Direct Preparation of 3-Iodochromenes from 3-Aryl- and 3-Alkyl-2-propyn-1-ols with Diaryliodonium Salts and NIS

Article abstract of DOI:10.1021/acs.orglett.5b03651

On the basis of a study of the O-phenylation of 3-phenyl-2-propyn-1-ol with diphenyliodonium triflate and t-BuONa, a variety of 4-aryl-3-iodo-2H-benzopyrans were prepared in good to moderate yields in one pot from the reaction of 3-aryl-2-propyn-1-ols wit

Full text of DOI:10.1021/acs.orglett.5b03651

Letter
pubs.acs.org/OrgLett
Direct Preparation of 3‑Iodochromenes from 3‑Aryl- and 3‑Alkyl-2-
propyn-1-ols with Diaryliodonium Salts and NIS
Teppei Sasaki,† Kotaro Miyagi,† Katsuhiko Moriyama,†,‡ and Hideo Togo*,†
†Graduate School of Science, Chiba University, Yayoi-cho 1-33, Inage-ku, Chiba 263-8522, Japan
‡Molecular Chirality Research Center, Chiba University, Yayoi-cho 1-33, Inage-ku, Chiba 263-8522, Japan
S
* Supporting Information
ABSTRACT: On the basis of a study of the O-phenylation of 3-phenyl-2-propyn-
1-ol with diphenyliodonium triflate and t-BuONa, a variety of 4-aryl-3-iodo-2H-
benzopyrans were prepared in good to moderate yields in one pot from the
reaction of 3-aryl-2-propyn-1-ols with diaryliodonium triflates and t-BuONa,
followed by the treatment with N-iodosuccinimide and BF3·OEt2, under
transition-metal-free and mild conditions. The formed 4-phenyl-3-iodo-2H-
benzopyran was converted into 4-phenyl-2H-benzopyran derivatives through C−C bond formations at the 3-position by Pd-
catalyzed coupling reactions and into coumarin with oxidants.
Table 1. O-Phenylation of 3-Phenyl-2-propyn-1-ol
hromene (2H-1-benzopyran) is an important building
Cunit because it is a precursor or an intermediate of natural
products, particularly for coumarins, and medicinals.1 Chro-
mene derivatives bearing anti-HIV,2a antitumor,2b and anti-
bacterial activities2c,d are known. The coumarin unit is a key
structure of natural products and biologically active molecules.3
Extensive studies of the preparation of 2H-benzopyrans have
been carried out.4 Typically, 2H-benzopyrans are prepared by
the cyclization of allyl o-vinylaryl ethers with Rh catalyst
through an intramolecular ene−metathesis reaction (RCM),4c,d
the cyclization of α-(o-hydroxyaryl)allyl alcohols with Au
catalyst via endo-cyclization,4e and the cyclization of aryl
propargyl ethers with Au, Ag, or Pt catalyst.4f−i An InI3-
catalyzed cyclization of aryl propargyl ethers4j and a AgOTf-
catalyzed cycloisomerization of cyclopropyl(o-hydroxyphenyl)-
carbinols4k into 2H-benzopyrans were also reported. As
transition-metal-free conditions, an IPy2BF4 and HBF4 system
in dichloromethane5 and an I2, ICl, or PhSeBr system in
nitromethane6 were used for the electrophilic iodocyclization of
aryl propargyl ethers to form 3-iodo-2H-benzopyrans.
It is well-known that diaryliodonium salts are efficient
reagents for the O-arylation of phenols, alcohols, carboxylic
acids, and oximes under transition-metal-free conditions.7 We
previously reported the O-arylation of various phenols using
diaryliodonium salts.7l Here, as part of our study of diary-
liodonium salts for organic synthesis, we report a one-pot
preparation of 3-iodo-2H-benzopyrans through the reaction of
3-aryl-2-propyn-1-ols and 3-alkyl-2-propyn-1-ols with diary-
liodoniums triflates and t-BuONa followed by the reaction with
N-iodosuccinimide (NIS) and BF3·OEt2 under transition-
metal-free conditions.
time
yield
(%)
entry
base
NaH
solvent
temp (°C)
(h)
1
2
3
4
5
6
7
DMF
0 to 80
0 to 60
0 to reflux
0 to 60
0 to 60
0 to 60
0 to 60
0 to 60
0 to 60
0 to 60
7
5
40
70
46
79
72
78
39
39
3
t-BuONa DMF
t-BuONa THF
5
t-BuONa benzene
t-BuONa toluene
25
23
2
t-BuOK
t-BuOLi
K2CO3
K2CO3
Cs2CO3
benzene
benzene
toluene
CH3CN
benene
7
a
8
15
5
9
10
11
5
79
83
89
87
t-BuONa benzene/DCE (1:1) 0 to 60
t-BuONa benzene/DCE (1:1) 0 to 60
3
b
12
c
3
13
t-BuONa benzene/DCE (1:1) 0 to 60
3
a
b
18-Crown-6 (10 mol %) was added. MgSO4 (0.2 equiv) was added.
c
MgSO4 (0.5 equiv) was added.
use of t-BuONa as the base in DMF, THF, benzene, or toluene
gave phenyl 3-phenyl-2-propynyl ether 2Aa in moderate to
good yields (Table 1, entries 1−10). Optimization of base in
benzene was performed, and it was found that t-BuONa and
Cs2CO3 in benzene were the best choices (Table 1, entries 4
and 10). Optimization of solvent revealed that the mixture of
benzene and 1,2-dichloroethane (benzene/DCE = 1:1) was the
most suitable (Table 1, entries 11−13), and the addition of
MgSO4 enhanced the reaction (Table 1, entries 12 and 13). t-
BuONa is less expensive than deliquescent Cs2CO3. Finally, t-
First, the O-arylation of 3-phenyl-2-propyn-1-ol 1a with
diphenyliodonium triflate A in the presence of bases, such as
NaH, t-BuONa, t-BuOK. t-BuOLi, K2CO3, and Cs2CO3 in
DMF, THF, benzene, toluene, and acetonitrile, was carried out
as shown in Table 1. Initial screening experiments revealed that
Received: December 25, 2015
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.5b03651
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Organic Letters
Letter
BuONa as a base and MgSO4 were chosen for the present
reaction. Next, the optimum conditions for the iodocyclization
of phenyl 3-phenyl-2-propynyl ether 2Aa with NIS were
studied, as shown in Table 2. When phenyl 3-phenyl-2-
60 °C for 3 h, followed by the reaction with NIS (1.1 equiv)
and BF3·OEt2 (1.1 equiv) at 0 °C for 1 h, together with the
addition of DCM (3.0 mL) was the best to give 3-iodo-4-
phenyl-2H-benzopyran 3Aa in 80% yield, as shown in Scheme
1. A gram-scale preparation of 3-iodo-4-phenyl-2H-benzopyran
Table 2. Iodocyclization of Phenyl 3-Phenyl-2-propynyl
Ether to 3-Iodo-4-phenyl-2H-benzopyran 3Aa
Scheme 1. One-Pot Transformation of 3-Aryl-2-propyn-1-ols
and 3-Alkyl-2-propyn-1-ols into 3-Iodo-2H-Benzopyrans 2
with Diphenyliodonium Triflate A
entry
1
additive
I2
solvent
temp (°C)
time (h)
yield (%)
CH3CN
CH3CN
CH3CN
CH3CN
DCM
0 to rt
0 to rt
0 to rt
rt
7
3
0
55
35
66
63
83
91
72
a,
b
2
3
4
5
6
7
8
b
,
c
I2
3
d
I2
16
3
a,
b
e
I2
0 to rt
0 to rt
0
I2
DCM
3
BF3·OEt2
BF3·OEt2
DCM
0.5
0.5
a,
DCM
0
a
b
c
NIS (2.0 equiv) was used. Additive (1.0 equiv) was used. DIH (1.0
equiv) was used instead of NIS. I2 (3.0 equiv) and NaHCO3 (3.0
equiv) were used, without NIS. Additive (2.0 equiv) was used.
d
e
propynyl ether 2Aa was treated with NIS only in CH3CN, 3-
iodo-4-phenyl-2H-benzopyran 3Aa was not obtained at all
(Table 2, entry 1). The addition of I2 (1.0 equiv) induced
iodocyclization to provide 3-iodo-4-phenyl-2H-benzopyran 3Aa
in moderate yield (Table 2, entry 2). Use of 1,3-diiodo-5,5-
dimethylhydantoin (DIH) instead of NIS did not enhance the
reaction (Table 2, entry 3). Employing I2 (3.0 equiv) and
NaHCO3 (3.0 equiv) in the absence of NIS gave 3-iodo-4-
phenyl-2H-benzopyran 3Aa in 66% yield (Table 2, entry 4).
Dichloromethane (DCM) was a better solvent than CH3CN as
a solvent (Table 2, entries 2 and 5), and treatment of phenyl 3-
phenyl-2-propynyl ether 2Aa with NIS (1.1 equiv) and I2 (1.1
equiv) in CH2Cl2 at 0 °C gave 3-iodo-4-phenyl-2H-benzopyran
3Aa in 83% yield (Table 2, entry 6). The addition of BF3·OEt2
instead of I2 markedly improved the reactivity: treatment of
phenyl 3-phenyl-2-propynyl ether 2Aa with NIS (1.1 equiv)
and BF3·OEt2 (1.1 equiv) in DCM at 0 °C for 30 min gave 3-
iodo-4-phenyl-2H-benzopyran 3Aa in 91% yield (Table 2, entry
7). On the other hand, the addition of excess NIS (2.0 equiv)
and BF3·OEt2 (2.0 equiv) reduced the yield of compound 3Aa
(Table 2, entry 8). On the basis of the results in Tables 1 and 2,
a one-pot transformation of 3-phenyl-2-propyn-1-ol 1a into 3-
iodo-4-phenyl-2H-benzopyran 3Aa was carried out. 3-Phenyl-2-
propyn-1-ol 1a was treated with diphenyliodonium triflate A in
the presence of t-BuONa and MgSO4 in a mixture of benzene
and DCE (1:1) at 60 °C for 3 h, and this was followed by the
reaction with NIS (1.1 equiv) and BF3·OEt2 (1.1 equiv) under
various reaction conditions to give 3-iodo-4-phenyl-2H-
benzopyran 3Aa. It was found that evaporation prior to the
second reaction step was not necessary for this reaction.
Consequently, the addition of DCM (3 mL) prior to the
second reaction step was the most effective. The use of 0.5
equiv of BF3·OEt2 afforded low reactivity, and BCl3, BBr3, and
B(C6F5)3 also showed low reactivity, particularly BBr3 (see the
Supporting Information). Thus, it was clarified that the
treatment of 3-phenyl-2-propyn-1-ol 1a with t-BuONa (1.1
equiv) and diphenyliodonium triflate A (1.1 equiv) in the
presence of MgSO4 in a mixture of benzene and DCE (1:1) at
a
b
Starting material (8.0 mmol) was used. The second reaction step
c
was carried out for 2 h. The second reaction step was conducted at
−20 °C for 30 min. The second reaction step was conducted at −10
°C for 20 h. The second reaction step was carried out for 30 min.
d
e
3Aa from 3-phenyl-2-propyn-1-ol 1a (8 mmol) was also
successfully carried out in 82% yield, as shown in Scheme 1.
Using the optimum reaction conditions, various 3-aryl-2-
propyn-1-ols 1b−k, bearing p-fluorophenyl, p-chlorophenyl,
p-methylphenyl, m-methylphenyl, o-methylphenyl, p-biphenyl,
p-methoxyphenyl, p-benzyloxyphenyl, 1-naphthyl, and 2-naph-
thyl groups at the 3-position, were treated with diphenyliodo-
nium triflate A in the presence of t-BuONa and MgSO4 in a
mixture of benzene and DCE (1:1) at 60 °C for 3 h, followed
by the reaction with NIS and BF3·OEt2 at 0 °C for 1 h, to give
B
DOI: 10.1021/acs.orglett.5b03651
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Organic Letters
Letter
the corresponding 3-iodo-4-aryl-2H-benzopyrans 3Ab−Ak in
good yields, as shown in Scheme 1. Thus, 3-aryl-2-propyn-1-ols
1 bearing an electron-withdrawing group or an electron-
donating group on the aromatic ring gave the corresponding 3-
iodo-4-aryl-2H-benzopyrans 3 in good yields. The same
treatment of 3-aryl-2-propyn-1-ols 1l−o bearing heteroaromatic
groups, such as 5-methyl-2-furyl, 2-benzofuryl, 2-benzothienyl,
and 1-(benzenesulfonyl)-3-indolyl groups at the 3-position of
the 3-aryl-2-propyn-1-ols, also gave the corresponding 3-iodo-4-
aryl-2H-benzopyrans 3Al−Ao in good to moderate yields,
respectively. In addition, the same treatment of 3-styryl-2-
propyn-1-ol 1p and 3-alkyl-2-propyn-1-ols, such as 2-hexyn-1-ol
1q and 2-decyn-1-ol 1r, also gave 4-styryl- and 4-alkyl-3-iodo-
2H-benzopyrans 3Ap−Ar in good to moderate yields,
respectively. In total, the yields of compounds 3 with 3-alkyl-
2-propyn-1-ols were lower than those with 3-aryl-2-propyn-1-
ols. We propose two reasons for this: one is that the O-
phenylation of 3-alkyl-2-propyn-1-ols 1 with diphenyliodonium
triflate A and t-BuONa does not proceed as smoothly as that of
3-aryl-2-propyn-1-ols 1, and the other is that 4-alkyl-3-iodo-2H-
benzopyrans 3Aq and 3Ar are not as stable as 4-aryl-3-iodo-2H-
benzopyrans 3Aa−Ao at room temperature. The same
treatment of 4-phenyl-3-butyn-2-ol 1s, a secondary propargyl
alcohol, gave 3-iodo-2-methyl-4-phenyl-2H-benzopyran 3As in
moderate yield.
Then, the substituent effect on the O-arylation of 3-phenyl-2-
propyn-1-ol 1a with diaryliodonium salts, such as di(p-
methylphenyl)iodonium triflate B, di(p-chlorophenyl)-
iodonium triflate C, di(p-bromophenyl)iodonium triflate D,
and di(p-tert-butylphenyl)iodonium triflate E, in the presence
of t-BuONa and MgSO4 in a mixture of benzene and DCE
(1:1) at 60 °C for 3 h followed by the reaction with NIS and
BF3·OEt2 at 0 °C was studied. 6-Methyl-3-iodo-4-phenyl-2H-
benzopyran 3Ba, 6-chloro-3-iodo-4-phenyl-2H-benzopyran
3Ca, and 6-bromo-3-iodo-4-phenyl-2H-benzopyran 3Da were
produced in good yields, as shown in Scheme 2, whereas the
yield of 6-tert-butyl-3-iodo-4-phenyl-2H-benzopyran 3Ea was
moderate.
The plausible reaction mechanism for the present iodocyc-
lization is shown in Scheme 3. Thus, BF3 promotes NIS-
iodocyclization of aryl 3-aryl(alkyl)-2-propynyl ether 2 to 3-
iodo-4-aryl(alkyl)-2H-benzopyran 3 through the intermediates
I and II.
Scheme 3. Plausible Reaction Mechanism for
Iodocyclization
Finally, the functional group transformation of 3-iodo-4-
phenyl-2H-benzopyran 3Aa was carried out, as shown in
Scheme 4, as chromenes and coumarins are important units for
pharmaceuticals and biologically active compounds.3
Scheme 4. Derivatization of 3-Iodo-4-Phenyl-2H-1-
Benzopyran
The structure of 6-bromo-3-iodo-4-phenyl-2H-benzopyran
3Da was determined by X-ray crystallographic analysis (see the
Supporting Information).
Scheme 2. One-Pot Transformation of 3-Phenyl-2-propyn-1-
ol 1a into 3-Iodo-4-Phenyl-2H-Benzopyrans 3 with
Diaryliodonium Triflates B−E
Oxidation of 3-iodo-4-phenyl-2H-benzopyran 3Aa into 3-
iodo-4-phenyl-2H-1-benzopyran-2-one 4Aa was carried out in
56% yield by the reaction with PCC in DCM. Reduction of 3-
iodo-4-phenyl-2H-benzopyran 3Aa into 4-phenyl-2H-benzo-
pyran 5Aa was carried out in 89% yield by treatment with Zn in
ethanol. Oxidation of 4-phenyl-2H-benzopyran 5Aa by DDQ
gave γ-phenylcoumarin 6Aa in 72% yield. Then, the
Sonogashira coupling reaction of 3-iodo-4-phenyl-2H-benzo-
pyran 3Aa with phenylacetylene and the Suzuki−Miyaura
coupling reaction of 3-iodo-4-phenyl-2H-benzopyran 3Aa with
phenylboronic acid and PdCl2(PPh3)2 provided the corre-
sponding coupling products 7Aa and 8Aa in 73% and 99%
yields, respectively. Moreover, treatment of 3-iodo-4-phenyl-
2H-benzopyran 3Aa with i-PrMgCl at −78 °C followed by the
reaction with ClCO2Me provided 3-(methoxycarbonyl)-4-
phenyl-2H-benzopyran 9Aa in 65% yield.
a
b
In conclusion, 3-aryl-2-propyn-1-ols and 3-alkyl-2-propyn-1-
ols were treated with diaryliodonium triflates in the presence of
t-BuONa followed by a reaction with NIS and BF3·OEt2 to give
The second reaction step was carried out for 2 h. NIS (1.3 equiv)
c
and BF3·OEt2 (1.3 equiv) were used. NIS (0.3 equiv) and BF3·OEt2
(0.3 equiv) were added after the second reaction step.
C
DOI: 10.1021/acs.orglett.5b03651
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
P. Org. Biomol. Chem. 2015, 13, 379. (k) Chan, P. W. H.; Teo, W. T.;
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3-iodo-4-aryl(alkyl)-2H-benzopyrans in good to moderate
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conditions, and the products can be functionalized by oxidation
or C−C bond-coupling reactions. The present one-pot method
would be useful for the preparation of various 3-iodo-4-aryl-2H-
benzopyrans and their derivatives.
(6) Worlikar, S. A.; Kesharwani, T.; Yao, T.; Larock, R. C. J. Org.
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.5b03651.
■
S
Experimental details, characterization data by IR, H
NMR, and C NMR of all products 3 (PDF)
X-ray analysis of 3Da (CIF)
AUTHOR INFORMATION
Corresponding Author
■
*E-mail: togo@faculty.chiba-u.jp.
Notes
89, 2122. (o) Gao, H.; Xu, Q.; Keene, C.; Kurti, L. Chem. - Eur. J.
̈
2014, 20, 8883. (p) Ghosh, R.; Stridfeldt, E.; Olofsson, B. Chem. - Eur.
J. 2014, 20, 8888. (q) Bhattarai, B.; Tay, J.; Nagorny, P. Chem.
Commun. 2015, 51, 5398.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support in the form of a Grant-in-Aid for Scientific
Research (No. 25105710) from the Ministry of Education,
Culture, Sports, Science, and Technology in Japan is gratefully
acknowledged.
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