Base-Promoted Tandem Reaction towards Conjugated Dienone or Chromone Derivatives with a Cyano Group: Insertion of Alkynes into C–C σ-Bonds of 3-Oxopropanenitriles

Article abstract of DOI:10.1002/adsc.201700565

Base-promoted insertion reactions of alkynes into the C–C σ-bonds of α-cyano ketones were established to construct highly functionalized conjugated olefins or chromone derivatives via transition metal-free tandem reactions. These reactions are initialized through the nucleophilic attack of α-cyano ketones to alkynones followed by intramolecular nucleophilic addition/ring-opening to furnish the cyano-containing alkenes. In the cases of alkynones bearing an ortho-halide-substituted aryl ring, a further C–O bond coupling reaction occurs to afford chromone derivatives in good to high yields. Various alkynones bearing alkyl or aryl substituents were compatible in the reaction. This reaction has the potential to become a general synthetic protocol for the preparation of cyano-substituted olefins and chromones due to the abundance of easily accessible starting materials possessing diverse substituent groups. (Figure presented.).

Full text of DOI:10.1002/adsc.201700565

Title: Base-Promoted Tandem Reaction to Conjugate Dienone or
Chromone Derivatives with Cyano Group: Insertion of Alkynes
into C-C σ-Bonds of 3-Oxopropanenitriles
Authors: Qiyi Yao, Lingkai Kong, Fangfang Zhang, Xianghua Tao, and
Yanzhong Li
This manuscript has been accepted after peer review and appears as an
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To be cited as: Adv. Synth. Catal. 10.1002/adsc.201700565
Link to VoR: http://dx.doi.org/10.1002/adsc.201700565

10.1002/adsc.201700565
Advanced Synthesis & Catalysis
COMMUNICATION
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
Base-Promoted Tandem Reaction to Conjugate Dienone or
Chromone Derivatives with Cyano Group: Insertion of Alkynes
into C-C σ-Bonds of 3-Oxopropanenitriles
Qiyi Yao, Lingkai Kong, Fangfang Zhang, Xianghua Tao, Yanzhong Li *
Shanghai Key Laboratory of Green Chemistry and Chemical Processes, School of Chemistry and Molecular Engineering,
East China Normal University, 500 Dongchuan Road, Shanghai 200241, China.
E-mail: yzli@chem.ecnu.edu.cn
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.((Please
delete if not appropriate))
Abstract: Base-promoted insertion reactions of alkynes
into C-C σ-bonds of-cyano ketones were established to
construct highly functionalized conjugate olefins or
chromone derivatives via transition-metal free tandem
reactions. These reactions are initialized through the
Nitrile structures could be found in many biologically
active compounds, such as pharmaceuticals, agrochemicals,
and natural products.[4] Thus, it is an important synthetic
challenge to develop versatile and efficient methods for the
introduction of a cyano group into organic molecules. In
the past two decades, insertion reactions of unsaturated
bonds into C−C -bonds of carbonyl cyanides have
nucleophilic attack of -cyano ketones to alkynones
followed
by
intramolecular
nucleophilic
addition/ring-opening to furnish the cyano-containing
alkenes. In the cases of alkynones bearing an
ortho-halide-substituted aryl ring, further C-O bond
coupling reaction occurs to afford chromone derivatives in
good to high yields. A variety of alkynones bearing alkyl or
aryl substituents were compatible in the reaction. This
reaction has the potential to become a general synthetic
protocol for the preparation of cyano substituted olefins and
chromones due to the abundance of easily accessible
starting materials possessing diverse substituent groups.
achieved
transition-metal-catalyzed
exciting
progress,
insertion
among
reactions
which
of
unsaturated C−C bonds[5] and Lewis-base-catalyzed
insertion reactions of carbon−heteroatom double bonds
(C=O, C=N) [6] are worth to remind. However, the insertion
reactions into C-C -bond were limited to cyanoformates
(Scheme 1a). Michael addition reaction occurred with the
case of ethyl 2-cyanoacetate instead of the cleavage of the
C−C bond (Scheme 1b).[6h] The phosphine-catalyzed
insertion of alkynoates into C-CN
Keywords: C-C insertion, chromones, hydroxydienes,
transition-metal-free, tandem reactions
It is a highly efficient method to synthesize useful
organic compounds by the direct insertion of unsaturated
bonds into C-C -bonds, due to the atom-efficient
construction of two C-C bonds simultaneously. However,
the inert and stable properties of C−C bond cause these
chemical transformations highly challenging. To improve
the reactivity, highly strained molecules were mostly
employed in such transformations in the past few
decades.[1] For unstrained systems, insertion reactions into
C-C -bonds are transition-metal catalyzed ones, mainly
with rhenium-catalysis.[2] For instance, Takai and
Kuninobu[2b-f] have developed excellent rhenium-catalyzed
reactions of terminal acetylenes[2e,2f] and internal
alkynes,[2d] of which C-C triple bonds insert into the C-C
-bonds of 1,3-dicarbonyl compounds. With regards to
transition-metal free reactions, insertion of alkynes into
C-C -bonds are rare with the exception of highly reactive
arynes or cyclohexyne.[3]
Scheme 1. Insertion into C-C -bond
1
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10.1002/adsc.201700565
Advanced Synthesis & Catalysis
bond of acyl cyanides was also reported (Scheme 1c).[5a]
Recently, we have developed novel methodologies for the
insertion reaction of alkynes into 2, 4-dione to synthesize
polycyclic systems,[7] such as xanthones, chromones or
cyclooctachromenones. Herein we expand the scope of this
alkyne insertion reaction manifold to 3-oxopropanenitriles
to construct highly functionalized conjugate olefins and
chromone derivatives bearing a cyano group, which are
prevalent in natural products and are widely recognized as
candidates for drug development due to their excellent
biological and pharmacological activities,[8] via
transition-metal free tandem reactions.
yield with the ratio of Z:E = 5:2 (Table 1, entry 6). At 110
oC, a decrease in the amount of base (1.0 equiv) resulted in
lower yield of 3a (Table 1, entry 7), and an increase in the
amount of base (2.5 equiv) did not give a better result
(Table 1, entry 8 vs. 1). Lastly, the effect of different
solvents were examined using Cs2CO3 (2.0 equiv) as a
o
base at 110 C (Table 1, entries 9-12). When the reaction
was performed in DMF (N, N-dimethylformamide) or
DMSO (dimethylsulfoxide), good yields of 3a was
obtained with much lower selectivity (Table 1, entries 9,
10). Highest yield and selectivity was acheived using
o
toluene as solvent at 110 C (Table 1, entry 11). When the
o
Table 1. Screening of Reaction Conditions [a]
reaction was carried out at 80 C, the decreased yield and
selectivity was observed (Table 1, entry 12).
With the optimal reaction conditions in hand (Table 1,
entry 11), we expanded the substrate scope of this C-C
insertion reactions to different substitued acetylenic
ketones (Table 2). Firstly, the R1 substituent on the aryl
ring was explored (Table 2 , 3a-3f). Both electron-donating
and electron-withdrawing groups on the aryl subsituents
R1 were tolerable to the reaction conditions, offering high
yields of the desired products with good selectivity. For
exmple, an electron-donating substituent (R1= 4-OMe)
gave 98% yield of product 3b (Z:E=14:1). Bulky
substituent
(3,4,5-tri-OMe)
also
reacted
with
3-oxo-3-phenylpropanenitrile (2a) smoothly to afford 3c in
88% yield. Introduction of a 4-Br electron-withdrawing
group to the substrate resulted in a slightly decline in the
yield of 3d. Notably, an alkyl R1 substituent could also be
successfully employed to give the corresponding 3f in 83%
yield with exellent selectivity. Subsequently, the
substituent on the triple bond terminus was explored. An
electron-withdrawing group (4-Cl) furnished the
[a] Reactions were conducted on a 0.3 mmol scale with the
ratio of 1a:2a = 1:1 in 3.0 mL of solvent under air.
[b] Isolated yield as a mixture of Z/E-isomers.
Table 2. Synthesis of 3[a]
[c]
1
Determined by H NMR analysis of the crude reaction
mixture.
[d] No reaction.
[e] 1.0 equiv of Cs2CO3 was added.
[f] 2.5 equiv of Cs2CO3 was added.
Initially, the reaction conditions were investigated using
3-phenyl-1-(p-tolyl)
prop-2-yn-1-one
(1a)
and
3-oxo-3-phenylpropanenitrile (2a) as the model substrates
with the ratio of 1a:2a = 1:1 (Table 1). Firstly, the effect of
different
bases
was
studied
in DMAc
(N,
N-dimethylacetamide) at 110 oC under air (Table 1, entries
1-4). When Cs2CO3 (80% yield, Z: E = 15:1) or K2CO3 (68%
yield, Z: E = 13:1) was employed in the reaction, good
yields of 3a could be obtained with excellent selectivities
of Z/E isomers (Table 1, entries 1 and 2). While almost no
[a]
t
Unless otherwise noted, the reactions were carried out
reaction occured in the cases with BuOK or DABCO
o
using 2.0 equiv of Cs2CO3 in 3.0 mL toluene at 110 C
(1,4-diazabicyclo[2.2.2]octane) as base (Table 1, entries 3
and 4). Next, the reaction temperature and the amount of
base were screened (Table 1, entries 5-8). Decreasing the
reaction temperature to 80 oC affected little in the
reactivity and the yield of product 3a, however the
selectivity of Z/E isomer of product dropped sharply
(Table 1, entry 5). The results indicated that the Z/E
selectivity could be improved at higher reaction
temperature. The preferential formation of the Z-isomer is
possibly due to that it is thermodynamically more stable
than the E-isomer. When the reaction was carried out with
under air on a 0.3 mmol scale with the ratio of 1:2a = 1:1.
the ratio of Z/E was determined by 1H NMR analysis of the
crude reaction mixture. Isolated yields of Z/E-isomers.
corresponding 3g in 79% yield. In the cases of substituents
bearing electron-donationg groups, such as 4-OMe, or
4-Me, the reaction proceeded smoothly to afford high
yields of the desired products with exellent selectivity.
Considering the interesting structure of compounds 3,
we envisioned that if
ortho-halide-substituted aryl ring on the carbonyl carbon
a
substrate bearing an
o
2.0 equiv of Cs2CO3 at 60 C, 3a was obtained in 76%
2
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10.1002/adsc.201700565
Advanced Synthesis & Catalysis
was used, it might undergo further intramolecular
cyclization to give chromone derivatives. Thus,
1-(2-bromophenyl)-3-phenylprop-2-yn-1-one (4a) was
used to react with 2a under the aforementioned optimal
reaction conditions. However, only trace amount of
cyclization product was detected in toluene (Table 3, entry
1). To improve the yield of chromone 5a, different solvents
and bases were screened. It was found that using 2.0 equiv
note that 4,4-dimethyl-3-oxopentanenitrile (2b) was found
to be a suitable substrate, offering the corresponding
pyranopyridin-4-one (5o) in 93% yield with nice
selectivity (Z/E = 10:2).
Table 4. Synthesis of 5 [a]
o
of Cs2CO3 in DMAc at 110 C maximized the product
yields and gave best Z/E selectivity (Table 3, entry 6).
Next, we investigated the substrate scope for the
synthesis of chromone derivatives 5 (Table 4). When
chloro or fluoro-substituted ynone was used instead of 4a,
the desired 5a could also be produced in 80 and 91% yields,
respectively. It was clear that ynones bearing a bromo
leaving group gave higher yield of the corresponding
product. Thus the following investigations concerning
substituents effects were carried out using substrate 4
bearing a bromo leaving group. The results are depicted
Table 3. Screening of Reaction Conditions [a]
[a]
Unless otherwise noted, the reactions were carried out
o
using 2.0 equiv of Cs2CO3 in 3.0 mL toluene at 110 C
under air on a 0.3 mmol scale with the ratio of 1:2a = 1:1.
the ratio of Z/E was determined by 1H NMR analysis of the
crude reaction mixture. Isolated yields of Z/E-isomers.
In order to clarify the reaction mechanism, the
experiment was performed under the optimized reaction
conditions at room temperature (Scheme 2).
Scheme 2. Control experiments
Full convertion of 4a was observed within 9 h according to
TLC (thin-layer chromatography), with Z/E-6a in 94%
isolated yield. After recrystallization, pure Z-isomer of 6a
was obtained and characterized by X-ray crystallography[9]
(see Supporting Information, including a CIF files).
Intermediates Z/E-6a was used as starting materials and
subjected to the general reaction conditions of our system,
resulting in product Z/E-5a in 98% yield. This indicates
that the Z/E-isomers were formed in the first step and the
desired chromone was obtained through a stepwise path.
[a]
Reactions were conducted on a 0.3 mmol scale with the
ratio of 4a:2a = 1:1 in 3.0 mL of solvent under air.
[b] Isolated yields of Z/E-isomers.
[c]
Determined by 1H NMR analysis of the crude reaction
mixture.
[d] 6a was obtained in 44% yield.
[e] 1.0 equiv of Cs2CO3 was added.
[f] 3.0 equiv of Cs2CO3 was added.
On the basis of our experimental results and the reported
work, a plausible reaction mechanism has been proposed
with model substrate 4a and 2a (Scheme 3). In the
presence of base, 3-oxo-3-phenylpropanenitrile (2a)
in Table 4. Good to excellent yields of the corresponding
chromone compounds 5 were obtained irrespective of the
presence of electron-donating or electron-withdrawing
groups of the aryl ring on the triple bond (5a-5g). However,
the selectivity of Z/E isomer of products decreased with
sterically hindered substituents (5d, 5e). An alkyl (nBu and
Me) substituted substrate also underwent the insertion
reaction to give good yield of 5h and 5i. The substituents
on the aryl ring of carbonyl side did not impact much on
the reactivities, delivering the corresponding products in
high yields (5j-n). Ynone bearing a pyridine ring also
reacted smoothly with 2a to provide the corresponding
pyridine-fused pyranone 5k in 75% yield. It is worth to
Scheme 3. Plausible Reaction Mechanism
undergoes an enol tautomerism and then attacks the alkyne
moiety of 1-(2-bromophenyl)-3-phenylprop-3-yn-1-one
3
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10.1002/adsc.201700565
Advanced Synthesis & Catalysis
(4a), giving an allene intermediate A. Next, through a
four-membered ring transition state, the insertion reaction
of C-C σ-bond is achieved to give 6a, which undergoes
intramolecular cyclization to afford chromone 5a.
Rev. 2004, 33, 610; f) M. Murakami, H. Amii, Y. Ito,
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In summary, we have developed a procedure for the
synthesis of conjugate olefins and chromone derivatives
bearing cyano functional groups, which was realized by a
base-promoted insertion reaction of alkynes into C-C
σ-bond of 3-oxo-propanenitriles and subsequent
cyclization reactions. High yields of the desired products
and easily accessible starting materials possessing diverse
substituents offer the potential for this system to become a
general synthetic protocol for the preparation of conjugate
olefin and chromone derivatives.
Experimental Section
Typical
Procedure
for
the
Preparation
of
(4Z)-5-hydroxy-4-(4-methylbenzoyl)-3,5-diphenylpenta-2,
4-dienenitrile (3a)
Under an atmosphere of air, to a Schlenk tube were added
3-phenyl-1-(p-tolyl)prop-2-yn-1-one (1a) (0.30 mmol, 66.1
mg) and Cs2CO3 (0.6 mmol, 195.5 mg), toluene (3.0 mL)
and 3-oxo-3-phenylpropanenitrile (2a) (0.30 mmol, 43.6
o
mg) was stirred at 110 C in 1 h. After the reaction was
completed as monitored by thin-layer chromatography, the
reaction mixture was then quenched by water, and the
water layers were extracted with ethyl acetate (10 mL × 3).
The combined organic layers were washed with brine,
dried over anhydrous Na2SO4, filtered, and concentrated
under reduced pressure. Purification by chromatography on
silica gel (petroleum ether/ethyl acetate = 10:1) afforded
[4] a) F. F. Fleming, L. Yao, P. C. Ravikumar, L. Funk, B.
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Y. Nakao, T. Hiyama, M. Ohashi, S. Ogoshi, J. Am.
desired
compound
(4Z)-5-hydroxy-4-(4-methylbenzoyl)-3,5-diphenylpenta-2,
4-dienenitrile (3a) as a yellow solid, 99.7 mg (91% yield,
Z/E=14:1), mp 169-171oC.
Supporting Information
Detailed descriptions of experimental procedures and their
spectroscopic data as well as the crystal structures are
presented in the Supporting Information. CCDC 1511164
(Z-6a) contains the supplementary crystallographic data for
this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Chem.
Soc.
2010,
132,
10070;
For
Acknowledgements
phosphine-Catalyzed insertion of alkyne, see: k) L.
Souillart, N. Cramer, Chem. Rev. 2015, 115, 9410.
We thank the National Natural Science Foundation of
China (Grant No. 21272074) and Program for Changjiang
Scholars and Innovative Research Team in University
(PCSIRT) for financial support.
[6] For selected examples, see: C=O insertion, a) C. S.
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10.1002/adsc.201700565
Advanced Synthesis & Catalysis
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5
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10.1002/adsc.201700565
Advanced Synthesis & Catalysis
COMMUNICATION
Base-Promoted Tandem Reaction to Conjugate
Dienone or Chromone Derivatives with Cyano
Group: Insertion of Alkynes into C-C σ-Bonds of
3-Oxopropanenitriles
Adv. Synth. Catal. 2017, Volume, Page – Page
Qiyi Yao, Lingkai Kong, Fangfang Zhang,
Xianghua Tao, Yanzhong Li *
6
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