Co(iii)-catalyzed: Z -selective oxidative C-H/C-H cross-coupling of alkenes with triisopropylsilylacetylene

Article abstract of DOI:10.1039/c9cc02347j

A Co(iii)-catalyzed direct oxidative C-H/C-H cross-coupling reaction of acrylamides with triisopropylsilylacetylene is presented. It is applicable to unsubstituted, internal and terminal acrylamides with a broad functionality tolerance. The feasibility of

Full text of DOI:10.1039/c9cc02347j

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Marilyn M. Olmstead, Alan L. Balch, Josep M. Poblet, Luis Echegoyenet al.
Reactivity differences of Sc
first methanofullerene derivatives of Sc
3
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DOI: 10.1039/C9CC02347J
Journal Name
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Co(III)-Catalyzed Z-Selective Oxidative C–H/C–H Cross-Coupling of
Alkenes with Triisopropylsilylacetylene
Tingxing Zhao, Dekun Qin, Weiguo Han, Shiping Yang, Boya Feng, Ge Gao* and Jingsong You*
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
A Co(III)-catalyzed direct oxidative C–H/C–H cross-coupling reaction was applied by employing preoxidized alkyne sources such as
9
10
of acrylamides with triisopropylsilylacetylene is presented. It is ethynylbenziodoxolones (EBX) and haloalkynes, which apparently
applicable to unsubstituted, internal and terminal acrylamides with sacrifices the atom- and step economy (Scheme 1a). The protocols
a broad functionality tolerance. The feasibility of this protocol is using EBX are generally mild enough to accommodate most alkenes,
successfully demonstrated by the late-stage alkynylation of a but only precious rhodium and iridium catalysts are now workable.
1
0e
10g
derivative of steroid drug Epristeride.
Although non-precious nickel and iron catalysts are applicable
when 1-bromoalkyne is employed, a very narrow scope of alkenes
(
1
Conjugated enynes are not only widely found in natural products,
only five examples) is reported. It should be noted that introduction
of a proper directing group (DG) could exclusively provide (Z)-
2
3
pharmaceuticals, bioactive molecules, and organic functional
4
materials, but also important synthetic intermediates toward furan
11
enynes.
derivatives, polycyclic lactones, multisubstituted aromatics, metal
5
complexes, polyynes, and allenes. Therefore, concise and efficient
a) previous work: coupling with preoxidized alkynes
protocols to synthesize enynes are very attractive and desired.
During the past decades, significant advances have been made in the
field of transition-metal catalyzed cross-coupling reactions for the C–
R1 DG
O
I
TIPS
R1 DG
[
Rh] or [Ir]
+
O
+
R2
R1 DG
R1
H
6
TIPS
R
C bond formation. The direct oxidative C–H/C–H cross-coupling of
R1 DG
[Pd], [Rh], [Ir],
Ni], or [Fe]
alkenes with alkynes is an ideal strategy to build enynes due to the
excellent atom- and step economy. However, this methodology is
much less developed with only sporadic reports in comparison with
the cross-coupling of arenes with alkynes.
The first example of the cross-coupling of alkenes with terminal
[
X
R
R1
X = Br, or I
R2
H
7
8
b) This work: coupling directly with an alkyne
O
O
R1
R1
R2
Q
N
Q
[
Co(III)]
O]
N
+
H
TIPS
H
alkynes was presented by Jung et al in 2009 using Pd(TFA)
catalyst, wherein (E)-enynes were obtained via a heck-type
2
as the
H
[
R2
H
TIPS
7
a
mechanism with inevitable homocoupling of alkynes. In 2012,
Zhong’s group reported the synthesis of (Z)-enynes via a Pd(OAc)
catalyzed cross-coupling of allylic ethers with terminal arylalkynes in
 Cobalt catalysis



Various substituted acrylamides Q =
Broad functional group tolerance
Z-selective enynes
2
-
N
7
b
the presence of a phosphine ligand. It is noted that only mono-
substituted ethylenes were reported in these two methods, and a
large excess of alkenes were necessary.
Scheme 1. Cross-coupling reactions of alkenes with alkynes.
The main challenges encountered are the easy homocoupling of
alkynes and side reactions of alkenes under oxidative conditions. To
address these issues, the so called “inverse Sonogashira strategy”
Due to our continuous interest in C–H functionalization of alkene
1
2
derivatives, we herein would like to report our success in the direct
alkynation of acrylamides with triisopropylsilylacetylene by using a
1
3
cobalt catalyst and the 8-aminoquinoline directing group (Scheme
b). This reaction is the first example of a general and inexpensive
1
Key Laboratory of Green Chemistry and Technology of Ministry of Education, College
of Chemistry, Sichuan University, 29 Wangjiang Road, Chengdu 610064,
P. R. China. E-mail: gg2b@scu.edu.cn, jsyou@scu.edu.cn.
oxidative C–H/C–H cross-coupling protocol between a broad scope
of alkene derivatives and a terminal alkyne. Very recently, limited
Electronic Supplementary Information (ESI) available. CCDC 1888693. For ESI and
crystallographic data in CIF or other electric format see DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
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examples of an Ir-catalyzed cross-coupling of cinnamamides with moderate to good yields. Nevertheless, active functionalities such as
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triisopropylsilylacetylene was reported.8g
hydroxy, amine and carboxylic acid were incompatible. It is noted
that the acrylamides with electron-donating groups reacted sluggish
and prolonged time was necessary. The same situation happened for
sterically hindered substrates (1e and 1l), and the corresponding
enynes were obtained in 51% and 40% yields, respectively. The
reactions of 2-thienyl and 2-furyl substituted acrylamides gave
complicated mixtures due to their decomposition under the catalytic
conditions, and the desired coupled products were isolated in
moderate yields. For the 3-pyridinyl substituted acrylamide, however,
the reaction ran clearly but slowly, affording 3o in 60% yield after 36
h.
DOI: 10.1039/C9CC02347J
Table 1. Optimization of the reaction conditionsa,b
O
O
O
[
Co] (10 mol %)
Q
oxidant (2 equiv)
Q
Q
N
N
N
+
+
TIPS
H
additive (1 equiv)
H
Ph
THF, 120 °C, 24 h Ph
Ph
TIPS
TIPS
1a
2
3a
4a
Entry
Oxidant
Additive
Yield of 3a (%)
1
2
Ag
Ag
2
CO
CO
3
3
KOAc
HOAc
39%
trace
2
Table 2. Scope of internal acrylamidesa,b
3
4
5
6
7
8
9
Ag
Ag
Ag
Ag
2
2
2
2
CO
3
Mn(OAc)
3
56%
73%
29%
27%
29%
trace
trace
11%
n.d
CO
3
Mn(OAc)
2
O
O
CO
CO
3
3
Zn(OAc)
2
Co(acac)3 (10 mol %)
Ag2CO3 (2 equiv)
R1
R2
R1
R2
Q
Q
N
N
+
TIPS
H
Mn(OAc) (1 equiv)
20 C,THF, 24 h
H
2
o
1
TIPS
Ag
Ag SO
2
O
Mn(OAc)
Mn(OAc)
Mn(OAc)
Mn(OAc)
Mn(OAc)
Mn(OAc)
2
2
2
2
2
2
1
2
3
3
c, R = p-MeO, 66%c
3d, R = p-AcO, 55%c
2
4
O
O
O
3
3
e, R = o-Me, 51%c
AgOAc
Me
Ph
Q
Q
Q
N
N
N
f, R = p-NO2, 52%
H
H
H
1
0
Cu(OAc)
2
Ph
3g, R = p-CHO, 42%
3h, R = p-CF3, 73%
3i, R = p-Cl, 56%
R
TIPS
TIPS
TIPS
1
1c
2 3
Ag CO
3a, 73%
3b, 70%
3j, R = m-Br, 57%
1
2
n.d
3k, R = m-F, 70%
O
O
O
O
aReaction conditions: Co(acac)
(0.01 mmol, 10 mol %), oxidant (0.2
Q
N
3
Q
Q
Q
N
N
N
H
H
H
H
mmol, 2.0 equiv), acrylamide 1a (0.1 mmol, 1.0 equiv), alkyne 2 (0.15
mmol, 1.5 equiv), additive (0.1 mmol, 1.0 equiv), and THF (1 mL) at
TIPS
S
TIPS
O
TIPS
TIPS
N
b
3l,40%c
3m, 40%
3n, 45%
3o, 60%c
1
20 °C for 24 h under a N
2
atmosphere. n.d. = not detected. Isolated
O
O
O
O
c
yield.
Without
Co(acac)
3
.
Q
=
8-quinolinyl.
nPr
Q
Me
Me
Q
N
Q
Q
N
H
N
N
H
H
H
nPr
nPr
We initiated our study with the reaction of (E)-2-methyl-3-phenyl-
N-(quinolin-8-yl)acrylamide 1a with triisopropylsilylacetylene 2
catalyzed by various nonprecious metal salts. It was found that
TIPS
TIPS
TIPS
TIPS
3s, 80%d
3p, 71%d
O
3q, 74%d
O
3r, 82%e
O
O
O
O
Q
Q
Q
N
Q
N
N
N
Co(acac)
2
and Co(acac)
3
provided 3a in around 40% yields.
H
H
H
H
O
Me
Interestingly, a mixture of the cross-coupled product 3a (35%) and
the annulated product 4a (5%) was obtained under the catalysis of
TIPS
TIPS
TIPS
O
TIPS
Ph
3t, 81%e
3u, 47%e
3v, 47%e
3w, 45%e
Co(acac)
Table 1, entry 1. For the detailed catalyst screening, see Table S1).
Addition of HOAc instead of KOAc ceased the reaction (Table 1, entry
). The use of Mn(OAc) increased the yield of 3a to 56%, and its yield
was further improved to 73% yield by using Mn(OAc) , while
Zn(OAc) showed no beneficial effect and gave a similar result to the
reaction with no additive (Table 1, entries 3-6). The exact role of
2
, while Co(acac)
3
gave 3a in 39% yield as the single product
O
Q
N
(
Me
H
Me
NC
H
H
TIPS
2
3
H
3
x, 78%e
2
2
aReaction conditions: Co(acac)
(0.01 mmol, 10 mol %), Ag CO (0.2
3 2 3
mmol, 2.0 equiv), Mn(OAc)2 (0.1 mmol, 1.0 equiv), internal
acrylamide 1 (0.1 mmol, 1.0 equiv), alkyne 2 (0.15 mmol, 1.5 equiv),
and THF (1 mL) at 120 °C for 24 h under a N
1
4
Mn(OAc)
revealed that Ag
No reaction took place in the absence of either Co(acac)
Table 1, entries 11-12), indicating this is a Co(III)-catalyzed oxidative
cross-coupling reaction. Finally, the optimal reaction was set to be
2
is unclear at current stage. Varying different oxidants
CO was the most effective (Table 1, entries 7-10).
or Ag CO
2
3
b
2
atmosphere. Isolated
3
2
3
c
d
yield. 36 h. Co(acac)
equiv), Mn(OAc)
as in
3
(0.02mmol, 20 mol %), Ag
(0.2 mmol, 2.0 equiv), 26 h. The same conditions
2
CO
3
(0.2 mmol, 2.0
(
e
2
d
except
reacting
for
48
h.
Co(acac)
3
(10 mol %), Ag
2
CO
3
(2.0 equiv), Mn(OAc)
2
(1.0 equiv) in THF
o
(1.0 mL) at 120 C for 24 h under N
2
(Table 1, entry 4).
β-Alkyl acrylamides are inert substrates toward the cross coupling
reaction with 2. The reaction could not finish under the standard
conditions even after extended time. Fortunately, addition of 20 mol%
3 2
Co(acac) and 2 equiv of Mn(OAc) was found effective. The reactions
With the optimized reaction conditions in hand (Table 1, entry
4
), the scope of internal acrylamides 1 was investigated (Table 2).
Acrylamides bearing methoxy, acetoxy, methyl, nitro, formyl,
trifluoromethyl, chloro, bromo, and fluoro groups on the β-phenyl
ring were all affordable to provide the targeted products (3a-3k) in
nicely afforded 3p and 3q in 71% and 74% yields, respectively.
2
| J. Name., 2012, 00, 1-3
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However, the acrylamide 1r with longer n-propyl chains on both the pivalic acid could suppress the annulation to the maxViimewuAmrticelexOtenlninte.
α and β positions is even more inert, the reaction took 48 h to give Under the modified conditions, a range of αD-aOrIy:l10a.c1r0y3la9/mCi9dCeCs0(253a4-7hJ)
3
r in a yield of 82%. Interestingly, although the enyne products were were successfully converted into the (Z)-enyne products (6a-h) in 42-
both obtained in similar yields around 80%, the cyclohexenyl 72% yields and the corresponding annulated products (7a-h) in 19-
substrate exhibited much lower reactivity than the cyclopentenyl 29% yields. The same trend as for β-aryl acrylamides was found:
counterpart as much longer reaction time was needed. It is also Products with an electron-donating group on the phenyl ring (6b vs
3
15
noted that the sp carbon alkynylated products were not observed.
6d) and more steric hindrance (6h vs 6g) were obtained in lower
The reaction of the (2E,4E)-5-phenylpenta-2,4-dienamide substrate yields. The instability of α-(3-thienyl) acrylamide resulted in a low
installed the alkynyl group on the 3-position to give 3u in 47% yield, yield of 33% for 6i. For α-alkyl and unsubstituted acrylamides, the
suggesting that the directing group plays an important role in this targeted enynes 6j-l were attained in moderate yields and almost no
reaction. The present protocol provides an efficient and concise annulated by-products were observed. It should be pointed out that
method for the late-stage modification of natural products and with this loading of Co(acac) (30 mol %) and Ag CO (2.0 equiv), the
3 2 3
pharmaceuticals. For examples, a pair of isomeric derivatives of cost of our protocol is still much lower than those methods utilizing
chromone were directly alkynylated in moderate yields (3v and 3w). Rh and Ir catalysts, even not considering the preparation of
1
8
2 3
Epristeride is a steroid drug used in the treatment of enlarged preoxidized alkyne reagents. Moreover, Ag CO could also be easily
1
9
prostate. A smooth alkynylation of its derivative 1x with 2 provided recycled by using a reported procedure (see Section V in ESI).
the desired product 3x in 78% yield. The structure of 3x was
confirmed to perserve the configuration by the single crystal X-ray
diffraction analysis.
O
O
O
1
6
Q
N
O
TBAF (4 equiv)
O
HCl (1.25 M)
H
THF (1 mL), rt, 3 h
Ph
Ph
MeOH, 80 ºC, 8 h Ph
TIPS
TIPS
Table 3. Scope of terminal acrylamidesa,b
3a
8, 70%
9, 95%
Co(acac)3 (30 mol %)
Ag2CO3 (2 equiv)
Mn(OAc)2 (1 equiv)
O
O
O
R1
Scheme 2. Removal of the directing and protecting groups
Q
R1
R1
N
Q
N
Q
TIPS
H
+
N
+
H
PivOH (2 equiv)
TIPS
8
0 oC,THF, 24 h
TIPS
Cl
The 8-aminoquinolinyl group could be easily removed under acidic
conditions.2 For example, enyne 3a was converted to its methyl
ester form 8 in 70% yield by refluxing in methanol in the presence of
hydrochloric acid for 8 h. Then the silyl group was removed by
treating with TBAF in THF at room temperature to afford the
corresponding terminal 1,3-enyne 9 in almost quantitative yield
(Scheme 2), providing opportunity for further derivation. To show
the practicability of this method, a gram-scale experiment was
conducted. The reaction of 1a on 4 mmol scale under the standard
conditions for 48 h provided 3a in 68% yield (see Section VII in ESI).
5
2
6
7
0
MeO
Ph
O
O
O
O
Q
Q
Q
N
Q
N
N
N
H
H
H
H
TIPS
TIPS
TIPS
TIPS
6
a, 70% (27%)
6b, 52% (26%)
6c, 50% (27%)
6d, 63% (29%)
O
O
O
O
Q
Q
Q
Q
N
Br
N
N
H
N
H
H
H
F
TIPS
TIPS
TIPS
TIPS
6
e, 49% (28%)
6f, 51% (19%)
6g, 72% (24%)
6h, 42% (23%)
S
O
O
O
Q
O
Me
Q
Q
N
Q
N
Ph
N
N
H
H
H
H
TIPS
TIPS
6k, 46% (<10%)
TIPS
(a) KIE experiments:
TIPS
6j, 46%c (trace)
O
Co(acac)3 (10 mol%)
Ag2CO3 (2 equiv)
Mn(OAc)2 (1 equiv)
O
6
i, 33% (18%)
6l, 47% (trace)
Q
Q
N
H
N
H
+
+
TIPS
TIPS
1
20 C,THF, t
aReaction conditions: Co(acac)
Ph
D
H
Ph
3
2 3
(0.03 mmol, 30 mol %), Ag CO (0.2
1
a
TIPS
Q
mmol, 2.0 equiv), Mn(OAc)
.0 equiv), terminal acrylamide 5 (0.1 mmol, 1.0 equiv), alkyne 2
0.15 mmol, 1.5 equiv), and THF (1 mL) at 80 °C for 24 h under a N
2
(0.1 mmol, 1.0 equiv), PivOH (0.2 mmol,
Co(acac)3 (10 mol%)
D
O
O
D
D
Ag CO3 (2 equiv)
2
(
Q
2
Mn(OAc)2 (1 equiv)
D
N
H
D
N
H
2
120 C,THF, t
Ph
Ph
D
b
c
atmosphere. Isolated yield. 48 h. Yields of 7 are in the parentheses.
KIE = KH/KD = 1.63
TIPS
1
a-d4
(
b) radical experiment:
Co(acac)3 (10 mol%)
Ag2CO3 (2 equiv)
Mn(OAc)2 (1 equiv)
TEMPO
A different situation was encountered when terminal acrylamides
were tested (Table 3). The desired coupled products 6 were
O
O
Q
Q
5
N
+
N
TIPS
H
H
1
20 C, THF, 4 h
generated in low yield accompanying with a comparable amount of
annulated products 7 under the standard conditions. For example,
the cross-coupling of 5a with 2 furnished 6a in only 20% yield and the
Ph
Ph
1a
TIPS
1
7
TEMPO (1 equiv), 3a, 38%
TEMPO (3 equiv), 3a, 13%
TEMPO (6 equiv), 3a, 15%
annulated product 7a in 13% yield. No 5a was left and a lot of Scheme 3. Mechanistic study.
impurities also emerged. Modification of the standard conditions
was then conducted (see Table S2 in ESI) and the key findings are: 1)
Lowering the temperature to 80 C resulted in a cleaner reaction effect (KIE) was calculated to be 1.63 based on two independent
To shed light on the reaction mechanism, the kinetic isotopic
o
giving both 6a and 7a in low yields with 5a recovered; 2) The yields reactions of 2 with 1a and 1a-d
of 6a and 7a were simultaneously raised with increased amounts of H bond cleavage in 1a might not be involved in the rate-determining
Co(acac) , and reached about 40% when 30 mol% of Co(acac) was step. Although the attempts to isolate the coordinated acrylamide-
employed; 3) 7a was inevitably generated, but addition of 2 equiv of Co intermediates were unsuccessful, the key intermediates were
4
(Scheme 3a), suggesting that the C–
3
3
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Liu, Y.-H. Liu, X.-S. Yin, W.-J. Gu, B.-F. Shi, Chem.VEieuwrA.rtJi.c,le2O0n1lin5e,
1, 205. (f) M. Shang, M.-M. Wang, T. G. Saint-Denis, M.-H. Li,
H.-X. Dai, J.-Q. Yu, Angew. Chem. Int. Ed., 2017, 56, 5317. (g)
G. Wu, W. Ouyang, Q. Chen, Y. Huo, X. Li, Org. Chem. Front.,
detected by the MALDI-TOF analysis (see Section VIII in ESI).
Moreover, when a radical scavenger 2,2,6,6-tetramethylpiperidine-
2
DOI: 10.1039/C9CC02347J
1
-oxyl (TEMPO) was added, the cross-coupling of 1a with 2 was
largely but incompletely suppressed, suggesting both a radical and
nonradical pathways could be involved (Scheme 3). Based on the
2
019, 6, 284.
9
1
(a) F. Xie, Z. Qi, S. Yu, X. Li, J. Am. Chem. Soc., 2014, 136, 4780.
(b) K. D. Collins, F. Lied, F. Glorius, Chem. Commun., 2014, 50,
2
0,21
preliminary results and previous reports,
is proposed in Scheme S1.
a plausible mechanism
4
5
1
459. (c) C. Feng, D. Feng, T.-P. Loh, Chem. Commun., 2014,
0, 9865. (d) C. Feng, D. Feng, Y. Luo, T.-P. Loh, Org. lett., 2014,
6, 5956. (e) P. Finkbeiner, U. Kloeckner, B. J. Nachtsheim,
In summary, we have developed a direct oxidative C–H/C–H cross-
coupling of acrylamides with triisopropylsilylacetylene by employing
a cobalt catalyst with the assistance of the bidentate 8-
aminoquinoline directing group. This reaction features mild reaction
conditions, inexpensive reagents, a broad acrylamide scope, good
functional group tolerance and Z-selectivity of enyne products, which
makes it a very useful protocol for late-stage modifications of
pharmaceuticals and natural products.
Angew. Chem. Int. Ed., 2015, 54, 4949. (f) L. D. Caspers, P.
Finkbeiner, B. J. Nachtsheim, Chem. Eur. J., 2017, 23, 2748.
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We acknowledge financial supports from the National NSF of
China (Nos 21472127, 21772134 and 21432005) and the
Fundamental Research Funds for the Central Universities.
1
39, 1325. (i) E. Tan, O. Quino-nero, M. Elena de Orbe, A. M.
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}
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] $382.50/g, [{Cp*IrCl
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2 2
} ]
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$450.00/g, Co(acac)
$2.68/g.
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$1.67/g, Ag
CO $3.06/g, and Mn(OAc)
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