Me), 25.96 (Me), 35.73 (C5),
55.14 (OMe), 84.44 (C3), 85.20 (C2) 104.81 (C1), 109.98
(Ci-Pr), 113.72 (C4). Found, %: C 38.32; H 5.45; Br 28.37.
C9H15BrO5. Calculated, %: C 38.18; H 5.34; Br 28.22.
Methyl-2,3-O-isopropylidene-4-methylene-β-D-
erythrofuranoside (IV). a. A mixture of 0.20 g
(0.64 mmol) of iodide VI and 0.1 g (0.70 mmol) of DBU
was stirred at 90°C for 30 min. The reaction mixture
was subjected to column chromatography on SiO2
(petroleum ether–ethyl acetate, 98:2) to obtain 0.08 g
(68%) of enol ether IV.
(4R)-Methyl-5-bromo-4-hydroxy-5-deoxy-2,3-O-
isopropylidene-α-D-ribofuranoside (4R,α-VIII).
1H NMR spectrum, δ, ppm (J, Hz): 1.32 s (3H, Me),
1.47 s (3H, Me), 3.43 m (1H, H5A), 3.45 s (3H, OMe),
2
b. To a solution of 0.46 g (1.28 mmol) of tosylate VII
in 15 ml of anhydrous THF was added at 0°C while
stirring 0.22 g (1.92 mmol) of t-BuOK. The reaction
mixture was stirred at room temperature for 1.5 h (TLC
monitoring), the precipitate was filtered off, and the
solution was evaporated in a vacuum. The residue was
purified by column chromatography on SiO2 (petroleum
ether– ethyl acetate, 95:5). Yield 0.16 g (67%), Rf 0.22
(petroleum ether–ethyl acetate, 9:1), [α]D20 +55.2° (c 1.15,
CHCl3). IR spectrum, ν, cm–1: 890, 1060, 1085, 1670,
3.65 d (1H, H5B, J5B,5A 11.0), 4.42 d (1H, OH,
4JOH,5A 1.6), 4.69 d (1H, H3, 3J3,2 5.67), 4.80 d (1H, H2,
3J2,3 5.67), 5.03 s (1H, H1). 13C NMR spectrum, δ, ppm:
24.80 (Me), 26.16 (Me), 35.88 (C5), 55.59 (OMe), 78.72
(C3), 84.19 (C2) 104.54 (C1), 106.06 (Ci-Pr), 113.18 (C4).
(4S)-Methyl-5-bromo-4-hydroxy-5-deoxy-2,3-O-
isopropylidene-α-D-ribofuranoside (4S,α-VIII).
1H NMR spectrum, δ, ppm (J, Hz): 1.35 s (3H, Me),
1.48 s (3H, Me), 2.99 d (1H, OH, 3JOH,1 9.8), 3.40 s (3H,
2
OMe), 3.60 d (1H, H5A, J5A,5B 11.3), 3.61 d (1H, H5B,
1
3085. H NMR spectrum, δ, ppm (J, Hz): 1.35 s (3H,
2J5B,5A 11.3), 4.68 d (1H, H3, 3J3,2 5.6), 4.71 d (1H, H2,
3J2,3 5.6), 5.35 d (1H, H1, 3J1,OH 9.8). 13C NMR spectrum,
δ, ppm: 24.89 (Me), 26.25 (Me), 35.96 (C5), 55.68
(OMe), 84.56 (C3), 85.31 (C2) 104.61 (C1), 113.30
(Ci-Pr), 113.83 (C4).
Me), 1.48 s (3H, Me), 3.41 s (3H, OMe), 4.38 br.s (1H,
H5A), 4.49 d (1H, H3, J3,2 5.90), 4.59 br.s (1H, H5B),
3
5.95 d (1H, H2, J2,3 5.90), 5.10 s (1H, H1). 13C NMR
3
spectrum, δ, ppm: 25.73 (Me), 26.73 (Me), 55.65 (OMe),
78.69 (C3), 82.66 (C2), 88.70 (C5), 108.35 (C1), 113.20
(Ci-Pr), 161.23 (C4). Found, %: C 57.98; H 7.39. C9H14O4.
Calculated, %: C 58.05; H 7.58.
(4R)-Methyl-5-bromo-4-hydroxy-5-deoxy-2,3-O-
isopropylidene-β-D-ribofuranoside (4R,β-VIII).
1H NMR spectrum, δ, ppm (J, Hz): 1.41 s (3H, Me),
1.55 s (3H, Me), 3.31 s (3H, OMe), 3.60 d (1H, H5A,
2J5A,5B 11.3), 3.61 d (1H, H5B, 2J5B,5A 11.3), 4.03 d (1H,
OH, 3JOH,1 12.5), 4.58 d (1H, H3, 3J3,2 5.9), 4.63 d.d (1H,
H2, 3J2,1 3.6, 3J2,3 5.9), 5.24 d.d (1H, H1, 3J1,2 3.6, 3J1,OH
12.5). 13C NMR spectrum, δ, ppm: 24.72 (Me), 25.05
(Me), 35.76 (C5), 55.22 (OMe), 78.85 (C2), 84.31(C3),
104.96 (C1), 106.11 (Ci-Pr), 110.09 (C4).
Reaction of enol ether IV with N-bromo-
succinimide. To a solution of 0.2 g (1.07 mmol) of enol
ether IV in 7 ml of a mixture THF–H2O, 3:1, was added
0.21 g (1.2 mmol) of NBS, and the stirring continued for
10 min (TLC monitoring). The reaction mixture was
evaporated, the residue was extracted with CHCl3, the
extract was washed with a saturated NaCl solution, dried
with Na2SO4, and evaporated in a vacuum. The residue
was purified by column chromatography on SiO2
(petroleum ether–ethyl acetate, 95:5) to isolate 0.2 g
(66%) of a mixture of methoxybromohydrins VIII as
two pairs of stereoisomers, and 0.09 g (32%) of com-
pound IX as three stereoisomers in a ratio 4:2:1.8
(measured by integral intensities of CH3 peaks in the 1H
NMR spectrum).
5-Bromo-4-hydroxy-5-deoxy-2,3-O-isopropylid-
ene-D-ribofuranose (IX). Rf 0.11 (petroleum ether–ethyl
acetate, 8:2, 2 runs). IR spectrum, ν, cm–1: 634, 2944,
1
3412. H NMR spectrum, δ, ppm (J, Hz): 1.32 s (3H,
Me), 1.38 s (3H, Me), 1.40 s (3H, Me), 1.48 s (3H, Me),
1.55 s (3H, Me), 1.56 s (3H, Me), 3.60–3.75 m (6H, H5),
4.60–4.85 m (6H, H2, H3), 5.40–5.50 m (3H, H1).
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 5 2007

IVANOVA et al.
746
13C NMR spectrum, δ, ppm, major isomer: 24.66 (Me),
26.04 (Me), 35.80 (C5), 82.93 (C3), 84.39 (C2), 103.68
(C1), 106.10 (C4), 113.18 (Ci-Pr); second isomer: 24.49
(Me), 25.82 (Me), 36.22 (C5), 84.71 (C3), 86.16 (C2),
96.00 (C1), 99.66 (C4), 113.70 (Ci-Pr); minor isomer:
24.32 (Me), 25.60 (Me), 36.35 (C5), 78.44 (C3), 79.06
(C2), 98.01 (C1), 103.68 (C4), 113.77 (Ci-Pr). Found, %:
C 35.58; H 5.04; Br 29.53. C8H13BrO5. Calculated, %:
C 35.71; H 4.87; Br 29.69.
REFERENCES
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2-Bromo-4,5-O-isopropylidene-2-cyclopenten-1-
one (XIV). To a dispersion of neutral Al2O3 in benzene
was added under an argon atmosphere 0.68 g of a mixture
of bromohydrins VIII and IX in benzene. The reaction
mixture was stirred for 3 h at reflux, then Al2O3 was
filtered off, and the solution was evaporated. The residue
was subjected to a chromatography on a column packed
with SiO2 (petroleum ether–ethyl acetate, 95:5) to isolate
0.08 g (15%) of enone XIV as colorless crystals, mp
86.5–88°C, Rf 0.35 (petroleum ether–ethyl acetate, 7:3),
[α]D20+4.4° (c 1.15, CHCl3). IR spectrum, ν, cm–1: 1582,
1
1744. H NMR spectrum, δ, ppm (J, Hz): 1.40 s (3H,
Me), 1.42 s (3H, Me), 4.58 d (1H, H5, 2J5,4 5.4), 5.23 d.d
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3
3
3
(1H, H4, J4,3 3.6, J4,5 5.4), 7.59 d (1H, H3, J3,4 3.6).
13C NMR spectrum, δ, ppm: 26.33 (Me), 27.45 (Me),
75.29 (C4), 77.52 (C5), 115.91 (Ci-Pr), 128.52 (C2), 157.10
(C3), 195.45 (C1). Found, %: C 41.11; H 3.78; Br 34.19.
C8H9BrO3. Calculated, %: C 41.23; H 3.89; Br 34.28.
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 43 No. 5 2007