A straightforward synthesis of glyco-2,7- and 2,8-dienes

Article abstract of DOI:10.1016/j.tet.2006.05.057

In this paper, we report the efficient preparation of carbohydrate-derived 2,7- and 2,8-dienes. By our synthetic approach, we have quickly converted d-glucose 1 to (E)-ethyl-2,3-dideoxy-d-gluco-oct-2-enoate 5, which led to the desired (E)-ethyl-9,9-dibrom

Full text of DOI:10.1016/j.tet.2006.05.057

Tetrahedron 62 (2006) 7756–7761
A straightforward synthesis of glyco-2,7- and 2,8-dienes
*
Franck Dolhem, Nicolas Smiljanic, Catherine Lievre and Gilles Demailly
`
´
Laboratoire des Glucides, UMR 6219, Universite de Picardie Jules Verne, 33 rue Saint-Leu, F-80 039 Amiens, France
Received 21 April 2006; revised 23 May 2006; accepted 24 May 2006
Available online 15 June 2006
Abstract—In this paper, we report the efficient preparation of carbohydrate-derived 2,7- and 2,8-dienes. By our synthetic approach, we have
quickly converted D-glucose 1 to (E)-ethyl-2,3-dideoxy-D-gluco-oct-2-enoate 5, which led to the desired (E)-ethyl-9,9-dibromo-2,3,8,9-
tetradeoxy-4,5,6,7-tetra-O-trimethylsilyl-D-gluco-nona-2,8-dienoate 19 with satisfying yield.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
unsaturated bond (19–25) from the primary hydroxyl group
via a Corey–Fuchs reaction. In this strategy, we used TMS
group as protecting groups for hydroxyls because a transfor-
mation can be carried out by a one-pot procedure to selec-
tively deprotect and then oxidize the primary alcohol.6
Synthesis of well-defined polyhydroxylated chiral building
blocks remains of interest in synthetic chemistry.1 Toward
this goal, the chiral pool is an attractive and economic source
of enantiomerically pure starting materials. The main task
remains to convert efficiently and rapidly these chiral mate-
rials into useful synthetic scaffolds for the construction
of useful ring systems.2 Part of our studies is to start from
carbohydrates to achieve the synthesis of chain-elongated
sugars. A few years ago, we tuned a Wittig type reaction that
allowed us to work on free carbohydrates.3 When aldoses
were reacted with methyl bromoacetate, tri-n-butylphos-
phine, and zinc, they gave the corresponding E-unsaturated
Wittig products in good yields and high stereoselectivity.
Moreover this procedure suppressed classical side reactions.
As a result of these studies, we conclude that it would be
of great value to transpose such smooth conditions to the
reaction with dibromotriphenylphosphonium bromide. This
goal was achieved by overcoming some difficulties, and we
have reported the synthesis of 1,1-dibromo-1-alkenes from
partially protected and unprotected aldoses.4 These com-
pounds were interesting scaffolds that can be used in many
transformations.5 Here we report the efficient synthesis
of (E)-alkyl-9,9-dibromo-D-glyco-nona-2,8-dienoates, (E)-
9,9-dibromo-D-gluco-nona-2,8-dienonitrile, and (E)-ethyl-
8,8-dibromo-D-ribo-octa-2,7-dienoate in a few steps from
commercially available monosaccharides. As shown in
Scheme 1, these 2,7- and 2,8-dienes were readily obtained
from aldoses. Our strategy is based on the prior transforma-
tion of the hemiacetal position from which we generated a
carbon–carbon double bond (5–11) by a Wittig type reaction
and in a second time on the creation of the second
HO
HO
OH
O
R
OH
0,1
n(HO)
n(HO)
0,1
5-11
1-4
OTMS
TMSO
TMSO
R
CHO R
n(TMSO)
0,1
0,1
n(TMSO)
12-18
Br
Br
TMSO
R
n(TMSO)
0,1
19-25
Scheme 1.
2. Results and discussion
2.1. Synthesis of olefins 5–11
The reaction of D-glucose 1 with ethyl bromoacetate, tert-
butyl bromoacetate, methyl bromoacetate or bromoaceto-
nitrile, and tri-n-butylphosphine in the presence of zinc in
refluxing 1,4-dioxane afforded mainly E-unsaturated Wittig
products 5–8 with yields ranging from 52% to 70%. NMR
and mass spectrometry experiments were used to establish
the structure of olefins 5–8. Indeed, as example, the NMR
spectra of 5 exhibited two characteristic peaks 148.2
and 121.6 ppm attributed, respectively, to C-3 and C-2 and
7.06 (dd) and 6.15 (dd) attributed, respectively, to H-3 and
H-2 and with J¼15.7 Hz. So, the mildness of our conditions
Keywords: Carbohydrate-derived 2,7- and 2,8-dienes; Oxidation; Wittig
type reaction; Corey–Fuchs reaction.
* Corresponding author. Tel.: +33 32 282 7661; fax: +33 32 282 7561;
e-mail: catherine.lievre@u-picardie.fr
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.05.057

F. Dolhem et al. / Tetrahedron 62 (2006) 7756–7761
7757
allowed us to form E-olefin on naked aldoses, preventing
formation of C-glycosides. 2-Deoxy-D-glucose 2 treated
with ethyl bromoacetate, tri-n-butylphosphine in the pres-
ence of zinc in refluxing 1,4-dioxane led to the desired
compound 9 in 80% yield. It appears that from 2-deoxy-D-
glucose 2 the yield was better than the one for D-glucose 1
in this Wittig type reaction. When these conditions were ap-
plied to D-mannose 3 and 2-deoxy-D-ribose 4, the expected
olefins 10 and 11 were obtained in 70% and 73% yields,
respectively (Scheme 2, Table 1).
results. The prior isolation of the persilylated compound
12 was not a positive solution either, due to the relative insta-
bility of the TMS groups on silica gel and use of fluorisil as
a separative agent was not practicable enough on a reason-
able scale. We then searched for a powerful silylating
reagent, which would in the same time create only easily
removable by-products. We turned our focus to N,O-bis-(tri-
methylsilyl)carbamate, and indeed BSC was the reactant of
choice since the only by-products of silylation are the gases
NH3 and CO2 and the products can be used in subsequent
reactions without any treatment but a simple removal of the
solvent.8 (Scheme 3, Table 2)
HO
HO
O
OH
R
OH
OTMS
a
HO
TMSO
n(HO)
n(HO)
0,1
0,1
R
OH
R
1-4
5-11
R : CO2Et, CO2t-Bu, CO2Me, CN
a
n(TMSO)
0,1
0,1
n(HO)
5-11
12-18
Br
Br
R
Scheme 2. Synthesis of olefins 5–11. Reagents and conditions: (a) BrCH2R
(2 equiv), n-Bu3P (2 equiv), Zn (2 equiv), 1,4-dioxane, reflux.
TMSO
b
Table 1. Synthesis of olefins 5–11
0,1
n(TMSO)
Aldoses 1–4
Olefins 5–11
HO
Yieldsa (%)
19-25
OH
Scheme 3. Synthesis of dienes 19–25. Reagents and conditions: (a) BSC
(1.2 equiv per OH), TBAF (0.01 equiv), NMP, rt. (b) (i) (COCl)2 (3 equiv),
DMSO (6 equiv), CH2Cl2, ꢀ70 ꢁC then Et3N, (ii) Ph3PCHBr3 (2.2 equiv),
t-BuOK (2.1 equiv), THF, rt.
R
HO
O
HO
HO
HO
69
52
70
70
OH
OH
5 : R = CO2Et
6 : R = CO2t-Bu
7 : R = CO2Me
8 : R = CN
HO
OH
1
Table 2. Synthesis of dienes 19–25
Olefins 5–11
OR1
Dienes 19–25
Yieldsa (%)
HO
HO
HO
HO
HO
OH
R1O
R1O
O
O
CO2Et
R
OH
80
Br
Br
TMSO
TMSO
HO
HO
9
2
CO2R
R1O
OR1
59
69
56
49
HO
HO
OH
5 R1 = H, R = CO2Et
6 R1 = H, R = CO2t-Bu
7 R1 = H, R = CO2Me
8 R1 = H, R = CN
CO2Et
TMSO
OTMS
OH
HO
HO
70
73
19 R = CO2Et
20 R = CO2t-Bu
21 R = CO2Me
22 R = CN
HO
HO
HO
OH
OH
10
3
12 R1 = TMS, R = CO2Et
13 R1 = TMS, R = CO2t-Bu
14 R1 = TMS, R = CO2Me
15 R1 = TMS, R = CN
O
OH
CO2Et
OH
HO
4
HO
Yield represents isolated yield.
11
Br
OR1
R1O
R1O
a
Br
CO2Et
TMSO
TMSO
CO2Et
2.2. Synthesis of 2,7- and 2,8-dienes 19–25
59
R1O
TMSO
9 R1 = H
The activated DMSO reagents, well-known for oxidizing
alcohol to the corresponding carbonyl compounds under
mild conditions, can also oxidize trimethyl and triethylsilyl
ethers.5 Furthermore, primary trimethyl and triethylsilyl
ethers are more reactive than their secondary analogues,
allowing the selective oxidation of the former in the presence
of the latter by the Swern reagent, oxalyl chloride, a good
activator for DMSO.7 So, in a three-step procedure on olefin
5, we carried out a standard silylation (trimethylsilyl chlo-
ride, triethylamine in dichloromethane at room temperature)
followed by a Swern oxidation and an addition of dibromo-
triphenylphosphonium bromide, t-BuOK in THF. Unfortu-
nately we could not recover more than 30% of the desired
diene 19. TLC monitoring of the reaction showed that the
silylation step was neither clean nor complete. Reaction with
HMDS as the silylating reagent leaded to the same kind of
16 R1 = TMS
23
Br
OR1
R1O
R1O
Br
CO2Et
TMSO
CO2Et
TMSO
50
57
R1O
OR1
TMSO
OTMS
10 R1 = H
17 R1 = TMS
24
Br
OR1 CO2Et
R1O
Br
CO2Et
TMSO
R1O
11 R1 = H
TMSO
18 R1 = TMS
25
a
Yield represents isolated yield from persylilated olefins 12–18.

7758
F. Dolhem et al. / Tetrahedron 62 (2006) 7756–7761
We have tested these silylation conditions (BSC, TBAF
in catalytic quantity in 1-methyl-2-pyrrolidinone (NMP) at
room temperature). So the starting material 5 was suc-
cessfully converted into 19 (59% yield) by this sequence
involving silylation with BSC followed by Swern oxidation
and an addition of dibromotriphenylphosphonium bromide,
t-BuOK in THF. The structure of 19 was confirmed by
NMR spectroscopy experiments, with the characteristic
resonances observed at d¼149.2, 139.7, 120.0, 89.8 ppm
attributed to C-3, C-8, C-2, C-9, respectively, and those at
d¼7.23, 6.60, 5.97 ppm attributed to H-3, H-8, H-2, respec-
tively. We then extended this three-step procedure to the
other olefins (6–11) described above, converting them into
their corresponding 2,7- and 2,8-dienes. These conditions
on olefins derived from D-glucose 6–9 afford the desired
compounds 20–23 with satisfying yields. When the reaction
is performed on olefins 10 and 11 derived from D-mannose
and D-ribose, respectively, the corresponding dienes are
isolated with 50% and 57% yields, respectively.
3.1.1. Preparation of olefins 5–11. General procedure 1: To
an anhydrous 1,4-dioxane solution (3.6 mL, 1 mmol) of zinc
(2 equiv) were successively added tri-n-butylphosphine
(2 equiv), ethyl bromoacetate or tert-butyl bromoacetate or
bromonitrile (2 equiv), and starting material (1–4). The reac-
tion was stirred under an argon atmosphere and allowed
to reflux. The reaction was monitored by TLC, and after
completion the mixture was cooled to room temperature
and filtered on sintered glass. After concentration, the crude
residue was purified by flash chromatography.
3.1.1.1. (E)-Ethyl-2,3-dideoxy-D-gluco-oct-2-enoate (5).
The compound 5 was prepared by general procedure 1 from
D-glucose 1 (1.37 g, 7.65 mmol). The reaction was completed
after 1 h. The crude residue was purified by flash chromato-
graphy (CH2Cl2/MeOH 95:5, 90:10, and then 85:15), and
5 was obtained as a colorless oil (1.32 g, 69%). Rf¼0.44
(CH2Cl2/MeOH 80:20); [a]2D7 ꢀ90 (c 1.0, MeOH); IR: nmax
1
3300, 1780, 1640, 1250, 1150, and 960 cmꢀ1; H NMR
(CD3OD): d 7.06 (dd, 1H, J¼5.3, 15.7 Hz, 3-H), 6.15 (dd,
1H, J¼1.6, 15.7 Hz, 2-H), 4.50 (dt, 1H, J¼1.6, 5.3, 5.3 Hz,
4-H), 4.20 (q, 2H, OCH2CH3), 3.80 (m, 2H, 5-H, 8a-H),
In summary, several polyhydroxylated 2,7- and 2,8-dienes
were prepared in a versatile manner in four steps from com-
mercially available monosaccharides with satisfying yields.
The quickness and efficiency of this methodology to prepare
functionalized chiral polyols is noticeable. Such compounds
are interesting scaffolds, in particular for the obtaining of
polyhydroxylated carbocycles and for the construction of
bridged and fused bicyclic systems. Indeed, a study toward
their cyclization is currently in progress in our laboratory
and any interesting result will be reported in due course.
As well, we are pursuing our study on conversion of carbo-
hydrates in interesting polyhydroxylated chiral scaffold
derivatives.
3.61 (m, 3H, 6-H, 7-H, 8b-H), 1.20 (t, 3H, OCH2CH3); 13
C
NMR (CD3OD): d 167.2, 148.2, 121.6, 72.9, 72.9, 72.7,
71.6, 63.7, 60.7, 13.6; Anal. Calcd for C10H18O7: C, 48.00;
H, 7.25. Found: C, 48.29; H, 7.37; MS: m/z 273.2 [M+Na]+.
3.1.1.2. (E)-tert-Butyl-2,3-dideoxy-D-gluco-oct-2-enoate
(6). The compound 6 was prepared by general procedure 1
from D-glucose 1 (1 g, 5.55 mmol). The reaction was com-
pleted after 1 h. The crude residue was purified by flash chro-
matography (CH2Cl2/MeOH 90:10), and 6 was obtained as
a colorless oil (0.8 g, 52%). Rf¼0.4 (CH2Cl2/MeOH 80:20);
[a]2D4 ꢀ39 (c 1.0, MeOH); IR: nmax 3300, 1760, 1630, 1250,
1
1150, and 960 cmꢀ1; H NMR (CD3OD): d 7.01 (dd, 1H,
J¼5.5, 15.6 Hz, 3-H), 6.03 (dd, 1H, J¼1.6, 15.6 Hz, 2-H),
4.39 (ddd, 1H, J¼1.6, 5.5, 6.2 Hz, 4-H), 3.78 (dd, 1H,
J¼1.7, 4.2 Hz, 8a-H), 3.68 (m, 1H, 5-H), 3.63 (m, 3H, 6-H,
7-H, 8b-H), 1.52 (s, 9H, OC(CH3)3); 13C NMR (CD3OD):
d 167.0, 147.0, 123.3, 81.7, 73.9, 73.8, 72.9, 72.7, 64.8,
28.4; Anal. Calcd for C12H22O7: C, 51.79; H, 7.97. Found:
C, 51.89; H, 8.11; MS: m/z 301.3 [M+Na]+.
3. Experimental
3.1. General
Unless otherwise specified, materials were purchased from
commercial suppliers and used without further purification.
THF was distilled from lithium aluminum hydride immedi-
ately before use. CH2Cl2 was distilled from calcium chloride
under argon. Moisture sensitive reactions were conducted in
oven-dried glassware under an argon atmosphere. Flash
chromatography was carried out on Kieselgel 60 (230–400
mesh, Merck) and analytical thin-layer chromatography
(TLC) was performed on E. Merck glass-backed silica gel
sheets (Silica Gel 60 F254). Melting points are uncorrected.
Optical rotations were measured using a sodium lamp
(l¼589 nm) and are uncorrected. 1H and 13C NMR spectra
were recorded at 300 and 75 MHz, respectively. Spectra
were recorded in CDCl3, C5D5N, D2O, or CD3OD and
chemicals shifts (d) were expressed in parts per million rela-
tive to residual CHCl3 or an internal standard. All signals in
13C NMR spectra were assigned through C,H-correlated
spectra. IR spectra were recorded as neat films (NaCl cell)
and KBr pellets (for solids). Infusion electrospray mass
spectra in the positive-ion mode were obtained with an up-
dated (3.6 GHz TDC) Q-TOF hybrid quadrupole-time-of-
flight instrument, equipped with a pneumatically assisted
electrospray ion source (Z-spray).
3.1.1.3. (E)-Methyl-2,3-dideoxy-D-gluco-oct-2-enoate
(7). The compound 7 was prepared by general procedure 1
from D-glucose 1 (1 g, 5.55 mmol). The reaction was com-
pleted after 1 h. The crude residue was purified by flash chro-
matography (CH2Cl2/MeOH 85:15), and 7 was obtained
as a colorless oil (0.91 g, 70%). Rf¼0.38 (CH2Cl2/MeOH
80:20); [a]2D7 ꢀ60 (c 1.0, MeOH); IR: nmax 3300, 1780,
1
1640, 1250, 1150, and 960 cmꢀ1; H NMR (D2O): d 7.01
(dd, 1H, J¼5.7, 15.5 Hz, 3-H), 6.17 (dd, 1H, J¼1.6,
15.5 Hz, 2-H), 4.48 (ddd, 1H, J¼1.5, 1.6, 5.7 Hz, 4-H),
3.85 (dd, 1H, J¼1.5, 1.8 Hz, 5-H), 3.82 (dd, 1H, J¼2.0,
11.7 Hz, 8b-H), 3.73 (ddd, 1H, J¼2.2, 6.1, 6.5 Hz, 7-H),
3.63 (dd, 1H, J¼6.1, 11.7 Hz, 8a-H), 2.69 (dd, 1H, J¼1.8,
6.5 Hz, 6-H), 3.80 (s, 3H, OCH3); 13C NMR (D2O):
d 172.0, 150.4, 124.8, 73.9, 73.7, 72.8, 72.3, 64.6, 53.9;
Anal. Calcd for C9H16O7: C, 45.76; H, 6.83. Found: C,
45.89; H, 6.98; MS: m/z 259.2 [M+Na]+.
3.1.1.4. (E)-2,3-Dideoxy-D-gluco-oct-2-enonitrile (8).
The compound 8 was prepared by general procedure 1

F. Dolhem et al. / Tetrahedron 62 (2006) 7756–7761
7759
from D-glucose 1 (1 g, 5.55 mmol). The reaction was com-
pleted after 1 h. The crude residue was purified by flash chro-
matography (CH2Cl2/MeOH 95:5), and 8 was obtained
as a colorless oil (0.796 g, 70%). Rf¼0.33 (CH2Cl2/MeOH
80:20); [a]2D5 ꢀ11 (c 0.9, MeOH); IR: nmax 3300, 2250,
(dd, 1H, 3.9, 11.3 Hz, 7a-H), 3.60 (ddd, 1H, J¼3.3, 7.1,
8.8 Hz, 5-H), 3.59 (dd, 1H, 6.2, 11.3 Hz, 7b-H), 3.47 (ddd,
1H, J¼3.9, 6.2, 7.1 Hz, 6-H), 2.63 (dddd, 1H, J¼1.5, 3.3,
7.4, 14.7 Hz, 4a-H), 2.37 (dddd, 1H, J¼1.5, 7.4, 8.8,
14.7 Hz, 4b-H), 1.30 (t, 3H, OCH2CH3); 13C NMR
(CD3OD): d 167.2, 147.0, 123.2, 74.8, 71.2, 63.7, 60.3,
36.2, 13.6; Anal. Calcd for C9H16O5: C, 52.93; H, 7.90.
Found: C, 52.99; H, 8.09; MS: m/z 227.3 [M+Na]+.
1600, 1250, 1150, and 960 cmꢀ1 1H NMR (C5D5N):
;
d 7.03 (dd, 1H, J¼4.3, 16.3 Hz, 3-H), 5.82 (dd, 1H, J¼2.0,
16.3 Hz, 2-H), 4.50 (dt, 1H, J¼2.0, 4.3, 5.3 Hz, 4-H), 3.81
(m, 2H, 5-H, 8a-H), 3.62 (m, 3H, 6-H, 7-H, 8b-H); 13C
NMR (C5D5N): d 158.5, 120.0, 100.2, 74.9, 73.8, 72.8,
63.8; Anal. Calcd for C8H13NO5: C, 47.29; H, 6.45; N,
6.89. Found: C, 47.42; H, 6.59; N, 6.91; MS: m/z 226.2
[M+Na]+.
3.1.2. Preparation of persilylated compounds 12–18.
General procedure 2: To the starting material (5–11) dis-
solved in 1-methyl-2-pyrrolidinone (NMP) (1 g/10 mL)
were successively added N,O-bis-(trimethylsilyl)carbamate
(1.2 equiv per OH) and dropwise tetra-n-butylammonium
fluoride (TBAF 1 M solution in THF) (0.01 equiv). The
reaction was stirred under an argon atmosphere for 24 h
at room temperature as monitored by TLC. Methanol was
added (3 mL) and the mixture was concentrated, and the
residue was diluted in hexane (3 mL hexane/1 mL NMP)
and washed with water. The combined organic layers were
dried (Na2SO4) and concentrated. The residue (12–18) was
used in subsequent reactions without further treatment.
3.1.1.5. (E)-Ethyl-2,3,4-trideoxy-D-gluco-oct-2-enoate
(9). The compound 9 was prepared by general procedure 1
from 2-deoxy-D-glucose 2 (1 g, 6.1 mmol). The reaction
was completed after 1 h. The crude residue was purified by
flash chromatography (CH2Cl2/MeOH 95:5), and 9 was
obtained as a solid (1.14 g, 80%). Rf¼0.43 (CH2Cl2/MeOH
85:15); [a]2D3 +17 (c 1.4, MeOH); mp¼114–117 ꢁC; IR:
nmax 3300, 1770, 1640, 1250, 1150, and 960 cmꢀ1 1H
;
NMR (CD3OD): d 7.06 (dt, 1H, J¼3.2, 3.2, 15.7 Hz, 3-H),
6.00 (dt, 1H, J¼1.5, 1.5, 15.7 Hz, 2-H), 4.20 (q, 2H,
OCH2CH3), 3.98 (ddd, 1H, J¼1.7, 5.5, 7.4 Hz, 5-H), 3.80
(dd, 1H, J¼3.0, 10.6 Hz, 8a-H), 3.69 (ddd, 1H, J¼3.0, 5.6,
8.1 Hz, 7-H), 3.63 (dd, 1H, J¼5.6, 10.6 Hz, 8b-H), 3.37
(dd, 1H, J¼1.7, 8.1 Hz, 6-H), 2.49 (m, 2H, 4a-H, 4b-H),
1.30 (t, 3H, OCH2CH3); 13C NMR (CD3OD): d 167.0,
147.0, 123.0, 73.1, 71.9, 69.5, 64.0, 60.4, 36.8, 13.5; Anal.
Calcd for C10H18O6: C, 51.27; H, 7.75. Found: C, 51.43; H,
7.99; MS: m/z 257.3 [M+Na]+.
3.1.2.1. (E)-Ethyl-2,3-dideoxy-4,5,6,7,8-penta-O-tri-
methylsilyl-D-gluco-oct-2-enoate (12). The compound 12
was prepared by general procedure 2 from 5 (1.32 g,
5.27 mmol). The reaction was treated after 24 h. Compound
12 was obtained as a colorless oil. Rf¼0.8 (Hexane/EtOAc
1
95:5); H NMR (CDCl3): d 7.30 (dd, 1H, J¼3.2, 15.7 Hz,
3-H), 6.00 (dd, 1H, J¼2.0, 15.7 Hz, 2-H), 4.45 (ddd, 1H,
J¼2.0, 3.2, 5.6 Hz, 4-H), 4.20 (q, 2H, OCH2CH3), 3.92
(ddd, 1H, J¼3.1, 5.2, 7.7 Hz, 7-H), 3.69 (dd, 1H, J¼3.1,
10.4 Hz, 8a-H), 3.60 (dd, 2H, 5-H, 6-H), 3.53 (dd, 1H,
J¼7.7, 10.4 Hz, 8b-H), 1.20 (t, 3H, OCH2CH3), 0.08–0.15
(s, 45H, Si(CH3)3); 13C NMR (CDCl3): d 167.0, 149.0,
121.0, 77.0, 77.0, 75.9, 74.0, 64.3, 60.5, 14.7, ꢀ0.1–1.4.
3.1.1.6. (E)-Ethyl-2,3-dideoxy-D-manno-oct-2-enoate
(10). The compound 10 was prepared by general procedure
1 from D-mannose 3 (1.5 g, 8.3 mmol). The reaction was
completed after 40 min. The crude residue was purified by
flash chromatography (CH2Cl2/MeOH 95:5, 90:10, and
then 85:15), and 10 was obtained as a colorless oil (1.45 g,
70%). Rf¼0.42 (CH2Cl2/MeOH 85:15); [a]2D8 +20 (c 1.0,
MeOH); IR: nmax 3300, 1780, 1640, 1250, 1150, and
3.1.2.2. (E)-tert-butyl-2,3-dideoxy-4,5,6,7,8-penta-O-
trimethylsilyl-D-gluco-oct-2-enoate (13). The compound
13 was prepared by general procedure 2 from 6 (0.8 g,
2.88 mmol). The reaction was treated after 24 h. Compound
13 was obtained as a colorless oil. Rf¼0.8 (Hexane/EtOAc
960 cmꢀ1
;
1H NMR (CD3OD): d 8.02 (dd, 1H, J¼4.0,
1
15.7 Hz, 3-H), 6.70 (dd, 1H, J¼1.8, 15.7 Hz, 2-H), 5.18
(ddd, 1H, J¼1.8, 4.0, 8.3 Hz, 4-H), 4.85 (dd, 1H, J¼2.0,
8.2 Hz, 6-H), 4.60 (m, 1H, 7-H), 4.68 (dd, 1H, J¼2.0,
8.3 Hz, 5-H), 4.50 (dd, 1H, J¼3.8, 10.9 Hz, 8a-H), 4.35
(dd, 1H, J¼2.9, 10.9 Hz, 8b-H), 4.20 (q, 2H, OCH2CH3),
1.20 (t, 3H, OCH2CH3); 13C NMR (CD3OD): d 167.1,
153.0, 120.9, 74.0, 73.7, 72.0, 72.0, 61.8, 60.4, 14.5; Anal.
Calcd for C10H18O7: C, 48.00; H, 7.25. Found: C, 48.23;
H, 7.39; MS: m/z 273.3 [M+Na]+.
95:5); H NMR (CDCl3): d 7.01 (dd, 1H, J¼5.5, 15.6 Hz,
3-H), 6.03 (dd, 1H, J¼1.6, 15.6 Hz, 2-H), 4.39 (ddd, 1H,
J¼1.6, 5.5, 6.2 Hz, 4-H), 3.78 (dd, 1H, J¼1.7, 4.2 Hz,
8a-H), 3.68 (m, 1H, 5-H), 3.63 (m, 3H, 6-H, 7-H, 8b-H),
1.52 (s, 9H, OC(CH3)3), 0.30–1.12 (s, 45H, Si(CH3)3);
13C NMR (CDCl3): d 166.7, 147.2, 122.7, 80.4, 77.8,
77.3, 75.3, 74.0, 64.1, 28.5, 0.1–0.2.
3.1.2.3. (E)-Methyl-2,3-dideoxy-4,5,6,7,8-penta-O-tri-
methylsilyl-D-gluco-oct-2-enoate (14). The compound 14
was prepared by general procedure 2 from 7 (0.91 g,
3.88 mmol). The reaction was treated after 24 h. Compound
14 was obtained as a colorless oil. Rf¼0.85 (Hexane/EtOAc
3.1.1.7. (E)-Ethyl-2,3,4-trideoxy-D-ribo-hept-2-enoate
(11). The compound 11 was prepared by general procedure
1 from 2-deoxy-D-ribose 4 (1 g, 7.45 mmol). The reaction
was completed after 1 h. The crude residue was purified by
two consecutive flash chromatographies (CH2Cl2/MeOH
98:2, 97:3, 95:5, and then EtOAc), and 11 was obtained
as a colorless oil (1.13 g, 73%). Rf¼0.63 (CH2Cl2/MeOH
90:10); [a]2D6 ꢀ7 (c 1.8, CHCl3); IR: nmax 3300, 1780,
1
95:5); H NMR (CDCl3): d 7.26 (dd, 1H, J¼3.5, 15.7 Hz,
3-H), 5.95 (dd, 1H, J¼2.6, 15.7 Hz, 2-H), 4.40 (ddd, 1H,
J¼1.4, 2.6, 3.5 Hz, 4-H), 3.86 (m, 2H, 7-H, 8b-H), 3.60
(s, 3H, OCH3), 3.58 (dd, 1H, J¼1.7, 6.4 Hz, 6-H), 3.50
(dd, 1H, J¼1.4, 1.7 Hz, 5-H), 3.48 (dd, 1H, J¼6.0,
11.6 Hz, 8a-H), ꢀ0.9–0.1 (s, 45H, Si(CH3)3); 13C NMR
(CDCl3): d 167.0, 149.1, 120.1, 76.8, 76.8, 75.7, 73.9,
64.1, 51.4, ꢀ0.3–1.6.
1650, 1250, 1150, and 960 cmꢀ1 1H NMR (CD3OD):
;
d 7.08 (dt, 1H, J¼7.4, 7.4, 15.7 Hz, 3-H), 5.94 (dt, 1H,
J¼1.5, 1.5, 15.7 Hz, 2-H), 4.18 (q, 2H, OCH2CH3), 3.75

7760
F. Dolhem et al. / Tetrahedron 62 (2006) 7756–7761
3.1.2.4. (E)-2,3-Dideoxy-4,5,6,7,8-penta-O-trimethyl-
20 min, the reaction mixture was warmed to room tempera-
ture, and a saturated solution of NH4Cl was added. The mix-
ture was extracted and the combined organic layers were
washed with water, dried (Na2SO4), and concentrated. The
residue was diluted in dry THF. The flask was then immersed
in a water bath. Dibromomethylenetriphenylphosphorane,
prepared from dibromomethyltriphenylphosphonium bro-
mide4 (2.2 equiv) and t-BuOK (2.1 equiv) in THF (10 mL)
at room temperature under an argon atmosphere for 15 min,
was then added dropwise. After filtration with Buchner, the
mixture was concentrated and the residue (19–25) was puri-
fied by flash chromatography.
silyl-D-gluco-oct-2-enonitrile (15). The compound 15
was prepared by general procedure 2 from 8 (0.79 g,
3.9 mmol). The reaction was treated after 24 h. Compound
15 was obtained as a colorless oil. Rf¼0.8 (Hexane/EtOAc
1
95:5); H NMR (CDCl3): d 7.30 (dd, 1H, J¼4.3, 15.9 Hz,
3-H), 5.80 (dd, 1H, J¼2.0, 15.9 Hz, 2-H), 4.45 (ddd, 1H,
J¼2.0, 4.3, 5.6 Hz, 4-H), 3.92 (ddd, 1H, J¼3.3, 5.0,
7.7 Hz, 7-H), 3.81 (dd, 1H, J¼3.3, 10.7 Hz, 8a-H), 3.72
(m, 2H, 5-H, 6-H), 3.62 (dd, 1H, J¼7.7, 10.7 Hz, 8b-H),
0.08–0.15 (s, 45H, Si(CH3)3); 13C NMR (CDCl3): d 157.0,
120.2, 100.4, 77.0, 77.0, 76.0, 74.3, 63.9, 0.1–1.4.
3.1.2.5. (E)-Ethyl-2,3,4-trideoxy-5,6,7,8-tetra-O-tri-
methylsilyl-D-gluco-oct-2-enoate (16). The compound 16
was prepared by general procedure 2 from 9 (1.06 g,
4.53 mmol). The reaction was treated after 24 h. Compound
16 was obtained as a colorless oil. Rf¼0.9 (Hexane/EtOAc
3.1.3.1. (E)-Ethyl-9,9-dibromo-2,3,8,9-tetradeoxy-
4,5,6,7-tetra-O-trimethylsilyl-D-gluco-nona-2,8-dienoate
(19). The compound 19 was prepared by general procedure 3
from 12 (1.32 g, 5.27 mmol). The crude residue was purified
by two consecutive flash chromatographies (Hexane/CH2Cl2
75:25 and Hexane/CHCl3 75:25), and 19 was obtained
as a colorless oil (2.14 g, 59%). Rf¼0.8 (Hexane/EtOAc
90:10); [a]2D3 +119 (c 1.0, CH2Cl2); IR (CHCl3): nmax
1
95:5); H NMR (CDCl3): d 6.95 (m, 1H, J¼1.0, 15.7 Hz,
3-H), 5.85 (dt, 1H, J¼1.0, 1.0, 15.7 Hz, 2-H), 4.21 (q, 2H,
J¼8.0 Hz, OCH2CH3), 3.75 (m, 2H, 5-H, 7-H), 3.71 (dd,
1H, J¼4.0, 10.4 Hz, 8b-H), 3.58 (dd, 1H, J¼3.1, 5.4 Hz,
6-H), 3.40 (dd, 1H, J¼6.8, 10.4 Hz, 8a-H), 2.45 (m, 2H,
4a-H, 4b-H), 1.30 (t, 3H, OCH2CH3), 0.1–1.1 (s, 36H,
Si(CH3)3); 13C NMR (CDCl3): d 167.7, 146.9, 123.6, 78.6,
73.6, 74.7, 64.2, 60.5, 37.1, 14.7, 0.1–1.4.
1
1730, 840, and 750 cmꢀ1; H NMR (CDCl3): d 7.23 (dd,
1H, J¼4.1, 15.7 Hz, 3-H), 6.60 (d, 1H, J¼8.7 Hz, 8-H),
5.97 (dd, 1H, J¼1.8, 15.7 Hz, 2-H), 4.46 (m, 1H, 4-H),
4.41 (dd, 1H, J¼2.6, 8.7 Hz, 7-H), 4.20 (q, 2H, J¼7.1 Hz,
OCH2CH3), 3.72 (dd, 1H, J¼2.6, 6.3 Hz, 6-H), 3.44 (t,
1H, J¼6.3, 6.3 Hz, 5-H), 1.28 (t, 3H, OCH2CH3), 0.09–
0.14 (s, 36H, Si(CH3)3); 13C NMR (CDCl3): d 167.0,
149.2, 139.7, 120.0, 89.8, 76.5, 76.0, 75.5, 73.9, 60.5,
14.7, 0.6–0.7; Anal. Calcd for C23H48Br2O6Si4: C, 39.88;
H, 6.98. Found: C, 40.11; H, 6.75; MS: m/z 713.7 [M+Na]+.
3.1.2.6. (E)-Ethyl-2,3-dideoxy-4,5,6,7,8-penta-O-tri-
methylsilyl-D-manno-oct-2-enoate (17). The compound
17 was prepared by general procedure 2 from 10 (1.45 g,
5.79 mmol). The reaction was treated after 24 h. Compound
17 was obtained as a colorless oil. Rf¼0.6 (Hexane/EtOAc
1
95:5); H NMR (CDCl3): d 7.11 (dd, 1H, J¼4.6, 15.6 Hz,
3.1.3.2. (E)-tert-Butyl-9,9-dibromo-2,3,8,9-tetradeoxy-
4,5,6,7-tetra-O-trimethylsilyl-D-gluco-nona-2,8-dienoate
(20). The compound 20 was prepared by general procedure 3
from 13 (0.80 g, 2.88 mmol). The crude residue was purified
by flash chromatography (Hexane/CH2Cl2 60:40), and 20
was obtained as a colorless oil (1.42 g, 69%). Rf¼0.8 (Hex-
ane/EtOAc 90:10); [a]2D7 +29 (c 1.0, CH2Cl2); IR (CHCl3):
3-H), 6.01 (dd, 1H, J¼1.8, 15.6 Hz, 2-H), 4.50 (m, 1H, 4-H),
4.22 (q, 2H, J¼8.1 Hz, OCH2CH3), 3.90 (m, 1H, 5-H), 3.80
(m, 1H, 7-H), 3.78 (m, 1H, 6-H), 3.72 (dd, 1H, J¼4.7,
10.1 Hz, 8a-H), 3.48 (dd, 1H, J¼6.4, 10.1 Hz, 8b-H), 1.18
(t, 3H, OCH2CH3), 0.1–0.3 (s, 45H, Si(CH3)3); 13C NMR
(CDCl3): d 167.1, 149.3, 120.9, 77.4, 76.7, 74.5, 74.2, 63.4,
60.5, 14.7, 0.1–1.4.
1
nmax 1730, 840, and 750 cmꢀ1; H NMR (CDCl3): d 7.05
(dd, 1H, J¼4.3, 15.7 Hz, 3-H), 6.63 (d, 1H, J¼8.8 Hz,
8-H), 5.88 (dd, 1H, J¼1.8, 15.7 Hz, 2-H), 4.40 (m, 1H, 7-H),
4.39 (m, 1H, 4-H), 3.72 (dd, 1H, J¼2.7, 6.2 Hz, 6-H), 3.43
(t, 1H, J¼6.2 Hz, 5-H), 1.52 (s, 9H, OC(CH3)3), 1.2–0.3
(s, 36H, Si(CH3)3); 13C NMR (CDCl3): d 166.3, 147.6,
139.5, 122.7, 80.4, 80.3, 77.8, 77.4, 75.3, 74.0, 28.5, 0.0–
0.2; Anal. Calcd for C25H52Br2O6Si4: C, 41.66; H, 7.27.
Found: C, 41.79; H, 7.57; MS: m/z 743.8 [M+Na]+.
3.1.2.7. (E)-Ethyl-2,3,4-trideoxy-5,6,7-tri-O-trimethyl-
silyl-D-ribo-hept-2-enoate (18). The compound 18 was pre-
pared by general procedure 2 from 11 (1.03 g, 5.04 mmol).
The reaction was treated after 24 h. Compound 18 was ob-
1
tained as a colorless oil. Rf¼0.7 (Hexane/EtOAc 95:5); H
NMR (CDCl3): d 6.94 (dt, 1H, J¼7.7, 7.7, 15.6 Hz, 3-H),
5.82 (dt, 1H, J¼0.5, 0.5, 15.6 Hz, 2-H), 4.20 (q, 2H,
J¼8.1 Hz, OCH2CH3), 3.77 (dt, 1H, J¼4.7, 4.7, 7.2 Hz,
5-H), 3.58 (dt, 1H, J¼4.7, 4.7, 12.0 Hz, 6-H), 3.48 (m,
2H, 7a-H, 7b-H), 2.35 (m, 2H, 4a-H, 4b-H), 1.20 (t, 3H,
OCH2CH3), 0.1–0.2 (s, 27H, Si(CH3)3); 13C NMR
(CDCl3): d 167.0, 147.0, 123.7, 77.0, 72.7, 64.3, 60.5,
36.4, 14.7, 0.1–1.4.
3.1.3.3. (E)-Methyl-9,9-dibromo-2,3,8,9-tetradeoxy-
4,5,6,7-tetra-O-trimethylsilyl-D-gluco-nona-2,8-dienoate
(21). The compound 21 was prepared by general procedure 3
from 14 (0.91 g, 3.88 mmol). The crude residue was purified
by flash chromatography (Hexane/CH2Cl2 60:40), and 21
was obtained as a colorless oil (1.47 g, 56%). Rf¼0.8 (Hex-
ane/EtOAc 95:5); [a]D25 +89 (c 1.0, CHCl3); IR (CHCl3):
3.1.3. Preparation of 2,7- and 2,8-dienes 19–25. General
procedure 3: To a CH2Cl2 (10 mL) solution of oxalyl chlo-
ride (3 equiv) was added dropwise dry methyl sulfoxide
(6 equiv) at ꢀ70 ꢁC under an argon atmosphere. After
5 min under stirring, a solution of substrate (12–18) in
CH2Cl2 (5 mL) was added. The reaction was monitored by
TLC. After 30 min, triethylamine (9 equiv) was then care-
fully added. After being stirred at low temperature for
1
nmax 1730, 840, and 750 cmꢀ1; H NMR (CDCl3): d 7.25
(dd, 1H, J¼4.2, 15.7 Hz, 3-H), 6.63 (d, 1H, J¼8.7 Hz,
8-H), 5.97 (dd, 1H, J¼1.7, 15.7 Hz, 2-H), 4.44 (m, 2H,
4-H, 7-H), 3.70 (m, 4H, 6-H, OCH3), 3.44 (t, 1H, J¼6.0,
6.0 Hz, 5-H), ꢀ0.9–0.1 (s, 36H, Si(CH3)3); 13C NMR
(CDCl3): d 167.4, 149.7, 144.0, 120.0, 89.8, 76.5, 76.1,
75.5, 73.9, 51.7, 0.0; Anal. Calcd for C22H46Br2O6Si4: C,

F. Dolhem et al. / Tetrahedron 62 (2006) 7756–7761
7761
38.93; H, 6.83. Found: C, 39.00; H, 6.78; MS: m/z 701.7
[M+Na]+.
0.09–0.14 (s, 36H, Si(CH3)3); 13C NMR (CDCl3): d 167.0,
148.6, 138.9, 122.1, 91.7, 76.6, 74.6, 73.8, 60.3, 14.5, 0.9–
1.1; Anal. Calcd for C23H48Br2O6Si4: C, 39.88; H, 6.98.
Found: C, 40.11; H, 6.75; MS: m/z 713.7 [M+Na]+.
3.1.3.4.
(E)-9,9-dibromo-2,3,8,9-tetradeoxy-4,5,6,7-
tetra-O-trimethylsilyl-D-gluco-nona-2,8-dienonitrile (22).
The compound 22 was prepared by general procedure 3
from 15 (0.79 g, 3.90 mmol). The crude residue was purified
by flash chromatography (Hexane/CH2Cl2 75:25), and 22
was obtained as a colorless oil (1.23 g, 49%). Rf¼0.75 (Hex-
ane/EtOAc 90:10); [a]2D3 +49 (c 1.0, CHCl3); IR (CHCl3):
3.1.3.7. (E)-Ethyl-8,8-dibromo-2,3,4,7,8-pentadeoxy-
5,6-di-O-trimethylsilyl-D-ribo-octa-2,7-dienoate (25). The
compound 25 was prepared by general procedure 3 from
18 (1.03 g, 5.04 mmol). The crude residue was purified by
flash chromatography (Pentane/Et2O 98:2), and 25 was
obtained as a colorless oil (1.44 g, 57%). Rf¼0.8 (Hexane/
EtOAc 95:5); [a]D23 ꢀ13 (c 0.9, CHCl3); IR (CHCl3): nmax
1
nmax 2230, 1730, 840, and 750 cmꢀ1; H NMR (CDCl3):
d 7.03 (dd, 1H, J¼4.2, 15.7 Hz, 3-H), 6.48 (d, 1H,
J¼8.8 Hz, 8-H), 6.00 (dd, 1H, J¼1.9, 15.7 Hz, 2-H), 4.61
(dd, 1H, J¼2.5, 8.8 Hz, 7-H), 4.45 (m, 1H, 4-H), 3.73 (dd,
1H, J¼2.5, 6.1 Hz, 6-H), 3.47 (t, 1H, J¼6.1, 6.1 Hz, 5-H),
0.09–0.14 (s, 36H, Si(CH3)3); 13C NMR (CDCl3): d 158.2,
140.1, 120.0, 100.0, 90.0, 75.0, 74.9, 73.5, 72.9, 0.6–0.7;
Anal. Calcd for C21H43Br2NO4Si4: C, 39.06; H, 6.71; N,
2.17. Found: C, 39.33; H, 6.57; N, 2.23; MS: m/z 668.7
[M+Na]+.
1
1728, 840, and 750 cmꢀ1; H NMR (CDCl3): d 6.95 (ddd,
1H, J¼7.2, 7.8, 15.7 Hz, 3-H), 6.35 (d, 1H, J¼8.0 Hz,
7-H), 5.85 (d, 1H, J¼15.7 Hz, 2-H), 4.20 (m, 3H, 6-H,
OCH2CH3), 3.70 (m, 1H, 5-H), 2.35 (m, 2H, 4a-H, 4b-H),
1.20 (t, 3H, OCH2CH3), 0.49–0.76 (s, 18H, Si(CH3)3); 13C
NMR (CDCl3): d 166.4, 145.8, 139.0, 124.0, 90.6, 76.8,
75.1, 60.3, 36.9, 14.6, 0.4–0.7; Anal. Calcd for
C16H30Br2O4Si2: C, 38.25; H, 6.02. Found: C, 38.33; H,
6.31; MS: m/z 525.4 [M+Na]+.
3.1.3.5. (E)-Ethyl-9,9-dibromo-2,3,4,8,9-pentadeoxy-
5,6,7-tri-O-trimethylsilyl-D-gluco-nona-2,8-dienoate (23).
The compound 23 was prepared by general procedure 3
from 16 (1.06 g, 4.53 mmol). The crude residue was purified
by flash chromatography (Cyclohexane/EtOAc 99:1), and 23
was obtained as a colorless oil (1.6 g, 59%). Rf¼0.5 (Cyclo-
hexane/EtOAc 95:5); [a]2D3 +9 (c 1.1, CHCl3); IR (CHCl3):
Acknowledgements
´
We thank the Conseil Regional de Picardie for financial sup-
port. F.D. is grateful to the French Ministry of Education,
Research, and Technology (MENRT) for a doctoral fellow-
ship.
1
nmax 1730, 840, and 750 cmꢀ1; H NMR (CDCl3): d 6.90
(ddd, 1H, J¼7.7, 7.9, 15.7 Hz, 3-H), 6.53 (d, 1H, J¼9.0 Hz,
8-H), 5.82 (d, 1H, J¼15.7 Hz, 2-H), 4.41 (dd, 1H, J¼3.4,
9.0 Hz 7-H), 4.16 (q, 2H, J¼7.1 Hz, OCH2CH3), 3.68 (m,
1H, 5-H), 3.57 (dd, 1H, J¼3.4, 5.1 Hz, 6-H), 2.48 (m, 1H,
4a-H), 2.31 (m, 1H, 4b-H), 1.19 (t, 3H, OCH2CH3), 0.08–
0.11 (s, 27H, Si(CH3)3); 13C NMR (CDCl3): d 166.3, 146.8,
139.3, 123.5, 90.6, 78.6, 73.8, 73.2, 60.0, 36.4, 14.2, 0.5–
0.6; Anal. Calcd for C20H40Br2O5Si3: C, 39.73; H, 6.67.
Found: C, 39.98; H, 6.83; MS: m/z 627.6 [M+Na]+.
References and notes
1. Bols, M. Carbohydrate Building Blocks; Wiley: New York, NY,
1996.
2. Leger, R.; Hanessian, S. J. Am. Chem. Soc. 1992, 114, 3115–
´
3117; Hydloft, L.; Madsen, R. J. Am. Chem. Soc. 2000, 122,
8444–8452; de Opazo, E.; Marco-Contelles, J. Tetrahedron
Lett. 2000, 41, 2439–2441; J. Org. Chem. 2000, 65, 5416–
5419; Boyer, F.-D.; Nolan, S. P.; Hanna, I. J. Org. Chem.
2001, 66, 4094–4096; Kadota, K.; Takeuchi, M.; Tanjuchi, T.;
Ogasawara, K. Org. Lett. 2001, 3, 1769–1772.
3.1.3.6.
(E)-Ethyl-9,9-dibromo-2,3,8,9-tetradeoxy-
4,5,6,7-tetra-O-trimethylsilyl-D-manno-nona-2,8-dienoate
(24). The compound 24 was prepared by general procedure 3
from 17 (1.45 g, 5.79 mmol). The crude residue was purified
by flash chromatography (Hexane/CH2Cl2 7:3), and 24 was
obtained as a colorless oil (2 g, 50%). Rf¼0.7 (Hexane/
EtOAc 95:5); [a]D23 +9 (c 1.0, CHCl3); IR (CHCl3): nmax
`
´
3. Le Mignot, V.; Lievre, C.; Frechou, C.; Demailly, G.
Tetrahedron Lett. 1998, 39, 983–984.
`
4. Dolhem, F.; Lievre, C.; Demailly, G. Tetrahedron Lett. 2002, 43,
1847–1849.
5. Dolhem, F.; Lievre, C.; Demailly, G. Eur. J. Org. Chem. 2003,
2336–2342; J. Org. Chem. 2004, 69, 3400–3407.
6. Muzart, J. Synthesis 1993, 11–27.
7. Rodriguez, A.; Nomen, M.; Spur, B. W.; Godfroid, J. J.
Tetrahedron Lett. 1999, 40, 5161–5164.
`
1
1730, 840, and 750 cmꢀ1; H NMR (CDCl3): d 7.05 (dd,
1H, J¼4.1, 15.7 Hz, 3-H), 6.57 (d, 1H, J¼8.7 Hz, 8-H),
6.00 (dd, 1H, J¼1.8, 15.7 Hz, 2-H), 4.31 (ddd, 1H, J¼1.8,
4.1, 6.3 Hz, 4-H), 4.28 (dd, 1H, J¼2.6, 8.7 Hz, 7-H), 4.20
(q, 2H, J¼7.1 Hz, OCH2CH3), 3.67 (dd, 1H, J¼2.6, 6.3 Hz,
6-H), 3.56 (t, 1H, J¼6.3 Hz, 5-H), 1.28 (t, 3H, OCH2CH3),
8. Birkhofer, L.; Sommer, P. J. Organomet. Chem. 1975, 99,
C1–C4.