Uncommon transformations of methyl (1S,2S,3R,4R)-2,3-isopropylidenedioxy-5- iodomethyl-2-tetrahydrofurylacetate initiated by bases

Article abstract of DOI:10.1134/S1070428006110169

Methyl (1S,2S,3R,4R)-2,3-isopropylidenedioxy-5-iodomethyl-2- tetrahydrofurylacetate prepared in two stages from D-ribose acetonide underwent a series of uncommon transformations under the treatment with bases providing the following different products dep

Full text of DOI:10.1134/S1070428006110169

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2006, Vol. 42, No. 11, pp. 1701−1705.  Pleiades Publishing, Inc. 2006.
Original Russian Text  N.A. Ivanova, Z.R. Valiullina, O.V. Shitikova, M.S. Miftakhov, 2006, published in Zhurnal Organicheskoi Khimii, 2006,
Vol. 42, No. 11, pp. 1713−1717.
Uncommon Transformations
of Methyl (1S,2S,3R,4R)-2,3-isopropylidenedioxy-5-iodomethyl-2-
tetrahydrofurylacetate Initiated by Bases
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 October 13, 2005
Abstract—Methyl (1S,2S,3R,4R)-2,3-isopropylidenedioxy-5-iodomethyl-2-tetrahydrofurylacetate prepared in two
stages from D-ribose acetonide underwent a series of uncommon transformations under the treatment with bases
providing the following different products depending on the base applied: methyl 3-(5-acetyl-2,2-dimethyl-1,3-
dioxol-4-yl)propionate (DBU), methyl 2,3-isopropylidenedioxy-7-oxabicyclo[2.2.1]heptane-6-carboxylate (t-BuOK),
methyl {(5R)-2,2-dimethyl-5-[(2R)-oxiranyl]-1,3-dioxolan-4-ylidene}propionate and methyl-(Ε)-3-{(4S,5R)-2,2-
dimethyl-5-[(1R)-(2-oxiranyl)]-1,3-dioxolan-4-yl}-2-propenoate (t-BuOK and LDA).
DOI: 10.1134/S1070428006110169
carbocyclization of compounds III or IV into struc-
tures V and VI hoping that under the action of
strong deprotonating reagents a retro-Michael decom-
position of compound III would be initiated provid-
ing enolate VII capable of repeated intramolecular Michael
ring closure involving the more nucleophilic carbo-
anion center and giving as a result cyclopentane deriva-
tive VI.
Application of sugars as chiral matrices in a directional
synthesis of biologically active compounds is covered in
a number of surveys and monographs [1–5]. In this
study in order to synthesize optically active polyfunc-
tional cyclopentanoids we investigated some reactions
of iodoester III prepared from D-ribose acetonide (I)
[6] via ester II [7, 8] occurring with assistance of basic
reagents. We planned to perform a new way of
1 '
2
O
5 O
O
'
2'
OH
1
HO
HO
R
CO2Me
CO2Me
4
'
'
3
a
b
or c
O
O
O
O
O
O
I
IIа (2'R),
IIb (2'S).
III (R = I),
IV (R = OTs).
CO2Me
O
_
O
O
CO2Me
O
O
CO2Me
O
O
O
O
V
VI
VII
Reagents and conditions: a. Ph3P=CHCO2Me, PhH, 80°C, 2 h (90%); b. I2, Ph3P, Im, PhMe, 90°C, 1 h (80%); c. TsCl, Py, 20°C,
20 h (89%).
1701

IVANOVA et al.
O
1702
1
3
CO2Me
5
4
'
'
1
"
а
2
2
"
V
O
2'
O
VIII, 70%
CO2Me
1
CO2Me
CO2Me
O 1"
H
O
5O6
H
H
3
2
"
4
1
2
4
5
'
2
3
'
b
+
+
III
H
H
3' O
'
O1
2
O
O
'
O
O
IX, 54%
X, 8%
XI, 8%
c
IX, 12.5% + X, 15.6%
X, 40% + XI, 11%
b
IV
Reagents and conditions: (a) 2.5 equiv. of DBU, PhH, 80°C, 2 h; (b) 1.5 equiv. of t-BuOK, THF, 0 ꢀ 20°C, 1 h (80%);
(c) 2 equiv. of LDA, THF, –50°C, 2 h; 0°C, 0.5 h; 20°C, 1 h.
Therefore studying the reaction with basic reagents
of methyl (1S,2S,3R,4R)-2,3-isopropylidenedioxy-5-iodo-
methyl-2-tetrahydrofurylacetate obtained from D-ribose
acetonide we discovered a previously unknown rear-
rangement and a number of uncommon transformations
leading to compounds promising as multipurpose chiral
blocks.
However this attempt failed. The stage of dehydro-
iodination of iodide III with DBU was found to take an
abnormal direction. It turned out that the arising exo-
enol ether V under the conditions of reaction rearranged
into a more stable derivative of 1,3-dioxol VIII.Analogs
of this rearrangement were not reported.
On treating iodide III with t-BuOK in THF we
obtained compounds IX–XI.As seen, t-BuOK converted
iodoester III not into enol ester V but into a number of
compounds resulting exclusively from the primary
enolyzation of the methoxycarbonyl function. The
formation of enol ester X is unexpected for it is less
thermodynamically preferable than ester XI. The fraction
of compound X was somewhat increased at replacing
LDA for t-BuOK although the overall yield of compounds
IX and X in this case was also rather moderate.
Compound X is interesting for attempting intramolecular
carbocyclization by Mukaiyma protocol [9]. The yield of
this compound at treating with t-BuOK tosylate IV
prepared under standard conditions attained ~ 40%.
EXPERIMENTAL
IR spectra were recorded on spectrophotometers UR-
20 and Specord M-80 from films. NMR spectra were
registered on a spectrometer BrukerAM-300 at operating
frequencies 300.13 (1H) and 75.47 MHz (13C) from
solutions in CDCl3 ot CD2Cl2, as internal reference served
the signals of solvents CDCl3 (CD2Cl2) [δH 7.27 (5.31),
δC 77.00 (53.86) ppm]. The reaction progress was
monitored by TLC on Silufol plates, spots were visualized
by 10% ethanol solution of anisaldehyde containing a little
of sulfuric acid [10]. GLC analysis was carried out on
a Shimadzu instrument equipped with a glass column
25 m long (sorbent OV-101).
Thus we found that methyl (1S,2S,3R,4R)-2,3-iso-
propylidenedioxy-5-iodomethyl-2-tetrahydrofurylacetate
easily obtained from D-ribose when treated with DBU,
t-BuOK, and LDA was converted into different in
structure products of rearrangement, intramolecular
cyclization and recyclization.
Reaction of acetonide I with methoxycarbonyl-
methylenetriphenylphosphorane. To a solution of
0.1 g (0.53 mmol) of acetonide I in 5 ml of anhydrous
benzene was added by portions 0.26 g (0.79 mmol) of
methoxycarbonylmethylenetriphenylphosphorane, and the
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 42 No. 11 2006

UNCOMMON TRANSFORMATIONS OF METHYL(1S,2S,3R,4R)-2,3-ISOPROPYLIDENEDIOXY-5...
1703
mixture was stirred at boiling till complete conversion of column chromatography on SiO2 (eluent petroleum ether).
the initial acetonide (TLC monitoring, 2 h). On evaporating Yield 1.95 g (79.6%), colorless oily substance, Rf 0.36
the solvent in a vacuum the residue was subjected to (petroleum ether–ethyl acetate, 7:3), [α]D20 –11.9° (c 1.0,
column chromatography on SiO2 to obtain 0.016 g (12.3%) CHCl3). IR spectrum, ν, cm–1: 1050 (C–O), 1745 (C=O).
of ester IIa and 0.10 g (76.7%) of ester IIb (1:6, GLC) 1H NMR spectrum (CDCl3), δ, ppm (J, Hz): 1.35 s (3H,
as oily fluids.
Me), 1.55 s (3H, Me), 2.62 d.d (1H, H2A, 3J2A,2' 6.9, 2J2A,2Β
15.9),2.72 d.d (1H, H2B, 3J2A,2' 5.6, 2J2A,2B 15.9), 3.25 d.d
Methyl (2R,3S,4R,5R)-5-hydroxymethyl-3,4-
isopropylidenedioxy-2-tetrahydrofurylacetate (IIa).
Rf 0.33 (CHCl3–MeOH, 97:3, average of 3 measure-
ments), [α]D20 +3.3° (c 1.0, CHCl3). IR spectrum, ν, cm–1:
1730 (C=O), 3470 (OH). 1H NMR spectrum (CD2Cl2),
δ, ppm (J, Hz): 1.35 s (3H, Me), 1.50 s (3H, Me), 2.2 br.s
(2H, H1"B, 3J1"B,5' 5.3, 2J1"A,1"B 10.4), 3.28 d.d (2H, H1"A
,
3J1"A,5' 4.4, 2J1"A,1"B 10.4), 3.71 s (3H, OMe), 3.91d.d (1H,
H5', 3J5’4' = 3J5',1"A = 4.4, 3J5',1"B 5.3), 4.30 d.d.d (1H, H2',
3
3
3
3J2',3' 4.0. J2',2Β 5.6, J2',2A 6.8), 4.5 d.d (1H, H3', J3',2'
4.0, 3J3',4' 6.7), 4.71 d.d (1H, H4', 3J4',5' 4.4, 3J4',3' 6.7).
13C NMR spectrum (CDCl3), δ, ppm: 7.11 (C1"), 25.52
(Me), 27.34 (Me), 38.12 (C2) 51.84 (OMe), 80.91 (C2'),
81.60 (C5'), 82.84 (C3'), 84.14 (C4'), 114.40 (Ci-Pr), 171.30
(C1). Found, %: C 37.28; H 4.62; I 35.40. C11H17IO5.
Calculated, %: C 37.10; H 4.81; I 35.63.
(1H, OH), 2.67 d.d (1H, H2A, J2A,2' 9.5, J2A,2Β 13.5),
2.73 d.d (1H, H2B, 3J2Β,2' 3.5, 2J2Β,2A 13.5), 3.61 d (2H,
H1", 3J1",5' 6.9), 3.70 s (3H, OMe), 4.05 t (1H, H5', 3J5',1"
6.9), 4.35 d.d.d (1H, H2', 3J2',2 3.5, 3J2',3' 4.1, 3J2',2A 9.5),
4.60 d (1H, H4', 3J4',3' 6.1), 4.75 d.d (1H, H3', 3J3',2' 4.1,
3J3',4' 6.1). 13C NMR spectrum (CD2Cl2), δ, ppm: 25.06
3
2
Methyl (2R,3S,4R,5R)-3,4-isopropylidenedioxy-
(Me), 26.33 (Me), 34.67 (C2) 51.95 (OMe), 62.12 (C1"), 5-p-toluenesulfonylmethyl-2-tetrahydrofurylacetate
77.28 (C2'), 81.76 (C5'), 82.94 (C3'), 84.62 (C4'), 112.89 (IV). To a stirred at 0°C solution of 1 g (4.06 mmol) of
(Ci-Pr), 171.95 (C1).
alcohol IIb in 15 ml of anhydrous pyridine was added by
portions 1.55 g (8.10 mmol) of TsCl. The reaction mixture
was stirred at room temperature for 20 h (TLC
monitoring), then it was poured into cold water, and
reaction products were extracted into chloroform. The
extract was dried over Na2SO4 and concentrated in
a vacuum, the residue was subjected to column
chromatography on SiO2 to give 1.44 g (89%) of tosylate
IV, Rf 0.22 (petroleum ether–ethylacetate, 7:3), [α]D25
+4.2° (c 1.0, CHCl3). IR spectrum, ν, cm–1: 1100 (C–O),
1190, 1370 (S=O), 1720, 1740 (C=O), 1600 (Ar). 1H NMR
spectrum (CD2Cl2), δ, ppm (J, Hz): 1.25 s (3H, Me),
1.48 s (3H, Me), 2.40 s (3H, MeAr) 2.52 t (1H, H2A, 3J2A,2'
7.0, 2J2A,2Β 15.9), 2.58 t (1H, H2Β, 3J2B,2' 5.6, 2J2B,2A 15.9),
3.62 s (3H, OMe), 4.05–4.07 m (3H, H5', 2H1"), 4.23 d.d.d
(1H, H2', 3J2',3' 4.2, 3J2',2B 5.6, 3J2',2A 7.0), 4.45 d.d (1H,
Methyl (2S,3S,4R,5R)-5-hydroxymethyl-2,3-
isopropylidenedioxy-2-tetrahydrofurylacetate (IIb).
Rf 0.49 (CHCl3–MeOH, 97:3, average of 3 measure-
ments), [α]D20 –5.2° (c1.0, CHCl3). IR spectrum, ν, cm–1:
1
1745 (C=O), 3420 (OH). H NMR spectrum (CDCl3),
δ, ppm (J, Hz): 1.34 s (3H, Me), 1.53 s (3H, Me),
2.62 d.d (1H, H2A, 3J2A,2' 6.7, 2J2A,2Β 16.0), 2.86 d.d (1H,
H2B, 3J2A,2' 4.9, 2J2A,2B 16.0), 3.62 d.d (2H, H1"A, 3J1"A,5'
3.9, 2J1"A,1"B 11.7), 3.71 s (3H, OMe), 3.82 d.d (2H, H1"B
,
2
3
3J1"B,5' 3.9, J1"A,1"B 11.7), 4.08 q (1H, H5', J5',1" 6.9),
4.42 d.d.d (1H, H2', J2',2Β = J2',3' = 4.9, J2',2A 6.7),
3
3
3
4.53 d.d (1H, H3', 3J3',2' 4.9, 3J3',4' 6.7), 4.74 d.d (1H, H4',
3
3J4',5' 3.9, J4',3' 6.7). 13C NMR spectrum (CDCl3), δ,
ppm: 25.48 (Me), 26.43 (Me), 37.60 (C2), 51.95 (OMe),
62.67 (C1"), 80.71 (C2'), 81.60 (C5'), 83.96 (C3'), 84.77
(C4'), 114.40 (Ci-Pr), 171.30 (C1). Found,%: C 53.88;
H 7.52. C11H18O6. Calculated, %: C 53.65; H 7.37.
3
3
3
H3', J3',2' 4.2, J3',4' 6.7), 4.51 d.d (1H, H4', J4',1" 3.5,
3J4,’3' 6.7), 7.36 m (3H, 2Hm, Hï ), 7.76 d (2H, HO, J 8.5).
13C NMR spectrum (CD2Cl2), δ, ppm: 21.69 (MeAr),
25.47 (Me), 27.39 (Me), 36.28 (C2), 51.91 (OMe), 69.91
(C1'’), 81.42 (C2' ), 81.73 (C3'), 82.02 (C5'), 84.45 (C4'),
114.87 (Ci-Pr), 128.25 (CO), 130.29 (Cm), 132.79 (Cï ),
145.65 (Cθ), 170.87 (C1). Found, %: C 52.08; H 5.77;
S 7.91. C18H24O9S. Calculated, %: C 51.91; H 5.81;
S 7.70.
Methyl (2R,3S,4R,5R)-3,4-isopropylidenedioxy-
5-iodomethyl-2-tetrahydrofurylacetate (III). To
a solution of 1.70 g (6.90 mmol) of alcohol IIb, 3.90 g
(15.18 mmol) of Ph3P, and 1.40 g (20.70 mmol) of
imidazole in 30 ml of anhydrous toluene was added by
portions at 95°C 3.50 g (13.80 mmol) of fine crystals of
iodine. The reaction mixture was stirred for 1 h, diluted
with an equal volume of ethyl acetate, washed with
a saturated water solution of Na2S2O3, and with H2O.
Reaction of iodide III with DBU. a. To a solution
of 0.2 g (0.56 mmol) of iodide III in 5 ml of anhydrous
The organic layer was dried over Na2SO4, filtered, and benzene was added 0.11 g (0.70 mmol) of DBU, and the
concentrated in a vacuum, the residue was subjected to mixture was stirred at 80°C for 2 h. The solution was
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 42 No. 11 2006

IVANOVA et al.
1704
concentrated in a vacuum, the residue was subjected to
column chromatography on SiO2 (eluent CH2Cl2). We
obtained 0.15 g of a mixture of iodide III and enol V in
a ratio 2:1 (1H NMR data).
ppm (J, Hz): 1.28 s (3H, Me), 1.47 s (3H, Me), 1.52 d.d
(1H, H5endo, 2J5endo,5exo 13.0, 3J5endo,6endo 9.1), 2.12 d.d.d
3
3
2
(1H, H5exo, J5exo,4 5.80, J5exo,6 9.1, J5exo,5endo 13.0),
3
3
2.41 d.d (1H, H6endo, J6endo,5exo 4.8, J6endo,5endo 9.1),
3.72 s (3H, OMe), 4.23 d (1H, H2endo, 3J2endo,3endo 9.5),
4.24 d (1H, H3endo, J3endo,2endo 9.5), 4.67 s (1H, H1).
b. Under similar conditions from 0.2 g (0.56 mmol) of
iodide III and 0.21 g (1.40 mmol) of DBU in 5 ml of
anhydrous benzene 0.09 g (70%) of compound VIII was
obtained.
3
13C NMR spectrum (CDCl3), δ, ppm: 25.15 (Me), 25.90
(Me), 27.86 (C5), 41.96 (C6), 52.41 (OMe), 78.70 (C4),
81.29 (C1), 81.95 (C2), 82.24 (C3), 111.85 (Ci-Pr), 173.03
[C(=O)]. Found, %: C 58.48; H 6.62. C11H16O5.
Calculated, %: C 57.88; H 7.07.
Methyl (2S,3S,4R)-3,4-isopropylidenedioxy-5-
methylene-2-tetrahydrofurylacetate (V). Colorless
oily substance, Rf 0.36 (petroleum ether–ethylacetate,
7:3). 1H NMR spectrum (CDCl3), δ, ppm (J, Hz): 1.37 s
(3H, Me), 1.47 s (3H, Me), 2.59 d.d (1H, H2A, 3J2A,2' 6.0,
2J2A,2B 11.8), 2.62 d.d (1H, H2B, 3J2B,2' 6.2, 2J2Β,2A 11.8),
3.70 s (3H, OMe), 4.26 br.s (1H, H1"A), 4.47 m (1H, H3'),
4.48 br.s (1H, H1"B), 4.62 d.d.d (1H, H2', 3J2',3' 2.0, 3J2',2A
Methyl-{(5R)-2,2-dimethyl-5-[(2R)-oxiranyl]-1,3-
dioxolan-4-ylidene}propionate (X). Rf 0.39 (benzene–
ethyl acetate, 95:5, average of 3 measurements), [α]D20
+17° (c 1.0, CHCl3). IR spectrum, ν, cm–1: 985 (trans-
C=C), 1060, 1080 (C–O), 1740 (C=O). 1H NMR spec-
trum (CD2Cl2), δ, ppm (J, Hz): 1.38 s (3H, Me), 1.50 s
(3H, Me), 2.73 d.d (1H, H2"A, 2J2"A,2"B 15.1, 3J2"A",1 2.5),
2.78 d.d (1H, H2"B, 2J2"B,2"A 15.1, 3J2"B,1" 3.8), 3.0 d.d.d
3
3
6.0, J2',2Β 6.2), 5.08 d (1H, H4', J4',3' 6.0). 13C NMR
spectrum (CDCl3), δ, ppm: 25.63 (Me), 27.07 (Me), 37.90
(C1"), 51.99 (OMe), 79.90 (C5), 82.47 (C3), 82.98 (C4),
86.46 (C1'), 161.47 (C2), 113.54 (Ci-Pr), 170.33 (C2").
3
3
3
(1H, H1", J1",5' 6.3, J1",2"B 3.8, J1",2"A 2.5), 3.09 d.d.d
(1H, H2A, 2J2A,2B 15.8, 3J2A,3 7.0, J2A,5' 1.5), 3.15 d.d.d
5
Methyl 3-(5-acetyl-2,2-dimethyl-1,3-dioxol-4-
yl)propanoate (VIII). Colorless oily substance, Rf 0.33
(benzene–ethyl acetate, 95:5, average of 3 measure-
ments). IR spectrum, ν, cm–1: 1050 (C–O), 1710, 1745
(1H, H2B, 2J2B,2A 15.8, 3J2B,3 7.0, 5J2B,5' 1.5), 3.66 s (3H,
OMe), 4.31 d.q (1H, H5', 3J5',1" 6.3, J5',2A = J5',2B
=
5
5
4J5',3 = 1.5), 4.50 d.d (1H, H3, 3J3,2A = J3,2B 7.0, J3,5'
1.5). 13C NMR spectrum (CD2Cl2), δ, ppm: 25.63 (Me),
26.67 (Me), 30.96 (C2), 45.11 (C2"), 51.96 (OMe),
52.84 (C1"), 76.56 (C5'), 88.94 (C3), 113.32 (Ci-Pr), 152.06
(C4'), 171.61 (C1). Found, %: C 58.20; H 7.25. C11H16O5.
Calculated, %: C 57.88; H 7.07.
3
4
1
(C=O). H NMR spectrum (CDCl3), δ, ppm (J, Hz):
1.55 s (6H, Me), 2.23 s (3H, Me), 2.58 t (2H, H2,
3
3J2,3 7.5), 2.95 t (2H, H3, J3,2 7.5), 3.70 s (3H, OMe).
13C NMR spectrum (CDCl3), δ, ppm: 21.49 (C3), 25.45
(Mei-Pr and C2'), 27.46 (Mei-Pr), 30.88 (C2), 51.60 (OMe),
115.22 (Ci-Pr), 134.90 (C5'), 148.08 (C4'), 173.50 (C1),
189.92 (C1'). Found, %: C 57.65; H 7.28. C11H16O5.
Calculated, %: C 57.88; H 7.07.
Methyl-(Ε)-3-{(4S,5R)-2,2-dimethyl-5-[(1R)-(2-
oxiranyl)]-1,3-dioxolan-4-yl}-2-propenoate (XI).
Rf 0.30 (benzene–ethylacetate, 95:5, average of 3 mea-
surements), [α]D20 –1.2° (c 0.9, CHCl3). IR spectrum, ν,
cm–1: 1035, 1070 (C–O), 1745 (C=O). 1H NMR spectrum
(CD2Cl2), δ, ppm (J, Hz): 1.20 s (3H, Me), 1.35 s (3H,
Reaction of iodide III with t-BuOK. To a solution
of 0.2 g (0.56 mmol) of iodide III in 6 ml of anhydrous
THF at 0°C under an argon atmosphere was added by
portions 0.1 g (0.88 mmol) of t-BuOK. After stirring for
1 h at room temperature (TLC monitoring) the mixture
was filtered and concentrated in a vacuum, the residue
was subjected to column chromatography on SiO2 (eluent
benzene–ethyl acetate, 98:2 > 95:5). We obtained 0.07 g
(54 %) of compound IX, 0.01 g (8%) of enol X, and 0.01
g (8%) ester XI.
3
2
Me), 2.47 d.d (1H, H2"A, J2"A,1" 2.5, J2"A,2"B 5.0),
2.63 d.d (1H, H2"B, 3J2"B,1" 4.0, 2J2"B,2"A 5.0), 2.68 d.d.d
(1H, H1", 3J1",2"A 2.5, 3J1",2"Β 4.0, 3J1",5' 7.4), 3.55 s (3H,
OMe), 3.64 d.d (1H, H5', J5',4' 6.8,3J5',1" 7.4), 4.72 d.d
3
(1H, H4', 4J4',2 1.7, 3J4',3 5.0, 3J4',5' 6.8). 13C NMR spectrum
(CD2Cl2), δ, ppm: 25.08 (Me), 27.49 (Me), 46.09 (C2"),
49.69 (C1"), 51.69 (OMe), 76.71 (C5'), 79.08 (C4'), 110.10
(Ci-Pr), 122.78 (C2), 141.92 (C3), 166.17 (C1). Found, %:
C 57.71; H 6.93. C11H16O5. Calculated, %: C 57.88;
H 7.07.
Methyl-2,3-isopropylidenedioxy-7-oxabicyclo-
[2.2.1]heptane-6-carboxylate (IX). Rf 0.19 (benzene–
ethyl acetate, 95:5, average of 3 measurements), [α]D20
–29.9° (c 1.0, CHCl3). IR spectrum, ν, cm–1: 1045, 1090
(C–O–C), 1730 (C=O). 1H NMR spectrum (CDCl3), δ,
Reaction of iodide III with LDA. To a solution of
0.113 g (1.12 mmol) of i-Pr2NH in 3 ml of anhydrous
THF was added 0.66 ml (1.12 mmol) of 1.7 N solution of
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UNCOMMON TRANSFORMATIONS OF METHYL(1S,2S,3R,4R)-2,3-ISOPROPYLIDENEDIOXY-5...
1705
BuLi at –10°C under an argon atmosphere. The reaction
mixture was stirred for 0.5 h at –10°C, then it was cooled
to –50°C , and a solution of 0.2 g (0.56 mmol) of iodide
III in 3 ml of anhydrous THF was added dropwise. The
mixture was stirred at –50°C for 2 h, at 0°C for 0.5 h,
and 1 h at room temperature (TLC monitoring). On
cooling the reaction mixture to –25°C 1 ml of saturated
NH4Cl solution was added, and the solution was
concentrated in a vacuum. The product was extracted
into ethyl acetate, the combined organic extracts were
washed with a saturated NaCl solution, and dried over
Na2SO4. On evaporating the solvent in a vacuum the
residue was subjected to column chromatography on SiO2
(eluent petroleum ether–ethyl acetate, 97:3 > 8:2) to isolate
0.016 g (12.5%) of compound IX and 0.02 g (15.6%) of
enol X.
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Reaction of tosylate IV with t-BuOK. To a solution
of 0.3 g (0.75 mmol) of tosylate IV in 7 ml of anhydrous
THF was added by portions 0.11 g (0.97 mmol) of
t-BuOK at 0°C in an argon atmosphere. The reaction
mixture was stirred for 0.5 h at room temperature (TLC
monitoring), filtered, the filtrate was concentrated, and
the residue was subjected to column chromatography on
SiO2 (eluent petroleum ether–ethyl acetate, 95:5) to isolate
0.07 (40%) of enol X and 0.02 g (11%) of ester XI.
10. Kirchner, J.G., Thin-Layer Chromatography, Perry, E.S., Ed.,
New York: Wiley, 1978, 2nd ed.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 42 No. 11 2006