Organocatalytic domino reaction of electron-deficient 2,4-dienes with 2-halo-1,3-dicarbonyl compounds: A highly regio-and stereoselective approach to functionalized five-membered carbocycles

Article abstract of DOI:10.1002/adsc.201300788

An unexpected domino reaction of electron- deficient 2,4-dienes with 2-halo-1,3-dicarbonyl compounds, employing the readily available N-(4- trifluoromethylbenzyl)cinchonium bromide as the phase-transfer catalyst, provides an access to functionalized cyclopentenes and fulvene derivatives with excellent regio-, chemo- and stereoselectivities. A plausible mechanism for this unprecedented domino reaction is given.

Full text of DOI:10.1002/adsc.201300788

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DOI: 10.1002/adsc.201300788
Organocatalytic Domino Reaction of Electron-Deficient 2,4-
Dienes with 2-Halo-1,3-Dicarbonyl Compounds: A Highly
Regio- and Stereoselective Approach to Functionalized
Five-Membered Carbocycles
Jian-Wu Xie,a,* Mei-Lan Xu,a Ren-Zun Zhang,a Jin-Yun Pan,a
and Wei-Dong Zhua,*
a
Key Laboratory of the Ministry of Education for Advanced Catalysis Materials, Institute of Physical Chemistry and
Department of Chemistry and Life Sciences, Zhejiang Normal University, 321004 Jinhua, Peopleꢀs Republic of China
Fax : (+86)-579-8228-2610; phone: (+86)-579-8228-2610; e-mail: xiejw@zjnu.cn or weidongzhu@zjnu.cn
Received: August 30, 2013; Revised: November 6, 2013; Published online: February 2, 2014
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201300788.
Abstract: An unexpected domino reaction of elec-
tron-deficient 2,4-dienes with 2-halo-1,3-dicarbonyl
compounds, employing the readily available N-(4-
trifluoromethylbenzyl)cinchonium bromide as the
phase-transfer catalyst, provides an access to func-
tionalized cyclopentenes and fulvene derivatives
with excellent regio-, chemo- and stereoselectivities.
A plausible mechanism for this unprecedented
domino reaction is given.
rings. Domino reactions have been served as a power-
ful tool for the rapid and efficient assembly of com-
plex structures from simple starting materials with
minimized waste production.[14]
Herein, we report an efficient, mild, and convenient
method for the preparation of fully substituted five-
membered carbocycles via a novel domino reaction of
electron-deficient 2,4-dienes with 2-halo-1,3-dicarbon-
yl compounds, by employing the readily available, low
cost N-(4-trifluoromethylbenzyl)cinchonium bromide
as phase-transfer catalyst under mild reaction condi-
tions.
Recently, we have demonstrated that 1,3-dicarbonyl
compounds and 2-halo-1,3-dicarbonyl compounds are
readily available and attractive precursors for the con-
struction of O-heterocycles via domino reactions.[15]
In addition, a,a-dicyanoalkenes which are electron-
Keywords: cyclopentenes; 1,3-dicarbonyl com-
pounds; domino reactions; fulvenes; organocataly-
sis
The five-membered carbocycles are constituents of deficient alkenes and inherently behave as electro-
a diverse assortment of natural products and biologi- philes, have been employed as multifunctional syn-
cally active agents,[1–3] and they are also valuable as thons in the construction of complex molecules.[16,17]
synthetic building blocks to access drugs and agri- We envisioned that multifunctionalized cyclopentenes
chemical targets. Consequently new and efficient could be obtained by the domino reaction of 2-halo-
methods for the preparation of this important five- 1,3-dicarbonyl compounds with electron-deficient 2,4-
membered carbocyclic ring system are of contempo- dienes which were prepared from chalcone and malo-
rary interest. Despite the great success achieved for nonitrile, as outlined in Scheme 1.
the formation of five-membered carbocycles, such as
To explore the domino reaction, electron-deficient
intramolecular Michael-type conjugate addition,[4,5] re- 2,4-diene (1a) and diethyl a-bromomalonate (2a)
arrangement,[6,7] intramolecular Morita–Baylis–Hill- were first chosen for the initial screening. The model
man reaction,[8] intramolecular ring-closing metathesis reaction was carried out in the presence of K2CO3 in
reaction,[9] intramolecular Wittig reaction,[10–12] and dichloromethane (DCM) at room temperature for
Nazarov cyclizations,[13] the construction of highly 24 h (entry 1, Table 1). Surprisingly, the result was not
functionalized five-membered carbocycles remains the one we expected but the unexpected multifunc-
challenging. Reactions that maximize molecular com- tionalized cyclopentene (4a) with three conjugated
plexity with a minimum of operations and generate double bonds was obtained while the stereoselectivity
À
new C C bonds are not only noteworthy but are also is very poor (Z/E=50:50, entry 1, Table 1). Then
fundamental for the construction of five-membered a series of organic solvents and bases was screened
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Jian-Wu Xie et al.
Scheme 1. Potential strategies for the cyclization of 2-halo-1,3-dicarbonyl compounds with electron-deficient 2-(1,3-diphenyl-
ACHTUNGTRENNUNGallylidene)malononitrile.
for this unexpected domino reaction. As shown in delight, the stereoselectivity was dramatically in-
Table 1, only cyclopentene (4a) was obtained under creased in the presence of 100 mol% K2CO3 and
different reaction conditions. In the presence of 20 mol% N-benzylcinchonium bromide I as chiral
100 mol% of a base, such as K2CO3 or DBU, 1a was phase-transfer catalyst (E/Z=71:29, entry 4, Table 1).
completely consumed within 24 h at room tempera- When the base loadings were reduced to 50 mol%,
ture providing 4a in high yield, while the stereoselec- the domino reaction provided 4a in 79% yield with
tivity is very poor (entries 1 and 2, Table 1). To our
a
high E-stereoselectivity (E/Z=93:7, entry 5,
Table 1). Other chiral phase-transfer catalysts derived
from Cinchona alkaloids were then evaluated
(Figure 1). We found that the introduction of an N-
2’,3’,4’-trifluorobenzyl moiety such as in II instead of
a N-benzyl group improves the catalytic activity and
a good yield was obtained, while the stereoselectivity
was decreased (entry 7, Table 1). The stereoselectivity
was dramatically decreased when the bulkier b-naph-
thyl moiety was introduced to the chiral phase-trans-
fer catalyst, such as III (entry 8, Table 1). N-(4-Tri-
fluoromethylbenzyl)cinchonium bromide IV exhibited
an excellent catalytic activity in the domino reaction
and both excellent stereoselectivity and good yield
were obtained (E/Z=96:4, 76% yield, entry 9,
Table 1). But the pseudoenantiomeric catalyst of V,
N-(4-trifluoromethylbenzyl)cinchonidinium bromide,
could give 4a in poor stereoselectivity (E/Z=57:43,
entry 10, Table 1) under the same reaction conditions.
Moreover, the hydroxy group also had an influence
on the yield and stereoselectivity, as shown in
entry 11. Chiral phase-transfer catalyst VI, which in-
cludes the O-allyl moiety, was found to be a less ef-
fective catalyst in the reaction and the stereoselectiv-
ity was decreased with poor yield (E/Z=91:9, 40%
yield, entry 11, Table 1). Subsequently, we investigat-
ed the effects of commonly used solvents and reaction
temperature. Non-polar solvents, such as toluene and
CH2Cl2, significantly increased the E-stereoselectivity
(entries 9 and 12, Table 1) while the polar solvents,
such as acetonitrile and acetone, decreased the E-ste-
reoselectivity (entries 13 and 14, Table 1). In the hope
of enhancing the E-stereoselectivity, the reaction was
carried out in DCM at 158C using IV as the catalyst,
the stereoselectivity was dramatically increased and
only the E-isomer was obtained (entry 15, Table 1).
Hence, running the domino reaction in DCM at 158C
with 20 mol% IV as the chiral phase-transfer catalyst
and 50 mol% K2CO3 appeared to be the optimal reac-
tion conditions.
Table 1. Optimization of the reaction conditions.[a]
Entry
Solvent
Catalyst/Base
E/Z[b]
Yield [%][c]
1
2
3
4
DCM
DCM
DCM
DCM
DCM
DCM
DCM
DCM
DCM
DCM
DCM
toluene
acetone
CH3CN
DCM
DCM
–/K2CO3
–/DBU
50:50
50:50
50:50
71:29
93:7
98
98
43
96
79
43
81
62
76
34
40
60
77
70
74
–
–/DABCO
I/K2CO3
I/K2CO3
I/K2CO3
II/K2CO3
III/K2CO3
IV/K2CO3
V/K2CO3
VI/K2CO3
IV/K2CO3
IV/K2CO3
IV/K2CO3
IV/K2CO3
IV
5[d]
6[e]
7[d]
8[d]
9[d]
10[d]
11[d]
12[d]
13[d]
14[d]
15[d,f]
16
91:9
83:17
69:31
96:4
57:43
91:9
96:4
87:13
77:23
only E
–
[a]
Unless otherwise noted, reactions performed with
0.1 mmol of 1a, 0.12 mmol of 2a, 100 mol% base in sol-
vent (1.0 mL) at room temperature for 24 h.
Determined by H NMR.
Isolated yields.
50 mol% K2CO3 were added.
20 mol% K2CO3 were added.
At 158C, 48 h.
[b]
[c]
[d]
[e]
[f]
1
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Organocatalytic Domino Reaction of Electron-Deficient 2,4-Dienes
Figure 1. Chiral phase-transfer catalysts.
With the optimized reaction conditions in hand, we ditionally made by the condensation of cyclopenta-
explored the scope of the unexpected domino reac- dienes with a carbonyl compound, and this method is
tion by using various electron-deficient 2,4-dienes typically limited by the availability of the cyclopenta-
1 and the corresponding results are summarized in
Table 2. Several points are noteworthy: (i) The scope
of this unexpected domino reaction proved to be
Table 2. Optimization of the reaction conditions.[a]
quite broad with respect to 2,4-dienes 1 and the novel
transformations were highly stereoselective, simulta-
neously giving the highly substituted cyclopentenes
with up to three conjugated double bonds. Interest-
ingly, only E-isomers were detected for all the reac-
tions. (ii) It appeared that substituentsꢀ electronics
had a minimal impact on the efficiency of the domino
reaction. Good yields were obtained in the domino
reaction of 2a with electron-withdrawing substituent
on the aryl ring of 2,4-dienes 1 (entries 2–8, 11–13,
Table 2). On the contrary, an electron-donating sub-
stituent on the aryl ring of 2,4-dienes 1 tended to de-
crease the yields (entries 9, 10, 14, 15, Table 2). (iii)
The aromatic ring of 2,4-dienes 1 with electron-with-
drawing substituents on the ortho, meta or para posi-
tions afford cyclopentenes with slightly inferior yields
(entries 5–7, 11–13). (iv) On replacement of diethyl a-
bromomalonate 2a by other 2-halo-1,3-dicarbonyl
compounds, such as diethyl a-chloromalonate 2b, only
the E-isomer with good yield was also obtained.
Entry Ar1
Ar2
1
2
4
Yield
[%][b]
1
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
1a 2a 4a 74
1b 2a 4b 80
1c
1d 2a 4d 73
1e 2a 4e 78
2
3
4
5
6
7
p-FC6H4
p-BrC6H4
o-BrC6H4
p-ClC6H4
o-ClC6H4
m-ClC6H4
2a 4c
77
1f
2a 4f
77
1g 2a 4g 73
1h 2a 4h 75
8
2,5-(Cl)2C6H3 Ph
Interestingly, under similar conditions to the afore-
mentioned ones, for ethyl 2-bromoacetoacetate 2c
which containa a CH3CO group, unexpected products
– fulvene derivatives 5 with good yields – were isolat-
ed (Table 3). Apparently the unexpected domino re-
action took place to afford products 4, and then a fur-
ther retro-Claisen reaction occurred to generate the
observed fulvene derivatives. Fulvenes and their de-
rivatives have attracted much attention due to their
unique properties in the fields of materials science, or-
ganometallics and medicinal chemistry since their dis-
covery by Thiele in 1900.[18,19] However, they are tra-
9
p-MeC6H4
p-MeOC6H4
Ph
Ph
1i
1j
2a 4i
2a 4j
67
60
10
11
12
13
14
15
16
Ph
Ph
Ph
Ph
Ph
Ph
p-ClC6H4
o-ClC6H4
m-ClC6H4
p-MeC6H4
p-MeOC6H4 1o 2a 4o 62
Ph 1a 2b 4a 71
1k 2a 4k 77
1l 2a 4l 72
1m 2a 4m 76
1n 2a 4n 68
[a]
Unless otherwise noted, reactions performed with
0.1 mmol of 1, 0.12 mmol of 2, 50 mol% base and
20 mol% IV in DCM (1.0 mL) at 158C for 48 h.
Isolated yields.
[b]
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Jian-Wu Xie et al.
Table 3. Synthesis of the substituted fulvene derivatives 5.[a]
the E-isomers were detected for all the reactions. It
appeared that substituentsꢀ electronics had a minimal
impact on efficiencies of the domino reaction. Elec-
tron-deficient 2,4-dienes 1 with substituents on the
meta or ortho positions as well as electron-deficient
2,4-dienes 1 with electron-denoting substituents on
the para positions afford fulvene derivatives 5 with
slightly inferior yields (entries 6, 7, 9, 11, 12 and 15,
Table 3). The replacement of ethyl 2-bromoacetoace-
tate 2c by 3-chloropentane-2,4-dione 2d, fulvene de-
rivative 5p was also obtained in moderate yield
(entry 16, Table 3).
The regio- and stereochemistry of the substituted
cyclopentenes and fulvene derivatives were confirmed
by the X-ray diffraction analysis of 4f and 5h
(Figure 2).
On the basis of the experimental observations,
a possible mechanism was proposed to explain the un-
expected one-pot tandem reaction. As shown in
Scheme 2, the Michael reaction proceeded smoothly
between electron-deficient 2,4-dienes and 2-halo-1,3-
dicarbonyl compounds under the base conditions, fol-
Entry Ar1
Ar2
1
2
5
Yield[b]
[%]
1
2
3
4
5
6
7
8
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
1a 2c 5a 66
1b 2c 5b 87
1c 2c 5c 76
1d 2c 5d 77
1e 2c 5e 70
1f 2c 5f 61
1g 2c 5g 62
1h 2c 5h 73
p-FC6H4
p-BrC6H4
o-BrC6H4
p-ClC6H4
o-ClC6H4
m-ClC6H4
2,5-(Cl)2C6H3 Ph
9
p-MeC6H4
Ph
1i
1k 2c 5j
1l
1m 2c 5l
1p 2c 5m 87
1n 2c 5n 77
2c 5i
64
83
10
11
12
13
14
15
16
Ph
Ph
Ph
Ph
Ph
Ph
Ph
p-ClC6H4
o-ClC6H4
m-ClC6H4
p-BrC6H4
p-MeC6H4
p-MeOC6H4 1o 2c 5o 66
Ph 1a 2d 5p 62
2c 5k 62
67
[a]
Unless otherwise noted, reactions performed with
0.1 mmol of 1, 0.12 mmol of 2, 50 mol% base and
20 mol% IV in DCM (1.0 mL) at 158C for 12 h.
Isolated yields.
[b]
dienes prepared from multistep procedures, in which
regioselectivity and functional group tolerance are
often major difficulties. As such, we turned our atten-
tion to the synthesis of fulvene derivatives 5 from
electron-deficient 2,4-dienes 1. To assess the impact
of the structural and functional motifs on the reaction,
we tested a range of electron-deficient 2,4-dienes 1,
and the corresponding results are summarized in
Table 3. The reaction scope proved to be broad with
respect to electron-deficient 2,4-dienes 1. These novel
transformations were highly stereoselective and only Scheme 2. Plausible reaction mechanism.
Figure 2. X-ray diffraction analysis of 4f and 5h.
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Organocatalytic Domino Reaction of Electron-Deficient 2,4-Dienes
5282 [RACHTNUTRGNE(NUG int)=0.0766], refinement by full-matrix least-
lowed by alkylation to afford intermediate cyclopro-
pane derivatives I. Because the g-C H of electron-de-
squares on F2, data/restraints/parameters 5282/0/294, good-
À
ness-of-fit on F2 =0.986, final R indices [I>2 sigma(I)] R1=
ficient dicyanoalkenes was easily deprotonated under
base conditions,[16,17] carbanion II was formed under
base conditions, and subsequent ring-opening helped
by a lone pair of II afforded intermediate III. Then,
the intramolecular nucleophilic addition of the carb-
anion group of III on the cyano moiety took place to
form products 4. A further retro-Claisen condensation
occurred to generate the observed fulvene derivatives
5 when the group R is methyl.
0.0550, wR2=0.1317,
R indices (all data) R1=0.1464,
wR2=0.1692, largest diff. peak and hole 0.247 and
À0.201 ꢂÀ3. CCDC 954456 contains the supplementary crys-
tallographic data for the structure of 4f. These data can be
obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/
cif or on application to CCDC, 12 Union Road, Cambridge
CB2 1EZ, U.K. [fax: (internat.) (+44)-1223/336-033;
e-mail: deposit@ccdc.cam.ac.uk].
In summary, we have successfully demonstrated
a novel domino Michael/alkylation/vinylcyclopropane
rearrangement of electron-deficient 2,4-dienes 1 to 2-
halo-1,3-dicarbonyl compounds 2 for the synthesis of
multifunctional cyclopentenes with excellent regio-,
chemo-, and stereoselectivity, by employing readily
Crystallographic Data for 5h
C22H16Cl2N2O2 (411.27). Triclinic, space group P-1, a=
9.6224(5) ꢂ,
b=10.3070(5) ꢂ,
c=11.4274(5) ꢂ,
V=
1000.76(8) ꢂ3, Z=4, specimen 0.263ꢃ0.216ꢃ0.132 mm3, T=
296(2) K, Siemens P4 diffractometer, absorption coefficient
available, low cost N-(4-trifluoromethylbenzyl)cincho- none, reflections collected 15828, independent 4517 [R-
AHCTUNGTREG(NNUN int)=0.0235], refinement by Full-matrix least-squares on
nium bromide IV as the phase-transfer catalyst. Fully
substituted fulvene derivatives were also obtained
through a further retro-Claisen reaction. Notably, the
reaction scope is quite substantial and only the E-iso-
mers were detected. A plausible mechanism for this
unprecedented domino reaction was given. Further
investigations to expand the synthetic utilities of this
protocol, such as synthesis of pharmaceutically intri-
guing compounds, are currently underway.
F2, data/restraints/parameters 4517/0/254, goodness-of-fit on
F2 =1.078, final R indices [I>2 sigma(I)] R1=0.0357, wR2=
0.0907, R indices (all data) R1=0.0478, wR2=0.0478, largest
diff. peak and hole 0.249 and À0.285 ꢂÀ3. CCDC 954457
contains the supplementary crystallographic data for the
structure of 5h. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif or on application
to CCDC, 12 Union Road, Cambridge CB2 1EZ,
U.K. [fax: (internat.) (+44)-1223/336–033; e-mail:
deposit@ccdc.cam.ac.uk].
Experimental procedures, characterization data and
model of possible transition states of the reaction are avail-
able in the Supporting Information in detail.
Experimental Section
Typical Experimental Procedure for the Domino
Reaction of 2,4-Dienes 1 and 2-Halo-1,3-dicarbonyl
Compounds 2 (entry 1, Table 2)
Catalyst IV (10.6 mg, 20 mol%) was added to the solution
of 2,4-diene 1a (26.0 mg, 10 mmol) and diethyl a-bromomal-
onate 2a (30.0 mg, 0.12 mmol) in DCM (1.0 mL) at 158C.
Then K2CO3 (7.0 mg, 0.05 mmol) was added. The mixture
was stirred at 158C for 48 h. Then the reaction mixture was
concentrated and the residue was purified by flash chroma-
tography on silica gel (petroleum ether/ethyl acetate=4:1)
Acknowledgements
We are grateful for financial support from NSFC (21272214
and 21036006) and Changjiang Scholars and Innovative Re-
search Team in Chinese Universities (IRT0980). The authors
are grateful for fruitful discussions with Dr. Xue-Feng Li
(Southwest University for Nationalities).
1
to give 4a; yield: 30 mg (74%); H NMR (400 MHz, CDCl3):
d=10.39 (s, 1H), 7.61 (s, 1H),7.31 (s, 1H), 7.25–7.11 (m,
5H), 6.99 (d, J=8.1 Hz, 1H), 6.89 (t, J=7.7 Hz, 1H), 6.79–
6.76 (m, 2H), 4.36 (q, J=7.1 Hz, 4H), 1.34 (t, J=7.1 Hz,
6H); 13C NMR (100 MHz, CDCl3): d=169.1, 166.5, 165.2,
135.7, 135.6, 135.1, 133.5, 131.1, 130.3, 129.8, 129.3, 129.2,
129.0, 128.7, 128.3, 128.1, 127.8, 127.2, 118.9, 112.9, 68.3,
63.4, 13.9. ESI-HR-MS: m/z=437.1492, calcd. for
[C25H22N2O4 +Na]: 437.1472.
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