Iron porphyrin-catalyzed C(SP3) -H activation for the formation of C–O bond via cross-dehydrogenative coupling of cycloether and aromatic acid

Article abstract of DOI:10.1016/j.tet.2017.10.046

An efficient cyclic ether benzoxylation was achieved by using iron porphyrin as the catalyst and di-tert-butyl peroxide oxidant. The benzoic acid substrates bearing electron donating or withdrawing groups could react with cyclic ether smoothly to afford t

Full text of DOI:10.1016/j.tet.2017.10.046

Accepted Manuscript
3
Iron porphyrin-catalyzed C(SP ) -H activation for the formation of C-O bond via cross-
dehydrogenative coupling of cycloether and aromatic acid
Wei-Hong Wen, An-Na Xie, Hua-Hua Wang, Dong-Xu Zhang, Atif Ali, Xiao Ying, Hai-
Yang Liu
PII:
S0040-4020(17)31074-8
10.1016/j.tet.2017.10.046
TET 29049
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 9 August 2017
Revised Date: 16 October 2017
Accepted Date: 17 October 2017
Please cite this article as: Wen W-H, Xie A-N, Wang H-H, Zhang D-X, Ali A, Ying X, Liu H-Y, Iron
3
porphyrin-catalyzed C(SP ) -H activation for the formation of C-O bond via cross-dehydrogenative
coupling of cycloether and aromatic acid, Tetrahedron (2017), doi: 10.1016/j.tet.2017.10.046.
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ACCEPTED MANUSCRIPT
Graphical Abstract
Iron porphyrin-catalyzed C(SP3)–H activation for
the formation of CꢀO bond via cross-dehydrogenative
coupling of cycloether and aromatic acid
Leave this area blank for abstract info.
Wei-Hong Wena, An-Na Xiea, Hua-Hua Wanga, Dong-Xu Zhanga, Atif Alia, Xiao Yingb and Hai-Yang
Liua*

1
ACCEPTED MANUSCRIPT
Tetrahedron
journal homepage: www.elsevier.com
Iron porphyrin-catalyzed C(SP3) ꢀH activation for the formation of CꢀO bond
via cross-dehydrogenative coupling of cycloether and aromatic acid
Wei-Hong Wena, An-Na Xiea, Hua-Hua Wanga, Dong-Xu Zhanga, Atif Alia, Xiao Yingb and Hai-Yang
Liua*
a Department of Chemistry, Key Laboratory of Functional Molecular Engineering of Guangdong Province, South China University of Technology, Guangzhou
510641, China
b Department of Applied Physics, South China University of Technology, Guangzhou 510641, China
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
An efficient cyclic ether benzoxylation was achieved by using iron porphyrin as the catalyst and
di-tert-butyl peroxide oxidant. The benzoic acid substrates bearing electron donating or
withdrawing groups could react with cyclic ether smoothly to afford the desired products. It was
found iron porphyrin catalyzed oxidative C(sp3)ꢀH activating esterification had the advantage of
short reaction time and low catalyst loading. The reaction had been proved to proceed via a
radical process.
Available online
Keywords:
Porphyrin
2016 Elsevier Ltd. All rights reserved
.
Iron
Cross-dehydrogenative coupling
Cycle ether
C-H activation
1. Introduction
The development of efficient, convenient, straightforward
and environmentally benign methods for CꢀX (C, O, N, etc.)
bonds formation has attracted continuous interest in recent years1.
Cross-dehydrogenative coupling (CDC) reaction plays an
important role for the construction of CꢀX bond, in which
transition metals such as palladium2, ruthenium3, nickel4, indium5
are the most commonly used catalysts. An alternative catalyst is
iron. Since the first report of FeCl2 catalyzed CDC reactions in
20076. Lots of effort has been devoted to the iron catalyzed CDC
reactions7. It demonstrated that iron catalyst was available for C-
O bond formation by the coupling of C(sp3)-H with O(sp3)-H8 or
O(sp2) ꢀ H9 and C(sp2) ꢀ H with O(sp2) ꢀ H10 via CDC
reactions. The direct esterification of aꢀC(sp3) ꢀH bonds is one
of the most important application of CDC reaction, which may
prepare some biologically active ester of practical usage in
medicine like artemisinin11. Compared to conventional
esterification reactions, the CDC reaction has the advantage of
using alkane instead of alcohol substrates. In 2014, Han et al. had
reported the iron-catalyzed oxidative CDC esterification of cyclic
ether CꢀH bonds with carboxylic acids, the reaction was carried
out at 20 mol% catalyst loading for 24 hours at temperature 120
ꢁC12. The reaction time could be further reduced to 12 hours by
using copper catalyst13.
Scheme 1. Molecular Structures of FeTECPCl and Fe-ꢀ-oxo
Metalloporphyrins are a class of versatile catalysts14. It shows
good catalytic activity in many reactions such as olefin
oxidation15, cyclopropanation16, olefination17, asymmetric
synthesis18, threeꢀcomponent reactions19 and CꢀH bond insertion
reactions20. Although there are many reports on metalloporphyrin
catalyzed reactions, the use of metalloporphyrin catalysts in CDC
reactions is scarce. In 2014, metal porphyrin was firstly used in
catalytic CDC reaction which enables direct activation of two
different sp3 C-H bonds of isoquinoline and nitromethane
under solvent-free conditions21. Two years later, Guo and his co-
workers had also reported the application of metal porphyrin in
CDC reaction22, in which they had successfully achieved aerobic
oxidative coupling of terminal alkynes. More recently, our group
has also reported the esterification of C(sp3) ꢀH via copper-
porphyrin catalyzed CDC reaction23. To continue our efforts in
the metalloporphyrin catalyzed CDC reactions, we here wish to
report the CDC esterification of cyclic ether by using iron chloro-
5,10,15,20-tetra-(ethoxylcarbonyl) porphyrin catalyst (Scheme 1,
FeTECPCl) and TBHP oxidant. The reaction completed in 4
hours with catalyst loading only 0.5%, showing iron porphyrin
was efficient in this kind of reaction.

2
Tetrahedron
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2. Result and discussion
effects of other oxidants and catalysts on the reaction was also
investigated to pursue the higher yield (Table 2, entries 6-14).
Unfortunately, we did not get satisfactory results. The yield
decreased when the reaction was performed at 100 ºC (Table 2,
entries 15). No significant improvement in the yield was
observed when the reaction was conducted at 140 ꢁC (Table 2,
entries 16). Note that the product 1a was not observed in the
absence of catalyst or oxidant (Table 2, entries 17-18).
X-ray diffraction analysis showed that the structure of
FeTECPCl had a formulation unit in the cell in the orthorhombic
P-1 space group, and no solvent molecule was crystallized. All
crystallographically independent atoms are located in the usual
position, except for the iron atom, which is located in the center
of the inversion of the crystal. The 24ꢀmembered macrocyclic
core of porphyrin is coplanar, and the five-coordinated iron atom
is located at the center of this almost completely flat porphyrin
macrocycle and forms a tetrahedron with four nitrogen atoms and
one chlorine atom (Scheme 2).
Table 2
Optimization of Reaction Conditionsa
The Fe–N bond lengths range from 2.058(4) to 2.066(4) Å
with an average value of 2.063(4) Å, the FeꢀCl bond length is
2.2188(15) Å, which is weaker interaction than the bond of metal
iron and nitrogen atom (Table 1). The bond between the four
nitrogen atoms (N1, N2, N3 and N4) and the iron atom and the
chlorine atom is 99.60(12), 104.11(12), 101.46(12), 104.16(12).
Entry
1
Catalyst (amt, %)
FeTECPCl (0.05)
FeTECPCl (0.25)
FeTECPCl (0.5)
FeTECPCl (1.0)
FeTECPCl (0.5)
FeTECPCl (0.5)
FeTECPCl (0.5)
FeTECPCl (0.5)
FeTECPCl (0.5)
FeTECPCl (0.5)
FeTPP (0.5)
Oxidant
DTBP
Yield %b
32
2
DTBP
61
3
DTBP
DTBP
DTBPc
PhI(AcO)2
PhIO
74
4
59
5
73
6
NR
NR
NR
NR
Trace
15
7
8
m-CPBA
d
9
H2O2
10
11
12
13
14
15
16
17
18
TBHP
DTBP
DTBP
DTBP
DTBP
DTBP
DTBP
MnTECPCl (0.5)
CoTECP (0.5)
Trace
Trace
NR
25e
FeCl3 (0.5)
FeTECPCl (0.5)
FeTECPCl (0.5)
FeTECPCl (0.5)
73f
NR
NR
DTBP
Scheme 2. ORTEP plots of FeTECPCl. (Showing 50% probability thermal
DTBP=di-tert-butyl peroxide, TBHP=tert-butyl hydroperoxide, 70 wt% in
displacement ellipsoids, hydrogen atoms are omitted for clarity)
H2O, m-CPBA=3-Chloroperbenzoic acid.
a Reaction condition: benzoic acid (0.5mmol), 1,4-dioxane (1mL), catalyst
Table 1 Selected bond lengths(Å) and angels(°) of the FeTECPCl
(0.5 mol %), oxidant (2 equiv), 120 ºC, 4 h.
b Isolated yield based on carboxylic acid.
c DTBP (3 equiv).
Bond Lengths/(Å)
Fe1-Cl1
Fe1-N1
Fe1-N2
2.2188(15)
2.058(3)
2.066(4)
Fe1-N3
Fe1-N4
2.064(4)
2.063(4)
d 30 wt% in H2O.
e 100 ºC
f 140 ºC
With the above optimized conditions in hand, we explored the
1,4-dioxane with other benzoic acid derivatives and the results
were listed in Table 3. The CDC reaction between methyl and
methoxy substituent tolerated in moderate yields of 72-84% (2a-
4a, 7a-9a). Gratifyingly, 4-tert-butylbenzoic acid also examined
and the desired product was obtained in 70% isolated yield (5a).
Not only alkyl substituents were tested, but also 2-phenylbenzoic
acid was investigated, affording 6a with an isolated yield of 74%
. There is no doubt that ortho, meta, para-benzoic acid has a
good yield. The reaction yield of ortho-substituents is minimally
reduced relative to meta- and para-positions. ortho-substituted
acids were lower yields as compared to their meta and para-
substituted analogues was due to steric hindrance imparted by
ortho-substituents (2a,7a,12a,15a). At the same time, we used
ortho and para-halogen substituents and hydroxyl substituents to
illustrate the substitution effect of the substrate on the reaction
(12a-18a). Strikingly, Electron deficient aromatic acids such as
4-nitrobenzoic acid, 4-halogenbenzoic acid, and 4-cyanobenzoic
acid have lower yields in comparison to electron donating groups
(19a-23a). Unfortunately, 2-naphthoic acid is not suitable for this
Bond Angles/(°)
N1-Fe1-Cl1
N2-Fe1-Cl1
N3-Fe1-Cl1
N4-Fe1-Cl1
N2-Fe1-N1
99.60(12)
N3-Fe1-N1
N3-Fe1-N2
N4-Fe1-N1
N4-Fe1-N2
N4-Fe1-N3
87.76(15)
87.56(16)
104.16(12)
86.76(16)
154.38(16)
104.11(12)
101.46(12)
104.16(12)
156.29(16)
Initially, the intermolecular oxidative reaction of benzoic acid
(1) with 1,4-dioxane (a) was chosen as a model reaction to
determine the optimum conditions. We commenced our
investigation in the presence of FeTECPCl as the catalyst and
DTBP as the oxidant under a solvent-free condition. At first, we
discussed the quantity of catalyst from 0.05 to 1.0 mol %, the
most efficiency of this transformation was 0.5 mol % (Table 2,
entries 1-4). No significant improvement in the product yield was
observed with 3 equiv of the DTBP (Table 2, entry 5). The

3
reaction (24a). Hydrocinnamic acid was used in this system to
react with 1,4-dioxane under the typical reaction conditions, we
were pleased to find that the reaction proceeded well and gave the
corresponding product 25a in 55% yield. 3-phenoxypropanoic
acid were reacted with 1,4-dioxane and gave the corresponding
products 26a (73%). Even more, the reaction did not work when
furan-3-carboxylic acid was used as substrate in this system
(27a).
hours, the yield of 2b may reach 40%, the further increasing of
ACCEPTED MANUSCRIPT
the reaction time did not affect the yield significantly.
Interestingly, no 2b’ product could be isolated. The reaction of
other benzoic acid derivatives bearing electron-donating or
withdrawing groups such as 4-methylbenzoic acid (2c), 4-
methoxybenzoic acid (2d), 2-phenylbenzoic acid (2e), 2-
fluorobenzoic acid (2f), 4-tert-butylbenzoic acid (2g) and α,α,α-
trifluoro-p-toluic acid (2h) with 1,4-dioxane provided moderate
yield of 73-83%.
Table 3
Iron-catalyzed CDC reaction of aromatic acid with 1,4-dioxanea
Table 4
Iron-catalyzed CDC reaction of aromatic acid with 1,3-dioxolanea
O
O
FeTECPCl (0.5mol%)
DTBP (4 equiv)
O
O
O
O
H
H
O
+
120°C 8h
O
O
O
O
O
2b'
a Catalytic condition: benzoic acid (0.5mmol), 1,4-dioxane (1mL), catalyst
(0.5 mol %), oxidant (4 equiv), 120 ºC, 8h.
To investigate the reaction mechanism, a series of experiments
was conducted. When the reaction was carried out in the presence
of radical scavenger such as 2,2,6,6-tetramethylpyridine N-oxide
(TEMPO) or butylated hydroxytoluene (BHT), no desired
product could be obtained (Scheme 3), indicating the reaction via
a radical mediated pathway. The intermolecular competing
kinetic isotope effect (KIE) experiment showed a KIE effect of
kH/kD = 4 (the KIE was determined by 1H NMR spectroscopy by
analyzing the ratio of 9a and [D]9a (Scheme 4). This suggested
that C(sp3) ꢀH bond cleavage of 1,4-dioxane was the kinetic
rate-determining step24. Interestingly, the UV-Vis spectra of the
catalyst changed remarkably after adding oxidant (Scheme 5),
such a spectra changes revealed the transformation of catalyst
FeTECP to its Fe-μ-oxo species25. That is, the real catalyst is a
porphyrin Fe-μ-oxo complex. (Scheme 5).
a Catalytic condition: benzoic acid (0.5mmol), 1,4-dioxane (1mL), catalyst
(0.5 mol %), oxidant (2 equiv), 120 ºC, 4h.
Scheme 3. Reaction carried out in the presence of TEMPO and BHT
After finishing the investigation of the 1,4-dioxane as a
substrate, we attempted to extend the substrate range by using
1,3-dioxolane to explore the selectivity and activity of the
reaction (Table 4). However, no reasonable yield of the product
could be obtained with the same reaction conditions. When
double the oxidant amount and prolong the reaction time to 8

4
Tetrahedron
butyl peroxide to form the active catalyst (FeTECP)2O (ꢀ-oxo-
ACCEPTED MANUSCRIPT
bis[5,10,15,20-tetraarylporphyrinatoiron(III)]), as evidenced by
UV-Vis experiment (Scheme 5). Secondly, (FeTECP)2O captures
the hydrogen of 1,4-dioxane to form a tetravalent iron-hydroxyl
porphyrin A and the active free radical B via a single electron
transfer (SET) mechanism. The axial ligand exchange of A with
benzoic acid to generate intermediate C. Finally, the intermediate
C and the intermediate B undergoes a cross-coupling process,
giving the final product 1a and regenerate the catalyst FeTECPCl.
Scheme 4. Kinetic Isotope Effect
The TEMPO was detected by electron paramagnetic
resonance (EPR) in the reaction mixture of benzoic acid, 1,4-
dioxane and FeTECPCl as shown in Scheme 6, line a, which is
TEMPO as a concentration standard26. At 25 °C and then
temperature increased up to 120 °C the free radicals were slightly
weakened as shown in Scheme 6, line b, and after 25 min no
change was observed. Followed by the addition of DTBP in the
mixture at 120 °C it very quickly reacts with TEMPO, no EPR
signal was observe. The radicals disappear shown as Scheme 3,
line c, indicating that the reactants produced free radicals at high
temperatures, confirming the free radical reaction.
Scheme 7. Proposed Mechanism for Esterification
Scheme 8. Regioselectivity of the Reaction on 1,3-Dioxolane
According to the previous report on the stereoelectronic
effects in hydrogen atom abstraction from cyclic ethers, we
proposed the mechanism is illustrated in Scheme 8. The reaction
of benzoic acid with 1,4-dioxane go through the pathway A
rather than the pathway B, this is probably mainly due to the fact
that bridgehead radicals are notoriously more difficult to form.
Therefore, we constructed the abnormal regiosectivity of the
reaction to give the final products 2b.
Scheme 5. UV spectrum of 1,4-dioxane (3mL), FeTECPCl (0.5 mol %),
DTBP (570ul) at room temperature, measure every ten minutes.
3. Conclusion
In summary, we have demonstrated iron-porphyrin catalyzed
C(SP3) ꢀH activation for the formation of C-O bond via cross-
dehydrogenative coupling of cycloether and aromatic acid. This
examples the first application of Fe porphyrin in cross-
dehydrogenative coupling reactions. When using phenol and
cycloether as substrate, the CDC reaction could go smoothly
also. Systematic investigation of iron porphyrin catalyzed CDC
reactions is still going on in our laboratory.
4. Experimental section
4.1. General experimental
All the reagents were commercial grade and purified
according to the established procedures. Organic extracts were
dried over anhydrous sodium sulphate. Solvents were removed in
a rotary evaporator under reduced pressure. Silica gel (100–200
mesh size) was used for the column chromatography. UV-Visible
absorption spectra were measured on Hitachi 3900H in 1 cm
optical path length quartz cell at room temperature. NMR spectra
were recorded in CDCl3 with tetramethylsilane as the internal
Scheme 6. EPR spectrum of (a) Benzoic acid (0.5mmol), 1,4-dioxane (1mL),
FeTECPCl (0.5 mol %) and TEMPO (50mM) in room temperature; (b)
Benzoic acid (0.5mmol), 1,4-dioxane (1mL), FeTECPCl (0.5 mol %) and
TEMPO (50mM) in 120 °C after 25 min; (c) Followed by the addition of
DTBP (2 equiv) in the mixture at 120 °C after 5 min.
1
Based on the above results and the previous reports12, we
proposed that the mechanism is likely to proceeds by a radical
way (Scheme 7). Firstly, FeTECPCl is oxidized by by di-tert-
standard for H NMR (400 MHz) CDCl3 solvent as the internal
standard for 13C NMR (100 MHz). HR‒MS spectra were
recorded on Bruker maxis impact mass spectrometer with an ESI
source.

5
4.2. Preparation of Catalyst
7.4 Hz, 1H), 7.35 (t, J = 7.6 Hz, 2H), 5.99 (s, 1H), 4.16 – 4.06
ACCEPTED MANUSCRIPT
(m, 1H), 3.78 (s, 2H), 3.71 (d, J = 5.1 Hz, 2H), 3.56 (d, J = 11.8
Hz, 1H). 13C NMR (101 MHz, CDCl3) δ 165.19, 133.40, 129.89,
129.74, 128.46, 89. 83, 67.81, 66.10, 61.75.
The synthesis of 5,10,15,20-tetrakis(ethoxycarbonyl)-
porphyrin
ligand
(TECP)
and
5,10,15,20-tetrakis-
(ethoxycarbonyl)porphyrin manganese (III) (MnTECPCl) were
performed by our recently reported procedure27. The
metalloporphyrin 5,10,15,20-tetrakis(ethoxycarbonyl)porphyrin
4.3.2. 1,4-dioxan-2-yl 2-methylbenzoate (2a). Yellow oil, yield
72%; H NMR (400 MHz, CDCl3) δ 8.10 – 8.03 (m, 1H), 7.47 –
1
Cobalt(II)
(CoTECP),
5,10,15,20-tetrakis(ethoxycarbonyl)-
7.39 (m, 1H), 7.28 (t, J = 7.0 Hz, 2H), 6.10 (t, J = 1.8 Hz, 1H),
4.31 – 4.16 (m, 1H), 3.90 (d, J = 1.8 Hz, 2H), 3.83 (dd, J = 6.7,
2.6 Hz, 2H), 3.70 (dt, J = 11.8, 2.6 Hz, 1H), 2.67 (s, 3H). 13C
NMR (101 MHz, CDCl3) δ 165.97, 140.86, 132.49, 131.84,
131.04, 128.87, 125.80, 89.69, 67.93, 66.13, 61.89, 21.93.
porphyrin iron (III) (FeTECPCl) and ꢀ-oxo-bis[5,10,15,20-
tetraarylporphyrinatoiron (III) ((FeTECP)2O) were prepared
using literature procedures28.
FeTECPCl was obtained by refluxing TECP with FeCl3•4H2O
in DMF solution for 2 h. After that it was diluted with CH2Cl2
and washed with saturated aqueous solution of NaCl several
times. The organic layer was collected and dried over anhydrous
Na2SO4. The filtrate was concentrated and the crude product was
purified on silica gel (100‒200 mesh) using CH2Cl2 as eluent.
Purple crystal was obtained after slow evaporation from
CH2Cl2/hexane (1:4 v/v). Yield: 90%. HR‒MS calcd for [M-Cl]+:
C32H28FeN4O8 652.1252, found 652.1248.
4.3.3. 1,4-dioxan-2-yl 3-methylbenzoate (3a). Yellow oil, yield
80%; H NMR (400 MHz, CDCl3) δ 7.91 (d, J = 5.8 Hz, 2H),
1
7.34 (dt, J = 15.6, 7.6 Hz, 2H), 6.07 (t,1H), 4.29 – 4.12 (m, 1H),
3.86 (t, J = 6.1 Hz, 2H), 3.80 (dd, J = 6.6, 2.1 Hz, 2H), 3.65 (dt, J
= 11.8, 2.6 Hz, 1H), 2.39 (s, 3H). 13C NMR (101 MHz, CDCl3) δ
165.37, 138.27, 134.18, 130.35, 129.69, 128.35, 127.09, 89.78,
67.87, 66.12, 61.82, 21.23.
4.3.4. 1,4-dioxan-2-yl 4-methylbenzoate (4a). Yellow oil, yield
79%; 1H NMR (400 MHz, CDCl3) δ 8.00 (t, J = 8.3 Hz, 2H), 7.24
(d, J = 8.0 Hz, 2H), 6.08 (s, 1H), 4.30 – 4.10 (m, 1H), 3.88 (d, J =
1.8 Hz, 2H), 3.81 (d, J = 5.6 Hz, 2H), 3.66 (dt, J = 11.6, 2.2 Hz,
1H), 2.40 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 165.23, 144.15,
129.94, 129.15, 127.00, 89.67, 67.86, 66.10, 61.79, 21.64.
MnTECPCl was synthesized similar to the procedure of
FeTECPCl, except FeCl3•4H2O was used instead of
Mn(OAc)2•4H2O. Yield: 80%17.
CoTECP was synthesized similar to the procedure of
FeTECPCl, except FeCl3•4H2O was used instead of
Co(OAc)2•4H2O. Yield: 82%. HR‒MS calcd for [M]+:
C32H28CoN4O8 655.1234, found 655.1236.
4.3.5. 1,4-dioxan-2-yl 4-(tert-butyl)benzoate (5a). Yellow oil,
1
yield 70%; H NMR (400 MHz, CDCl3) δ 8.05 (d, J = 8.5 Hz,
2H), 7.46 (d, J = 8.5 Hz, 2H), 6.08 (s, 1H), 4.30 – 4.11 (m, 1H),
3.91 – 3.76 (m, 4H), 3.65 (dt, J = 11.7, 2.5 Hz, 1H), 1.33 (s, 9H).
13C NMR (101 MHz, CDCl3) δ 165.19, 157.13, 129.83, 126.97,
125.43, 89.63, 67.89, 66.13, 61.78, 35.12, 31.10.
Fe-ꢀ-oxo was synthesized by FeTECPCl with NaOH solution
for
1
h, Yield: 95%. MALDI-TOF calcd for [M+Na]-:
C64H56Fe2N8O17Na 1343.2340, found 1343.0590.
4.3. General procedure
4.3.6. 1,4-dioxan-2-yl [1,1'-biphenyl]-2-carboxylate (6a). Yellow
oil, yield 73%; 1H NMR (400 MHz, CDCl3) δ 7.94 (d, J = 6.9 Hz,
1H), 7.58 (t, J = 7.5 Hz, 1H), 7.48 – 7.33 (m, 7H), 5.85 (s, 1H),
3.70 – 3.57 (m, 4H), 3.42 (dd, J = 28.5, 10.7 Hz, 2H). 13C NMR
(101 MHz, CDCl3) δ 167.51, 142.74, 141.42, 131.55, 130.87,
130.44, 130.14, 128.53, 128.17, 127.23, 90.12, 67.39, 65.84,
61.57.
In a Schlenk tube equipped with a magnetic stir bar was added
FeTECPCl (0.33 mg, 0.5 ꢀmol) and benzoic acid (61 mg, 0.5
mmol). 1,4-Dioxane (1.0 mL, 7.5 – 12.5 mmol) and DTBP (di-
tert-butyl peroxide, 1 mmol, 190 ꢀL) were added. The resulting
reaction mixture was stirred at 120 °C for 4 h. After the required
reaction time, the mixture was cooled to room temperature. The
reaction mixture was extracted with dichloromethane. The
organic phases were evaporated under reduced pressure. The
crude product was purified by column chromatography on silica
gel (hexane/ethyl acetate 95/5) to accord the corresponding
product.
4.3.7. 1,4-Dioxan-2-yl 2-methoxybenzoate (7a). Yellow oil, yield
1
75%; H NMR (400 MHz, CDCl3) δ 7.89 (d, J = 7.5 Hz, 1H),
7.48 (t, J = 7.7 Hz, 1H), 7.06 – 6.87 (m, 2H), 6.08 (s, 1H), 4.34 –
4.12 (m, 1H), 3.90 (s, 3H), 3.86 (s, 2H), 3.79 (d, J = 4.9 Hz, 2H),
3.66 (d, J = 11.7 Hz, 1H). 13C NMR (101 MHz, CDCl3) δ 164.56,
159.60, 134.02, 131.87, 120.09, 119.40, 112.13, 89.60, 67.80,
66.10, 61.73, 55.98.
For ESR experiments, 1 mL glass micropipettes equipped
with a stopper at the bottom were used as ESR tubes (inner
diameter 1.2mm). Spectra were recorded on an X-band ESR
instrument (Bruker-A300) using the following adjustments: HF
(100 kHz) field modulation amplitude 100 kHz; microwave
power 20 mW; scan range 100 G; sweep time 122 s; conversion
time 120 ms, time constant 655 ms, temperature 120 -121ꢁC and
23-24 ꢁC.
4.3.8. 1,4-Dioxan-2-yl 3-methoxybenzoate (8a). Yellow oil, yield
1
83%; H NMR (400 MHz, CDCl3) δ 8.02 (d, J = 8.8 Hz, 2H),
6.87 (d, J = 8.7 Hz, 2H), 6.01 (s, 1H), 4.26 – 4.06 (m, 1H), 3.82
(d, J = 0.5 Hz, 2H), 3.79 (s, 3H), 3.75 (dd, J = 6.4, 2.2 Hz, 2H),
3.61 (d, J = 11.8 Hz, 1H). 13C NMR (101 MHz, CDCl3) δ 165.09,
159.61, 131.02, 129.48, 122.27, 119.75, 114.43, 89.92, 67.77,
66.08, 61.79, 55.43.
4.4. Mechanistic investigation: Trapping of radical
intermediates with radical scavenger.
4.3.9. 1,4-Dioxan-2-yl 4-methoxybenzoate (9a). Yellow oil, yield
1
88%; H NMR (400 MHz, CDCl3) δ 8.02 (d, J = 8.8 Hz, 2H),
TEMPO (or BHT): An oven-dried reaction vessel was charged
with p-Anisic acid (2) (76 mg, 0.5 mmol), FeTECPCl (1.7 mg,
0.5 mol%), DTBP (190 µL, 1 mmol), radical scavenger (0.5
mmol) in 1,4-dioxane (a) (1 mL). The flask was fitted to a
condenser and the resultant reaction mixture was stirred in a
preheated oil bath at 120 ꢂ for 4 h. The reaction after 4 h
afforded traces (<5%) of the desired product (9a).
6.87 (d, J = 8.7 Hz, 2H), 6.01 (s, 1H), 4.26 – 4.06 (m, 1H), 3.82
(d, J = 0.5 Hz, 2H), 3.79 (s, 3H), 3.75 (dd, J = 6.4, 2.2 Hz, 2H),
3.61 (d, J = 11.8 Hz, 1H). 13C NMR (101 MHz, CDCl3) δ 164.86,
163.73, 131.96, 122.00, 113.69, 89.49, 67.87, 66.08, 61.77, 55.40.
4.3.10. 1,4-Dioxan-2-yl 2,6-dimethoxybenzoate (10a). Yellow oil,
yield 72%; 1H NMR (400 MHz, CDCl3) δ 7.29 (t, J = 8.4 Hz, 1H),
6.56 (d, J = 8.4 Hz, 2H), 6.10 (s, 1H), 4.32 – 4.20 (m, 1H), 3.86 –
3.77 (m, 10H), 3.65 (d, J = 11.8 Hz, 1H). 13C NMR (101 MHz,
1
4.3.1. 1,4-Dioxan-2-yl benzoate (1a). Yellow oil, yield 74%; H
NMR (400 MHz, CDCl3) δ 8.02 (d, J = 7.7 Hz, 2H), 7.46 (d, J =

6
Tetrahedron
CDCl3) δ 165.34, 157.55, 131.29, 112.63, 103.96, 89.84, 67.74,
5.3 Hz, 2H), 3.73 (d, J = 11.7 Hz, 1H). 13C NMR (101 MHz,
ACCEPTED MANUSCRIPT
66.11, 61.36, 56.00.
CDCl3) δ 165.95, 133.98, 131.59, 130.97, 128.64, 128.06, 126.26,
125.79, 124.49, 89.90, 67.99, 66.21, 61.94.
4.3.11. 1,4-dioxan-2-yl 2,4-dimethoxybenzoate (11a). Yellow oil,
yield 74%; H NMR (400 MHz, CDCl3) δ 7.89 (d, J = 8.4 Hz,
1
4.3.20. 1,4-dioxan-2-yl 3-phenylpropanoate (25a). Yellow solid,
1H NMR (400 MHz, CDCl3) δ 7.39 – 7.13 (m, 5H), 5.83 (s, 1H),
4.12 – 3.88 (m, 1H), 3.83 – 3.62 (m, 4H), 3.56 (m, 1H), 2.98 (t, J
= 7.7 Hz, 2H), 2.71 (t, J = 7.7 Hz, 2H). 13C NMR (101 MHz,
CDCl3) δ 171.65, 140.24, 128.54, 128.33, 126.35, 89.31, 67.70,
66.02, 61.65, 35.86, 30.77.
1H), 6.44 (d, J = 10.2 Hz, 2H), 6.00 (s, 1H), 4.22 – 4.08 (m, 1H),
3.83 (s, 3H), 3.79 (s, 5H), 3.74 (d, J = 6.1 Hz, 2H), 3.60 (d, J =
11.7 Hz, 1H). 13C NMR (101 MHz, CDCl3) δ 164.71, 163.79,
161.94, 134.11, 111.52, 104.69, 98.92, 89.25, 67.91, 66.11, 61.81,
55.96, 55.47.
4.3.12. 1,4-dioxan-2-yl 2-fluorobenzoate (12a). Yellow oil, yield
75%; 1H NMR (400 MHz, CDCl3) δ 7.94 (t, J = 7.5 Hz, 1H), 7.48
(dd, J = 13.5, 6.9 Hz, 1H), 7.17 (dd, J = 14.8, 7.2 Hz, 1H), 7.12 –
7.05 (m, 1H), 6.05 (s, 1H), 4.28 – 4.05 (m, 1H), 3.82 (s, 2H),
3.61 (d, J = 11.8 Hz, 1H). 13C NMR (101 MHz, CDCl3) δ 163.51,
160.92, 134.92, 132.30), 124.01, 118.27, 117.22, 90.22, 67.72,
66.14, 61.80. 19F NMR (376 MHz, CDCl3) δ -108.66 (s).
4.3.21. 1,4-dioxan-2-yl 3-phenoxypropanoate (26a). Yellow oil,
1H NMR (400 MHz, CDCl3) δ 7.31 – 7.24 (m, 2H), 7.00 – 6.87
(m, 3H), 5.91 (t, J = 1.8 Hz, 1H), 4.34 – 4.23 (m, 2H), 4.17 –
4.06 (m, 1H), 3.80 – 3.71 (m, 4H), 3.61 (dt, J = 11.7, 2.6 Hz, 1H),
2.89 (t, J = 6.3 Hz, 2H). 13C NMR (101 MHz, CDCl3) δ 169.92,
158.47, 129.48, 121.13, 114.71, 89.57, 67.67, 66.05, 63.18, 61.65,
34.74. HRMS (ESI+): m/z calcd for [C13H16O5 + Na] 275.0890,
found 275.0886.
4.3.13. 1,4-dioxan-2-yl 4-fluorobenzoate (13a). Yellow oil, yield
1
79%; H NMR (400 MHz, CDCl3) δ 8.12 (dd, J = 8.9, 5.4 Hz,
4.3.22. 1,4-Dioxolan-4-yl 4-methylbenzoate (2c). Yellow oil,
1
2H), 7.11 (t, J = 8.7 Hz, 2H), 6.07 (t, J = 1.7 Hz, 1H), 4.26 – 4.13
(m, 1H), 3.87 (d, J = 1.9 Hz, 2H), 3.81 (dd, J = 6.8, 2.6 Hz, 2H),
3.66 (dt, J = 11.8, 2.6 Hz, 1H). 13C NMR (101 MHz, CDCl3) δ
167.30, 164.77, 164.23, 132.55, 125.99, 115.75, 115.53, 89.97,
67.81, 66.11, 61.80. 19F NMR (376 MHz, CDCl3) δ -104.83 (s).
yield 79%; H NMR (400 MHz, CDCl3) δ 7.83 (d, J = 8.2 Hz,
2H), 7.13 (d, J = 8.0 Hz, 2H), 6.47 (dd, J = 4.0, 1.8 Hz, 1H), 5.06
(d, J = 17.5 Hz, 2H), 4.03 (ddd, J = 11.3, 9.5, 3.0 Hz, 2H), 2.30 (s,
3H). 13C NMR (101 MHz, CDCl3) δ 165.83, 144.30, 129.83,
129.17, 126.72, 95.85, 94.56, 70.68, 21.66.
4.3.14. 1,4-dioxan-2-yl 4-(trifluoromethyl) benzoate (14a).
Yellow oil, yield 74%; 1H NMR (400 MHz, CDCl3) δ 8.15 (d, J =
8.1 Hz, 2H), 7.63 (d, J = 8.3 Hz, 2H), 6.03 (s, 1H), 4.26 – 4.07
(m, 1H), 3.82 (s, 2H), 3.75 (d, J = 4.8 Hz, 2H), 3.60 (d, J = 11.8
Hz, 1H). 13C NMR (101 MHz, CDCl3) δ 164.04, 134.96, 134.64,
133.04, 130.27, 125.47, 90.40, 67.68, 66.07, 61.76. 19F NMR
(376 MHz, CDCl3) δ -63.23 (s).
4.3.23. 1,4-Dioxolan-4-yl 4-methoxybenzoate (2d). Yellow oil,
yield 76%; H NMR (400 MHz, CDCl3) δ 7.96 (d, J = 8.9 Hz,
2H), 6.88 (d, J = 8.9 Hz, 2H), 6.53 (dd, J = 4.1, 1.9 Hz, 1H), 5.13
(d, J = 17.1 Hz, 2H), 4.10 (ddd, J = 11.4, 9.5, 3.0 Hz, 2H), 3.82 (s,
3H). 13C NMR (101 MHz, CDCl3) δ 165.48, 163.82, 131.89,
121.76, 113.71, 95.81, 94.43, 70.67, 55.43.
1
4.3.24. 1,4-Dioxolan-4-yl 2-phenylbenzoate (2e). Yellow oil,
1
4.3.15. 1,4-Dioxan-2-yl 4-chlorobenzoate (16a). White solid,
yield 73%; H NMR (400 MHz, CDCl3) δ 7.90 (d, J = 7.9 Hz,
1
yield 71%; H NMR (400 MHz, CDCl3) δ 8.05 (d, J = 8.6 Hz,
1H), 7.56 (t, J = 7.0 Hz, 1H), 7.49 – 7.27 (m, 8H), 6.32 (dd, J =
4.3, 1.9 Hz, 1H), 4.95 (s, 1H), 4.61 (s, 1H), 3.87 (dd, J = 9.4, 4.4
Hz, 1H), 3.37 (dd, J = 9.4, 1.9 Hz, 1H). 13C NMR (101 MHz,
CDCl3) δ 167.95, 142.83, 141.47, 131.76, 130.82, 130.27, 130.05,
128.45, 128.10, 127.30, 95.49, 94.34, 69.98.
2H), 7.43 (d, J = 8.6 Hz, 2H), 6.08 (s, 1H), 4.28 – 4.10 (m, 1H),
3.88 (d, J = 1.8 Hz, 2H), 3.82 (dd, J = 6.7, 2.5 Hz, 2H), 3.68 (dt, J
= 11.8, 2.5 Hz, 1H). 13C NMR (101 MHz, CDCl3) δ 164.41,
139.93, 131.30, 128.85, 128.20, 90.07, 67.79, 66.13, 61.81.
4.3.16. 1,4-Dioxan-2-yl 4-bromobenzoate (18a). Yellow solid,
yield 74%; H NMR (400 MHz, CDCl3) δ 7.93 (d, J = 8.4 Hz,
2H), 7.55 (d, J = 8.4 Hz, 2H), 6.04 (s, 1H), 4.22 – 4.04 (m, 1H),
3.84 (s, 2H), 3.78 (d, J = 5.3 Hz, 2H), 3.63 (d, J = 11.8 Hz, 1H).
13C NMR (101 MHz, CDCl3) δ 164.46, 131.80, 131.38, 128.65,
128.56, 90.06, 67.73, 66.08, 61.75.
4.3.25. 1,4-Dioxolan-4-yl 2-fluorobenzoate (2f). Yellow oil, yield
83%; 1H NMR (400 MHz, CDCl3) δ 7.91 (t, J = 7.5 Hz, 1H), 7.51
(dd, J = 12.8, 6.0 Hz, 1H), 7.14 (dt, J = 19.2, 7.8 Hz, 2H), 6.56
(dd, J = 4.1, 1.8 Hz, 1H), 5.14 (d, J = 9.6 Hz, 2H), 4.11 (dd, J =
24.3, 12.5 Hz, 2H). 13C NMR (101 MHz, CDCl3) δ 163.42,
160.83, 135.12, 132.18, 124.01, 118.00, 117.17, 95.90, 94.83,
70.64. 19F NMR (376 MHz, CDCl3) δ -108.79 (s).
1
4.3.17. 1,4-dioxan-2-yl 4-((1,4-dioxan-2-yl)oxy)benzoate (20a).
Yellow soild, yield 36%; HR‒MS calcd for [M+Na]-:
C15H18NaO7 333.2918, found 333.0945. 1H NMR (400 MHz,
CDCl3) δ 8.09 (d, J = 8.8 Hz, 2H), 7.13 (d, J = 8.8 Hz, 2H), 6.07
(s, 1H), 5.36 (d, J = 13.8 Hz, 1H), 4.27 – 4.05 (m, 2H), 4.00 –
3.73 (m, 8H), 3.64 (dd, J = 26.7, 11.8 Hz, 2H). 13C NMR (101
MHz, CDCl3) δ 165.13, 161.14, 132.00, 123.23, 121.52, 116.01,
115.38, 93.19, 89.43, 67.90, 66.11, 61.71, 61.07.
4.3.26. 1,4-Dioxolan-4-yl 4-tert-butylbenzoate (2g). Yellow oil,
1
yield 80%; H NMR (400 MHz, CDCl3) δ 7.88 (d, J = 8.5 Hz,
2H), 7.35 (d, J = 8.5 Hz, 2H), 6.48 (dd, J = 4.1, 1.9 Hz, 1H), 5.06
(d, J = 14.4 Hz, 2H), 4.03 (ddd, J = 11.3, 9.5, 3.0 Hz, 2H), 1.23 (s,
9H). 13C NMR (101 MHz, CDCl3) δ 165.77, 157.24, 129.71,
126.70, 125.43, 95.83, 94.55, 70.70, 35.12, 31.07, 28.20.
4.3.27. 1,4-Dioxolan-4-yl 4-(trifluoromethyl)benzoate (2i).
Yellow oil, yield 74%; 1H NMR (400 MHz, CDCl3) δ 7.83 (d, J =
8.2 Hz, 2H), 7.13 (d, J = 8.0 Hz, 2H), 6.47 (dd, J = 4.0, 1.8 Hz,
1H), 5.06 (d, J = 17.5 Hz, 2H), 4.03 (ddd, J = 11.3, 9.5, 3.0 Hz,
2H), 2.30 (s, 3H). 13C NMR (101 MHz, CDCl3) δ 164.63, 134.77,
132.73, 130.19, 125.51, 122.17, 96.12, 95.13, 70.71. 19F NMR
(376 MHz, CDCl3) δ -63.25 (s).
4.3.18. 1,4-Dioxan-2-yl 4-cyanobenzoate (23a). Yellow solid,
1
yield 49%; H NMR (400 MHz, CDCl3) δ 8.21 (d, J = 8.3 Hz,
2H), 7.76 (d, J = 8.3 Hz, 2H), 6.10 (s, 1H), 4.36 – 4.07 (m, 1H),
3.90 (d, J = 1.7 Hz, 2H), 3.84 (dd, J = 6.9, 2.3 Hz, 2H), 3.69 (d, J
= 11.8 Hz, 1H). 13C NMR (101 MHz, CDCl3) δ 163.70, 133.61,
132.32, 130.39, 117.88, 116.85, 90.65, 67.66, 66.10, 61.79.
4.3.19. 1,4-Dioxan-2-naphthalenecarboxylic (24a). Yellow solid,
yield 27%; H NMR (400 MHz, CDCl3) δ 9.02 (d, J = 8.5 Hz,
Acknowledgments
1
1H), 8.36 (d, J = 7.0 Hz, 1H), 8.06 (d, J = 7.9 Hz, 1H), 7.90 (d, J
= 7.9 Hz, 1H), 7.64 (t, J = 7.4 Hz, 1H), 7.54 (dd, J = 16.4, 8.1 Hz,
2H), 6.22 (s, 1H), 4.44 – 4.19 (m, 1H), 3.96 (s, 2H), 3.86 (d, J =
We gratefully acknowledge financial support from the
National Natural Science Foundation of China (No. 21371059,
21671068)

7
26.
Krylov, I. B.; Terent'ev, A. O.; Timofeev, V. P.; Shelimov, B.
Supplementary Material
ACCEPTED MANUSCRIPT
N.; Novikov, R. A.; Merkulova, V. M.; Nikishin, G. I. Adv Synth
Catal. 2014, 356, 2266-2280.
Wang, H.-H.; Jiang, Y.-Y.; Mahmood, M. H. R.; Liu, H.-Y.; Sung,
H. H. Y.; Williams, I. D.; Chang, C. K. Chinese Chemi Lett. 2015,
26, 529-533.
The Supporting Information is available free of charge at
http://dx.doi.org/ 10.1016/j.tetlet.xxxxxxx.
27.
Experimental details; single crystal results of FeTECPCl; spectral
and analytical data. (PDF)
28.
Adler, A.; Longo, F.; Váradi, V.; Little, R. John Wiley & Sons Inc.
1976, 16, 213-220.
Crystallographic data for FeTECPCl (CIF)
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