Ni-Catalyzed Formal Carbonyl-Ene Reaction of Terminal Alkenes via Carbon Dioxide Insertion

Article abstract of DOI:10.1055/s-0036-1591845

Nickel catalyzes the multicomponent coupling reaction of terminal alkenes, carbon dioxide, and organoaluminum reagents, leading to the synthesis of homoallylic alcohols in moderate-to-good yields with excellent regio- and stereoselectivities.

Full text of DOI:10.1055/s-0036-1591845

SYNLETT
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© Georg Thieme Verlag Stuttgart · New York
2017, 28, A–E
cluster
A
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Y. Mori et al.
Cluster
Synlett
Ni-Catalyzed Formal Carbonyl-Ene Reaction of Terminal Alkenes
via Carbon Dioxide Insertion
Yasuyuki Moria
Chieko Shigenob
Ying Luob
R2
R2
cat. Ni(cod)2/PCy3
OH
CO2
+
+
Me3Al
R1
C
R1
1,4-dioxane
(1 atm)
Me
Me
Bun Chanb
Gen Onoderab
Masanari Kimura*b
13 examples
up to 86% yield
E-selective (R2 = H)
0
0
0
0
0-
0
0
3
2-
9
0
0
9-
5
5
4
E/Z = 4:1 (R1 = 4-(t-Bu)PhCH2, R2 = Me)
a Molecular Engineering Institute, Kindai University,
11-6 Kayanomori Iizuka, Fukuoka 820-8555, Japan
ymori@moleng.fuk.kindai.ac.jp
b Graduate School of Engineering, Nagasaki University,
Bunkyo-machi 1-14, Nagasaki 852-8521, Japan
masanari@nagasaki-u.ac.jp
Published as part of the Cluster C–C Activation
R2
Received: 27.09.2017
Accepted after revision: 07.11.2017
Published online: 08.12.2017
R2
O
cat. Ni(cod)2/PPh3
Et3SiOTf, Et3N
OH
+
R1
R1
R3
DOI: 10.1055/s-0036-1591845; Art ID: st-2017-b0716-c
R3
Scheme 1 Ni-catalyzed carbonyl-ene-type reaction of monosubstitut-
ed alkenes with aldehydes in the presence of triethylsilyl triflate
Abstract Nickel catalyzes the multicomponent coupling reaction of
terminal alkenes, carbon dioxide, and organoaluminum reagents, lead-
ing to the synthesis of homoallylic alcohols in moderate-to-good yields
with excellent regio- and stereoselectivities.
Ni-catalyzed C–C bond formation is one of the most
useful synthetic tools for accessing complicated pharma-
ceutical compounds and fine chemicals.7 We have devel-
oped Ni-catalyzed multicomponent coupling reactions of
unsaturated hydrocarbons, such as conjugated dienes and
enynes, and carbonyl compounds with organometallic re-
agents as alkyl, aryl, and hydride sources that give highly
functionalized organic compounds in a single manipula-
tion.8 Recently, Jamison reported the carbonyl-ene reaction
of monosubstituted alkenes with aliphatic and aromatic
aldehydes that involved a Ni catalyst and was promoted by
triethylsilyl triflate (Scheme 1).9 In this case, the regioselec-
tivities depended on the phosphine ligand; PCy2Ph led to
allylic alcohols, whereas PPh3 led to homoallylic alcohols.
Herein, we introduce the Ni-catalyzed multicomponent
coupling reaction of terminal alkenes, carbon dioxide, and
trimethylaluminum, leading to the synthesis of homoallylic
alcohols (Scheme 2). This transformation can be regarded
as a formal carbonyl-ene reaction of simple alkenes with
ketones to form homoallylic alcohols with high regio- and
stereoselectivities in a single operation.
Key words nickel catalyst, carbon dioxide, carbonyl-ene, ketone,
organoaluminum
In modern organic chemistry, carbonyl-ene reactions
are important and efficient synthetic tools for C–C bond
formation using alkenes and carbonyl compounds.1 In gen-
eral, combinations of electron-rich alkenes, such as di- or
multialkylated substituted alkenes, and more electron-defi-
cient carbonyl compounds, such as glyoxylates and trifluoro-
pyruvates, are effective for C–C bond construction.2 Carbon-
yl-ene reactions involving ketones as the enophiles are less
useful than those involving aldehydes owing to lower elec-
trophilicity.3 Therefore, it is necessary to activate the ke-
tones by introducing electron-withdrawing substituents or
with highly reactive Lewis acids for more sophisticated C–C
bond constructions.
Carbon dioxide is a useful carbon resource owing to its
nontoxicity, abundance, and availability.4 Therefore, trans-
formation of carbon dioxide to various functional groups
can be a convenient and practical method to utilize this
useful carbon feedstock. However, most examples of using
carbon dioxide have led to the formation of carboxylic
acids,5 although the transformation of carbon dioxide to
other functional groups also deserves attention not only to
enhance the synthetic availability of carbon dioxide but
also for the development of carbon dioxide fixation pro-
cesses.6
R2
R2
Ni catalyst
OH
Me
CO2
+
R1
R1
(1 atm)
Me3Al
Me
Scheme 2 Ni-catalyzed three-component coupling reaction of
alkenes, CO2, and Me3Al
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

B
Y. Mori et al.
Cluster
Synlett
The reaction was conducted using allylbenzene, Me3Al,
and a catalytic amount of Ni(cod)2 and various ligands in
1,4-dioxane under a carbon dioxide atmosphere. The re-
sults are summarized in Table 1. Monodentate arylphos-
phine ligands such as PPh3 were ineffective for the coupling
reaction (entry 1, Table 1). With trialkylphosphines such as
P(n-Bu)3 and PCyp3, the three-component coupling reaction
of allylbenzene, Me3Al, and carbon dioxide proceeded to
give the expected homoallylic alcohol 3aa in moderate
yields with small amounts of allylic alcohol 4aa as a minor
product (entries 2 and 3, Table 1). The reaction using PCy3
gave homoallylic alcohol 3aa with high regio- and stereose-
lectivities in good yield as the sole product (entry 4, Table
1). With bulkier ligands, such as P(t-Bu)3 and XPhos, the
three-component coupling reaction did not proceed at all
(entries 5 and 6, Table 1). Bidentate phosphine and N-hetero-
cyclic carbene (NHC) ligands were not effective for the cou-
pling reaction and the starting material was recovered
quantitatively (entries 7–10, Table 1).
alkenes, namely 1-allylnaphthalene and 3-allylindole, the
desired coupling reaction proceeded to give the homoallylic
alcohols in moderate to high yields (entries 5 and 6, Table
2). Simple terminal alkenes such as 1-octene could be used
in the coupling reaction and led to high regio- and stereose-
lectivities (entry 7, Table 2). Reactions with 4-phenyl-1-
butene, 5-hexen-1-ol, and methyl 5-hexenoate gave the
corresponding products in moderate yields (entries 8–10,
Table 2). With 3,3-diphenyl-1-propene, the three-compo-
nent coupling reaction proceeded to afford the homoallylic
alcohol in a low yield (entry 11, Table 2). The reaction with
4-(4-tert-butyl)phenyl-3-methyl-1-butene gave the desired
coupling product as a mixture of stereoisomers in a 4:1 ra-
tio (entry 12, Table 2).
Table 2 Ni-Catalyzed Coupling Reaction of Alkenes, CO2, and Me3Ala
R2
R2
cat. Ni(cod)2/PCy3
OH
Me Me
CO2
+
R1
R1
Me3Al
1
(1 atm)
3
Table 1 Ni-Catalyzed Coupling Reaction of Allylbenzene, CO2, and Me3Ala
Entry
R1
1 R2
1b H
Yield of 3 (%)b
OH
Me
Ph
cat. Ni(cod)2/ligand
Me3Al
CO2
+
Ph
1
2-MeC6H4
4-MeC6H4
4-MeOC6H4
4-FC6H4
3ba 64
3ca 68
3da 70
3ea 77
3fa 54
3ga 86
3ha 54
3ia 42
3ja 30
3ka 24
3la 25
3ma 49d
Me
3aa
4aa
1a
(1 atm)
2
1c H
1d H
1e H
1f H
OH
Me
3
Ph
Me
4
5
1-naphthyl
3-indolyl
CH3(CH2)4
Ph(CH2)2
Entry
Ligand (mmol)
Yield (%, 3aa/4aa)b
6c
7
1g H
1h H
1i H
1
2
PPh3 (0.1)
0
P(n-Bu)3 (0.1)
PCyp3 (0.1)
PCy3 (0.1)
27 (94:6)
8
3
37 (95:5)
9c
HO(CH2)3
MeO2C(CH2)3
Ph
1j H
4
73 (99:1)
10
1k H
1l Ph
1m Me
5c
6
P(t-Bu)3 (0.1)
XPhos (0.1)
dCype (0.05)
IDM (0.05)
ICy (0.05)
0
0
0
0
0
0
11
12
4-t-BuPhCH2
7
a Reaction conditions: The reaction was conducted using Ni(cod)2
(0.05 mmol), PCy3 (0.1 mmol), alkene (0.5 mmol), and trimethylaluminum
(1.5 mmol; 1 M solution in n-hexane) in 1,4-dioxane (4 mL) at 40 °C for 24 h
under carbon dioxide (1 atm).
8d
9d
10d
b Only E stereoisomer was formed.
IMes (0.05)
c 2.0 mmol of trimethylaluminum was used.
d E/Z = 4:1. Stereochemistry was determined by NOE experimental analysis.
a Conditions: The reaction was conducted using Ni(cod)2 (0.05 mmol),
ligand (0.05–0.1 mmol), allylbenzene (0.5 mmol), and trimethylaluminum
(1.5 mmol; 1 M solution in n-hexane) in solvent (4 mL) at 40 °C for 24 h
under carbon dioxide (1 atm).
Next, various organoaluminum reagents were investi-
gated under the same conditions. The results are summa-
rized in Table 3. Other organometallic reagents such as Me-
Li, MeMgBr, Me2Zn, and Me3B did not react to provide the
expected homoallylic alcohols at all. Although Me3Al pro-
moted the desired reaction to afford homoallylic alcohol
3aa in good yield and with high regio- and stereoselectivi-
ties (entry 1, Table 3), reactions using (CH2CHCH2)Et2Al and
(PhCH2)Et2Al did not provide the products at all; instead,
triallylmethanol 5b and tribenzylmethanol 5c were pro-
duced (entries 2 and 3, Table 3). Even in the absence of
Ni(cod)2 and PCy3, 5b and 5c were formed. Therefore, it was
b E Stereoisomers were formed.
c P(t-Bu)3 was generated in situ from P(t-Bu)3·HBF4 (0.1 mmol) and NEt(i-Pr)2
(0.1 mmol).
d NHC ligands were generated in situ from the HCl salts (0.05 mmol) and
KOt-Bu (0.05 mmol).
Various 1-alkenes were examined in the coupling reac-
tion under similar conditions. The results are summarized
in Table 2. The 2-methyl-, 4-methyl-, 4-methoxy-, and 4-
fluoro-substituted allylbenzenes gave the corresponding
products in good yields and with high regio- and stereo-
selectivities (entries 1–4, Table 2). With other aryl terminal
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

C
Y. Mori et al.
Cluster
Synlett
concluded that the combination of the Ni catalyst and
Me3Al would be enough to accomplish the coupling reac-
tion with alkenes under carbon dioxide (entries 4 and 5,
Table 3).
Ni(cod)2 (0.05 mmol)
PCy3 (0.1 mmol)
OH
Ph
Ph
CO2H
0.5 mmol
Me3Al (1.5 mmol)
1,4-dioxane (4 mL)
40 °C , 24 h
Me Me
3aa: 0%
O
OH
Me
Table 3 Ni-Catalyzed Coupling Reaction of Allylbenzene, CO2, and
Ph
+
Ph
0.5 mmol
Various Organoaluminum Reagentsa
Me
the same as above
the same as above
Me
Me
1.5 mmol
3aa: 52% [E only]
OH
cat. Ni(cod)2/PCy3
Ph
CO2
+
3
Ph
R
R
OH
CO2
+
Ph
Cl
Ph
R3Al or REt2Al
(1 atm)
1a
Me
3aa: 0%
Me
OH
R
0.5 mmol
(1 atm)
5
R
R
Scheme 3 Alternative strategies for the Ni-catalyzed formation of ho-
moallylic alcohol 3aa
Entry
Organoaluminum 2
Yield of 3b or 5 (%)
3aa 73
1
2a Me3Al
2c
2b (CH2CHCH2)Et2Al
2c (PhCH2)Et2Al
2b (CH2CHCH2)Et2Al
2c (PhCH2)Et2Al
5b 51 R = CH2CHCH2
5c 34 R = Bn
nates with the nickel metal center, leading to the formation
of five-membered oxanickelacycle intermediate II. Here,
Me3Al serves as a Lewis acid, activating acetone and pro-
moting the oxidative cyclization.14 The phosphine ligand,
PCy3, enhances the Ni complex, accelerating β-hydride
elimination, which generates the C=C double bond (IV).15
Finally, transmetalation with Me3Al occurs via σ-bond
metathesis, and this is followed by evolution of methane
and regeneration of the Ni(0) active species through reduc-
tive elimination. After the hydrolysis of VI, the expected
homoallylic alcohol, 3, with the E configuration is obtained.
In conclusion, we have developed the Ni-catalyzed multi-
component coupling reaction of simple alkenes, carbon di-
oxide, and Me3Al that affords homoallylic alcohols with
high regio- and stereoselectivities.16 Because a ketone is
3c
4c,d
5c,d
5b 51 R = CH2CHCH2
5c 35 R = Bn
a Conditions: The reaction was conducted using Ni(cod)2 (0.05 mmol), PCy3
(0.1 mmol), alkene (0.5 mmol), and organoaluminum reagent (1.5 mmol)
in 1,4-dioxane (4 mL) at 40 °C for 24 h under carbon dioxide (1 atm).
b Only E stereoisomer was formed.
c Organoaluminum reagents 2b and 2c were prepared from Et2AlCl (1 M
solution in hexanes) and (CH2CHCH2)MgBr (1 M solution in diethyl ether)
and PhCH2MgBr (0.9 M solution in THF), respectively.
d The reaction was conducted without Ni(cod)2 and PCy3.
In order to consider the reaction mechanism, the direct
conversions of cinnamyl moieties to homoallylic alcohol
3aa were examined, and the results are displayed in
Scheme 3. First, trans-4-phenyl-3-butenoic acid was used
as a substrate in the presence of catalytic amounts of
Ni(cod)2 and PCy3 and excess Me3Al. However, desired
homoallylic alcohol 3aa was not obtained. Next, we investi-
gated the reaction using acetone as the enophile instead of
carbon dioxide. The direct coupling of allylbenzene with
acetone produced desired homoallylic alcohol 3aa with the
E configuration in 52% yield as a single isomer.10 However,
in the absence of the Ni catalyst, this coupling reaction did
not proceed at all. Thus, the Ni catalyst is indispensable in
these carbonyl-ene-type reactions for the formation of homo-
allylic alcohols from terminal alkenes. We attempted to
confirm the formation of an allylic anion from cinnamyl
chloride in the presence of Ni(cod)2, PCy3, and Me3Al, but
the expected coupling reaction with carbon dioxide was
unsuccessful.11 According to these results, it seems doubtful
that an allylic anion species is formed in situ to react with
acetone to afford desired homoallylic alcohol 3aa.12
H
H
H
H
R
R
H
H
H
H
H
R
H
H
H
H
H
H
favorable
Me
H
H
H
Ni(0)/L
H
R
Me
O
Me
Me
H
Ni0
R
acetone
Me3Al
oxidative
cyclization
Ni
H
AlMe3
L
H
O
H
L
II
AlMe3
I
Me
Me
O
Me
H
R
H
Me
H
O
Ni
b-hydride
elimination
H
AlMe3
R
HNi
H
AlMe3
L
III
IV
L
Me
Based on our results for the formation of homoallylic al-
cohols, a possible reaction mechanism for the coupling re-
action was proposed and is shown in Scheme 4. First, car-
bon dioxide reacts with Me3Al to give acetone in situ,13 and
then the alkene coordinates with Ni(0) in such a way that
minimizes steric repulsion through I. Acetone also coordi-
Me
Me
Me
H
H
H
H
O
O
R
AlMe2
Me
R
AlMe2
E-selective
HNi
L
Ni(0)/L, CH4
VI
V
Scheme 4 Plausible reaction mechanism for Ni-catalyzed coupling re-
action of an alkene, CO2, and Me3Al
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

D
Y. Mori et al.
Cluster
Synlett
generated from carbon dioxide using an organoaluminum
reagent, these coupling reactions can be regarded as formal
carbonyl-ene-type reactions via oxanickelacycle intermedi-
ates. It is considered that the activation of the simple
alkenes and carbon dioxide is the driving force behind this
carbonyl-ene-type reaction, which will be an important
synthetic tool for C–C bond formation.
(3) It has been reported carbonyl-ene reaction of disubstituted
alkenes with acetone; see: Jackson, A. C.; Goldman, B. E.; Snider,
B. B. J. Org. Chem. 1984, 49, 3988.
(4) Carbon Dioxide as a Chemical Feedstock; Aresta, M., Ed.; Wiley-
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Hofmann, P.; Limbach, M. Chem. Eur. J. 2014, 20, 16858.
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metallics 2014, 33, 3657.
(6) (a) Molla, R. A.; Iqubal, M. A.; Ghosh, K.; Islam, S. M. Green Chem.
2016, 18, 4649. (b) Tani, Y.; Kuga, K.; Fujihara, T.; Terao, J.; Tsuji,
Y. Chem. Commun. 2015, 51, 13020. (c) Yu, B.; Zhao, Y.; Zhang,
H.; Xu, J.; Hao, L.; Gao, X.; Liu, Z. Chem. Commun. 2014, 50, 2330.
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Weinheim, 2005. (b) Tasker, S. Z.; Standley, E. A.; Jamison, T. F.
Nature 2014, 509, 299. (c) Standley, E. A.; Tasker, S. Z.; Jensen, K.
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Funding Information
We gratefully acknowledge funding from the Grants-in-Aid for Scien-
tific Research (B) (26288052) from the Ministry of Education, Culture,
Sports and Technology (MEXT), Japan.
)(
Acknowledgment
We gratefully acknowledge funding from the Grants-in-Aid for Scien-
tific Research (B) (26288052) from the Ministry of Education, Culture,
Sports and Technology (MEXT), Japan.
(8) (a) Mori, Y.; Kawabata, T.; Onodera, G.; Kimura, M. Synthesis
2016, 48, 2385. (b) Mori, Y.; Onodera, G.; Kimura, M. Chem. Lett.
2014, 43, 97. (c) Mori, Y.; Mori, T.; Onodera, G.; Kimura, M. Syn-
thesis 2014, 46, 2287. (d) Mori, T.; Akioka, Y.; Onodera, G.;
Kimura, M. Molecules 2014, 19, 9288. (e) Nakamura, T.; Mori, T.;
Togawa, M.; Kimura, M. Heterocycles 2012, 84, 339. (f) Kimura,
M.; Togawa, M.; Tatsuyama, Y.; Matsufuji, K. Tetrahedron Lett.
2009, 50, 3982. (g) Kimura, M.; Tatsuyama, Y.; Kojima, K.;
Tamaru, Y. Org. Lett. 2007, 9, 1871. (h) Kimura, M.; Kojima, K.;
Tatsuyama, Y.; Tamaru, Y. J. Am. Chem. Soc. 2006, 128, 6332.
(i) Kimura, M.; Ezoe, A.; Mori, M.; Tamaru, Y. J. Am. Chem. Soc.
2005, 127, 201. (j) Kimura, M.; Ezoe, A.; Mori, M.; Iwata, K.;
Tamaru, Y. J. Am. Chem. Soc. 2006, 128, 8559. (k) Kimura, M.;
Fujimatsu, H.; Ezoe, A.; Shibata, K.; Shimizu, M.; Matsumoto, S.;
Tamaru, Y. Angew. Chem. Int. Ed. 1999, 38, 397. (l) Kimura, M.;
Ezoe, A.; Shibata, K.; Tamaru, Y. J. Am. Chem. Soc. 1998, 120,
4033.
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(b) Ho, C.-Y.; Ng, S.-S.; Jamison, T. F. J. Am. Chem. Soc. 2006, 128,
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(10) An excess amount of Me3Al is required for the coupling reaction
of allylbenzene and acetone. However, in the case of a catalytic
amount of Me3Al, the desired reaction did not proceed. It seems
that Me3Al serves as a promoter for regeneration of Ni(0) active
species as well as Lewis acid for activation of acetone.
Supporting Information
Supporting information for this article is available online at
https://doi.org/10.1055/s-0036-1591845.
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Org. Chem. 2009, 898. (c) Lee, W.-C.; Wang, C.-H.; Lin, Y.-H.;
Shin, W.-C.; Ong, T.-G. Org. Lett. 2013, 15, 5358. (d) Bielinski, E.
A.; Dai, W.; Guard, L. M.; Hazari, N.; Takase, M. K. Organometal-
lics 2013, 32, 4025.
(13) Acetone would be readily produced from a mixture of carbon
dioxide and Me3Al. Thus the formed acetone in situ might be
subsequently consumed via Ni-catalyzed oxidative cyclization
with alkenes promoted by Me3Al. It has been reported that the
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E

E
Y. Mori et al.
Cluster
Synlett
reaction of trialkylaluminum reagents with carbon dioxide pro-
ceeds to provide the trialkylcarbinols through the ketones; see:
Yur’ev, V. P.; Kuchin, A. V.; Tolstikov, G. A. Russ. Chem. Bull. 1974,
23, 817.
vacuo. The residual oil was subjected to column chromatogra-
phy over silica gel (hexane/ethyl acetate = 2:1, v/v) to give 3aa
(64.3 mg, 0.36 mmol, 73%) as a pale yellow oil.
(E)-2-Methyl-5-phenylpent-4-en-2-ol (3aa)
(14) It has been reported Lewis acids promote the formation of
oxanickelacycles from alkene and ketone in intramolecular
manner; see: Hayashi, Y.; Hoshimoto, Y.; Kumar, R.; Ohashi, M.;
Ogoshi, S. Chem. Lett. 2017, 46, 1096.
(15) β-Hydride elimination from oxanickelacyclopentane occurs
selectively instead of methylation via reductive elimination in
the presence of Me3Al; see: Ogoshi, S.; Ueta, M.; Arai, T.;
Kurosawa, H. J. Am. Chem. Soc. 2005, 127, 12810.
TLC: Rf = 0.25 (hexane/ethyl acetate = 4:1, v/v). IR (neat): 3387
(m), 3059 (m), 2970 (s), 1599 (s), 1497 (m), 1377 (s), 1140 (s),
968 (s), 692 (s) cm–1 1H NMR (400 MHz, CDCl3): δ = 1.27 (s, 6
.
H), 1.54 (br, 1 H), 2.39 (d, J = 7.6 Hz, 2 H), 6.28 (dt, J = 15.9, 7.6
Hz, 1 H), 6.46 (d, J = 15.9 Hz, 1 H), 7.21 (t, J = 7.3 Hz, 1 H), 7.30 (t,
J = 7.3 Hz, 2 H), 7.34 (d, J = 7.3 Hz, 2 H). 13C NMR (100 MHz,
CDCl3): δ = 29.3, 47.4, 70.9, 125.7, 126.1, 127.2, 128.5, 133.6,
137.3. HRMS: m/z calcd for C12H16O: 176.1201; found: m/z (rela-
tive intensity) = 176.1203 (9) [M+], 118 (100).
(16) General Procedure for the Ni-Catalyzed Three-Component
Coupling Reaction of Alkene, CO2, Organoaluminum Reagent
(Table 1, Entry 4)
(E)-2-Methyldec-4-en-2-ol (3ha)
Pale yellow oil; yield 46.0 mg (0.27 mmol, 54%); TLC: Rf = 0.50
(hexane/ethyl acetate = 4:1, v/v). IR (neat): 3361 (br), 2962 (s),
The reaction was undertaken as follows: Into a carbon dioxide
purged flask with Ni(cod)2 (13.8 mg, 0.05 mmol) and PCy3 (28.1
mg, 0.1 mmol) were introduced successively 1,4-dioxane (4
mL), allylbenzene (59.1 mg, 0.5 mmol), and Me3Al (1.5 mL of 1
M solution in n-hexane, 1.5 mmol) via syringe. The homoge-
neous mixture was stirred at 40 °C for 24 h, during which the
reaction was monitored by TLC. Then the mixture was
quenched by adding 2 N HCl (10 mL) and extracted with ethyl
acetate three times. The combined organic extracts were
washed with brine and then dried (MgSO4) and concentrated in
2927 (s), 2856 (m), 1497 (w), 1377 (w), 1151 (w), 972 (w) cm–1
.
1H NMR (400 MHz, CDCl3): δ = 0.89 (t, J = 6.8 Hz, 3 H), 1.20 (s, 6
H), 1.26–1.41 (m, 6 H), 1.50 (br, 1 H), 2.03 (q, J = 7.3 Hz, 2 H),
2.16 (d, J = 6.8 Hz, 2 H), 5.46 (dt, J = 15.1, 7.3 Hz, 1 H), 5.53 (dt, J
= 15.1, 6.8 Hz, 1 H). 13C NMR (100 MHz, CDCl3): δ = 14.0, 22.5,
29.0, 29.2, 31.4, 32.7, 47.0, 70.4, 125.2, 135.4. HRMS: m/z calcd
for
C11H22O: 170.1671; found: m/z (relative intensity) =
170.1668 (14) [M+], 155 (100).
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 28, A–E