Selective and CO-retentive addition reactions of acid chlorides to terminal alkynes in synthesis of β-Chloro-α,β-unsaturated ketones using ZnO

Article abstract of DOI:10.1246/bcsj.20110040

The addition reaction of acid chlorides with terminal alkynes to afford β-Chloro-α,β-unsaturated ketones using ZnO as catalyst has been studied under solvent-free conditions. All the reactions were done at room temperature and β-Chloro-α,β-unsaturated ket

Full text of DOI:10.1246/bcsj.20110040

778
Bull. Chem. Soc. Jpn. Vol. 84, No. 7, 778-782 (2011)
© 2011 The Chemical Society of Japan
Selective and CO-Retentive Addition Reactions of Acid Chlorides
to Terminal Alkynes in Synthesis of ¢-Chloro-¡,¢-unsaturated
Ketones Using ZnO
Mona Hosseini-Sarvari* and Zahra Mardaneh
Department of Chemistry, Faculty of Science, Shiraz University, Shiraz 71454, Iran
Received February 8, 2011; E-mail: hossaini@shirazu.ac.ir
The addition reaction of acid chlorides with terminal alkynes to afford ¢-chloro-¡,¢-unsaturated ketones using ZnO
as catalyst has been studied under solvent-free conditions. All the reactions were done at room temperature and ¢-chloro-
¡,¢-unsaturated ketones were obtained with selectivity in high yields.
¢-Chloro-¡,¢-unsaturated ketones have received consider-
able attention due to their utility as synthetic intermediates
particularly for the synthesis of heterocyclic systems.1 A useful
reaction for the synthesis of ¢-chloro-¡,¢-unsaturated ketones
involves the addition of acid chloride derivatives to terminal
alkynes. However, the addition of acid chlorides to alkynes
often proceeds with concomitant decarbonylation.2 In 1996,
Miura and co-workers3 reported for the first time rhodium-
catalyzed addition of acid chlorides to alkynes. This reaction
proceeded with complete decarbonylation. Tanaka,4 Chung,5
and co-workers reported rhodium-catalyzed addition reactions
of chloroformates,4a,5 ethoxalyl chloride,4b perfluorinated acid
chlorides,4c and chloroacetyl chlorides4d to terminal alkynes.
The electronegative substituent bond to the carbonyl group
appeared to play an important role to prevent possible
decarbonylation in these reactions.
The addition reaction of acid chlorides to alkynes using a
stoichiometric or catalytic amount of Lewis acids such as
AlCl3, FeBr2, or CeCl3 is known.6 However, as is expected in
using the Lewis acid catalysts, the major products are usually
(E)-isomers or suffer from the lack of stereoselectivity.
Recently Tsuji and co-workers7 reported the addition of
acid chlorides to alkynes proceeded without decarbon-
ylation although this reaction suffered from one or more
of the following disadvantages: long reaction times (20 h),
use of expensive or unavailable reagents, high temperature
(90 °C), toxic solvent (toluene), and not applicable for aliphatic
acid chlorides. Therefore, a capable, efficient, low-cost, and
commercially available catalyst must be developed for the
reaction.
O
O
Cl
ZnO
R1
Cl
R1
R2
H
R2
+
solvent-free
room temp.
H
2
1
3
R2 = aryl
alkyl
R1 = aryl
alkyl
Scheme 1.
Results and Discussion
First, the reaction between benzoyl chloride (1a) and
phenylacetylene (2a) in 1:1 molar ratio was optimized using
different metal oxides such as TiO2, MgO, CaO, etc. (Table 1).
As is clear from Table 1, the synthesis of compound 3a is
completed after 70 min at room temperature in 90% isolated
yields using 20 mol % of ZnO. Other inorganic solids as
catalyst have also been examined on the yield of the compound
3a (Entries 2-7). For comparison, when CaO, Al2O3, TiO2,
and ZnCl2 were used in place of ZnO under the same
conditions, reactions were ineffective. In fact, only 32%
and 21% conversions were observed when MgO and SiO2
were used, respectively. In the next instance, the effect of
the amount of catalyst on promotion of the reaction was
examined (Entries 8-11). It was observed that the variation for
ZnO had an effective influence. The best amount of nano ZnO
is 20 and 50 mol %, which afforded the desired product in 90%
yields (Entries 1 and 10). We also examined the effect of
solvents. Although the reaction proceeded smoothly in THF or
dioxane, only 75% and 70% yields of the product were
detected after long reaction times (Entries 14 and 15).
Probably, ZnO surface contributes to the reaction so the
solvents maybe deactivate the catalyst and decrease the reaction
yields. In addition, the reaction did not proceed without any
catalysts (Entry 17). As a result, ZnO was found the most
effective catalyst, affording 3a in 90% yield after 70 min at
room temperature with high Z-selectivity (Table 1, Entry 1)
showing regio- and stereoselectivity.
In recent years, inorganic solid oxides like SiO2, Al2O3,
ZnO, and others have received considerable interest because
of their chemoselectivity and availability at low cost.
Hence, according to our previous work on the application
of metal oxides as catalyst,8 herein we successfully report
the addition of acid chlorides 1 to terminal alkynes 2, catalyzed
by ZnO, to afford (Z)-adducts selectively without decarbon-
ylation at room temperature under solvent-free conditions
(Scheme 1).
Published on the web July 2, 2011; doi:10.1246/bcsj.20110040

M. Hosseini-Sarvari et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 7 (2011)
779
Table 1. Solvent Screening for the Reaction of Benzoyl
Chloride (1a) with Phenylacetylene (2a) Using ZnOa)
mixture and centrifuged until the catalyst was deposited at the
bottom of centrifuge tube. The deposited ZnO was washed with
ethyl acetate 2-3 times to complete removal of organic
residuals, dried in an oven at 100-120 °C for 5-6 h and then
the catalyst was reused for the same reaction. It was shown that
ZnO can be recovered and is reusable. The results of the
reusability of ZnO are listed in Table 3.
XRD patterns of solid ZnO before and after using in the
reaction are shown in Figure 1. The observed diffraction peaks
in all the recorded XRD patterns are in agreement with those of
the JCPDS card 89-7102 for hexagonal ZnO with wurtzite
structure. No peaks of any other phase were detected. From the
FWHM of diffraction lines, crystallite size is estimated
employing Scherrer’s formula. Average size is >1 ¯m. The
XRD pattern of the reused catalyst is shown in Figure 1b.
Clearly, the ZnO structure of the catalyst remains intact. Thus,
the catalyst is stable in the reaction condition.
Reaction time
/h
Yield
/%b),c)
Entry Catalyst (mol %) Solvent
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
ZnO (20)
MgO (20)
SiO2 (20)
CaO (20)
Al2O3 (20)
TiO2 (20)
ZnCl2 (20)
ZnO (5)
ZnO (10)
ZnO (50)
ZnO (100)
ZnO (20)
ZnO (20)
ZnO (20)
ZnO (20)
ZnO (20)
none
none
none
none
none
none
none
none
none
none
none
none
CH3CN
CH2Cl2
THF
Dioxane
H2O
1:10’
15
15
24
24
24
24
2
1.5
1:10’
2
24
24
13
9.5
24
24
90
32
21
trace
0
trace
0
86
87
90
75
trace
0
75
70
0
Conclusion
In conclusion, a new strategy, ZnO-catalyzed addition of
acid chlorides with alkynes is established as a tool of
defunctionalization of terminal acetylenes for the regio- and
stereoselective synthesis of highly functionalized olefins.
Further studies on the reaction mechanism and the application
of ZnO are under investigation. So, herein we have presented
the first example of ZnO-catalyzed synthesis of ¢-chloro-¡,¢-
unsaturated ketones under mild conditions. This new and
efficient catalytic method provides a protocol that enables the
synthesis of (Z)-¢-chloro-¡,¢-unsaturated ketones in stereo-
and regioselectively, while displaying good functional group
tolerance. This protocol benefits from short reaction times,
operational simplicity, neutral reaction conditions, reusability
of the catalyst, avoidance of solvents, reduced environmental
and economic impacts, and chemoselectivity. No toxic reagent
or by product were involved and no laborious purifications
were necessary.
none
0
a) Conditions: 1a (1.0 mmol), 2a (1.0 mmol), at rt. b) Isolated
1
yields. c) The product was characterized by IR, H NMR, and
13C NMR.
After preliminary experiments, we found that the represen-
tative procedure could be successfully used to obtain various ¢-
chloro-¡,¢-unsaturated ketones 3 with high regio- and stereo-
selectivity from 1 and 2. The results are shown in Table 2.
The terminal alkynes and catalyst are air stable and the
humidity is not high enough to hydrolyze the acid chloride.
Therefore, an inert atmosphere is not required and all reactions
were done at room temperature in an open vessel. To prove this,
the addition reaction of 1a, 1b, and 1f with 2a in the presence
of ZnO were completed under an inert atmosphere and gave the
same results as those obtained under air (Table 2, Entries 1, 2,
and 6).
Experimental
As shown in Table 2, the addition reactions have taken place
with regio- and stereoselectivity. Routine workup allowed
isolation of Z- and E-isomers, which were fully characterized
1H NMR and 13C NMR spectra were recorded on a Bruker
Advance DPX FT 250 and 62.9 MHz spectrometer with TMS
as an internal reference. IR spectra were obtained on a Perkin-
Elmer or FTIR-8300 instruments. Mass spectra were obtained
on a Shimadzu GCMS0QP 1000EX at 20 and/or 70 eV.
Elemental analyses were performed on a Thermo Finnigan,
Flash EA 1112 series microanalyzer by the head of the CHN
lab.
General Procedure for Synthesis of ¢-Chloro-¡,¢-unsat-
urated Ketones. The acid chlorides (1.0 mmol) were added to
a mixture of ZnO (0.016 g, 20 mol %) and phenylacetylene
(1.0 mmol) with stirring at room temperature. The reaction
progress was monitored by TLC. After completion, the crude
reaction mixture was extracted with water and EtOAc
(3 © 15 mL). The organic layers were dried with MgSO4 and
evaporated. The resulting crude material was purified by
column chromatography (hexan/EtOAc), affording pure (Z)-3-
chloro-1,3-diphenyl-2-propen-1-one (3a).
1
by comparing with the known H NMR data reported previ-
ously.7 Electron-withdrawing and electron-donating substituent
acid chlorides were converted to the corresponding ¢-chloro-
¡,¢-unsaturated ketones 3b and 3c in high yield and stereo-
selectivity without decarbonylation (Entries 2 and 3). The
electronic effect of the para-substituents is not significant; the
highly electronegative p-nitro-substituent decreases the reac-
tivity (Entry 4). Heteroatom and aliphatic acid chloride such as
2-thienyl chloride (1e) and cyclohexanoyl chloride (1f) also
conforms to the reaction (Entries 5 and 6). To understand the
scope and the generality of this protocol, aliphatic alkynes were
synthesized and reacted with benzoyl chloride in the presence
of ZnO. As shown in Table 2, aliphatic alkynes reacted
smoothly with benzoyl chloride and afforded the corresponding
ketones 3g and 3h in high yield and stereoselectivity (Entries 7
and 8).
Reusability of the ZnO was studied through a condensation
reaction of 1a with 2a. After completion of the reaction
(monitored by TLC), ethyl acetate was added to the reaction
Spectral Data.
one (3a): Pale yellow oil; IR (neat): ¯ 1666.4, 1600.8, 1573.8,
1490.9, 1236.3 cm¹1; 1H NMR (250 MHz, CDCl3): ¤ 8.02-7.98
(Z)-3-Chloro-1,3-diphenyl-2-propen-1-

780
Bull. Chem. Soc. Jpn. Vol. 84, No. 7 (2011)
Addition of Acid Chlorides to Terminal Alkynes by ZnO
Table 2. Addition of Acid Chlorides 1 to Terminal Alkynes 2 Using ZnO at Room Temperature under Solvent-Free Conditionsa)
Time
/min
Yield
Entry
1
Acid chloride
Alkyne
Product 3
Z/Ec)
95/5
/%b)
O
O
Cl
Ph
90
(87)d)
Cl
70
40
H
3a
2a
2a
1a
1b
O
O
Cl
Cl
Ph
85
(83)d)
2
3
90/10
95/5
H
MeO
Cl
MeO
3b
O
O
Cl
Ph
Ph
Cl
2a
180
70
H
Cl
3c
1c
O
O
Cl
Cl
4
5
2a
2a
240
20
0
0
H
O2N
O2N
3d
1d
O
O
Cl
90
90/10
S
S
Cl
H
Ph
1e
3e
O
O
Cl
Cl
95
(91)d)
Cl
Ph
6
2a
10
100/0
H
3f
1f
O
n
n
C8H17
7
8
1a
60
10
90
95
90/10
100/0
C8H17
H
H
2b
3g
1a
Cl
O
O
O
Ph
2c
H
3h
a) Conditions: 1 (1.0 mmol), 2 (1.0 mmol), ZnO (0.016 g, 20 mol %) were mixed at rt, under solvent-free condition.
b) Isolated yields. c) Determined by 1H NMR and GC analysis. d) The reaction was performed under nitrogen
atmosphere.
(m, 2H, Ar-H), 7.78-7.74 (m, 2H, Ar-H), 7.61-7.54 (m,
1H, Ar-H), 7.50-7.42 (m, 5H, Ar-H), 7.36 (s, 1H, -COCH=
C(Cl)-); 13C NMR (62.89 MHz, CDCl3): ¤ 189.6, 143.1, 137.6,
137.1, 133.3, 130.6, 128.7, 128.6, 128.1, 127.1, 121.5; EI-MS:
m/z 244 (16.8% [M + 2]+), 243 (36.2 [M + 1]+), 242 (57.3,
[M]+), 241 (100 [M ¹ 1]+), 165 (29.0), 105 (61.7), 77 (83.4);
Anal. Calcd for C15H11ClO: C, 74.23; H, 4.57%. Found: C,
74.14; H, 4.66%.
(s, 1H, -COCH=C(Cl)-), 6.95 (d, J = 8.95 Hz, 2H, Ar-H),
3.89 (s, 3H, -OMe); 13C NMR (62.89 MHz, CDCl3): ¤ 188.7,
163.8, 141.9, 137.2, 131.1, 130.5, 130.3, 128.6, 127.0, 122.0,
113.8, 55.5; EI-MS: m/z 274 (13.1% [M + 2]+), 273 (26.5
[M + 1]+), 272 (36.6 [M]+), 165 (27.2), 135 (100), 77 (55.6);
Anal. Calcd for C16H13ClO2: C, 70.46; H, 4.80%. Found: C,
70.34; H, 4.76%.
(Z)-3-Chloro-1-(4-chlorophenyl)-3-phenyl-2-propen-1-
(Z)-3-Chloro-1-(4-methoxyphenyl)-3-phenyl-2-propen-1-
one (3c): Pale yellow solids: mp: 64-66 °C (Lit.1 66-67 °C);
one (3b): Pale yellow solids; mp: 86-88 °C (Lit.1 88-89 °C);
IR (KBr): ¯ 1658.7, 1591.2, 1573.8, 1203.5, 759.9 cm ;
¹1
¹1
IR (KBr): ¯ 1651.0, 1602.7, 1585.4, 1573.8, 1238.2 cm
;
1H NMR (250 MHz, CDCl3): ¤ 7.94 (d, J = 8.6 Hz, 2H, Ar-H),
7.78-7.73 (m, 2H, Ar-H), 7.49-7.44 (m, 5H, Ar-H), 7.28 (s,
1H, -COCH=C(Cl)-); 13C NMR (62.89 MHz, CDCl3): ¤
1H NMR (250 MHz, CDCl3): ¤ 7.99 (d, J = 8.97 Hz, 2H, Ar-
H), 7.75-7.72 (m, 2H, Ar-H), 7.44-7.41 (m, 3H, Ar-H), 7.28

M. Hosseini-Sarvari et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 7 (2011)
781
(m, 5H, cyclohexyl), 1.42-1.21 (m, 5H, cyclohexyl); 13C NMR
(62.89 MHz, CDCl3): ¤ 201.1, 142.3, 137.3, 130.4, 128.5,
127.1, 122.6, 51.4, 28.2, 28.0, 26.09, 25.8; EI-MS: m/z 250
(2.4% [M + 2]+), 249 (2.5 [M + 1]+), 248 (6.7 [M]+), 213
(11.3), 165 (100), 137 (10), 102 (27.1); Anal. Calcd for
C15H17ClO: C, 72.43; H, 6.89%. Found: C, 72.31; H, 6.77%.
(Z)-3-Chloro-1-phenyl-2-undecen-1-one (3g): Pale yel-
Table 3. Reusability of the ZnO Catalysts in Synthesis of 3a
Entry
Catalytic runs 1a/mmol Catalyst/g Yield/%a)
1
2
3
4
Fresh
5
4
3
2
0.2
90
90
87
85
1
2
3
0.16
0.12
0.08
a) Isolated yields.
low oil; IR (neat): ¯ 2925.8, 2856.4, 1695.3, 1598.9, 1448.4,
1218.9 cm
¹1
;
1H NMR (250 MHz, CDCl3): ¤ 7.93 (d, J =
8.0 Hz, 2H, Ar-H), 7.59-7.42 (m, 3H, Ar-H), 6.81 (s, 1H,
-COCH=C(Cl)-), 2.53 (t, J = 7.2 Hz, 2H, -CH=C(Cl)-CH2-
), 1.72-1.59 (m, 2H, -CH=C(Cl)-CH2-CH2-), 1.33-1.25 (m,
10H, -CH=C(Cl)-C2H4-C5H10-CH3), 0.90 (t, J = 6.59 Hz,
3H, -CH3); 13C NMR (62.89 MHz, CDCl3): ¤ 189.6, 147.7,
137.6, 133.1, 128.56, 128.45, 121.1, 41.16, 31.8, 29.2, 29.1,
28.6, 27.3, 22.6, 14.0; EI-MS: m/z 279 (2.7% [M + 1]+), 278
(4.4 [M]+), 243 (1.4 [M ¹ Cl]+), 105 (100), 77 (47); Anal.
Calcd for C17H23ClO: C, 73.23; H, 8.31%. Found: C, 73.08; H,
8.23%.
(a)
500
400
300
200
100
0
(Z)-3-Chloro-4-(1-naphthalenyloxy)-1-phenyl-2-buten-1-
one (3h): Pale brown solids; mp: 130 °C; IR (KBr): ¯ 1647.1,
¹1
;
1H NMR (250 MHz,
3
10
20
30
40
50
60
70
80
90
100
1616.2, 1573.8, 1508.2, 1228.6 cm
CDCl3): ¤ 8.40-8.31 (m, 2H, Ar-H), 7.85 (d, J = 8.5 Hz, 2H,
Ar-H), 7.61-7.45 (m, 7H, Ar-H, COCH=C(Cl)-), 6.94 (d,
2H, J = 8.08 Hz, Ar-H), 4.95 (s, 2H, -OCH2-); 13C NMR
(62.89 MHz, CDCl3): ¤ 197.28, 155.98, 139.18, 132.68,
132.63, 130.6, 130.3, 129.1, 129.07, 128.3, 126.0, 125.8,
125.7, 122.3, 103.5, 76.2; EI-MS: m/z 323 (0.3% [M + 1]+),
322 (0.4 [M]+), 286 (49), 247 (91.7), 191 (68.7), 105 (100), 77
(60.4); Anal. Calcd for C20H15ClO2: C, 74.42; H, 4.68%.
Found: C, 74.37; H, 4.56%.
(b)
300
200
100
10
We gratefully acknowledge the support of this work by the
Shiraz University Research Council and the Iran National
Science Foundation (Grant No. 87040564).
2
10
20
30
40
50
60
70
80
90
100
2θ /degree
Figure 1. The XRD patterns of ZnO; (a) before reaction,
(b) after reaction.
References
188.6, 143.9, 139.8, 137.1, 136.0, 130.7, 130.0, 129.0, 128.7,
127.2, 120.9; EI-MS: m/z 278 (34.9% [M + 2]+), 277 (69.8
[M + 1]+), 276 (56.3 [M]+), 275 (100 [M ¹ 1]+), 165 (34.9),
139 (65.6), 102 (71.4), 75 (59.4); Anal. Calcd for C15H10Cl2O:
C, 65.01; H, 3.64%. Found: C, 64.91; H, 3.50%.
(Z)-3-Chloro-3-phenyl-1-(2-thienyl)-2-propen-1-one (3e):
Pale yellow-brown oil; IR (neat): ¯ 1643, 1585.4, 1573.8,
1446.5, 1245.9 cm¹1; 1H NMR (250 MHz, CDCl3): ¤ 7.78-7.73
(m, 3H, Ar-H), 7.69-7.66 (m, 1H), 7.47-7.45 (m, 2H, Ar-H),
7.44-7.43 (m, 1H), 7.34 (s, 1H, -COCH=C(Cl)), 7.15-7.13
(m, 1H, Ar-H); 13C NMR (62.89 MHz, CDCl3): ¤ 181.0, 145.5,
144.4, 137.3, 134.3, 132.1, 130.7, 128.7, 128.3, 127.3, 120.3;
EI-MS: m/z 250 (18.5% [M + 2]+), 249 (42.6 [M + 1]+), 248
(53.7 [M]+), 247 (100 [M ¹ 1]+), 184 (30.6), 165 (14.8), 111
(95.5), 102 (53.7); Anal. Calcd for C13H9ClOS: C, 62.77; H,
3.65%. Found: C, 62.61; H, 3.55%.
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1
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