Efficient Synthesis of Functionalized β-Keto Esters and β-Diketones through Regioselective Hydration of Alkynyl Esters and Alkynyl Ketones by Use of a Cationic NHC–AuICatalyst

Article abstract of DOI:10.1002/ejoc.201601025

Regioselective hydration of α-alkynyl esters and ketones by using a cationic NHC–Au^Icatalyst results in β-keto esters and β-diketones, respectively. Controlled release of water in acetone by aldol self-condensation under the reaction conditions makes acetone as better solvent than 1,4-dioxane/water for the hydration of α-alkynyl esters having sensitive ester moieties.

Full text of DOI:10.1002/ejoc.201601025

DOI: 10.1002/ejoc.201601025
Full Paper
Gold Catalysis
Efficient Synthesis of Functionalized ꢀ-Keto Esters and ꢀ-
Diketones through Regioselective Hydration of Alkynyl Esters
and Alkynyl Ketones by Use of a Cationic NHC–AuI Catalyst
Chandrahas Tarigopula,[a] Ganesh Kumar Thota,[a] and Rengarajan Balamurugan*[a]
Dedicated to Professor Veejendra K. Yadav on the occasion of his 60th birthday
Abstract: Regioselective hydration of α-alkynyl esters and ket- tions makes acetone as better solvent than 1,4-dioxane/water
ones by using a cationic NHC–AuI catalyst results in ꢀ-keto es-
ters and ꢀ-diketones, respectively. Controlled release of water
in acetone by aldol self-condensation under the reaction condi-
for the hydration of α-alkynyl esters having sensitive ester moie-
ties.
Introduction
catalyst. However, they did not elaborate the study to assess its
applicability with functionalized substrates. Among gold cata-
lysts, NHC–AuI catalysts in 1,4-dioxane/water have shown their
superiority for the hydration of simple alkynes.[6l] We have
found that the IPrAuCl/AgSbF6 catalyst system in acetone pro-
motes regioselective hydration of functionalized 2-alkynoates
to result in corresponding ꢀ-keto esters in promising yields. The
regioselectivity is due to the polarization of the triple bond
caused by the attached ester group, which favours ꢀ-attack. It
is believed that water generated by aldol self-condensation of
acetone under Lewis-acidic conditions is involved in this mild
hydration.
ꢀ-Keto esters and ꢀ-diketones are important and common
building blocks in the synthesis of biologically active natural
products including heterocycles.[1] In addition, they, especially
ꢀ-diketones, exhibit tremendous coordination ability with metal
ions to form useful small metal complexes to single molecular
magnetic clusters.[2] Traditionally, they are made by base-medi-
ated Claisen ester condensation.[3] In addition, other methods
involving different strategies[4] are also available. However, syn-
thesis of functionalized ꢀ-keto esters and ꢀ-diketones by using
simple base-mediated Claisen condensations is not straightfor-
ward. Hence, alternate methods involving milder reaction con-
ditions, are desirable to make such compounds.
Gold catalysts have proved their efficiency to carry out a
range of organic transformations under milder reaction condi-
tions.[5] Among gold-catalyzed functional group transforma-
Results and Discussion
tions, hydration of alkynes has drawn certain attention.[5u,6] Substrate 2a has intriguing structural features because of its
Controlling the regioselectivity of hydration is a crucial factor in various functionalities. To mention a few, it contains an acti-
this reaction and is generally achieved by using neighbouring vated methylene carbon atom, Michael acceptors, a carbonyl
group participation.[6b,6f,6j] Regioselective hydration of α-alkynyl group and two different esters. In other words, all of the carbon
esters and ketones at the ꢀ-carbon is a practical approach to centres can be functionalized selectively; therefore, it can serve
make ꢀ-keto esters and ꢀ-diketones. Very recently, Mohapatra as a useful intermediate in organic synthesis. We are exploring
and co-workers have reported the synthesis of γ-acetoxy-ꢀ-keto different synthetic utilities of this compound, which was previ-
esters using Ph3PAuCl/AgOTf.[6b] In this reaction, hydration of ously synthesized in multi-step processes.[7] We envisaged that
the 2-alkynoic ester is assisted by the neighbouring group par- compound 2a could easily be made by the hydration of 1a,
ticipation of the acetoxy group. Hammond and co-workers have which is accessible in quantitative yield from ethyl propiolate
utilized NaAuCl4 for the ester-assisted regioselective hydration using a literature method.[8]
of 3-alkynoates to make γ-keto esters.[6j] In this study they
Initial attempts to hydrate 1a using gold catalysts under
made an α,ꢀ-keto ester from 2-alkynoic ester using the same
known conditions were not fruitful. For example, reactions us-
ing EtOH/H2O and MeOH/H2O solvent systems resulted in eth-
anol- and methanol-added products, respectively, along with
unreacted starting material (Table 1, entries 1–8). Heating the
reactions to reflux resulted in complex product mixtures (en-
tries 3 and 7). Using Ph3PAuCl/AgSbF6 in 1,4-dioxane/MeNO2
(20:1) with H2O (3 equiv.),[9] resulted in trace amounts of the
[a] School of Chemistry, University of Hyderabad,
Gachibowli, Hyderabad 500046, INDIA
E-mail: rbsc@uohyd.ernet.in
http://chemistry.uohyd.ac.in/~rb/
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under http://dx.doi.org/10.1002/ejoc.201601025.
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Table 1. Optimization of gold-catalyzed hydration.
Entry
Catalyst (mol-%)
Solvent
Temp. [°C]
Time [h]
Yield of 2a [%][a]
1
2
3
4
5
6
7
8
NaAuCl4·2H2O (2)
NaAuCl4·2H2O (2)
NaAuCl4·2H2O (2)
AuCl3 (2)
EtOH/H2O (4:1)
MeOH/H2O (4:1)
EtOH/H2O (4:1)
EtOH/H2O (4:1)
EtOH/H2O (4:1)
EtOH/H2O (4:1)
EtOH/H2O (4:1)
EtOH/H2O (4:1)
1,4-dioxane/MeNO2 (20:1), H2O (3 equiv.)
acetone
acetone
H2O/1,4-dioxane (1:2)
acetone
acetone
acetone
r.t.
r.t.
reflux
r.t.
r.t.
r.t.
r.t.
reflux
r.t.
60
24
24
2
24
24
24
24
3
12
2
48
1.5
6
25[b] (42)[e]
16[c] (38)[e]
complex mixture
15[b] (46)[e]
AuCl3/3AgSbF6 (2)
Ph3PAuCl/AgSbF6 (2)
Ph3PAuCl/AgOTf(2)
Ph3PAuCl/AgSbF6 (2)
Ph3PAuCl/AgSbF6 (2)
Ph3PAuCl/AgSbF6 (2)
Ph3PAuCl/AgSbF6 (2)
(IPr)AuCl/AgSbF6 (1)
(IPr)AuCl/AgSbF6 (0.3)
(IPr)AuCl/AgSbF6 (0.3)
(IPr)AuCl/AgSbF6 (0.1)
(IPr)AuCl/AgSbF6 (0.3)
(IPr)AuCl/AgSbF6 (0.3)
(IPr)AuCl/AgSbF6 (0.3)
(IPr)AuCl (0.3)
16[b] (43)[e]
34[b] (30)[e]
30[b] (37)[e]
complex mixture
trace
72
45
71
85
70
79
9
0
11
12
13
14
15
16
17
18
19
20
21
r.t.
110
60
r.t.
60
110
60
60
60
60
60
72
11
1.5
4
H2O/1,4-dioxane (1:2)
acetone/H2O (1:1)
acetone/D2O (1:1)
acetone
acetone
acetone
69
62
5
65[d]
48
38
3
61
45
AgSbF6 (0.3)
TfOH (10)
Decomposition
[a] Isolated yield. [b] Yield of 3a. [c] Yield of 3b. [d] 1:1.2 mixture of 2a and 2a-d2. [e] Values in parenthesis represent the percentage of recovered starting
material.
product (entry 9). In prior studies on the synthesis of bicyclic bly facilitates ester hydrolysis, which might have caused lower
acetals and dioxolanes, we found that water generated by gold- yields. 3-Aryl-2-alkynoates with electron-donating and -with-
catalyzed aldol self-condensation of acetone is crucially in- drawing groups on the aryl ring underwent smooth hydration
volved in the reaction.[10] Therefore hydration was attempted to give the respective ꢀ-keto esters (2d, 2e, 2g, 2h). Hydration
using 2 mol-% of Ph3PAuCl/AgSbF6 in refluxing acetone at of diethyl acetylenedicarboxylate resulted in product 2i, which
60 °C. To our delight, this reaction resulted in 72 % of the de- is generally prepared by base-promoted Claisen condensation
sired product 2a (entry 10). The same reaction at room temper- of ethyl acetate and diethyloxalate or by the reaction of diethyl
ature resulted in only 45 % yield (entry 11). The use of a cationic acetylenedicarboxylate with stoichiometric amounts of methyl
NHC–AuI catalyst in 1,4-dioxane/water (2:1) at 110 °C resulted hydrazine and sulfuric acid.[11] Interestingly, ethyl 5-phenyl-
in 71 % yield (entry 12). With the same catalyst system in acet- penta-2,4-diynoate resulted in ꢀ,δ-diketo ester 2j by hydration
one at 60 °C, the yield improved significantly to 85 % (entry 13). of the conjugated alkyne functionalities in a regioselective fash-
It should be noted that only 0.3 mol-% of the NHC–AuI catalyst ion. A protected γ-hydroxy-α-alkynoate ester could also be
was required. The efficiency of the reaction was comparatively hydrated to give 2k in good yield. Even a furan-substituted 2-
lower when 0.1 mol-% of the catalyst was used (entry 15). Be- alkynoate or a ꢀ-alkyl-α-alkynoate could be hydrated to give 2l
cause it is believed that water involved in the hydration is gen- or 2m, respectively. To check whether acetone is generally a
erated from acetone, a couple of reactions were carried out better solvent, hydration of different alkynones to ꢀ-diketones
using 1:1 mixtures of acetone/H2O and acetone/D2O (entries 17 was attempted. In all these cases, 1,4-dioxane/water was found
and 18). Although both reactions took less time for completion to be a better solvent system (2n–2r). More reactive ꢀ-diket-
in comparison to that in entry 13, the yields were lower. In the ones may react with acetone under the reaction conditions,
reaction involving D2O, the corresponding methylene-deuter- which could have decreased the yields of the ꢀ-diketones.
ated product 2a-d2 was obtained along with 2a in a ratio of
1.2:1. Based on these results, the substrate scope was evaluated
by using the optimized reaction conditions from entry 13 and
additionally from entry 16 for comparison.
In order to confirm the role of acetone, three control experi-
ments were carried out (Scheme 1). No reaction occurred when
NHC–AuI-catalyzed hydration of 1d was attempted in acetone
in the presence of 4 Å molecular sieves (i). When the reaction
Different 2-alkynoates prepared by simple synthetic proce- was carried out in [D6]acetone, 86 % of the deuterated product
dures were subjected to NHC–AuI-catalyzed hydration. The re- 2d-d2 was obtained along with 7 % of 2d (ii). The reaction in
sults are presented in Table 2 (products 2a–2m). Although the [D6]acetone took more time than that in regular acetone, which
reactions are faster in 1,4-dioxane/water than in acetone, the clearly shows the involvement of acetone in the protodemetal-
yields are significantly lower. Refluxing 1,4-dioxane/water possi- lation step.[10,12] Considering the results of the first two control
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Table 2. NHC–AuI catalyzed synthesis of ꢀ-keto esters and ꢀ-diketones.[a]
[a] Isolated yield.
Scheme 1. Control experiments.
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using EtOAc/hexanes as eluent to get pure 1k. Yield (246 mg, 82 %);
colourless liquid; Rf = 0.54 in EtOAc/hexanes (1:10). 1H NMR
(400 MHz, CDCl3): δ = 7.18 (t, J = 8.0 Hz, 1 H), 6.83 (d, J = 8.0 Hz, 1
H), 6.75 (d, J = 8.0 Hz, 1 H), 6.74 (s, 1 H), 4.78 (s, 2 H), 4.23 (q, J =
7.2 Hz, 2 H), 2.34 (s, 3 H), 1.29 (t, J = 7.2 Hz, 3 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 157.3, 152.9, 139.3, 129.3, 122.8, 115.7, 111.6,
experiments, it can be argued that water, which is produced in
the aldol self-condensation of acetone under Lewis-acidic con-
ditions is responsible for the hydration. In another control ex-
periment, 2d was heated to reflux in [D6]acetone along with
the gold catalyst to check whether deuterium incorporation
takes place after product formation. However, deuterium incor-
poration was not observed (iii).
81.9, 78.5, 62.2, 55.4, 21.4, 13.9 ppm. IR (neat): ν = 2964, 2925, 2860,
˜
1747, 1490, 1369, 1145, 1030, 761, 615 cm–1. HRMS: calcd. for
C13H14NaO3 [M + Na]+ 241.0841; found 241.0842.
1-(3,5-Dinitrophenyl)non-2-yn-1-one (1r): To a mixture of 3,5-di-
nitrobenzoyl chloride (849 mg, 3.7 mmol) and 1-octyne (340 mg,
3.09 mmol) in dry THF (20 mL) were added Pd(PPh3)2Cl2 (14 mg,
0.02 mmol), Et3N (0.52 mL, 3.7 mmol) and CuI (11 mg, 0.062 mmol).
The reaction mixture was heated to reflux for 4 h. After completion
of the reaction, the mixture was filtered through celite and the
filtrate was concentrated. The crude product was purified by col-
umn chromatography using EtOAc/hexanes as eluent to get pure
1r. Yield (130 mg, 14 %); Yellow liquid; Rf = 0.50 in EtOAc/hexanes
(1:10). 1H NMR (400 MHz, CDCl3): δ = 9.26–9.24 (m, 3 H), 2.62 (t, J =
7.2 Hz, 2 H), 1.75 (m, 2 H), 1.56–1.51 (m, 2 H), 1.38–1.34 (m, 4 H),
0.92 (t, J = 7.2 Hz, 3 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 173.0,
148.7, 139.5, 128.8, 122.7, 101.8, 78.6, 31.2, 28.7, 27.5, 22.4, 19.4,
Conclusions
We have synthesized substituted ꢀ-keto esters and ꢀ-diketones
by using a cationic NHC–AuI catalyst for the hydration of 2-
alkynoates and alkynones, respectively. While acetone is a bet-
ter solvent for the hydration of 2-alkynoates, 1,4-dioxane/water
is more appropriate for the hydration of alkynones. Water, gen-
erated from acetone by aldol self-condensation, is responsible
for this hydration reaction. Exploration of the synthetic utilities
of compound 2a is in progress.
Experimental Section
14.0 ppm. IR (neat): ν = 3099, 2929, 2209, 1661, 1625, 1547, 1345,
˜
1262, 1154, 921, 719 cm–1. HRMS: calcd. for C15H17N2O5 [M + H]+
305.1138; found 305.1137.
General Information: All the reagents were obtained commercially
and used without further purification unless otherwise mentioned.
For TLC, silica gel plates 60 F254 were used, and the spots were
visualized with UV light, Seebach's stain [phosphomolybdic acid
(2.5 g), Ce(SO4)2 (1 g), conc. H2SO4 (6 mL), H2O (94 mL)], and I2
vapour. Column chromatography was performed on silica gel (100–
200 mesh) using mixtures of ethyl acetate and hexanes as eluent.
1H and 13C NMR spectra of the synthesized compounds were re-
corded with an NMR spectrometer (400 MHz) by using solutions in
General Procedure for the Hydration Reactions
Condition A: To a stirred solution of alkynyl ester or alkynyl ketone
in acetone (3 mL/mmol) were added simultaneously IPrAuCl
(0.3 mol-%) and AgSbF6 (0.3 mol-%). Then, the reaction was heated
to 60 °C. The progress of the reaction was monitored by TLC period-
ically.
Condition B: To a stirred solution of alkynyl ester or alkynyl ketone
in 1,4-dioxane (2 mL/mmol) were added simultaneously IPrAuCl
(0.3 mol-%) and AgSbF6 (0.3 mol-%). Water (1 mL/mmol) was added,
and the reaction was heated to 110 °C. TLC analysis was performed
periodically to check the completion of the reaction.
1
CDCl3. The H NMR and 13C NMR signals were referred to TMS and
the central line of CDCl3 peaks, respectively. IR spectra were re-
corded using a FTIR spectrometer. High resolution mass spectra
(HRMS) were recorded using the ESI-Q-TOF technique. Melting
points were determined by using a visual melting range apparatus.
Synthesis and data of many alkynyl ketones and alkynyl esters em-
ployed in this work are already reported in the literature.[13–22]
(2Z,4E)-Diethyl 3-Hydroxyhexa-2,4-dienedioate (2a):[7] Yield
(91 mg, 85 %, from 100 mg of 1a, condition A; 74 mg, 69 % from
100 mg of 1a, condition B); colourless liquid; Rf = 0.58 in EtOAc/
Ethyl 3-(3-Nitrophenyl)propiolate (1e): To a mixture of 1-iodo-3-
nitrobenzene (250 mg, 1.0 mmol) and ethyl propiolate (390 mg,
4.016 mmol) in dry THF (10 mL) were added Pd(PPh3)2Cl2 (14 mg,
0.02 mmol), K2CO3 (554 mg, 4.0 mmol) and CuI (7 mg, 0.04 mmol).
The reaction mixture was heated to reflux for 3.5 h. After that, the
reaction mixture was filtered through Celite, and the filtrate was
concentrated. The crude product was purified by column chroma-
tography using EtOAc/hexanes as eluent to get pure 1e. Yield
1
hexanes (1:9). H NMR (400 MHz, CDCl3): δ = 11.66 (s, 1 H), 6.92 (d,
J = 15.6 Hz,1 H), 6.64 (d, J = 15.6 Hz, 1 H), 5.29 (s, 1 H), 4.28–4.23
(m, 4 H), 1.34–1.30 (m, 6 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
172.0, 165.9, 165.8, 137.2, 125.7, 96.5, 60.9, 60.7, 14.1 ppm.
(2Z,4E)-Diethyl 2-Deuterio-3-deuterioxyhexa-2,4-dienedioate
(2a-d2): Prepared from 1a; colourless liquid; Yield = 35 %; Rf = 0.38
1
in EtOAc/hexanes (1:10). H NMR (500 MHz, CDCl3): δ = 6.95 (d, J =
1
(204 mg, 92 %); yellow liquid; Rf = 0.51 in EtOAc/hexanes (1:10). H
15.5 Hz, 1 H), 6.46 (d, J = 15.5 Hz, 1 H), 4.19 (q, J = 7.0 Hz, 4 H),
1.29 (t, J = 7.0 Hz, 6 H) ppm. 13C NMR (125 MHz, CDCl3): δ = 165.1,
NMR (400 MHz, CDCl3): δ = 8.54 (s, 1 H), 8.32 (d, J = 7.2 Hz, 1 H),
7.90 (d, J = 8.0 Hz, 1 H), 7.61 (t, J = 8.0 Hz, 1 H), 4.34 (q, J = 7.2 Hz,
2 H), 1.39 (t, J = 8.0 Hz, 3 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
153.2, 148.0, 138.2, 129.8, 127.5, 125.1, 121.5, 82.4, 82.3, 62.4, 13.9
160.6, 134.8, 126.7, 99.8, 61.2, 14.1 ppm. IR (neat): ν = 2926, 1736,
˜
1643, 1583, 1309, 1216, 1073, 882 cm–1. C10H12D2O5 (216.23): calcd.
C 55.55, H 7.46; found C 55.46, H 7.51.
ppm. IR (neat): ν = 3084, 2975, 2926, 2849, 1720, 1463, 1353, 1194,
˜
(E)-Bis[(1R,2S,5R)-2-isopropyl 5-Methylcyclohexyl]4-oxohex-2-
enedioate (2b): Yield (98 mg, 94 %, from 100 mg of 1b, condition
A; 30 mg, 58 %, from 50 mg of 1b, condition B); pale yellow solid;
1024, 893, 734, 673 cm–1. HRMS: calcd. for C11H10NO4 [M + H]+
220.0610; found 220.0612.
Ethyl 4-(m-Tolyloxy)but-2-ynoate(1k): To a solution of 1-methyl-
m.p.: 113–115 °C; enol form: Rf = 0.43 in EtOAc/hexanes (1:9); [α]D26
=
3-(prop-2-yn-1-yloxy)benzene[17] (200 mg, 1.38 mmol) in dry THF
–290 (c = 0.35, CH2Cl2). 1H NMR (400 MHz, CDCl3): δ = 11.73 (s, 1
(5 mL) was added nBuLi (0.8 mL, 1.38 mmol) followed by ethyl H), 6.89 (d, J = 15.2 Hz, 1 H), 6.61 (d, J = 15.6 Hz, 1 H), 5.25 (s, 1 H),
chloroformate (1.2 mL, 2.07 mmol) at –78 °C. After 1 h, the reaction
mixture was allowed to stir at r.t. for 3 h. Then the reaction mixture
was extracted with ethyl acetate and the organic layer was concen-
trated. The crude product was purified by column chromatography
4.81–4.73 (m, 2 H), 2.02–1.99 (m, 2 H), 1.86–1.81 (m, 2 H), 1.69–1.66
(m, 4 H), 1.44–1.37 (m, 4 H), 1.14–0.97 (m, 3 H), 0.91–0.87 (m, 16 H),
0.76–0.74 (m, 6 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 171.7, 166.0,
165.4, 138.2, 137.1, 126.1, 74.9, 74.7, 47.0, 46.9, 40.83, 40.79, 34.2,
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34.1, 31.3, 29.6, 26.3, 23.5, 21.9, 20.7, 20.6, 16.4 ppm. IR (neat): ν = Ethyl 3-Oxo-3-[3-(trifluoromethyl)phenyl]propanoate (2h): Yield
˜
2958, 2865, 1709, 1649, 1588, 1409, 1178, 986, 947, 810 cm–1. HRMS (98 mg, 92 %, from 100 mg of 1h, condition A; 84 mg, 78 %, from
(ESI): calcd. for C26H42NaO5 [M + Na]+ 457.2930; found 457.2934.
100 mg of 1h, condition B); colourless liquid; keto/enol tautomers
(1:0.5); Rf = 0.47 in EtOAc/hexanes (1:9). H NMR (400 MHz, CDCl3):
1
(2Z,4E)-Ethyl 3-Hydroxy-5-phenylpenta-2,4-dienoate (2c): Yield
(83 mg, 76 %, from 100 mg of 1c, condition A; 74 mg, 68 %, from
100 mg of 1c, condition B); yellow liquid; 3:2 keto-enol tautomers:
Rf = 0.47 in EtOAc/hexanes (1:9); 1H NMR (400 MHz, CDCl3): δ =
11.99 (d, J = 1.2 Hz, 1 H), 7.62 (s, 1 H), 7.58–7.55 (m, 3 H), 7.51–7.46
(m, 2 H), 7.43–7.39 (m, 4 H), 7.37–7.32 (m, 2 H), 6.81 (d, J = 16.4 Hz,
1 H), 6.44 (dd, J = 14.6, 1.2 Hz, 1 H), 5.17 (s, 1 H), 4.25 (q, J = 7.2 Hz,
2 H), 4.21 (q, J = 7.2 Hz, 2 H), 3.70 (s, 2 H), 1.32 (t, J = 7.2 Hz, 3 H),
1.29 (t, J = 7.2 Hz, 3 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 192.0,
172.9, 169.2, 167.4, 144.7, 136.8, 135.4, 134.1, 131.0, 129.4, 129.0,
128.8, 128.5, 127.6, 125.2, 121.9, 92.0, 61.5, 60.2, 47.7, 14.3, 14.1
δ = 12.60 (s, 1 H), 8.85- 7.53 (m, 8 H), 5.72 (s, 1 H), 4.28 (q, J =
5.6 Hz, 2 H), 4.22 (q, J = 5.6 Hz, 2 H), 4.02 (s, 2 H), 1.34 (t, J = 5.6 Hz,
3 H), 1.26 (t, J = 5.6 Hz, 3 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
191.2, 172.8, 169.4, 166.9, 136.5, 134.34, 134.31, 131.8, 131.6, 131.5,
131.4, 131.3, 131.04, 131.00, 130.0, 129.4, 129.1, 127.6, 127.5, 125.33,
125.30, 124.8, 124.6, 122.9, 122.8, 122.6, 122.4, 88.5, 61.6, 60.5, 45.9,
14.1, 13.9 ppm. IR (neat): ν = 2964, 2931, 2865, 1747, 1720, 1632,
˜
1463, 1309, 1238, 1095, 942, 849 cm–1. HRMS (ESI): calcd. for
C
12H11F3NaO3 [M + Na]+ 283.0558; found 283.0556.
Diethyl 2-Hydroxyfumarate (2i): Yield (70 mg, 85 %, from 75 mg
ppm. IR (neat): ν = 3394, 3058, 2934, 1645, 1739, 1418, 1226, 1143, of 1i, condition A; 41 mg, 73 %, from 50 mg of 1i, condition B);
˜
1045, 802, 734 cm–1. HRMS (ESI): calcd. for C13H15O3 [M + H]+
219.1022; found 219.1023.
colourless liquid; keto/enol tautomers (0.5:1); Rf = 0.46 in EtOAc/
hexanes (1:9). H NMR (400 MHz, CDCl3): δ = 11.66 (s, 1 H), 6.02 (s,
1
1 H), 4.36 (q, J = 5.6 Hz, 2 H), 4.34 (q, J = 5.6 Hz, 2 H), 1.38 (t, J =
5.6 Hz, 3 H), 1.27 (t, J = 5.6 Hz, 3 H) ppm. 13C NMR (100 MHz, CDCl3):
δ = 171.8, 161.7, 159.3, 96.8, 62.3, 61.2, 45.2, 14.0, 14.0, 13.9 ppm.
Ethyl 3-(4-Methoxyphenyl)-3-oxopropanoate (2d): Yield (50 mg,
92 %, from 50 mg of 1d, condition A; 36 mg, 66 %, from 50 mg of
1d, condition B); colourless liquid, Rf = 0.49 in EtOAc/hexanes (1:9).
1H NMR (400 MHz, CDCl3): δ = 7.92 (d, J = 8.0 Hz, 2 H), 6.94 (d, J =
8.0 Hz, 2 H), 4.21 (q, J = 8.0 Hz, 2 H), 3.94 (s, 2 H), 3.84 (s, 3 H), 1.23
(t, J = 8.0 Hz, 3 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 191.0, 167.7,
164.0, 130.9, 129.1, 127.7, 113.9, 61.4, 55.5, 45.8, 14.1 ppm. IR (neat):
IR (neat): ν = 1627, 1528, 1473, 1374, 1216, 915, 728 cm–1. HRMS
˜
(ESI): calcd. for C8H12NaO5 [M + Na]+ 211.0582; found 211.0577.
(Z)-Ethyl 5-Hydroxy-3-oxo-5-phenylpent-4-enoate(2j):[24] Yield
(46 mg, 65 %, from 60 mg of 1j, condition A; 35 mg, 50 %, from
60 mg of 1j, condition B); yellow colour liquid; Rf = 0.34 in EtOAc/
hexanes (1:9). 1H NMR (400 MHz, CDCl3): δ = 15.78 (br. s, 1 H), 7.89–
7.87 (m, 2 H), 7.54–7.52 (m, 1 H), 7.47–7.43 (m, 2 H), 6.30 (s, 1 H),
4.23 (q, J = 7.2 Hz, 2 H), 3.4 (s, 2 H), 1.30 (t, J = 7.2 Hz, 3 H) ppm.
13C NMR (100 MHz, CDCl3): δ = 189.2, 182.6, 167.5, 134.1, 132.6,
128.8, 127.1, 96.7, 61.5, 45.9, 14.1 ppm.
ν = 2980, 2832, 1736, 1676, 1600, 1512, 1463, 1315, 1249, 1167,
˜
1024, 843 cm–1. HRMS (ESI): calcd. for C12H14NaO4 [M + Na]+
245.0790; found 245.0785.
Ethyl 3-(3-Nitrophenyl)-3-oxopropanoate (2e): Yield (68 mg,
90 %, from 70 mg of 1e, condition A; 90 mg, 83 %, from 100 mg of
1e, condition B); yellow solid; m.p.: 85–87 °C; keto/enol tautomers
(1:7); Rf = 0.43 in EtOAc/hexanes (1:9). 1H NMR (400 MHz, CDCl3):
δ = 12.63 (s, 1 H), 8.78 (s, 1 H), 8.62 (s, 1 H), 8.46 (d, J = 7.6 Hz, 1
H), 8.33–8.29 (m, 2 H), 8.10 (d, J = 7.6 Hz, 1 H), 7.73 (dd, J = 16.0,
Ethyl 3-Oxo-4-(m-tolyloxy)butanoate (2k): Yield (80 mg, 75 %,
from 100 mg of 1k, condition A; 56 mg, 49 %, from 100 mg of 1k,
condition B); colourless liquid; keto/enol tautomers (9:1); Rf = 0.43
8.0 Hz, 1 H), 7.63 (dd, J = 16.0, 8.0 Hz, 1 H), 5.78 (s,1 H), 4.30 (q, J = in EtOAc/hexanes (1:9). 1H NMR (400 MHz, CDCl3): δ = 7.17 (t, J =
7.2 Hz, 2 H), 4.23 (q, J = 7.2 Hz, 2 H), 4.07 (s, 2 H), 1.36 (t, J = 7.2 Hz,
8.0 Hz, 1 H), 6.82 (d, J = 7.2 Hz, 1 H), 6.71 (s, 1 H), 6.67 (d, J = 8.0 Hz,
1 H), 4.61 (s, 2 H), 4.18 (q, J = 8.0 Hz, 2 H), 3.61 (s, 2 H), 2.32 (s, 3
3 H), 1.28 (t, J = 7.2 Hz, 3 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
190.5, 172.7, 168.2, 166.7, 148.5, 137.2, 135.2, 134.0, 131.6, 130.1, H), 1.26–1.23 (J = 8.0 Hz, 3 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
129.7, 127.9, 125.5, 123.4, 121.0, 89.2, 61.8, 60.8, 45.9, 14.2, 14.0
200.7, 172.5, 166.7, 157.4, 139.8, 129.4, 122.7, 115.3, 111.2, 89.1, 72.4,
ppm. IR (neat): ν = 2970, 2936, 1621, 1528, 1402, 1030, 915, 728
66.2, 61.4, 60.3, 46.0, 21.4, 14.1, 14.0 ppm. IR (neat): ν = 2975, 2920,
˜
˜
cm–1. HRMS (ESI): calcd. for C11H11NNaO5 [M + Na]+ 260.0535; found 2361, 1720, 1583, 1490, 1369, 1260, 1156, 926, 772 cm–1. HRMS
260.0532.
(ESI): calcd. for C13H16NaO4 [M + Na]+ 259.0946; found 259.0944.
(Z)-Ethyl 3-Hydroxy-3-phenylacrylate (2f):[23] Yield (93 mg, 84 %,
from 100 mg of 1f, condition A; 79 mg, 72 %, from 100 mg of 1f,
condition B); colourless liquid; keto/enol tautomers (9:1); Rf = 0.47
Ethyl 3-(Furan-2-yl)-3-oxopropanoate (2l): Yield (153 mg, 85 %,
from 160 mg of 1l, condition A; 50 mg, 60 %, from 75 mg of 1l,
condition B); brown liquid; Rf = 0.41 in EtOAc/hexanes (1:9). 1H NMR
(400 MHz, CDCl3): δ = 7.61 (dd, J = 1.2, 0.8 Hz, 1 H), 7.27 (dd, J =
3.6, 1.2 Hz, 1 H), 6.57 (dd, J = 3.6, 0.8 Hz, 1 H), 4.23 (q, J = 8.0 Hz, 2
H), 3.87 (s, 2 H), 1.28 (t, J = 8.0 Hz, 3 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 181.1, 167.0, 152.0, 147.0, 118.3, 112.7, 61.5, 45.5, 14.0
1
in EtOAc/hexanes (1:9). H NMR (400 MHz, CDCl3): δ = 7.95 (d, J =
7.6 Hz, 2 H), 7.60 (t, J = 7.6 Hz, 1 H), 7.48 (t, J = 7.6 Hz, 2 H), 4.22
(q, J = 8 Hz, 2 H),3.99 (s, 3 H), 1.26 (t, J = 8 Hz, 3 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 192.4, 173.1, 171.3, 167.4, 135.9, 133.5, 131.1,
128.6, 128.4, 125.9, 87.2, 61.3, 60.1, 45.8, 14.1, 13.9 ppm.
ppm. IR (neat): ν = 2975, 2931, 1742, 1682, 1561, 1463, 1276, 1024,
˜
761 cm–1. HRMS (ESI): calcd. for C9H10NaO4 [M + Na]+ 205.0477;
found 205.0475.
Ethyl 3-Oxo-3-(m-tolyl)propanoate(2g): Yield (80 mg, 72 %, from
100 mg of 1g, condition A; 33 mg, 58 %, from 50 mg of 1g, condi-
tion B); colourless liquid; keto/enol tautomers (1:0.5): Rf = 0.43 in
EtOAc/hexanes (1:9). 1H NMR (400 MHz, CDCl3): δ = 12.57 (s, 1 H),
7.75–7.71 (m, 4 H), 7.40–7.35 (m, 4 H), 5.65 (s, 1 H), 4.24 (q, J =
8.0 Hz, 2 H), 4.19 (q, J = 8.0 Hz, 2 H), 3.96 (s, 2 H), 2.40 (s, 3 H), 2.38
Ethyl 3-Oxooctanoate (2m): Yield (89 mg, 81 %, from 100 mg of
1m, condition A; 100 mg, 91 %, from 100 mg of 1m, conditions B);
colourless liquid; Rf = 0.54 in EtOAc/hexanes (1:9). 1H NMR
(400 MHz, CDCl3): δ = 4.19 (q, J = 8.0 Hz, 2 H), 3.42 (s, 2 H), 2.53 (t,
(s. 3 H) 1.32 (t, J = 8.0 Hz, 3 H), 1.22 (t, J = 8.0 Hz, 3 H) ppm. 13C J = 7.2 Hz, 2 H), 1.60 (quint., J = 7.2 Hz, 2 H), 1.30–1.26 (m, 7 H),
NMR (100 MHz, CDCl3): δ = 192.6, 173.1, 171.6, 167.5, 138.5, 136.0,
0.89 (t, J = 7.2 Hz, 3 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 202.9,
134.4, 131.9, 128.8, 128.5, 128.3, 126.5, 125.7, 123.1, 87.2, 61.3, 60.2,
179.0, 172.7, 167.2, 88.9, 61.2, 59.8, 49.2, 42.9, 34.9, 31.1, 25.8, 23.0,
45.9, 21.2, 14.2, 14.0 ppm. IR (neat): ν = 2969, 2925, 2849, 1742,
22.3, 14.2, 14.0, 13.8 ppm. IR (neat): ν = 1742, 1687, 1627, 1490,
˜
˜
1682, 1627, 1462, 1276, 1145, 1030, 794 cm–1. HRMS (ESI): calcd. for
C12H14NaO3 [M + Na]+ 229.0841; found 229.0840.
1320, 1248, 1161, 1073, 1035, 805, 767, 690 cm–1. HRMS (ESI): calcd.
for C10H18NaO3 [M + Na]+ 209.1154; found 209.1156.
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(Z)-3-Hydroxy-1-phenyl-3-(3,4,5-trimethoxyphenyl)prop-2-en-
1-one (2n): Yield (82 mg, 79 %, from 100 mg of 1n, condition A;
ppm. 13C NMR (100 MHz, CDCl3): δ = 166.4, 166.3, 163.0, 135.1,
124.6, 97.3, 64.1, 60.7, 60.1, 14.3, 14.2, 14.0 ppm. HRMS: calcd. for
91 mg, 89 %, from 100 mg of 1n, condition B); yellow liquid; enol C12H18NaO5 [M + Na]+ 265.1052; found 265.1051.
tautomer; Rf = 0.47 in EtOAc/hexanes (1:9). 1H NMR (400 MHz,
CDCl3): δ = 7.98 (d, J = 8.0 Hz, 2 H), 7.53 (t, J = 8.0, 1.2 Hz, 2 H),7.47
(t, J = 1.6 Hz, 1 H), 7.22 (s, 2 H), 6.76 (s, 1 H), 3.95 (s, 9 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 186.2, 184.3, 153.1, 142.0, 135.1, 132.3,
(2Z,4E)-Diethyl 3-Methoxyhexa-2,4-dienedioate (3b): Colourless
liquid; Rf = 0.41 in EtOAc/hexanes (1:10). 1H NMR (400 MHz, CDCl3):
δ = 7.01 (d, J = 16.0 Hz, 1 H), 6.30 (d, J = 15.6 Hz, 1 H), 5.41 (s, 1
H), 4.25 (q, J = 7.2 Hz, 2 H), 4.20 (q, J = 7.2 Hz, 2 H), 3.94 (s, 3 H),
1.33–1.29 (m, 6 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 165.9, 164.5,
140.0, 124.6, 106.9, 61.4, 60.9, 60.3, 14.2, 14.1 ppm. HRMS: calcd. for
130.9, 128.6, 126.9, 104.6, 92.7, 60.8, 56.2 ppm. IR (neat): ν = 2936,
˜
2838, 1556, 1495, 1424, 1331, 1232, 1167, 1002, 953, 854, 767,
695 cm–1. HRMS (ESI): calcd. for C18H19O5 [M + H]+ 315.1227; found
315.1231.
C
11H17O5 [M + H]+ 229.1077; found 229.1078.
(Z)-3-(Furan-2-yl)-3-hydroxy-1-phenylprop-2-en-1-one (2o):[25]
Yield (85 mg, 78 %, from 100 mg of 1o, condition A; 96 mg, 90 %,
from 100 mg of 1o, condition B); yellow liquid; Rf = 0.51 in EtOAc/
hexanes (1:9). 1H NMR (400 MHz, CDCl3): δ = 16.17 (br. s, 1 H), 7.96–
7.94 (m, 2 H), 7.60 (dd, J = 1.6, 0.7 Hz, 1 H), 7.53–7.44 (m, 3 H), 7.24
(dd, J = 3.5, 0.7 Hz, 1 H), 6.76 (s, 1 H), 6.57 (dd, J = 3.5, 1.6 Hz, 1 H)
ppm. 13C NMR (100 MHz, CDCl3): δ = 182.4, 177.6, 151.0, 146.1,
134.6, 132.3, 128.6, 126.9, 115.8, 112.6, 92.7 ppm.
Acknowledgments
The authors thank the Department of Science and Technology
(DST) and the Science and Engineering Research Board (SERB),
India for financial assistance. C. T. and G. K. T. thank the Univer-
sity Grants Commission (UGC), India for fellowships.
Keywords: Hydration · Alkynes · Homogeneous catalysis ·
Gold · ꢀ-Keto esters · ꢀ-Diketones
(Z)-3-Hydroxy-1-phenylhept-2-en-1-one (2p): Yield (80 mg, 74 %,
from 100 mg of 1p, condition A; 98 mg, 91 %, from 100 mg of 1p,
1
condition B); colourless liquid; Rf = 0.61 in EtOAc/hexanes (1:9). H
NMR (400 MHz, CDCl3): δ = 7.88 (d, J = 7.6 Hz, 2 H), 7.51 (d, J =
7.6 Hz, 1 H), 7.44 (t, J = 8.0 Hz, 2 H), 6.18 (s, 1 H), 2.43 (t, J = 7.6 Hz,
2 H), 1.68 (pent, J = 7.6 Hz, 2 H), 1.41 (sext, J = 7.6 Hz, 2 H), 0.95 (t,
J = 7.6 Hz, 3 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 197.0, 183.4,
135.0, 132.1, 128.5, 126.9, 96.0, 38.9, 27.9, 22.4, 13.8 ppm. IR (neat):
[1] a) For reviews on the synthesis of heterocycles using ꢀ-keto esters, see:
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ν = 2958, 2925, 2871, 1731, 1605, 1462, 1380, 1265, 1172, 1095,
˜
761 cm–1. HRMS (ESI): calcd. for C13H16NaO2 [M + Na]+ 227.1042;
found 227.1048.
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(Z)-4-Hydroxy-4-phenylbut-3-en-2-one (2q): Yield (90 mg, 80 %,
from 100 mg of 1q, condition A; 94 mg, 84 %, from 100 mg of 1q,
condition B); yellow solid; Rf = 0.58 in EtOAc/hexanes (1:9). H NMR
(400 MHz, CDCl3): δ = 16.17 (br. s, 1 H), 7.88–7.86 (m, 2 H), 7.53–
7.50 (m, 1 H),7.46–7.42 (m, 2 H), 6.18 (s,1 H), 2.20 (s, 3 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 193.7, 183.3, 134.8, 132.2, 128.8, 128.6,
127.0, 96.7, 25.8 ppm.
1
(Z)-1-(3,5-Dinitrophenyl)-3-hydroxynon-2-en-1-one (2r): Yield
(83 mg, 79 %, from 100 mg of 1r, condition A; 89 mg, 84 %, from
100 mg of 1r, condition B); yellow liquid; Rf = 0.50 in EtOAc/hexanes
(1:9). 1H NMR (400 MHz, CDCl3): δ = 9.16 (m, 1 H), 9.02 (m, 2 H),
6.34 (s, 1 H), 2.45 (t, J = 7.6 Hz, 2 H), 1.73 (m, 2 H), 1.35 (m, 4 H),
1.34 (m, 4 H), 0.91 (t, J = 6.8 Hz, 3 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 199.2, 177.4, 148.8, 138.8, 128.8, 126.7, 121.1, 97.0, 39.5,
31.5, 28.9, 25.5, 22.4, 14.0 ppm. IR (neat): ν = 3420, 3105, 2924, 2209,
˜
1625, 1542, 1340, 1257, 1143, 916, 729 cm–1. HRMS (ESI): calcd. for
C15H19N2O6 [M + H]+ 323.1244; found 323.1239.
Ethyl 3-(4-Methoxyphenyl)-3-oxopropanoate-d2 (2d-d2): Yield
(46 mg, 86 %, from 50 mg of 1d, condition A ([D6]acetone); colour-
less liquid; Rf = 0.49 in EtOAc/hexanes (1:9). 1H NMR (400 MHz,
CDCl3): δ = 7.98 (d, J = 8.0 Hz, 2 H), 6.94 (d, J = 8.0 Hz, 2 H), 4.10
(q, J = 8.0 Hz, 2 H), 3.86 (s, 3 H), 1.15 (t, J = 8.0 Hz, 3 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 194.2, 169.1, 163.6, 130.8, 113.8, 60.9,
55.4, 14.0 ppm. IR (neat): ν = 2975, 2838, 1731, 1671, 1520, 1457,
˜
1309, 1271, 1172, 1024, 838 cm–1. HRMS (ESI): calcd. for C12H13D2O4
[M + H]+ 225.1091; found 225.1095.
(2Z,4E)-Diethyl 3-Ethoxyhexa-2,4-dienedioate (3a): Colourless
liquid; Rf = 0.61 in EtOAc/hexanes (1:10, triple run). 1H NMR
(400 MHz, CDCl3): δ = 8.38 (d, J = 15.6 Hz, 1 H), 6.49 (d, J = 15.6 Hz,
1 H), 5.25 (s, 1 H), 4.22 (q, J = 7.2 Hz, 2 H), 4.16 (q, J = 7.2 Hz, 2 H),
3.88 (q, J = 6.8 Hz, 2 H), 1.37 (t, J = 7.2 Hz, 3 H), 1.31–1.25 (m, 6 H)
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Received: August 18, 2016
Published Online: ■
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Gold Catalysis
C. Tarigopula, G. K. Thota,
R. Balamurugan* ................................ 1–8
Efficient Synthesis of Functionalized
ꢀ-Keto Esters and ꢀ-Diketones
through Regioselective Hydration of
Alkynyl Esters and Alkynyl Ketones
by Use of a Cationic NHC–AuI Cata-
lyst
A cationic NHC–AuI catalyst opens the ꢀ-keto esters and ꢀ-diketones, respec-
way to regioselective hydration of α- tively.
alkynyl esters and ketones to afford
DOI: 10.1002/ejoc.201601025
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www.eurjoc.org
8
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim