In situ formed acetals facilitated direct Michael addition of unactivated ketones

Article abstract of DOI:10.1039/C6NJ02954J

TfOH-promoted synthesis of 1,5-diketones by the Michael reaction of unactivated ketones with chalcones has been described. Acetals formed under HC(OMe)₃/TfOH conditions generate the required enol-equivalents for a smooth Michael reaction. A wide array of symmetrical and unsymmetrical 1,5-diketones has been synthesised.

Full text of DOI:10.1039/C6NJ02954J

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In Situ Formed Acetal Facilitated Direct Michael Addition of
Unactivated Ketones
Received 00th January 20xx,
Accepted 00th January 20xx
Srinivasa Rao Koppolu and Rengarajan Balamurugan*
DOI: 10.1039/x0xx00000x
TfOH-promoted synthesis of 1,5-diketones by the Michael reaction of unactivated ketones and chalcones has been
3
described. Acetals formed under HC(OMe) /TfOH condition generate required enol-equivalent for smooth Michael
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reaction.
A
wide array of symmetrical and unsymmetrical 1,5-diketones have been synthesised.
unactivated ketones (Scheme 1).
Introduction
Michael reaction plays a significant role in organic synthesis due to
1
the efficient formation of carbon-carbon bond. The broader scope
of Michael reaction in organic synthesis is mainly attributed to the
2
,3
possibility of further synthetic manipulation of Michael products.
,5-Diketones have usually been synthesised by Michael reaction of
ketone enolates with α,β-unsaturated ketones under basic reaction
1
4
, 5
conditions. Base-mediated one pot aldol/Michael reactions have
also been evaluated for making 1,5-diketones by reacting
benzaldehydes with excess of acetophenones. These 1,5-diketones
Scheme 1 Approaches for Michael reaction of unactivated ketones
5
are quite useful substrates for the synthesis of carbocyles, nitrogen
heterocyles and other important complex molecules. When it
3
Results and discussion
comes to direct Michael reaction, 1,3-diketones are widely Preliminary evaluation of Michael addition of unactivated ketones
6
employed nucleophiles because of their low pK
a
values. Since the via in situ formed acetals was attempted using acetophenone 1a
1
,3-dicarbonyls exist in enolic form, they can be used in and chalcone 2a using 1 equivalent each of TfOH and trimethyl
7
Lewis/Brønsted acid-catalyzed/promoted Michael reactions. But, orthoformate (TMOF). Carbon tetrachloride was chosen as the
direct utilisation of unactivated ketones such as acetophenones in
solvent as it worked better in the alkylation of unactivated
Michael reaction under acid catalysis is quite challenging owing to
the high pK
a
values of the α-hydrogens. For the Michael reaction of Table 1 Optimization of stoichiometry of reactants for the synthesis of 1,5-diketones
8
unactivated ketones, metal/non-metal enolates such as silyl,
9
10
11
lithium, few other metal enolates and enamines have been
employed (Scheme 1). Some of them such as silyl enol ether have to
be pre-formed. Recently, Akio Baba et al. reported the Michael
reaction of enol acetates with chalcones in the presence of catalytic
O
O
O
O
CH(OMe)
TfOH (1 equiv)
CCl , rt, 7 h
3
(1 equiv)
3
a
2
a
4
1
a
3
amount of InCl and TMSCl to furnish the enol acetate of Michael
adduct. Jung and co-worker have reported the Michael reaction of
simple ketones with cyclohexenone by heating the reaction mixture
1
2
a
Entry
Ketone (equiv)
Chalcone (equiv)
Yield (%)
1
2
3
4
5
1.0
2.0
3.0
5.0
1.0
5.0
5.0
1.5
1.0
1.0
1.0
5.0
1.0
1.0
1.0
40
51
58
77
70
50
30
56
in a microwave reactor in the presence of P O and 3 equivalents of
2
5
1
3
TfOH.
Recently, we had shown that unactivated ketones could be
alkylated at the α-position using benzylic alcohols via in situ formed
b
14
6
acetals. Very recently, same reaction following our strategy was
reported using a reusable catalyst system, Amberlyst-15/ionic
c
7
d
1
5
8
5.0
liquid. We anticipated that such vinyl ether generated via in situ
formed acetal could be used for the direct Michael addition of
a
b
c
d
Isolated yields. 20 mol% of TfOH was used. Without TMOF. 5 equiv of
acetophenone dimethylacetal was used in the absence of trimethyl
orthoformate.
a.
School of Chemistry, University of Hyderabad, Prof. C. R. Rao Road, Gachibowli,
Hyderabad-500046, India. E-mail: rbsc@uohyd.ernet.in;Tel: 040-23134817.
1
Electronic Supplementary Information (ESI) available: Copies of the H and
spectra of the products.
13
C
This journal is © The Royal Society of Chemistry 20xx
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1
4a
poor yields of 3a (Table 2, entries 5 and 6). Among the Lewis acids,
AgSbF resulted in 27% of the expected product (Tabel 2, entry 11).
ketones.
The results are given in Table 1. The reaction of 1
6
equivalent of acetophenone 1a and 1.5 equivalents of chalcone 2a
resulted in 40% yield of the desired product 3a. When
acetophenone was taken in 2 fold excess with respect to chalcone
an improved yield of 51% was observed. This result prompted us to
find the apt stoichiometry that favours better yield of 3a. A
maximum of 77% yield of 3a was obtained when the reaction was
carried out using 5 equivalents of acetophenone 1a with respect to
chalcone 2a (Table 1, entry 4). Reducing the amount of TfOH to 20
mol% reduced the yield of the product to 50% (Table 1, entry 6). In
the absence of trimethyl orthoformate the reaction worked,
however, yielding only 30% of the product (Table 1, entry 7).
Acetophenone dimethylacetal also reacted with chalcone 2a and
furnished 3a in moderate yield (Table 1, entry 8). The reduction in
yield in this case compared to the reaction presented in entry 4
might be due to the conversion of acetal into its corresponding
poor reactive ketone under the acidic condition. This experiment
indicates that the in situ formed acetal plays a certain role in
increasing the yield, perhaps, by generating the enol equivalent
methyl vinyl ether from acetophenone. To get more insight into the
requirement of 5 equivalents of acetophenone, a reaction was
carried out using equimolar amounts of trimethyl orthoforamte and
acetophenonone in the presence of 1 equivalent TfOH. This
reaction, however, resulted in the formation of aldol self-
Based on these results, the substrate scope was evaluated using the
condition mentioned in the entry 4 of Table 1. While preparing the
manuscript Gu and co-workers published the synthesis of
1
6
benzofurans from unactivated ketones and 1,4-benzoquinones.
This reaction involves initial Michael reaction of methyl vinyl ether
generated from ketone via in situ formed acetal with 1,4-
benzoquinone.
Chalcones 2a-2f were made by trivial base-promoted aldol
condensation of acetophenones with aryl aldehydes. A variety of
chalcones with methyl, methoxy, chloro and methylenedioxy
substituents thus synthesis
ed were subjected to TfOH-promoted Michael addition. Aryl methyl
ketones having electron donating groups such as OMe and Me and
accepting groups such as halo on the aryl ring were employed.
Overall, there was no substantial effect of the substituents on the
yield of the products except few trends. The aryl methyl ketones
with electron donating substituents on the aryl ring resulted in
better yields than their counterparts having electron withdrawing
groups (Table 3, 3c-3g). Even 2-acetylthiophene underwent Michael
addition (Table 3, 3k). Aliphatic ketones such as acetone and
cyclohexanone did not undergo such Michael additions under the
condensation product of acetophenone in 30% yield after 7 h. present conditions. When the aryl at the β-position of the enone
Further, the expected acetal was not isolated, indicating a possible has electron donating groups like OMe, the yields of the products
equilibrium between the ketone and its corresponding acetal. The were comparatively less (Table 3, 3h, 3o and 3p) and (Table 4, 5b),
same reaction without trimethyl orthoformate resulted in 12% of perhaps, due to the reduction of electrophilicity at the β-carbon.
1
the aldol self-condensation product. H NMR analysis of the The effect was very much seen
reaction of equimolar quantities trimethyl orthoformate and
Table 3 Results of triflic acid mediated synthesis of 1,5-diketones from unactivated
acetophenone in the presence of 50 mol% of triflic acid in
CDCl /CCl in a NMR tube showed the peak corresponding to OMe
a
ketones
3
4
of acetal but in minor quantity. The other methyl peak of the acetal
is merged in the water peak. This experiment supports the
formation of acetal intermediate.
Table 2 Results of reaction of direct Michael reaction under different Brønsted/Lewis
acid conditions
O
O
O
O
CH(OMe)3 (1 equiv)
acid (1 equiv)
CCl4, rt
1a
2a
3a
a
b
Entry
Acid (1 equiv)
Time (h)
24
Yield (%)
1
2
3
4
5
6
7
8
9
p-TSA
NR
Trifluoroacetic acid
Acetic acid
24
NR
12
NR
Camphor sulfonic acid
24
NR
HClO
CH SO
TfOH
4
24
10
3
3
H
24
48
7
77
c
HSbF
6
24
NR
c
Cu(OTf)
2
24
NR
c
1
1
0
1
AgOTf
24
NR
c
AgSbF
6
24
27
a
b
c
Chalcone (1 equiv) and ketone (5 equiv) was used. Isolated yield. 20 mol% of
a
acid was used.
Reaction
conditions:
Chalcone
(1
equiv),
ketone
(5
equiv),
b
c
trimethylorthoformate (1 equiv) and TfOH (1 equiv) in CCl
4
, rt. Isolated yield. 20
The reaction was then screened using a set of Brønsted and Lewis
acids (Table 2). Among the Brønsted acids screened, apart from
d
mol% of TfOH was used. 50 mol% of TfOH was used.
4 3 3
TfOH, HClO and CH SO H promoted the reaction but resulted in
2
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when methylenedioxy substituent was there on the β-aryl (Table 3, Scheme 2 Plausible mechanism for the Michael addition of unactivated ketones via in
situ formed acetals
3
o & 3p). At the same time, prominent electron withdrawing nitro
group on β-aryl did not improve the yield significantly either (Table
, 3l & 3m). On the other hand, introducing electron withdrawing
3
Conclusions
groups on the aryl ring of enones did improve the yields (Table 4,
compare 5b and 5c).
In summary, acid-promoted Michael addition of unactivated
ketones with chalcones proceeds smoothly in the presence of
trimethyl orthoformate. It is believed that the acetal formed in situ
under the reaction condition facilitate the Micahel addition. The
substrate scope was evaluated using different substituted aryl
methyl ketones and chalcones and found to result the respective
adducts in good yields. Developing asymmetric version of this
transformation using chiral Brønsted acid catalysis is currently being
pursuaded.
α,β-Unsaturated ketones bearing an alkyl substitution at the β-
carbon can also be used. Reaction of (E)-1-phenylbut-2-en-1-one
with acetophenone resulted 3n in 61% yield. However, α,β-
unsaturated ketones having alkyl group attached at the carbonyl
group are not suitable substrates for the present Michael reaction.
For example, reaction of (E)-4-phenylbut-3-en-2-one resulted in a
bicyclo[2.2.2]octane derivative. Formation of such derivative under
17
the acidic condition is known in the literature.
Then, a few reactions were carried out using ethyl phenyl ketone
Table 4, 5a-5d). These reactions resulted in a mixture of
Experimental
(
diastereomers, marginally favoring the syn diastereomer over the
anti diastereomer.
General
All reagents were obtained commercially and used without further
purification unless otherwise mentioned. TfOH was purchased from
Sigma-Aldrich chemical company and used without any further
purification. Trimethyl orthoformate was distilled prior to use. HPLC
Table 4. Results of triflic acid mediated synthesis of
a
diastereomeric 1,5-diketones from propiophenone
4
grade CCl procured from MERCK was used as solvent for Michael
reaction. Thin-layer chromatography was performed by using Merck
silica gel F-254 coated aluminum plates and the visualization of
spots were done using UV illumination and charring the TLC plates
sprayed with Seebach solution. Column chromatography was
performed on silica gel 100-200 mesh, using ethyl acetate and
1
13
hexane mixture as eluent. H and C NMR spectra of the
synthesised compounds were recorded in Bruker Avance 400 NMR
1
13
machine using their solutions in CDCl . The H NMR and C NMR
Reaction conditions: Chalcone (1 equiv), ketone (5 equiv), were recorded with TMS as an internal standard. IR spectra were
3
a
b
trimethylorthoformate (1 equiv) and TfOH (1 equiv) in CCl
c
4
, rt. Isolated yield. recorded using JASCO FT/IR-5300 spectrometer. High resolution
1
d
Syn/anti ratio based on H NMR. Syn/anti ratio based on isolated yields of the mass spectra (HRMS) were recorded using electrospray ionization
syn and anti diastereomers.
technique in Bruker Maxis machine.
Chalcones were made by base-promoted aldol condensation of
acetophenones with aryl aldehydes. Methyl, methoxy, chloro,
methylenedioxy and nitro substituted chalcones were synthesised
Although the reaction required 5 equivalents of ketone, the
unreacted ketone was recovered in all the reactions without much
loss. Also, this reaction works well only when 1 equivalent of TfOH
was used. The yield of the product decreased when lesser amount
of TfOH (50 mol%) was used (Table 3, 3a, 3c and 3j).
1
13
and characterised. The H and C NMR data of synthesised
19-22
chalcones were found in agreement with the reported data.
1
4b
Procedure for Michael addition of 1a on 2a
As proposed earlier, the ketone is expected to form the acetal I,
which will set up an equilibrium with the enol ether II. In the
presence of acid, chalcones will be activated for efficient Michael
reaction with the enol ether II as shown in scheme 2. It is believed
that, this methyl vinyl ether II under the reaction conditions acts as
an enolate equivalent and reacts with the electrophilic chalcone 2
to furnish 1,5-diketone 3 efficiently.
To a solution of chalcone 2a (50 mg, 0.24 mmol, 1 equiv)
and acetophenone 1a (145 mg, 1.2 mmol, 5 equiv) in carbon
tetrachloride (2 mL), trimethylorthoformate (27 µL, 0.24 mmol, 1
equiv) was added. After 5 min., triflic acid (22 µL, 0.24 mmol, 1
equiv) was added to the reaction mixture. The reaction mixture was
stirred at room temperature. After completion of the reaction as
indicated by TLC, the reaction mixture was concentrated under
vaccum and directly loaded onto the silica gel column and purified
using ethylacetate and hexane as eluents to get pure 3a in 77%
yield (61 mg)
Same procedure was followed for the preparation of
other 1,5-diketones.
2
2
1
,3,5-Triphenylpentane-1,5-dione 3a
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1
6
4
7
2
1
1 mg, Yield: 77%; H NMR (400 MHz, CDCl ) : δ 7.94 (d, J = 8.0 Hz, 46 mg, Yield: 50%; Yellow liquid; R = 0.4 (ethyl acetate/hexane,
3
f
-1
1
H), 7.56-7.52 (m, 2H), 7.45-7.41 (m, 4H), 7.28-7.25 (m, 4H), 7.20- 1:5); IR (KBr, Cm ): 2898, 1676, 1582, 1484, 1232, 985, 547; H NMR
.15 (m, 1H), 4.06 (quint, J = 7.0 Hz, 1H), 3.49 (dd, J = 16.6, 6.9 Hz, (400 MHz, CDCl ) : δ 7.93 (d, J = 7.4 Hz, 2H), 7.80 (d, J = 8.4 Hz, 2H),
H), 3.35 (dd, J = 16.6, 7.0 Hz, 2H); C NMR (100 MHz, CDCl
98.7, 143.9, 136.9, 133.2, 128.7, 128.2, 127.5, 126.8, 45.0, 37.2.
3
13
3
) : δ 7.59-7.54 (m, 3H), 7.46-7.42 (m, 2H), 7.25-7.19 (m, 4H), 4.02 (quint,
1
3
C
J = 6.9 Hz, 1H), 3.46 (dd, J = 16.8, 6.7 Hz, 2H), 3.34-3.22 (m, 2H);
NMR (100 MHz, CDCl ) : δ 198.2, 197.2, 142.1, 136.7, 135.5, 133.4,
132.5, 132.0, 129.7, 128.9, 128.8, 128.7, 128.5, 128.1, 44.7, 44.6,
3
2
3
1
-(4-Methoxyphenyl)-3,5-diphenylpentane-1,5-dione 3b
+
3
2
6.5; HRMS (ESI) m/z calcd for C23H18BrClO [M+Na] = 441.0257,
1
4
7 mg, Yield: 54%; H NMR (400 MHz, CDCl ) : δ 7.95-7.91 (m, 4H), found = 441.0256.
3
7
.55-7.51 (m, 1H), 7.44-7.41 (m, 2H), 7.29-7.24 (m, 4H), 7.19-7.14
2
2
(
m, 1H), 6.90 (d, J = 8.6 Hz, 2H), 4.05 (quint, J = 7.0 Hz, 1H), 3.84 (s, 3-(4-Methoxyphenyl)-1,5-diphenylpentane-1,5-dione 3h
13
3H), 3.52-3.39 (m, 2H), 3.36-3.26 (m, 2H);
C NMR (100 MHz,
1
CDCl ) : δ 198.7, 197.2, 163.5, 144.0, 136.9, 133.1, 130.5, 130.0, 41 mg, Yield: 55%; H NMR (400 MHz, CDCl ) : δ 7.94 (d, J = 7.2 Hz,
3
3
128.6, 128.2, 127.5, 126.7, 113.8, 55.5, 45.0, 44.7, 37.4.
4H), 7.55-7.52 (m, 2H), 7.45-7.41 (m, 4H), 7.19 (d, J = 8.6 Hz, 2H),
6
.80 (d, J = 8.6 Hz, 2H), 4.02 (quint, J = 7.0 Hz, 1H), 3.74 (s, 3H), 3.46
2
2
13
3
-(4-Chlorophenyl)-1,5-diphenylpentane-1,5-dione 3c
(dd, J = 16.6, 6.8 Hz, 2H), 3.30 (dd, J = 16.6, 7.2 Hz, 2H); C NMR
100 MHz, CDCl ) : δ 198.8, 158.2, 136.9, 135.8, 133.1, 128.6, 128.4,
) : δ 7.93 (d, J = 7.6 Hz, 128.2, 114.0, 55.2, 45.2, 36.5.
(
3
1
72 mg, Yield: 97%; H NMR (400 MHz, CDCl
3
4H), 7.57-7.53 (m, 2H), 7.46-7.43 (m, 4H), 7.25-7.23 (m, 4H), 4.06
(
quint, J = 7.0 Hz, 1H), 3.48 (dd, J = 16.9, 6.9 Hz, 2H), 3.32 (dd, J = 3-(4-Methoxyphenyl)-1-phenyl-5-p-tolylpentane-1,5-dione 3i
1
3
1
6.7, 7.3 Hz, 2H); C NMR (100 MHz, CDCl ) : δ 198.3, 142.4, 136.8,
3
1
33.3, 132.4, 129.0, 128.8, 128.7, 128.2, 44.8, 36.5.
55 mg, Yield: 70%; Colour less liquid;
R
f
= 0.33 (ethyl
-1
acetate/hexane, 1:5); IR (KBr, Cm ): 3002, 2926, 1676, 1610, 1506,
4
a
1
3-(4-Chlorophenyl)-1-phenyl-5-p-tolylpentane-1,5-dione 3d
1243, 1183, 756; H NMR (400 MHz, CDCl ) : δ 7.94 (d, J = 7.5 Hz,
3
2
H), 7.84 (d, J = 8.0 Hz, 2H), 7.55-7.51 (m, 1H), 7.45-7.41 (m, 2H),
1
6
2
7
3
1
1
5 mg, Yield: 83%; H NMR (400 MHz, CDCl
3
) : 7.92 (d, J = 7.8 Hz, 7.25-7.17 (m, 4H), 6.80 (d, J = 8.8 Hz, 2H), 4.00 (quint, J = 7.0 Hz,
H), 7.83 (d, J = 8.1 Hz, 2H), 7.55-7.52 (m, 1H), 7.45-7.41 (m, 2H), 1H), 3.74 (s, 3H), 3.49-3.39 (m, 2H), 3.32-3.24 (m, 2H), 2.39 (s, 3H);
1
3
.24-7.22 (m, 6H), 4.04 (quint, J = 7.1 Hz, 1H), 3.50-3.40 (m, 2H),
C NMR (100 MHz, CDCl
3
) : δ 198.8, 198.4, 158.2, 143.9, 137.0,
13
.33-3.25 (m, 2H), 2.38 (s, 3H); C NMR (100 MHz, CDCl
97.9, 144.1, 142.4, 136.8, 134.3, 133.2, 132.2, 129.4, 128.9, 128.7, 45.1, 36.6, 29.7, 21.7; HRMS (ESI) m/z calcd for C25
3
) : δ 198.3, 136.0, 134.5, 133.0, 129.3, 128.6, 128.4, 128.3, 128.2, 114.0, 55.2,
+
24 3
H O [M+Na] =
28.2, 44.7, 36.6, 21.7.
395.1623, found = 395.1622.
3-(4-Chlorophenyl)-1-(4-methoxyphenyl)-5-phenylpentane-1,5-
1,3-Bis(4-methoxyphenyl)-5-phenylpentane-1,5-dione 3j
dione 3e
7
4 mg, Yield: 90%; Yellow liquid; R
f
= 0.26 (ethyl acetate/hexane,
-1
6
5
mg, Yield: 80%; Light brown liquid;
R
f
=
0.33 (ethyl 1:5); IR (KBr, Cm ): 2931, 2838, 1676, 1600, 1506, 1249, 1178,
acetate/hexane, 1:5); IR (KBr, Cm ): 2367, 1676, 1583, 1068, 986, 1030, 832; H NMR (400 MHz, CDCl
-1
1
3
): δ 7.95-7.92 (m, 4H), 7.55-7.51
1
5
1
4
1
3
1
1
C
42; H NMR (400 MHz, CDCl
3
) : δ 7.94-7.91 (m, 4H), 7.56-7.52 (m, (m, 1H), 7.44-7.41 (m, 2H), 7.18 (d, J = 8.7 Hz, 2H), 6.90 (d, J = 8.8
H), 7.45-7.41 (m, 2H), 7.25-7.22 (m, 4H), 6.91 (d, J = 8.7 Hz, 2H), Hz, 2H), 6.80 (d, J = 8.5 Hz, 2H), 4.00 (quint, J = 7.0 Hz, 1H), 3.84 (s,
.03 (quint, J = 7.0 Hz, 1H), 3.84 (s, 3H), 3.48 (dd, J = 16.8, 6.6 Hz, 3H), 3.74 (s, 3H), 3.47 (dd, J = 16.4, 6.7 Hz, 1H), 3.40 (dd, J = 16.0,
H), 3.41 (dd, J = 16.7, 6.7 Hz, 1H), 3.30 (dd, J = 16.7, 7.4 Hz, 1H), 7.0 Hz, 1H), 3.29 (dd, J = 16.5, 7.5 Hz, 1H), 3.24 (dd, J = 16.3, 7.0 Hz,
.25 (dd, J = 16.4, 7.2 Hz, 1H); C NMR (100 MHz, CDCl ) : δ 198.3, 1H); C NMR (100 MHz, CDCl ): δ 198.9, 197.4, 163.5, 158.2, 137.0,
3 3
96.8, 163.6, 142.5, 136.8, 133.2, 132.3, 130.4, 129.9, 129.0, 128.7, 135.9, 133.1, 130.5, 130.3, 130.0, 128.6, 128.4, 128.2, 114.0, 113.8,
28.6, 128.1, 113.8, 55.5, 44.8, 44.5, 36.7; HRMS (ESI) m/z calcd for 113.6, 55.5, 55.2, 45.2, 44.9, 36.8, 24.7; HRMS (ESI) m/z calcd for
13
13
+
+
24
H
21ClO
3
[M+Na] = 393.1257, found = 393.1260.
,3-Bis(4-chlorophenyl)-5-phenylpentane-1,5-dione 3f
f
8 mg, Yield: 71%; Light brown solid; m.p. 54-56 °C; R = 0.45 (ethyl
25 24 4
C H O [M+Na] = 411.1572, found = 411.1573.
1
1-(4-Chlorophenyl)-3-(4-methoxyphenyl)-5-(thiophen-2-
yl)pentane-1,5-dione 3k
5
-1
acetate/hexane, 1:5); IR (KBr, Cm ): 3063, 2920, 1682, 1600, 1210, 56 mg, Yield: 76%; White solid; m.p. 116-118 °C; R
f
= 0.25 (ethyl
3
) : δ 7.92 (d, J = 7.7 Hz, acetate/hexane, 1:5); IR (KBr, Cm ): 2936, 2838, 1676, 1517, 1419,
1
-1
1
2
2
084, 810, 690; H NMR (400 MHz, CDCl
H), 7.87 (d, J = 8.1 Hz, 2H), 7.57-7.53 (m, 1H), 7.45 (d, J = 7.7 Hz, 1243, 1035, 843, 717; H NMR (400 MHz, CDCl
H), 7.40 (d, J = 8.5 Hz, 2H), 7.25-7.19 (m, 4H), 4.03 (quint, J = 7.0 Hz, 2H), 7.74 (d, J = 3.7 Hz, 1H), 7.61 (m, 1H), 7.41 (d, J = 8.6 Hz, 2H),
1
3
): δ 7.88 (d, J = 8.4
Hz, 1H), 3.46 (dd, J = 16.7, 6.8 Hz, 1H), 3.31 (d, J = 17.3, 7.0 Hz, 2H), 7.17 (d, J = 8.7 Hz, 2H), 7.12-7.10 (m, 1H), 6.80 (d, J = 8.7 Hz, 2H),
1
3
3
1
1
.26 (d, J = 14.4, 5.4 Hz, 1H); C NMR (100 MHz, CDCl
97.1, 142.1, 139.6, 135.0, 133.3, 132.4, 129.5, 129.2, 128.9, 128.5, 1H), 3.36 (dd, J = 16.0, 7.3 Hz, 1H), 3.29-3.20 (m, 2H); C NMR (100
28.1, 122.4, 44.6, 36.4; HRMS (ESI) m/z calcd for C23 MHz, CDCl ): δ 197.5, 191.6, 158.4, 144.3, 139.5, 135.3, 133.8,
132.2, 129.6, 129.0, 128.4, 128.2, 114.1, 55.2, 45.9, 44.9, 37.0;
3
) : δ 198.2, 3.97 (quint, J = 7.0 Hz, 1H), 3.75 (s, 3H), 3.47 (dd, J = 16.5, 6.6 Hz,
1
3
2
H18Cl O
2
3
+
[
M+H] = 397.0762, found = 397.0761.
+
3
HRMS (ESI) m/z calcd for C22H19ClO S [M+Na] = 421.0641, found =
1-(4-Bromophenyl)-3-(4-chlorophenyl)-5-phenylpentane-1,5-dione 421.0642.
3g
5
b
3
-(4-Nitrophenyl)-1,5-diphenylpentane-1,5-dione 3l
4
| New J. Chem., 2015, 00, 1-3
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DOI: 10.1039/C6NJ02954J
NJC
ARTICLE
1
4
2
6
(
1
7 mg, Yield: 64%; H NMR (400 MHz, CDCl ) : δ 8.14 (d, J = 8.2 Hz, 3-(4-Methoxyphenyl)-2-methyl-1,5-diphenylpentane-1,5-dione 5b
3
H), 7.93 (d, J = 7.7 Hz, 4H), 7.57 (t, J = 7.3 Hz, 2H), 7.50-7.43 (m,
H), 4.21 (quint, J = 6.8 Hz, 1H), 3.55 (dd, J = 16.7, 6.5 Hz, 2H), 3.40 43 mg, Yield: 55%; Light brown liquid; Rf
dd, J = 16.0, 7.5 Hz, 2H); C NMR (100 MHz, CDCl
36.5, 133.4, 130.1, 128.7, 128.5, 128.0, 123.8, 44.2, 36.7.
=
0.33 (ethyl
1
3
-1
3
): δ 197.6, 151.7, acetate/hexane, 1:5); IR (KBr, Cm ): 2958, 2931, 1676, 1512, 1249,
1
3
1178, 706; H NMR (400 MHz, CDCl ) : δ 8.04 (d, J = 8.3 Hz, 2H),
7
(
8
.86-7.83 (m, 3.5H), 7.59-7.57 (m, 1H), 7.52-7.48 (m, 4H), 7.42-7.38
m, 3H), 7.15 (d, J = 8.6 Hz, 0.9H), 7.08 (d, J = 8.6 Hz, 2H), 6.79 (d, J =
.6 H, 2H), 6.72 (d, J = 8.6 Hz, 0.8H), 3.93-3.85 (m, 1.7H), 3.83-3.78
5 mg, Yield: 76%; White solid; m.p. 90-92 °C; R = 0.26 (ethyl (m, 1H), 3.75 (s, 3H), 3.70 (s, 1.2H), 3.41-3.34 (m, 2H), 3.18 (dd, J =
1
-(4-Iodophenyl)-3-(4-nitrophenyl)-5-phenylpentane-1,5-dione 3m
7
f
-1
acetate/hexane, 1:5); IR (KBr, Cm ): 1671, 1572, 1512, 1342, 980; 15.7, 9.3 Hz, 1H), 1.27 (d, J = 6.6 Hz, 1.7H), 1.00 (d, J = 6.6 Hz, 3H);
1
13
H NMR (400 MHz, CDCl ) : δ 8.13 (d, J = 8.6 Hz, 2H), 7.92 (d, J = 8.4
3
C NMR (100 MHz, CDCl ) : δ 204.0, 198.8, 158.3, 137.0, 136.9,
3
Hz, 2H), 7.81 (d, J = 8.1 Hz, 2H), 7.64 (d, J = 8.4 Hz, 2H), 7.59-7.55 133.4, 133.3, 132.9, 129.3, 128.9, 128.8, 128.6, 128.5, 128.4, 128.2,
(
m, 1H), 7.49-7.43 (m, 4H), 4.18 (quint, J = 6.7 Hz, 1H), 3.56-3.49 (m, 128.0, 113.8, 55.2, 46.1, 45.9, 43.7, 42.2, 40.2, 16.5, 14.3; HRMS
13
+
2
1
1
H), 3.42-3.31 (m, 2H); C NMR (100 MHz, CDCl
51.4, 146.6, 138.0, 136.4, 135.6, 133.5, 129.4, 128.7, 128.5, 128.0,
23.8, 101.5, 44.1, 44.0, 36.5; HRMS (ESI) m/z calcd for C23
3
25 24 3
): δ 197.5, 196.9, (ESI) m/z calcd for C H O [M+Na] = 395.1623, found = 395.1622.
H
18INO
4
5-(4-chlorophenyl)-3-(4-methoxyphenyl)-2-methyl-1-
phenylpentane-1,5-dione 5c
+
[M+Na] = 522.0178, found = 522.0176.
3
-(Benzo[d][1,3]dioxol-5-yl)-1,5-diphenylpentane-1,5-dione 3n
61 mg, Yield: 82%; Light brown liquid;
R
f
=
0.33 (ethyl
-
1
acetate/hexane, 1:5); IR (KBr, Cm ): 1676, 1506, 1243, 1101, 1030;
1
22 mg, Yield: 30%; Light yellow solid; m.p. 112-114 °C; R = 0.3
3
H NMR (400 MHz, CDCl ) : δ 8.04 (d, J = 8.5 Hz, 2H), 7.87-7.82 (m,
f
-1
(
ethyl acetate/hexane, 1:4); IR (KBr, Cm ): 2882, 1682, 1490, 1249, 3H), 7.61-7.57 (m, 1H), 7.52-7.48 (m, 2H), 7.42-7.39 (m, 1H), 7.27-
1
1
7
2
035, 750, 690; H NMR (400 MHz, CDCl
.57-7.53 (m, 2H), 7.46-7.43 (m, 4H), 6.77 (br s, 1H), 6.73-6.68 (m, 2H), 3.83 (s, 3H), 3.34 (dd, J = 14.2, 3.6 Hz, 1H), 3.16 (d, J = 15.3, 9.4
H), 5.89 (s, 2H), 3.99 (quint, J = 7.0 Hz, 1H), 3.44 (dd, J = 16.6, 6.9 Hz, 1H) 1.27 (d, J = 6.5 Hz, 3H), 1.00 (d, J = 6.7 Hz, 3H); C NMR (100
3
): δ 7.95 (d, J = 7.4 Hz, 4H), 7.23 (m, 2H), 7.20-7.17 (m, 5H), 6.90-6.85 (m, 2H), 3.96-3.87 (m,
1
3
1
3
Hz, 2H), 3.29 (dd, J = 16.6, 7.2 Hz, 2H); C NMR (100 MHz, CDCl
3
): δ MHz, CDCl
3
): δ 203.9, 197.6, 158.3, 136.7, 135.1, 133.2, 133.0,
1
1
3
98.6, 147.8, 146.2, 137.7, 136.9, 133.2, 128.7, 128.2, 120.6, 108.4, 129.6, 129.4, 129.1, 128.8, 128.7, 128.5, 128.3, 128.1, 113.8, 113.7,
+
07.9, 101.0, 45.2, 37.1; HRMS (ESI) m/z calcd for C24
73.1440, found = 373.1439.
20 4
H O
[M+H] = 55.0, 45.9, 43.8, 43.7, 42.1, 40.0, 16.7, 14.1 ; HRMS (ESI) m/z calcd
+
3
for C25H23ClO [M+H] = 407.1414, found = 407.1416.
3
3
-(Benzo[d][1,3]dioxol-5-yl)-1-phenyl-5-p-tolylpentane-1,5-dione
o
3-(4-Chlorophenyl)-2-methyl-1,5-diphenylpentane-1,5-dione
(Syn isomer)
5d
5
1 mg, Yield: 66%; Light brown liquid; R
f
=
0.40 (ethyl
2
f
7 mg, Yield: 35%; Light yellow solid; m.p. 96-98 °C; R = 0.3 (ethyl
-1
-1
acetate/hexane, 1:5); IR (KBr, Cm ): 3057, 2925, 1681, 1254, 969,
acetate/hexane, 1:4); IR (KBr, Cm ): 2920, 1682, 1490, 1249, 1035,
1
1
8
(
7
32, 744; H NMR (400 MHz, CDCl
d, J = 7.6 Hz, 2H), 7.63 (m, 1H), 7.54 (t, J = 6.8 Hz, 3H), 7.43 (t, J =
.6 Hz, 2H), 7.28-7.25 (m, 2H), 7.17 (d, J = 7.9 Hz, 2H), 3.94-3.83 (m,
2H), 3.41 (dd, J = 16.2, 4.0 Hz, 1H), 3.24 (dd, J = 16.2, 9.2 Hz, 1H),
3
) : δ 8.07 (d, J = 8.4 Hz, 2H), 7.87
8
8
6
3
05; H NMR (400 MHz, CDCl ) : δ 7.94 (d, J = 7.5 Hz, 2H), 7.85 (d, J =
.2 Hz, 2H), 7.56-7.52 (m, 1H), 7.46-7.42 (m, 2H), 7.25-7.23 (m, 2H),
.77 (br s, 1H), 6.72-6.67 (m, 2H), 5.88 (m, 2H), 3.98 (quint, J = 6.9
13
Hz, 1H), 3.47-3.37 (m, 2H), 3.30-3.23 (m, 2H), 2.39 (s, 3H); C NMR
13
1
1
1
C
3
.03 (d, J = 6.5 Hz, 3H); C NMR (100 MHz, CDCl ) : δ 203.4, 198.2,
(100 MHz, CDCl
3
) : δ 198.6, 198.2, 147.7, 146.2, 144.0, 137.8, 136.9,
40.0, 136.7, 136.6, 133.3, 133.0, 132.4, 129.7, 128.8, 128.6, 128.5,
1
4
3
34.4, 133.1, 129.3, 128.6, 128.3, 128.2, 120.5, 108.4, 107.9, 100.9,
5.2, 45.1, 37.1, 21.7; HRMS (ESI) m/z calcd for C25
87.1596, found = 387.1596.
+
28.4, 128.1, 45.5, 43.7, 43.3, 16.6; HRMS (ESI) m/z calcd for
22 4
H O [M+H] =
+
24
H
21ClO
2
[M+H] = 377.1308, found = 377.1309.
2
4
3
-(4-Chlorophenyl)-2-methyl-1,5-diphenylpentane-1,5-dione 5d'
3
-Methyl-1,5-diphenylpentane-1,5-dione 3p
(
Anti isomer)
1
5
6 mg, Yield: 61%; H NMR (400 MHz, CDCl
3
) : δ 8.01-7.99 (m, 4H),
2
2 mg, Yield: 29%; Light brown liquid; R
f
=
0.34 (ethyl
7
.58-7.54 (m, 2H), 7.48-7.45 (m, 4H), 3.02-3.15 (m, 2H), 2.90-2.85
-1
1
3
acetate/hexane, 1:5); IR (KBr, Cm ): 3062, 2931, 1681, 1489, 1243,
1
7
(m, 3H), 1.09-1.07 (m, 3H); C NMR (100 MHz, CDCl
3
): δ 199.6,
1
013, 689; H NMR (400 MHz, CDCl
3
) : δ 7.84 (d, J = 7.7 Hz, 4H),
137.0, 133.0, 128.6, 128.1, 45.4, 26.6, 20.3.
.56-7.50 (m, 2H), 7.44-7.39 (m, 4H), 7.16 (q, J = 14.3, 8.5 Hz, 4H),
2
5
3.96-3.87 (m, 2H), 3.42 (d, J = 6.3 Hz, 2H), 1.28 (d, J = 6.3 Hz, 3H);
2
-Methyl-1,3,5-triphenylpentane-1,5-dione 5a
1
3
C NMR (100 MHz, CDCl
133.1, 129.3, 129.2, 128.7, 128.5, 128.4, 128.1, 128.0, 127.9, 45.7,
3
) : δ 202.9, 198.2, 141.3, 136.9, 136.5,
1
5
2
7
1
0 mg, Yield: 61%; H NMR (400 MHz, CDCl
3
) : δ 8.04 (d, J = 7.8 Hz,
+
4
3
2.3, 40.1, 14.6; HRMS (ESI) m/z calcd for C24
77.1308, found = 377.1310.
2
H21ClO [M+H] =
H), 7.87-7.83 (m, 3.5H), 7.58-7.57 (m, 1H), 7.51-7.47 (m, 3H), 7.42-
.37 (m, 3H), 7.27-7.23 (m, 3H), 7.19-7.17 (m, 3H), 3.95-3.94 (m,
.5H), 3.84-3.83 (m, 1H), 3.47-3.35 (m, 1.7H), 3.24 (dd, J = 16.0, 9.4
Hz, 1H), 1.27 (d, J = 6.0 Hz, 1.9H), 1.00 (d, J = 6.6 Hz, 3H); C NMR
100 MHz, CDCl ) : δ 203.8, 203.3, 198.6, 198.5, 142.9, 141.5, 137.1,
37.0, 136.9, 133.3, 133.0, 132.9, 128.8, 128.7, 128.6, 128.5, 128.4,
13
Acknowledgements
(
3
1
1
1
We thank the SERB, India for financial assistance. SRK thankful to
CSIR for a Fellowship. The authors thank Mr. Ramana Niddana for
28.2, 128.0, 127.9, 126.9, 126.5,46.0, 45.7, 44.4, 43.5, 42.8, 39.9,
6.7, 14.1.
This journal is © The Royal Society of Chemistry 2015
New J. Chem., 2015, 00, 1-3 | 5
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ARTICLE
NJC
carrying out the additional experiments required for revision of the
manuscript.
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Graphical Abstract
A facile Michael addition of unactivated ketones under Brønsted acid condition for the synthesis of 1,5-
diketones.