Hypervalent iodine catalyzed cyclization of aryl-substituted alkanoic acids

Article abstract of DOI:10.1002/hlca.201300311

A novel and efficient procedure was developed for direct preparation of aryl-substituted lactones from corresponding aryl-substituted alkanoic acids, catalyzed by the in situ generated hypervalent iodine intermediate from iodobenzene (PhI). In this protocol, aryl-substituted alkanoic acids were treated with m-chloroperbenzoic acid (mCPBA) and KBr in the presence of a catalytic amount of PhI in 2,2,2-trifluoroethanol at room temperature for 24 h, resulting in corresponding aryl lactones in moderate-to-good yields. Copyright

Full text of DOI:10.1002/hlca.201300311

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Helvetica Chimica Acta – Vol. 97 (2014)
Hypervalent Iodine Catalyzed Cyclization of Aryl-Substituted Alkanoic
Acids
by Tingting Li, Changbin Xiang, Bijun Zhang, and Jie Yan*
College of Chemical Engineering and Materials Sciences, Zhejiang University of Technology, Hangzhou
10032, P. R. China (fax: þ 86-571-88320238; e-mail: jieyan87@zjut.edu.cn)
3
A novel and efficient procedure was developed for direct preparation of aryl-substituted lactones
from corresponding aryl-substituted alkanoic acids, catalyzed by the in situ generated hypervalent iodine
intermediate from iodobenzene (PhI). In this protocol, aryl-substituted alkanoic acids were treated with
m-chloroperbenzoic acid (mCPBA) and KBr in the presence of a catalytic amount of PhI in 2,2,2-
trifluoroethanol at room temperature for 24 h, resulting in corresponding aryl lactones in moderate-to-
good yields.
Introduction. – The chemistry of hypervalent iodine organic compounds has
experienced impressive developments since the early 1990s. Due to their low toxicity,
ready availability, easy handling, and reactivity similar to that of heavy-metal reagents
or anodic oxidation, they have been found broad application in organic chemistry and
frequently used in synthesis [1 – 9]. They are usually used as stoichiometric oxidants in
synthesis and after the oxidations, at least equimolar amounts of iodoarenes are
produced as by-products, most of them are disposed of and are not well utilized,
restricting further applications. In 2005, Ochiai et al. and Kita et al. independently
reported the first hypervalent iodine-catalyzed oxidative coupling reactions [10][11].
Since then, the catalytic utilization of hypervalent iodine reagents has been increasing
in importance, with growing interest in the development of environmentally benign
synthetic transformations [12 – 18]. In these catalyzed reactions, a catalytic amount of
an I-containing molecule together with a stoichiometric oxidant is used. The oxidant
generates the hypervalent iodine reagent in situ and, after the oxidative transformation,
the reduced I-containing molecule is re-oxidized.
Recently, Kita and co-workers developed a new and metal-free oxidative
cyclization for direct formation of aryl lactones from aryl-substituted alkanoic acids,
in which a stoichiometric hypervalent iodine reagent, 4-methoxyphenyliodine(III)
diacetate (4-MeOC H I(OAc) ) was used as oxidant, and a benzyl radical formed via
6
4
2
3
sp CꢀH abstraction mechanism was hypothesized [19]. However, the same reaction
using a catalytic amount of iodobenzene (PhI) in place of a stoichiometric hypervalent
iodine reagent, which is more environmentally benign has not been reported before.
Although Ishihara and co-workers reported a similar cyclization of keto carboxylic
acids to keto lactones catalyzed by hypervalent iodine intermediate in 2009 [20], the
protocol is different from the method of Kita et al. in substrates and mechanism.
To develop a novel catalytic cyclization for direct preparation of aryl lactones from
aryl-substituted alkanoic acids and to extend the scope of catalytic use of hypervalent
ꢀ
2014 Verlag Helvetica Chimica Acta AG, Zꢁrich

Helvetica Chimica Acta – Vol. 97 (2014)
855
Scheme 1. Catalytic Cyclization of Aryl-Substituted Alkanoic Acid-Catalyzed by Hypervalent Iodine(III)
iodine reagents for organic synthesis, we first selected a simple protocol to investigate
the oxidation of benzylic CꢀH bonds to the corresponding ketones via the benzyl
radical intermediate, and found that two systems of PhI/mCPBA/KBr and PhI/
mCPBA/t-BuOOH can improve this procedure [21][22]. Based on the success, we have
investigated the novel catalytic cyclization of aryl-subsituted alkanoic acids in the
presence of a catalytic amount of PhI, and obtained indeed the desired aryl lactones
(
Scheme 1).
Results and Discussion. – First, we investigated the reaction of 4-phenylbutanoic
acid with mCPBA and KBr in the presence of a catalytic amount of PhI. Generally, the
reaction was carried out in organic solvents at room temperature for 12 h, and the
desired product, g-phenyl-g-lactone, was obtained (Table 1).
In light of successful formation of the phenyl lactone, the reaction conditions were
optimized, and the results are compiled in Table 1. It was found that the solvent
influenced the reaction distinctly: when 1.0 equiv. of 4-phenylbutanoic acid was mixed
with 1.0 equiv. of KBr, 1.2 equiv. of mCPBA, and 0.2 equiv. of PhI in CH Cl or 2,2,2-
2
2
trifluoroethanol (TFE) at room temperature and stirred for 12 h, the reaction gave
moderate yields; other solvents led to rather poor yields (Entries 1 – 8). Several
oxidants were tested under the same conditions, and mCPBA turned out to be the most
effective one in TFE (Entries 8 – 11). The amount of PhI was checked, and 0.2 equiv.
was the best choice (Entries 8 and 13 – 15). However, in the absence of PhI, no desired
lactone was observed (Entry 12). We examined the amount of KBr, and found that
more KBr promoted the reaction, and finally 5.0 equiv. of KBr was selected for the
reaction (Entries 8 and 16 – 19). When KCl was used in the reaction in place of KBr, a
rather poor yield was obtained. It was observed that the reaction provided a good yield
of 77% after 24 h (Entries 19 – 21).
We also checked the cyclization of 4-phenylbutanoic acid under the cyclization
conditions of Ishibara and co-workers [20]; however, no g-phenyl-g-lactone was
obtained.
With the optimal conditions in hand, and to check the general applicability of this
method, aryl-substituted alkanoic acids were reacted with 0.2 equiv. of PhI, 1.2 equiv. of
mCPBA, and 5.0 equiv. of KBr in TFE 24 h (Table 2).
It is obvious from Table 2 that the catalytic cyclization was compatible with most of
aryl-substituted alkanoic acids and the corresponding aryl lactones were obatined in
moderate-to-good yields (Entries 1 – 3, 5, and 7 – 10). Similar treatment of 3-phenyl-
propanoic acid (1d) and 6-phenylhexanoic acid (1f), did not furnish the expected
product 2d due to the instability of four-membered lactones (Entry 4); another seven-

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Helvetica Chimica Acta – Vol. 97 (2014)
Table 1. Optimization of the Catalytic Cyclization of 4-Phenylbutanoic Acid
Entry Solvent
Oxidant (1.2 equiv.) PhI [equiv.] KBr [equiv.] Time [h] Yield [%]a)
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
CH Cl
THF
mCPBA
mCPBA
mCPBA
mCPBA
mCPBA
mCPBA
mCPBA
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0.2
0
0.1
0.3
0.4
0.2
0.2
0.2
0.2
0.2
0.2
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
1.0
0
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
8
60
31
29
20
17
29
28
64
19
31
20
0
50
56
54
0
35
65
70
52
77
2
2
MeCN
MeOH
EtOH
AcOEt
DMF
CF CH OH mCPBA
3
2
CF CH OH NaBO · 4 H O
3
2
3
2
1
1
1
1
1
1
1
1
1
1
2
2
CF CH OH Oxoneꢂ
3 2
CF CH OH Na S O
8
3
2
2
2
CF CH OH mCPBA
3
2
CF CH OH mCPBA
3
2
CF CH OH mCPBA
3
2
CF
3
CH
2
OH mCPBA
CF CH OH mCPBA
3
2
CF CH OH mCPBA
0.5
1.5
5.0
5.0
5.0
3
2
CF CH OH mCPBA
3
2
CF CH OH mCPBA
3
2
CF CH OH mCPBA
3
2
CF CH OH mCPBA
24
3
2
a) Yield of isolated 2a.
membered ring product 2f was obtained in a yield of only 18% (Entry 6). Therefore,
the catalytic cyclization was suitable for the preparation of five-membered and six-
membered aryl lactones, especially with respect of g-aryl-g-lactones.
A plausible reaction pathway for the present reaction is outlined in Scheme 2. PhI is
first oxidized by mCPBA to the hypervalent iodine intermediate, which is then
transformed to the active key species by treatment with KBr, followed by a benzyl
3
radical formation via sp CꢀH abstraction. Finally, the intramolecular cyclization takes
place to provide the corresponding aryl lactones. The reduced by-product PhI is re-
oxidized into hypervalent iodine reagent by mCPBA in the recycling reaction.
Conclusions. – Lactones are important and ubiquitous building blocks in organic
synthesis, material science, medicine, polymer field, and natural-product chemistry
[
23 – 27]. Because some aryl-substituted lactones possess several significant biological
features, such as antibiotic and cytotoxic activities [28 – 33], the methods for their
preparation have been of increasing importance. The direct oxidative cyclizations from
the corresponding aryl-substituted alkanoic acids is a convenient and attractive route
for the synthesis of these lactones [34 – 38]. However, the use of expensive, unstable, or

Helvetica Chimica Acta – Vol. 97 (2014)
857
Table 2. Catalytic Cyclization of Aryl Alkanoic Acids
Entry
1
R
n
Lactone (2)
Yield [%]a)
1
2
3
4
5
6
7
8
9
1a
1b
1c
1d
1e
1f
1g
1h
1i
H
1
1
1
0
2
3
0
0
0
1
1
2a
2b
2c
2d
2e
2f
2g
2h
2i
77
70
60
0
58
18
72
55
57
67
43
Br
Me
H
H
H
H
Me
Br
H
1
1
0
1
1j
1k
2j
2k
Me
a) Yield of isolated 2.
Scheme 2. A Possible Catalytic Cycle for Cyclization of Aryl-Substituted Alkanoic Acids
toxic metal oxidants and the need of higher reaction temperatures in these procedures
has limited their oxidative cyclizations [39 – 43]. Our novel method using a catalytic
amount of PhI and mCPBA as the terminal oxidant in the presence of KBr has reduced
the amount of expensive hypervalent iodine reagent distinctly, offering a more
environmentally benign procedure. It has some advantages such as mild reaction
conditions and simple procedure, and it affords moderate-to-good yields. Further
investigation of the cyclizations of aryl-substituted alkanioc acids catalyzed by the in
situ generated hypervalent iodine intermediate will be reported in due course.

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Helvetica Chimica Acta – Vol. 97 (2014)
Experimental Part
General. Alkanoic acids, mCPBA, PhI, and KBr were commercially available. M.p.: XT-4 melting-
ꢀ
1
1
13
point apparatus; uncorrected. IR Spectra: Thermo-Nicolet 6700 instrument; ˜n in cm . H- and C-NMR
spectra: Bruker AVANCE III (500 MHz) spectrometer; d in ppm rel. to Me Si as internal standard, J in
4
Hz. MS: Thermo-ITQ 1100 mass spectrometer; in m/z.
General Procedure for the Catalytic Cyclization of Alkanoic Acids. To TFE (5.0 ml), alkanoic acid 1
(
0.5 mmol), mCPBA (75%, 0.6 mmol), PhI (0.1 mmol), and KBr (2.5 mmol) were added. The resulting
soln. was stirred at r.t. for 24 h. Then, H O (10 ml), sat. aq. Na S O (4 ml) and sat. aq. Na CO (4 ml)
2
2
2
3
2
3
were poured into the mixture. The mixture was extracted with CH Cl (3 ꢁ 10 ml), and the combined org.
2
2
layer was washed with brine, dried (Na SO ), filtered and concentrated under reduced pressure. The
2
4
residue was purified by prep. TLC (silica gel; hexane/AcOEt 3 :1) to give the pure aryl lactone 2.
4
,5-Dihydro-5-phenyl-2(3H)-furanone (2a). Yield: 62 mg (77%). White solid. M.p. 35 – 368 ([19]:
1
3
5
1
5 – 368). IR (film): 3070, 1754, 1616, 1493, 1297, 1216, 1176, 1140, 1022, 762, 698. H-NMR: 7.43 – 7.34 (m,
13
H); 5.53 (t, J ¼ 5.0, 1 H); 2.72 – 2.64 (m, 3 H); 2.24 – 2.18 (m, 1 H). C-NMR: 176.87; 139.40; 128.77;
þ
28.45; 125.28; 81.22; 30.95; 28.94. ESI-MS: 162 (47, M ), 117 (100).
5
-(4-Bromophenyl)-4,5-dihydro-2(3H)-furanone (2b). Yield: 84 mg (70%). White solid. M.p. 81 –
1
8
28 ([44]: 81.5 – 82.58). IR (film): 1763, 1592, 1490, 1178, 1142, 1008, 828, 804. H-NMR: 7.53 (d, J ¼
.0, 2 H); 7.23 (d, J ¼ 5.0, 2 H); 5.49 – 5.46 (m, 1 H); 2.68 – 2.65 (m, 3 H); 2.19 – 2.13 (m, 1 H).
5
13
þ
79
C-NMR: 176.48; 138.44; 131.94; 126.96; 122.40; 80.42; 30.90; 28.83. ESI-MS: 240 (19, M (Br )), 242
þ
81
(
20, M (Br )), 161 (100).
4
,5-Dihydro-5-(4-methylphenyl)-2(3H)-furanone (2c). Yield: 53 mg (60%). White solid. M.p. 73 –
1
7
48 ([45]: 71 – 72.58). IR (film): 3036, 2932, 1721, 1603, 1493, 1165, 1139, 1037, 1008, 852. H-NMR:
7
.23 (d, J ¼ 5.0, 4 H); 5.50 (dd, J ¼ 10.0, 5.0, 1 H); 2.68 – 2.63 (m, 3 H); 2.37 (s, 3 H); 2.22 – 2.19 (m, 1 H).
13
þ
C-NMR: 176.96; 138.33; 136.35; 129.41; 125.35; 81.33; 30.94; 29.03; 21.13. ESI-MS: 176 (26, M ), 91
100).
,4,5,6-Tetrahydro-6-phenyl-2H-pyran-2-one (2e). Yield: 51 mg (58%). White solid. M.p. 75 – 768
(
3
1
(
5
1
[19]: 76 – 788). IR (film): 3043, 2969, 2950, 1727, 1493, 1245, 1035, 764, 705. H-NMR: 7.42 – 7.33 (m,
H); 5.38 (dd, J ¼ 10.0, 5.0, 1 H); 2.76 – 2.69 (m, 1 H); 2.63 – 2.56 (m, 1 H); 2.21 – 2.17 (m, 1 H); 2.03 –
13
.99 (m, 2 H); 1.93 – 1.86 (m, 1 H). C-NMR: 171.31; 139.75; 128.61; 128.27; 125.70; 81.63; 30.52; 29.52;
þ
1
8.61. ESI-MS: 176 (5.6, M ), 104 (100).
7
-Phenyloxepan-2-one (2f). Yield: 15 mg (18%). White solid. M.p. 67 – 688 ([19]: 66 – 678). IR (film):
1
2
1
1
924, 1766, 1616, 1520, 1183, 1147, 1011, 940, 773, 723. H-NMR: 7.41 – 7.36 (m, 5 H); 5.31 (d, J ¼ 10.0,
13
H); 2.82 – 2.76 (m, 2 H); 2.16 – 2.02 (m, 4 H); 1.81 – 1.75 (m, 2 H). C-NMR: 174.84; 140.79; 128.57;
þ
28.10; 125.86; 82.11; 37.49; 34.98; 28.63; 22.86. ESI-MS: 190 (47, M ), 117 (100).
2
-Benzofuran-1(3H)-one (2g). Yield: 48 mg (72%). White solid. M.p. 72 – 748 ([19]: 73 – 748). IR
1
(
1
1
film): 3023, 2927, 2888, 1742, 1600, 1490, 1457, 1249, 1220, 1144, 1029, 752. H-NMR: 7.93 (d, J ¼ 10.0,
13
H); 7.71 – 7.68 (m, 1 H); 7.56 – 7.50 (m, 2 H); 5.34 (s, 2 H). C-NMR: 171.08; 146.54; 134.00; 129.05;
þ
25.79; 122.09; 69.64. ESI-MS: 134 (2.1, M ), 105 (100).
6
-Methyl-2-benzofuran-1(3H)-one (2h). Yield: 41 mg (55%). White solid. M.p. 85 – 868 ([46]: 888).
1
IR (film): 3037, 2925, 1759, 1591, 1496, 1457, 1156, 1056, 996, 821, 770. H-NMR: 7.67 (s, 1 H); 7.48 (d, J ¼
13
5
1
.0, 1 H); 7.37 (d, J ¼ 10.0, 1 H); 5.26 (s, 2 H); 2.44 (s, 3 H). C-NMR: 171.16; 143.82; 139.14; 135.10;
þ
25.75; 125.50; 121.73; 69.51; 21.12. ESI-MS: 148 (8.1, M ), 91(100).
6
-Bromo-2-benzofuran-1(3H)-one (2i). Yield: 61 mg (57%). White solid. M.p. 97 – 988 ([47]: 96 –
1
9
1
1
88). IR (film): 3076, 1769, 1458, 1358, 1212, 1191, 1046, 997, 870, 824, 767. H-NMR: 8.08 (d, J ¼ 5.0,
13
H); 7.82 (d, J ¼ 10.0, 1 H); 7.41 (d, J ¼ 5.0, 1 H); 5.30 (s, 2 H). C-NMR: 169.42; 145.09; 137.09; 128.83;
þ
79
þ
81
27.91; 123.65; 123.05; 69.46. ESI-MS: 212 (11, M (Br )), 214 (13, M (Br ), 133 (100).
,4-Dihydro-3H-2-benzopyran-3-one (2j). Yield: 50 mg (67%). White solid. M.p. 80 – 818 ([48]: 81 –
1
1
8
2
1
28). IR (film): 3023, 2889, 1746, 1489, 1458, 1392, 1252, 1224, 1147, 1034, 761. H-NMR: 7.37 – 7.31 (m,
H); 7.27 – 7.23 (m, 2 H); 5.33 (s, 2 H); 3.73 (s, 2 H). C-NMR: 170.66; 131.55; 130.97; 128.82; 127.37;
27.07; 124.68; 70.08; 36.18. ESI-MS: 148 (5.0, M ), 104 (100).
13
þ
1,4-Dihydro-6-methyl-3H-2-benzopyran-3-one (2k). Yield: 35 mg (43%). White solid. M.p. 70 – 718
(
[48]: 72 – 738). IR (film): 2921, 1725, 1616, 1590, 1501, 1461, 1255, 1216, 1157, 1126, 1021, 833, 780.

Helvetica Chimica Acta – Vol. 97 (2014)
859
1
13
H-NMR: 7.13 (dd, J ¼ 10.0, 5.0, 2 H); 7.05 (s, 1 H); 5.29 (s, 2 H); 3.68 (s, 2 H); 2.38 (s, 3 H). C-NMR:
þ
1
70.85; 138.81; 130.93; 128.60; 127.99; 127.70; 124.54; 70.01; 36.20; 21.19. ESI-MS: 162 (53, M ), 117
(
100).
Financial support from the Natural Science Foundation of China (Project 21072176) is greatly
appreciated.
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Received August 9, 2013