Chiral multifunctional thiourea-phosphine catalyzed asymmetric [3 + 2] annulation of Morita-Baylis-Hillman carbonates with maleimides

Article abstract of DOI:10.3762/bjoc.8.121

We have developed a multifunctional thiourea-phosphine catalyzed asymmetric [3 + 2] annulation of Morita-Baylis-Hillman (MBH) carbonates with maleimides, which can efficiently construct functionalized cyclopentenes bearing three contiguous stereocenters in moderate to excellent yields and excellent diastereo- and enantioselectivities. A plausible mechanism has been also proposed on the basis of control experiments and previous literature.

Full text of DOI:10.3762/bjoc.8.121

Chiral multifunctional thiourea-phosphine catalyzed
asymmetric [3 + 2] annulation of
Morita–Baylis–Hillman carbonates with maleimides
Hong-Ping Deng1, De Wang2, Yin Wei1 and Min Shi*1,2,§
Letter
Open Access
Address:
Beilstein J. Org. Chem. 2012, 8, 1098–1104.
1State Key Laboratory of Organometallic Chemistry, Shanghai
Institute of Organic Chemistry, Chinese Academy of Sciences,
354 Fenglin Road, Shanghai 200032, People’s Republic of China and
2Key Laboratory for Advanced Materials and Institute of Fine
Chemicals, School of Chemistry & Molecular Engineering, East China
University of Science and Technology, and 130 MeiLong Road,
Shanghai 200237, People’s Republic of China
doi:10.3762/bjoc.8.121
Received: 24 April 2012
Accepted: 06 June 2012
Published: 16 July 2012
This article is part of the Thematic Series "Organocatalysis".
Guest Editor: B. List
Email:
Min Shi* - Mshi@mail.sioc.ac.cn
© 2012 Deng et al; licensee Beilstein-Institut.
License and terms: see end of document.
* Corresponding author
§ Fax: +86-21-64166128
Keywords:
asymmetric [3 + 2] annulation; maleimides; Morita–Baylis–Hillman
carbonates; multifunctional thiourea-phosphine; organocatalysis
Abstract
We have developed a multifunctional thiourea-phosphine catalyzed asymmetric [3 + 2] annulation of Morita–Baylis–Hillman
(MBH) carbonates with maleimides, which can efficiently construct functionalized cyclopentenes bearing three contiguous stereo-
centers in moderate to excellent yields and excellent diastereo- and enantioselectivities. A plausible mechanism has been also
proposed on the basis of control experiments and previous literature.
Introduction
Highly functionalized cyclopentene derivatives are important tion of a 1,3-dipolar synthon by using a catalytic amount of
subunits in a variety of biologically active molecules and have phosphines have been directed toward the following two paths:
attracted the broad attention of synthetic and pharmaceutical phosphines attack the middle carbon atom of allenes to produce
chemists [1,2]. Among numerous synthetic approaches, phos- the 1,3-dipolar synthon (Scheme 1, reaction 1), and phosphines
phine-mediated [3 + 2] annulation of electron-deficient olefins add to the β-position of MBH carbonate to remove carbon
is an efficient method to construct this interesting structural dioxide and tert-butanol, affording the 1,3-dipolar synthon
motif [3-10]. According to the pioneering work of Lu [11-20], (Scheme 1, reaction 2). Concerning the asymmetric [3 + 2]
all phosphine-mediated [3 + 2] annulations proceeded through annulation catalyzed by chiral phosphines, Zhang and
an important intermediate “1,3-dipolar synthon”. The forma- co-workers first reported the asymmetric [3 + 2] annulation of
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Beilstein J. Org. Chem. 2012, 8, 1098–1104.
allenoates with acrylates catalyzed by a bicyclic chiral phos- which can efficiently construct functionalized cyclopentene
phine in 1997 [21]. Moreover, Fu [22-24], Marinetti [25-28], Lu derivatives bearing three contiguous stereocenters in moderate
[29-31] and other researchers [32-36] have also developed to excellent yields along with excellent diastereo- and enantio-
asymmetric [3 + 2] annulations of allenoates to give the corres- selectivities.
ponding cyclopentene derivatives in good yields with excellent
enantioselectivities [37].
Results and Discussion
In our previous work, it was shown that chiral multifunctional
thiourea-phosphines were excellent catalysts for the asym-
metric aza-MBH reaction, asymmetric allylic substitution of
MBH adducts, and asymmetric [3 + 2] annulation of MBH
carbonates with electron-deficient olefins [52-56]. Hence, we
initially used multifunctional thiourea-phosphine (TP), which
could be easily prepared from L-phenylalanine in four steps
[57], as a catalyst to investigate the asymmetric [3 + 2] annula-
tion of N-phenylmaleimide (1a) with MBH carbonate 2a in
toluene at room temperature. We were pleased to find that the
corresponding highly functionalized cyclopentene 3a was
obtained in 54% yield with 96% ee after 24 h (Table 1, entry 1).
The examination of solvent effects revealed that toluene is the
Scheme 1: Paths to the formation of 1,3-dipolar synthons by using a
catalytic amount of phosphines.
On the other hand, some examples of phosphine-catalyzed best solvent (Table 1, entries 2–4). Increasing the ratio of 1a/2a
[3 + 2] annulation of MBH carbonates with electron-deficient from 1:1.3 to 2:1 afforded 3a in 74% yield and 96% ee, while
alkenes have been reported in the literature recently. Lu and continuously increasing the ratio of 1a/2a to 4:1 gave 3a in
co-workers first disclosed the formation of 1,3-dipoles through lower yield (Table 1, entries 5 and 6).
phosphine-catalyzed MBH carbonates under mild conditions,
which can efficiently react with various electron-deficient Having identified the optimal reaction conditions, we next set
olefins to afford the desired cyclic products in good yields along out to examine the scope and limitations of this asymmetric
with high regioselectivities, through intra- and intermolecular [3 + 2] annulation of maleimides with MBH carbonates, and the
[3 + n] annulations [38-47]. To the best of our knowledge, there results are summarized in Table 2. All of the reactions
is little in the literature regarding the asymmetric version of this proceeded smoothly under the optimal conditions, providing
reaction. In 2010, Tang and co-workers reported the first annulation products with good to excellent diastereo- and
example of asymmetric intramolecular [3 + 2] annulations of enantioselectivities. Using MBH carbonate 2a as a substrate, we
MBH carbonates tethered with another electron-deficient olefin examined its reaction with maleimides 1b–1e and found that the
in the presence of spirobiindane-based chiral phosphines, giving reactions proceeded smoothly to give the corresponding prod-
the corresponding cycloadducts in good yields along with high ucts 3b–3e in excellent yields along with excellent ee values
ee values [48]. Barbas and co-workers first reported asym- (Table 2, entries 2–5). Taking N-benzhydrylmaleimide (1d) as a
metric intermolecular [3 + 2] cycloaddition of MBH carbonates substrate, we found that substrates with an electron-with-
with methyleneindolinones to afford the corresponding spirocy- drawing substituent on the aromatic ring of MBH carbonates 2
clopentaneoxindoles in good yields and high ee values in 2011 produced 3f and 3g in good yields and excellent ee values
[49]. Moreover, Lu and co-workers have recently explored a (Table 2, entries 6 and 7), and MBH carbonate 2d gave the
series of thiourea-phosphine catalysts derived from L-threonine, corresponding annulation product 3h in 3:1 dr value with 74%
which are effective catalysts in the [3 + 2] annulation of MBH yield of major isomer and 97% ee (Table 2, entry 8). A variety
carbonates with isatylidene malononitriles to give the desired of MBH carbonates 2 having either electron-donating or -with-
products in high yields with high enantioselectivities [50]. drawing groups as substituents at the para- and meta-position of
Furthermore, our group recently also synthesized a series of the benzene ring and N-methylmaleimide (1b) underwent this
L-phenylalanine-derived multifunctional thiourea-phosphine asymmetric [3 + 2] annulation smoothly, affording the corres-
catalysts and used them in the [3 + 2] annulation of MBH ponding products 3 in moderate to excellent yields with excel-
carbonates with trifluoroethylidenemalonates to give the lent ee values upon lengthening of the reaction time (Table 2,
cycloadducts in high yields along with excellent diastereo- and entries 9–11, 13–15). Substrate 2k, incorporating a heteroaro-
enantioselectivities [51]. Herein we wish to report the develop- matic group, could also react with 1b under the same reaction
ment of a multifunctional thiourea-phosphine catalyzed asym- conditions, giving the corresponding cyclopentene 3p in 69%
metric [3 + 2] annulation of MBH carbonates with maleimides, yield with 96% ee, and substrates 2l and 2m derived from
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Beilstein J. Org. Chem. 2012, 8, 1098–1104.
Table 1: Optimization of the reaction conditions for asymmetric [3 + 2] annulation of MBH carbonates and maleimides.
entrya
1a/2a
solvent
yield (%)b
ee (%)c
1
1/1.3
1/1.3
1/1.3
1/1.3
2/1
toluene
CHCl3
THF
54
54
25
12
74
62
96
96
90
43
96
96
2
3
4
CH3CN
toluene
toluene
5d
6e
4/1
aReactions were performed with 1a (0.1 mmol) and 2a (0.13 mmol) in toluene (1.0 mL) at room temperature for 24 h. bIsolated yield of major isomer.
cDetermined by chiral HPLC. dReaction was performed with 1a (0.2 mmol) and 2a (0.1 mmol) in toluene (1.0 mL) at room temperature for 24 h.
eReaction was performed with 1a (0.4 mmol) and 2a (0.1 mmol) in toluene (1.0 mL) at room temperature for 24 h.
Table 2: Substrate scope of asymmetric [3 + 2] annulation.
entrya
R1
R2
EWG
yield (%)b
ee (%)c
1
1a, Ph
2a, 4-NO2C6H4
2a, 4-NO2C6H4
2a, 4-NO2C6H4
2a, 4-NO2C6H4
2a, 4-NO2C6H4
2b, 3-NO2C6H4
2c, 4-CNC6H4
2d, 4-BrC6H4
2d, 4-BrC6H4
2e, 4-ClC6H4
2f, 3-ClC6H4
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
CO2Et
COMe
COMe
CO2Et
3a, 74
3b, 99
3c, 86
3d, >99
3e, 91
3f, 87
3g, 84
3h, 74
3i, 79
3j, 90
3k, 81
3l, 39
3m, 74
3n, 64
3o, 55
3p, 69
3q, >99
3r, 92
–
96
98
94
98
96
94
96
97
95
96
97
73
94
96
98
96
97
98
–
2
1b, Me
3
1c, Bn
4
1d, benzhydryl
1e, 1-methylnaphthyl
1d, benzhydryl
1d, benzhydryl
1d, benzhydryl
1b, Me
5
6
7
8d,e
9e
10e
11e
12f
13f
14f
15f
16f
17
18
19f
1b, Me
1b, Me
1b, Me
2g, 2-ClC6H4
2h, C6H5
1b, Me
1b, Me
2i, 4-MeC6H4
2j, 4-MeOC6H4
2k, 2-furyl
1b, Me
1b, Me
1b, Me
2l, 4-NO2C6H4
2m, 4-NO2C6H4
2n, (CH3)2CH
1b, Me
1b, Me
aReactions were performed with 1 (0.2 mmol), 2 (0.1 mmol) in toluene (1.0 mL) at room temperature for 24 h. bIsolated yield of major isomer.
cDetermined by chiral HPLC. ddr = 3:1. eReaction was performed for 36 h. fReaction was performed for 48 h.
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Beilstein J. Org. Chem. 2012, 8, 1098–1104.
methyl vinyl ketone (MVK) afforded the corresponding annula- having a chlorine substituent at the ortho-position of the
tion products 3q and 3r in excellent yields and ee values under aromatic ring, this produced 3l in lower yield and ee value,
the standard conditions (Table 2, entries 16–18). The absolute perhaps due to the steric effect; reaction of MBH carbonate 2n
configuration of the major product 3r was determined as derived from isobutyraldehyde did not occur (entries 12 and
(1S,2R,3S) by X-ray crystal structure. Its ORTEP plot is shown 19). When we utilized dimethyl maleate or dimethyl fumarate
in Figure 1 and the corresponding CIF data are presented in the instead of maleimides, it was found that the reactions could not
Supporting Information File 2 [58]. As for MBH carbonate 2g, be performed either.
As aforementioned, increasing the ratio of 1a/2a from 1:1.3 to
2:1 obtained the highest yield. In order to explain this finding,
three control experiments were performed in CDCl3 and the
results were studied by using 31P NMR spectroscopy (Figure 2,
also see Figure SI-1 in the Supporting Information File 1). The
NMR studies revealed that catalyst TP seems to react with
N-phenylmaleimide (1a) to form a new species (Figure 2,
spectra b), which costs some maleimide 1a. Thus, the excess 1a
has to be added in order to make the reaction complete. This is
why increasing the ratio of 1a/2a raised the yield of product 3a
(Table 1, entry 5). On the other hand, if too much maleimide 1a
is used in this reaction, it will waste some of the catalyst TP,
leading to a decrease in the yield of product 3a (Table 1, entry
6). The allylic phosphorus ylide species can be recognized in
spectra c from the combination of 2d and TP (1:1) (Figure 2,
also see Figure SI-1 in the Supporting Information File 1) [59].
As reported before [15,51], TP attacks MBH carbonate to afford
allylic phosphorus ylide I, which attacked the maleimide to
produce intermediate II (Scheme 2). Since there is a steric
Figure 1: The ORTEP plot of compound 3r.
effect between the phenyl group and the benzyl group in inter-
Figure 2: 31P NMR spectra (161.9 MHz, CDCl3) of control experiments.
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Beilstein J. Org. Chem. 2012, 8, 1098–1104.
Scheme 2: Proposed transition models.
mediate II-B, allylic phosphorus ylide I using its Si-face to
attack maleimide is favored (intermediate II-A). Undergoing
Michael addition and elimination of catalyst along with the
double-bond formation, intermediate I affords the corres-
ponding highly functionalized cyclopentene product and
completes the catalytic cycle. The control experiments demon-
strated that catalyst TP can react with maleimide, affording an
unidentified complex and partially wasting maleimide and cata-
lyst (spectra d in Figure 2). Hypothetically, the activity of the in
situ generated allylic phosphorous ylide I is crucial for the yield
of product. If the activity of phosphorous ylide is not high
enough, it may deprotonate the NH proton in TP, which will
cause the catalyst to lose activity (See Table 2, entries 12–16).
In addition, if the phosphorous ylide is not active enough to
react with maleimide, maleimide can directly react with the
Scheme 3: Dihydroxylation of 3c.
catalyst to form the other unidentified species as indicated in the Conclusion
31P NMR spectroscopy (spectra b in Figure 2), which may In conclusion, we have developed a novel multifunctional
retard the desired catalytic cycle.
thiourea-phosphine catalyzed asymmetric [3 + 2] annulation of
MBH carbonates with maleimides, which can efficiently
To illustrate the synthetic utility of these products 3 obtained construct functionalized cyclopentenes bearing three contiguous
from the above asymmetric [3 + 2] annulation, the further trans- stereocenters in moderate to excellent yields and excellent
formation of 3c was performed in the presence of RuCl3 and diastereo- and enantioselectivities, and the product can be effi-
NaIO4 under mild conditions (Scheme 3) [22,60]. Upon dihy- ciently transformed into a cyclopentane containing five stereo-
droxylation of 3c, the corresponding product 4c containing five centers under mild conditions, which was difficult to construct
stereocenters was produced in 69% yield and good diastereo- by other synthetic methodologies. Current efforts are in
selectivity on the basis of NMR spectroscopic data (dr = 20:1, progress to apply this new methodology to synthesize bio-
see Supporting Information File 1).
logically active products.
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Beilstein J. Org. Chem. 2012, 8, 1098–1104.
Experimental
General procedure for asymmetric [3 + 2]
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temperature for 24–48 h. Then the solvent was removed under
reduced pressure, and the residue was chromatographed on
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We thank the Shanghai Municipal Committee of Science and
Technology (11JC1402600), National Basic Research Program
of China (973)-2010CB833302, and the National Natural
Science Foundation of China for financial support (21072206,
20472096, 20872162, 20672127, 21121062 and 20732008) and
Mr. Jie Sun for performing X-ray diffraction.
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