Carbonylation of 1-lithiobutadiene with carbon monoxide followed by intramolecular acyllithiation of C=C double bond and intermolecular acylation with acid chloride: Scope, applications, and mechanistic aspects

Article abstract of DOI:10.1021/jo300631d

The carbonylation of a 1-lithio-1,3-butadiene derivative with CO gave rise to a butadienyl acyllithio intermediate, which underwent an immediate intramolecular acyllithiation of the C=C double bond, affording a lithio cyclopentadienyl enolate. The X-ray structural analysis of the enolate revealed a dimer connected with a Li₂O₂ four-membered ring. Subsequent intermolecular acylation of this enolate with acid chlorides afforded β-keto-3-cyclopentenones, γ-keto-2-cyclopentenones, or cyclopentadienyl ester derivatives. The stereo- and regioselectivity of the in situ generated lithio cyclopentadienyl enolate with various acid chlorides was investigated and analyzed, showing that the formation of the above products was significantly dependent on both the substituents on the butadienyl skeleton and the bulkiness of acid chlorides.

Full text of DOI:10.1021/jo300631d

Article
pubs.acs.org/joc
Carbonylation of 1-Lithiobutadiene with Carbon Monoxide Followed
by Intramolecular Acyllithiation of CC Double Bond and
Intermolecular Acylation with Acid Chloride: Scope, Applications,
and Mechanistic Aspects
Heng Li,† Lantao Liu,† Fei Zhao,† Congyang Wang,† Chao Wang,† Qiuling Song,† Wen-Xiong Zhang,†
and Zhenfeng Xi*,†,‡
†Beijing National Laboratory for Molecular Sciences, and Key Laboratory of Bioorganic Chemistry and Molecular Engineering of
Ministry of Education, College of Chemistry, Peking University, Beijing 100871, China
‡State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry (SIOC), Shanghai 200032, China
S
* Supporting Information
ABSTRACT: The carbonylation of a 1-lithio-1,3-butadiene
derivative with CO gave rise to a butadienyl acyllithio
intermediate, which underwent an immediate intramolecular
acyllithiation of the CC double bond, affording a lithio
cyclopentadienyl enolate. The X-ray structural analysis of the
enolate revealed a dimer connected with a “Li2O2” four-
membered ring. Subsequent intermolecular acylation of this
enolate with acid chlorides afforded β-keto-3-cyclopentenones,
γ-keto-2-cyclopentenones, or cyclopentadienyl ester deriva-
tives. The stereo- and regioselectivity of the in situ generated
lithio cyclopentadienyl enolate with various acid chlorides was
investigated and analyzed, showing that the formation of the
above products was significantly dependent on both the substituents on the butadienyl skeleton and the bulkiness of acid
chlorides.
Scheme 1. Known Strategies to Apply Acyllithio Species
Generated in situ from RLi and CO
INTRODUCTION
■
For decades, the carbonylative reactions have been important
methods for organic synthesis by direct application of carbon
monoxide as a convenient one-carbon source.1 Among them,
the reaction of organolithium reagents with carbon monoxide
has attracted much attention because it provides the most
straightforward strategy to introduce a carbonyl group.1b,2
Acyllithium species, which are of significant importance as
reagents, have been commonly accepted as the initial
intermediates.3 However, because of their high reactivity, few
selective and meaningful reactions have been developed using
acyllithium compounds.4,5 Generally, two different strategies
have been successfully applied to control the complicated
reactions. Seyferth and others reported the intermolecular
pattern, in which electrophiles were used to trap the
carbonyllithium species under careful reaction conditions.6,7
Meanwhile, the other strategy involving an intramolecular
pattern by converting reactive carbonyllithium species to
enolates or ynolates was studied by Murai and others (Scheme
1).8,9
cyclopentenones is less studied.14 Recently, we have demon-
strated that 1,4-dilithio-1,3-diene derivatives 1 are of interesting
and useful reactivities toward carbon monoxide. The reaction of
1,4-dilithio-1,3-diene derivatives 1 with carbon monoxide
represents a novel example of highly efficient cyclocarbonyla-
tion of organolithium compounds generating 3-cyclopente-
nones 3 after hydrolysis.15a Additionally, the first oxy-
cyclopentadienyl dilithium intermediates (OCp dianions)
obtained from the reaction between 1,4-dilithio-1,3-diene 1
and carbon monoxide have been isolated and structurally
Cyclopentenones represent an important family of organic
molecules widely existing in pharmaceuticals and natural
products.10 Many strategies for the synthesis of 2-cyclo-
pentenones have been reported,11−13 but the synthesis of 3-
Received: March 27, 2012
Published: April 23, 2012
© 2012 American Chemical Society
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characterized.15b The OCp dianions displayed unique struc-
tures and novel reaction chemistry. By intermolecular acylation
with acid chlorides, doubly acylated and O-acylated species
could be obtained with perfect selectivity.15 In 2002, the
reaction between 1-lithio-1,3-diene derivatives 2 and carbon
monoxide was reported, affording the same type product 3-
cyclopentenones 3 in an unprecedented way (Scheme 2).16
Table 1. Formation of Multiply Substituted β-Keto-3-
cyclopentenone Derivatives
Scheme 2. Reactions of Dienyllithium Reagents with Carbon
Monoxide
We tried to investigate further on the reaction of 1-lithio-1,3-
diene derivatives 2 with carbon monoxide, with particular
interest in the isolation and synthetic applications of the
reactive carbonyllithio intermediates. In this paper, we report
our systematic investigation of the cyclocarbonylation of
substituted 1-lithio-1,3-diene derivatives 2 followed by acylation
with acid chlorides. A wide variety of β-keto-3-cyclopentenone
derivatives 4 and cyclopentadienyl ester derivatives 5 could be
prepared (Scheme 2). Moreover, the reaction selectivity and
mechanism were also studied by intermediate characterization
and relevant LDA promoted deprotonation−lithiation experi-
ments.
a
b
Isolated yields. Only cis isomer. The two ethyl/propyl groups were
in the same face.
and propargyl halides.16 More importantly, these reactions
proceeded in excellent regio- and stereoselectivity in which only
cis products were obtained (cis here refers to the two identical
substituents at positions 2 and 5). The structure of product 4e
was determined by single-crystal X-ray structural analysis. The
two ethyl groups adjacent to the carbonyl group were
confirmed in the cis positions (Figure 1).
In order to further investigate the effect of substitution
patterns on the butadienyl skeletons, we prepared the 1,2-
disubstitued 1-lithio-1,3-dienes 2d. Interestingly, γ-C-acylation
reactions took place to yield γ-keto-2-cyclopentenone deriva-
tives 6 as sole products (Scheme 3). From the above
experimental results, we found that the substitution patterns
of the butadienyl skeleton of these monolithium reagents had
important influences on the regioselectivity of their inter-
molecular acylation reactions.
According to the synthetic method mentioned above,
multisubstituted stereodefined β-keto-3-cyclopentenone deriv-
atives 4 and some γ-keto-2-cyclopentenone derivatives 6 could
be easily constructed in one pot. In addition, the two carbonyl
RESULTS AND DISCUSSION
■
Reaction of 1-Lithio-1,3-dienes with Carbon Mon-
oxide Followed by Intermolecular Trapping with Acid
Chlorides: Formation of Multiply Substituted 3-Cyclo-
pentenone. The 1-lithio-1,3-diene 2, generated in situ from its
corresponding monohalo compound and t-BuLi, was allowed to
react with carbon monoxide at −78 °C for 1 h. After that, the
corresponding reaction intermediate was trapped by an acid
chloride, affording β-keto-3-cyclopentenone derivatives 4a−4f
in high isolated yields (Table 1). Only β-C-acylation product
was observed. The regioselectivity was similar to the application
of alkylation reagents, such as methyl iodide, benzyl halides,
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Table 2. Formation of Multiply Substituted
Cyclopentadienyl Ester Derivatives
Figure 1. ORTEP drawings of 4e with 30% thermal ellipsoids.
Hydrogen atoms are omitted for clarity. Selected bond lengths [Å]:
C1−C5 1.516(6), C1−C2 1.337(6), C2−C3 1.519(6), C3−C4
1.517(6), C4−C5 1.549(6), C4−O2 1.210(5), C3−C12 1.542(6),
C5−C15 1.550(6), C15−O1 1.214(5).
Scheme 3. Formation of Multiply Substituted γ-Keto-2-
cyclopentenone Derivatives
groups and the C−C double bonds in the relevant skeletons
might be further modified for wider applications.17
a
Isolated yields.
Reaction of 1-Lithio-1,3-dienes with Carbon Mon-
oxide Followed by Intermolecular Trapping with Bulky
Acid Chlorides: Formation of Multiply Substituted
Cyclopentadienyl Ester. In order to study the steric effect
deeply, bulky acid chlorides such as t-BuCOCl and AdCOCl
were applied as the electrophiles. Surprisingly, C-acylation
products were not observed. Instead, cyclopentadienyl ester
derivatives 5a−c were generated in moderate isolated yields
(entries 1−3, Table 2). Moreover, when the reaction mixture of
1-lithio-4-phenyl-1,3-diene 2e with carbon monoxide was
treated with 1 equiv of relatively small PhCOCl or MeCOCl,
only O-acylation products 5d, 5e were obtained in 57 and 72%
yield, respectively (entries 4, 5, Table 2). This could be
explained by the steric effect of the phenyl group on the
skeleton of 2e.
Cyclopentadienyl ester derivatives 5 are interesting and
potential building blocks for synthetic chemistry and organo-
metallic chemistry.18 The reaction reported here provides a
practical method for such compounds. Furthermore, these
results indicate the existence of lithio cyclopentadienyl enolate
intermediates.
carbonylation of 1,2,3,4-tetrasubstituted 1-lithio-1,3-dienes and
carbon monoxide could form a cyclic monoanion intermediate,
which might be represented by three possible resonance
structures 8−10 (Scheme 4). Because of the proposed
intriguing transformation, we set our mind on making clear
this novel cyclocarbonylation process by isolating the
intermediates.
As shown in Scheme 5, the unsymmetrical substituted 1-
lithio-1,3-diene 2f was in situ generated from its corresponding
monohalo compound with t-BuLi and was allowed to react with
carbon monoxide under similar reaction conditions to those
described above. Treatment of the reaction mixture with 1
equiv of t-BuCOCl afforded the cyclopentadienyl ester
derivative 5f in 67% isolated yield. This result is in consistence
with the examples listed in Table 2. Hydrolysis of the reaction
mixture afforded a mixture of two products, 3f and 3f′, which
could be separated and obtained in 24 and 48% isolated yield,
respectively. The structure of 3f was determined by single-
crystal X-ray structural analysis (see the Supporting Informa-
tion for details).
Mechanistic Study on the Reaction of 1,2,3,4-
Tetrasubstituted 1-Lithio-1,3-dienes with Carbon Mon-
oxide. According to the proposed mechanism, the cyclo-
The intermediate 10f formed from the reaction of 1-lithio-
1,3-diene 2f with carbon monoxide was successfully obtained in
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Recrystallization of 10f from THF/hexane mixed solvents
afforded crystals suitable for single-crystal X-ray structural
analysis (Figure 2). It features a dimeric lithio cyclopentadienyl
Scheme 4. Proposed Mechanism in Reactions of 1,2,3,4-
Tetrasubstituted 1-Lithio-1,3-dienes with Carbon Monoxide
Figure 2. ORTEP drawing of 10f with 30% thermal ellipsoids.
Hydrogen atoms are omitted for clarity. Selected bond lengths [Å]:
C1−C2 1.535(4), C1−C5 1.350(4), C2−C3 1.534(4), C3−C4
1.358(4), C4−C5 1.456(4), C1−O1 1.317(3), O1−Li1 1.828(6),
O1−Li2 1.913(5), O2−Li1 1.837(5), O2−Li2 1.908(5), C21−O2
1.307(3), C21−C22 1.549(4), C21−C25 1.358(4), C22−C23
1.532(4), C23−C24 1.357(4), C24−C25 1.455(4).
Scheme 5. Isolation of the Intermediate of 3-
Cyclopentenones
enolate structure, being connected through a 4-membered
“Li2O2” moiety.15b,19 Quantitative formation of 5f or the
mixture of 3f/3f′ (1:2 molar ratio) was observed when the
isolated 10f was treated with t-BuCOCl or H2O, respectively.
Regioselectivity and Stereoselectivity Analysis. As
described above, these reactions displayed high regioselectivity
depending on the substituents on the butadienyl skeleton and
the bulkiness of acid chlorides. Generally, the lithio cyclo-
pentadienyl enolate intermediate 10 was trapped by acid
chloride affording β-C-acylation products 4. The regioselectivity
is summarized in Scheme 7.
The γ-C-acylation species 6 could be obtained when the
disubstituted enolate lithium intermediate was used. For the
corresponding reaction intermediate, the γ position was
sterically favored in nucleophilic substitution. However, if a
62% isolated yield (Scheme 5). Meanwhile, treatment of the
mixture of 3f/3f′ with LDA generated the same lithio species
10f in 87% isolated yield. This result indicates that upon
deprotonation−lithiation with LDA, the two isomers of 3f and
3f′ were transformed into a single lithio intermediate. This
deprotonation lithiation using LDA was also applied to other 3-
cyclopentenone derivatives such as 3a (a mixture of cis and
trans isomers obtained via hydrolysis of the reaction mixture of
2a with CO) and 3b.16 Similar reaction process took place,
affording their corresponding acylated products 4a and 4c in
excellent yields (Scheme 6). Thus, we confirmed that the same
lithio cyclopentadienyl enolate intermediate could be obtained
from both cyclocarbonylation of 1-lithio-1,3-dienes and LDA-
promoted deprotonation−lithiation of 3-cyclopentenones.
Scheme 7. Regioselectivity Analysis
Scheme 6. Deprotonation−Lithiation of 3-Cyclopentenones
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1
MHz for 13C; FT, 500 MHz for H; 125 MHz for 13C) at room
temperature. Infrared spectra (IR) were recorded on a FT-IR
spectrometer. High-resolution mass spectra (HRMS) were recorded
on a FTMS mass spectrometer using ESI (electrospray ionization) and
FT-ICR mass analyzer or mass spectrometer using EI (electro-
ionization). Organometallic samples for NMR spectroscopic measure-
ments were prepared in the glovebox by use of J. Young valve NMR
tubes.
bulky lithio cyclopentadienyl enolate intermediate or acid
chloride was tried, O-acylation cyclopentadienyl ester deriva-
tives were formed. These results could be explained by the
steric effect of the phenyl group in the corresponding lithio
cyclopentadienyl enolate and bulky acid chloride.
Besides the high regioselectivity, excellent stereoselectivity
was also observed in these cyclocarbonylation reactions
affording solely cis isomer products because of the acid chloride
attack at the less-hindered face (Scheme 8). For the hydrolysis
of the lithium dienolate, although the thermodynamically
controlled process is possible, the kinetically controlled path
seems more likely.
Typical Procedure for Hydrolysis of the Carbonylation
Reaction Mixture of the Full-Substituted 1-Lithio-1,3-dienes
Derivatives and Carbon Monoxide. To a solution of 1-halo-1,3-
butadienes (0.5 mmol) in THF−Et2O (5 mL, 1:1) was added 2 equiv
of t-BuLi at −78 °C. After it was stirred at −78 °C for 1 h, CO was
then bubbled into the reaction mixture for 0.5 h. The above reaction
mixture was stirred for an additional 0.5 h under CO atmosphere.
Then, the reaction mixture was quenched by water and allowed to
warm to room temperature. Aqueous layer of the above quenched
mixture was extracted with Et2O, and the combined organic layer was
washed with brine. Solvent was evaporated, and the residue was
purified by column chromatography to give corresponding product 3.
The isolated lithio cyclopentadienyl enolate 10f was quenched by
water affording the same results.
Scheme 8. Stereoselectivity Analysis
2,3,4,5-Tetraethyl-2-methylcyclopent-3-enone (3b). Yellow
liquid: isolated yield 75% (78 mg); 1H NMR (300 MHz, CDCl3,
SiMe4) δ 0.64 (t, J = 7.5 Hz, 3H, CH3), 0.90 (t, J = 7.5 Hz, 3H, CH3),
1.01−1.10 (m, 9H, CH3), 1.38−1.60 (m, 2H, CH2), 1.64−1.82 (m,
2H, CH2), 1.97−2.08 (m, 2H, CH2), 2.15−2.22 (m, 1H, CH2), 2.39−
2.46 (m, 1H, CH2), 2.85 (t, J = 5.7 Hz, 1H, CH); 13C NMR (75 MHz,
CDCl3, SiMe4) δ 9.8, 11.2, 12.5, 15.0, 18.0, 19.3, 20.9, 23.8, 28.5, 51.8,
56.5, 137.5, 140.8, 224.3; IR (neat) ν (CO) = 1741 cm−1; HRMS
(ESI) calcd. for C14H25O [M + H]+ 209.1900, found 209.1902.
2,4,5-Trimethyl-2,3-diphenylcyclopent-3-enone (3f). White
1
solid: isolated yield 24% (33 mg); mp 98−99 °C; H NMR (300
MHz, CDCl3, SiMe4) 1.28 (d, J = 7.2 Hz, 3H, CH3), 1.46 (s, 3H,
CH3), 1.96 (s, 3H, CH3), 3.21 (q, J = 7.2 Hz, 1H, CH), 6.94−6.97 (m,
2H, CH), 7.19−7.35 (m, 8H, CH); 13C NMR (75 MHz, CDCl3,
SiMe4) 13.4, 13.8, 20.0, 49.1, 60.7, 126.5, 126.9, 127.1, 127.9, 128.7,
129.0, 135.5, 136.8, 140.5, 140.7, 217.9; IR (neat) ν (CO) = 1749
cm−1; HRMS (ESI) calcd. for C20H21O [M + H]+ 277.1587, found
277.1581. Anal. Calcd. for C20H20O: C, 86.92; H, 7.29. Found: C,
86.96; H, 7.32. Recrystallization of 3f from hexane at room
temperature afforded single crystals for X-ray analysis.
CONCLUSION
■
In summary, we have described a highly efficient and selective
cyclocarbonylation of monolithiobutadienes with carbon
monoxide affording 3-cyclopentenone derivatives. When
various acid chlorides were used to trap the reaction mixture
of monolithiobutadienes and carbon monoxide, 3-cyclo-
pentenone and cyclopentadienyl ester derivatives could be
obtained. Meanwhile, relevant results clearly demonstrated that
the substitution patterns on the butadienyl skeletons and the
bulkiness of acid chloride markedly influenced the regiose-
lectivity and stereoselectivity. In order to understand the
reaction mechanism deeply, the lithio cyclopentadienyl enolate
intermediate was isolated and characterized by single-crystal X-
ray structural analysis. The designed LDA-promoted deproto-
nation−lithiation experimental results confirmed the presence
of an enolate−Li intermediate.
2,4,5-Trimethyl-2,3-diphenylcyclopent-3-enone (3f′). Color-
1
less liquid: isolated yield 48% (66 mg); H NMR (300 MHz, CDCl3,
SiMe4) 1.31 (d, J = 7.8 Hz, 3H, CH3), 1.51 (s, 3H, CH3), 1.89 (s, 3H,
CH3), 3.08 (q, J = 7.8 Hz, 1H, CH), 6.91−6.94 (m, 2H, CH), 7.17−
7.29 (m, 8H, CH); 13C NMR (75 MHz, CDCl3, SiMe4) 13.4, 14.7,
20.6, 49.9, 61.2, 126.8, 127.0, 127.2, 127.8, 128.4, 129.2, 135.5, 136.7,
140.6, 141.6, 220.3; IR (neat) ν (CO) = 1747 cm−1; HRMS (ESI)
calcd. for C20H21O [M + H]+ 277.1587, found 277.1581.
Typical Procedure for the Reaction of 1-Lithio-1,3-dienes
with Carbon Monoxide Followed by Intermolecular Trapping
with Acid Chlorides in Et2O−THF. To a solution of 1-halo-1,3-
butadienes (0.5 mmol) in THF−Et2O (5 mL, 1:1) was added 2 equiv
of t-BuLi at −78 °C. After it was stirred at −78 °C for 1 h, CO was
then bubbled into the reaction mixture for 0.5 h. The above reaction
mixture was stirred for an additional 0.5 h under CO atmosphere.
Next, for 4−6, acid chloride (0.5 mmol) was added, and the reaction
mixture was allowed to warm to room temperature. Then, the reaction
mixture was quenched by water after 1 h. Aqueous layer of the above
quenched mixture was extracted with Et2O, and the combined organic
layer was washed with brine. Solvent was evaporated, and the residue
was purified by column chromatography to give products 4−6. The
isolated lithio cyclopentadienyl enolate 10f was allowed to react with
acid chlorides to afford the same results.
EXPERIMENTAL SECTION
■
General Method. All reactions were carried out under a slightly
positive pressure of dry and oxygen-free nitrogen by using standard
Schlenk line techniques or under a nitrogen atmosphere in a Glovebox.
The nitrogen in the glovebox was constantly circulated through a
copper/molecular sieves catalyst unit. The oxygen and moisture
concentrations in the glovebox atmosphere were monitored by an O2/
H2O Combi-Analyzer to ensure both were always below 1 ppm.
Unless otherwise noted, all starting materials were commercially
available and were used without further purification. Solvent was
distilled from sodium/benzophenone ketyl under a nitrogen
atmosphere. All 1-halo-1,3-butadiene derivatives used as starting
materials were synthesized following the reported procedure.20 1-
Lithio-1,3-butadienes were synthesized by lithium−halogen exchange
reactions.
2-Benzoyl-2,3,4,5-tetrapropylcyclopent-3-enone (4a). Color-
less liquid: isolated yield 76% (135 mg); 1H NMR (300 MHz, CDCl3,
SiMe4) δ 0.84−0.97 (m, 12H, CH3), 1.03−1.81 (m, 12H, CH2), 2.00−
2.44 (m, 4H, CH2), 3.03 (t, J = 4.5 Hz, 1H, CH), 7.27−7.43 (m, 3H,
CH), 7.59−7.62 (m, 2H, CH); 13C NMR (75 MHz, CDCl3, SiMe4) δ
1H NMR and 13C NMR spectra were recorded on spectrometers
1
1
(FT, 300 MHz for H; 75 MHz for 13C; FT, 400 MHz for H; 100
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14.1, 14.1, 14.4, 14.6, 17.6, 20.3, 20.5, 22.7, 28.5, 28.8, 31.5, 35.5, 53.7,
74.8, 127.6, 128.1, 131.7, 137.6, 139.1, 141.3, 198.9, 217.9; IR (neat) ν
(CO) = 1676, 1740 cm−1; HRMS (ESI) calcd. for C24H35O2 [M +
H]+ 355.2632, found 355.2636.
22.9, 23.2, 26.2, 29.6, 29.9, 30.6, 40.2, 44.9, 46.6, 143.3, 171.7, 207.2,
215.3; HRMS (EI) calcd. for C18H30O2 278.2246, found 278.2244.
2,3,4,5-Tetrapropylcyclopenta-1,3-dien-1-yl Pivalate (5a).
1
Colorless liquid: isolated yield 55% (92 mg); H NMR (300 MHz,
2-Acetyl-2,3,4,5-tetrapropylcyclopent-3-enone (4b). Color-
less liquid: isolated yield 62% (91 mg); 1H NMR (300 MHz,
CDCl3, SiMe4) δ 0.90−1.01 (m, 12H, CH3), 1.26−1.74 (m, 10H,
CH2), 1.90−2.15 (m, 7H, 1CH3, 2CH2), 2.35−2.45 (m, 2H, CH2),
3.07 (t, J = 6 Hz, 1H, CH); 13C NMR (75 MHz, CDCl3, SiMe4) δ
14.2, 14.3, 14.5, 14.7, 17.9, 20.3, 20.9, 22.6, 26.7, 28.5, 28.7, 30.9, 32.5,
53.4, 76.4, 136.1, 142.2, 203.9, 218.0; IR (neat) ν (CO) = 1708,
1742 cm−1; HRMS (ESI) calcd. for C19H33O2 [M + H]+ 293.2475,
found 293.2478.
CDCl3, SiMe4) δ 0.79−1.21 (m, 14H, 1CH2, 4CH3), 1.30−1.50 (m,
17H, 4CH2, 3CH3), 1.96−2.34 (m, 6H, CH2), 3.37 (t, J = 3.2 Hz, 1H,
CH); 13C NMR (75 MHz, CDCl3, SiMe4) δ 14.2, 14.2, 14.3, 14.6,
17.4, 22.3, 23.5, 23.9, 26.3, 27.3, 27.8, 28.6, 29.8, 39.1, 48.3, 129.3,
137.4, 137.7, 150.6, 177.2; HRMS (EI) calcd. for C22H38O2 334.2872,
found 334.2875.
2,3,4,5-Tetraethyl-5-methylcyclopenta-1,3-dien-1-yl Piva-
1
late (5b). Colorless liquid: isolated yield 55% (80 mg); H NMR
(300 MHz, CDCl3, SiMe4) δ 0.53 (t, J = 7.2 Hz, 3H, CH3), 0.98−1.08
(m, 12H, CH3), 1.31 (s, 9H, CH3), 1.47 (q, J = 7.2 Hz, 2H, CH2),
2.00−2.27 (m, 6H, CH2); 13C NMR (75 MHz, CDCl3, SiMe4) δ 8.1,
13.2, 14.6, 15.0, 17.7, 17.9, 19.0, 21.0, 27.4, 27.8, 39.1, 54.2, 130.2,
138.8, 141.3, 151.4, 176.1; HRMS (EI) calcd. for C19H32O2 292.2402,
found 292.2400.
2,3,4,5-Tetraethyl-5-phenylcyclopenta-1,3-dien-1-yl Ada-
mantane-1-carboxylate (5c). Colorless liquid: isolated yield 59%
(128 mg); 1H NMR (300 MHz, CDCl3, SiMe4) δ 0.70−0.75 (m, 6H,
CH3), 1.04−1.13 (m, 6H, CH3), 1.59−1.74 (m, 11H, 3CH, 4CH2),
1.93−2.21 (m, 10H, CH2), 2.32 (q, J = 7.5 Hz, 2H, CH2), 7.11−7.21
(m, 5H, CH); 13C NMR (75 MHz, CDCl3, SiMe4) δ 7.7, 13.1, 14.2,
14.9, 18.1, 18.8, 19.1, 23.2, 27.9, 36.4, 38.7, 40.9, 61.6, 126.1, 126.9,
127.7, 131.9, 140.0, 140.8, 142.3, 151.8, 174.0; HRMS (EI) calcd. for
C30H40O2 432.3028, found 432.3030.
2,3,4,5-Tetraethyl-5-phenylcyclopenta-1,3-dien-1-yl Ben-
zoate (5d). Colorless liquid: isolated yield 57% (107 mg); 1H
NMR (300 MHz, CDCl3, SiMe4) δ 0.74 (t, J = 7.5 Hz, 3H, CH3), 0.82
(t, J = 7.5 Hz, 3H, CH3), 1.07−1.17 (m, 6H, CH3), 1.97−2.16 (m, 4H,
CH2), 2.23−2.40 (m, 4H, CH2), 7.13−7.34 (m, 5H, CH), 7.34−7.39
(m, 2H, CH), 7.48−7.53 (m, 1H, CH), 7.91−7.93 (m, 2H, CH); 13C
NMR (75 MHz, CDCl3, SiMe4) δ 7.8, 13.0, 14.2, 14.9, 18.3, 18.8, 19.1,
23.1, 61.8, 126.2, 126.8, 128.0, 128.3, 129.8, 130.0, 132.6, 133.0, 140.0,
140.5, 143.0, 151.7, 163.0; HRMS (EI) calcd. for C26H30O2 374.2246,
found 374.2244.
2-Benzoyl-2,3,4,5-tetraethyl-5-methylcyclopent-3-enone
1
(4c). Colorless liquid: isolated yield 89% (139 mg); H NMR (300
MHz, CDCl3, SiMe4) δ 0.79 (t, J = 7.5 Hz, 3H, CH3), 0.87 (t, J = 7.5
Hz, 3H, CH3), 0.97 (s, 3H, CH3), 1.05 (t, J = 7.5 Hz, 3H, CH3), 1.17
(t, J = 7.5 Hz, 3H, CH3), 1.44−1.73 (m, 3H, CH2), 2.16−2.37 (m, 4H,
CH2), 2.53−2.60 (m, 1H, CH2), 7.29−7.41 (m, 3H, CH), 7.67−7.69
(m, 2H, CH); 13C NMR (75 MHz, CDCl3, SiMe4) δ 9.1, 9.7, 14.1,
14.3, 18.9, 19.8, 21.9, 27.3, 30.3, 56.8, 74.8, 127.9, 128.1, 131.3, 137.8,
139.4, 145.7, 200.0, 218.4; HRMS (EI) calcd. for C21H28O2 312.2089,
found 312. 2092.
2,3,4,5-Tetraethyl-2-methyl-5-(thiophene-2-carbonyl)-
cyclopent-3-enone (4d). Colorless liquid: isolated yield 83% (132
1
mg); H NMR (300 MHz, CDCl3, SiMe4) δ 0.80 (t, J = 7.5 Hz, 3H,
CH3), 0.90 (t, J = 7.5 Hz, 3H, CH3), 1.07 (t, J = 7.5 Hz, 3H, CH3),
1.10 (s, 3H, CH3), 1.20 (t, J = 7.5 Hz, 3H, CH3), 1.51−1.56 (m, 1H,
CH2), 1.72−1.86 (m, 2H, CH2), 2.14−2.38 (m, 4H, CH2), 2.56−2.60
(m, 1H, CH2), 7.04 (t, J = 4.5 Hz, 1H, CH), 7.54 (d, J = 5.1 Hz, 1H,
CH), 7.94 (d, J = 4.2 Hz, 1H, CH); 13C NMR (75 MHz, CDCl3,
SiMe4) δ 9.1, 10.0, 14.1, 14.2, 19.0, 20.4, 22.4, 28.1, 29.7, 56.7, 74.2,
127.8, 133.3, 133.4, 138.4, 143.1, 145.3, 190.4, 216.9; HRMS (EI)
calcd. for C19H26O2S 318.1654, found 318.1651.
2,3,4,5-Tetraethyl-2-(4-iodobenzoyl)-5-methylcyclopent-3-
1
enone (4e). Colorless solid: isolated yield 71% (155 mg); H NMR
(300 MHz, CDCl3, SiMe4) δ 0.79 (t, J = 7.5 Hz, 3H, CH3), 0.85 (t, J =
7.5 Hz, 3H, CH3), 1.03 (t, J = 7.5 Hz, 3H, CH3), 1.02 (s, 3H, CH3),
1.17(t, J = 7.5 Hz, 3H, CH3), 1.45−1.52 (m, 1H, CH2), 1.62−1.74 (m,
2H, CH2), 2.12−2.37 (m, 4H, CH2), 2.50−2.58 (m, 1H, CH2), 7.45−
7.48 (m, 2H, CH), 7.68−7.71 (m, 2H, CH); 13C NMR (75 MHz,
CDCl3, SiMe4) δ 9.0, 9.7, 14.1, 14.3, 18.8, 19.8, 22.0, 27.5, 30.2, 56.8,
74.6, 98.9, 129.8, 137.1, 137.8, 138.3, 145.8, 198.9, 218.1; HRMS (EI)
calcd. for C21H27IO2 438.1056, found 438.1060. Recrystallization of 4e
from hexane solvent at room temperature afforded single crystals for
X-ray analysis.
2,3,4,5-Tetraethyl-5-phenylcyclopenta-1,3-dien-1-yl Acetate
1
(5e). Colorless liquid: isolated yield 72% (112 mg); H NMR (300
MHz, CDCl3, SiMe4) δ 0.68−0.74 (m, 6H, CH3), 1.06−1.13 (m, 6H,
CH3), 1.90−2.08 (m, 7H, 2CH2, 1CH3), 2.20 (q, J = 7.5 Hz, 2H,
CH2), 2.32 (q, J = 7.5 Hz, 2H, CH2), 7.18 (s, 5H, CH); 13C NMR (75
MHz, CDCl3, SiMe4) δ 7.6, 12.9, 14.1, 14.9, 18.2, 18.7, 19.1, 20.7, 22.9,
61.5, 126.2, 126.8, 127.9, 132.3, 140.0, 140.4, 142.8, 151.8, 167.5;
HRMS (EI) calcd. for C21H28O2 312.2098, found 312.2092.
2,3,5-Trimethyl-4,5-diphenylcyclopenta-1,3-dien-1-yl Piva-
late (5f). White solid: isolated yield 67% (121 mg); mp 76−78 °C;
1H NMR (400 MHz, CDCl3, SiMe4) δ 1.12 (s, 9H, CH3), 1.41 (s, 3H,
2-Benzoyl-5-methyl-2,3,4,5-tetrapropylcyclopent-3-enone
1
(4f). Colorless liquid: isolated yield 58% (107 mg); H NMR (300
MHz, CDCl3, SiMe4) δ 0.82−1.05 (m, 15H, CH3), 1.00−1.60 (m,
12H, CH2), 2.04−2.21 (m, 3H, CH2), 2.44 (m, 1H, CH2), 7.29−7.41
(m, 3H, CH), 7.65−7.68 (m, 2H, CH); 13C NMR (75 MHz, CDCl3,
SiMe4) δ 14.7 (2 CH3), 15.0, 15.1, 17.8, 18.3, 22.4, 22.9, 23.0, 28.6,
29.6, 36.7, 40.0, 56.7, 74.6, 127.9, 128.1, 131.3, 137.1, 139.3, 144.5,
199.9, 218.5; HRMS (EI) calcd. for C25H36O2 368.2715, found
368.2717.
CH3), 1.76 (s, 3H, CH3), 2.01 (s, 3H, CH3), 6.83−6.85 (m, 2H, CH),
7.14−7.23 (m, 8H, CH); 13C NMR (100 MHz, CDCl3, SiMe4) δ 10.2,
12.8, 18.2, 27.1, 39.0, 58.2, 125.0, 126.3, 126.4, 126.6, 127.8, 128.1,
128.9, 135.9, 136.1, 139.3, 143.4, 156.2, 175.2; IR (neat) ν (CO) =
1751 cm−1; HRMS (ESI) calcd. for C25H29O2 [M + H]+ 361.2162,
found 361.2171.
Typical Procedure for the Isolation of Intermediate 10f from
the Reaction of 1-Lithio-1,3-diene 2f with Carbon Monoxide.
To a solution of 1-halo-1,3-butadienes (0.5 mmol) in THF−Et2O (5
mL, 1:1) was added 2 equiv of t-BuLi at −78 °C. After it was stirred at
−78 °C for 1 h, CO was then bubbled into the reaction mixture for 0.5
h. The above reaction mixture was stirred for additional 0.5 h under
CO atmosphere. Next, the reaction mixture was allowed to warm to
room temperature. Then, the solvents were removed under vacuum in
glovebox, and the residue was dissolved in hexane and filtered. This
step may need to be repeated several times until the residue powder
can be totally dissolved in hexane to form a clear solution. Thus
obtained powder as salt free 10f is pure enough for NMR analysis.
Lithio Cyclopentadienyl Enolate Intermediate (10f). Yellow
solid: 1H NMR (500 MHz, C4D8O) δ 1.30 (s, 3H, CH3), 1.70 (s, 3H,
CH3), 2.09 (s, 3H, CH3), 6.75−7.18 (m, 10H, CH); 13C NMR (100
MHz, C4D8O) δ 9.5, 14.6, 20.3, 58.9, 101.3, 123.0, 125.2, 127.6, 127.8,
4-Benzoyl-2,3-dibutylcyclopent-2-enone (6a). Colorless
1
liquid: isolated yield 91% (136 mg); H NMR (300 MHz, CDCl3,
SiMe4) δ 0.85 (t, J = 6.6 Hz, 3H, CH3), 0.92 (t, J = 6.6 Hz, 3H, CH3),
1.31−1.47 (m, 8H, CH2), 2.23−2.32 (m, 3H, CH2), 2.53−2.60 (m,
1H, CH2), 2.39−2.46 (m, 1H, CH2), 2.70−2.79 (m, 1H, CH2). 4.71−
4.73 (m, 1H, CH), 7.49−7.65 (m, 3H, CH), 7.99−8.01 (m, 2H, CH);
13C NMR (75 MHz, CDCl3, SiMe4) δ 13.7, 14.0, 22.7, 22.8, 23.2, 29.6,
29.7, 30.6, 39.4, 47.6, 128.5, 129.0, 133.8, 136.4, 143.0, 171.4, 199.4,
206.9; IR (neat) ν (CO) = 1682, 1702 cm−1; HRMS (EI) calcd. for
C20H26O2 298.1933, found 298.1934.
2,3-Dibutyl-4-pivaloylcyclopent-2-enone (6b). Colorless
liquid: isolated yield 42% (58 mg); 1H NMR (300 MHz, CDCl3,
SiMe4) δ 0.88−0.94 (m, 6H, CH3), 1.22−1.52 (m, 17H, 4 CH2, 3
CH3), 2.02−2.23 (m, 4H, CH2), 2.46−2.61 (m, 2H, CH2), 4.23−4.25
(m, 1H, CH); 13C NMR (75 MHz, CDCl3, SiMe4) δ 13.8, 14.0, 22.7,
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127.9, 128.3, 130.1, 139.7, 143.8, 147.5, 182.8. Recrystallization of 10f
from THF−hexane at room temperature afforded single crystals for X-
ray analysis.
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Typical Procedure for the Preparation of Intermediate 10f
from the Deprotonation Lithiation of 3-Cyclopentenones
Using LDA. One equivalent of LDA was added into the solution of
3-cyclopentenones 3f−3f′ (0.5 mmol, 1:2) in Et2O−THF (5 mL, 1:1)
at −78 °C. After it was stirred at −78 °C for 1 h, the reaction mixture
was allowed to warm to room temperature for 3 h. Then, the solvents
were removed under vacuum in a glovebox, and the residue was
dissolved in hexane and filtered. The resulting powders 10f were
recrystallized from hexane at −30 °C, affording suitable crystals for
NMR analysis and X-ray analysis.
ASSOCIATED CONTENT
* Supporting Information
■
S
(9) (a) Smith, K.; Pritchard, G. J. Angew. Chem., Int. Ed. Engl. 1990,
29, 282−283. (b) Smith, K.; El-Hiti, G. A.; Hawes, A. C. Synlett 1999,
945−947. (c) Smith, K.; El-Hiti, G. A.; Pritchard, G. J.; Hamilton, A. J.
Chem. Soc., Perkin Trans. 1 1999, 2299−2303.
Crystallographic data for 3f, 4e, and 10f and NMR spectra for
new compounds. This material is available free of charge via the
Internet at http://pubs.acs.org.
(10) (a) Rossi, A.; Kapahi, P.; Natoli, G.; Takahshi, T.; Chen, Y.;
Karin, M.; Santoro, M. G. Nature 2000, 403, 103−108. (b) Roberts, S.
M.; Santoro, M. G.; Sickle, E. S. J. Chem. Soc., Perkin Trans. 1 2002,
1735−1742.
AUTHOR INFORMATION
Corresponding Author
*Fax: 86 10 62759728. E-mail: zfxi@pku.edu.cn.
■
(11) (a) Takahashi, T.; Huo, S.; Hara, R.; Noguchi, Y.; Nakajima, K.;
Sun, W. J. Am. Chem. Soc. 1999, 121, 1094−1095. (b) Shi, X.; Gorin,
D. J.; Toste, F. D. J. Am. Chem. Soc. 2005, 127, 5802−5803. (c) Davie,
C. P.; Danheiser, R. L. Angew. Chem., Int. Ed. 2005, 44, 5867−5870.
(d) Zhang, L.; Wang, S. J. Am. Chem. Soc. 2006, 128, 1442−1443.
(e) Qi, X.; Ready, J. M. Angew. Chem., Int. Ed. 2008, 47, 7068−7070.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Natural Science Foundation of
China and the Major State Basic Research Development
Program (2011CB808700).
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