Iron-promoted synthesis of substituted 1-halo-1,4-pentadienes by reaction of 1,3-diarylpropenes with ethynylbenzenes via sp3 C-H bond activation

Article abstract of DOI:10.1021/jo1006398

(Figure Presented) An iron-promoted sp³ C-H bond activation and C-C bond formation reaction between 1,3-diarylpropenes and ethynylbenzenes was realized with BQ (benzoquinone) as an oxidant. The reaction afforded 1-halo-1,4-pentadiene derivative

Full text of DOI:10.1021/jo1006398

pubs.acs.org/joc
iron-catalyzed formation of C-C and C-heteroatom bonds
Iron-Promoted Synthesis of Substituted 1-Halo-1,4-
pentadienes by Reaction of 1,3-Diarylpropenes with
Ethynylbenzenes via sp3 C-H Bond Activation
is becoming popular, the direct formation of C-C bonds
through iron-catalyzed C-H bond activation has been
reported only in limited cases.13
Hanjie Mo and Weiliang Bao*
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Department of Chemistry, Zhejiang University (Xixi
Campus), Hangzhou 310028, People’s Republic of China
wlbao@css.zju.edu.cn
Received April 4, 2010
An iron-promoted sp3 C-H bond activation and C-C
bond formation reaction between 1,3-diarylpropenes and
ethynylbenzenes was realized with BQ (benzoquinone) as an
oxidant. The reaction afforded 1-halo-1,4-pentadiene deri-
vatives in moderate to good yields under mild conditions.
With the emergence of the concepts of “atom eco-
nomy”1 and “green chemistry”,2 C-C bond formation
via transition-metal-catalyzed C-H bond activation has
attracted great attention recently, and a number of ex-
cellent results have been obtained.3 Various oxidative
intermolecular cross-dehydrogenative-coupling (CDC)
reactions directly between two different C-H bonds have
also been developed, such as (i) sp3 C-H with sp3 C-H,4
(ii) sp2 C-H with sp2 C-H,5 (iii) sp3 C-H with sp2 C-H,6
and (iv) sp3 C-H with sp C-H.7 Owing to its inexpensive
and environmentally benign characteristics, iron salts
have emerged as alternative and promising catalysts for
a wide range of organic transformations.8-12 As one of the
most abundant metals on earth, iron has been increasingly
explored in modern catalysis to discover its unique and novel
reactivity toward carbon-carbon and carbon-heteroatom
bond formation, which have been typically achieved by
rare and expensive transition-metal catalysts. Although the
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J. C. Green Chemistry: Theory and Practice; Oxford University Press: New
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2008, 3352. (g) Horvath, I. T.; Anastas, P. T. Innovations and Green Chemistry.
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4856 J. Org. Chem. 2010, 75, 4856–4859
Published on Web 06/17/2010
DOI: 10.1021/jo1006398
r
2010 American Chemical Society

Mo and Bao
JOCNote
Recently, we reported the indolation reaction of allylic
compounds using DDQ as the oxidant via sp3 C-H bond
activation and C-C bond formation.14 Due to the achievement
of oxidative C-H bond activation of allylic compounds, we
designed an iron-promoted C-C bond-formation reaction.
1-Halo-1,4-pentadiene derivatives are potentially useful
intermediates in organic synthesis due to the multifunction-
ality contained in the molecules, which may be utilized in
subsequent substitution and coupling reactions.15 In addi-
tion, 1-halo-1,4-pentadiene derivatives are useful intermedi-
ates in the synthesis of some natural products in recent
years.16 In the past few years, several methods to synthesize
1-halo-1,4-pentadiene derivatives or dihalo-1,4-pentadiene
derivatives have been developed, mainly using alkynes,
aldehydes, and BuLi,17g TiX4,17b,i BX3,17a,d,f FeX3,17e,h
GaX317c as the reagents. Herein, we report an iron-promoted
synthesis of 1-halo-1,4-pentadiene derivatives by the reac-
tion of 1,3-diphenylpropenes with ethynylbenzenes via sp3
C-H bond activation and C-C bond formation.
TABLE 1. Optimization of the Reaction Conditionsa
temp yield
(%)
entry
metal (equiv)
none
BF3 Et2O (1.0)
HOTf (1.0)
ZnCl2 (1.0)
Fe(OTf)3 (1.0)
CuCl2 (1.0)
FeCl3 (1.0)
FeCl3 (1.0)
FeCl3 (1.0)
oxidant
BQ
BQ
BQ
BQ
solvent
DCE
(°C)
1
2
3
4
5
6
7
8
9
80
80
80
80
80
100
80
ND
ND
ND
<15
ND
ND
65
DCE
DCE
DCE
DCE
toluene
DCE
DCE
DCE
3
BQ
BQ
DDQ
TBHP
tert-butyl
peroxide
BQ
BQ
BQ
BQ
80
80
trace
ND
10
FeCl3 (1.0)
DCE
DCE
DCE
DCE
DCE
toluene
DMF
NMP
benzene
1,4-dioxane
CH2Cl2
CHCl3
80
80
80
80
80
100
90
80
50
80
50
50
70
67
51
15
64
36
<20
trace
45
11b FeCl3 (1.0)
12
13
14
15
16
17
18
19
20
21
FeCl3 (0.3)
FeCl3 (0.1)
FeCl3 6H2O (1.0) BQ
To begin our study, we chose 1,3-diphenylpropene (1a) and
ethynylbenzene (2a) as the standard substrates to search for
suitable reaction conditions. BQ (benzoquinone) is a well-
known oxidation reagent for organic synthesis.18 When 1a
and 2a were mixed with a stoichiometric amount of BQ, no
desired product was detected (Table 1, entry 1). Then Bronsted
3
FeCl3 (1.0)
FeCl3 (1.0)
FeCl3 (1.0)
FeCl3 (1.0)
FeCl3 (1.0)
FeCl3 (1.0)
FeCl3 (1.0)
BQ
BQ
BQ
BQ
BQ
BQ
BQ
28
43
68
acids such as BF3 Et2O, HOTf, and Fe(OTf)3 were tested, but
3
no desired product was found (Table 1, entries 2, 3, and 5).
When ZnCl2 was used, less than 15% desired product was
isolated (Table 1, entry 4). This was not a satisfactory result.
When FeCl3 and DDQ were used, the yield was improved to
65% (Table 1, entry 7, in DCE at 80 °C). Further, BQ, TBHP,
and tert-butyl peroxide were screened as the oxidant, for they
performed well in C-H bond activation reactions. The yield
was improved to 70% when BQ was used as the oxidant in
DCE at 80 °C (Table 1, entry 10), and no isomers were detected.
When we performed the reaction under an atmosphere of dry
aUnless otherwise specified, the reaction was carried out using 0.5
mmol of 1a, 0.6 mmol of 2a, 1.5 mL of solvent, and 0.6 mmol of oxidant
in open air atmosphere. bThe reaction was carried out under an atmo-
sphere of dry nitrogen.
nitrogen, the desired product also could be obtained in 67%
yield (Table 1, entry 11). When the amount of FeCl3 was
decreased to 0.33 equiv (total chlorine ∼1.0 equiv), the yield
was decreased to 51% (Table 1, entry 12). When the amount of
FeCl3 was reduced to 0.1 equiv, the desired product was
obtained in 15% yield (Table 1, entry 13), suggesting that the
second and/or third chlorides in the promoter took part in the
(13) (a) Yoshikai, N.; Matsumoto, A.; Norinder, J.; Nakamura, E.
Angew. Chem., Int. Ed. 2009, 48, 2925. (c) Ilies, L.; Tsuji, H.; Nakamura,
E. Org. Lett. 2009, 11, 3966. (c) Yoshikai, N.; Matsumoto, A.; Norinder, J.;
reaction. In addition, when 1.0 equiv of FeCl3 6H2O was used,
ꢀ
Nakamura, E. Synlett 2010, 313. (d) Vallee, F.; Mousseau, J. J.; Charette,
3
A. B. J. Am. Chem. Soc. 2010, 132, 1514. (e) Wei, H.; Hao, C.; Aiwen Lei, L.
Angew. Chem., Int. Ed. 2010, 49, 2004. (f) Jones, W. D.; Foster, G. P.;
Putinas, J. M. J. Am. Chem. Soc. 1987, 109, 5047. (g) Norinder, J.;
Matsumoto, A.; Yoshikai, N.; Nakamura, E. J. Am. Chem. Soc. 2008, 130,
5858. (h) Li, Z.; Cao, L.; Li, C.-J. Angew. Chem. 2007, 119, 6625; Angew.
Chem., Int. Ed. 2007, 46, 6505. (i) Li, Z.; Yu, R.; Li, H. Angew. Chem. 2008, 120,
7607; Angew. Chem., Int. Ed. 2008, 47, 7497. (j) Zhang, Y.; Li, C.-J. Eur. J.
Org. Chem. 2007, 4654. (k) Wen, J.; Zhang, J.; Chen, S.-Y.; Li, J.; Yu, X.-Q.
Angew. Chem. 2008, 120, 9029; Angew. Chem., Int. Ed. 2008, 47, 8897. (l) Li,
Y. Z.; Li, B. J.; Lu, X. Y.; Lin, S.; Shi, Z. J. Angew. Chem., Int. Ed. 2009, 48, 3817.
(m) Plietker, B. Angew. Chem., Int. Ed. 2006, 45, 1469. (n) Plietker, B. Angew.
the desired product was also obtained in good yield (Table 1,
entry 14). A number of solvents were screened, and the desired
product was obtained in moderate yield in toluene, benzene,
CH2Cl2, and CHCl3. However, considerable amounts of un-
desired products were formed in DMF, NMP, and 1,4-dioxane
(Table 1, entries 15-21).
With the optimized reaction conditions established, various
substrates were subjected to the reactions, and representative
results are summarized in Table 2. Ethynylbenzene with an
electron-withdrawing group reacted well with the diarylpro-
penes under the standard reaction conditions (Table 2, entry 2).
However, a moderate yield was achieved when ethynylbenzenes
with electron-donating groups were used (Table 2, entries 3-5).
Unfortunately, no desired product was obtained when 2-ethynyl-
pyridine (it polymerized rapidly while the reaction temperature
rose), 1-ethynyl-4-methoxy-benzene, 2-ethynyl-1,3-dimethyl-
benzene, and 1-hexyne reacted as the substrates. To expand
the scope of the reaction, we further examined the mono- and
disubstituted 1,3-diarylpropenes. High yields of the coupling
products were obtained when they had an electron-donating
group on the aromatic ring, while moderate yields were given if
they had an electron-withdrawing group on the aromatic ring
€
Chem., Int. Ed. 2006, 45, 6053. (o) Plietker, B.; Dieskau, A.; Mows, K.; Jatsch, A.
Angew. Chem., Int. Ed. 2008, 47, 198. (p) Jegelka, M.; Plietker., B. Org. Lett.
2009, 11, 3463.
(14) Mo, H. J.; Bao, W. L. Adv. Synth. Catal. 2009, 351, 2845.
(15) (a) Suzuki, A. Pure Appl. Chem. 1986, 58, 829. (b) Suzuki, A. Rev.
Heteroatom. Chem. 1997, 17, 271.
(16) Hoye, T. R.; Wang, J. J. Am. Chem. Soc. 2005, 127, 6950.
(17) (a) Kabalka, G. W.; Wu, Z.; Ju, Y. Org. Lett. 2002, 4, 1491. (b)
Kabalka, G. W.; Wu, Z.; Ju, Y. Org. Lett. 2002, 4, 3415. (c) Yadav, J. S.;
Reddy, B. V. S.; Eeshwaraiah, B.; Gupta, M. K.; Biswas, S. K. Tetrahedron
Lett. 2005, 46, 1161. (d) Kabalka, G. W.; Yao, M.-L.; Borella, S.; Wu, Z.
Chem. Commun. 2005, 2492. (e) Miranda, P. O.; Diaz, D. D.; Padron, J. I.;
Ramirez, M. A.; Martin, V. S. J. Org. Chem. 2005, 70, 57. (f) Kabalka, G. W.;
Yao, M.-L.; Borella, S.; Wu, Z.; Ju, Y.; Quick, T. J. Org. Chem. 2008, 73,
2668. (g) Kabalka, G. W.; Borella, S.; Yao, M.-L. Synthesis 2008, 325. (h)
Biswas, S.; Maiti, S.; Jana, U. Eur. J. Org. Chem. 2009, 2354. (i) Yao, M.-L.;
Quick, T. R.; Wu, Z.; Quinn, M. P.; Kabalka, G. W. Org. Lett. 2009, 11,
2647.
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J. Org. Chem. Vol. 75, No. 14, 2010 4857

Mo and Bao
JOCNote
TABLE 2. Iron-Catalyzed/Promoted Synthesis of Substituted 1-Halo-
1,4-pentadienesa
SCHEME 2. Palladium-Catalyzed Coupling of 4a with Ethy-
nylbenzene
entry
Ar1, Ar2
C6H5, C6H5
C6H5, C6H5
C6H5, C6H5
C6H5, C6H5
C6H5, C6H5
p-Me-C6H4, p-Me-C6H4 C6H5
p-Cl-C6H4, p-Cl-C6H4 C6H5
p-Br-C6H4, p-Br-C6H4 C6H5
Ar3
C6H5
p-Cl-C6H4 Cl 3b
p-Me-C6H4 Cl 3c
p-Et-C6H4 Cl 3d
p-Pr-C6H4 Cl 3e
X
product yieldb(%)
1
2
3
4
5
6
7
8
9
Cl 3a
70
79
61
58
55
75
56
47
57
70c
65c
74c
56c
aReaction conditions: 0.5 mmol of 4a, 0.6 mmol of 2a, 5 mol % of Pd
catalyst, 5 mol % of CuI, 1 mmol of Et3N, 1.5 mL of THF, N2 protection,
60 °C, overnight.
Cl 3f
Cl 3g
Cl 3h
Cl 3i, 3j
Br 4a
SCHEME 3. Preparation of (1Z,4E)-Penta-1,4-dienes from 4a
p-Cl-C6H4, C6H5
C6H5
C6H5
10 C6H5, C6H5
11 C6H5, C6H5
12 C6H5, C6H5
13 p-Cl-C6H4, p-Cl-C6H4 C6H5
p-Et-C6H4 Br 4b
p-Cl-C6H4 Br 4c
Br 4d
a0.5 mmol of diarylpropenes, 0.6 mmol of ethynylbenzenes, 1.5 mL of
b
DCE, 0.6 mmol of BQ, 1.0 equiv of FeCl3, 80 °C, overnight. Based on
diarylpropene. c0.5 mmol of diarylpropenes, 0.6 mmol of ethynylbenzenes,
aReaction conditions: (1) 1 mmol of 4a, 3 mmol of BuLi, 10 mL of dry THF,
-78 °C, under an atmosphere of dry nitrogen; (2) 15 mL of H2O, rt.
1.5 mL of CHCl3, 0.6 mmol of BQ, 1.0 equiv of FeBr3, 50 °C, overnight.
protocol has provided a route to vinylic C-Cl and C-Br bond
formation.
SCHEME 1. Proposed Mechanism
Experimental Section
General Procedure for Products 3. A sealed tube was charged
with diarylpropenes (0.5 mmol), ethynylbenzenes (0.6 mmol),
BQ (0.6 mmol), FeCl3 (0.5 mmol), and DCE (1.5 mL). The
mixture was stirred at 80 °C overnight. The reaction mixture was
washed with water and extracted with EtOAc. The combined
organic layers were dried over anhydrous MgSO4. After eva-
poration and column chromatography on silica gel (pure petro-
leum ether), the fraction with an Rf = 0.4 was collected to give
the desired product.
(Table 2, entries 6-9). No desired product was obtained when
(E)-4,40-(prop-1-ene-1,3-diyl)bis(nitrobenzene), (E)-4,40-(prop-
1-ene-1,3-diyl)bis(methoxybenzene), (E)-4-phenylbut-3-eneni-
trile, (E)-ethyl 4-phenylbut-3-enoate, and allylbenzene were used
as the substrates. In the same fashion as using FeCl3 as the pro-
moter, FeBr3-promoted reactions produced bromine-incorpo-
rated products 4a, 4b, 4c, and 4d in 56-74% yield (Table 2,
entries 10-13).
On the basis of these observations, a plausible mechanism
is proposed in Scheme 1. First, BQ abstracted a hydride from
1a to form the conjugated intermediate A,19a and the re-
ductant B electrophilic attacked the ethynylbenzene (2a)
followed by C-C bond formation with intermediate A to
give the desired product 3a.19b
Product 3 or 4 can further react with ethynylbenzenes to
form 1-yne-3,6-heptadiene derivatives. For example, 4a was
successfully reacted with ethynylbenzene (2a) and the pro-
duct 5a was obtained in 49% yield (Scheme 2).
To learn the geometry of the halogenated double bond,
product 4a was treated with BuLi; (1Z,4E)-1,3,5-triphenyl-
penta-1,4-diene (6a) was obtained (see the Supporting In-
formation, NOESY spectrum of 6a) in 89% yield (Scheme 3),
and no isomers were detected.
((1E,4E)-1-Chloropenta-1,4-diene-1,3,5-triyl)tribenzene (3a).
1H NMR (400 MHz, CDCl3): δ = 7.45-7.21 (m, 15H), 6.47
(d, J = 16 Hz, 1H), 6.35 (dd, J = 6, 16 Hz, 1H), 6.23 (d, J = 10.4
Hz, 1H), 4.34 (dd, J = 6.4, 10.4 Hz, 1H). 13C NMR (100 MHz,
CDCl3): δ = 48.4, 126.3, 126.8, 127.5, 127.6, 128.3, 128.5, 128.6,
128.8, 128.9, 130.3, 130.7, 131.2, 131.5, 136.91, 136.94, 142.2. IR
(neat): 3059, 3026, 1597, 1492, 1445, 966, 906, 729, 694 cm-1
.
MS (70 eV, EI): m/z = 330.
General Procedure for Products 4. A sealed tube was charged
with diarylpropenes (0.5 mmol), ethynylbenzenes (0.6 mmol),
BQ (0.6 mmol), FeBr3 (0.5 mmol), and CHCl3 (1.5 mL). The
mixture was stirred at 50 °C overnight. The reaction mixture was
washed with water and extracted with EtOAc. The combined
organic layers were dried over anhydrous MgSO4. After eva-
poration and column chromatography on silica gel (pure pet-
roleum ether), the fraction with an Rf = 0.4 was collected to give
the desired product.
((1E,4E)-1-Bromopenta-1,4-diene-1,3,5-triyl)tribenzene (4a).
1H NMR (400 MHz, CDCl3): δ=7.43-7.20 (m, 15H), 6.48-
6.43 (m, 2H), 6.33 (dd, J=6, 16 Hz, 1H), 4.27 (dd, J=6, 10 Hz,
1H). 13C NMR (100 MHz, CDCl3): δ=49.4, 121.3, 126.3, 126.9,
127.6, 127.7, 128.4, 128.5, 128.6, 128.7, 128.8, 130.8, 130.9,
134.5, 137.0, 138.4, 142.0. IR (neat): 3058, 3025, 1597, 1491,
1444, 965, 907, 742, 693 cm-1. MS (70 eV, EI): m/z = 374.
General Procedure for Products 5. A sealed tube was charged
with 4 (0.5 mmol), ethynylbenzenes (0.6 mmol), Et3N (1 mmol),
Pd(PPh3)2Cl2 (5 mol %), CuI (5 mol %), and THF (1.5 mL)
under an atmosphere of dry nitrogen. The mixture was stirred at
In summary, FeCl3- and FeBr3-promoted synthesis of 1-halo-
penta-1,4-diene derivatives by the reaction of 1,3-diarylpro-
penes with ethynylbenzenes has been realized. The present
(19) (a) Cheng, D. P.; Bao, W. L. Adv. Synth. Catal. 2008, 350, 1263. (b)
Xu, T.; Yu, Z; Wang, L. Org. Lett. 2009, 11, 2113.
4858 J. Org. Chem. Vol. 75, No. 14, 2010

Mo and Bao
JOCNote
60 °C overnight. The resulting mixture was purified by flash
column chromatography on silica gel (petroleum ether/ethyl
acetate = 20/1), and the fraction with an Rf = 0.5 was collected
to give the desired product.
EtOAc (3 ꢀ 5 mL). The combined organic layers were dried over
anhydrous MgSO4. Evaporation and column chromatography
on silica gel afforded 6.
1
(1Z,4E)-Penta-1,4-diene-1,3,5-triyltribenzene (6a). H NMR
(3E,6E)-Hepta-3,6-dien-1-yne-1,3,5,7-tetrayltetrabenzene (5a).
1H NMR (400 MHz, CDCl3): δ=7.50-7.23 (m, 20H), 6.54-
6.47 (m, 2H), 6.40 (dd, J=6, 16 Hz, 1H), 4.56 (dd, J = 6, 10.4 Hz,
1H). 13C NMR (100 MHz, CDCl3): δ = 47.9, 88.7, 91.0, 123.3,
124.1, 126.3, 126.7, 127.4, 127.8, 128.0, 128.1, 128.2, 128.4,
128.5, 128.6, 128.7, 128.8, 130.8, 131.5, 137.2, 137.3, 139.3,
142.6. IR (neat): 3025, 2924, 1713, 1597, 1490, 1443, 1362,
1071, 1028, 965, 754, 691 cm-1. MS (70 eV, EI) m/z = 396.
HRMS (EI): m/z calcd for C31H24 (Mþ) 396.1878, found
396.1881.
General Procedure for Products 6. Under an atmosphere of
dry nitrogen, BuLi (1.5 mL, 2 M in hexane) was dropped into a
solution of 4 (1 mmol) in 10 mL of dry THF at -78 °C. The
progress of the reaction was monitored by TLC, and the mixture
was stirred until the starting material disappeared. The reaction
mixture was quenched with 15 mL of water and extracted with
(400 MHz, CDCl3): δ = 7.42-7.23 (m, 15H), 6.69 (d, J=11.2,
1H), 6.55 (d, J=16 Hz, 1H), 6.45 (dd, J = 6, 16 Hz, 1H), 5.92 (t,
J = 10.4 Hz, 1H), 4.77 (dd, J = 6.4, 10 Hz, 1H). 13C NMR (100
MHz, CDCl3): δ = 46.9, 126.3, 126.6, 127.0, 127.3, 127.8, 128.3,
128.5, 128.6, 128.7, 129.5, 130.5, 132.3, 132.8, 137.1, 137.4,
143.4. IR (neat): 3024, 2927, 1808, 1598, 1447, 1256, 1075,
1027, 968, 737, 697 cm-1. MS (70 eV, EI): m/z = 296.
Acknowledgment. This work was financially supported by
the Specialized Research Fund for the Doctoral Program of
Higher Education of China (20060335036).
Supporting Information Available: Experimental proce-
dures along with copies of spectra. This material is available
free of charge via the Internet at http://pubs.acs.org.
J. Org. Chem. Vol. 75, No. 14, 2010 4859