Copper-catalyzed tandem phosphination-decarboxylation-oxidation of alkynyl acids with H-phosphine oxides: A facile synthesis of β-ketophosphine oxides

Article abstract of DOI:10.1039/c5cc01904d

The general method for the tandem phosphination-decarboxylation-oxidation of alkynyl acids under aerobic conditions has been developed. In the presence of CuSO₄·5H₂O and TBHP, the reactions provide a novel access to β-ketophosphine oxides in good to excellent yields. This transformation allows the direct formation of a P-C bond and the construction of a keto group in one reaction.

Full text of DOI:10.1039/c5cc01904d

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DOI: 10.1039/C5CC01904D
Journal Name
RSCPublishing
COMMUNICATION
CopperꢀCatalyzed
Tandem
Phosphinationꢀ
DecarboxylationꢀOxidation of Alkynyl Acids with Hꢀ
Phosphine Oxides: A Facile Synthesis of βꢀ
Ketophosphine Oxides
Cite this: DOI: 10.1039/x0xx00000x
Received 00th January 2012,
Accepted 00th January 2012
a
a
a
a
b
a,
Pengbo Zhang, Liangliang Zhang, Yuzhen Gao, Jian Xu, Hua Fang, Guo Tang, *
a
DOI: 10.1039/x0xx00000x
and Yufen Zhao
www.rsc.org/
The general method for the tandem phosphinationꢀ solids without an unpleasant smell and are convenient to synthesize,
decarboxylationꢀoxidation of alkynyl acids under aerobic store, and transport. On the basis of this viewpoint, Wu’s group
fulfilled the decarboxylative coupling of arylpropiolic acids with
conditions has been developed. In the presence of
CuSO ·5H O and TBHP, the reactions provide a novel access
to βꢀketophosphine oxides in good to excellent yields. This
transformation allows the direct formation of a PꢀC bond and
the construction of a keto group in one reaction.
P(O)H to construct a CspꢀP bond with the assistance of a copper
4
2
14
catalyst system. Recently, our group developed an efficient
synthesis of Eꢀalkenylphosphine oxides via copperꢀcatalyzed
decarboxylative crossꢀcoupling of alkynyl acids with Hꢀphosphine
15
oxides. To the best of our knowledge, the example of βꢀ
ketophosphine oxide formation via decarboxylative coupling of
alkynyl acids has yet to be reported.
Organophosphorus compounds have broad applications in the
1
2
3
fields of organic synthesis, materials, medicinal chemistry, and
4
ligand chemistry. Thus, to develop new efficient method for C–P
Reactions involving organophosphorus radicals have a long
history, and are useful reactive species in organic synthetic
bond construction has attracted increasing attention. βꢀ
ketophosphine oxides can facilitate carbon–carbon bond formation
and then the diphenylphosphinyl group can be easily removed to
16
chemistry. Owing to our continuous interests in the P−C bond
17
18
5
6
7
formation and the reaction of organophosphorus radicals, we
present herein our recent progress in constructing valuable βꢀ
ketophosphine oxides via tandem phosphinationꢀdecarboxylationꢀ
oxidation of alkynyl acids. This transformation allows the direct
formation of a PꢀC bond and the construction of a keto group in one
reaction via a radical process.
give olefins, cyclopropanes, and branched ketones. βꢀ
ketophosphine oxides can also be used for liquidꢀliquid extraction of
8
metal ions because of their prominent metalꢀcomplexing abilities.
The traditional methods to prepare βꢀketophosphine oxides are based
on the acylation of alkyl phosphine oxides with carboxylic acid
derivatives which employ stoichiometric amounts of the hazardous
9
10
organometallic reagents. In recent years, our group and other
researchers
11
reported many practical approaches to βꢀ
ketophosphonates, but these methods are not ideal choices for the
synthesis of βꢀketophosphine oxides.
In 1966, Nilsson reported the pioneering work of
1
2
decarboxylative coupling. Since 2002, a series of transitionꢀmetalꢀ
catalyzed decarboxylative C−C and C−heteroatom bonds formation
1
3
reactions have been extensively developed. Compared with the
traditional crossꢀcouplings and C–H activation, decarboxylative
coupling reactions using carboxylic acid derivatives have several
advantages. Instead of metal waste from organometallic coupling
reagents, less toxic carbon dioxide is released as a byproduct after
the complete conversion, which reduces the cost of the process for
the treatment of waste. It is noteworthy that as a practical alternative,
the use of arylpropiolic acids as terminal arylacetylene surrogates is
safer and more attractive because arylpropiolic acids are usually
Scheme 1. C−P bond formation via decarboxylative coupling.
J. Name., 2012, 00, 1-3 | 1
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DOI: 10.1039/C 1904D
Jou5CrnC0al Name
a
16h
Table 1. Reaction conditions optimization.
could promote the reaction efficiently. Gratifyingly, the yield
increased tremendously when TBHP was employed as oxidant.
However, the other oxidants like K S O , BQ (pꢀbenzoquinone),
2
2
8
DTBP (diꢀtertꢀbutyl peroxide), and H O did not improve the yield
2
2
(entries 17ꢀ22). The solvent systems employed also notably affected
the related reaction efficiencies. Conducting the reaction in EtOH,
c
DMF, DMSO and 1,4ꢀdioxane gave the product 3a in very low yield
Yield
%)
b
Entry
Catalyst
Base
Solvent
Oxidant
(entries 23ꢀ26), while the reaction conducted in MeCN gave a high
(
yield (entry 18). Moreover, the yield was reduced to 30% using O2
instead of TBHP (entry 22). No desired product was afforded
without copper salt (entry 27). The yield of product 3a decreased
1
2
3
4
5
6
8
9
CuSO
CuBr
CuBr
Cu
4
·5H
2
O
NH
NH
NH
NH
NH
NH
NH
NH
3
3
3
3
3
3
3
3
·H
·H
·H
·H
·H
·H
·H
·H
ꢀ
2
2
2
2
2
2
2
2
O
O
O
O
O
O
O
O
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
DMF
air
air
air
air
air
air
air
air
air
air
air
air
air
air
air
43
14
43
25
37
o
2
when the temperature was raised to 70 C or decreased to room
2
O
temperature (entry 28). However, the attempt to decrease the amount
of 2a was failed (entry 29). After optimization of the reaction
conditions, we established a highly efficient route to the tandem
decarboxylationꢀphosphinationꢀoxidation of alkynyl acids (entry 18).
With this preliminary result in hand, the generality of the method
was explored under the optimized conditions [alkynyl acid (0.2
mmol), P(O)ꢀH (0.8 mmol), CuSO ·5H O (10 mmol %), TBHP (2
CuO
CuI
trace
trace
40
CuCl
Cu(OTf)
2
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
CuSO
CuSO
CuSO
CuSO
4
4
4
4
·5H
2
2
2
2
O
O
O
O
26
·5H
·5H
·5H
Cs
2
CO
3
25
4
2
K
2
CO
3
33
o
equiv), NH ·H O (25%, 0.25 mL) in MeCN at 60 C under air for 2
3
2
NaOAc
33
h], and the results are summarized in Table 2. In general, a variety of
functional groups on the phenyl ring of arylpropiolic acids were
compatible under this procedure, affording the desired products in
good to excellent yields. The methyl substituted arylpropiolic acids,
such as metaꢀmethyl, paraꢀmethyl, and 3,5ꢀdimethyl groups on the
aryl ring, reacted with 2a efficiently and gave the desired products
CuBr
CuBr
CuBr
2
2
2
(iPr)
2
3
NEt
N
trace
18
Et
pyridine
NH ·H
NH ·H
6
CuSO
4
·5H
2
2
2
2
2
2
2
2
2
2
O
O
O
O
O
O
O
O
O
O
3
2
O
H
2
O
2
12
CuSO
4
·5H
·5H
·5H
·5H
·5H
·5H
·5H
·5H
·5H
3
2
O
O
O
O
O
O
O
O
O
O
O
O
TBHP
90
CuSO
CuSO
CuSO
CuSO
CuSO
CuSO
CuSO
CuSO
4
NH
NH
NH
NH
NH
NH
NH
NH
NH
NH
NH
3
3
3
3
3
3
3
3
3
3
3
·H
·H
·H
·H
·H
·H
·H
·H
·H
·H
·H
2
BQ
16
3
cꢀ3e in high yields. The orthoꢀsubstituted arylpropiolic acids
4
4
4
4
4
4
4
2
2
2
2
2
2
2
2
2
2
K
2
S
2
O
8
48
exhibited a particularly distinct steric hindrance effect (3b–3e), and
the corresponding βꢀketophosphine oxide 3b was obtained in a
slightly lower yield (75%). Halogen atoms such as fluoro, chloro,
bromo, and iodo on the aromatic ring were unaffected under the
present reaction conditions to afford the corresponding products 3fꢀ
DTBP
trace
30
O
2
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
TBHP
24
DMSO
EtOH
56
52
3
j in good yields, which could allow for further synthetic
1,4ꢀdioxane
MeCN
MeCN
MeCN
28
transformations. Arylpropiolic acids bearing electronꢀwithdrawing
ꢀ
0
CF , COOEt, CN groups reacted smoothly to give the corresponding
3
d
e
CuSO
4
·5H
2
2
O
O
80 (5)
products in good yields (3kꢀ3n). Treatment of diphosphine oxide
with methoxyꢀsubstituted arylpropiolic acid led to the formation of
product 3o in 50% yield. Replacing methoxy group with
trifluoromethoxy group resulted in a higher yield (3p, 87%). More
bulky substrates such as 3ꢀ(naphthalenꢀ1ꢀyl)propiolic acid also
smoothly reacted with diphosphine oxide and gave product 3q in
f
2
9
CuSO
4
·5H
70
a
Reaction conditions: 1a (0.2 mmol), 2a (0.8 mmol), catalyst (10 mol %),
base, oxidant, solvent (1.5 mL) in an open flask at 60 C for 2 h. Unless
otherwise specified, NH ·H O (25%) was 0.25 mL, other bases were 0.4
mmol. Yields were determined by H NMR. At 70 C. At room
temperature. 2a (0.4 mmol).
o
b
3
2
c
1
d
o
e
f
5
6% yield. In addition, 3ꢀ(thiophenꢀ2ꢀyl)propiolic acid could also
provide the expected product 3s in 46% yield.
At the outset of our investigation, phenylpropiolic acid (1a) and
The substrate scope was further investigated by reacting
phenylpropiolic acid (1a) with different organophosphorous
reagents. Apart from 2a, diꢀpꢀtolylphosphine oxide (2b) and bis(4ꢀ
chlorophenyl)phosphine oxide (2c) were all suitable substrates,
generating the corresponding products 3t and 3u in 86% and 65%
yields, respectively. However, diarylphosphine oxide involving a
paraꢀbromo substituent 2d produced the desired product 3v in only
H(O)PPh (2a) were chosen as the model substrates to survey the
2
reaction conditions. Gratifyingly, when a mixture of 1a (0.2 mmol),
2
a (0.8 mmol), CuSO ·5H O (0.02 mmol) and NH ·H O (25%, 0.25
4 2 3 2
o
mL) in MeCN was heated to 60 C under air for 2 h, the desired
product 3a was obtained in 43% yield (Table 1, entry 1).
Subsequently, various Cu(I) and Cu(II) salts were further checked
and the results showed that Cu(II) salts were more effective to give 43% yield. The butyl(pꢀtolyl)phosphine oxide (2e) also efficiently
the desired product (entries 1ꢀ9). A brief survey of bases such as reacted with 1a and led to the corresponding product 3w in 89%
Cs CO , K CO , NaOAc, (iPr) NEt, NEt , pyridine, and NH ·H O yield. Treatment of ethyl phenylphosphinate (2f) with 1a afforded
2
3
2
3
2
3
3
2
the desired product 3x in a lower yield of 42%. When diethyl
(
25%) led to the observation that NH ·H O (25%) gave the highest
3 2
phosphonate (2g) was used, an only 22% yield of βꢀketophosphonate
yield of 3a (entries 9ꢀ16). In our previous synthesis of aꢀhydroxy
phosphonates from Hꢀphosphonates and alcohols, we found that the
combination use of Cu(II) and TBHP (tertꢀbutylhydroperoxide)
3
y was obtained. Alkynyl acid was also examined. Unfortunately,
3
1
only trace amount of the desired product was detected by P NMR.
2
| J. Name., 2012, 00, 1-3
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DOI: 10.1039/C5CC01904D
Table 2. Reaction of P(O)ꢀH compounds with alkynyl acids.
O
CuSO 5H O (0.02 mmol)
4 2
R1
R2
O
O
R1
TBHP (0.4mmol)
R
COOH + HP
P
R
R2
Scheme 2. Synthesis of 1,3ꢀdiphenylpropanꢀ1ꢀone.
In an effort to improve our understanding of the reaction profile,
NH H O, MeCN
3
2
o
3
1
2
air, 60 C, 2 hr
0
.2 mmol
0.8 mmol
1
8
a series of isotope labeling studies were conducted. When H2 O or
1
2
1
2
1
2
2
2
2
a: R = R = C H 2b: R = R = 4-MeC H 2c: R = R = 4-ClC H
6 4 6 4 6 4
1
2
1
2
1
2
D O was added to the reaction mixture under the optimal conditions,
d: R = R = 4-BrC H 2e: R = n-Bu R = C H 2f: R = OEt R = C H
6 4
2
6
4
6
4
1
2
1
g: R = R = OEt
no isotopeꢀlabeled product was detected by H NMR and ESIꢀMS
spectrum (Scheme 3, a and b). In the absence of air, the
transformation could still proceed smoothly to provide 3a in a good
yield of 78% (Scheme 3, c). It was suggested that the oxygen of the
newly formed carbonyl group of 3a mainly originated from TBHP.
When 2a was treated with 1.2 equiv of (phenylethynyl)copper under
the optimized reaction condition, only a trace amount of the desired
product was observed, illustrating that (phenylethynyl)copper might
not be a intermediate in this process (d). A radical scavenger such as
TEMPO could completely restrain the reaction, thus suggesting that
the radical processes might be involved. Based on these
experimental results and previous mechanistic studies, a plausible
mechanism is proposed as shown in Scheme 4.
Scheme 3. Experiments for the mechanistic study.
With the synthetic βꢀketophosphine oxides in hand, we next
prepared αꢀbenzyl βꢀketodiphenylphosphine oxide 4 from benzyl
bromide and 3a in good yield, which was converted into 1,3ꢀ
diphenylpropanꢀ1ꢀone 5 in 98% yield via a dephosphinoylation
process (Scheme 2).
Scheme 4. Proposed reaction mechanism.
First, TBHP generates the tertꢀbutoxy radical and hydroxyl
radical in the presence of Cu(II). Then, tertꢀbutoxy radical triggers
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Jou5CrnC0al Name
the phosphorus radical A formation from H(O)PPh . Reaction of the
Roland, M. Seifer, D. Standring, R. Storer and C. B. Dousson, J. Med.
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Kayser and Z. Wang, J. Med. Chem., 2012, 55, 3837.
2
phenylpropiolic acid with Cu(II) generates a salt of cupric
carboxylate B. Subsequently, addition of phosphorus radical A to the
αꢀposition of the triple bond of B gives intermediate C, which is
ultimately trapped by hydroxyl radical to form intermediate D. Then
D release one molecular CO to produce alkenyl copper intermediate
2
4
(a) H. A. McManus and P. J. Guiry, Chem. Rev., 2004, 104, 4151; (b) J.
Fischer, M. Schürmann, M. Mehring, U. Zachwieja and K. Jurkschat,
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E. Finally, the protonolysis of intermediate lead to the formation of
F, which isomerizes and affords the desired product.
In conclusion, we have successfully developed the first facile
method for the preparation of βꢀketophosphine oxides via
decarboxylationꢀphosphinationꢀoxidation of various alkynyl acids
with Hꢀphosphine oxides. Importantly, this transformation would
5
6
J. Clayden and S. Warren, Angew. Chem. Int. Ed., 1996, 35, 241.
T. Boesen, D. J. Fox, W. Galloway, D. S. Pedersen, C. R. Tyzack and S.
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provide a new pathway for formation of Csp ꢀP and C=O bonds
in one step. This method is highly efficient and provides a rapid
access to a broad spectrum of βꢀketophosphine oxides in good to
excellent yields. Moreover, the use of inexpensive CuSO ·5H O
8
(a) C. N. Lestas and Mary R. Truter, J. Chem. Soc. (A), 1971, 738; (b) D. J.
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2
9
1
catalyst, using readily available alkynyl acids only producing
0 (a) X. Li, G. Hu, P. Luo, G. Tang, Y. Gao, P. Xu and Y. Zhao, Adv. Synth.
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CO mean that this facile protocol will be attractive for academia
2
and industry.
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G. Tang and Y. Zhao, Org. Lett., 2013, 15, 4214.
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Some selected publications: (a) T. S. Kumar, S. Y. Zhou, B. V. Joshi, R.
Balasubramanian, T. H. Yang, B. T. Liang and K. A. Jacobson, J. Med.
Chem., 2010, 53, 2562; (b) F. R. Alexandre, A. Amador, S. Bot, C. Caillet, 18 (a) Y. Gao, J. Wu, J. Xu, P. Zhang, G. Tang and Y .Zhao, RSC Adv.,
T. Convard, J. Jakubik, C. Musiu, B. Poddesu, L. Vargiu, M. Liuzzi, A.
2014, 4, 51776; (b) Y. Gao, X. Li, J. Xu, Y. Wu, W. Chen, G. Tang and
Y. Zhao, Chem. Commun., 2015, 51,1605.
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| J. Name., 2012, 00, 1-3
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