Catalytic acceptorless dehydrogenative coupling of arylhydrazines and alcohols for the synthesis of arylhydrazones

Article abstract of DOI:10.1021/jo501161u

The direct synthesis of arylhydrazones via catalytic acceptorless dehydrogenative coupling of arylhydrazines and alcohols has been accomplished. More importantly, complete selectivity for arylhydrazones and none of the N-alkylated byproducts were generated in this process, which exhibit new potential and provide a new horizon for the development of catalytic acceptorless dehydrogenative coupling reactions.

Full text of DOI:10.1021/jo501161u

Article
pubs.acs.org/joc
Catalytic Acceptorless Dehydrogenative Coupling of Arylhydrazines
and Alcohols for the Synthesis of Arylhydrazones
Feng Li,* Chunlou Sun, and Nana Wang
Key Laboratory for Soft Chemistry and Functional Materials, Ministry of Education, Nanjing University of Science and Technology,
Nanjing 210094, People’s Republic of China
S
* Supporting Information
ABSTRACT: The direct synthesis of arylhydrazones via catalytic acceptorless dehydrogenative coupling of arylhydrazines and
alcohols has been accomplished. More importantly, complete selectivity for arylhydrazones and none of the N-alkylated
byproducts were generated in this process, which exhibit new potential and provide a new horizon for the development of
catalytic acceptorless dehydrogenative coupling reactions.
based on the “hydrogen autotransfer (or hydrogen-borrowing)
process” (Scheme 1).12 Moreover, the scope of substrates is still
INTRODUCTION
■
Arylhydrazones constitute an important class of nitrogen-
containing compounds that have been widely utilized as key
synthetic intermediates in the construction of indoles,1
carbazoles,2 pyrazoles,3 indazoles,4 and other heterocyclic
compounds.5 They also exhibit remarkable biological activities,6
including applications as inhibitors of macrophage migration
inhibitory factor (MIF),6a trypanosomatid parasites antago-
nists,6b monoamine oxidase (MAO) inhibitors,6c protein
tyrosine phosphatase-2 (Shp2) inhibitors,6d and potent
antimalarial agents.6e Traditionally, arylhydrazones are synthe-
sized via the condensation of arylhydrazines or aryldiazonium
salts with carbonyl compounds.1,7 Pd-catalyzed coupling of
hydrazones with aryl halides has been developed for the
preparation of arylhydrazones.8 However, the latter procedure
suffers from the generation of the stoichiometric amount of
halogen acids as harmful byproducts.
Scheme 1. Dehydrogenative Coupling of Amines with
Alcohols for the Synthesis of Imines
limited to amines and these catalysts are generally not
commercially available, which limited the application of this
strategy. Despite the potential importance, the direct synthesis
of arylhydrazones via the acceptorless dehydrogenative
coupling of arylhydrazines and alcohols remains unexplored.13
Recently, we have reported transition-metal-catalyzed
regioselective N-alkylation with alcohols as alkylating agents
for the preparation of 2-(N-alkylamino)azoles,14a−d 2-(N-
alkylamino)quinazolines,14e N,N′-alkylarylureas, and N,N′-
dialkylureas.14f We have also demonstrated the direct synthesis
of N-alkylated amides from aldoximes and alcohols via tandem
rearrangement/N-alkylation reactions catalyzed by a Ru/Ir dual
catalyst system,15 Ir-catalyzed direct coupling of indoles with
methanol to 3,3′-bisindoles (3,3′-BIM’s),16 and the N-
alkylation of sulfonamides with alcohols in water catalyzed by
In 2010, Milstein and co-workers reported an efficient
strategy for the synthesis of imines via direct coupling of amines
and alcohols with the liberation of hydrogen gas catalyzed by
PNP-type ruthenium princer complexes.9 This protocol is
apparently attractive because alcohols are readily accessible,
inexpensive, low toxic, and easy to handle and store. Inspired by
Milstein’s research, several groups developed further this
transformation by using other transition-metal complexes,10
such as a NHC-type ruthenium complex,10a ruthenium complex
with a PNP-pincer-type phosphaalkene ligand,10b bifunctional
ruthenium PCP pincer complex,10c POP-type osmium
complex,10d and cationic cobalt(II) alkyl complex.10e Although
significant advances have been made,11 it is still extremely
challenging to control selectivity of reactions. In the above
process, the resulting imines undergo easily the hydrogenation
by the metal hydride species formed in the dehydrogenative
step of alcohols, and thus, N-alkylated amines would be
generated inevitably as byproducts (even with high proportion)
Received: May 25, 2014
© XXXX American Chemical Society
A
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the water-soluble iridium complex [Cp*Ir(6,6′-(OH)2bpy)-
(H2O)][OTf]2.17 As part of a continuing interest in exploring
new potential of alcohols as electrophiles, herein we wish to
report the direct synthesis of arylhydrazones via catalytic
acceptorless dehydrogenative coupling of arylhydrazines and
alcohols.
alcohols was examined, and these results are summarized in
Table 2. Similar to the case of benzyl alcohol 1a, reactions with
benzylic alcohols bearing one or two electron-donating groups,
such as methyl 2b−2c, isopropyl 2d, methoxy 2e, and
dimethoxy 2f, afforded the corresponding products 3ab−3af
in 82−89% yields (Table 2, entries 1−5). Benzylic alcohols
bearing one or two halogen atoms, such as fluoro 2g, chloro
2h−2i, and bromo 2j, were converted into the desired products
3ag−3aj in 75−87% yields (Table 2, entries 6−9). When
benzylic alcohols bearing a strong electron-withdrawing group,
such as trifluoromethyl 2k and trifluoromethoxy 2l, were used
as substrates, products 3ak and 3al were obtained in 81% and
88% yields, respectively, although 1 equiv of base was required
(Table 2, entries 10−11). This coupling was also applied to
naphthalenemethanols 2m−2n, thiophenylmethanol 2o, and
pyridinylmethanol 2p, affording the desired products 3am−3ap
in 78−87% yields (Table 2, entries 12−15). In the case of a
challenging secondary alcohol with high steric hindrance 2q,
the corresponding product 3aq could be successfully obtained
in 52% yield (Scheme 2).19
RESULTS AND DISCUSSION
■
Our initial efforts focused on the direct coupling of 1-methyl-1-
phenylhydrazine 1a and benzyl alcohol 2a catalyzed by
[Cp*IrCl2]2 (Cp* = pentamethylcyclopentadienyl), which is
commercially available and has been widely used as the efficient
catalyst for the synthesis of N-alkylated amines via the N-
alkylation of amines with alcohols.18,14b−e In the presence of
[Cp*IrCl2]2 (0.5 mol %), the reaction of 1a and 2a was carried
out in p-xylene at 130 °C for 12 h. To our surprise, none of the
N-alkylated product was detected and only the dehydrogenative
coupling product (E)-2-benzylidene-1-methyl-1-phenylhydra-
zine 3aa was obtained, albeit in 10% yield (Table 1, entry 1). A
Apart from benzylic-type alcohols, a series of aliphatic
alcohols were also used as substrates for this coupling reaction
(Table 3). When the linear aliphatic alcohols (3 equiv), such as
1-butanol 2r, 1-hexanol 2s, and 1-octanol 2t, were used as
reagents and solvents instead of p-xylene, the desired products
3ar−3at were obtained in 78−82% yields (Table 3, entries 1−
3).20 Transformations of the branched-chain alcohols, such as
3-methylbutan-1-ol 2u and cyclohexylmethanol 2v, afforded
also the corresponding products 3au and 3av in 75% and 77%
yields, respectively (Table 3, entries 4−5).
To expand further the scope of the reaction, the coupling of a
range of arylhydrazines with benzyl alcohol 2a was then
investigated (Table 4). Reactions of phenylhydrazines bearing
one or two electron-donating substituents, such as methyl 1b,
dimethyl 1c, and methoxy 1d, gave the desired products 3ba−
3da in 80−82% yields (Table 4, entries 1−3). Phenylhydrazines
bearing a halogen atom, such as fluoro 1e and chloro 1f, were
proven to be suitable substrates, and reactions gave the desired
products 3ea and 3fa in 75% and 79% yields, respectively
(Table 4, entries 4 and 5). Furthermore, phenylhydrazines
bearing a stronger electron-withdrawing trifluoromethoxy 1g
and the pyridylhydrazine 1h were successfully converted into
the corresponding products 3ga and 3ha in 83% and 72%
yields, respectively (Table 4, entries 6 and 7). For phenyl-
hydrazines bearing different alkyl groups on the N1 atom, such
as ethyl 1i, butyl 1j, and benzyl 1k, the desired products 3ia−
3ka were also obtained in high yields (Table 4, entries 8−10).
The unsubstituted phenylhydrazine 1l could be converted into
the desired product 3la, albeit in 50% yield (Table 4, entry
11).21
Table 1. Coupling of 1-Methyl-1-phenylhydrazine 1a and
Benzyl Alcohol 2a under Various Conditions
a
b
entry
catal.
base
temp.
x
yield (%)
1
2
[Cp*IrCl2]2
[Cp*IrCl2]2
[Cp*IrCl2]2
[Cp*IrCl2]2
[Cp*IrCl2]2
[Cp*IrCl2]2
[Ir(cod)Cl]2
[Cp*RhCl2]2
[Rh(cod)Cl]2
[Ru(p-cymene)Cl2]2
[Cp*IrCl2]2
[Cp*IrCl2]2
[Cp*IrCl2]2
130
130
130
130
130
130
130
130
130
130
130
120
110
130
10
12
50
73
85
78
80
63
43
38
77
80
75
n.d.
Na2CO3
Cs2CO3
NaOH
KOH
KOtBu
KOH
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.3
0.2
0.3
0.3
0.3
3
4
5
6
7
8
KOH
9
KOH
10
11
12
13
14
KOH
KOH
KOH
KOH
KOH
a
Reaction conditions: 1a (1 mmol), 2a (1.2 mmol), catal. (0.5 mol %),
b
p-xylene (0.5 mL), 12 h. Isolated yield.
series of bases, including Na2CO3, Cs2CO3, NaOH, KOH, and
KOtBu, were used as additives for this reaction. Apart from
Na2CO3, other bases exhibited an obvious effect on this
transformation (Table 1, entries 2−6). Among them, KOH was
found to be the most effective and the product 3aa could be
obtained in 85% yield (Table 1, entry 5). Using [Ir(cod)Cl]2
(cod = 1,5-cyclooctadienyl) as an alternative iridium source, the
reaction gave the product 3aa in 80% yield (Table 1, entry 7).
When other transition-metal complexes, such as [Cp*RhCl2]2,
[Rh(cod)Cl]2, and [Ru(p-cymene)Cl2]2, were tested, the
product 3aa could be obtained in only 38−63% yields (Table
1, entries 8−10). It was also found that decreasing the reaction
temperature or reducing the amount of KOH resulted in
relatively low yields (Table 1, entries 11−13). In the individual
presence of KOH, no reaction took place (Table 1, entry 14).
With the optimal reaction conditions established (Table 1,
entry 5), the coupling of 1a with a variety of benzylic-type
It should be pointed that none of the N-alkylated byproducts
were observed in all cases. The experimental results are in sharp
contrast with previous reports about transition-metal-catalyzed
dehydrogenative coupling of amines and alcohols, in which N-
alkylated products were inevitably produced.9,10 In addition, as
mentioned in previous reported documents,13,22 the minor N-
methylanilines as byproducts (<5% yields) resulting from N−N
bond cleavage of arylhydrazines were observed.
On the basis of the previous reports9,10 and our experimental
results, a speculative mechanism is proposed to account for the
direct synthesis of arylhydrazones via iridium-catalyzed accept-
orless dehydrogenative coupling of arylhydrazines and alcohols
(Scheme 3). The initial step involves the formation of alkoxo
B
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a b c d e
, , , ,
Table 2. Coupling of 1-Methyl-1-phenylhydrazine 1a and a Variety of Benzylic-type Alcohols 2
a
b
Reaction conditions: 1a (1 mmol), 2 (1.2 mmol), [Cp*IrCl2]2 (0.5 mol %), KOH (0.3 equiv), p-xylene (0.5 mL), 130 °C, 12 h. Isolated yield.
c
d
e
150 °C. KOH (0.5 equiv). KOH (1 equiv).
Scheme 2. Coupling of 1a and Secondary Alcohol 2q
arylhydrazones as products. Finally, catalytic active alkoxo
iridium species A were regenerated and hydrogen gas was
liberated via the reaction of iridium hydride species B and
alcohols. It is speculated that, under the present reaction
conditions, the iridium hydride could not be transferred to the
CN bond of arylhydrazones on the species C to form amido-
iridium species D, which is crucial for the generation of N-
alkylated products.24
To support the proposed mechanism, the liberation of
hydrogen gas in the iridium-catalyzed coupling of 1a and 2a
(Table 1, entry 5) was first confirmed by GC analysis and was
measured to be 20.3 mL (22 °C, 101 160 Pa, 84% yield) by a
gas buret by water displacement.
iridium species A by the reaction of iridium species with
alcohols under the acceleration of base. Accompanied by the β-
hydrogen elimination of alkoxo iridium species A, iridium
hydride species B and aldehydes were generated.23 Further-
more, the condensation between the resulting aldehydes and
arylhydrazines occurred to afford iridium hydride species
coordinated with arylhydrazones C, which were dissociated
subsequently to give iridium hydride species B and to release
C
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Table 3. Coupling of 1-Methyl-1-phenylhydrazine 1a and a
Variety of Aliphatic Alcohols 2
Table 4. Coupling of a Range of Arylhydrazines 1 and Benzyl
Alcohol 2a
a b c
, ,
a b c
, ,
a
Reaction conditions: 1a (1 mmol), 2 (3 mmol), [Cp*IrCl2]2 (0.5 mol
b
c
%), KOH (0.3 equiv), 130 °C, 12 h. Isolated yield. 18 h.
The catalytic transfer hydrogenation of an arylhydrazone
with an alcohol as a hydrogen source was then investigated.25,26
As shown in Scheme 4, the reaction of 3aa with 2a was
conducted for 12 h in the presence of the [Cp*IrCl2]2/KOH
system in p-xylene at 130 °C, and none of product 4 was
1
detected from the H NMR spectrum of the crude reaction
mixture. Similarly, no reaction occurred when isopropanol 5 (3
mL) was used as a hydrogen source. These results confirm that
arylhydrazones are stable enough under present reaction
conditions, and thus, they could not be hydrogenated by
iridium hydride species formed in the dehydrogenative step of
alcohols (Scheme 3, from C to D). Furthermore, the catalytic
hydrogenation of 3aa with H2 (10 atm) at 130 °C was carried
out in the presence of the [Cp*IrCl2]2/KOH system for 12 h
and no reaction occurred as well (Scheme 5). Appearently, 3aa
could not undergo the hydrogenation with the hydrogen
liberated from this step (Scheme 3, from B to A). These results
support the proposed mechanism.
CONCLUSION
■
In summary, we have demonstrated a novel and efficient
strategy for the direct synthesis of arylhydrazones via catalytic
coupling of arylhydrazines and alcohols with the liberation of
hydrogen gas. More importantly, complete selectivity for
arylhydrazones and none of the N-alkylated byproducts were
generated in this process, which exhibit new potential and
provide a new horizon for the development of catalytic
acceptorless dehydrogenative coupling reactions.
a
Reaction conditions: 1 (1 mmol), 2a (1.3 mmol), [Cp*IrCl2]2 (0.5
b
mol %), KOH (0.3 equiv), p-xylene (0.5 mL), 130 °C, 12 h. Isolated
yield. 2a (2.0 mmol).
c
D
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Scheme 3. Possible Reaction Mechanism
Scheme 5. Ir-Catalyzed Hydrogenation of an Arylhydrazone
with H2
MHz using a spectrometer. Chemical shifts are reported in delta (δ)
units, parts per million (ppm) downfield from tetramethylsilane or
ppm relative to the center of the singlet at 7.26 ppm for CDCl3 and
2.50 ppm for DMSO-d6. Coupling constants J values are reported in
hertz (Hz), and the splitting patterns were designated as follows: s,
singlet; d, doublet; t, triplet; m, multiplet; b, broad. Carbon-13 nuclear
magnetic resonance (13C NMR) spectra were recorded at 125 MHz.
Chemical shifts are reported in delta (δ) units, ppm relative to the
center of the triplet at 77.0 ppm for CDCl3. 13C NMR spectra were
routinely run with broadband decoupling. Substrates 1a−g,27 1i−1k,27
and 1h28 were prepared according to literature methods. Substrate 1l
is commercially available. All reactions were run under an atmosphere
of nitrogen, unless otherwise indicated. Analytical thin-layer
chromatography (TLC) was carried out using 0.2 mm commercial
silica gel plates.
Synthesis of [Cp*IrCl2]2 (Cp* = Pentamethylcyclo-
pentadienyl).29 To an oven-dried, nitrogen-purged 200 mL Schlenk
tube were added iridium trichloride hydrate (1 g, 2.83 mmol),
pentamethylcyclopentadiene (0.75 mL, 4.72 mmol), and methanol (20
mL). The mixture was heated at reflux for 36 h under an atmosphere
of nitrogen. The reaction was allowed to cool to room temperature,
and the orange precipitate was collected by filtration. The product was
purified by recrystallization from chloroform/hexane. 70% yield (0.79
1
g); mp 245−246 °C; H NMR (500 MHz, CDCl3) δ 1.59 (s, 15H);
13C NMR (125 MHz, CDCl3) δ 86.2, 9.3. [Cp*IrCl2]2 is very stabile
even under air conditions, and an inert atmosphere is not necessary.
General Procedure for Direct Synthesis of Arylhydrazones
via Iridium-Catalyzed Acceptorless Dehydrogenative Cou-
pling of Arylhydrazine and Alcohol. To an oven-dried, nitrogen-
purged 25 mL Schlenk tube were added arylhydrazine 1 (1 mmol),
alcohol 2 (1.2 mmol), [Cp*IrCl2]2 (0.005 mmol, 0.5 mol %), KOH
(0.3 mmol, 0.3 equiv), and 0.5 mL of p-xylene. The mixture was
heated at 130 °C for 12 h. Then, the reaction mixture was allowed to
cool to ambient temperature, concentrated in vacuo, and purified by
flash column chromatography with hexanes/ethyl acetate to afford the
corresponding product.
Scheme 4. Ir-Catalyzed Transfer Hydrogenation of an
Arylhydrazone with an Alcohol as the Hydrogen Source
(E)-2-Benzylidene-1-methyl-1-phenylhydrazine (3aa).30 85% yield
(178 mg); mp 104−105 °C (lit.30 mp 104−105 °C); H NMR (500
1
MHz, CDCl3) δ 7.70 (d, J = 7.7 Hz, 2H), 7.50 (s, 1H), 7.40−7.25 (m,
7H), 6.93 (t, J = 7.2 Hz, 1H), 3.43 (s, 3H); 13C NMR (125 MHz,
CDCl3) δ 147.9, 136.8, 131.8, 129.0, 128.5, 127.7, 126.0, 120.5, 115.2,
33.0.
(E)-1-Methyl-2-(4-methylbenzylidene)-1-phenylhydrazine
(3ab).31 89% yield (199 mg); mp 120−121 °C (lit.31 mp 110−112
°C); 1H NMR (500 MHz, CDCl3) δ 7.59 (d, J = 8.1 Hz, 2H), 7.49 (s,
1H), 7.38 (d, J = 8.2 Hz, 2H), 7.32 (t, J = 8.0 Hz, 2H), 7.17 (d, J = 8.0
Hz, 2H), 6.92 (t, J = 7.2 Hz, 1H), 3.41 (s, 3H), 2.36 (s, 3H); 13C
NMR (125 MHz, CDCl3) δ 148.0, 137.6, 134.0, 132.1, 129.3, 129.0,
126.0, 120.3, 115.1, 32.9, 21.3; HRMS-EI (70 eV) m/z calcd for C15
H17N2 [M + H]+ 225.1392, found 225.1383.
(E)-1-Methyl-2-(2-methylbenzylidene)-1-phenylhydrazine (3ac).
1
82% yield (183 mg); mp 65−66 °C; H NMR (500 MHz, CDCl3)
δ 7.91 (d, J = 7.6 Hz, 1H), 7.67 (s, 1H), 7.39−7.37 (m, 2H), 7.34−
7.30 (m, 2H), 7.24−7.21 (m, 1H), 7.17−7.16 (m, 2H), 3.42 (d, J = 0.8
Hz, 3H), 2.50 (s, 3H); 13C NMR (125 MHz, CDCl3) δ 148.0, 135.1,
134.6, 130.7, 130.5, 129.0, 127.5, 126.1, 125.8, 120.5, 115.2, 33.0, 20.0;
HRMS(ESI) m/z calcd for C15H17N2 [M + H]+ 225.1392, found
225.1388.
EXPERIMENTAL SECTION
■
General Experimental Details. High-resolution mass spectra
(HRMS) were obtained on an HPLC-Q-Tof MS (Micro)
spectrometer and are reported as m/z (relative intensity). Accurate
masses are reported for the molecular ion [M + Na]+ or [M + H]+.
Melting points were measured on a micromelting apparatus. Proton
nuclear magnetic resonance (1H NMR) spectra were recorded at 500
(E)-2-(4-Isopropylbenzylidene)-1-methyl-1-phenylhydrazine
1
(3ad). 86% yield (216 mg); oil; H NMR (500 MHz, CDCl3) δ 7.62
(d, J = 8.2 Hz, 2H), 7.48 (s, 1H), 7.38−7.36 (m, 2H), 7.33−7.29 (m,
E
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2H), 7.23−7.22 (m, 2H), 6.91 (t, J = 7.1 Hz, 1H), 3.39 (d, J = 0.7 Hz,
3H), 2.91 (heptet, J = 7.0 Hz, 1H), 1.26 (d, J = 7.0 Hz, 6H); 13C NMR
(125 MHz, CDCl3) δ 148.6, 147.9, 134.4, 132.0, 128.9, 126.6, 126.1,
120.3, 115.1, 33.9, 32.9, 23.9. HRMS(ESI) m/z calcd for C17 H21N2
[M + H]+ 253.1705, found 253.1700.
125.6, 125.0, 123.9, 120.7, 115.4, 33.1; HRMS(ESI) m/z calcd for
C18H17N2 [M + H]+ 261.1392, found 261.1384.
(E)-1-Methyl-2-(naphthalen-2-ylmethylene)-1-phenylhydrazine
1
(3an). 81% yield (211 mg); mp 178−179 °C; H NMR (500 MHz,
CDCl3) δ 8.07 (dd, J = 8.7 Hz and J = 1.6 Hz, 1H), 7.89 (s, 1H),
7.84−7.81 (m, 3H), 7.66 (s, 1H), 7.48−7.42 (m, 4H), 7.37−7.33 (m,
2H), 6.95 (t, J = 7.3 Hz, 1H), 3.47 (s, 3H); 13C NMR (125 MHz,
CDCl3) δ 147.8, 134.5, 133.6, 133.2, 131.9,129.0, 128.2, 127.9, 127.8,
126.2, 126.1, 125.8, 123.1, 120.6, 115.3, 33.0; HRMS-EI (70 eV) m/z
calcd for C18H16N2 [M + H]+ 261.1392, found 261.1379.
(E)-2-(4-Methoxybenzylidene)-1-methyl-1-phenylhydrazine
(3ae).31 87% yield (209 mg); mp 113−114 °C; H NMR (500 MHz,
1
CDCl3) δ 7.64 (d, J = 8.3 Hz, 2H), 7.48 (s, 1H), 7.37 (d, J = 8.4 Hz,
2H), 7.31 (t, J = 7.6 Hz, 2H), 6.92−6.89 (m, 3H), 3.83 (s, 3H), 3.40
(s, 3H); 13C NMR (125 MHz, CDCl3) δ 159.5, 148.0, 131.9, 129.7,
129.0, 127.3, 120.2, 115.0, 114.0, 55.3, 33.0. HRMS(ESI) m/z calcd for
C15H17N2O [M + H]+ 241.1341, found 241.1332.
(E)-1-Methyl-1-phenyl-2-(thiophen-2-ylmethylene)hydrazine
(3ao).30 87% yield (188 mg); mp 79−80 °C; H NMR (500 MHz,
1
(E)-2-(3,4-Dimethoxybenzylidene)-1-methyl-1-phenylhydrazine
CDCl3) δ 7.68 (s, 1H), 7.35−7.30 (m, 4H), 7.20 (d, J = 5.1 Hz, 1H),
7.09 (d, J = 3.2 Hz, 1H), 7.01−6.99 (m, 1H), 6.92 (tt, J = 6.7 Hz and J
= 1.7 Hz, 1H), 3.39 (s, 3H); 13C NMR (125 MHz, CDCl3) δ 147.5,
142.7, 129.0, 127.1, 126.9, 125.4, 124.8, 120.6, 115.2, 33.2.
(3af).32 85% yield (229 mg); mp 97−98 °C; H NMR (500 MHz,
1
CDCl3) δ 7.47 (s, 1H), 7.40 (s, 1H), 7.37−7.30 (m, 4H), 7.12 (d, J =
8.4 Hz, 1H), 6.92 (t, J = 7.0 Hz, 1H), 6.87 (d, J = 8.3 Hz, 1H), 3.96 (s,
3H), 3.91(s, 3H), 3.42 (s, 3H); 13C NMR (125 MHz, CDCl3) δ 149.3,
149.1, 148.0, 132.0, 130.0, 128.9, 120.2, 119.8, 115.1, 110.9, 107.7,
55.9, 55.8, 33.1.
(E)-2-((2-Methyl-2-phenylhydrazono)methyl)pyridine (3ap).33
1
80% yield (168 mg); oil; H NMR (500 MHz, CDCl3) δ 8.54−8.52
(m, 1H), 8.01 (dt, J = 8.1 Hz and J = 1.0 Hz, 1H), 7.67 (td, J = 7.8 Hz
and J = 1.7 Hz, 1H), 7.62 (s, 1H), 7.41−7.38 (m, 2H), 7.36−7.32 (m,
2H), 7.15−7.12 (m, 1H), 6.98 (tt, J = 7.2 Hz and J = 1.2 Hz, 1H), 3.46
(s, 3H); 13C NMR (125 MHz, CDCl3) δ 155.8, 148.9, 147.4, 136.1,
132.5, 129.0, 121.8, 121.2, 119.0, 115.6, 33.3.
(E)-2-(4-Fluorobenzylidene)-1-methyl-1-phenylhydrazine (3ag).
1
75% yield (170 mg); mp 96−97 °C; H NMR (500 MHz, CDCl3)
δ 7.67 (t, J = 6.8 Hz, 2H), 7.47 (s, 1H), 7.38−7.31 (m, 4H), 7.06 (t, J
= 8.4 Hz, 2H), 6.94 (t, J = 7.0 Hz, 1H), 3.42 (s, 3H); 13C NMR (125
MHz, CDCl3) δ 162.5 (d, JC−F = 245.7 Hz), 147.8, 133.0, 130.7, 129.0,
127.5 (d, JC−F = 7.6 Hz), 120.6, 115.5 (d, JC−F = 21.6 Hz), 115.3, 33.1;
HRMS-EI (70 eV) m/z calcd for C14H14FN2 [M + H]+ 229.1141,
found 229.1134.
(E)-1-Methyl-1-phenyl-2-(1-phenylethylidene)hydrazine (3aq).34
1
52% yield (116 mg); oil; H NMR (500 MHz, CDCl3) 7.92−7.91
(m, 2H), 7.44−7.41 (m, 3H), 7.29−7.26 (m, 2H), 6.97 (d, J = 7.7 Hz,
2H), 6.90 (t, J = 7.3 Hz, 1H), 3.17 (s, 3H), 2.35 (s, 3H); 13C NMR
(125 MHz, CDCl3) δ 165.5, 151.3, 138.3, 129.8, 128.8, 128.4, 126.7,
120.0, 115.5, 42.8, 16.5.
(E)-2-(4-Chlorobenzylidene)-1-methyl-1-phenylhydrazine
(3ah).32 87% yield (212 mg); mp 108−109 °C; 1H NMR (500 MHz,
CDCl3) δ 7.62 (d, J = 8.4 Hz, 2H), 7.43 (s, 1H), 7.37−7.31 (m, 6H),
6.95 (t, J = 7.1 Hz, 1H), 3.41 (s, 3H); 13C NMR (125 MHz, CDCl3) δ
147.7, 135.3, 133.1, 130.3, 129.0, 128.7, 127.1, 120.8, 115.3, 33.1.
(E)-2-(2-Chlorobenzylidene)-1-methyl-1-phenylhydrazine (3ai).
(E)-2-Butylidene-1-methyl-1-phenylhydrazine (3ar). 78% yield
1
(138 mg); oil; H NMR (500 MHz, CDCl3) δ 7.28−7.21 (m, 4H),
6.87−6.81 (m, 2H), 3.20 (s, 3H), 2.37−2.33 (m, 2H), 1.63−1.56 (m,
2H), 1.01−0.97 (m, 3H); 13C NMR (125 MHz, CDCl3) δ 148.4,
136.0, 128.9, 119.7, 114.8, 35.0, 33.0, 20.9, 13.8; HRMS-EI (70 eV) m/
z calcd for C11H17N2 [M + H]+ 177.1392, found 177.1385.
1
83% yield (203 mg); mp 47−48 °C; H NMR (500 MHz, CDCl3)
δ 8.07 (d, J = 8.1 Hz, 1H), 7.77 (s, 1H), 7.37−7.35 (m, 2H), 7.32−
7.28 (m, 3H), 7.23 (t, J = 7.5 Hz, 1H), 7.15−7.11 (m, 1H), 6.94 (t, J =
6.9 Hz, 1H), 3.38 (s, 3H); 13C NMR (125 MHz, CDCl3) δ 147.6,
133.9, 132.6, 129.6, 129.0, 128.3, 128.1, 126.8, 126.2, 120.9, 115.4,
33.2; HRMS-EI (70 eV) m/z calcd for C14H14ClN2 [M + H]+
245.0846, found 245.0841.
(E)-2-Hexylidene-1-methyl-1-phenylhydrazine (3as). 80% yield
1
(163 mg); oil; H NMR (500 MHz, CDCl3) δ 7.28−7.22 (m, 4H),
6.86−6.81 (m, 2H), 3.20 (s, 3H), 2.38−2.34 (m, 2H), 1.60−1.54 (m,
2H), 1.38−1.34 (m, 4H), 0.91 (t, J = 6.8 Hz, 3H); 13C NMR (125
MHz, CDCl3) δ 148.4, 136.2, 128.9, 119.6, 114.8, 33.0, 31.5, 27.3,
22.5, 14.0; HRMS-EI (70 eV) m/z calcd for C13H21N2 [M + H]+
205.1705, found 205.1700.
(E)-2-(4-Bromobenzylidene)-1-methyl-1-phenylhydrazine (3aj).
87% yield (250 mg); mp 125−126 °C; 1H NMR (500 MHz,
CDCl3) δ 7.56 (d, J = 8.6 Hz, 2H), 7.48 (d, J = 8.5 Hz, 2H), 7.42 (s,
1H), 7.38−7.31 (m, 4H), 6.95 (t, J = 7.1 Hz, 1H), 3.42 (s, 3H); 13C
NMR (125 MHz, CDCl3) δ 147.7, 135.8, 131.6, 130.4, 129.0, 127.4,
121.3, 120.9, 115.4, 33.2; HRMS-EI (70 eV) m/z calcd for
C14H13BrN2Na [M + Na]+ 311.0160, found 311.0157.
(E)-1-Methyl-1-phenyl-2-(4-(trifluoromethyl)benzylidene)-
hydrazine (3ak). 81% yield (226 mg); mp 87−88 °C; 1H NMR (500
MHz, CDCl3) δ 7.77 (d, J = 7.0 Hz, 2H), 7.60 (d, J = 7.4 Hz, 2H),
7.48 (s, 1H), 7.40−7.33 (m, 4H), 6.98 (t, J = 6.6 Hz, 1H), 3.45 (s,
3H); 13C NMR (125 MHz, CDCl3) δ 147.6, 140.3, 129.8, 129.1, 129.0
(E)-1-Methyl-2-octylidene-1-phenylhydrazine (3at). 82% yield
1
(191 mg); oil; H NMR (500 MHz, CDCl3) δ 7.20−7.14 (m, 4H),
6.78−6.73 (m, 2H), 3.12 (s, 3H), 2.30−2.26 (m, 2H), 1.48 (quint, J =
7.4 Hz), 1.32−1.18 (m, 8H), 0.81 (t, J = 7.0 Hz, 3H); 13C NMR (125
MHz, CDCl3) δ 148.4, 136.2, 128.9, 119.6, 114.7, 33.0, 32.9, 31.8,
29.2, 29.1, 27.6, 22.6. 14.1; HRMS-EI (70 eV) m/z calcd for C15H25N2
[M + H]+ 233.2018, found 233.2013.
(E)-1-Methyl-2-(3-methylbutylidene)-1-phenylhydrazine (3au).
1
75% yield (142 mg); oil; H NMR (500 MHz, CDCl3) δ 7.28−7.21
(m, 4H), 6.86−6.80 (m, 2H), 3.21 (s, 3H), 2.27−2.24 (m, 2H), 1.88
(heptet, J = 6.8 Hz, 1H), 0.98 (d, J = 6.7 Hz, 6H); 13C NMR (125
MHz, CDCl3) δ 148.4, 135.4, 128.9, 119.7, 114.8, 41.9, 33.1, 27.4,
22.4; HRMS-EI (70 eV) m/z calcd for C12H19N2 [M + H]+ 191.1548,
found 191.1545.
(q, JC−F = 32.1 Hz), 126.0, 125.5 (q, JC−F = 3.1 Hz), 124.3 (q, JC−F
=
270.4 Hz), 121.3, 115.6, 33.3; HRMS-EI (70 eV) m/z calcd for
C15H13F3N2Na [M + Na]+ 301.0929, found 301.0927.
(E)-1-Methyl-1-phenyl-2-(4-(trifluoromethoxy)benzylidene)-
1
hydrazine (3al). 88% yield (259 mg); mp 59−60 °C; H NMR (500
(E)-2-(Cyclohexylmethylene)-1-methyl-1-phenylhydrazine (3av).
MHz, CDCl3) δ 7.70 (d, J = 8.8 Hz, 2H), 7.46 (s, 1H), 7.38−7.31 (m,
4H), 7.21 (d, J = 8.4 Hz, 2H), 6.95 (tt, J = 7.1 Hz and J = 1.3 Hz, 1H),
3.43 (s, 3H); 13C NMR (125 MHz, CDCl3) δ 148.5, 147.7, 135.6,
130.0, 129.0, 127.1, 121.1, 120.9, 120.5 (q, JC−F = 255.4 Hz), 115.4,
33.1; HRMS-EI (70 eV) m/z calcd for C15H14F3N2O [M + H]+
295.1058, found 295.1053.
1
77% yield (167 mg); oil; H NMR (500 MHz, CDCl3) δ 7.27−7.22
(m, 4H), 6.83 (t, J = 7.0 Hz, 1H), 6.71(d, J = 5.0 Hz, 1H), 3.18 (s,
3H), 2.36−2.29 (m, 1H), 1.90−1.88 (m, 2H), 1.81−1.77 (m, 2H),
1.70−1.66 (m, 1H), 1.38−1.20 (m, 5H); 13C NMR (125 MHz,
CDCl3) δ 148.5, 140.3, 128.9, 119.5, 114.6, 41.2, 32.7, 31.3, 26.2, 25.8;
HRMS-EI (70 eV) m/z calcd for C14H21N2 [M + H]+ 217.1705, found
217.1699.
(E)-1-Methyl-2-(naphthalen-1-ylmethylene)-1-phenylhydrazine
1
(3am). 78% yield (202 mg); mp 92−93 °C; H NMR (500 MHz,
(E)-2-Benzylidene-1-methyl-1-(p-tolyl)hydrazine (3ba). 80% yield
(179 mg); mp 81−82 °C; 1H NMR (500 MHz, CDCl3) δ 7.68 (d, J =
7.5 Hz, 2H), 7.45 (s, 1H), 7.36 (t, J = 7.6 Hz, 2H), 7.26 (t, J = 8.0 Hz,
3H), 7.12 (d, J = 8.4 Hz, 2H), 3.40 (s, 3H), 2.31 (s, 3H); 13C NMR
(125 MHz, CDCl3) δ 145.8, 136.9, 131.3, 130.0, 129.5, 128.5, 127.5,
CDCl3) δ 8.66 (d, J = 8.5 Hz, 1H), 8.17 (s, 1H), 7.99 (d, J = 7.3 Hz,
1H), 7.88 (d, J = 8.2 Hz, 1H), 7.79 (d, J = 8.2 Hz, 1H), 7.58−7.55 (m,
1H), 7.52−7.49 (m, 2H), 7.44 (d, J = 8.1 Hz, 2H), 7.35 (t, J = 8.0 Hz,
2H), 6.96 (t, J = 7.3 Hz, 1H), 3.55 (s, 3H); 13C NMR (125 MHz,
CDCl3) δ 148.0, 134.0, 132.1, 130.6, 129.1, 128.7, 128.1, 126.2, 125.6,
F
dx.doi.org/10.1021/jo501161u | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
126.0, 115.5, 33.4, 20.5; HRMS-EI (70 eV) m/z calcd for C15H17N2
[M + H]+ 225.1392, found 225.1389.
(d, J = 7.6 Hz, 2H), 7.37 (t, J = 7.4 Hz, 2H), 7.31−7.25 (m, 3H), 7.12
(d, J = 7.8 Hz, 2H), 6.87 (t, J = 7.4 Hz, 1H); 13C NMR (125 MHz,
CDCl3) δ 144.7, 137.3, 135.3, 129.3, 128.6, 128.4, 126.2, 120.1, 112.8.
Catalytic Transfer Hydrogenation of Arylhydrazone 3aa
with Benzylic Alcohol 2a as a Hydrogen Source (Scheme 4,
Top Equation). To an oven-dried, nitrogen-purged 25 mL Schlenk
tube were added arylhydrazone 3aa (1 mmol), benzyl alcohol 2a (1.2
mmol), [Cp*IrCl2]2 (0.005 mmol, 0.5 mol %), KOH (0.3 mmol, 0.3
equiv), and 0.5 mL of p-xylene. The mixture was heated at 130 °C for
12 h. No conversion was observed by the analysis of the spectrum of
the crude reaction mixture.
(E)-2-Benzylidene-1-(3,5-dimethylphenyl)-1-methylhydrazine
1
(3ca). 82% yield (196 mg); mp 68−69 °C; H NMR (500 MHz,
CDCl3) δ 7.69 (d, J = 7.8 Hz, 2H), 7.47 (s, 1H), 7.37 (t, J = 7.4 Hz,
2H), 7.27−7.24 (m, 1H), 7.01 (s, 2H), 6.60 (s, 1H), 3.40 (s, 3H), 2.34
(s, 6H); 13C NMR (125 MHz, CDCl3) δ 148.0, 138.6, 136.9, 131.5,
128.5, 127.5, 126.0, 122.6, 113.4, 33.3, 21.7; HRMS-EI (70 eV) m/z
calcd for C16H18N2Na [M + Na]+ 261.1368, found 261.1364.
(E)-2-Benzylidene-1-(4-methoxyphenyl)-1-methylhydrazine
1
(3da). 81% yield (194 mg); mp 128−129 °C; H NMR (500 MHz,
Catalytic Transfer Hydrogenation of Arylhydrazone 3aa
with Isopropanol 5 as Hydrogen Source (Scheme 4, Bottom
Equation). To an oven-dried, nitrogen-purged 25 mL Schlenk tube
were added arylhydrazone 3aa (1 mmol), [Cp*IrCl2]2 (0.005 mmol,
0.5 mol %), KOH (0.3 mmol, 0.3 equiv), and isopropanol 5 (3 mL).
The mixture was heated at 130 °C for 12 h. No conversion was
observed by the analysis of the spectrum of the crude reaction mixture.
Catalytic Transfer Hydrogenation of Arylhydrazone 3aa
with H2 (Scheme 5). To an oven-dried autoclave containing a stirring
bar were added arylhydrazone 3aa (1 mmol), [Cp*IrCl2]2 (0.005
mmol, 0.5 mol %), KOH (0.3 mmol, 0.3 equiv), and p-xylene (2 mL).
After nitrogen displacement, the autoclave was pressured to 10 atm of
hydrogen and stirred at 130 °C for 12 h. The autoclave was cooled
down to room temperature, and the remaining hydrogen was carefully
vented. No conversion was observed by the analysis of the spectrum of
the crude reaction mixture.
CDCl3) δ 7.67 (d, J = 7.8 Hz, 2H), 7.42 (s, 1H), 7.35 (t, J = 7.6 Hz,
2H), 7.29−7.22 (m, 3H), 6.89 (d, J = 9.1 Hz, 2H), 3.79 (s, 3H), 3.38
(s, 3H); 13C NMR (125 MHz, CDCl3) δ 154.4, 142.4, 137.0, 131.2,
128.5, 127.4, 125.9, 117.2, 114.4, 55.7, 34.2; HRMS-EI (70 eV) m/z
calcd for C15H16N2NaO [M + Na]+ 263.1160, found 263.1157.
(E)-2-Benzylidene-1-(4-fluorophenyl)-1-methylhydrazine (3ea).
1
75% yield (172 mg); mp 82−83 °C; H NMR (500 MHz, CDCl3)
δ 7.67 (d, J = 7.4 Hz, 2H), 7.45 (s, 1H), 7.36 (t, J = 7.7 Hz, 2H),
7.30−7.23 (m, 3H), 7.03−6.99 (m, 2H), 3.37 (s, 3H); 13C NMR (125
MHz, CDCl3) δ 157.7 (d, JC−F = 238.0 Hz), 144.5, 136.6, 132.0, 128.6,
127.7, 126.0, 116.6 (d, JC−F = 7.3 Hz), 115.4 (d, JC−F = 22.0 Hz), 33.6;
HRMS-EI (70 eV) m/z calcd for C14H14FN2 [M + H]+ 229.1141,
found 229.1138.
(E)-2-Benzylidene-1-(4-chlorophenyl)-1-methylhydrazine (3fa).
79% yield (193 mg); mp 101−102 °C; 1H NMR (500 MHz,
CDCl3) δ 7.69 (d, J = 7.2 Hz, 2H), 7.50 (s, 1H), 7.37 (t, J = 7.7 Hz,
2H), 7.31−7.25 (m, 5H), 3.40 (s, 3H); 13C NMR (125 MHz, CDCl3)
δ 146.5, 136.4, 132.6, 128.9, 128.6, 128.0, 126.1, 125.4, 116.2, 33.0;
HRMS-EI (70 eV) m/z calcd for C14H14ClN2 [M + H]+ 245.0846,
found 245.0842.
Procedure for the Hydrogen Evolution Experiment.36
Arylhydrazone 3aa (1 mmol), benzyl alcohol 2a (1.2 mmol),
[Cp*IrCl2]2 (0.005 mmol, 0.5 mol %), KOH (0.3 mmol, 0.3 equiv),
and 0.5 mL of p-xylene were added to a thick walled glass vessel fitted
with a side arm and a rubber septum. The vessel was previously
degassed three times and placed under a N2 atmosphere. The vessel
was connected to the gas collection apparatus (standard water
displacement apparatus, using a graduated cylinder to determine
volume), and the entire system was flushed with N2 for 5 min and
allowed to equilibrate for 5 min. The reaction was stirred vigorously at
a constant temperature until gas evolution ceased (12 h). The
presence of hydrogen in the collected gas was confirmed by GC
analysis.
The GC analysis was performed on a gas chromatograph and TCD
detector. Injector temprature = 120 °C, column temprature = 120 °C
(isothemal), detector temperature (TCD) = 130 °C, carrier gas = He, t
= 1.23 min.
The volume of 1 mol of H2 at 22 °C, 101 160 Pa was calculated
according to the van der Waals equation as shown below
(E)-2-Benzylidene-1-methyl-1-(4-(trifluoromethoxy)phenyl)-
hydrazine (3ga). 83% yield (244 mg); mp 52−53 °C; 1H NMR (500
MHz, CDCl3) δ 7.68 (d, J = 7.6 Hz, 2H), 7.50 (s, 1H), 7.39−7.33 (m,
4H), 7.28 (tt, J = 7.3 Hz and J = 1.2 Hz, 1H), 7.17 (d, J = 9.0 Hz, 2H),
3.40 (s, 3H); 13C NMR (125 MHz, CDCl3) δ 146.6, 142.8, 136.4,
132.8, 128.6, 128.0, 126.2, 121.9, 120.7 (q, JC−F = 254.4 Hz), 115.7,
32.9; HRMS-EI (70 eV) m/z calcd for C15H13F3N2ONa [M + Na]+
317.0878, found 317.0875.
(E)-2-Benzylidene-1-methyl-1-(pyridin-2-yl)hydrazine (3ha).5d
72% yield (151 mg); mp 100−101 °C; 1H NMR (500 MHz,
CDCl3) δ 8.22 (d, J = 4.4 Hz, 1H), 7.75−7.72 (m, 3H), 7.65 (s, 1H),
7.61−7.58 (m, 1H), 7.39 (t, J = 7.6 Hz, 2H), 7.30 (t, J = 7.3 Hz, 1H),
6.78 (t, J = 5.9 Hz, 1H), 3.67 (s, 3H); 13C NMR (125 MHz, CDCl3) δ
157.8, 146.9, 137.4, 136.3, 133.9, 128.6, 128.2, 126.3, 115.4, 109.9,
29.3.
(E)-2-Benzylidene-1-ethyl-1-phenylhydrazine (3ia). 80% yield
(180 mg); oil; H NMR (500 MHz, CDCl3) δ 7.71−7.69 (m, 2H),
7.55 (s, 1H), 7.38−7.30 (m, 6H), 7.28−7.24 (m, 1H), 6.92 (tt, J = 7.1
Hz and J = 1.2 Hz, 1H), 4.02 (q, J = 7.2 Hz, 2H), 1.27 (t, J = 7.2 Hz,
3H); 13C NMR (125 MHz, CDCl3) δ 146.8, 136.9, 130.9, 129.1,
128.5, 127.6, 126.0, 120.3, 114.7, 39.6, 10.1; HRMS-EI (70 eV) m/z
calcd for C15H17N2 [M + H]+ 225.1392, found 225.1386.
2
⎛
⎞
⎟
n a
1
p +
(V − nb) = nRT
⎜
⎝
V2 ⎠
where R = 8.3145 m3 Pa·mol−1·K−1; T = 295.15 K; p = 101 160 Pa; a =
0.002476 m6·Pa·mol−1; b = 0.02661 × 10−3 m3·mol−1; thus, V (H2, 22
°C, 101 160 Pa) = 24.28 L·mol−1.
The collected volume of gas in the experiment above was 20.3 mL,
which corresponds to 0.84 mmol of H2.
(E)-2-Benzylidene-1-butyl-1-phenylhydrazine (3ja). 82% yield
1
(207 mg); mp 64−65 °C; H NMR (500 MHz, CDCl3) δ 7.70 (d,
J = 7.8 Hz, 2H), 7.52 (s, 1H), 7.39−7.36 (m, 4H), 7.32 (t, J = 7.8 Hz,
2H), 7.28−7.25 (m, 1H), 6.92 (t, J = 7.2 Hz, 1H), 3.91 (t, J = 7.9 Hz,
2H), 1.68 (quint, J = 7.8 Hz, 2H), 1.47 (sextet, J = 7.4 Hz, 2H), 1.01
(t, J = 7.4 Hz, 3H); 13C NMR (125 MHz, CDCl3) δ 147.2, 136.9,
130.9, 129.0, 128.5, 127.6, 126.0, 120.2, 114.7, 45.0, 26.9, 20.4, 13.9;
HRMS-EI (70 eV) m/z calcd for C17H21N2 [M + H]+ 253.1705, found
253.1698.
ASSOCIATED CONTENT
■
S
* Supporting Information
1
Copies of H and 13C NMR spectra for all products. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(E)-1-Benzyl-2-benzylidene-1-phenylhydrazine (3ka).5d 84% yield
(240 mg); mp 109−110 °C; 1H NMR (500 MHz, CDCl3) δ 7.62 (d, J
= 8.3 Hz, 2H), 7.42−7.39 (m, 3H), 7.36−7.31 (m, 6H), 7.28−7.22 (m,
4H), 6.95 (t, J = 7.3 Hz, 1H), 5.19 (s, 2H); 13C NMR (125 MHz,
CDCl3) δ 147.9, 136.5, 135.7, 132.5, 129.1, 129.0, 128.5, 127.8, 127.3,
126.2, 126.0, 120.7, 114.8, 50.4.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: fengli@njust.edu.cn.
(E)-1-Benzylidene-2-phenylhydrazine (3la).35 50% yield (98 mg);
Notes
1
mp 157−158 °C; H NMR (500 MHz, CDCl3) δ 7.68 (s, 1H), 7.66
The authors declare no competing financial interest.
G
dx.doi.org/10.1021/jo501161u | J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
(f) Bahn, S.; Imm, S.; Neubert, L.; Zhang, M.; Neumann, H.; Beller,
M. ChemCatChem 2011, 3, 1853−1864. (g) Marr, A. C. Catal. Sci.
Technol. 2012, 2, 279−287. (h) Pan, S.; Shibata, T. ACS Catal. 2013, 3,
704−712.
ACKNOWLEDGMENTS
■
This work was supported by the National Natural Science
Foundation of China (No. 21272115) and Fundamental
Research Funds for the Central Universities (No.
30920130111005 and No. 30920130122002).
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NOTE ADDED AFTER ASAP PUBLICATION
[Ir(cod)Cl2]2 and [Rh(cod)Cl2]2 were corrected in Table 1 and
the text on August 8, 2014.
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dx.doi.org/10.1021/jo501161u | J. Org. Chem. XXXX, XXX, XXX−XXX