Rh(iii)-Catalyzed regioselective mono- and di-iodination of azobenzenes using alkyl iodide

Article abstract of DOI:10.1039/c8ob00318a

A new approach for highly regioselective iodination of azobenzenes with alkyl iodide as the iodinating reagent enabled by Rh-catalyzed oxidative C-H activation has been developed. By changing the oxidant, various mono- and di-iodinated azobenzenes were smoothly obtained in moderate to excellent yields, respectively. The preliminary mechanistic study reveals that the reaction process might undergo electrophilic substitution of the directed ortho metalated five-membered rhodacycle compound by an iodine cationic species generated in situ from alkyl iodide and oxidant.

Full text of DOI:10.1039/c8ob00318a

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COMMUNICATION
Takeharu Haino et al.
Solvent-induced emission of organogels based on tris(phenylisoxazolyl)
benzene
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Rh(Ⅲ)-Catalyzed Regioselective Mono- and Di-iodination of
Azobenzenes Using Alkyl Iodide
Jixing Li,*a Wenxia Cong,a Zeng Gao b,c, Jinlong Zhang b, Huameng Yang b and Gaoxi Jiang *b
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
A new approach for highly regioselective iodination of azobenzenes with alkyl iodide as the iodinating reagent enabled by
Rh-catalyzed oxidative C-H activation has been developed. By changing the oxidant, various mono- and di-iodinated
azobenzenes were smoothly obtained in moderate to excellent yields, respectively. Preliminary mechanistic study reveals
that the reaction process might undergo electrophilic substitution of the directed ortho metalated five-membered
rhodacycle compound by an iodine cationic species generated in situ from alkyl iodide and oxidant.
www.rsc.org/
knowledge it is unprecedented to be an iodinating reagent. As
a continuation of our efforts towards the Rh-catalyzed C-H
functionalization,11 herein, we report a novel Rh-catalyzed
Introduction
Aromatic iodides represent an important class of organic
compounds due to their highly reactive activity and wide-
spread synthetic utility in organochemistry.1 Traditional
accesses to such compounds involve lithiation followed by
halogen quenching,2 electrophilic substitution,3 and
Sandmeyer reaction,4 which usually suffer from many
disadvantages, such as low yield, poor regioselectivity, harsh
reaction conditions, dangerous operations, and toxic reagent
requirement. Therefore, exploitation of efficient and selective
synthetic approaches to construct aryl iodides is always of
great demand. In principle, transition metal-catalyzed
straightforward C-H iodination is extremely attractive from the
point of atom/step economy. Consequently, Pd,5 Rh,6 Ru,7 Ni,8
Cu,9 and Co10 along with meritorious directing group (DG)
strategy has been intensively used for this goal developed by
Sanford, Yu, Glorius, Ackermann, Tian, Shi, and other groups,
independently. In these well documented methods, various
iodinating reagents were used, for instance, NIS,5a,d-e; 6; 7; 9b-c, 10
I2,5f-g, i, k; 8a, c; 9a IOAc,5b-c KIO3/K2S2O8,5j cyclic hypervalent iodine
reagent,5h and MI/PhI(OAc)2 (M = Na, Li, K)8b, 9d (Scheme 1, 1).
Despite these important advances, great challenge for highly
regioselective C-H iodination of aromatic hydrocarbon remains
in terms of substrate scope, chemoselectivity, and the
limitation of current iodinating reagent. Alkyl iodides as a class
of frequently-used synthetic building block always function as
alkyl group donor in organic synthesis, but to the best of our
highly selective mono and di-iodination of azobenzenes with
alkyl iodide as the iodinating reagent for the first time (scheme
1, 2). Both di-iodination and oxidant-control regioselectivity
are unprecedented in other reported metal-catalysis. The new
process features advantages of tunable mono- and di-
iodination by simple change of oxidant, high regioselectivity,
and good substrate tolerance as well as the further valuable
diversifications of iodinated products to interesting N-
containing compounds.
1. Previous work:
DG
DG
Pd, Rh, Ru, Ni, Cu
"I"
NIS, I2, I(III),
+
H
I
MI(M= Li, Na, K)/[O],
KIO3, others
♦ new iodinating reagent ♦ mono- and di-selectivity control
2. This wor k:
R2
N
N
R1
H
Cu(OAc)2
PhI(OAc)2
R2
I
N
N
[Rh]
R1
Bu
I
+
I
H
R2
N
I
N
R1
Scheme 1. Metal-Catalyzed C-H Iodination Reaction
Results and discussion
a.School of Chemistry & Chemical Engineering, Linyi University, Linyi 276005, P. R.
China. E-mail: jxli1987123@126.com
Encouraged by our previous result,11 we initially carried out
the reaction of azobenzene 1a with 4 equiv of n-BuI in the
presence of [Cp*RhCl2]2 (2.5 mol %), AgSbF6 (10 mol %), and
2.5 equiv of Cu(OAc)2 in 1,2-dichloroethane (DCE) at 90 °C for
12 h (Table 1, entry 1). To our delight, the desired product 2a
was detected in 35% yield. Significantly, changing AgSbF6 to
b.State Key Laboratory for Oxo Synthesis and Selective Oxidation, Center for
Excellence in Molecular Synthesis, Suzhou Research Institute of LICP, Lanzhou
Institute of Chemical Physics (LICP), Chinese Academy of Sciences, Lanzhou
730000, P. R. China. E-mail: gxjiang@licp.cas.cn
c. University of Chinese Academy of Sciences, Beijing 100049, P. R. China
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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AgBF4 improved the yield of 2a up to 86%, which revealed a decreased the yield of 2a to 50% (entry 12). Other transition-
5b-c
strong counterion effect on the reactivity (entry 2). mental catalysts such as [Cp*IrCl2]2 or Pd(OAc)2 gave lower
Simultaneously, only trace amount of di-iodinated product 3a yield or even inactive to the iodination process, suggesting
was observed, implying the overwhelming selectivity of this that rhodium catalyst played a vital role in the reaction (entries
transformation. Further examination of oxidants, including 13-14). The replacement of PhI(OAc)2 with PhI(OCOCF3)2 led to
TBHP, DDQ, and K2S2O8 gave the reaction dramatically adverse the di-iodinated product in 80% yield (entry 15). 3a was
effect (entries 3-5). While with PhI(OAc)2 as the oxidant, the di- obtained in 90% yield exclusively when the reaction took place
iodinated product 3a was obtained predominantly in 70% yield, at 60 °C (entry 16). We tried other alkyl iodides, such as (2-
unexpectedly (entry 6).
A careful screening of solvents iodoethyl)benzene and 1-iodopentane, to give similar results
revealed that DCE is optimal (entries 7-10). Decreasing the for the iodation reaction. Remarkably, 1-(2,6-diiodophenyl)-2-
loading of n-BuI to 3.0 equiv lowered slightly the yields (entry phenyldiazene or tri-/tetra-iodinated products were not
11). Lowering the reaction temperature from 90 °C to 70 °C observed that disclose exclusive chemoselectivity.5b-c
Table 1 Optimization of the Reaction Conditionsa
entry
1
catalyst/additive
[Cp*RhCl2]2/AgSbF6
[Cp*RhCl2]2/AgBF4
[Cp*RhCl2]2/AgBF4
[Cp*RhCl2]2/AgBF4
[Cp*RhCl2]2/AgBF4
[Cp*RhCl2]2/AgBF4
[Cp*RhCl2]2/AgBF4
[Cp*RhCl2]2/AgBF4
[Cp*RhCl2]2/AgBF4
[Cp*RhCl2]2/AgBF4
[Cp*RhCl2]2/AgBF4
[Cp*RhCl2]2/AgBF4
[Cp*IrCl2]2/AgBF4
Pd(OAc)2
[O]
Cu(OAc)2
Cu(OAc)2
TBHP
solvent
DCE
DCE
DCE
DCE
DCE
DCE
Et2O
THF
2a(%)b
35
3a(%)b
<5
2
86c
<5
3
<5
<5
4
DDQ
<5
<5
5
K2S2O8
<5
<5
70c
6
PhI(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
PhI(OCOCF3)2
PhI(OCOCF3)2
<5
7
40
<5
8
<5
<5
9
DCM
DMF
DCE
DCE
DCE
DCE
DCE
DCE
75c
n.r.d
76c
50c
10
<5
10
11e
12f
13
14g
15
16h
<5
<5
<5
<5
n.r.d
<5
[Cp*RhCl2]2/AgBF4
[Cp*RhCl2]2/AgBF4
<5
80c
90c
<5
a Reaction conditions: 1a (0.2 mmol), n-BuI (0.8 mmol), catalyst (2.5 mol %), Ag salt (10 mol %), oxidant (2.5 equiv), solvent (1 mL), 90 °C, 12 h. b GC yields. c isolated
yield. d no reaction. e 3.0 equiv of n-BuI. f at 70 °C. g with or without AgBF4. h at 60 °C.
With the optimized reaction conditions in hand, we started compatible with this transformation and readily gave rise to 2o
to explore the reaction scope of mono-iodination of and 2p in 65% and 77% yields, respectively. Additionally, we
azobenzenes (Table 2). Generally, a variety of azobenzenes also investigated the more challenging unsymmetrical
were feasibly transformed into the corresponding ortho- azobenzenes 1q-r and found that such ortho-iodination took
iodinated products in moderate to excellent yields. Both place preferentially on the electron-rich aromatic ring with
electron-rich and electron-deficient azobenzenes showed a moderate regioselectivity.
comparable reactivity. For instance, besides azobenzene 1a
1b bearing alkyl groups on para-position of aryl rings azobenzenes with butyl iodide. As shown in Table 3, the
converted easily into the desired products 2b in 68-88% reactions proceeded smoothly to provide the desired products
yields. Readily, 2g was obtained in 76% yield if the 4-methoxyl with 55%-90% yields. A series of symmetrically substituted
substituted reactant 1g was treated to the reaction. azobenzenes 1a were employed and the reactions proceeded
Halogenated substrates 1h afforded products 2h in slightly facilely to furnish di-iodination adducts 3a in 68-90% yields
lower yields. The iodination of meta-substituted azobenzenes regardless of the electronic character of substitutes. It’s
1k proceeded well to give 2k as single regioisomer with notable that meta-isopropyl substituted azobenzene 1l and
,
Next, we investigated the di-iodination reaction of
-f
-f
-i
-j
-j
-i
-m
-m
79%-83% yields through selective cleavage of the less hindered unsymmetrical azobenzene 1q afforded exclusively 3l and 1q
C-H bond. Gratifyingly, ortho-methyl substituted azobenzene in 68% and 75% yields, respectively, which demonstrates
1n was also amenable to the reaction conditions, providing 2n excellent regioselectivity. However, ortho-methyl and 2,4-
in 72% yield. Di-substituted azobenzenes 1o and 1p were also methyl substituted azobenzenes 1n and 1o assembled the
2 | J. Name., 2012, 00, 1-3
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Table 2. Scope of Mono-iodination Reaction
be readily obtained in good yields by Sonogashira coupling
reaction of 2a with ethynylbenzene, respectively.16
Furthermore, di-iodinated product 3f could transformed into
di-silylated compound 4e by the reaction with n-BuLi/ClSiHPh2,
followed by fluorination with AgF to provide 2,2'-
Bis(fluorodiphenylsilyl)azobenzene 4f in good yield, the latter
possesses unique coloration property due to its intrinsic N···Si
coordination interaction.17 Our method provides an
alternatively practical excess to these valuable compounds
from easily accessible nonprefunctionalized azobenzenes.18
To investigate the mechanism of this transformation,
several controlled reactions were executed (Scheme 3). No
reaction occurred without either of [Cp*RhCl2]2 or AgBF4
reveals that the combination of Rh/Ag is indispensable to the
process (eq 1). Using inorganic sodium iodide salt (NaI) instead
of 1-iodobutane as iodine surrogate, similar results were
observed (eq 2). Consequently, 1a was recovered in more than
95% in the absence of oxidant. As a contrast, iodinated
products 2a and 3a can be isolated in 80% and 90% yields
respectively in the presence of Cu(OAc)2 and PhI(OCOCF3)2.
a Reaction conditions: 1 (0.2 mmol), n-BuI (0.8 mmol), [Cp*RhCl2]2 (2.5 mol %),
AgBF4 (10 mol %), Cu(OAc)2 (2.5 equiv), DCE (1 mL), 90 °C, 12 h, isolated yield
given. b recovered azobenzene in the parentheses.
NaN3 (1.5 eq)
N
CuI (10 mol %), TMEDA (20 mol %)
CTAB (20 mol %), H2O, 130 °C,16 h
N
Ph
N
4a, 89%
N
N
1) Pd(PPh3)2Cl2 (5 mol %)
NaOH (3.0 eq), EtOH, rt, 2 h
N
N
I
2a
mono-iodinated products 2n and 2o due to the steric
hindrance reasonably even raised the reaction temperature up
to 120 °C.
Ph
O
O
2) 70 °C, 2 h, N2,
COOEt
4b, 83%
OEt
N2 (2.0 eq)
Pd(PPh3)2Cl2 (4 mol %)
CuI (8 mol %), n-BuNH2 (6.0 eq)
Table 3. Scope of Di-iodination Reaction
Ph (2.0 eq), THF, rt
N
N
Ph
Ph
Pd(PPh3)2Cl2 (4 mol %)
CuI (8 mol %), Et3N (3.0 eq)
Ph
N
N
•
(2.0 eq),
THF, 40 °C
Ph
Ph
4c, 80%
4d, 81%
Ph
Ph
Ph
Si
Ph
Si
R
R
I
R
H
N
F
1) n-BuLi
2) ClSiHPh2
AgF
THF, rt
N
F
N
N
N
N
H
THF, -105 °C
Ph
Ph
R
Si
Ph
R
Si
Ph
R
I
3f, R= n-Bu
4e, 82%
4f, 79%
Scheme 2. Further Transformation of Iodinated Products
Direct use of I2 (eq 3) for the oxidative process resulted in
recovery of azobenzene 1a. Addition of Cu(OAc)2 to the
reaction conditions provided 2a (43%) and 3a (50%) in total 93%
yield possibly due to more active iodide intermediate.
Subsequently, with PhI(OCOCF3)2 as the oxidant, 3a was
furnished in 98% yield exclusively. The treatment of BuI to
both Cu(OAc)2 and PhI(OCOCF3)2 under the reaction conditions
resulted in the formation of I2 (by starch solution), butan-1-ol,
butyraldehyde, and others (by GC-Mass) (eq 4).
a Reaction conditions: 1 (0.2 mmol), n-BuI (0.8 mmol), [Cp*RhCl2]2 (2.5 mol %),
AgBF4 (10 mol %), PhI(OCOCF3)2 (2.5 equiv), DCE (1 mL), 60 °C, 12 h, isolated yield
given.
As a kind of versatile building blocks, above iodinated
products can be readily converted into other interesting N-
containing compounds that highlights the synthetic value of
the selective iodination reaction (Scheme 2). 2-aryl-2H-
benzo[1,2,3]triazole 4a was given easily in 89% yield from 2a
by an azidation-denitrogentive coupling cascade.11-13 The
treatment of 2a with acydiazoacetate in the presence of Pd-
catalyst afforded 2H-indazole 4b in high yield.14 Such skeleton
Although the mechanism of this catalytic transformation is
not completely clear yet, on the basis of previous reports for
Rh-catalyzed functionalization of azobenzenes6 and the above-
mentioned observations, the reaction process might undergo
electrophilic substitution of the directed ortho metalated five-
extensively
presents
in
natural
products
and
membered rhodacycle compound
A by an iodine cationic
pharmaceuticals.15 Alkyne 4c and (3-isoindazolyl)allene 4d can
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species generated in situ from alkyl iodide and oxidant General procedures for the products 2: Azobenzenes
1
(0.2
(Scheme 4).
mmol), n-BuI (0.8 eq), [Cp*RhCl2]2 (2.5 mol %), silver
tetrafluoroborate (10 mol %) and Cu(OAc)2 (2.5 eq) was added
to a flame-dried Schlenck tube which charged with a magnetic
stir bar in 1.0 mL 1,2-dichloroethane (DCE). The resulting
suspension was stirred at 90
℃ under N2 for 12 h. After celite
filtration and evaporation of the solvents in vacuo, the crude
product was purified by column chromatography on silica gel
(petroleum/ethyl acetate = 100:1) to yield products
2.
General procedures for the synthesis of 3: Azobenzenes
1
(0.2
mmol), n-BuI (0.8 eq), [Cp*RhCl2]2 (2.5 mol %), silver
tetrafluoroborate (10 mol %) and PhI(OAc)2 (2.5 eq) was added
to a flame-dried Schlenck tube which charged with a magnetic
stir bar in 1.0 mL 1,2-dichloroethane (DCE). The resulting
suspension was stirred at 60
℃ under N2 for 12 h. After celite
filtration and evaporation of the solvents in vacuo, the crude
product was purified by column chromatography on silica gel
(petroleum/ethyl acetate = 100:1-100:5) to yield products 3.
Experimental characterization data for products: Compounds
2a5f
3a5f
,
,
2b5f
3b17
,
2k5f
3f17
,
2n5f
,
2c14
,
2h5f
,
2i14
,
2j14
4d16
,
2l14
, , , ,
2m14 2q14 2r14
,
,
4a12
,
4b14
,
4c16
,
,
4e17, and 4f17 have
previously been reported and their structure has been
confirmed by comparison with the published spectral data.
Scheme 3. Preliminary Mechanistic Study
(E)-1-(2-iodophenyl)-2-phenyldiazene
(2a):
The
title
compound was prepared according to the general procedure
as a yellow solid (52.9 mg, 86%). 1H NMR (400 MHz, CDCl3) δ =
8.10-8.08 (m, 3H), 7.70-7.72 (m, 1H), 7.60-7.56 (m, 3H), 7.47-
7.45 (m, 1H), 7.23-7.19 (m, 1H). 13C NMR (100 MHz, CDCl3) δ =
152.34, 151.29, 139.88, 132.27, 131.65, 129.25, 129.23, 128.95,
123.64, 117.40, 102.72.
Scheme 4. The Working Hypothesis for Reaction Process
(E)-1-(2-iodo-4-methylphenyl)-2-(p-tolyl)diazene (2b): The
title compound was prepared according to the general
procedure as a red oil (56.5 mg, 84%). 1H NMR (400 MHz,
CDCl3) δ = 7.90-7.86 (m, 3H), 7.56 (d, J = 8.0 Hz, 1H), 7.32 (d, J =
8.0 Hz, 2H), 7.22 (d, J = 8.0 Hz, 1H), 2.45 (s, 1H), 2.38 (s, 1H).
13C NMR (CDCl3, 100 MHz) δ = 150.55, 149.29, 142.75, 141.91,
140.09, 129.84, 129.79, 129.73, 123.43, 116.84, 102.99, 21.57,
20.85.
Conclusions
In summary, we have developed a highly chemoselective
oxidative access to ortho-iodinated azobenzenes by a Rh(III)-
catalysis with alkyl iodide as the iodinating reagent. Both di-
iodination
and
oxidant-control
regioselectivity
are
unprecedented in other reported metal-catalysis. The process
features advantages of good substrate scope and tunable
regioselectivity by simple change of oxidant, along with the
further valuable functionalization of the iodinated products.
The transformation might take place via electrophilic
substitution of five-membered rhodacycle intermediate with in
situ formed reactive iodine cationic species.
(E)-1-(4-ethyl-2-iodophenyl)-2-(4-ethylphenyl)diazene
(2c):
The title compound was prepared according to the general
procedure as a red oil (64.1 mg, 88%). 1H NMR (400 MHz, CDCl3)
δ = 7.97 (d, J = 8.0 Hz, 2H), 7.92 (d, J = 0.8 Hz, 1H), 7.63 (d, J =
8.0 Hz, 1H), 7.40 (d, J = 8.0 Hz, 2H), 7.32-7.28 (m, 1H), 2.79 (q, J
= 8.0 Hz, 2H), 2.72 (q, J = 8.0 Hz, 2H), 1.36-1.30 (m, 6H). 13C
NMR (100 MHz, CDCl3) δ = 150.77, 149.50, 148.97, 148.18,
138.99, 128.68, 128.62, 128.61, 123.55, 117.02, 103.09, 28.92,
28.28, 15.45, 15.26.
Experimental
(E)-1-(2-iodo-4-isopropylphenyl)-2-(4-isopropylphenyl)diazen-
e (2d): The title compound was prepared according to the
general procedure as a red oil (64.3 mg, 82%). 1H NMR (400
MHz, CDCl3) δ = 7.98 (d, J = 8.0 Hz, 2H), 7.94 (d, J = 1.5 Hz, 1H),
7.63 (d, J = 8.0 Hz, 1H), 7.43 (d, J = 8.0 Hz, 2H), 7. 33 (dd, J = 8.0,
1.5 Hz, 1H), 3.07-2.96 (m, 2H), 1.37-1.33(m, 12H). 13C NMR
(100 MHz, CDCl3) δ = 153.53, 152.72, 150.88, 149.64, 137.66,
127.35, 127.33, 127.23, 127.19, 123.55, 117.08, 117.05, 103.09,
34.20, 33.75, 23.88, 23.75. HRMS (ESI) calcd. For C18H22IN2
[M+H]: 393.0828, found: 393.0819.
General Information: All NMR spectra were run at 400 MHz
(1H NMR) or 100 MHz (13C NMR) in CDCl3 solution and
tetramethylsilane (TMS) was used as the internal standard..
High resolution mass spectra (HRMS) were recorded on Bruker
MicrOTOF-Q II mass instrument (ESI). The other reagents were
commercially available and were used without further
purification. All the reactions were monitored using thin-layer
chromatography (TLC).
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(E)-1-(4-(tert-butyl)-2-iodophenyl)-2-(4-(tert-butyl)phenyl)di-
7.41 (m, 2H), 7.32 (d, J = 8.0 Hz, 1H), 7.02-6.99 (m, 1H), 2.48 (s,
azene (2e): The title compound was prepared according to the 3H), 2.38 (s, 3H). 13C NMR (100 MHz, CDCl3) δ = 152.47, 151.19,
general procedure as a yellow solid (57.1 mg, 68%). 1H NMR 139.42, 139.16, 139.06, 133.17, 132.30, 128.99, 123.98, 120.83,
(400 MHz, CDCl3) δ = 8.03 (d, J = 1.6 Hz, 1H), 7.95 (d, J = 8.0 Hz, 117.87, 98.53 , 21.45, 21.01. HRMS (ESI) calcd. For C14H14IN2
2H), 7.60-7.55 (m, 3H), 7.46 (dd, J = 8.0, 1.5 Hz, 1H), 1.39 (s, [M+H]: 337.0202, found: 337.0196.
9H), 1.37 (s, 9H). 13C NMR (100 MHz, CDCl3) δ = 155.82, 154.93, (E)-1-(2-iodo-5-isopropylphenyl)-2-(3-isopropylphenyl)diaze-
150.45, 149.32, 136.71, 126.21, 126.08, 123.20, 116.73, 103.03, ne (2l): The title compound was prepared according to the
35.07, 34.88, 31.28, 31.17. HRMS (ESI) calcd. For C20H26IN2 general procedure as a red oil (62.7 mg, 80%). 1H NMR (400
[M+H]: 421.1141, found: 421.1130.
MHz, CDCl3) δ = 7.94 (d, J = 8.0 Hz, 2H), 7.85-7.83 (m, 1H), 7.52
(E)-1-(4-butyl-2-iodophenyl)-2-(4-butylphenyl)diazene
(2f): (d, J = 2.0 Hz, 1H), 7.46 (t, J = 8.0 Hz, 1H), 7.39 (d, J = 8.0 Hz,
The title compound was prepared according to the general 1H), 7.08 (dd, J = 8.0, 2.1 Hz, 1H), 3.06 (m, 1H), 2.97 (m, 1H),
procedure as a red oil (63.8 mg, 76%). 1H NMR (400 MHz, 1.35 (d, J = 8.0 Hz, 6H), 1.30 (d, J = 8.0 Hz, 6H). 13C NMR (100
CDCl3) δ = 7.92 (d, J = 8.0 Hz, 2H), 7.86 (d, J = 1.5 Hz, 1H), 7.57 MHz, CDCl3) δ = 152.65, 151.23, 150.21, 150.06, 139.54,
(d, J = 8.0 Hz, 1H), 7.33 (d, J = 8.0 Hz, 2H), 7.23 (dd, J = 8.0, 1.7 130.61, 129.81, 129.06, 122.36, 120.28, 115.31, 99.08, 44.49,
Hz, 1H), 2.70 (t, J = 8.0 Hz, 2H), 2.63 (t, J = 8.0 Hz, 2H), 1.68- 34.07, 33.90, 23.95, 23.79. HRMS (ESI) calcd. For C18H22IN2
1.62 (m, 4H), 1.43-1.36 (m, 4H), 0.98-0.94 (m, 6H). 13C NMR [M+H]: 393.0828, found: 393.0823.
(100 MHz, CDCl3) δ = 150.74, 149.49, 147.73, 146.89, 139.48, (E)-1-(2-iodo-5-methoxyphenyl)-2-(3-methoxyphenyl)diazene
129.16, 129.10, 123.45, 116.92, 102.99, 35.64, 34.99, 33.44, (2m): The title compound was prepared according to the
33.26, 22.35, 22.31, 13.96, 13.92. HRMS (ESI) calcd. For general procedure as a yellow solid (61.1 mg, 83%). 1H NMR
C20H26IN2 [M+H]: 421.1141, found: 421.1135.
(400 MHz, CDCl3) δ = 7.87 (d, J = 8.0 Hz, 1H), 7.65 (d, J = 8.0 Hz,
(E)-1-(2-iodo-4-methoxyphenyl)-2-(4-methoxyphenyl)diazene 1H), 7.56 (s, 1H), 7.46-7.42 (m, 1H), 7.25 (d, J = 4.0 Hz, 1H),
(2g): The title compound was prepared according to the 7.08-7.06 (m, 1H), 6.84-7.81 (m, 1H), 3.91 (s, 3H), 3.86 (s, 3H).
general procedure as a yellow solid (55.9 mg, 76%). 1H NMR 13C NMR (100 MHz, CDCl3) δ = 160.60, 160.33, 153.47, 151.61,
(400 MHz, CDCl3) δ = 7.95 (d, J = 8.0 Hz, 2H), 7.66 (d, J = 8.0 Hz, 139.86, 129.85, 120.06, 118.39, 117.98, 106.36, 101.62, 92.32,
1H), 7.53 (d, J = 2.5 Hz, 1H), 7.01 (d, J = 8.0 Hz, 2H), 6.96 (dd, J 55.63, 55.45.
= 8.0, 2.5 Hz, 1H), 3.89 (s, 3H), 3.86 (s, 3H). 13C NMR (100 MHz, (E)-1-(2-iodo-6-methylphenyl)-2-(o-tolyl)diazene (2n): The
CDCl3) δ = 161.99, 161.65, 146.88, 145.38, 125.12, 123.74, title compound was prepared according to the general
117.76, 115.39, 114.36, 114.24, 114.15, 114.08, 104.50, 55.82, procedure as a red oil (48.4 mg, 72%). 1H NMR (400 MHz, CDCl3)
55.59. HRMS (ESI) calcd. For C14H14IN2O2 [M+H]: 369.0100, δ = 7.90 (d, J = 8.0 Hz, 1H), 7.82 (d, J = 8.0 Hz, 1H), 7.46-7.43 (m,
found: 369.0093.
2H), 7.36 (t, J = 7.4 Hz, 1H), 7.31 (d, J = 7.0 Hz, 1H), 6.98 (t, J =
(E)-1-(4-fluoro-2-iodophenyl)-2-(4-fluorophenyl)diazene (2h): 7.7 Hz, 1H), 2.77 (s, 3H), 2.39 (s, 3H). 13C NMR (100 MHz, CDCl3)
The title compound was prepared according to the general δ = 152.09, 150.63, 138.69, 137.46, 132.06, 131.65, 131.40,
1
procedure as a light yellow solid (41.3 mg, 60%). H NMR (400 129.75, 129.20, 126.56, 115.79, 19.64, 17.86. HRMS (ESI) calcd.
MHz, CDCl3) δ = 8.01-7.97 (m, 2H), 7.76-7.74 (m, 1H), 7.69-7.65 For C14H14IN2 [M+H]: 337.0202, found: 337.0197.
(m, 1H), 7.23-7.14 (m, 3H). 13C NMR (100 MHz, CDCl3) δ = (E)-1-(2,4-dimethylphenyl)-2-(2-iodo-4,6-dimethylphenyl)dia-
165.98, 164.99, 163.46, 162.44, 148.74, 148.70, 147.69, 147.66, zene (2o): The title compound was prepared according to the
126.64, 126.39, 125.61, 125.52, 118.23, 118.14, 116.32, 116.31, general procedure as a red solid (47.3 mg, 65%). 1H NMR (400
116.10, 103.11, 103.02.
MHz, CDCl3) δ = 7.71 (d, J = 8.0 Hz, 2H), 7.18 (s, 1H), 7.11 (d, J =
(E)-1-(4-chloro-2-iodophenyl)-2-(4-chlorophenyl)diazene (2i): 8.0 Hz, 1H), 7.06 (s, 1H), 2.68 (s, 3H), 2.41 (s, 3H), 2.34 (s, 3H),
The title compound was prepared according to the general 2.34 (s, 3H). 13C NMR (100 MHz, CDCl3) δ = 149.48, 148.81,
1
procedure as a light yellow solid (52.1 mg, 69%). H NMR (400 141.90, 139.42, 138.63, 137.92, 133.03, 131.87, 129.53, 127.33,
MHz, CDCl3) δ = 8.02 (d, J = 2.1 Hz, 1H), 7.93-7.91 (m, 2H), 7.58 115.60, 96.15, 21.45, 20.51, 19.97, 17.84. HRMS (ESI) calcd.
(d, J = 8.0 Hz, 1H), 7.51-7.49 (m, 2H), 7.40 (dd, J = 8.0, 2.1 Hz, For C16H18IN2 [M+H]: 365.0515, found: 365.0506.
1H). 13C NMR (100 MHz, CDCl3) δ = 150.50, 139.20, 137.87, (E)-1-(3,4-dimethylphenyl)-2-(2-iodo-4,5-dimethylphenyl)dia-
137.76, 129.57, 129.52, 129.23, 124.83, 117.76, 104.51, 103.18. zene (2p): The title compound was prepared according to the
(E)-1-(4-bromo-2-iodophenyl)-2-(4-bromophenyl)diazene (2j): general procedure as a yellow solid (56.1 mg, 77%). 1H NMR
The title compound was prepared according to the general (400 MHz, CDCl3) δ = 7.79 (s, 1H), 7.77 (s, 1H), 7.74 (d, J = 8.0
procedure as a yellow solid (55.1 mg, 59%). 1H NMR (400 MHz, Hz, 1H), 7.44 (s, 1H), 7.28 (d, J = 8.0 Hz, 1H), 2.38 (s, 3H), 2.35
CDCl3) δ = 8.18 (d, J = 1.8 Hz, 1H), 7.85 (d, J = 8.0 Hz, 2H), 7.66 (s, 3H), 2.28 (s, 3H), 2.27 (s, 3H). 13C NMR (100 MHz, CDCl3) δ
(d, J = 8.0 Hz, 2H), 7.57-7.50 (m, 2H). 13C NMR (100 MHz, CDCl3) =150.94, 149.52, 141.69, 140.55, 140.20, 137.70, 137.43,
δ = 150.84, 149.96, 141.93, 132.52, 132.16, 132.14, 126.47, 130.31, 124.42, 121.06, 117.95, 99.40, 19.96, 19.94, 19.62,
126.17, 125.02, 118.06, 103.53. HRMS (ESI) calcd. For 19.44. HRMS (ESI) calcd. For C16H18IN2 [M+H]: 365.0515, found:
C12H8Br2IN2 [M+H]: 464.8099, found: 464.8086.
365.0516.
(E)-1-(2-iodo-5-methylphenyl)-2-(m-tolyl)diazene (2k): The (E)-1-(2-iodophenyl)-2-(p-tolyl)diazene
+
(E)-1-(2-iodo-4-
title compound was prepared according to the general methylphenyl)-2-phenyldiazene (2q+2q’): The title compound
1
procedure as a red solid (53.0 mg, 79%). H NMR (400 MHz, was prepared according to the general procedure as a res oil
CDCl3) δ = 7.89 (d, J = 8.0 Hz, 1H), 7.81 (d, J = 1.2 Hz, 2H), 7.45- (54.7 mg, 85%). 1H NMR (400 MHz, CDCl3) δ = 8.03 (d, J = 8.0
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Hz, 0.8H), 8.00 (d, J = 8.0 Hz, 1.8H), 7.92 (d, J = 8.2 Hz, 1H), 7.87 (E)-1,2-bis(4-butyl-2-iodophenyl)diazene (3f): The title
(s, 0.8H), 7.65-7.62 (m, 0.8H), 7.58 (d, J = 8.0 Hz, 1H), 7.57- compound was prepared according to the general procedure
7.51(m, 2.8H), 7.42 (t, J = 8.0 Hz, 0.8H), 7.34 (d, J = 8.0 Hz, as a red oil (74.3 mg, 68%). 1H NMR (400 MHz, CDCl3) δ = 7.95
1.6H), 7.23 (d, J = 8.0 Hz, 1H), 7.18-7.11 (m, 0.8H), 2.46 (s, (d, J = 8.0 Hz, 2H), 7.76 (s, 2H), 7.38 (d, J = 8.0 Hz, 2H), 2.72 (t, J
2.4H), 2.39 (s, 3H).13C NMR (100 MHz, CDCl3) δ = 152.37, = 8.0 Hz, 2H), 2.56 (t, J = 8.0 Hz, 2H), 1.69-1.57 (m, 4H), 1.39 (m,
150.53, 149.24, 143.12, 142.30, 140.18, 139.78, 131.92, 131.30, 4H), 0.96 (m, 6H). 13C NMR (100 MHz, CDCl3) δ = 151.00,
130.02, 129.86, 129.77, 129.25, 129.15, 128.90, 128.84, 123.58, 149.49, 148.00, 145.82, 140.17, 129.27, 123.31, 87.86, 35.72,
123.46, 117.34, 116.88, 103.31, 21.63, 20.90.
34.19, 33.42, 33.24, 22.39, 22.22, 13.97, 13.88. HRMS (ESI)
(E)-1-(4-chlorophenyl)-2-(2-iodophenyl)diazene
+
(E)-1-(4- calcd. For C20H25I2N2 [M+H]: 547.0107, found: 547.0101.
chloro-2-iodophenyl)-2-phenyldiazene (2r +2r’): The title (E)-1,2-bis(4-fluoro-2-iodophenyl)diazene (3g): The title
compound was prepared according to the general procedure compound was prepared according to the general procedure
as a yellow solid (50.0 mg, 73%).1H NMR (400 MHz, CDCl3) δ = as a light yellow solid (75.2 mg, 80%). 1H NMR (400 MHz, CDCl3)
8.03 (d, J = 8.0 Hz, 1.4H), 8.01-7.98 (m, 0.8H), 7.94 (d, J = 8.0 Hz, δ = 7.97 (s, 1H), 7.95 (s, 3H), 7.55 (d, J = 8.0 Hz, 2H). 13C NMR
2H), 7.63 (dd, J = 8.0, 1.3 Hz, 1H), 7.60 (d, J = 8.0 Hz, 1H), 7.54 (100 MHz, CDCl3) δ = 151.40, 149.32, 139.60, 138.85, 134.67,
(s, 0.4H), 7.52-7.49 (m, 2.8H), 7.44-7.39 (m, 1.4H), 7.20- 7.15 129.65, 124.61, 87.75. HRMS (ESI) calcd. For C12H7F2I2N2 [M+H]:
(m, 1H). 13C NMR (100 MHz, CDCl3) δ = 151.07, 150.66, 139.94, 470.8667, found: 470.8672.
139.11, 137.59, 132.49, 131.85, 129.48, 129.24, 129.21, 128.93, (E)-1,2-bis(4-chloro-2-iodophenyl)diazene (3h): The title
124.79, 123.65, 117.83, 117.30.
(E)-1,2-bis(2-iodophenyl)diazene (3a): The title compound was as a yellow solid (75.5 mg, 75%). 1H NMR (400 MHz, CDCl3) δ =
prepared according to the general procedure as a yellow solid 8.10-8.06 (m, 2H), 7.76 (d, J = 8.0 Hz, 2H), 7.32-7.27 (m, 2H) 13
compound was prepared according to the general procedure
C
(78.1 mg, 90%). 1H NMR (400 MHz, CDCl3) δ = 8.09-8.08 (m, NMR (100 MHz, CDCl3) δ = 166.61, 164.08, 163.93, 161.88,
2H), 7.98 (d, J = 8.0 Hz, 2H), 7.64-7.62 (m, 3H), 6.78 (t, J = 7.9 159.32, 147.53, 127.46, 127.21, 125.56, 125.47, 116.50, 116.27,
Hz, 1H). 13C NMR (100 MHz, CDCl3) δ = 153.39, 151.26, 140.14, 87.41, 87.33. HRMS (ESI) calcd. For C12H7Cl2I2N2 [M+H]:
132.45, 130.41, 129.52, 129.31, 123.46, 123.34, 87.67.
502.8076, found: 502.8072.
(E)-1,2-bis(2-iodo-4-methylphenyl)diazene (3b): The title (E)-1,2-bis(4-bromo-2-iodophenyl)diazene (3i): The title
compound was prepared according to the general procedure compound was prepared according to the general procedure
as a yellow oil (75.8 mg, 82%). 1H NMR (400 MHz, CDCl3) δ = as a yellow solid (82.9 mg, 70%). 1H NMR (400 MHz, CDCl3) δ =
7.93 (d, J = 8.0 Hz, 2H), 7.77 (s, 2H), 7.37 (d, J = 8.0 Hz, 2H), 8.09 (s, 2H), 7.88 (d, J = 8.0 Hz, 2H), 7.71 (d, J = 8.0 Hz, 2H). 13
C
2.47 (s, 3H), 2.32 (s, 3H). 13C NMR (100 MHz, CDCl3) δ = 150.83, NMR (100 MHz, CDCl3) δ = 151.87, 149.69, 142.21, 132.69,
149.35, 143.03, 140.81, 140.75, 129.91, 123.30, 87.85, 21.69, 132.66, 127.48, 124.78, 122.55, 88.19. HRMS (ESI) calcd. For
19.98.
C12H7Br2I2N2 [M+H]: 590.7065, found: 590.7060.
(E)-1,2-bis(4-ethyl-2-iodophenyl)diazene (3c): The title (E)-1,2-bis(2-iodo-5-isopropylphenyl)diazene
(
3l): The title
compound was prepared according to the general procedure compound was prepared according to the general procedure
1
as a red solid (69.6 mg, 71%). 1H NMR (400 MHz, CDCl3) δ = as a red oil (70.5 mg, 68%). H NMR (400 MHz, CDCl3) δ = 7.94
7.96 (d, J = 8.0 Hz, 2H), 7.78 (s, 2H), 7.40 (d, J = 8.0 Hz, 2H), (s, 1H), 7.92 (s, 1H), 7.65 (d, J = 1.9 Hz, 2H), 7.10 (dd, J = 8.0,
2.77 (q, J = 7.6 Hz, 2H), 2.61 (q, J = 7.6 Hz, 2H), 1.32 (t, J = 7.6 2.0 Hz, 2H), 3.01-2.94 (m, 2H), 1.30(s, 6H), 1.29(s, 6H).13C NMR
Hz, 3H), 1.25 (t, J = 7.6 Hz, 3H). 13C NMR (100 MHz, CDCl3) δ = (100 MHz, CDCl3) δ = 150.82, 150.27, 139.56, 131.27, 116.28,
151.05, 149.52, 149.24, 147.04, 139.71, 128.73, 123.41, 87.93, 116.25, 99.71, 33.77, 23.72. HRMS (ESI) calcd. For C18H21I2N2
28.99, 27.52, 15.42, 15.30. HRMS (ESI) calcd. For C16H17I2N2 [M+H]: 518. 9794, found: 518. 9787.
[M+H]: 490.9481, found: 490.9475.
(E)-1-(2-iodo-4-methylphenyl)-2-(2-iodophenyl)diazene (3q):
(E)-1,2-bis(2-iodo-4-isopropylphenyl)diazene (3d): The title The title compound was prepared according to the general
1
compound was prepared according to the general procedure procedure as a red solid (67.2 mg, 75%). H NMR (400 MHz,
as a red oil (88.1 mg, 85%). 1H NMR (400 MHz, CDCl3) δ = 7.98 CDCl3) δ = 8.04-8.01 (m, 2H), 7.78 (s, 2H), 7.58-7.56 (m, 3H),
(d, J = 8.0 Hz, 2H), 7.80 (s, 2H), 7.44 (d, J = 8.0 Hz, 2H), 3.03 (m, 2.32 (s, 3H). 13C NMR (100 MHz, CDCl3) δ = 151.22, 150.71,
1H), 2.87 (m, 1H), 1.33 (d, J = 8.0 Hz, 6H), 1.27 (d, J = 8.0 Hz, 141.03, 140.83, 140.82, 132.20, 129.24, 123.26, 87.82, 19.98.
6H). 13C NMR (100 MHz, CDCl3) δ = 153.79, 151.65, 151.22, HRMS (ESI) calcd. For C13H11I2N2 [M+H]: 448. 9012, found:
149.60, 138.44, 127.33, 123.44, 87.98, 34.31, 33.18, 23.87, 448.9005.
23.76. HRMS (ESI) calcd. For C18H21I2N2 [M+H]: 518. 9794,
found: 518. 9784.
Conflicts of interest
(E)-1,2-bis(4-(tert-butyl)-2-iodophenyl)diazene (3e): The title
compound was prepared according to the general procedure
as a red oil (89.5 mg, 82%).1H NMR (400 MHz, CDCl3) δ = 7.99
(d, J = 8.0 Hz, 2H), 7.94 (s, 2H), 7.61 (d, J = 8.0 Hz, 2H), 1.41 (s,
9H), 1.34 (s, 9H). 13C NMR (100 MHz, CDCl3) δ = 156.00, 154.03,
151.03, 149.18, 137.57, 126.43, 126.24, 123.10, 122.47, 87.86,
35.19, 34.52, 31.28, 31.16. HRMS (ESI) calcd. For C20H25I2N2
[M+H]: 547.0107, found: 547.0098.
There are no conflicts of interest to declare.
Acknowledgements
We are grateful to the National Natural Science Foundation of
China (No. 21602231), and the Natural Science Foundation of
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Sharma, S. H. Han, S. Han, W. Ji, J. Oh, S. Lee, J. S. Oh, Y. H.
Jung and I. S. Kim, Org. Lett., 2015, 17, 2852. (j) S. Han, N. K.
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Organic & Biomolecular Chemistry
Page 8 of 8
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DOI: 10.1039/C8OB00318A
We developed a highly chemoselective oxidative access to ortho-iodinated azobenzenes by
Rh(III)-catalysis with alkyl iodide as the iodinating reagent.