Phosphine-catalyzed regiodivergent annulations of γ-substituted allenoates with conjugated dienes

Article abstract of DOI:10.1039/c9cc05207k

A phosphine catalyzed regiodivergent annulation of γ-substituted allenoates with conjugated dienes is reported, and highly functionalized cyclohexenes or cyclopentenes were obtained in high yields and regioselectivities. This transformation takes advantag

Full text of DOI:10.1039/c9cc05207k

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S. J. Connon, M. O. Senge et al.
Conformational control of nonplanar free base porphyrins:
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Phosphine-Catalyzed Regiodivergent Annulations of γ-Substituted
Allenoates with Conjugated Dienes
Zhenjie Gan,a Yanchuan Gong,a Yunpeng Chu,a Er-Qing Li,*,a You, Huang*,b and Zheng Duan*,a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
A phosphine catalyzed regiodivergent annulations of γ-substituted most of these reactions occurred at α, β, γ- or β′-positions of 2,
allenoates with conjugated dienes is reported, and the highly 3-butadienoates and α-substituted allenoates to form various
functionalized cyclohexenes or cyclopentenes were obtained in (1 + 4),8 (2 + 2 + 2),9 (2 + 3),10 (3 + 2),11 (4 + 1)12 and (4 + 2)13
high yields and regioselectivities. This transformation takes cyclized products. In 2009, He’s group and Huang’s groups
advantage of mild conditions, wide substrate scope and significant reported the first phosphine-catalyzed annulation reactions at
functional group tolerance. The high regioselectivity can be less reactive δ site of γ-methyl allenoates, respectively.14 Series
achieved by tuning the nucleophilicity of the phosphine catalyst.
of phosphine-catalyzed domino reactions of γ-benzyl
allenoates15 and γ-acetoxymethyl substituted allenoates16
were developed. The presence of a phenyl or acetoxy moiety
improves the reactivity of δ carbon. However, Lu’s (3 + 2)
reaction has remained dormant due to the higher
electrophilicity of allenoate's α site.17 It is still a challenge for
developing new methods involving the δ site of γ-methyl
allenoate in a highly controllable manner.18
Functionalized cyclohexenes are valuable intermediates in
organic synthesis, and they are also widely found in natural
products and pharmaceuticals (Figure 1).1-4 Thus, the
development of efficient strategies for the construction of
these motifs is highly desirable in the field of synthetic
chemistry and medicinal chemistry.5
HO
OH
(1) Traditional reaction style
H
H
H
H
electrophilic site

O
H
electrophilic site
O

H
NH
H

Ar
CO2R
O
O

O
OH
(2) Radosevich's P(NMe2)3-mediated umpolung tandem reaction
Ph

B: Levonorgestrel
CO2Me
A: Altercrasin A
O

Ph

P(NMe2)3 (1.05 eq)

Ph
CO2Me

MeO
OH

-78 C-rt
MeO2C
O
Ph
CO2Me
Cl
H
O
OH
nucleophilic site
H
H
NMe
OMe
P(NMe2)3

CO2Me
P(NMe2)3
CO2Me
O
O
O
N
OH
H
O
O
Ph
Ph

O
OMe
nucleophilic site
C: (+)-Fusarisetin A
D: Acutumine
(3) Our work: phosphine-catalyzed regiodivergent annulations
 -electron-withdrawing group
Figure 1. Selected natural products and bioactive molecules
Since Lu’s (3 + 2) was reported in 1995,6 phosphine-catalyzed
annulation of allenoates has become one of the most efficient
methods to construct diverse cyclic compounds.7 However,
R4O2C
CO2R4
CO2R4
P(4-FC6H4)3
R3
R2O2C

R3


2


PBu3
CO2R
CO2R2
+
Ar1
CO2R
1
Ar1
CO2R1
R3


Ar1

CO2R1
R3
PBu3
CO2R2
PPh3 R3
R4O2C
CO2R2
CO2R1
nucleophilic site
R4O2C
Ph
a. College of Chemistry and Molecular Engineering, International Phosphorus
Laboratory, International Joint Research Laboratory for Functional
Organophosphorus Materials of Henan Province, Zhengzhou University,
Zhengzhou 450001, P. R. China. E-mail: lierqing@zzu.edu.cn.
duanzheng@zzu.edu.cn.


CO2R1
Ph
nucleophilic site
Scheme 1. Phosphine-catalyzed annulations of allenoates
b. State Key Laboratory and Institute of Elemento-Organic Chemistry, College of
Chemistry, Nankai University, Tianjin 300071 (China). E-mail:
hyou@nankai.edu.cn.
Nucleophilic addition of β, γ-unsaturated α-ketoester
usually occurs at more electrophilic α or γ site (Scheme 1,
(1)).19 In 2013, Radosevich reported a P(NMe2)3-mediated
Electronic Supplementary Information (ESI) available: CCDC 1911637. For ESI and
crystallographic
data
in
CIF
or
other
electronic
format
See
DOI: 10.1039/x0xx00000x
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nucleophilic/electrophilic umpolung of the γ-site of β, γ-
unsaturated α-ketoester (Scheme 1, (2)).20 Inspired by this prepared with (4-FC6H4)3P catalyst, the results are summarized
result, we developed and utilized a molecular engineering in Scheme 2. The reactions proceeded smoothly with various
approach for a catalytic γ-umpolung. Herein, we report a conjugated dienes 1 and γ-substituted allenoates (Scheme 2,
phosphine-catalyzed regiodivergent annulation of γ- 3a-3y). The aryl moieties bearing functional groups such as
substituted allenoates with a new diene moiety (Scheme 1, (3)). para-F (3q, 3r), para-Br (3s, 3t, 3w), and meta-Me (3u, 3x)
It should be noted that the selectivity between (4 + 2) (δ- were all well-converted into the desired products in 73−88%
Journal Name
A wide range of cyclohexenes 3 have been selectively
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DOI: 10.1039/C9CC05207K
addition) and (3 + 2) (α-addition) annulations can be tuned by yields. The structures of
3 were characterized by a
the Lewis basicity of the phosphine catalysts. combination of NMR, HRMS spectra, and single crystal X-ray
Initially, we investigated the reaction of conjugated diene analysis (3w) (see Supporting Information).
1a and benzyl γ-methyl allenoates 2a as model substrates
under the influence of a variety of phosphines and solvents, as
shown in Table 1. Both PPh3 (Table 1, entries 1-4) and (4-
R4O2C
R2O2C
R3
R3
(4-FC6H4)3P
(20 mol %)
CO2R2
CO2R1
+
CO2R1
CO2R4
Ar
CHCl3, rt
8h
Ar
MeOC6H4)3P (entry 7) were less effective for the model
reaction, giving (4 + 2) and (3 + 2) annulations products in low
selectivity. A series of other solvents, including CH2Cl2 (entry 2),
toluene (entry 3), and THF (entry 4), were also examined, but
none of these solvents performed better than CHCl3 (entry 1).
In contrast, when the reaction was carried out using Ph2PMe
(entry 5) or (4-FC6H4)3P (entry 8), (3 + 2) product 4a (entry 5)
and (4 + 2) product 3a (entry 8) were obtained, respectively, in
high yields and good selectivity. The selectivity for 4a could be
improved further by using PBu3 as catalyst (entry 6). In the
case of (4-FC6H4)3P catalyzed (4 + 2) cyclization, increasing the
reaction temperature (entry 5) or the loading of the catalyst
(entries 11, 12) resulted in higher conversions at the cost of
selectivity. Running the reaction at 0 °C led to almost no
formation of the desired product (entry 9). Therefore,
complementary conditions (entries 6, 8) were established to
access both regioisomers.
1
2
3
EtO2C
BnO2C
MeO2C
R3
CO2R2
CO2R1
CO2Et
CO2Me
3 = H, 80% yield
3 = Me, 85% yield
3 = Ph, 77% yield
CO2R2
CO2R1
Ph
Ph
Ph
3j R1 = Et, R2 = Et, 86% yield
3k R1 = Et, R2 = Bn, 80% yield
3l R1 = Me, R2 = Bn, 72% yield
3m
3d
R
1 = Me, R2 = Et, 80% yield
1 = Et, R2 = Bn, 85% yield
R1 = iPr, R2 = Bn, 77% yield
3a
3b
3c
R
3e
3f
R
R
R
1 = iPr, R2 = Et, 84% yield
1
R
1 = iPr, R2 = Bn, 80% yield
3g
3h
3i
R
R
R1 = iPr, R2 = Et, 85% yield
=
nBu, R2 = Bn, 79% yield
3n
3o
3p
R1
=
nBu, R2 = Bn, 69% yield
R1 = Bn, R2 = Bn, 90% yield
R1 = Bn, R2 = Bn, 56% yield
R4O2C
MeO2C
EtO2C
CO2Bn
CO2Et
CO2Et
CO2R1
CO2Et
CO2Me
Ar
Ar
Ar
Ar = 4-FC6H4, R4 = Et, 79% yield
Ar = 4-FC6H4, R4 = Me, 88% yield
Ar = 4-BrC6H4, R4 = Et, 76% yield
Ar = 4-BrC6H4, R4 = Me, 81% yield
3q
3r
3s
3t
Ar = 3-CH3C6H4, R1 = Me, 86% yield
Ar = 4-CH3C6H4, R1 = Me, 78% yield
Ar = 4-BrC6H4, R1 = Et, 76% yield
3u
3x
3y
Ar = 3-CH3C6H4, 73% yield
Ar = 4-CH3C6H4, 88% yield
3v
3w
a
Unless otherwise specified, all reactions were carried out
using 1a (0.3 mmol) and 2a (0.45 mmol) at room temperature.
b Isolated yield.
Scheme 2. Substrate scope for the synthesis of products 3.
The representative results of the PBu3-catalyzed (3 + 2)
annulations are listed in Scheme 3. In all cases, the desired
Table 1. Optimization of the reaction conditions.a
CO2Bn
BnO2C
EtO2C
PR3 (x mol %)
Solvent
CO2Et
CO2Me
CO2Et
+
+
Ph
Ph
CO2Me
CO2Bn
Ph
CO2Me
1a
2a
3a
4a
products were isolated in high yields and good selectivities.
entry
catalyst
solvent time
(h)
yield (%)b
CO2R3
R2O2C
3a
43
27
4a
35
13
PBu3
(20 mol %)
CO2R2
CO2R1
1
2
3
4
5
6
7
8
PPh3 (20)
PPh3 (20)
PPh3 (20)
PPh3 (20)
Ph2PMe (20)
PBu3 (20)
CHCl3
CH2Cl2
Toluene
THF
5
5
5
+
CO2R1
CO2Bn
CO2R3
Ar
Ar
CHCl3, rt
0.2 h
4
1
2
trace trace
trace trace
CO2Et
CO2Et
5
CO2Et
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
CHCl3
4
0.2
8
8
20
5
5
-
72
90
CO2Bn
CO2iPr
CO2Et
Ph
CO2iPr
Ph
Ph
CO2Me
(4-MeOC6H4)3P (20)
(4-FC6H4)3P (20)
(4-FC6H4)3P (20)
(4-FC6H4)3P (20)
(4-FC6H4)3P (50)
(4-FC6H4)3P (100)
19
80
7
78
61
66
10
2
trace
14
26
4a
4b
87% yield
CO2Me
82% yield
CO2Bn
4c
4f
73% yield
CO2Et
9c
10d
11
CO2Et
CO2Me
CO2Et
CO2Bn
CO2Bn
Ph
CO2Me
5
3
76% yield
CO2Me
4e
84% yield
CO2Et
4d
90% yield
CO2Et
12
25
a
Unless otherwise specified, all reactions were carried out
CO2Et
CO2Et
CO2Bn
CO2Me
CO2Et
CO2Me
using 1a (0.3 mmol) and 2a (0.45 mmol) at room temperature.
b
c
d
Isolated yield. Reaction temperature: 0 °C. Reaction
Br
4i
82% yield
4h
89% yield
4g
88% yield
temperature: 50 °C.
a
Unless otherwise specified, all reactions were carried out
Subsequently, the scope of the substrates has been
investigated under optimized conditions to evaluate the
control of selectivity between 3 and 4.
using 1a (0.3 mmol) and 2a (0.45 mmol) at room temperature.
b Isolated yield.
Scheme 3. Substrate scope for the synthesis of products 4.
2 | J. Name., 2012, 00, 1-3
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On the basis of these results, 21 a plausible mechanism was financial support of this research. The authors thank Dr.
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DOI: 10.1039/C9CC05207K
proposed (Scheme 4). The reaction was initiated by the Bingxin Yuan (ZZU) for helpful discussions and comments.
nucleophilic attack of the phosphine catalyst on the allenoates
2 to form intermediates A or B. We hypothesized that the
phosphine might impose different inducing effects to achieve
Conflicts of interest
site selectivity, which depended on the Lewis basicity. The
electron-rich PBu3 is more prone to A, while B is preferred by
the electron-deficient (4-FC6H4)3P. Intermediates A and B
undergo addition reaction with 1 to produce intermediate C
and E, respectively. The following annulation reaction and
proton-transfer process lead to the formation of 3 or 4 with
the regeneration of the catalyst.
The authors declare no competing financial interests.
Notes and references
1
2
3
P. M. Dewick, Medicinal Natural Products; Wiley: Hoboken,
NJ, 2009; pp 7−38.
W. F. J., Karstens, P. G. M. Conti, C. M. Timmers, R. Plate, C. J.
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(a) C. Liu, Z. Zeng, R. Chen, X. Jiang, Y. Wang, Y. Zhang, Org.
Lett. 2016, 18, 624; (b) J. Deng, B. Zhu, Z. Lu, H. Yu, A. Li, J.
Am. Chem. Soc. 2012, 134, 920.
CO2Me
2
PBu3
P(4-FC6H4
)
3
path B
path A
4
5
M. Tomita, Y. Okamoto, T. Kikuchi, K. Osaki, M. Nishikawa, K.
Kamiya, Y. Sasaki, K. Matoba, K. Goto, Chem. Pharm. Bull.
1971, 19, 770.
P(4-FC6H4
)
3
PBu3
MeO2
C
CO2Me
A
B
Selected examples, see: (a) J. Wu, Y. Tang, W. Wei, Y. Wu, Y.
Li, J. Zhang, Y. Zheng, S. Xu, Angew. Chem. Int. Ed. 2018, 57,
6284; (b) Y. Qiu, B. Yang, C. Zhu, J.-E. Bӓckvall, Chem. Sci.
2017, 8, 616; (c) J. Min, G. Xu, J. Sun, J. Org. Chem. 2017, 82,
5492. (d) G. Zhang, W. Xu, J. Liu, D. K. Das, S. Yang, S.
Perveen, H. Zhang, X. Li, X. Fang, Chem. Commun. 2017, 53,
13336.
MeO2
C
Ph
CO2Me
MeO2
C
1
Ph
CO2Me
1
P(4-FC6H4
)
3
MeO2
C
CO2Me
PBu3
CO2Me
Ph
CO2Me
E
6
7
C. Zhang, X. Lu, J. Org. Chem. 1995, 60, 2906.
Ph
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MeO2
C
CO2Me
P(4-FC6H4
)
3
C
MeO2
C
CO2Me
Ph
CO2Me
F
PBu3
CO2Me
-P(4-FC6H4
)
3
1,2-H shift
Ph
MeO2
C
CO2Me
D
MeO2
C
CO2Me
CO2Me
1,2-H shift
-PBu3
Ph
3
CO2Me
CO2Me
Ph
8
9
X. Meng, Y. Huang, R. Chen, Org. Lett. 2009, 11, 137.
X.-F. Zhu, C. E. Henry, J. Wang, T. Dudding, O. Kwon, Org.
Lett. 2005, 7, 1387.
MeO2
C
4
Scheme 4. Proposed mechanism
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Conclusions
In summary, we have designed and developed a phosphine
catalyzed site selective annulations of γ-substituted allenoates
with conjugated dienes. The impact of catalyst and substrate
on the final product suggest that the activity and selectivity
could be tuned through appropriate molecular engineering.
The method has also enabled the selective preparation of
cyclohexenes and cyclopentenes in good yields. Further
studies on an asymmetric version of these annulations and
applications for the synthesis of biologically active molecules
are underway.
We are grateful to the National Natural Science Foundation
of China (No. 21702189, 21672193, 21272218), China
Postdoctoral Science Foundation (No. 2017M610458,
2018T110737), Postdoctoral Research Grant in Henan Province
(No. 001701006) and Zhengzhou University of China for
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
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