Efficient synthesis of 1-iodoalkynes: Via Al2O3 mediated reaction of terminal alkynes and N -iodosuccinimide

Article abstract of DOI:10.1039/d0ra00251h

Iodination of terminal alkynes using N-iodosuccinimide (NIS) in the presence of γ-Al₂O₃ was developed to afford 1-iodoalkynes with good to excellent yields (up to 99%). This described approach featured excellent chemoselectivity, good functional group tolerance, and utilization of an inexpensive catalyst.

Full text of DOI:10.1039/d0ra00251h

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Efficient synthesis of 1-iodoalkynes via Al2O3
mediated reaction of terminal alkynes and N-
iodosuccinimide†
Cite this: RSC Adv., 2020, 10, 3946
a
a
ab
Jingjing Zhang,ab Sen Yang, Hangxing Xiong,
Li Li,ab E. Liua
*
*
Ming Yao,
and Hong Shia
Received 9th January 2020
Accepted 16th January 2020
Iodination of terminal alkynes using N-iodosuccinimide (NIS) in the presence of g-Al2O3 was developed to
afford 1-iodoalkynes with good to excellent yields (up to 99%). This described approach featured excellent
chemoselectivity, good functional group tolerance, and utilization of an inexpensive catalyst.
DOI: 10.1039/d0ra00251h
rsc.li/rsc-advances
1-Iodoalkynes are both highly versatile synthons in organic years.12,13 But the utilization of aluminum oxide in synthetic
synthesis and valuable building blocks in materials and poly- organic chemistry especially for halogenation of aromatic
mer sciences.1,2 Traditional procedures for generating 1- compounds and alkynes is very little.14–18 g-Aluminum oxide is
iodoalkynes include iodination of metal acetylides (Scheme 1, one of the three common crystal forms of aluminum oxide.
path a),3 direct iodination of terminal alkynes (path b),4 iodin- Pagni and Kabalka described g-Al2O3 mediated iodination of
ation of propiolic acid/trialkylsilylacetylides (path c),5,6 and alkynes and aromatic substrates with I2 to afford E-diio-
a two-step homologation/iodination or elimination sequence doalkenes and iodinated aromatic compounds, respectively.14
from aldehydes or benzylic bromides (path d).7,8 Among these Those iodinations did not occur without the activation of g-
achievements, path b, the preparation of 1-iodoalkynes from Al2O3.
terminal alkynes, is highly desirable. In this regard, various
N-Iodosuccinimide (NIS) is a well-known iodinating agent
iodinating conditions, including nBuLi/I2,4a EtMgBr/I2,4b I2/ and widely used in organic synthesis. Iodination with N-iodo-
DMAP,4c NIS/AgNO3,4d NIS/BnN3,4e NIS/DBU,4f NIS/Ag/C3N4,4g succinimide (NIS) oen needs activating reagents. However, any
KI/CuI/PhI(OAc)2/Et3N,4h Me3SiI/PhI(OAc)2,4i CuI/TBAB/Et3N,4j accompanying reagents used along with iodinating reagents
TBAI/Oxone,4k KI/TBHP,4l TBAI/PhI(OAc)2,4m chloramine-B/KI,4n should be easily available to exploit more simple and efficient
KI/Cu2SO4/BPDS,4o ZnI2/TBN,4p NIS/[Au(AIPr)(NEt3)][HF2],4q iodination procedure. Inspired by the indispensable role of g-
HMBMIBDCI/DBU,4r NaI/MeOH/divided cell,4s and N-iodomor- Al2O3 in the iodination of alkynes and aromatic compounds,14
phonine/CuI,4t have been reported. However, some of these we envisioned that g-Al2O3 could activate the N-iodosuccini-
approaches might suffer from expensive metal catalysts, mide to generate 1-iodoalkynes from terminal alkynes. Herein,
hazardous or toxic reagents, harsh reaction conditions, or we report the g-Al2O3 mediated direct iodination of terminal
generation of wastes that bring about environmental problems,
thereby restricting their practical applications. Though
considerable progress has been achieved, the development of
efficient and environmentally benign protocols is still required.
It is well recognized that solids can play a vital role in
developing new cleaner technologies via their capacities to serve
as catalysts or support reagents and inuence product selec-
tivity, and some books have documented the applications of
solids in organic synthesis.9–11 Aluminum oxide (Al2O3) is an
inert, odorless and white amorphous material, and has been
used as catalyst in various industrial processes for many
aJingchu University of Technology, 33 Xiangshan Road, Jingmen, Hubei 448000, P. R.
China. E-mail: yaomingcep@jcut.edu.cn
bWuhan Institute of Technology, 206 Guanggu First Road, Wuhan, Hubei 430205, P. R.
China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/d0ra00251h
Scheme 1 Approaches towards to 1-iodoalkynes.
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alkynes for the synthesis of 1-iodoalkynes under mild reaction neutral Al2O3. The effort to decrease the reaction temperature to
ꢀ
condition.
25 C only led to low yield (entry 6). Subsequently, we probed
As shown in Table 1, the initial experiment was carried out by different solvents including DMF, THF, EA, MeOH and hexane,
adding N-iodosuccinimide (NIS) 2a (2.2 mmol) to a solution of but those solvents resulted in poor yields of desired product
phenyl acetylene 1aa (2.0 mmol) and neutral g-Al2O3 (2.6 mmol) (entry 7–11). Moreover, the reaction was investigated by varying
in CH3CN. Surprisingly, the reaction afforded the desired the amount of Al2O3 and NIS to enhance the performance of the
product 1-(iodoethynyl)benzene 3aa in 90% yield aer stirred at reaction (Table 1, entry 12–15). With 1.0 equivalents of NIS, the
80 ꢀC for 1 h (Table 1, entry 1). To our delight, the reaction could reaction generated 81% yield of 1-iodoalkyne 3aa (entry 12).
ꢀ
provide 98% yield with the aid of 4 A MS (entry 2). At the same However, when higher or lower amount of Al2O3 was used, low
time, the product 3aa could be obtained in 95% yield without yields of the desired product were observed (entry 13–15).
ꢀ
the help of 4 A MS when the amount of CH3CN used in the Finally, the best conditions to obtain the 1-iodoalkyne 3aa were
reaction was reduced from 10 mL to 2 mL (entry 2). Markedly, treatment of 1aa with 1.1 equivalents of NIS, 1.3 equivalents of
ꢀ
ꢀ
we obtained a mixture of 1aa, 3aa, 1,2-diiodovinylbenzene 4 and neutral g-Al2O3 and 4 A MS in CH3CN at 80 C for 1 h. With the
ꢀ
2,2-diiodo-1-phenylethanone 5 in the absent of 4 A MS and optimized conditions in hand, we also studied the halogenation
Al2O3 (entry 3). In addition, the 3aa was obtained in 41% yield of phenyl acetylene 1aa and used various halogenated reagents,
ꢀ
only in the presence of 4 A MS (entry 3). Therefore, the Al2O3 was including
N-bromosuccinimide,
1,3-dibromo-5,5-
indispensable to this iodination reaction (Table S1†). Similarly, dimethylhydantoin, pyridinium tribromide and N-chlor-
high yields of 1-iodoalkyne 3aa were also obtained when basic osuccinimide. These attempts did not provide satised results
and acidic Al2O3 were used instead of neutral Al2O3 (entry 4–5). (Scheme S1†).
Hence, the reaction was further examined in the presence of
Based on the optimized reaction conditions, the generality of
the direct iodination of various terminal alkynes was investi-
gated (Table 2). Firstly, a wide variety of aromatic alkynes were
rstly evaluated and could react with NIS to afford the corre-
sponding 1-iodoalkynes 3ab–3au with good to excellent yields.
Substrates having both electron-donating (e.g. Me, OMe,
CH2CN) and electron-withdrawing (e.g. Cl, Br, CF3, CO2Me, CN)
groups were effectively furnished the desired products. The
halogen substituted aromatic alkynes gave the respective 1-
iodoalkynes 3ab–3aj in excellent yields in relation to the posi-
tion of the halogen on the phenyl ring and the electronegativity
of the halogen. Among them, the meta bromo substituted
alkyne 1ai gave the best yield (99%). The para substituted
aromatic alkynes 1ak–1ap afforded the corresponding products
3ak–3ap in good to excellent yields. Although the para formyl
substituted alkyne 1am yielded the 1-iodoalkyne 3am in 82%
yield, the alkyne 1al could provide the corresponding product in
99% yield. Notably, the para cyanomethyl substituted alkyne
1ap afforded the desired product in almost quantitative yield
(>99%). The dimethoxy substituted alkyne 1at provided better
yield than the single methoxy substituted alkynes (1aq–1as).
The 1,4-diethynylbenzene 1au could also be iodinated to
generate the desired bisiodinated product in 99% yield.
Secondly, the hetero aromatic and aliphatic alkynes were
examined under the optimized conditions. The hetero aromatic
alkynes delivered the iodination products 3av, 3aw and 3ax in
88%, 93% and 91% yield, respectively. The iodination reaction
of aliphatic alkynes underwent smoothly to afford the corre-
sponding products 3ay–3bb in good yields. The conjugated
enyne 1bc could also react with NIS and gave the anticipated
product 3bc in 80% yield. In addition, the iodination of more
reactive alkyne 1bd was also evaluated and gave the syntheti-
cally useful 3bd in 93% yield. Finally, we also chose ve terminal
alkynes (1ab, 1af, 1al, 1an, 1ar) to examine the direct iodination
Table 1 Optimization of the reaction conditionsa
2a
(equiv.)
T
(ꢀC)
Entry
Solvent
Al2O3 (equiv.)
Yieldb (%)
1
2
3
4
5
6
7
8
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
DMF
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.1
1.0
1.1
1.1
1.1
80
80
80
80
80
25
80
80
80
80
80
80
80
80
80
1.3
1.3
—
90c
98(95h)
—d(41e)
96
97
42
63
78
86
79
1.3f
1.3g
1.3
1.3
1.3
1.3
1.3
1.3
1.3
1.0
0.1
2.0
THF
EA
9
10
11
12
13
14
15
MeOH
Hexane
CH3CN
CH3CN
CH3CN
CH3CN
62
81
84
70
91
a
Unless noted otherwise, all reaction were conducted using
phenylacetylene 1aa (2.0 mmol), N-iodosuccinimide 2a (2.2 mmol),
200 mg 4 A MS, 265.0 mg neutral Al2O3 in 10 mL CH3CN at 80 ꢀC for
ꢀ
b
c
d
ꢀ
ꢀ
1 h. Isolated yield. No 4 A MS. No Al2O3 and 4 A MS, HPLC
analysis of the reaction mixture aer reacting at 80 ꢀC for 1 h showed
the molar ratio of 1aa to 1-iodoalkyne 3aa to 1,2-diiodovinylbenzene 4 requiring a small amount of solvent. The yields of solvent-
e
f
to 2,2-diiodo-1-phenylethanone 5 was 8 : 23 24 45. No Al2O3. Basic
reduced reaction (values in parentheses) performed in 2 mL
CH3CN were comparable to the yields of the reaction conducted
g
h
Al2O3 was used.
Acidic Al2O3 was used.
The reaction was
conducted in 2 mL CH3CN. EA ¼ ethyl acetate.
˚
in 10 mL CH3CN. These results further conrmed that the 4 A
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Table 2 Scope of Al2O3/NIS mediated iodinationa
Scheme 2 A Scale-up synthesis of 1-iodoalkynes.
MS was not essential for the Al2O3 mediated iodination (Table
S1†).
To further explore the potential of this protocol, we con-
ducted the Al2O3 mediated direct iodination system for larger-
scale synthesis (Scheme 2). The iodination reaction with
(10 mmol, 1.0213 g) of phenylacetylene 1aa in 50 mL CH3CN
afforded 96% yield. Delightfully, when the reaction was per-
formed in 4 mL CH3CN, the yield could reach to 98% (value in
parentheses). Moreover, the iodination of 1af, 1ak and 1ap
proceeded smoothly in CH3CN, producing the corresponding 1-
iodoalkynes in 97%, 94% and 98% yield, respectively. Finally,
the larger scale reaction of aliphatic alkyne 1bb, could also
generate 3bb in 90% yield. These excellent results indicated the
promise of this direct iodination system for larger-scale prepa-
ration of 1-iodoalkynes from terminal alkynes.
As presented in Scheme 3, we also tried to construct mono-,
di-, and tri-iodination of terminal alkynes based on direct
iodination mediated by g-Al2O3 using phenyl acetylene 1aa as
a
ꢀ
Reaction conditions: 1 (2.0 mmol), 2a (2.2 mmol), 4 A MS (200 mg),
Al2O3 (2.6 mmol), CH3CN (10 mL), 80 ꢀC, 1 h. Isolated yields are
given. The values in parentheses are the yields of reaction conducted
ꢀ
in 2 mL CH3CN in the absent of 4 A MS.
Scheme
3
Al2O3 mediated chemoselective iodination of phenyl
acetylene.
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the model substrate. As depicted in the literature,14b the di-
iodination product 6 could be obtained in 97% yield aer stir-
red at 80 ꢀC for 2 h in the presence of I2. Combining the NIS and
I2 system in one pot provided the corresponding tri-iodination
product 7 in 94% yield.
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ꢀ
Finally, we studied the recyclability of Al2O3 and 4 A MS.
ꢀ
Al2O3 and 4 A MS could be used as a recyclable catalyst for the
direct iodination of phenyl acetylene 1aa (10 mmol) as it
provided 96%, 93% and 88% yield at the rst, second and third
run, respectively (Fig. S1†). The severe decrease of the yield of
the iodination was probably because the active sites of Al2O3
were blocked by unknown compounds and the unavoidable loss
of solid catalyst during recovery and washing.
Although the detailed mechanism for the g-Al2O3 mediated
iodination remains unclear, we proposed that the dehydrated
surface of g-Al2O3, which contains partly exposed Al3+ and O2ꢁ
,
could serve as an effective medium for electrophilic iodination
and greatly increase the chemoselectivity and rate of the reac-
tion. Investigation of the detail mechanism and further appli-
cations of this methodology are toward in our laboratory.
Conclusions
In conclusion, we have developed an efficient approach for the
synthesis of 1-iodoalkynes via g-Al2O3 mediated direct iodin-
ation of terminal alkynes in the presence of NIS. Firstly, this
protocol has excellent reactivity, high chemoselectivity and
good functional group tolerance, and can be used for large-scale
preparation of various 1-iodoalkynes. Secondly, with the aid of
Al2O3 the mono-, di-, and tri-iodination products could be ob-
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ꢀ
tained in high yield. Thirdly, the Al2O3 and 4 A MS could be
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without severe decrease of the yield.
Conflicts of interest
There are no conicts to declare.
Acknowledgements
We gratefully acknowledge the Hubei Provincial Department of
Education (T201719) for generous nancial support.
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