Ruthenium-Catalyzed Hydrocarboxylation of Internal Alkynes

Article abstract of DOI:10.1002/ejoc.201501583

The application of the highly efficient ruthenium catalyst [Ru(CO)₂{P(p-CF₃-C₆H₄)₃}₂(O₂CPh)₂] (1) in the selective syn-addition of carboxylic acids to internal alkynes

Full text of DOI:10.1002/ejoc.201501583

DOI: 10.1002/ejoc.201501583
Full Paper
Ruthenium Catalysis
Ruthenium-Catalyzed Hydrocarboxylation of Internal Alkynes
Janine Jeschke,[a] Tony B. Engelhardt,[a] and Heinrich Lang*[a]
Abstract: The application of the highly efficient ruthenium cat- acidity of the carboxylic acid. The catalytic activity can be signif-
alyst [Ru(CO)2{P(p-CF3–C6H4)3}2(O2CPh)2] (1) in the selective syn- icantly increased by the addition of catalytic amounts of
addition of carboxylic acids to internal alkynes, yielding valua- B(C6F5)3. Relative to known catalysts for the synthesis of (E)-
ble trisubstituted enol esters with (E)-configuration, is de- enol esters, this methodology offers improved selectivity and
scribed. All reactions feature excellent stereoselectivities and requires lower catalyst loadings. Moreover, a broad range of
good regioselectivities. The regioselectivity is dictated by elec- alkynes and carboxylic acids can be successfully converted to
tronic and steric aspects of the alkyne substituents and the their corresponding (E)-enol esters in high yields.
Introduction
{IPr = N,N′-bis(2,6-diisopropylphenyl)imidazol-2-ylidene}. How-
ever, these catalysts lead to the selective formation of (Z)-con-
figured enol esters. To the best of our knowledge, the only
catalyst reported to favor formation of (E)-enol esters is
Ru3(CO)12.[32–34] However, this approach requires high catalyst
loadings and renders poor reaction selectivity.
Recently, we demonstrated that the mononuclear ruthenium
complex [Ru(CO)2{P(p-CF3–C6H4)3}2(O2CPh)2] (1) is a highly effi-
cient and selective catalyst for the addition of carboxylic acids
to terminal alkynes and propargylic alcohols under mild reac-
tion conditions.[40–42] In continuing these studies, we have in-
vestigated the catalytic activity of 1 for hydrocarboxylation of
challenging internal alkynes. Herein, the effect of catalytic
amounts of various additives on reaction efficiency and selectiv-
ity as well as substrate scope is explored and discussed.
The transition metal-catalyzed hydrocarboxylation of alkynes is
the most efficient and atom economic approach for the synthe-
sis of valuable enol esters.[1,2] Such esters can be applied as
monomers in numerous polymerization reactions[3,4] and are
important intermediates in organic synthesis.[5–11] The first
metal found to catalyze this reaction was mercury.[12–14] How-
ever, due to its high toxicity, alternatives to mercury have been
explored with an emphasis on both effectivity and lack of
toxicity.[15–17] Today, the most widely applied catalysts in the
addition of carboxylic acids to alkynes are ruthenium com-
plexes.[18–25] However, most of these catalysts fail to enable
hydrocarboxylation of internal alkynes since their conversion
requires much higher activation energies, the result of signifi-
cant steric barriers.[26–28] Another challenge involves the control
of selectivity; this is especially relevant to the addition of carb-
oxylic acids to unsymmetrically substituted internal alkynes, as
this reaction can render up to four isomers whose separation is
difficult to achieve (Scheme 1).[29]
Results and Discussion
To study the activity and selectivity of [Ru(CO)2{P(p-CF3–
C6H4)3}2(O2CPh)2] (1) (Figure 1) in the addition of carboxylic
acids to internal alkynes, the conversion of benzoic acid with
symmetrically substituted 3-hexyne was selected as a model
reaction. Toluene was chosen as solvent since it had proven to
be the best solvent for this catalytic system.[40–42] By applying
1.0 mol-% of catalyst 1, a conversion of 70 % was reached after
6 h at 140 °C (Table 1, Entry 1). Interestingly, this reaction led
to the formation of (E)-2a as the exclusive product.[43] Relative
to our previously reported protocol for the conversion of
terminal alkynes, higher reaction temperatures were required
due to the increased activation energy.[42]
Scheme 1. Addition of carboxylic acids to unsymmetrically substituted inter-
nal alkynes.
To date only few active catalysts for the hydrocarboxylation
of internal alkynes have been developed, including ruth-
enium,[30–34] palladium,[35,36] silver[37] and gold[38,39] metal com-
plexes. The best catalytic activities have been reported for the
gold complexes [Au(PPh3)Cl][38] and [{Au(IPr)}2(μ-OH)][BF4][39]
[a] Technische Universität Chemnitz, Faculty of Natural Sciences, Institute of
Chemistry, Inorganic Chemistry,
09107 Chemnitz, Germany
E-mail: heinrich.lang@chemie.tu-chemnitz.de
https://www.tu-chemnitz.de/chemie/anorg/
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/ejoc.201501583.
Figure 1. Structure of catalyst 1.
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Table 1. Influence of additives on the catalytic performance of 1 in the addi-
(Table 1, Entry 6). A possible explanation for this finding might
be that initially formed (E)-product isomerizes to the (Z)-isomer.
This hypothesis is especially compelling since trifluorometh-
anesulfonic acid and their metal salts are known to catalyze
this reaction.[38,44] Other silver compounds gave again (E)-2a as
major product with excellent selectivities of up to 100 %
(Table 1, Entries 7–9). The best set of reaction conditions, in
terms of activity and selectivity, was achieved upon addition of
B(C6F5)3 (Entry 10).[45] The accelerating effect of B(C6F5)3 may
be the result of π-coordination of the boron to the triple bond,
since B(C6F5)3 is known to activate alkynes towards nucleophilic
attack.[46,47] Moreover, B(C6F5)3 can also enhance the acidity of
the carboxylic acid via carbonyl oxygen coordination.[47–49] Due
to its accelerating effect all following reactions of symmetrically
substituted internal alkynes were carried out in the presence of
1.0 mol-% 1 and B(C6F5)3, respectively.
tion of benzoic acid to 3-hexyne.[a]
Entry
Additive
Yield[b]
[%]
Selectivity [%][c]
(Z)-2a
(E)-2a
1
2
3
4
5
6
7
8
9
–
70
69
41
86
85
55
73
82
90
100
0
0
0
1
1
55
2
2
0
0
100
100
100
99
99
45
98
98
100
100
Na2CO3
DMAP
KOTf
Mg(OTf)2
AgOTf
AgPF6
AgNO3
AgBF4
B(C6F5)3
To assess the substrate scope of this reaction as well as its
tolerance for various functional groups, diverse symmetrically
substituted internal alkynes were reacted with carboxylic acids
(Scheme 2). Reactions were monitored on the basis of regular
10
[a] Reaction conditions: benzoic acid (1.0 mmol), 3-hexyne (1.5 mmol), 1
(1.0 mol-%), additive (1.0 mol-%), acenaphthene (0.5 mmol), toluene (1 mL),
140 °C, 6 h. [b] Total yield determined by 1H NMR spectroscopy using ace-
naphthene as an internal standard. [c] Relative ratio of isomers determined
by 1H NMR spectroscopy.
1
sampling by H NMR spectroscopy in order to optimize the re-
action times. All products of this substrate screening were iso-
lated in good to excellent yields (67–99 %) and were character-
1
ized by H and 13C{1H} NMR spectroscopy. Additionally, novel
compounds were characterized by high resolution mass spec-
trometry (HRMS).
In former studies on the preparation of enol esters it could
be shown that the addition of catalytic amounts of Lewis acids
or bases can significantly enhance the reaction rate or allow for
Several aliphatic alkynes of different chain lengths were ex-
control of the selectivity.[23,25,36,38,42] To improve the activity, the amined, revealing that conversion of 4-octyne (2c, Scheme 2)
impact of diverse additives (1.0 mol-%) was examined (Table 1). needed significantly longer reaction times than did 3-hexyne
From Table 1 it is obvious that the addition of bases such as (2a). Correspondingly, the smallest substrate, 2-butyne (2b),
Na2CO3 or 4-(dimethylamino)pyridine (DMAP) had no impact could be successfully converted at a decreased reaction tem-
on catalytic performance (Table 1, Entry 2) or even led to a drop perature of 120 °C. Not surprisingly, the reaction of sterically
of activity (Table 1, Entry 3). On the contrary, the addition of more challenging diphenylacetylene (2d) required the longest
triflates like KOTf or Mg(OTf)2 resulted in a slight increase in reaction time of 24 h, whereas dimethyl acetylenedicarboxylate
yields (Table 1, Entries 4 and 5). However, when the reaction (2e) was smoothly converted within 6 h. In addition to the sub-
was performed in the presence of AgOTf reaction selectivity strate scope of the alkyne, reaction tolerance of various carb-
was reversed and (Z)-2a was observed as the main isomer oxylic acids was investigated. Hereby, not only para-substituted
Scheme 2. Substrate screening for conversion of symmetrically substituted internal alkynes. Reaction conditions: carboxylic acid (1.0 mmol), alkyne (1.5 mmol),
1 (1.0 mol-%), B(C6F5)3 (1.0 mol-%), toluene (1 mL), 140 °C, isolated yields, optimized reaction times are given in parentheses. [a] Reaction performed at 120 °C.
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benzoic acids (2g,h), but also, single or double ortho-substi-
tuted carboxylic acids (2f,g) were converted in very good yields.
Reactions involving electron-deficient acids gave excellent
results (2h), whereas electron-rich substrates correlated to
slightly reduced yields (2g). In addition, the reaction proceeded
smoothly in the presence of ferrocenecarboxylic acid (2i) and
was not affected by functional groups like the free hydroxyl
group of salicylic acid (2f). In addition, aliphatic acids such as
diphenylacetic acid (2j) were also found to be well tolerated.
Table 2. Influence of additives on the catalytic performance of 1 in the addi-
tion of benzoic acid to 2-hexyne.[a]
Entry
Additive
Yield[b]
[%]
Selectivity [%][c]
(Z)-3a
(E)-3a
(Z)-3b
(E)-3b
1
2
3
4
5
6
7
8
9
–
63
73
35
76
100
61
75
92
46
100
0
0
0
5
3
36
13
0
7
0
68
68
67
61
63
9
49
68
57
69
0
0
0
5
3
41
16
0
7
0
32
32
33
29
30
14
21
32
29
31
Of particular note in the conversion of all symmetrically sub-
stituted internal alkynes is that only a single isomer bearing the
(E)-configuration was obtained. Hence, the reaction proceeds
by a syn-addition of the carboxylic acid to the alkyne. This can
be rationalized by insertion of the coordinated triple bond into
the Ru–O bond as presented in complex C (Scheme 3).
Na2CO3
DMAP
KOTf
Mg(OTf)2
AgOTf
AgPF6
AgNO3
AgBF4
B(C6F5)3
10
[a] Reaction conditions: benzoic acid (1.0 mmol), 2-hexyne (1.5 mmol), 1
(1.0 mol-%), additive (1.0 mol-%), acenaphthene (0.5 mmol), toluene (1 mL),
140 °C, 6 h. [b] Total yield determined by 1H NMR spectroscopy using ace-
naphthene as an internal standard. [c] Relative ratio of isomers determined
by 1H NMR spectroscopy.
only two out of four possible isomers were formed in a ratio of
2:1 for 3a:3b. The products formed (3a,b) both possess the (E)-
configuration indicating a syn-addition of the carboxylic acid.
None of the additives tested led to an improvement in selectiv-
ity. In fact, the addition of several triflates (Table 2, Entries 4–6),
AgPF6 (Table 2, Entry 7) and AgBF4 (Table 2, Entry 9) diminished
reaction selectivity. Full conversion within 6 h was obtained
upon addition of B(C6F5)3 (Table 2, Entry 10). Because of the
enhanced activity and the unchanged selectivity of 2:1 for (E)-
3a:(E)-3b, all further reactions with unsymmetrically substituted
internal alkynes were performed in the presence of B(C6F5)3
additive.
In the substrate screening reactions with unsymmetrically
substituted internal alkynes only the two syn-addition products
with (E)-configuration have been observed. As a result, it ap-
pears that the regioselectivity of nucleophilic attack by the
carboxylic acid is subject to the influence of triple bond substit-
uents (Table 3). The more different the electronic or steric de-
mands of the alkyne substituents are, the greater the regiose-
lectivity of the reaction is likely to be. The highest selectivity
was obtained for the conversion of 1-phenyl-1-hexyne (Table 3,
Entry 4), whereas the lowest selectivity was observed for the
reaction of 3-octyne (Table 3, Entry 2). Rotem and Shvo have
performed a similar addition of benzoic acid to 1-phenyl-1-
heptyne with Ru3(CO)12 as the catalyst, but observed the forma-
tion of all four possible isomers, in addition to two rearranged
Scheme 3. Proposed mechanistic cycle for enol ester generation.[34]
In cases 2f–j (Scheme 2), when carboxylic acids other than
benzoic acid were applied, the formation of up to 2 % of the
benzoate product 2a was observed, presumably arising from
conversion of the benzoate ligands on initial catalyst 1.[40–42]
Compared to previously reported results on the formation of
(E)-isomers, the current conditions employing 1 and B(C6F5)3
led to higher selectivities while using both lower catalyst load-
ings and similar or even reduced reaction times.[32–34]
Having demonstrated that, with catalyst 1, a broad range of
symmetrically substituted internal alkynes could be successfully
converted to isomerically pure (E)-enol esters, we were encour-
aged to study the reaction with unsymmetrically substituted
internal alkynes. Consequently, the influences of several addi-
tives on the activities and selectivities achievable in the addi-
tion of benzoic acid to 2-hexyne were investigated (Table 2).
In the absence of additive, hydrocarboxylation of 2-hexyne products of type R1CO2CH=CR2R3.[33] In addition to the alkyne
with benzoic acid proceeded with a conversion of 63 % after substituents, the acidity of the carboxylic acid also appears to
6 h at 140 °C (Table 2, Entry 1); this is comparable to the reac- exert a small influence. Consequently, reaction regioselectivity
tion with symmetrically substituted 3-hexyne (Table 1, Entry 1). may be slightly improved via the use of more acidic acids
In considering the selectivity of the reaction, it is notable that (Table 3, Entries 5 and 6).
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Table 3. Substrate screening for the conversion of unsymmetrically substituted internal alkynes.[a]
[a] Reaction conditions: carboxylic acid (1.0 mmol), alkyne (1.5 mmol), 1 (1.0 mol-%), B(C6F5)3 (1.0 mol-%), acenaphthene (0.5 mmol), toluene (1 mL), 140 °C.
[b] Isolated yield. [c] Relative ratio of isomers determined by 1H NMR spectroscopy.
Conclusions
sion of diverse internal alkynes and carboxylic acids en route to
enol esters.
We demonstrate herein that [Ru(CO)2{P(p-CF3–C6H4)3}2(O2CPh)2]
(1) is a highly efficient and selective catalyst for the hydro-
carboxylation of internal alkynes to give trisubstituted enol es-
ters. All reactions proceeded by a syn-addition of the carboxylic
acid and hence, led to selective formation of the (E)-configured
products. Consequently, the conversion of symmetrically substi-
Experimental Section
General Information: Compound 1 was prepared according to a
previously published procedure.[40] Toluene was dried using a sol-
vent purification system (MB SPS-800, MBraun). Acenaphthene was
tuted alkynes resulted in generation of a single product with purified by sublimation at 75 °C (1.0 mbar). All other chemicals
were purchased from commercial suppliers and were used without
further purification. For column chromatography silica with a parti-
cle size of 40–60 μm [230–400 mesh (ASTM), Macherey–Nagel] was
used. NMR spectra were recorded with a Bruker Advance III 500
spectrometer operating at 500.3 MHz for 1H and 125.7 MHz for
13C{1H} spectra in the Fourier transform mode at 298 K. Chemical
shifts are reported in δ (ppm) downfield from tetramethylsilane
with the solvent as reference signal [1H NMR, CHCl3 δ = 7.26; 13C(1H)
NMR, CDCl3 δ = 77.16 ppm]. High resolution mass spectra were
recorded with a Bruker Daltonite micrOTOF-QII spectrometer using
100 % stereoselectivity. Conversely, the reaction of unsymmetri-
cally substituted alkynes afforded two regioisomers. Regiose-
lectivity was found to be influenced by electronic and steric
effects associated with the alkyne substituents as well as the
acidity of the carboxylic acid. Furthermore, the catalytic activity
could be significantly increased by the addition of catalytic
B(C6F5)3 which had no impact upon reaction selectivity. Relative
to previously reported catalysts for the formation of (E)-enol
esters,[32–34] our catalytic system requires lower catalyst load-
ings, is highly selective, and broadly applicable to the conver- electro-spray ionization (ESI).
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General Procedure for the Catalytic Reactions: In a screw-capped
vial and under an atmosphere of argon the carboxylic acid
(1.0 mmol), the alkyne (1.5 mmol), the ruthenium catalyst 1
(0.01 mmol, 1.0 mol-%), the additive (0.01 mmol, 1.0 mol-%) and
acenaphthene (77 mg, 0.5 mmol) were dissolved in toluene (1 mL).
The sealed vial was immersed in a heating mantle preheated to
140 °C and stirred for 4–24 h. The progress of the reaction was
monitored by regular sampling and analysis by 1H NMR spectro-
scopy applying acenaphthene as an internal standard. Analytically
pure products were isolated by column chromatography on silica
gel (volume: 3 × 7 cm) using n-hexane/ethyl acetate (99:1, v/v) as
eluent. All catalytic results have been verified by at least two inde-
pendent experiments.
H, =CH), 7.45–7.51 (m, 2 H, m-CH/Ph), 7.60–7.66 (m, 1 H, p-CH/Ph),
8.05–8.10 (m, 2 H, o-CH/Ph) ppm. 13C{1H} NMR (125.7 MHz, CDCl3,
25 °C): δ = 52.4, 53.1, 115.5, 127.8, 128.8, 130.5, 134.5, 147.6, 161.8,
163.7, 164.4 ppm. The analytical data are in agreement with ref.[33]
(E)-Hex-3-en-3-yl 2-Hydroxybenzoate (2f): Salicylic acid (138 mg,
1.0 mmol) was reacted with 3-hexyne (123 mg, 1.5 mmol) for 6 h
at 140 °C, yielding 2f as a yellow liquid after appropriate work-up
(178 mg, 81 %). 1H NMR (500.3 MHz, CDCl3, 25 °C): δ = 1.06 (t, JH,H
=
7.5 Hz, 3 H, CH3), 1.08 (t, JH,H = 7.6 Hz, 3 H, CH3), 2.14 (dt, JH,H = 7.6,
JH,H = 7.6 Hz, 2 H, CH2), 2.40 (q, JH,H = 7.5 Hz, 2 H, CH2), 5.25 [t,
JH,H = 7.7 Hz, 1 H, =CH(Et)], 6.90 (ddd, JH,H = 8.1, 7.3, 1.0 Hz, 1 H,
CH/Ph), 7.00 (dd, JH,H = 8.4, JH,H = 0.8 Hz, 1 H, CH/Ph), 7.48 (ddd,
JH,H = 8.8, 7.4, 1.7 Hz, 1 H, CH/Ph), 7.91 (dd, JH,H = 8.0, 1.7 Hz, 1 H,
CH/Ph) ppm. 13C{1H} NMR (125.7 MHz, CDCl3, 25 °C): δ = 11.8, 14.5,
19.9, 22.5, 112.5, 117.8, 119.3, 119.8, 130.3, 136.1, 149.5, 162.1,
169.4 ppm. HRMS (ESI-TOF): calcd. for C13H16O3Na [M + Na]+
243.0992, found 243.1009.
Characterization Data of Catalysis Products
(E)-Hex-3-en-3-yl Benzoate (2a): Benzoic acid (122 mg, 1.0 mmol)
was reacted with 3-hexyne (123 mg, 1.5 mmol) for 6 h at 140 °C,
yielding 2a as a yellow liquid after appropriate work-up (203 mg,
1
99 %). H NMR (500.3 MHz, CDCl3, 25 °C): δ = 1.05 [t, JH,H = 7.5 Hz,
(E)-Hex-3-en-3-yl 2,4,6-Trimethylbenzoate (2g): 2,4,6-Trimethyl-
benzoic acid (164 mg, 1.0 mmol) was reacted with 3-hexyne
(123 mg, 1.5 mmol) for 6 h at 140 °C, yielding 2g as a yellow solid
after appropriate work-up (167 mg, 68 %). 1H NMR (500.3 MHz,
3 H, CH3], 1.08 (t, JH,H = 7.5 Hz, 3 H, CH3), 2.13 (dt, JH,H = 7.6, JH,H
7.6 Hz, 2 H, CH2), 2.40 (q, JH,H = 7.5 Hz, 2 H, CH2), 5.22 [t, JH,H
=
=
7.7 Hz, 1 H, =CH(Et)], 7.42–7.48 (m, 2 H, m-CH/Ph), 7.54–7.60 (m, 1
H, p-CH/Ph), 8.07–8.12 (m, 2 H, o-CH/Ph) ppm. 13C{1H} NMR
(125.7 MHz, CDCl3, 25 °C): δ = 11.8, 14.6, 19.9, 22.5, 119.1, 128.5,
129.9, 130.3, 133.2, 150.0, 165.5 ppm. HRMS (ESI-TOF): calcd. for
C13H16O2Na [M + Na]+ 227.1043, found 227.1026.
CDCl3, 25 °C): δ = 1.07 (t, JH,H = 7.5 Hz, 3 H, CH3), 1.12 (t, JH,H
=
7.6 Hz, 3 H, CH3), 2.15 (dt, JH,H = 7.6, JH,H = 7.6 Hz, 2 H, CH2), 2.30
(s, 3 H, CH3), 2.38 (s, 6 H, CH3), 2.42 (q, JH,H = 7.6 Hz, 2 H, CH2), 5.24
[t, JH,H = 7.7 Hz, 1 H, =CH(Et)], 6.87–6.89 (m, 2 H, CH/Ph) ppm.
13C{1H} NMR (125.7 MHz, CDCl3, 25 °C): δ = 12.2, 14.6, 19.9, 20.0,
21.2, 22.8, 119.2, 128.6, 131.0, 135.2, 139.4, 150.2, 169.1 ppm. HRMS
(ESI-TOF): calcd. for C16H23O2 [M + H]+ 247.1693, found 247.1700.
(E)-But-2-en-2-yl Benzoate (2b): Benzoic acid (122 mg, 1.0 mmol)
was reacted with 2-butyne (81 mg, 1.5 mmol) for 24 h at 120 °C,
yielding 2b as a pale yellow liquid after appropriate work-up
(171 mg, 97 %). 1H NMR (500.3 MHz, CDCl3, 25 °C): δ = 1.70 (dq,
JH,H = 7.1, JH,H = 1.1 Hz, 3 H, CH3), 1.98 (dq, JH,H = 2.3, JH,H = 1.1 Hz,
3 H, CH3), 5.30 [qq, JH,H = 7.1, JH,H = 1.1 Hz, 1 H, =CH(Me)], 7.42–
7.48 (m, 2 H, m-CH/Ph), 7.54–7.59 (m, 1 H, p-CH/Ph), 8.05–8.11 (m,
2 H, o-CH/Ph) ppm. 13C{1H} NMR (125.7 MHz, CDCl3, 25 °C): δ =
11.9, 15.1, 112.2, 128.5, 129.9, 130.3, 133.2, 146.1, 165.4 ppm. The
analytical data are in agreement with ref.[50]
(E)-Hex-3-en-3-yl 4-Acetylbenzoate (2h): 4-Acetylbenzoic acid
(164 mg, 1.0 mmol) was reacted with 3-hexyne (123 mg, 1.5 mmol)
for 4 h at 140 °C, yielding 2h as a yellow liquid after appropriate
work-up (226 mg, 92 %). 1H NMR (500.3 MHz, CDCl3, 25 °C): δ =
1.05 (t, JH,H = 7.5 Hz, 3 H, CH3), 1.07 (t, JH,H = 7.6 Hz, 3 H, CH3), 2.13
(dt, JH,H = 7.5, JH,H = 7.5 Hz, 2 H, CH2), 2.40 (q, JH,H = 7.5 Hz, 2 H,
CH2), 2.64 [s, 3 H, C(O)CH3], 5.23 [t, JH,H = 7.7 Hz, 1 H, =CH(Et)], 8.00–
8.04 (m, 2 H, CH/Ph), 8.14–8.18 (m, 2 H, CH/Ph) ppm. 13C{1H} NMR
(125.7 MHz, CDCl3, 25 °C): δ = 11.9, 14.6, 19.9, 22.4, 27.0, 119.4,
128.4, 130.2, 134.1, 140.5, 150.0, 164.7, 197.6 ppm. HRMS (ESI-TOF):
calcd. for C15H19O3 [M + H]+ 247.1329, found 247.1365.
(E)-Oct-4-en-4-yl Benzoate (2c): Benzoic acid (122 mg, 1.0 mmol)
was reacted with 4-octyne (165 mg, 1.5 mmol) for 16 h at 140 °C,
yielding 2c as a yellow liquid after appropriate work-up (155 mg,
1
67 %). H NMR (500.3 MHz, CDCl3, 25 °C): δ = 0.96 (t, JH,H = 7.4 Hz,
3 H, CH3), 0.97 (t, JH,H = 7.4 Hz, 3 H, CH3), 1.41–1.56 (m, 4 H, CH2),
2.07–2.14 (m, 2 H, CH2), 2.37 (t, JH,H = 7.4 Hz, 2 H, CH2), 5.27 [t,
(E)-Hex-3-en-3-yl Ferrocene Carboxylate (2i): Ferrocene carb-
oxylic acid (230 mg, 1.0 mmol) was reacted with 3-hexyne (123 mg,
1.5 mmol) for 6 h at 140 °C, yielding 2i as an orange solid after
appropriate work-up (281 mg, 90 %). 1H NMR (500.3 MHz, CDCl3,
25 °C): δ = 1.05 (t, JH,H = 7.5 Hz, 3 H, CH3), 1.11 (t, JH,H = 7.6 Hz, 3
J
H,H = 7.8 Hz, 1 H, =CH(nPr)], 7.43–7.48 (m, 2 H, m-CH/Ph), 7.55–7.60
(m, 1 H, p-CH/Ph), 8.07–8.11 (m, 2 H, o-CH/Ph) ppm. 13C{1H} NMR
(125.7 MHz, CDCl3, 25 °C): δ = 13.81, 13.83, 20.3, 23.0, 28.7, 31.1,
118.3, 128.5, 130.0, 130.4, 133.2, 149.0, 165.5 ppm. The analytical
data are in agreement with ref.[33]
H, CH3), 2.12 (dt, JH,H = 7.5, JH,H = 7.5 Hz, 2 H, CH2), 2.37 (q, JH,H
=
7.6 Hz, 2 H, CH2), 4.24 (s, 5 H, C5H5), 4.41–4.43 (m, 2 H, C5H4), 4.84–
4.86 (m, 2 H, C5H4), 5.16 [t, JH,H = 7.7 Hz, 1 H, =CH(Et)] ppm. 13C{1H}
NMR (125.7 MHz, CDCl3, 25 °C): δ = 12.0, 14.7, 20.0, 22.6, 69.9, 70.5,
71.2, 71.6, 118.9, 150.0, 170.7 ppm. HRMS (ESI-TOF): calcd. for
C17H21FeO2 [M + H]+ 313.0886, found 313.0898.
(E)-1,2-Diphenylvinyl Benzoate (2d): Benzoic acid (122 mg,
1.0 mmol) was reacted with diphenylacetylene (267 mg, 1.5 mmol)
for 24 h at 140 °C, yielding 2d as a yellow liquid after appropriate
work-up (210 mg, 70 %). 1H NMR (500.3 MHz, CDCl3, 25 °C): δ =
6.69 [s, 1 H, =CH(Ph)], 7.23–7.28 (m, 5 H, CH/Ph), 7.33–7.37 (m, 3 H,
CH/Ph), 7.51–7.56 (m, 4 H, CH/Ph), 7.63–7.68 (m, 1 H, CH/Ph), 8.22–
8.25 (m, 2 H, CH/Ph) ppm. 13C{1H} NMR (125.7 MHz, CDCl3, 25 °C):
δ = 120.3, 127.4, 128.4, 128.5, 128.6, 128.9, 129.0, 129.1, 129.8, 130.2,
133.5, 134.4, 134.7, 147.8, 165.2 ppm. The analytical data are in
agreement with ref.[32,33]
(E)-Hex-3-en-3-yl 2,2-Diphenylacetate (2j): Diphenylacetic acid
(212 mg, 1.0 mmol) was reacted with 3-hexyne (123 mg, 1.5 mmol)
for 4 h at 140 °C, yielding 2j as a yellow liquid after appropriate
work-up (288 mg, 98 %). 1H NMR (500.3 MHz, CDCl3, 25 °C): δ =
0.89 (t, JH,H = 7.5 Hz, 3 H, CH3), 1.01 (t, JH,H = 7.5 Hz, 3 H, CH3), 2.07
(dt, JH,H = 7.6, JH,H = 7.6 Hz, 2 H, CH2), 2.27 (q, JH,H = 7.5 Hz, 2 H,
CH2), 5.09–5.13 [m, 2 H, =CH(Et), CH(Ph)2], 7.27–7.31 (m, 2 H, CH/
Ph), 7.33–7.42 (m, 8 H, CH/Ph) ppm. 13C{1H} NMR (125.7 MHz, CDCl3,
25 °C): δ = 11.7, 14.5, 19.8, 22.3, 57.2, 118.9, 127.4, 128.7, 128.8,
138.7, 150.0, 171.3 ppm. HRMS (ESI-TOF): calcd. for C20H23O2 [M +
Dimethyl 2-(Benzoyloxy)maleate (2e): Benzoic acid (122 mg,
1.0 mmol) was reacted with dimethyl acetylenedicarboxylate
(213 mg, 1.5 mmol) for 6 h at 140 °C, yielding 2e as a yellow liquid
after appropriate work-up (224 mg, 85 %). 1H NMR (500.3 MHz,
CDCl3, 25 °C): δ = 3.80 (s, 3 H, OCH3), 3.85 (s, 3 H, OCH3), 6.23 (s, 1 H]+ 295.1693, found 295.1699.
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3: Benzoic acid (122 mg, 1.0 mmol) was reacted with 2-hexyne
(123 mg, 1.5 mmol) for 6 h at 140 °C, yielding a mixture of (E)-hex-
2-en-3-yl benzoate (3a) and (E)-hex-2-en-2-yl benzoate (3b) as a
yellow liquid after appropriate work-up (203 mg, 99 %, ratio 3a:3b =
1.55–1.64 (m, 2 H, CH2), 2.63–2.69 (m, 2 H, CH2), 6.43 [s, 1 H, =
CH(Ph)], 7.25–7.42 (m, 5 H, CH/Ph), 7.45–7.55 (m, 2 H, CH/Ph), 7.58–
7.65 (m, 1 H, CH/Ph), 8.13–8.19 (m, 2 H, CH/Ph) ppm. 13C{1H} NMR
(125.7 MHz, CDCl3, 25 °C): δ = 13.9, 22.5, 29.1, 29.9, 119.3, 127.0,
128.3, 128.6, 128.9, 130.1, 133.4, 135.1, 151.9, 165.2 ppm. HRMS (ESI-
TOF): calcd. for C19H21O2 [M + H]+ 281.1536, found 281.1551. 6b: 1H
NMR (500.3 MHz, CDCl3, 25 °C): δ = 0.92 (t, JH,H = 7.3 Hz, 3 H, CH3),
1.35–1.44 (m, 2 H, CH2), 1.45–1.53 (m, 2 H, CH2), 2.30–2.36 (m, 2 H,
67:33). 3a: 1H NMR (500.3 MHz, CDCl3, 25 °C): δ = 0.96 (t, JH,H
=
7.4 Hz, 3 H, CH3), 1.48–1.57 (m, 2 H, CH2), 1.72 (d, JH,H = 7.1 Hz, 3
H, CH3), 2.37 (t, JH,H = 7.4 Hz, 2 H, CH2), 5.32 [q, JH,H = 7.1 Hz, 1 H, =
CH(CH3)], 7.43–7.48 (m, 2 H, m-CH/Ph), 7.55–7.60 (m, 1 H, p-CH/Ph),
8.06–8.11 (m, 2 H, o-CH/Ph) ppm. 13C{1H} NMR (125.7 MHz, CDCl3, CH2), 5.63 [t, JH,H = 7.8 Hz, 1 H, =CH(nBu)], 7.25–7.42 (m, 5 H, CH/
25 °C): δ = 11.9, 13.7, 20.2, 30.8, 112.7, 128.5, 130.0, 130.4, 133.2,
Ph), 7.45–7.55 (m, 2 H, CH/Ph), 7.58–7.65 (m, 1 H, CH/Ph), 8.13–8.19
149.5, 165.5 ppm. HRMS (ESI-TOF): calcd. for C13H16O2Na [M + Na]+
(m, 2 H, CH/Ph) ppm. 13C{1H} NMR (125.7 MHz, CDCl3, 25 °C): δ =
227.1043, found 227.1068. 3b: 1H NMR (500.3 MHz, CDCl3, 25 °C): 14.0, 22.4, 27.0, 32.2, 120.8, 128.30, 128.32, 128.4, 128.6, 130.1, 133.3,
δ = 0.96 (t, JH,H = 7.4 Hz, 3 H, CH3), 1.42–1.50 (m, 2 H, CH2), 1.98 (d,
134.8, 146.4, 165.5 ppm.
JH,H = 0.9 Hz, 3 H, CH3), 2.08 (q, JH,H = 7.4 Hz, 2 H, CH2), 5.25 [t,
7: 4-Methoxybenzoic acid (152 mg, 1.0 mmol) was reacted with 2-
hexyne (123 mg, 1.5 mmol) for 6 h at 140 °C, yielding a mixture of
(E)-hex-2-en-3-yl 4-methoxybenzoate (7a) and (E)-hex-2-en-2-yl 4-
methoxybenzoate (7b) as a yellow liquid after appropriate work-up
(213 mg, 91 %, ratio 7a:7b = 62:38). 7a: 1H NMR (500.3 MHz, CDCl3,
25 °C): δ = 0.94 (t, JH,H = 7.4 Hz, 3 H, CH3), 1.48–1.55 (m, 2 H, CH2),
1.70 (d, JH,H = 7.1 Hz, 3 H, CH3), 2.35 (t, JH,H = 7.4 Hz, 2 H, CH2), 3.86
(s, 3 H, OCH3), 5.29 [q, JH,H = 7.1 Hz, 1 H, =CH(CH3)], 6.90–6.94
(m, 2 H, m-CH/Ph), 8.01–8.04 (m, 2 H, o-CH/Ph) ppm. 13C{1H} NMR
(125.7 MHz, CDCl3, 25 °C): δ = 11.9, 13.7, 20.2, 30.8, 55.5, 112.5,
113.8, 122.7, 132.0, 149.5, 163.6, 165.3 ppm. HRMS (ESI-TOF): calcd.
for C14H18O3Na [M + Na]+ 257.1148, found 257.1137. 7b: 1H NMR
(500.3 MHz, CDCl3, 25 °C): δ = 0.95 (t, JH,H = 7.4 Hz, 3 H, CH3), 1.40–
J
H,H = 7.8 Hz, 1 H, =CH(nPr)], 7.43–7.48 (m, 2 H, m-CH/Ph), 7.55–7.60
(m, 1 H, p-CH/Ph), 8.06–8.11 (m, 2 H, o-CH/Ph) ppm. 13C{1H} NMR
(125.7 MHz, CDCl3, 25 °C): δ = 13.8, 15.4, 22.8, 28.8, 117.8, 128.5,
130.0, 130.3, 133.2, 145.8, 165.4 ppm. The analytical data are in
agreement with ref.[50]
4: Benzoic acid (122 mg, 1.0 mmol) was reacted with 3-octyne
(165 mg, 1.5 mmol) for 16 h at 140 °C, yielding a mixture of (E)-
oct-3-en-4-yl benzoate (4a) and (E)-oct-3-en-3-yl benzoate (4b) as a
yellow liquid after appropriate work-up (170 mg, 73 %, ratio 4a:4b =
56:44). 4a: 1H NMR (500.3 MHz, CDCl3, 25 °C): δ = 0.91 (t, JH,H
=
7.3 Hz, 3 H, CH3), 1.05 (t, JH,H = 7.5 Hz, 3 H, CH3), 1.33–1.42 (m, 4 H,
CH2), 2.10–2.17 (m, 2 H, CH2), 2.38 (t, JH,H = 7.4 Hz, 2 H, CH2), 5.25
[t, JH,H = 7.8 Hz, 1 H, =CH(Et)], 7.43–7.49 (m, 2 H, m-CH/Ph), 7.55–
7.60 (m, 1 H, p-CH/Ph), 8.07–8.11 (m, 2 H, o-CH/Ph) ppm. 13C{1H}
NMR (125.7 MHz, CDCl3, 25 °C): δ = 14.0, 14.6, 20.1, 22.3, 22.4, 28.8,
119.8, 128.5, 130.0, 130.4, 133.2, 148.8, 165.5 ppm. HRMS (ESI-TOF):
1.48 (m, 2 H, CH2), 1.96 (d, JH,H = 0.9 Hz, 3 H, CH3), 2.06 (q, JH,H
=
7.4 Hz, 2 H, CH2), 3.86 (s, 3 H, OCH3), 5.22 [t, JH,H = 7.8 Hz, 1 H, =
CH(nPr)], 6.90–6.94 (m, 2 H, m-CH/Ph), 8.01–8.04 (m, 2 H, o-CH/
Ph) ppm. 13C{1H} NMR (125.7 MHz, CDCl3, 25 °C): δ = 13.8,
15.5, 22.9, 28.8, 55.5, 113.7, 117.6, 122.7, 132.0, 145.8, 163.6,
165.2 ppm.
1
calcd. for C15H20O2Na [M + Na]+ 255.1356, found 255.1338. 4b: H
NMR (500.3 MHz, CDCl3, 25 °C): δ = 0.93 (t, JH,H = 7.1 Hz, 3 H, CH3),
1.07 (t, JH,H = 7.5 Hz, 3 H, CH3), 1.42–1.51 (m, 4 H, CH2), 2.09–2.15
(m, 2 H, CH2), 2.40 (q, JH,H = 7.3 Hz, 2 H, CH2), 5.21 [t, JH,H = 8.2 Hz,
1 H, =CH(nBu)], 7.43–7.49 (m, 2 H, m-CH/Ph), 7.55–7.60 (m, 1 H, p-
CH/Ph), 8.07–8.11 (m, 2 H, o-CH/Ph) ppm. 13C{1H} NMR (125.7 MHz,
CDCl3, 25 °C): δ = 11.8, 14.0, 22.5, 26.2, 29.3, 32.0, 117.6, 128.5,
130.0, 130.4, 133.2, 150.3, 165.5 ppm.
8: 4-(Trifluoromethyl)benzoic acid (190 mg, 1.0 mmol) was reacted
with 2-hexyne (123 mg, 1.5 mmol) for 6 h at 140 °C, yielding a
mixture of (E)-hex-2-en-3-yl 4-(trifluoromethyl)benzoate (8a) and
(E)-hex-2-en-2-yl 4-(trifluoromethyl)benzoate (8b) as a yellow liquid
after appropriate work-up (262 mg, 96 %, ratio 8a:8b = 72:28). 8a:
1H NMR (500.3 MHz, CDCl3, 25 °C): δ = 0.95 (t, JH,H = 7.4 Hz, 3 H,
CH3), 1.47–1.56 (m, 2 H, CH2), 1.72 (d, JH,H = 7.1 Hz, 3 H, CH3), 2.37
(t, JH,H = 7.4 Hz, 2 H, CH2), 5.34 [q, JH,H = 7.1 Hz, 1 H, =CH(CH3)],
7.69–7.73 (m, 2 H, m-CH/Ph), 8.16–8.21 (m, 2 H, o-CH/Ph) ppm.
13C{1H} NMR (125.7 MHz, CDCl3, 25 °C): δ = 11.8, 13.7, 20.2, 30.7,
113.1, 123.8 (q, JC,F = 273 Hz, CF3), 125.5–125.6 (m, m-CH/Ph), 130.4,
133.6, 134.7 (q, JC,F = 32.7 Hz, CCF3), 149.4, 164.3 ppm. HRMS (ESI-
TOF): calcd. for C14H15F3O2Na [M + Na]+ 295.0916, found 295.0920.
5: Benzoic acid (122 mg, 1.0 mmol) was reacted with 1-phenyl-1-
propyne (174 mg, 1.5 mmol) for 8 h at 140 °C, yielding a mixture
of (E)-1-phenylprop-1-en-1-yl benzoate (5a) and (E)-1-phenylprop-
1-en-2-yl benzoate (5b) as a yellow liquid after appropriate work-
up (230 mg, 97 %, ratio 5a:5b = 67:33). 5a: 1H NMR (500.3 MHz,
CDCl3, 25 °C): δ = 1.92 (d, JH,H = 7.4 Hz, 3 H, CH3), 5.71 [q, JH,H
=
1
7.4 Hz, 1 H, =CH(Me)], 7.27–7.41 (m, 4 H, CH/Ph), 7.46–7.54 (m, 3 H,
CH/Ph), 7.58–7.65 (m, 1 H, p-CH/Ph), 8.13–8.19 (m, o-CH/Ph) ppm.
13C{1H} NMR (125.7 MHz, CDCl3, 25 °C): δ = 13.0, 114.9, 128.29,
8b: H NMR (500.3 MHz, CDCl3, 25 °C): δ = 0.96 (t, JH,H = 7.4 Hz, 3
H, CH3), 1.41–1.49 (m, 2 H, CH2), 1.98 (d, JH,H = 0.9 Hz, 3 H, CH3),
2.06 (q, JH,H = 7.4 Hz, 2 H, CH2), 5.27 [t, JH,H = 7.8 Hz, 1 H, =CH(nPr)],
128.33, 128.6, 130.0, 130.07, 130.10, 133.4, 134.5, 147.0, 165.6 ppm. 7.69–7.73 (m, 2 H, m-CH/Ph), 8.16–8.21 (m, 2 H, o-CH/Ph) ppm.
HRMS (ESI-TOF): calcd. for C16H15O2 [M + H]+ 239.1067, found 13C{1H} NMR (125.7 MHz, CDCl3, 25 °C): δ = 13.7, 15.3, 22.8, 28.8,
1
239.1076. 5b: H NMR (500.3 MHz, CDCl3, 25 °C): δ = 2.27 (d, JH,H
=
118.1, 123.8 (q, JC,F = 273 Hz, CF3), 125.5–125.6 (m, m-CH/Ph), 130.4,
133.6, 134.7 (q, JC,F = 32.7 Hz, CCF3), 145.7, 164.2 ppm.
1.0 Hz, 3 H, CH3), 6.44 [s, 1 H, =CH(Ph)], 7.27–7.41 (m, 4 H, CH/Ph),
7.46–7.54 (m, 3 H, CH/Ph), 7.58–7.65 (m, 1 H, p-CH/Ph), 8.13–8.19
(m, o-CH/Ph) ppm. 13C{1H} NMR (125.7 MHz, CDCl3, 25 °C): δ = 17.4,
119.1, 127.0, 128.4, 128.5, 128.6, 128.9, 130.0, 133.5, 135.0, 148.3,
165.2 ppm.
Supporting Information (see footnote on the first page of this
article): Copies of the 1H and 13C{1H} NMR spectra of all catalysis
products can be found in the Supporting Information.
6: Benzoic acid (122 mg, 1.0 mmol) was reacted with 1-phenyl-1-
hexyne (237 mg, 1.5 mmol) for 16 h at 140 °C, yielding a mixture
of (E)-1-phenylhex-1-en-2-yl benzoate (6a) and (E)-1-phenylhex-1-
en-1-yl benzoate (6b) as a yellow liquid after appropriate work-up
(224 mg, 80 %, ratio 6a:6b = 72:28). 6a: 1H NMR (500.3 MHz, CDCl3,
Acknowledgments
The Fonds der Chemischen Industrie is gratefully acknowledged
25 °C): δ = 0.90 (t, JH,H = 7.4 Hz, 3 H, CH3), 1.35–1.44 (m, 2 H, CH2), for financial support and for a Chemiefonds fellowship to J. J.
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Received: December 17, 2015
Published Online: February 16, 2016
Eur. J. Org. Chem. 2016, 1548–1554
www.eurjoc.org
1554
© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim