Iridium(I)-Catalyzed Alkylation Reactions to Form α-Alkylated Ketones

Article abstract of DOI:10.1021/acs.joc.8b00043

A highly effective and green procedure for the formation of α-alkylated ketones has been disclosed via the reaction of primary alcohols with secondary alcohols and ketones by using [IrCl(COD)(NHC)] complexes as a catalyst. Various α-alkylated ketones were obtained in high yields from the alkylation of alcohol with alcohol and ketone with alcohol through a borrowing hydrogen reaction by using 0.05-0.5 mol % iridium(I) and a catalytic amount of KOH (5-10 mol %) as the base under air atmosphere and within very short reaction times.

Full text of DOI:10.1021/acs.joc.8b00043

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Article
Iridium(I) Catalyzed Alkylation Reactions to form #-Alkylated Ketones
Sertaç Genç, Salih Günnaz, Bekir Cetinkaya, Süleyman Gülcemal, and Derya Gülcemal
J. Org. Chem., Just Accepted Manuscript • Publication Date (Web): 12 Feb 2018
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The Journal of Organic Chemistry
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Iridium(I) Catalyzed Alkylation Reactions to form α-Alkylated Ke-
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Sertaç Genç, Salih Günnaz, Bekir Çetinkaya, Süleyman Gülcemal, Derya Gülcemal*
Ege University, Chemistry Department, 35100 Bornova, Izmir, Turkey
Supporting Information
ABSTRACT: A highly effective and green procedure for the formation of α-alkylated ketones has been disclosed via the reaction
of primary alcohols with secondary alcohols and ketones by using [IrCl(COD)(NHC)] complexes as a catalyst. Various α-alkylated
ketones were obtained in high yields from the alkylation of alcohol with alcohol and ketone with alcohol through a borrowing hy-
drogen reaction by using 0.05-0.5 mol% iridium(I), catalytic amount of KOH (5-10 mol%) as the base under air atmosphere and
within very short reaction times.
the catalysts for hydrogen transfer reactions. These complexes
have exhibited very high catalytic activities in these transfor-
INTRODUCTION
Transition metal (TM) catalyzed carbon‒carbon bond for-
mation has become an important synthetic method in organic
chemistry to synthesize functionalized molecules.1 Among the
numerous protocols, alkylation represents a class of the most
important reactions for this transformation. Traditionally,
mutagenic alkyl halides have been employed as alkylating
reagents with equivalent or excess amount of strong base
which generates a stoichiometric amount of salts as waste.
Considering the demand of environmentally benign processes,
the use of alcohols as inexpensive and greener alkylating
agents via TM catalyzed hydrogen autotransfer (HA) process,
also designated borrowing hydrogen (BH) methodology, has
attracted great attention.2 In this context, α‒alkylation of ke-
tones with primary alcohols based on the HA procedure to
prepare biologically and synthetically important α‒alkylated
ketones using various transition metal complexes such as Mn, 3
Re,4 Fe, 5 Ru, 6 Co, 7 Rh, 8 Ir9 and Pd10 and catalyst free condi-
tions11 have been reported. More recently, α‒alkylated ke-
tones have been synthesized by direct dehydrogenative cou-
pling of primary alcohols with secondary alcohols using heter-
ogeneous12 and homogeneous Ru,13,6c Rh8b and Ir9e,13c,14 cata-
lysts. In most cases, a stoichiometric amount of base, a high
catalyst loading, or prolonged reaction times are needed. Cata-
lytic activities of recently reported various complexes in such
reactions to give α‒alkylated ketones are listed in Scheme 1.
Although considerable improvement has been made in this
field, the final turnover frequencies (TOF) of these catalysts
are still significantly low. Therefore, it is essential to develop
more effective and sustainable processes for this reaction with
a greater TOF and low amount of base.
mations and it was found that the electronic and steric charac-
ter of the NHC ligand perform a critical function for the cata-
lytic activity.16 In addition, similar complexes have found
application in the dehydrogenation of alcohols and selective
formation of β‒alkylated secondary alcohols from coupling of
primary and secondary.17 During the course of our continuing
work on IrI–NHC catalyzed acceptorless dehydrogenation of
alcohols, we reasonably envisioned that these complexes
might be used as the catalyst for cross‒coupling of primary
alcohols with secondary alcohols and also with ketones to give
α‒alkylated ketones.
In this study, we compare catalytic activities of a series of
[IrCl(COD)(NHC)] (COD = cyclooctadiene) complexes (1a-f)
(Scheme 2) and report a remarkably active catalytic system for
the reaction of primary alcohols with secondary alcohols and
also with ketones to give α‒alkylated ketones by using 0.05-
0.1 equiv. KOH under air with the highest TOF ever reported.
Notably, this system overcomes all the following limitations
for the reaction: including (1) the use of a stoichiometric
amount or expensive bases, (2) high catalyst loading, (3) an
excess amount of primary alcohol or any other additives, (4)
very long reaction times, (5) inert reaction conditions.
Scheme 1. Recent Examples of Catalysts for C‒C Bond
Formation Reactions to form α-Alkylated Ketones.
Ir-NHC (NHC = N-heterocyclic carbene) complexes have
revealed a wealth of catalytic reactions. Among them, transfer
hydrogenation (TH), a process that transfers hydrogen from 2-
propanol to an unsaturated molecule in combination with a
strong base, have received a great deal of attention in the past
decade.15 These iridium complexes have great advantages
including their remarkable tunable character, the ease of syn-
thesis and the high stability. We recently reported a series of
IrI–NHC complexes and the application of these complexes as
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Scheme 2. Preparation of IrI–NHC Complexes 1a-f Stud-
ied in This Work.
2
3
KOH
KOH
KOH
KOH
KOH
KOH
KOH
KOtBu
NaOH
KOH
–
1
1
1
1
1
2
2
2
2
2
2
2
2
100
100
100
100
100
100
100
100
100
100
0
62:38
44:56
15:85
60:40
68:32
93:7
91:9
90:10
86:14
73:27
–
1b
1
2
3
4
5
6
7
8
1c
4
1d
5
1e
6
1f
7
8d
1f
1f
9
1f
10
11e
12
13
14
1f
9
1f
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1f
–
KOH
0
–
KOH
12
30:70
[IrCl(COD)]2
aReaction Conditions: 2a (1.0 mmol), 3a (1.0 mmol), 1a-f (0.5
RESULTS AND DISCUSSION
b
mol%), base (10 mol%), toluene (2.0 mL), 130 ºC, under air. GC
Based on our previous experience on [IrCl(COD)(NHC)]
catalyzed TH reactions,16 we decided to prepare a set of
[IrCl(COD)(NHC)] complexes (1a-f) having electron deficient
and electron withdrawing benzyl substituents as wingtip on the
nitrogen atom of imidazole or 4,5-dichloroimidazole (Scheme
2). All the new complexes were prepared in high yields as air-
and moisture-stable yellow solids and were characterized by
NMR spectroscopy and HRMS analysis.
To probe the potential of these IrI-NHC catalysts for the
reaction of primary alcohols with secondary alcohols, 1-
phenylethanol (2a) and benzyl alcohol (3a) were selected as
benchmark substrates (Table 1). In the presence of 1a-f as the
catalyst (0.5 mol%) and KOH (10 mol%), the reaction was
carried out in toluene (2 mL) at 130 ºC under air for 1 h (en-
tries 1‒6). All the reactions resulted in complete conversion of
conversion. cRatios were determined by 1H NMR analyses. dReac-
tion was performed under an argon atmosphere. eKOH (5 mol%).
To examine the scope of the reaction, various secondary
and primary alcohols were reacted under the optimized condi-
tions (Scheme 3). All reactions resulted in complete conver-
sion of starting materials affording selective formation of the
corresponding ketone 4. Various electron‒rich or electron‒
deficient 1-arylethanols (2a–g) were effectively transformed
into the corresponding ketones (4aa–4ga) in high isolated
yields by using 1f (0.5 mol%) as the catalyst. Reactions of
electron‒rich substituted 1-phenylethanols (2b,c) afforded the
desired products 4ba and 4ca in 93 and 98% yields respective-
ly. Furthermore, 1-(2-naphthyl)ethanol (2d) and α‒tetralol (2e)
gave the corresponding ketones 4da and 4ea in 86 and 96%
yields, respectively. In the case of halogenated 1-
phenylethanols 2f and 2g longer reaction time (4 h) required to
obtain good selectivity and desired products 4fa and 4ga were
obtained in 73 and 72%. This result is consistent with our
previous observations on iridium‒catalyzed acceptorless de-
hydrogenative oxidation of secondary alcohols, where we
found that dehydrogenation of electron‒deficient secondary
alcohols were more difficult.18 We also investigated the reac-
tions with respect to primary alcohols. Transformation of 1-
phenylethanol with various primary alcohols including elec-
tron‒donating (3b–d), electron‒withdrawing (3e and 3f), more
sterically hindered (3g–i), heteroaromatic (3j) and aliphatic
(3k and 3l) gave the corresponding ketones 4ab–4al in 67–
94% isolated yield within 2–4 h.
substrates and complex 1f, which bore
a 1,3-bis(4-
trifluorobenzyl)-4,5-dichloroimidazol-2-ylidene ligand, pro-
vided the highest selectivity to ketone product 4aa (entry 6)
while more electron deficient complex 1d, which is one of the
most active NHC‒based catalysts for the transfer hydrogena-
tion of carbonyl compounds,16b affording selective formation
of alcohol product 4ʹaa (entry 4). Clearly, the electronic char-
acter of the NHC ligand is important for the selectivity. In-
creasing the reaction time to 2 h led to increase of the corre-
sponding α‒alkylated ketone (4aa:4ʹaa ratio 93:7) (entry 7).
The reaction conducted under an argon atmosphere was also
resulted in complete conversion of starting alcohols and af-
forded the 4aa selectively (entry 8). Other strong bases such as
KOtBu and NaOH resulted with slightly lower selectivity for
the formation of 4aa (entries 9 and 10). Reducing the amount
of KOH from 0.1 equiv. to 0.05 equiv. lowered the selectivity
of 4aa to 73:27 (entry 11). Additional experiments were car-
ried out in the absence of KOH or IrI-NHC catalyst and no
product formation was observed (entries 12 and 13). However,
with [IrCl(COD)]2 and 0.1 equiv. of KOH, only 12% conver-
sion was observed, which indicates the critical role of the
NHC ligand (entry 14).
After studying the iridium–catalyzed reaction of primary
alcohols with secondary alcohols to give α‒alkylated ketones,
we focused our interest on α‒alkylation of ketones with prima-
ry alcohols, a processes using HA methodology.3-11 Our initial
investigation focused on the α‒alkylation of acetophenone
(5a) (1.0 mmol) with 3a (1.0 mmol) in the presence of a very
low amount 1f (0.05 mol%) as catalyst and KOH (5.0 mol %)
at 130 °C and this reaction resulted in complete conversion of
substrates affording formation of 4aa with an isolated yield of
91% within 2 h (Scheme 4). Encouraged by the result, we
further expanded the reaction generality with respect to methyl
ketones (5b‒g) (Scheme 4). Methyl ketones with different
electronic nature all reacted with benzyl alcohol (3a) affording
the corresponding ketones 4ba–4ga with excellent isolated
yields (86–97%). Next, we examined the scope of α‒
alkylation of ketones with respect to primary alcohols. Aceto-
phenone (4a) reacted smoothly with a variety of primary alco-
hols (3b–l) to give excellent isolated yields (81–96%) of α‒
Table 1. Optimization of Reaction Conditionsa
time conv.b
ratioc
4aa:4ʹaa
entry
1
cat.
base
(h)
(%)
KOH
1
100
45:55
1a
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alkylated ketones (4ab–4al) irrespective of the electronic and
Scheme 4. Scope of α‒Alkylation of Ketones with Primary
Alcohols Catalyzed by Complex 1fa
1
2
3
4
steric nature of primary alcohol within 2 h. Comparing the
results in Scheme 3 with those in Scheme 4 shows that the α‒
alkylation of ketones is considerably easier than the direct
dehydrogenative coupling of primary alcohols with secondary
alcohols to produce 4, requiring lower catalyst and base load-
ings.
5
6
7
8
Scheme 3. Scope of Dehydrogenative Coupling of Primary
and Secondary Alcohols Catalyzed by Complex 1fa
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aReaction Conditions: Ketone (1.0 mmol), primary alcohol (1.0
mmol), 1f (0.05 mol%), base (5.0 mol%), toluene (1.0 mL), 130
ºC, under air. Isolated yields.
aReaction Conditions: Secondary alcohol (1.0 mmol), primary
alcohol (1.0 mmol), 1f (0.5 mol%), base (10 mol%), toluene (2.0
mL), 130 ºC, under air. Isolated yields.
Monitoring the time profile of the direct dehydrogenative
coupling of 2a with 3a revealed that the reaction is very fast
and results in complete conversion of substrates to 4aa and
4ʹaa with a ratio of 49:51 within 12.5 minutes (Figure 1).
Then, initially formed 4ʹaa gradually undergoes dehydrogena-
tion to form 4aa. From the above observations, a plausible
mechanism for this reaction can be proposed as shown in
Scheme 5.13a,14a The mechanism involves decoordination of Cl
in the presence of KOH to generate [Ir(COD)(NHC)]+ inter-
mediate. Then, dehydrogenation of 2 and 3 generates transient
iridium–hydride.17b The resulting ketone (5) and aldehyde (3ʹ)
may give the α,β‒unsaturated ketone in the presence of base.
This enone can be reduced to afford the 4ʹ and 4 by iridium–
hydride. Last of all, in the presence of catalyst, dehydrogena-
tion of 4ʹ gives the desired product 4. To gain further insight
into the reaction mechanism, the reaction of 2a and 3a in
Total conversion
4'aa
4aa
100
90
80
70
60
50
40
30
20
10
0
0
2.5
5
7.5 10 12.5 15 30 45 60 75 90 105 120
Time (min.)
1
toluene-d8 was monitored by H NMR spectroscopy. During
1
the reaction H NMR revealed two singlets in the hydridic
Figure 1. Time course of the direct dehydrogenative coupling of
benzyl alcohol with 1-phenylethanol. Reaction Conditions: 2a
(1.0 mmol), 3a (1.0 mmol), 1f (0.5 mol%), KOH (10 mol%),
region resonating at −9.34 and −10.87 ppm and persisted
throughout the reaction which indicated the presence of iridi-
um hydride species.
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MeOH (5 mL) and Et2O (30 mL) was added. The colorless solid that
separated out was filtered and washed with Et2O (2×20 mL) and dried
under reduced pressure (2.44 g, 91%). M.p. = 205 ºC. H NMR (400
toluene (2.0 mL), 130 ºC, under air. Conversions and ratios were
determined by 1H NMR analyses.
1
2
3
4
5
6
7
8
1
MHz, DMSO-d6, TMS, 25ºC, ppm): δ = 9.95 (s, 1 H, NCHN+), 7.75
(dd, J = 8.0 Hz, 8 H, Ar-H), 5.71 (s, 4 H, NCH2Ar). 13C NMR (100.6
MHz, DMSO-d6, TMS): δ = 137.8 (d, J = 6.0 Hz, NCHN+), 129.8 (q,
J(C,F) = 31.8 Hz), 129.6 (Ar-C), 125.9 (q, J(C,F) = 3.6 Hz), 124.4 (q,
J(C,F) = 272.4 Hz), 119.9 (NC=CN), 51.4 (NCH2Ar). 19F NMR (376
MHz, CDCl3, TMS, 25ºC, ppm): δ = ‒ 61.3. HRMS (APCI) m/z: [M–
Br]+ Calcd for C19H13BrCl2F6N2 453.0360; Found: 453.0351.
Scheme 5. Plausible Reaction Mechanism.
- H2
OH
O
OH
R2
OH
+
+
R1
R2
R1
R2
R1
Synthesis of IrI–NHC complexes used in this study. Under an
argon atmosphere, a mixture of La-f (0.5 mmol) and Ag2O (58 mg,
0.25 mmol) was suspended in degassed CH2Cl2 (10 mL) and stirred at
ambient temperature for 1 h shielded from light. [IrCl(COD)]2 (168
mg, 0.25 mmol) was then added to the suspension and the reaction
mixture was stirred at ambient temperature for more 12 h. The result-
ing suspension was filtered over Celite®. The remaining solid was
washed with CH2Cl2 (2×5 mL) and the solvent of the filtrate was
evaporated. The residue was purified by column chromatography on
silica gel (eluent: CH2Cl2) to give pure complex as a yellow solid.
Complexes 1b, 1c, 1e and 1f are new compounds and spectroscopic
data are given below.
Complex 1b. Yield: 85%, 305 mg. 1H NMR (400 MHz, CDCl3,
TMS, 25ºC, ppm): δ = 7.64 (d, 4 H, J = 8.0 Hz, Ar-H), 7.52 (d, 4 H, J
= 8.0 Hz, Ar-H), 6.71 (s, 2 H, NCH=CHN), 6.01 (d, J = 14.8 Hz, 2 H,
NCH2Ar), 5.58 (d, J = 14.8 Hz, 2 H, NCH2Ar), 4.69 (t, J = 2.8 Hz, 2
H, COD-CH), 2.90 (t, J = 2.8 Hz, 2 H, COD-CH), 2.21-2.08 (m, 4 H,
COD-CH2), 1.78-1.72 (m, 2 H, COD-CH2), 1.62-1.56 (m, 2 H, COD-
CH2). 13C NMR (100.6 MHz, CDCl3, TMS, 25ºC, ppm): δ = 182.1
(Ir-Ccarbene), 140.1 (Ar-C), 130.5 (d, J(C,F) = 32.0 Hz), 128.4 (Ar-C),
125.9 (q, J(C,F) = 4.0 Hz), 123.9 (d, J(C,F) = 271.0 Hz), 120.8
(NHC=CHN), 86.1 (COD-CH), 53.8 (NCH2Ar), 52.2 (COD-CH),
33.5 (COD-CH2), 29.9 (COD-CH2). 19F NMR (376 MHz, CDCl3,
TMS, 25ºC, ppm): δ = ‒ 62.7. Anal. Calcd for C27H26ClF6IrN2: C,
45.03; H, 3.64; N, 3.89. Found: C, 44.98; H, 3.66; N, 3.88. HRMS
(APCI) m/z: [M–Cl+H]+ Calcd for C27H27F6IrN2 684.1684 (59.5%);
Found 684.1718.
Complex 1c. Yield: 81%, 262 mg. 1H NMR (400 MHz, CDCl3,
TMS, 25ºC, ppm): δ = 7.32 (d, 4 H, J = 8.4 Hz, Ar-H), 6.89 (d, 4 H, J
= 8.4 Hz, Ar-H), 6.62 (s, 2 H, NCH=CHN), 5.75 (d, J = 14.4 Hz, 2 H,
NCH2Ar), 5.46 (d, J = 14.4 Hz, 2 H, NCH2Ar), 4.66 (t, J = 2.6 Hz, 2
H, COD-CH), 3.79 (s, 6 H, OCH3), 2.99 (t, J = 2.6 Hz, 2 H, COD-
CH), 2.21-2.16 (m, 4 H, COD-CH2), 1.76-1.68 (m, 2 H, COD-CH2),
1.64-1.57 (m, 2 H, COD-CH2). 13C NMR (100.6 MHz, CDCl3, TMS,
25ºC, ppm): δ = 180.3 (Ir-Ccarbene), 159.5 (Ar-C), 129.7 (Ar-C), 128.3
(Ar-C), 120.1 (NHC=CHN), 114.2 (Ar-C), 84.7 (COD-CH), 55.3
(OCH3), 53.4 (NCH2Ar), 51.8 (COD-CH), 33.6 (COD-CH2), 29.5
(COD-CH2). Anal. Calcd for C27H32ClIrN2O2: C, 50.34; H, 5.01; N,
4.35. Found: C, 50.41; H, 5.02; N, 4.31. HRMS (APCI) m/z: [M–Cl]+
Calcd for C27H32IrN2O2 609.2093; Found: 609.2094.
Complex 1e. Yield: 89%, 292 mg. 1H NMR (400 MHz, CDCl3,
TMS, 25ºC, ppm): δ = 7.38-7.29 (m, 10 H, Ar-H), 5.83 (dd, J = 15.6
Hz, 4 H, NCH2Ar), 4.71 (t, J = 2.8 Hz, 2 H, COD-CH), 2.69 (t, J =
2.8 Hz, 2 H, COD-CH), 2.17-2.08 (m, 2 H, COD-CH2), 1.93-1.84 (m,
2 H, COD-CH2), 1.71-1.64 (m, 2 H, COD-CH2), 1.47-1.40 (m, 2 H,
COD-CH2). 13C NMR (100.6 MHz, CDCl3, TMS, 25ºC, ppm): δ =
182.7 (Ir-Ccarbene), 135.5 (NC=CN), 128.7 (Ar-C), 127.9 (Ar-C), 127.2
(Ar-C), 116.8 (Ar-C), 86.7 (COD-CH), 53.6 (NCH2Ar), 53.2 (COD-
CH), 33.3 (COD-CH2), 29.2 (COD-CH2). Anal. Calcd for
C25H26Cl3IrN2: C, 45.98; H, 4.01; N, 4.29. Found: C, 46.07; H, 3.97;
N, 4.27. HRMS (APCI) m/z: [M–Cl]+ Calcd for C25H26Cl2IrN2
617.1102; Found: 617.1096.
2
3
4'
4
[Ir]-Cl
base
9
- Cl
10
11
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[Ir]+
- 2H2
+ 2H2
+ H2
[Ir]-H
O
O
base
- H2O
R2
+
O
R1
R2
R1
5
3'
enone
[Ir] = [Ir(COD)(NHC)]
CONCLUSIONS
In conclusion, we have synthesized a series of easily tuna-
ble [IrCl(COD)(NHC)] complexes having electron deficient
and electron withdrawing benzyl substituents as wingtip on the
nitrogen atom of imidazole or 4,5-dichloroimidazole. The
complex 1f proved that it is a general and highly effective
catalyst for the direct dehydrogenative cross‒coupling reac-
tions under air atmosphere within very short reaction times.
Importantly, this catalytic system revealed exceptionally high
TOFs (up to 98 h‒1 for reaction of secondary alcohols with
primary alcohols and up to 970 h‒1 for α‒alkylation of ketones
with primary alcohols). To the best of our knowledge, these
TOF values are the highest among all the reported transition
metal complexes for these transformations.
EXPERIMENTAL SECTION
Experimental Details. Experiments involving air or moisture sen-
sitive reagents were performed under an atmosphere of dry argon
using standard Schlenk techniques. Unless otherwise specified, all
reagents were obtained commercially and used without further purifi-
cation. [IrCl(COD)]2 was prepared according to the published proce-
dure.19 Imidazolium salts La-c18, Ld16b, Le20 and complexes 1a21 and
1d16b were synthesized according to published procedure and the
physical properties and spectroscopic data of the obtained compound
are in accordance with previous reports. NMR spectra were recorded
on Varian AS 400 Mercury NMR spectrometer and reported in units
of parts per million (ppm) relative to tetramethyl silane (δ = 0 ppm) or
CDCl3 (δ = 7.26 ppm for 1H and δ = 77.0 ppm for 13C NMR). Melting
points measured on Gallenkamp electrothermal melting point appa-
ratus without correction. HRMS were carried out on Agilent 6530
Accurate-Mass Q-TOF mass spectrometer at Atatürk University East
Anatolia High Technology Application and Research Center. Gas
chromatography (GC) analysis was performed on an Agilent 6890N
gas chromatograph with a HP-5 Agilent 19091J-413 column.
Synthesis of imiazolium salt Lf. A mixture of 4,5-dichloro-1-H-
imidazole (685 mg, 5.0 mmol) and K2CO3 (760 g, 11 mmol) was
suspended in CH3CN (10 mL) and stirred at ambient temperature for
1 h. 4-(Trifluoromethyl)benzyl bromide (1.20 g, 5 mmol) was then
added to the suspension. The reaction mixture was stirred under reflux
conditions for 2 h. The solution was filtered-off and the solvent was
removed under reduced pressure. To the resulting crude product
second portion of 4-(Trifluoromethyl)benzyl bromide (1.20 g, 5
mmol) was added and stirred at 160 ºC for 1 h. The colorless mixture
first melted and then solidified. The resulting solid dissolved in
Complex 1f. Yield: 90%, 356 mg. 1H NMR (400 MHz, CDCl3,
TMS, 25ºC, ppm): δ = 7.65 (d, 4 H, J = 8.0 Hz, Ar-H), 7.55 (d, 4 H, J
= 8.0 Hz, Ar-H), 6.07 (d, J = 15.6 Hz, 2 H, NCH2Ar), 5.72 (d, J =
14.8 Hz, 2 H, NCH2Ar), 4.75 (t, J = 2.8 Hz, 2 H, COD-CH), 2.67 (t, J
= 2.8 Hz, 2 H, COD-CH), 2.18-2.09 (m, 2 H, COD-CH2), 1.99-1.90
(m, 2 H, COD-CH2), 1.77-1.69 (m, 2 H, COD-CH2), 1.56-1.49 (m, 2
H, COD-CH2). 13C NMR (100.6 MHz, CDCl3, TMS, 25ºC, ppm): δ =
182.3 (Ir-Ccarbene), 139.1 (Ar-C), 130.4 (q, J(C,F) = 32.7 Hz), 127.7
(Ar-C), 125.8 (q, J(C,F) = 3.6 Hz), 123.9 (d, J(C,F) = 269.1 Hz),
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116.9 (NC=CN), 87.9 (COD-CH), 53.3 (NCH2Ar), 53.1 (COD-CH),
199.3, 144.0, 140.0, 133.3, 132.5, 129.3, 128.7, 128.4, 127.5, 126.6,
126.1, 49.5, 35.7, 28.6, 27.7.
33.3 (COD-CH2), 29.2 (COD-CH2). 19F NMR (376 MHz, CDCl3,
TMS, 25ºC, ppm): δ = ‒ 62.7. Anal. Calcd for C27H24Cl3F6IrN2: C,
41.10; H, 3.07; N, 3.55. Found: C, 41.04; H, 3.04; N, 3.51. HRMS
(APCI) m/z: [M–Cl]+ Calcd for C27H24Cl2F6IrN2753.0850; Found:
753.0841.
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1-(4-Bromophenyl)-3-phenylpropan-1-one (4fa).5,7,14a,26 White sol-
id; 73% yield (211 mg) for Scheme 3 and 90% yield (260 mg) for
Scheme 4. 1H NMR (CDCl3, 400 MHz) δ (ppm): 7.81 (d, J = 8.8 Hz,
2H), 7.59 (d, J = 8.4 Hz, 2H), 7.32-7.21 (m, 5H), 3.26 (t, J = 7.6 Hz,
2H), 3.06 (t, J = 7.6 Hz, 2H); 13C NMR (CDCl3, 100 MHz) δ (ppm):
198.1, 141.0, 135.6, 131.9, 129.6, 128.6, 128.4, 128.2, 126.2, 40.4,
30.1.
General procedure for the dehydrogenative coupling of sec-
ondary alcohols with primary alcohols to give α-alkylated ke-
tones. In a 20 mL reaction tube (1 cm × 20 cm) with a condenser
were added KOH (5.6 mg, 0.1 mmol, 0.1 equiv.) secondary alcohol
(1.0 mmol), primary alcohol (1.0 mmol) and a solution of complex 1
(0.005 mmol, 0.5 mol%) in toluene (2.0 mL) under air atmosphere.
The reaction mixture was vigorously stirred (1200 rpm) under reflux
in a preheated oil bath at 130 ºC for 2–4 h. Then the reaction mixture
was cooled to ambient temperature and a 10 ꢀL solution was syringed
out for GC analysis. The solvent was evaporated and the crude prod-
uct was submitted for NMR analysis to calculate the conversion and
product selectivity (4:4ʹ). All the crude products were combined after
analysis and purified by silica gel column chromatography using
hexane and ethyl acetate (9:1) mixture as eluent to afford the desired
ketone.
1-(4-Chlorophenyl)-3-phenylpropan-1-one (4ga).5,7,14a,27 White sol-
id; 72% yield (176 mg) for Scheme 3 and 86% yield (210 mg) for
Scheme 4. 1H NMR (CDCl3, 400 MHz) δ (ppm): 7.89 (d, J = 8.8 Hz,
2H), 7.42 (d, J = 8.8 Hz, 2H), 7.32-7.19 (m, 5H), 3.27 (t, J = 7.4 Hz,
2H), 3.06 (t, J = 7.6 Hz, 2H); 13C NMR (CDCl3, 100 MHz) δ (ppm):
197.9, 141.1, 139.5, 135.2, 129.4, 129.0, 128.9, 128.6, 128.5, 128.4,
126.2, 40.4, 30.1.
1-Phenyl-3-(p-tolyl)propan-1-one (4ab).6f,7,9d White solid; 93%
yield (209 mg) for Scheme 3 and 92% yield (206 mg) for Scheme 4.
1H NMR (CDCl3, 400 MHz) δ (ppm): 7.99 (d, J = 8.0 Hz, 2H), 7.56
(tt, J1 = 7.2 Hz, J2 = 1.2 Hz, 1H), 7.49-7.45 (m, 2H), 7.19-7.13 (m,
4H), 3.30 (t, J = 7.6 Hz, 2H), 3.07 (t, J = 8.0 Hz, 2H), 2.36 (s, 3H);
13C NMR (CDCl3, 100 MHz) δ (ppm): 199.3, 138.2, 137.0, 135.6,
133.0, 129.2, 128.6, 128.3, 128.1, 40.6, 29.8, 21.0.
3-(4-Methoxyphenyl)-1-phenylpropan-1-one (4ac).6,7,9,12 White sol-
id; 91% yield (219 mg) for Scheme 3 and 96% yield (231 mg) for
Scheme 4. 1H NMR (CDCl3, 400 MHz) δ (ppm): 7.97 (d, J = 8.0 Hz,
2H), 7.56 (tt, J1 = 7.2 Hz, J2 = 2.8 Hz, 1H), 7.45 (t, J = 7.6 Hz, 2H),
7.18 (d, J = 8.8 Hz, 2H), 6.85 (d, J = 9.2 Hz, 2H), 3.79 (s, 3H), 3.28
(t, J = 7.2 Hz, 2H), 3.03 (t, J = 8.0 Hz, 2H); 13C NMR (CDCl3, 100
MHz) δ (ppm): 199.3, 158.0, 136.9, 133.3, 132.9, 129.3, 128.6, 128.0,
113.9, 55.3, 40.7, 29.3.
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General procedure for the α-alkylation of ketones with primary
alcohols to give α-alkylated ketones. In a 20 mL reaction tube (1 cm
× 20 cm) with a condenser were added KOH (2.8 mg, 0.05 mmol,
0.05 equiv.) ketone (1.0 mmol), primary alcohol (1.0 mmol) and a
solution of complex 1 (0.0005 mmol, 0.05 mol%) in toluene (1.0 mL)
under air atmosphere. The reaction mixture was vigorously stirred
(1200 rpm) under reflux in a preheated oil bath at 130 ºC for 2–4 h.
Then the reaction mixture was cooled to ambient temperature and a
10 ꢀL solution was syringed out for GC analysis. The solvent was
evaporated and the crude product was submitted for NMR analysis to
calculate the conversion. All the crude products were combined after
analysis and purified by silica gel column chromatography using
hexane and ethyl acetate (9:1) mixture as eluent to afford the desired
ketone.
3-(4-Isopropylphenyl)-1-phenylpropan-1-one (4ad).12b,14a Colorless
oil; 87% yield (220 mg) for Scheme 3 and 90% yield (227 mg) for
Scheme 4. 1H NMR (CDCl3, 400 MHz) δ (ppm): 8.01 (d, J = 7.2 Hz,
2H), 7.58 (t, J = 7.2 Hz, 1H), 7.48 (t, J = 7.6 Hz, 2H), 7.26-7.21 (m,
5H), 3.33 (t, J = 7.6 Hz, 2H), 3.10 (t, J = 8.0 Hz, 2H), 2.98-2.91 (m,
1H), 1.31 (d, J = 6.8 Hz, 6H), ;
13C NMR (CDCl3, 100 MHz) δ
(ppm): 199.3, 146.7, 138.6, 137.0, 133.0, 128.6, 128.4, 128.1, 126.6,
1,3-Diphenylpropan-1-one (4aa).5,6f,7,14a,22 White solid; 89% yield
1
(187 mg) for Scheme 3 and 91% yield (191 mg) for Scheme 4. H
NMR (CDCl3, 400 MHz) δ (ppm): 7.98 (d, J = 7.6 Hz, 2H), 7.57 (t, J
= 7.4 Hz, 1H), 7.47 (t, J = 7.6 Hz, 2H), 7.34-7.21 (m, 5H), 3.32 (t, J =
7.6 Hz, 2H), 3.10 (t, J = 7.6 Hz, 2H); 13C NMR (CDCl3, 100 MHz) δ
(ppm): 199.1, 141.3, 136.9, 133.0, 128.6, 128.6, 128.5, 128.0, 126.1,
40.4, 30.2.
3-Phenyl-1-(p-tolyl)propan-1-one (4ba).14a,23 White solid; 93%
yield (209 mg) for Scheme 3 and 97% yield (218 mg) for Scheme 4.
1H NMR (CDCl3, 400 MHz) δ (ppm): 7.89 (d, J = 8.0 Hz, 2H), 7.34-
7.23 (m, 7H), 3.29 (t, J = 7.4 Hz, 2H), 3.09 (t, J = 7.6 Hz, 2H), 2.42
(s, 3H); 13C NMR (CDCl3, 100 MHz) δ (ppm): 198.8, 143.8, 141.4,
134.5, 129.3, 128.5, 128.4, 128.2, 126.1, 40.3, 30.3, 21.6.
40.6, 33.8, 29.8, 24.1.
3-(4-Bromophenyl)-1-phenylpropan-1-one (4ae).7,9d,14a,28 White sol-
id; 81% yield (234 mg) for Scheme 3 and 92% yield (266 mg) for
Scheme 4. 1H NMR (CDCl3, 400 MHz) δ (ppm): 7.95 (d, J = 7.6 Hz,
2H), 7.56 (t, J = 7.0 Hz, 1H), 7.45 (t, J = 7.4 Hz, 2H), 7.41 (d, J = 8.4
Hz, 2H), 7.13 (d, J = 8.4 Hz, 2H), 3.28 (t, J = 7.4 Hz, 2H), 3.03 (t, J =
7.4 Hz, 2H); 13C NMR (CDCl3, 100 MHz) δ (ppm): 198.7, 140.2,
136.7, 133.1, 131.5, 130.2, 128.6, 127.9, 119.8, 40.0, 29.4.
3-(4-Chlorophenyl)-1-phenylpropan-1-one (4af).7,9d,14a,27 White
solid; 74% yield (181 mg) for Scheme 3 and 94% yield (230 mg) for
Scheme 4. 1H NMR (CDCl3, 400 MHz) δ (ppm): 7.95 (d, J = 7.6 Hz,
2H), 7.56 (t, J = 7.2 Hz, 1H), 7.45 (t, J = 8.0 Hz, 2H), 7.26 (d, J = 8.4
Hz, 2H), 7.18 (d, J = 8.4 Hz, 2H), 3.28 (t, J = 7.6 Hz, 2H), 3.05 (t, J =
7.4 Hz, 2H); 13C NMR (CDCl3, 100 MHz) δ (ppm): 198.7, 139.7,
136.7, 133.1, 131.8, 129.8, 128.6, 128.5, 127.9, 40.09, 29.38.
3-(2-Chlorophenyl)-1-phenylpropan-1-one (4ag).9c White solid;
67% yield (164 mg) for Scheme 3 and 85% yield (208 mg) for
Scheme 4. 1H NMR (CDCl3, 400 MHz) δ (ppm): 7.97 (d, J = 8.0 Hz,
2H), 7.56 (tt, J1 = 7.4 Hz, J2 = 1.4 Hz, 1H), 7.45 (t, J = 7.6 Hz, 2H),
7.37-7.30 (m, 2H), 7.22-7.14 (m, 2H), 3.32 (t, J = 8.0 Hz, 2H), 3.18 (t,
J = 7.4 Hz, 2H); 13C NMR (CDCl3, 100 MHz) δ (ppm): 198.9, 138.8,
136.8, 133.9, 133.1, 130.8, 129.6, 128.6, 128.0, 127.7, 126.7, 38.4,
28.3.
1-(4-Methoxyphenyl)-3-phenylpropan-1-one (4ca).3,7,14a,24 White
solid; 98% yield (235 mg) for Scheme 3 and 96% yield (231 mg) for
Scheme 4.. 1H NMR (CDCl3, 400 MHz) δ (ppm): 7.95 (d, J = 8.8 Hz,
2H), 7.32-7.19 (m, 5H), 6.93 (d, J = 8.8 Hz, 2H), 3.86 (s, 3H), 3.25 (t,
J = 7.8 Hz, 2H), 3.07 (t, J = 7.6 Hz, 2H); 13C NMR (CDCl3, 100
MHz) δ (ppm): 197.8, 163.4, 141.5, 130.3, 130.0, 128.5, 128.4, 126.1,
113.7, 55.4, 40.1, 30.3.
1-(Naphthalen-2-yl)-3-phenylpropan-1-one (4da).5,7,14a,25 White
solid; 86% yield (224 mg) for Scheme 3 and 94% yield (245 mg) for
1
Scheme 4. H NMR (CDCl3, 400 MHz) δ (ppm): 8.47 (s, 1H), 8.06
(dd, J1 = 7.6 Hz, J2 = 2.0 Hz, 1H), 7.95 (d, J = 8.0 Hz, 1H), 7.89 (t, J
= 7.2 Hz, 2H), 7.63-7.53 (m, 2H), 7.37-7.29 (m, 4H), 7.27-7.20 (m,
1H), 3.45 (t, J = 7.6 Hz, 2H), 3.16 (t, J = 7.6 Hz, 2H); 13C NMR
(CDCl3, 100 MHz) δ (ppm): 199.1, 141.4, 135.6, 134.2, 132.5, 129.6,
129.5, 129.1, 128.6, 128.5, 128.4, 128.4, 127.7, 126.7, 126.2, 123.8,
40.5, 30.3.
2-Benzyl-3,4-dihydronaphthalen-1-one (4ea).5,7,11,14a Yellow oil;
96% yield (227 mg) for Scheme 3 and 89% yield (210 mg) for
Scheme 4. 1H NMR (CDCl3, 400 MHz) δ (ppm): 8.11 (d, J = 7.6 Hz,
1H), 7.48 (t, J = 7.4 Hz, 1H), 7.35-7.22 (m, 7H), 3.52 (dd, J1 = 13.6
Hz, J2 = 4.0 Hz, 1H), 2.99-2.88 (m, 2H), 2.81-2.65 (m, 2H), 2.16-2.09
(m, 1H), 1.86-1.75 (m, 1H); 13C NMR (CDCl3, 100 MHz) δ (ppm):
3-(2,4,6-Trimethylphenyl)-1-phenylpropan-1-one (4ah).29 White
solid; 88% yield (222 mg) for Scheme 3 and 82% yield (207 mg) for
Scheme 4. 1H NMR (CDCl3, 400 MHz) δ (ppm): 7.96 (d, J = 7.2 Hz,
2H), 7.57 (t, J = 7.6 Hz, 1H), 7.46 (t, J = 7.6 Hz, 2H), 6.88 (s, 2H),
3.14-3.02 (m, 4H), 2.32 (s, 6H), 2.27 (s, 3H); 13C NMR (CDCl3, 100
MHz) δ (ppm): 199.5, 136.9, 136.1, 135.5, 134.8, 133.1, 129.1, 128.7,
128.1, 38.0, 23.8, 20.9, 19.8.
3-(2-Methoxyphenyl)-1-phenylpropan-1-one (4ai).3,7 White solid;
92% yield (221 mg) for Scheme 3 and 96% yield (231 mg) for
1
Scheme 4. H NMR (CDCl3, 400 MHz) δ (ppm): 7.99 (t, J = 6.8 Hz,
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2H), 7.55 (t, J = 7.8 Hz, 1H), 7.46 (t, J = 7.4 Hz, 2H), 7.24-7.20 (m,
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L.-Y.; Liu, C.-Y.; Ren, Z.-G.; Young, D. J.; Lang, J.-P. Tetrahedron
2017, 73, 2374−2381. (c) Chang, W.; Gong, X.; Wang, S.; Xiao, L.-
P.; Song, G. Org. Biomol. Chem. 2017, 15, 3466−3471. (d) Yang, Y.;
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1433−1439. (e) Schlepphorst, C.; Maji, B.; Glorius, F. ACS Catal.
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Ramon, D. J.; Yus, M. Tetrahedron 2005, 46, 3683.
2H), 6.93-6.86 (m, 2H), 3.84 (s, 3H), 3.28 (t, J = 7.8 Hz, 2H), 3.07 (t,
J = 7.8 Hz, 2H); 13C NMR (CDCl3, 100 MHz) δ (ppm): 199.9, 157.5,
137.0, 132.9, 130.2, 129.6, 128.5, 128.1, 127.5, 120.6, 110.3, 55.2,
38.9, 25.7.
3-(Furan-2-yl)-1-phenylpropan-1-one (4aj).6f,14a Yellow oil; 80%
yield (160 mg) for Scheme 3 and 85% yield (170 mg) for Scheme 4.
1H NMR (CDCl3, 400 MHz) δ (ppm): 7.98 (d, J = 7.2 Hz, 2H), 7.57
(tt, J1 = 7.2 Hz, J2 = 2.8 Hz, 1H), 7.46 (t, J = 8.6 Hz, 2H), 7.31 (d, J =
1.6 Hz, 1H), 6.28 (dd, J1 = 3.0 Hz, J2 = 1.8 Hz, 1H), 6.05 (d, J = 3.2
Hz, 1H), 3.34 (t, J = 7.6 Hz, 2H), 3.10 (t, J = 7.4 Hz, 2H); 13C NMR
(CDCl3, 100 MHz) δ (ppm): 198.6, 154.7, 141.1, 136.8, 133.1, 128.6,
128.0, 110.2, 105.3, 36.9, 22.5.
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1-Phenylnonan-1-one (4ak).30 Colorless oil; 91% yield (199 mg)
for Scheme 3 and 81% yield (177 mg) for Scheme 4. 1H NMR
(CDCl3, 400 MHz) δ (ppm): 7.95 (d, J = 8.0 Hz, 2H), 7.53 (t, J = 7.4
Hz, 1H), 7.44 (t, J = 7.6 Hz, 2H), 2.95 (t, J = 7.4 Hz, 2H), 1.77-1.69
(m, 2H), 1.39-1.27 (m, 10H), 0.88 (t, J = 7.0 Hz, 3H); 13C NMR
(CDCl3, 100 MHz) δ (ppm): 200.5, 137.1, 132.7, 128.5, 128.0, 38.6,
31.8, 29.4, 29.4, 29.1, 24.4, 22.6, 14.0.
(8) (a) Wang, R.; Huang, L.; Du, Z.; Feng, H. J. Orgmet. Chem..
2017, 846, 40−43. (b) Yu, X.; Wang, Q. Y.; Wu, Q. J.; Wang, D. W.
Russ. J. Gen. Chem. 2016, 86, 178−183.
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82, 1943−1950. (b) Quan, X.; Kerdphon, S.; Andersson, P. G. Chem.
−Eur. J. 2015, 21, 3576−3579. (c) Wang, D.; Zhao, K.; Ma, P.; Xu,
C.; Ding, Y. Tetrahedron Lett. 2014, 55, 7233−7235. (d) Li, F.; Ma,
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1-Phenyldecan-1-one (4al).7,14a,31 Colorless oil; 94% yield (218
1
mg) for Scheme 3 and 85% yield (198 mg) for Scheme 4. H NMR
(CDCl3, 400 MHz) δ (ppm): 7.95 (d, J = 8.8 Hz, 2H), 7.54 (t, J = 7.2
Hz, 1H), 7.45 (t, J = 7.6 Hz, 2H), 2.95 (t, J = 7.4 Hz, 2H), 1.77-1.70
(m, 2H), 1.40-1.27 (m, 12H), 0.88 (t, J = 7.0 Hz, 3H); 13C NMR
(CDCl3, 100 MHz) δ (ppm): 200.4, 137.1, 132.8, 128.5, 128.0, 38.6,
31.9, 29.5, 29.4, 29.4, 29.3, 24.4, 22.6, 14.1.
(10) Mamidala, R.; Samser, S.; Sharma, N.; Lourderaj, U.; Venka-
tasubbaiah, K. Organometallics 2017, 36, 3343−3351.
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ASSOCIATED CONTENT
Supporting Information
(12) (a) Yoshida, K.; Kon, K.; Shimizu, K. Top. Catal. 2016, 59,
1740−1747. (b) Liu, X.; Ding, R.-S.; He, Lin.; Liu, Y.-M.; Cao, Y.;
He, H.-Y.; Fan, K.-N. ChemSusChem 2013, 6, 604−608. (c) R.; Yus,
M.; Ramón, D. J. Chem. Commun. 2012, 48, 7628−7630. (d) Shimi-
zu, K.; Sato, R.; Satsuma, A. Angew. Chem., Int. Ed. 2009, 48,
3982−3986. (e) Cho, C. S.; Ren, W. X.; Shim, S. C. Bull. Korean
Chem. Soc. 2005, 26, 1611−1613.
The Supporting Information is available free of charge on the
ACS Publications website.
Traces of 1H, 13C NMR and HRMS spectra (PDF)
(13) (a) Sahoo, A.R.; Lalitha, G.; Murugesh, G.; Bruneau, C.;
Sharma, G. V. M.; Suresh, S.; Achard, M. J. Org. Chem. 2017, 82,
10727−10731. (b) Jumde, V. R.; Gonsalvi, L.; Guerriero, A.; Peruzzi-
ni, M.; Taddei, M. Eur. J. Org. Chem. 2015, 1829−1833. (c) Musa,
S.; Ackermann, L.; Gelman, D. Adv. Synth. Catal. 2013, 355,
3077−3080.
AUTHOR INFORMATION
Corresponding Author
* E-mail: derya.gulcemal@ege.edu.tr
Notes
The authors declare no competing financial interest.
(14) (a) Wang, R.; Ma, J.; Li, F. J. Org. Chem. 2015, 80,
10769−10776. (b) Wang, D.; Zhao, K.; Yu, X.; Miao, H.; Ding, Y.
RSC Adv. 2014, 4, 42924−42929.
ACKNOWLEDGMENT
(15) Gülcemal, S.; Çetinkaya, B. Reduction Reactions with NHC-
Bearing Complexes. In N-heterocyclic carbenes: From laboratory
curiosities to efficient synthetic tools; S. Díez-González (Ed.) 2nd Ed.;
Royal Society of Chemistry, Cambridge, 2017; pp 484–533.
The authors thank to Ege University and The Turkish Academy of
Science for the financial support. We also thank to Asst. Prof. Dr.
Haydar Kılıç for HRMS analyses.
REFERENCES
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