Synthesis of aryl allyl alkynes via reaction with allyl amine and aryl alkynoic acids through decarboxylation

Article abstract of DOI:10.1080/00397911.2020.1726398

Allyl alkynoic esters were synthesized by the reaction of allyl amines and alkynoic acids via deaminative esterification. The reaction of allyl alkynoic esters with Pd(dba)₂ and Xantphos in digylme at 110 °C for 12 h afforded the desired decarb

Full text of DOI:10.1080/00397911.2020.1726398

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Synthesis of aryl allyl alkynes via reaction with
allyl amine and aryl alkynoic acids through
decarboxylation
Jieun Lee, Kye Chun Nam & Sunwoo Lee
To cite this article: Jieun Lee, Kye Chun Nam & Sunwoo Lee (2020): Synthesis of aryl allyl
alkynes via reaction with allyl amine and aryl alkynoic acids through decarboxylation, Synthetic
Communications, DOI: 10.1080/00397911.2020.1726398
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SYNTHETIC COMMUNICATIONSV
https://doi.org/10.1080/00397911.2020.1726398
Synthesis of aryl allyl alkynes via reaction with allyl amine
and aryl alkynoic acids through decarboxylation
Jieun Lee, Kye Chun Nam, and Sunwoo Lee
Department of Chemistry, Chonnam National University, Gwangju, Republic of Korea
ABSTRACT
ARTICLE HISTORY
Received 28 December 2019
Allyl alkynoic esters were synthesized by the reaction of allyl amines
and alkynoic acids via deaminative esterification. The reaction of allyl
alkynoic esters with Pd(dba)2 and Xantphos in digylme at 110ꢀC for
12 h afforded the desired decarboxylated allyl alkynes in good yields.
KEYWORDS
Allyl alkyne; allylation; allyl
amine; decarboxylation;
intramolecular coupling
GRAPHICAL ABSTRACT
Introduction
Decarboxylative coupling reactions have received considerable attention for the synthesis
of key molecules in the pharmaceutical, agricultural, and materials industries.[1]
Decarboxylative coupling of alkynoic acids has been widely used to introduce alkynyl
groups into target molecules.[2] This approach affords several advantages compared to
the Sonogashira coupling reaction, which employs terminal alkynes as the alkyne source.
Aryl alkynoic acid derivatives are readily prepared via direct coupling of propiolic acid
and aryl halides (or pseudo halides) and are easily purified and isolated through aque-
ous workup.[3] Alkynoic acids are also stable and the reaction releases only carbon diox-
ide, which is relatively nontoxic compared to the organometallic waste generated at the
end of the coupling reaction. A variety of coupling partners have been employed for the
formation of C–C, C–N, and C–P bonds in decarboxylative coupling reactions.[4]
Transition-metals such as Pd, Ni, Cu, and Ag are generally used as the catalysts, and
metal-free conditions have also been reported.[5]
Allyl alkynes are one of the useful building blocks in organic synthesis.[6] Several
methods employing the transition-metal-catalyzed allylation of alkynes have been
reported.[7] We reported the synthesis of allyl alkynes via nickel-catalyzed decarboxyla-
tive coupling of alkynoic acids and allyl acetates.[8] While this was the first example of
the intermolecular decarboxylative allylation of an alkyne, intramolecular decarboxyl-
ation of allyl esters was reported by Tunge and coworkers.[9] Although they reported
palladium-catalyzed intramolecular decarboxylation, they provided only a few examples
CONTACT Kye Chun Nam
kcnam@chonnam.ac.kr; Sunwoo Lee
sunwoo@chonnam.ac.kr
Department of
Chemistry, Chonnam National University, Gwangju 61186, Republic of Korea.
Supplemental data for this article can be accessed on the publisher’s website.
ß 2020 Taylor & Francis Group, LLC

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J. LEE ET AL.
of the decarboxylation of allyl alkynoic esters. Therefore, general methods of intramo-
lecular decarboxylation for the synthesis of allyl alkynes are in demand.
A variety of synthetic methods for the preparation of esters have been developed. It
is well known that allyl and benzyl primary amines react with carboxylic acids to give
the corresponding allyl and benzyl esters via deamination in the presence of NaNO2.[10]
During our studies of decarboxylative coupling reactions, we found that the preparation
of allylic alkynoic esters from the reaction with allyl amines has not been reported. In add-
ition, only a few examples of the intramolecular decarboxylative coupling of allylic alkynoic
esters have been documented.[9] Herein, we report the synthesis of allyl alkynes via the
intramolecular decarboxylation of alkynoic esters, which were prepared by deamination.
Results and discussion
To accomplish this goal, we evaluated the optimal conditions for the formation of allyl
esters from allyl amines and phenyl propiolic acid. When allyl amine (1) was reacted
with NaNO2 and phenylpropiolic acid in the presence of several solvents containing
water, the desired allyl phenyl propiolate (3a) was formed in low yields (entries 1–3).
The reactions were carried out in dried solvents, such as dioxane, CH3CN, and toluene
to give the desired product 3a in 52, 26, and 31% yield, respectively (entries 4–6).
When the amount of phenylpropiolic acid was increased to three equivalents, 3a was
formed in 86% yield (entry 7). By employing HCl instead of additional phenylpropiolic
acid, the desired product was obtained in 92% yield when the reaction was conducted
with one equivalent of HCl (entry 8). However, the addition of two equivalents of HCl
with 1.0 equivalent of phenylpropiolic acid did not provide a satisfactory result (entry
9). The optimal conditions for the preparation of allyl alkynoic esters are as follows:
allyl amine (1.0 equiv), HCl (1.0 equiv), and NaNO2 (2.0 equiv) were reacted at 0 ꢀC for
30 min; alkynoic acid (2.0 equiv) was then added to the reaction mixture and stirred at
25 ꢀC for 6 h (Table 1).
Table 1. Optimal conditions for deaminative esterificationa.
Ratio
1a/NaNO2/2a
Entry
Solvent
Dioxane/H2O
CH3CN/H2O
Toluene/H2O
Dioxane
CH3CN
Toluene
Dioxane
Dioxane
Yield (%)d
1
2
3
4
5
6
1/2/2
1/2/2
1/2/2
1/2/2
1/2/2
1/2/2
1/2/3
1/2/2
1/2/1
19
12
Trace
52
26
32
86
92
45
7
8b
9c
Dioxane
aReaction conditions: 1a (0.3 mmol) and NaNO2 were reacted at 0 ꢀC for 30 min; 2a was then added and the reaction
proceeded at 25 ꢀC for 6 h.
bHCl (0.3 mmol) was added.
cHCl (0.6 mmol) was added.
1
dDetermined by H NMR with internal standard.

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SYNTHETIC COMMUNICATIONSV
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Table 2. Optimal conditions for intramolecular decarboxylationa.
Entry
Pd
Ligand
Solvent
Toluene
Toluene
Toluene
Toluene
Diglyme
DMSO
Yield (%)b
1
2
3
4
5
6
7
Pd(PPh3)4
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
Pd(dba)2
–
77
60
67
82
91
24
47
PPh3
Dppb
Xantphos
Xantphos
Xantphos
Xantphos
DMF
aReaction conditions: 3a (0.3 mmol), Pd (0.03 mmol), and ligand (0.06 mmol) were reacted in solvent (1.0 mL) at 110 ꢀC for 12h.
1
bDetermined by H NMR with internal standard.
Further, the conditions for the intramolecular decarboxylation were optimized. When
Pd(PPh3)4 was employed and the reaction was allowed to proceed at 100 ꢀC for 12 h,
the desired decarboxylated allyl alkyne 4a was formed in 77% yield (entry 1). The use
of Pd(dba)2 as a palladium source for reaction with ligands like PPh3, 1,4-bis(diphenyl-
phosphino)butane (dppb), and Xantphos afforded the desired product 4a in 60, 67, and
82% yields, respectively (entries 2–4). The highest product yield was obtained with
digylme as the solvent (entries 5–7) (Table 2).
Under the optimal conditions, various aryl alkynoic acids were evaluated for the for-
mation of allyl alkynoic esters. As expected, when phenylpropiolic acid was employed
under the optimal conditions, the desired product 3a was obtained in 90% isolated
yield. The reactions with ortho-, meta-, and para-methyl substituted phenylpropiolic
acids afforded the allylated products 3b, 3c, and 3d in 62, 85, and 65% yields. In add-
ition, the reactions with ortho-, meta-, and para-methoxy-substituted phenylpropiolic
acids also afforded good yields of the allylated congeners. 4-Biphenyl and 1-naphthyl
propiolic acids gave the corresponding products 3h and 3i in 63 and 80% yields,
respectively. 4-Bromophenylpropiolic acid gave 3j in 63% yield. Phenylpropiolic acids
having ketone and ester groups provided the desired products 3k and 3l, respectively,
in good yields (Scheme 1).
The intramolecular decarboxylation was conducted with these allyl alkynoic esters.
Phenylpropiolic acid provided the desired allyl alkyne 4a in 90% isolated yield. Methyl-
and methoxy-substituted allyl phenylpropiolates afforded the desired products in good
yields. Allyl 4-biphenylpropiolate 3h gave 4h in 72% yield. Allyl 4-acetylphenylpropio-
late 3k also provided 4k in 55% yield. However, the desired products were not obtained
in pure form via reactions with other allyl propiolates, such as 3i, 3j, and 3l. They all
showed many unidentified spots in TLC (Scheme 2).
Conclusion
In summary, allyl alkynoic esters were synthesized via deaminative esterification. The
reaction of an allyl amine, NaNO2, HCl, and alkynoic acid in a ratio of 1:2:1:2 afforded
the desired allyl alkynoic esters in good yields. Pd(dba)2/Xantphos was the optimal cata-
lytic system for intramolecular decarboxylation in the synthesis of allyl alkynes.

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J. LEE ET AL.
a
Scheme 1. Synthesis of allyl alkynoic estersa. Reaction conditions: 1 (1.0 mmol), NaNO2 (2.0 mmol),
and HCl (1.0 mmol) were reacted at 0 ꢀC for 30 min and reacted with 2 (2.0 mmol) at 25 ꢀC for 6 h.
Numbers in parentheses are isolated yields.
Experimental details
All solvents and reagents were purchased and used without further purification. Thin-
layer chromatography (TLC) on precoated plated of silica gel was performed on TLC
silica gel 60 F254 with ethyl acetate/n-hexane (2:8) systems. Preparative flash chroma-
tography was performed by elution from columns of silica gel (230–400 mesh size). The
TLC plates were visualized by shortwave (254 nm) UV light. Melting points were deter-
mined on a capillary melting point apparatus and are uncorrected using electrothermal
1
melting point apparatus. H NMR (500 MHz) and 13C NMR (125 MHz) spectra were
recorded in CDCl3 using VARIAN VnmrJ. Chemical shifts are given in parts per mil-
lion (ppm) downfield from tetramethylsilane (TMS) as an internal reference and cou-
pling constants (J-values) are in hertz (Hz).
General procedure for the synthesis of ally alkynoic esters
The aqueous solution of HCl (1.0 mmol) and NaNO2 (2.0 mmol) was mixed with allyl
amine (1.0 mmol) in 1,4-dioxane (5 mL). The resulting mixture was stirred about 30 min
at 0 ꢀC. After that, phenylpropiolic acid (2.0 mmol) was added to the mixture and
stirred at room temperature for 6 h. The reaction mixture was diluted with EtOAc, and

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SYNTHETIC COMMUNICATIONSV
5
a
Scheme 2. Synthesis of allyl alkynesa. Reaction conditions: 3 (1.0 mmol), Pd(dba)2 (0.1 mmol), and
Xantphos (0.2 mmol) were reacted in diglyme at 110ꢀC for 12 h. Numbers in parentheses are iso-
lated yields.
washed with water for three times. The organic layer was dried over MgSO4 and then
the solvent was evaporated under reduced pressure. The crude mixture was purified by
column chromatography on silica gel (hexane:EtOA ¼ 10:1).
Aryl allyl propiolate (1.0 mmol), Pd(dba)2 (0.1 mmol) and Xantphos (0.2 mmol) were
mixed in diglyme at 110 ꢀC for 12 h. The resulting mixture was diluted with EtOAc and
washed with water. The organic layer was dried over MgSO4 and then the solvent was
evaporated under reduced pressure. The crude mixture was purified by column chroma-
tography on silica gel (hexane:EtOA ¼ 20:1).
Selected product
Allyl 3-phenylpropiolate (3a)
Propiolic acid (146.0 mg, 1.0 mmol) afforded 3a (167.4 mg, 0.9 mmol, 90% yield) as col-
1
orless oil. H NMR (400 MHz, CDCl3) d 7.61–7.58 (m, 2H), 7.49–7.36 (m, 3H), 5.98
(ddt, J ¼ 17.1, 10.4, 5.9 Hz, 1H), 5.44–5.38 (m, 1H), 5.34–5.30 (m, 1H), 4.74–4.72 (m,
2H); 13C NMR (101 MHz, CDCl3) d 153.8, 133.1, 131.2, 130.7, 128.6, 119.54, 119.49,
86.6, 80.4, 66.6; MS (EI) m/z: 186; Anal. Calcd for for C12H10O2: C, 77.40; H, 5.41;
Found: C, 77.51; H, 5.55.[11]
Pent-4-en-1-ynyl benzene (4a)
Allyl 3-phenylpropiolate (186.2 mg, 1.0 mmol) afforded 4a (127.8 mg, 0.9 mmol, 90%) as
1
colorless oil. H NMR (400 MHz, CDCl3) d 7.45–7.40 (m, 2H), 7.31–7.26 (m, 3H),

6
J. LEE ET AL.
5.96–5.84 (m, 1H), 5.44–5.38 (m, 1H), 5.19–5.15 (m, 1H), 3.20 (dt, J ¼ 5.3, 1.8 Hz, 2H);
13C NMR (101 MHz, CDCl3) d 132.5, 131.6, 128.2, 127.8, 123.7, 116.3, 86.6, 82.9, 23.7;
MS (EI) m/z: 142; Anal. Calcd for C11H10: C, 92.91; H, 7.09; Found: C, 92.88;
H, 7.12.[9b]
Full experimental detail and 1H and 13C NMR spectra have been provided in
supporting information. This material can be found via the “Supplementary Content”
section of this article’s webpage.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Funding
This work was supported by the National Research Foundation of Korea (NRF) and funded by
the Korea Government (MSIP) [grant number NRF-2017R1D1A3B03035736], [grant number
NRF-2015R1A4A1041036]. The spectral data were obtained from the Korea Basic Science
Institute, Gwangju branch.
ORCID
Sunwoo Lee
http://orcid.org/0000-0001-5079-3860
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