A one-pot synthesis of bisarylhydrazones by Cu(I)-catalyzed aerobic oxidation

Article abstract of DOI:10.1016/j.tet.2013.08.073

An efficient Cu(I)-catalyzed one-pot synthesis of N-substituted (or NH) bisarylhydrazones is reported. A further cyclization reaction could occur towards the synthesis of benzimidazoles or triazoles with elevated temperature. A plausible alkylation-oxidation-alkylation mechanism is proposed based on experimental results and literature.

Full text of DOI:10.1016/j.tet.2013.08.073

Tetrahedron 69 (2013) 9865e9869
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A one-pot synthesis of bisarylhydrazones by Cu(I)-catalyzed aerobic
oxidation
*
Jiu-Rong Hu , Wan-Jia Zhang, Da-Gui Zheng
Key Laboratory of Applied Organic Chemistry, Higher Institutions of Jiangxi Province, School of Chemistry and Chemical Engineering,
Shangrao Normal University, Jiangxi 334001, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 30 April 2013
Received in revised form 28 August 2013
Accepted 30 August 2013
Available online 9 September 2013
An efficient Cu(I)-catalyzed one-pot synthesis of N-substituted (or NH) bisarylhydrazones is reported. A
further cyclization reaction could occur towards the synthesis of benzimidazoles or triazoles with ele-
vated temperature. A plausible alkylationeoxidationealkylation mechanism is proposed based on ex-
perimental results and literature.
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Cu(I)/O2 catalyst system
Aerobic oxidative coupling
Bisarylhydrazones
One-pot reaction
1. Introduction
nonlinear optics (NLO),7e10 and as precursors towards some func-
tional heterocyclic compounds.11e13 The traditional preparation of
Imine derivatives are prominent structural motifs in organic
synthesis,1 catalysts,2 natural products,3 and materials.4 Bisar-
ylhydrazones as an important series of imines have received con-
siderable attention because of their wide applications in sensors,5,6
this moiety includes the acid-catalyzed condensation reaction of
aldehydes or ketones with aryl hydrazines,5e13 the dehydrogenate
coupling of alcohols and amines catalyzed by Os,14 Ru,15 Pd16-cat-
alysts, and the FeCl3 catalyzed coupling with azides (Scheme 1).17
Scheme 1. Synthesis of bisarylhydrazones.
Furthermore, the common method used for the synthesis of
the N-substituted bisarylhydrazones always involves the con-
struction of NH bisarylhydrazones firstly,5e17 and subsequently
alkylation with aryl bromide.11e13 This reaction has some
* Corresponding author. Fax: þ86 793 8150621; e-mail address: jiuronghu@
163.com (J.-R. Hu).
0040-4020/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2013.08.073

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J.-R. Hu et al. / Tetrahedron 69 (2013) 9865e9869
drawbacks such as involvement of strong base (NaH) with harsh
anhydrous condition and requirement of two-steps. Herein we
reported a Cu(I)-catalyzed aerobic oxidative coupling synthesis of
N-substituted (or NH) bisarylhydrazones through a one-pot se-
quential reaction. A further cyclization reaction could occur to-
wards the synthesis of benzimidazoles or triazoles with elevated
temperature.
substituents (3n, 3o) and electron-withdrawing substituents (3p)
resulting in lower yields. Other alkyl bromides (EtBr or n-BuBr)
gave no desired products. The structures of products 3aeq were
fully characterized and the structure of compound 3a was further
confirmed by single-crystal determination (see SD-Fig. 1 in the
Supplementary data).
In order to further understand this reaction mechanism, some
controlled experiments were conducted. Some possible in-
termediates (Scheme 2, 3I-1, 3I-2, 3I-3) were independently syn-
thesized and subjected to the standard conditions. Only trace
amount of PhCHO (<5%) was detected when only PhCH2Br was
present, indicating that no condensation process occurred in the
reaction. Therefore, a possible alkylationeoxidationealkylation
mechanism is proposed as shown in Scheme 3. Initially, the re-
action of 1 and 1 equiv 2 may give intermediate I1 via alkylation in
the presence of K2CO3, followed by an oxidation of I1 to form I2
2. Results and discussion
Phenyl hydrazine (1a) and 2.1 equiv 8-bromomethylquinoline
(2a) were chosen as model substrates to test the reaction. The use of
CuBr (5%) as the catalyst and tert-butyl hydroperoxide (TBHP) as
oxidant at 60 ꢀC in CH3CN afforded the target product 3a in 31%
(Table 1, entry 1). Other organic or inorganic oxidants such as DDQ,
K2S2O8 failed to improve the yield (Table 1, entries 2e4). To our
Table 1
Optimization of the reaction conditions
Entrya
Catalyst (mol %)
Oxidant
Solvent/T (ꢀC)
Yield (%)b
1
2
3
4
5
6
7
8
CuBr (5)
CuBr (5)
CuBr (5)
CuBr (5)
CuBr (5)
CuBr (5)
CuCl (5)
CuCl2 (5)
Cu(OAc)2 (5)
FeCl3 (5)
CoCl2 (5)
CuBr (5)
CuBr (10)
No
TBHP
DDQ
TBP
K2S2O8
CH3CN/60
CH3CN/60
CH3CN/60
CH3CN/60
CH3CN/60
CH3CN/60
CH3CN/60
CH3CN/60
CH3CN/60
CH3CN/60
CH3CN/60
EtOH/75
31
<5
12
<5
42
61
49
25
<5
16
0
1 atm air
1 atm O2
1 atm O2
1 atm O2
1 atm O2
1 atm O2
1 atm O2
1 atm O2
1 atm O2
1 atm O2
9
10
11
12
13
14
76
79
0
EtOH/75
EtOH/75
a
Conditions: 1a (0.2 mmol), 2a (0.42 mmol), catalyst (5 mol %), K2CO3 (0.5 mmol), oxidant, in 5 mL solvent, (entries 1e4) under Ar, (entry 5) under air, (entries 6e14)
under O2.
b
Isolated yield.
18e25
delight, using air as an oxidant improved the yield to 42% (Table 1,
entry 5) and the use of pure O2 further enhanced the yield to 61%
(Table 1, entry 6). Screening of other catalysts failed to further
improve the yield (Table 1, entries 7e11). Conducting the reaction
in EtOH improved the yield to 76% (Table 1, entry 12). A controlled
experiment without adding any metal failed to provide any prod-
uct, indicating the importance of transitional metals in this trans-
formation (Table 1, entry 14). A more detailed optimization table is
listed in SD-Table 1.
using Cu(I)/O2
and finally by a second alkylation11e13 to give
the desired products.
To further demonstrate the synthetic utility of this trans-
formation, 3fem were further converted into benzimidazoles or
triazoles 4fem when elevating the reaction temperature from
75 ꢀC to 110 ꢀC in EtOH, according to the related literature,11,13 and
the results are listed in Table 3. However, 3aee failed to cyclize and
no cyclized product was detected. This might be due to the
electron-deficient nature of the heterocyclic arenes.26e29
With the optimized reaction conditions in hand, we next
started to explore the scope of this one-pot sequential reaction as
summarized in Table 2. This reaction showed excellent functional
group compatibility, providing the products in modest to excellent
yields (up to 95%). The benzylic bromides 2 were found to be
tolerant of quinolines (3aed), pyridine (3e) and phenyl group (3f).
Benzylic bromides 2 with electron-donating groups lead to the
products in higher yield (3c>3d>3a>3b; 3f>3a, 3b, 3c, 3d). In
contract, aromatic hydrazines with electron-withdrawing groups
afforded the products in higher yields (3g>3i>3h). NH-
Bisarylhydrazones (3jeq, Table 2) could also be generated in
good yields when only 1.1 equiv 2 was used. This reaction is
sensitive to the steric and electronic effects, with more-hindered
3. Conclusions
In summary, we have developed an efficient synthesis of N-
substituted (or NH) bisarylhydrazones through a one-pot sequence
by Cu(I)/O2 catalyst system. Some of N-substituted bisarylhy-
drazones can be converted into benzimidazoles or triazoles at an
elevated temperature. On the basis of controlled experiments and
related literature,
a plausible alkylationeoxidationealkylation
mechanism is suggested. This reaction has several advantages over
traditional reaction systems, such as using inexpensive CuBr as
catalyst and the use of O2 as an ideal oxidant under mild reaction
conditions with simple operation.

J.-R. Hu et al. / Tetrahedron 69 (2013) 9865e9869
9867
Table 2
Preparation and structures of compounds 3ae3q
Conditions: 1 (0.2 mmol), 2 (0.22 mmol), CuBr (5 mol %), K2CO3 (0.5 mmol), stirring for 6 h
in 5 mL EtOH at 75 oC under 1 atm O2. For 3a–3i, additional benzyl bromide is needed.
Scheme 3. Proposed formation mechanism for compound 3.
4. Experiment
4.1. General
Synthesis of 3aei: A mixture of 1 (0.2 mmol), 2 (0.42 mmol),
CuBr (1.43 mg, 0.01 mmol), and K2CO3 (69.11 mg, 0.5 mmol) in EtOH
Scheme 2. The reactivity for possible intermediates.

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J.-R. Hu et al. / Tetrahedron 69 (2013) 9865e9869
Table 3
The structures of compounds 4fem
(5 mL) was stirred at 75 ꢀC under 1 atm O2 atmosphere for 6 h;
Synthesis of 3jeq: A mixture of 1 (0.2 mmol), 2 (0.22 mmol), CuBr
(1.43 mg, 0.01 mmol), and K2CO3 (69.11 mg, 0.5 mmol) in EtOH
(5 mL) was stirred at 75 ꢀC under 1 atm O2 atmosphere for 6 h;
Synthesis of 4fem: The same as synthesis of 3fem except that the
reaction time at 75 ꢀC for 6 h firstly and at 110 ꢀC for another 12 h.
After the reaction system was cooled to room temperature, satu-
rated NH4Cl solution (30 mL) and EtOAc (20 mL) were added. The
combined organic phases were dried over Na2SO4 and then con-
centrated to give crude products. Further separation by column
chromatography on silica gel (eluant with EtOAc and n-hexane)
gave the corresponding products.
119.5,118.5,117.0,114.7,100.8, 38.6; [M]þ: HRMS for C38H28N4 calcd.
540.6557, found 540.6558.
Compound 3e: (74%) mp 133e135 ꢀC; 1H NMR (500 MHz,
CDCl3):
d
7.83 (d, J¼7.2 Hz, 2H), 7.38e7.29 (m, 11H), 7.05 (t, J¼8.8 Hz,
1H), 5.26 (s, 2H); 13C NMR (125 MHz, CDCl3):
d
149.2, 147.6, 141.4,
140.5, 138.7, 137.9, 136.2, 130.5, 129.7, 128.4, 126.3, 124.2, 120.6,
119.7, 105.2, 37.9; [M]þ: HRMS for C18H16N4 calcd. 288.3464, found
288.3460.
Compound 3f:11 (91%) mp 110e112 ꢀC; 1H NMR (500 MHz,
CDCl3):
d
7.65 (d, J¼7.2 Hz, 2H), 7.40e7.21 (m, 13H), 6.98 (t, J¼7.3 Hz,
1H), 5.15 (s, 2H); [M]þ: HRMS for C20H18N2 calcd. 286.3703, found
286.3705.
Compound 3g:11 (95%) mp 120e122 ꢀC; 1H NMR (500 MHz,
CDCl3):
d
7.62 (d, J¼7.7 Hz, 2H), 7.37e7.19 (m, 13H), 5.14 (s, 2H);
4.2. Characterization data
[M]þ: HRMS for C20H17ClN2 calcd. 320.8154, found 320.8149.
Compound 3h:11 (68%) mp 110e113 ꢀC; 1H NMR (500 MHz,
Compound 3a: (76%) mp 237e239 ꢀC; 1H NMR (500 MHz,
CDCl3): d 7.60e7.58 (m, 2H), 7.37e7.21 (m, 11H), 6.87e6.84 (m, 2H),
CDCl3):
d
9.11 (d, J¼5.5 Hz, 1H), 8.92 (s, 1H), 8.61 (d, J¼2.5 Hz, 1H),
5.11 (s, 2H), 3.82 (s, 3H); [M]þ: HRMS for C21H20N2O calcd.
316.3963, found 316.3967.
8.57 (d, J¼10.0 Hz, 1H), 8.45 (d, J¼10.0 Hz, 1H), 8.27 (d, J¼10.0 Hz,
1H), 7.89 (m, 2H), 7.68 (m, 2H), 7.57 (d, J¼10.0 Hz, 2H), 7.49 (t,
J¼10.0 Hz,1H), 7.41 (m,1H), 7.38e7.33 (m, 3H), 6.96 (t, J¼10 Hz,1H),
Compound 3i:11 (71%) mp 135e138 ꢀC; 1H NMR (500 MHz,
6.07 (s, 2H); 13C NMR (125 MHz, CDCl3):
d 150.9, 147.5, 143.6, 142.8,
CDCl3):
d 7.64e7.60 (m, 2H), 7.35e7.24 (m, 11H), 7.15e7.12 (m, 2H),
5.15 (s, 2H), 2.35 (s, 3H); [M]þ: HRMS for C21H20N2 calcd. 300.3969,
found 300.3965.
139.2,137.8,135.4,134.8,131.9,130.4,129.1,128.9,128.5,128.1,127.2,
126.8, 126.1, 124.9, 120.8, 119.5, 118.5, 117.0, 100.8, 38.6; [M]þ: HRMS
for C26H20N4 calcd. 388.4638, found 388.4635.
Compound 3j:30 (88%) mp 95e98 ꢀC; 1H NMR (500 MHz, CDCl3):
Compound 3b: (62%) mp 237e239 ꢀC; 1H NMR (500 MHz,
d
7.70e7.65 (m, 3H), 7.38 (t, J¼7.1 Hz, 2H), 7.35e7.26 (m, 3H),
7.16e7.11 (m, 2H), 6.90 (t, J¼7.5 Hz, 1H); [M]þ: HRMS for C13H12N2
CDCl3):
d
9.19 (d, J¼5.5 Hz, 1H), 9.03 (s, 1H), 8.87 (d, J¼9.2 Hz, 1H),
calcd. 196.2478, found 196.2480.
8.75 (d, J¼10.0 Hz, 1H), 8.61 (d, J¼10.0 Hz, 1H), 8.35 (d, J¼10.0 Hz,
1H), 7.89 (m, 2H), 7.68 (m, 2H), 7.56 (t, J¼10.0 Hz, 1H), 7.45 (m, 1H),
7.42e7.36 (m, 3H), 6.84 (t, J¼10 Hz, 1H), 6.11 (s, 2H), 2.45 (s, 3H),
Compound 3k: (91%) mp 103e105 ꢀC; 1H NMR (500 MHz,
DMSO-d6):
d 10.35 (s, 1H, NH), 7.85 (s, 1H), 7.65 (m, 2H), 7.40 (m,
2H), 7.30 (m, 1H), 7.08 (d, J¼1.7 Hz, 2H), 7.05 (s, 2H); 13C NMR
2.36 (s, 3H); 13C NMR (125 MHz, CDCl3):
d 178.5, 176.3, 155.8, 150.1,
(125 MHz, DMSO-d6): d 157.3, 142.1, 136.9, 135.4, 129.2, 128.5, 125.7,
146.3, 144.5, 141.2, 138.5, 135.4, 134.7, 131.8, 130.9, 129.5, 129.1,
128.6, 128.1, 127.9, 126.3, 126.0, 125.2, 124.9, 121.7, 118.5, 117.9, 101.5,
40.5, 25.6, 24.3; [M]þ: HRMS for C30H24N4O2 calcd. 472.5372, found
472.5370.
117.1, 110.3; [M]þ: HRMS for C13H11ClN2 calcd. 230.6928, found
230.6925.
Compound 3l:31 (82%) mp 83e85 ꢀC; 1H NMR (500 MHz, CDCl3):
Compound 3c: (85%) mp 242e245 ꢀC; 1H NMR (500 MHz,
d
7.66 (m, 3H), 7.52 (br, 1H, NH), 7.40 (m, 2H), 7.30 (m, 1H), 7.09 (m,
2H), 6.89 (m, 2H), 3.81 (s, 3H); [M]þ: HRMS for C14H14N2O calcd.
226.2738, found 226.2740.
CDCl3):
d
8.95 (d, J¼6.3 Hz, 1H), 8.75 (s, 1H), 8.67 (d, J¼9.0 Hz, 1H),
8.65 (d, J¼10.0 Hz, 1H), 8.57 (d, J¼10.0 Hz, 1H), 8.31 (d, J¼10.0 Hz,
1H), 7.82 (m, 2H), 7.58 (m, 2H), 7.54 (t, J¼10.0 Hz, 1H), 7.35 (m, 1H),
7.32e7.26 (m, 3H), 6.89 (t, J¼10 Hz, 1H), 6.03 (s, 2H), 3.87 (s, 3H),
Compound 3m:31 (85%) mp 93e94 ꢀC; 1H NMR (500 MHz,
CDCl3):
d 7.67 (m, 3H), 7.51 (br, 1H, NH), 7.41 (m, 2H), 7.31 (m, 1H),
7.09 (d, J¼8.2 Hz, 2H), 7.04 (d, J¼8.2 Hz, 2H), 2.32 (s, 3H); [M]þ:
HRMS for C14H14N2 calcd. 210.2744, found 210.2739.
3.81 (s, 3H); 13C NMR (125 MHz, CDCl3):
d 152.1, 148.5, 145.7, 144.9,
140.3, 138.1, 136.8, 134.9, 132.4, 130.2, 129.7, 129.3, 128.5, 128.4,
127.6, 126.7, 126.1, 125.8, 124.2, 120.6, 118.3, 117.5, 100.9, 64.3, 63.8,
41.7; [M]þ: HRMS for C28H24N4O2 calcd. 448.5158, found 448.5153.
Compound 3d: (81%) mp 203e205 ꢀC; 1H NMR (500 MHz,
Compound 3n: (69%) mp 113e114 ꢀC; 1H NMR (CDCl3,
500 MHz):
d 8.04e8.01 (m, 2H), 7.78 (s, 1H), 7.38e7.21 (m, 5H),
7.10e7.03 (m, 2H), 6.98e6.93 (m, 1H), 2.43 (s, 3H); 13C NMR (CDCl3,
125 MHz):
d 144.4, 133.6, 132.8, 132.6, 129.7, 129.4, 129.2, 127.0,
CDCl3):
d
9.05 (d, J¼6.3 Hz, 1H), 8.98 (s, 1H), 8.61 (m, 2H), 8.43 (m,
126.7, 120.5, 112.9, 16.1; [M]þ: HRMS for C14H14N2 calcd. 210.2744,
found 210.2745.
6H), 7.95 (m, 4H), 7.61 (m, 4H), 7.57 (d, J¼10.0 Hz, 2H), 7.45 (t,
J¼10.0 Hz,1H), 7.42 (m, 1H), 7.33e7.26 (m, 3H), 6.91 (t, J¼10 Hz,1H),
Compound 3o: (45%) mp 125e128 ꢀC; 1H NMR (CDCl3,
6.03 (s, 2H); 13C NMR (125 MHz, CDCl3):
d 150.9, 149.2, 147.5, 146.5,
500 MHz):
d 8.08e8.05 (m, 2H), 7.76 (s, 1H), 7.48e7.32 (m, 5H),
143.6, 142.8, 139.2, 137.8, 135.4, 134.8, 133.8, 131.9, 130.4, 129.1,
128.9, 128.5, 128.1, 127.2, 126.8, 126.1, 125.5, 124.9, 123.2, 120.8,
7.15e7.09 (m, 2H), 6.91e6.88 (m, 1H), 1.49 (s, 9H); 13C NMR (CDCl3,

J.-R. Hu et al. / Tetrahedron 69 (2013) 9865e9869
9869
125 MHz):
d
144.4, 133.6, 132.8, 132.6, 129.7, 129.4, 129.2, 127.0,
Technological Landing Project of Higher Education of Jiangxi
Province (no. KJLD12094), and the Science and Technology Re-
search Project of Key Laboratory of Higher Institutions of Jiangxi
Province (no. GJJ12704).
126.7, 120.5, 112.9, 39.8, 26.5; [M]þ: HRMS for C17H20N2 calcd.
252.3541, found 252.3545.
Compound 3p: (58%) mp 153e154 ꢀC; 1H NMR (500 MHz,
DMSO-d6):
d
10.65 (s, 1H), 7.96 (dt, J¼8.4, 1.7 Hz, 2H), 7.90 (s, 1H),
7.77 (dt, J¼8.4, 1.7 Hz, 2H), 7.28e7.22 (m, 2H), 7.18e7.08 (m, 2H),
6.88e6.76 (m, 1H); 13C NMR (125 MHz, DMSO-d6): 144.7, 140.4,
134.7, 129.5, 129.1, 128.1, 125.4, 119.3, 112.2; [M]þ: HRMS for
Supplementary data
Experimental procedures and evaluation of reaction conditions
(SD-Table 1); crystallographic data and structural refinement de-
tails, crystal structure for compound 3a (CCDC-935975) are pro-
vided in SD-Table 2 and SD-Fig. 1. Supplementary data related
to this article can be found at http://dx.doi.org/10.1016/
j.tet.2013.08.073.
C
13H11N3O2 calcd. 241.2453; found, 241.2449.
Compound 3q: (86%) mp 135e137 ꢀC; 1H NMR (500 MHz,
DMSO-d6):
d
10.15 (s, 1H), 7.80 (s, 1H), 7.54 (dt, J¼8.7, 2.0 Hz, 2H),
7.32e7.19 (m, 2H), 7.09e7.03 (m, 2H), 6.97 (dt, J¼8.7, 2.0 Hz, 2H),
6.78e6.68 (m, 1H), 3.75 (s, 3H); 13C NMR (125 MHz, DMSO-d6):
159.0, 146.1, 136.8, 129.2, 128.7, 126.5, 118.2, 114.3, 111.8, 54.9; [M]þ:
HRMS for C14H14N2O calcd. 226.2817; found, 226.2823.
Compound 4f:11 (68%) mp 132e134 ꢀC; 1H NMR (500 MHz,
References and notes
CDCl3):
d
7.90 (d, J¼8.0 Hz, 1H), 7.70 (d, J¼7.7 Hz, 2H), 7.48 (d,
J¼7.2 Hz, 3H), 7.35e7.30 (m, 4H), 7.25e7.19 (m, 2H), 7.11 (d,
J¼6.8 Hz, 2H), 5.48 (s, 2H); [M]þ: HRMS for C20H16N2 calcd.
284.3544, found 284.3541.
1. Adams, J. P. J. Chem. Soc., Perkin Trans. 1 2000, 125e139.
2. Gupta, K. C.; Sutar, A. K. Coord. Chem. Rev. 2008, 252, 1420e1450.
3. Mistry, B. M.; Jauhari, S. Res. Chem. Intermed. 2013, 39, 1049e1068.
4. Wang, Q.-H.; Qiu, W.-W.; Wu, J.-P.; Zhang, M.-J. Struct. Chem. 2013, 24, 295e301.
5. Saravanakumar, D.; Devaraj, S.; Lyyampillai, S.; Mohandoss, K.; Kandaswamy,
M. Tetrahedron Lett. 2008, 49, 127e132.
Compound 4g:11 (73%) mp 143e146 ꢀC; 1H NMR (500 MHz,
CDCl3):
d
7.85 (d, J¼1.8 Hz, 1H), 7.68e7.65 (m, 2H), 7.48 (d, J¼7.0 Hz,
2H), 7.34e7.30 (m, 2H), 7.19e7.17 (m, 2H), 7.11e7.06 (m, 4H), 5.45 (s,
2H); [M]þ: HRMS for C20H15ClN2 calcd. 318.7995, found 318.7990.
Compound 4h:11 (82%) colorless liquid; 1H NMR (500 MHz,
6. Zhang, Y.-M.; lin, Q.; Wei, T.-B.; Wang, D.-D.; Yao, H.; Wang, Y.-L. Sens. Actuators,
B 2009, 137, 447e455.
7. Wong, M. S.; Gramlich, V.; Bosshard, C.; Gunter, P. J. Mater. Chem. 1997, 7,
€
2021e2026.
€
CDCl3):
d
7.68e7.64 (m, 2H), 7.45 (d, J¼6.5 Hz, 3H), 7.35e7.30 (m,
8. Choi, E.-Y.; Kim, P.-J.; Jazbinsek, M.; Kim, J.-T.; Lee, Y. S.; Gunter, P.; Lee, S. W.;
Kwon, O.-P. Cryst. Growth Des. 2011, 11, 3049e3055.
4H), 7.10e7.06 (m, 3H), 6.90 (dd, J¼8.7 Hz, 2.5 Hz, 1H), 5.40 (s, 2H),
3.89 (s, 3H); [M]þ: HRMS for C21H18N2O calcd. 314.3804, found
314.3801.
9. Seo, J.-Y.; Lee, S.-H.; Jazbinsek, M.; Yun, H.; Kim, J.-T.; Lee, Y. S.; Baek, I.-H.;
Rotermund, F.; Kwon, O.-P. Cryst. Growth Des. 2012, 12, 313e319.
10. Kwon, O.-P.; Jazbinsek, M.; Seo, J.-I.; Choi, E.-Y.; Yun, H.; Brunner, F. D. J.; Lee, Y.
Compound 4i:11 (65%) mp 146e148 ꢀC; 1H NMR (500 MHz,
€
S.; Gunter, P. J. Chem. Phys. 2009, 130, 134708-1e134708-7.
11. Guru, M. M.; Ali, M. A.; Punniyamurthy, T. J. Org. Chem. 2011, 76, 5295e5308.
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13. Guru, M. M.; Punniyamurthy, T. J. Org. Chem. 2012, 77, 5063e5073.
CDCl3):
d
7.69e7.65 (m, 3H), 7.47 (d, J¼6.6 Hz, 3H), 7.34e7.30 (m,
3H), 7.10e7.07 (m, 4H), 5.42 (s, 2H), 2.51 (s, 3H); [M]þ: HRMS for
ꢀ
~
14. Esteruelas, M. A.; Honczek, N.; Olivan, M.; Onate, E.; Valencia, M. Organome-
tallics 2011, 30, 2468e2471.
C
21H18N2 calcd. 298.3810, found 298.3812.
Compound 4j:13 (61%) mp 125e127 ꢀC; 1H NMR (500 MHz,
15. Gnanaprakasam, B.; Zhang, J.; Milstein, D. Angew. Chem., Int. Ed. 2010, 49,
1468e1471.
16. Tang, L.; Sun, H.-Y.; Li, Y.-F.; Zha, Z.-G.; Wang, Z.-Y. Green Chem. 2012, 14,
3423e3428.
17. Barrettm, L. C.; Langille, J. D.; Kerr, M. A. J. Org. Chem. 2000, 65, 6268e6269.
18. Tolman, W. B. Acc. Chem. Res. 1997, 30, 227e237.
CDCl3):
d
8.29 (d, J¼8.5 Hz, 2H), 7.75e7.72 (m, 4H), 7.56 (t, J¼8.0 Hz,
2H), 7.48e7.44 (m, 6H), 7.41 (t, J¼7.5 Hz, 1H); [M]þ: HRMS for
C
20H15N3 calcd. 297.3532, found 297.3530.
Compound 4k:13 (73%) mp 95e97 ꢀC; 1H NMR (500 MHz,
CDCl3):
d
8.15 (d, J¼9.2 Hz, 2H), 7.68e7.63 (m, 4H), 7.49 (d, J¼8.7 Hz,
19. Zhang, C.; Jiao, N. Angew. Chem., Int. Ed. 2010, 49, 6174e6177.
2H), 7.42e7.38 (m, 6H); [M]þ: HRMS for C20H14ClN3 calcd. 331.7983,
found 331.7980.
20. Zhang, C. X.; Liang, H.-C.; Kim, E.; Shearer, J.; Helton, M. E.; Kaderli, S.; Incarvito,
€
C. D.; Zuberbuhler, A. D.; Rheingold, A. L.; Karlin, K. D. J. Am. Chem. Soc. 2003,
125, 634e635.
Compound 4l:13 (58%) mp 103e105 ꢀC; 1H NMR (500 MHz,
21. Obias, H. V.; Lin, Y.; Murthy, N. N.; Pidcock, E.; Solomon, E. I.; Ralle, M.;
€
Blackburn, N. J.; Neuhold, Y.-M.; Zuberbuhler, A. D.; Karlin, K. D. J. Am. Chem.
CDCl3):
d
8.10 (d, J¼8.8 Hz, 2H), 7.64e7.61 (m, 4H), 7.38 (m, 6H), 6.98
Soc. 1998, 120, 12960e12961.
(d, J¼9.1 Hz, 2H), 3.85 (s, 3H); [M]þ: HRMS for C21H17N3O calcd.
327.3792, found 327.3791.
22. Itoh, S.; Taki, M.; Nakao, H.; Holland, P. L.; Tolman, W. B.; Que, L.; Fukuzumi, S.,
Jr. Angew. Chem., Int. Ed. 2000, 39, 398e400.
23. Mahadevan, V.; Henson, M. J.; Solomon, E. I.; Stack, T. D. P. J. Am. Chem. Soc.
2000, 122, 10249e10250.
24. Kunishita, A.; Ishimaru, H.; Nakashima, S.; Ogura, T.; Itoh, S. J. Am. Chem. Soc.
2008, 130, 4244e4245.
25. Taki, M.; Teramae, S.; Nagatomo, S.; Tachi, Y.; Kitagawa, T.; Itoh, S.; Fukuzumi, S.
J. Am. Chem. Soc. 2002, 124, 6367e6377.
Compound 4m: (68%) mp 103e105 ꢀC; 1H NMR (500 MHz,
CDCl3):
d
8.10 (d, J¼8.8 Hz, 2H), 7.62 (m, 4H), 7.37 (m, 6H), 6.98 (d,
J¼9.0 Hz, 2H), 2.31 (s, 3H); 13C NMR (125 MHz, CDCl3): 160.4, 145.9,
130.1, 128.5, 128.3, 124.6, 119.9, 114.5, 114.2, 21.2; [M]þ: HRMS for
C
21H17N3 calcd. 311.3798, found 311.3792.
26. Deng, G.-J.; Li, C.-J. Org. Lett. 2009, 11, 1171e1174.
27. Lewis, J. C.; Bergman, R. G.; Ellman, J. A. J. Am. Chem. Soc. 2007, 129, 5332e5333.
28. Bergman, R. G.; Lewis, J. C.; Ellman, J. A. J. Am. Chem. Soc. 2008, 130,
14926e14927.
Acknowledgements
29. Nakao, Y.; Kanyiva, K. S.; Hiyama, T. J. Am. Chem. Soc. 2008, 130, 2448e2449.
30. Gordon, M. S.; Sojka, S. A.; Krause, J. G. J. Org. Chem. 1984, 49, 97e100.
31. Lundgren, R. J.; Stradiotto, M. Angew. Chem., Int. Ed. 2010, 49, 8686e8690.
This work was supported by the National Natural Science
Foundation of China (no. 21261020), the Scientific and