2-Aminopyrazine-functionalized MCM-41 nanoporous silica as a new efficient heterogeneous ligand for Cu-catalyzed allylic C–H bonds oxidation of olefins

Article abstract of DOI:10.1007/s11164-019-03967-1

In spite of the importance of the application of allylic C–H bond oxidation of olefins in organic synthesis and existence of the numerous reports, lots of limitations such as large excess of the olefin respect to the oxidant, low chemical yield, long time of reaction and a large amount of the catalyst were reminded. We introduced a novel catalytic system using functionalized MCM-41 as catalyst support to promote efficiency of this reaction. The heterogeneous ligand Pyr-MCM-41 was prepared by substituted 2-aminopyrazine ligand on functionalized MCM-41 with 3-chloropropyltrimthoxysilane and characterized by FT-IR, XRD, SEM, EDX, BET, TGA, CHN techniques. In situ immobilized Pyr-MCM-41 by copper (I) trifluoromethanesulfonate (CuOTf) was applied in direct catalytic esterification of inert C–H bonds in olefins using various peresters at room temperature.

Full text of DOI:10.1007/s11164-019-03967-1

Research on Chemical Intermediates
https://doi.org/10.1007/s11164-019-03967-1
2‑Aminopyrazine‑functionalized MCM‑41 nanoporous silica
as a new efcient heterogeneous ligand for Cu‑catalyzed
allylic C–H bonds oxidation of olefns
Saadi Samadi1 · Akram Ashouri1 · Shadi Kamangar1 · Fatemeh Pourakbari1
Received: 29 May 2019 / Accepted: 6 September 2019
© Springer Nature B.V. 2019
Abstract
In spite of the importance of the application of allylic C–H bond oxidation of ole-
fns in organic synthesis and existence of the numerous reports, lots of limitations
such as large excess of the olefn respect to the oxidant, low chemical yield, long
time of reaction and a large amount of the catalyst were reminded. We introduced a
novel catalytic system using functionalized MCM-41 as catalyst support to promote
efciency of this reaction. The heterogeneous ligand Pyr-MCM-41 was prepared
by substituted 2-aminopyrazine ligand on functionalized MCM-41 with 3-chloro-
propyltrimthoxysilane and characterized by FT-IR, XRD, SEM, EDX, BET, TGA,
CHN techniques. In situ immobilized Pyr-MCM-41 by copper (I) trifuoromethane-
sulfonate (CuOTf) was applied in direct catalytic esterifcation of inert C–H bonds
in olefns using various peresters at room temperature.
Keywords 2-Aminopyrazine · MCM-41 · In situ immobilized · Olefn · Allylic C–H
bond oxidation · Copper trifuoromethanesulfonate · Allylic esters
Introduction
An efcient procedure for preparation of heterogeneous catalysts is the use of
mesoporous materials as hosts for a variety of catalytically active functional groups,
containing acidic and basic sites [1–5]. High surface area and tunable nanopores includ-
ing solid-acid and solid-based mesoporous catalysts were synthesized by postgrafting
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s1116
4-019-03967-1) contains supplementary material, which is available to authorized users.
* Saadi Samadi
s.samadi@uok.ac.ir
1
Laboratory of Asymmetric Synthesis, Department of Chemistry, Faculty of Science, University
of Kurdistan, Sanandaj 66177-15175, Iran
Vol.:(0123456789)
1 3

S. Samadi et al.
organosilanes of them [6, 7], which can be used for various reactions such as catalytic
allylic oxidation [8].
Copper-catalyzed allylic oxidation with a stoichiometric perester oxidant generally
refers to the Kharasch–Sosnovsky reaction which produces allylic esters with the dou-
ble bond untouched [9, 10]. Due to further transformations of allylic esters to other
organic compounds, these products are of crucial importance in total synthesis and
target-oriented synthesis. Some applications of allylic esters were reported as essential
routes to the synthesis of leukotriene B4 [11, 12], chrysanthemic acid [13], brevetoxin
[14] and amyrin [15]. Various factors such as the type of copper salts, oxidative state of
copper, a counter anion, perester, temperature, solvent and additive are efected on the
rate and yield of the allylic oxidation [9, 10, 16–22]. In our previous work, we accom-
plished allylic C–H bonds oxidation of olefns using tert-butyl p-nitrobenzoperoxoate
in the presence of novel Hal-based catalytic system immobilized with Cu(CH3CN)4PF6
which promoted the reaction under mild conditions, afording the desired allylic esters
in good yield and shorter reaction time compared with previous reports [23]. However,
despite the efcient promotion of reaction, it has still sufered from long reaction time,
high ratio of olefn to oxidant (5:1), and the high quantity of required catalyst. In addi-
tion, allylic C–H bond oxidation reaction with ligated copper complexes aford in the
higher chemical yield and rate of reaction than those with unligated copper; thus, the
nature of ligand is also another important factor on this reaction [8–10, 16, 24–31]. As
a result, to overcome these limitations and improve the reactivity, reaction yield and
expanding diversity of allylic esters [8, 10, 26–28], we investigated allylic C–H bonds
oxidation of olefns by altering synthesized perester in the presence of a new bifunc-
tional heterogeneous ligand Pyr-MCM-41 and CuOTf for the frst time.
Experimental
Typical procedure for functionalization of Cl‑MCM‑41 by 2‑aminopyrazine ligand
According to the literature reports, the MCM-41 and Cl-MCM-41 were synthesized [8,
32] (S2–3, S8–9 in Supplementary Material).
A round-bottomed fask contained the anhydrous toluene (20 mL) was charged with
1 g of Cl-MCM-41 under the nitrogen atmosphere. A stirred solution of 2-aminopyra-
zine (3 mmol, 0.3 g) and triethylamine (0.6 mL) were slowly added to the mixture of
reaction and refuxed for overnight. By fltration, the prepared heterogeneous ligand
Pyr-MCM-41 was collected and washed with CH2Cl2/CH3OH and then extracted by
soxhlet (CH2Cl2:CH3OH, 1:1) for 24 h to remove any remaining ligand that was not
immobilized. The obtained light yellow solid was vacuum dried (Scheme 1) [8].
Typical procedure for allylic C–H bonds oxidation of olefns
In a sealed schlenk tube, Pyr-MCM-41 at 50 °C was heated. After cooling to
room temperature, copper (I) trifuoromethanesulfonate (0.025 mmol, 5 mg)
and anhydrous acetonitrile (3 mL) were added and stirred for 2 h under nitrogen
1 3

2‑Aminopyrazine‑functionalized MCM‑41 nanoporous silica…
N
N
N
O
O
O
OH
O
O
OH
OH
O
O
O
OH
O
O
H
2N
Si
Si
NH
NH
Si
Si
Cl
Cl
N
3
24 h
N
N
Si
(MeO)3
Cl
Et N
Toluene,
Reflux,
Then Soxhlet with
41
1
OH
OH
OH
OH
OH
4
-
24 h
Toluene, Reflux,
Then Soxhlet with
M
C
MCM-
M
:
CH2Cl2 MeOH
(1:1)
:
CH2Cl2 MeOH
(1:1)
O
O
MCM-41
Cl-MCM-41
Heterogeneous Ligand (Pyr-MCM-41)
Scheme 1 Synthesis of heterogeneous ligand Pyr-MCM-41
atmosphere. Afterward, olefn (2 mmol) and prepared perester 3 (0.85 mmol) in
Scheme 2 [27] were added to the mixture of the reaction. When the reaction was
completed (by TLC monitoring), the catalyst was fltered, washed with methylene
chloride and water, dried by vacuum and stored for subsequent runs. The meth-
ylene chloride phase was washed with ammonia solution (10%, 5 ml), aqueous
sodium bicarbonate (5%, 2 × 10 ml) and dried over MgSO4. After evaporation
of the solvent, the obtained product was purifed with column chromatography
(EtOAc/n-Hexane 2–10%) to provide white solid up to 95% yield (Scheme 2)
(S2–6, S9–29 in the supplementary material) [8].
Scheme 2 Allylic C–H bonds oxidation of olefns
1 3

S. Samadi et al.
Results and discussion
New supported heterogeneous ligand Pyr-MCM-41 was prepared by reaction of
2-aminopyrazine and Cl-MCM-41 in toluene [8, 32] (Scheme 1).
Characterization of heterogeneous ligand Pyr‑MCM‑41
The observation of prominent peaks (3444, 2928 and 803 cm−1) in FT-IR spectra
of Cl-MCM-41 in comparison with MCM-41 proved the presence of choloropro-
pyltrimethoxysilane group on the surface of the mesoporous silicas that clearly
displayed that the mesoporous structure of MCM-41 was not signifcantly changed
during immobilization. The characteristic band at 1083–1236 cm−1, 2959 cm−1 and
3416 cm−1, which observed in the FT-IR spectrum of heterogeneous ligand Pyr-
MCM-41, was related to the Si–O stretching in Si–O–Si structure, CH2 groups of
the propyl chain of the silylating agent and hydroxyl group on the surface, respec-
tively. Moreover, the asymmetric stretching vibration in 1642 cm−1 for C=N demon-
strated the immobilization of 2-aminopyrazine group (Fig. 1).
The organic content of the samples Cl-MCM-41 and Pyr-MCM-41 was consid-
ered using TGA measurement. As shown in Fig. 2, the weight loss of the samples at
the temperature range of 150–600 °C was 15.25 wt% and 26.5 wt% for Cl-MCM-41
and Pyr-MCM-41, respectively. The TGA analysis of Pyr-MCM-41 presented
the weight loss of 2.7 wt% at around 100 °C, corresponding to the elimination of
adsorbed water and the stability of the covalent attachment of 2-aminopyrazine to
MCM-41 up to 330 °C. According to the TGA analysis of Cl-MCM-41, the load-
ing of choloropropyltrimethoxysilane was 15/25% (1.90 mmol chlorine/gr of SiO2),
and the 2-aminopyrazine loading in catalyst Pyr-MCM-41 was 11/25% (1.17 mmol
aminopyrazine/gr of SiO2).
Fig. 1 FT-IR spectra of MCM-41, Cl-MCM-41, Pyr-MCM-41
1 3

2‑Aminopyrazine‑functionalized MCM‑41 nanoporous silica…
Fig. 2 Thermogravimetric
Cl-MCM-41 (a)
Pyr-MCM-41 (b)
98
analysis (TGA) of Cl-MCM-41
and Pyr-MCM-41
93
88
83
78
73
a
b
0
200
400
600
800
Temperature (°C)
XRD patterns of MCM-41, Cl-MCM-41, and Pyr-MCM-41 outlined in Fig. 3
which shown an intense peak corresponding to refections at (1 0 0) and two low-
intensity peaks related to (1 1 0) and (2 0 0). These results demonstrated that hex-
agonally ordered mesostructures remained unchanged after grafting. However, after
functionalization, the insignifcant changes were accrued in the XRD pattern and the
main order difraction peak was shifted to the higher angle same as previous stud-
ies that confrmed the functionalization was accrued inside the pores of MCM-41
(Fig. 3) [8].
The surface area and pore diameter of MCM-41, Cl-MCM-41 and Pyr-MCM-41
were determined by N2 adsorption–desorption information as presented in Table 1. The
Fig. 3 XRD patterns of the MCM-41, Cl-MCM-41 and Pyr-MCM-41
1 3

S. Samadi et al.
Table 1 N2 adsorption–desorption information of MCM-41, Cl-MCM-41, Pyr-MCM-41
Sample
d (1 0 0) (Å)a
a0 (Å)b
BET surface area Pore diameter WTH (Å)c
(m2/g)
(Å)
MCM-41
Cl-MCM- 41
Pyr-MCM-41
36.33
35.40
34.91
41.95
40.92
40.30
950
680
310
33.2
31.5
30.0
8.75
9.42
10.3
aλ=2d1 0 0 sin θ (λ=1.54060 Cu)
bUnit cell parameter: a0 =2d1 0 0/√3
cWall thicknesses were calculated as: a0—pore size
Fig. 4 Scanning electron micrographs of Pyr-MCM-41 (a). At 1 μm scale (b). At 10 μm scale (c). EDX
spectrum of the Pyr-MCM-41
grafting organic groups into mesoporous materials decreased the surface area and pore
size of MCM-41. The thickness of the silicate wall of Pyr-MCM-41 was 10.3 Å which
estimated by combining the results of XRD and pore size analysis [8] (Table 1). The
surface morphology of the synthesized nanoporous silica MCM-41, Cl-MCM-41 and
Pyr-MCM-41 (Fig. 4a,b) was examined by scanning electron microscopy. The micro-
graphs exhibited no signifcant alterations in the mesostructures after the immobiliza-
tion. The elemental composition of the Pyr-MCM-41 was illustrated by EDX that con-
frmed the presence of Si, O, C and nitrogen (N) elements in it [8] (Fig. 4c).
Catalytic activity
Most reports regarding the allylic C–H bonds oxidation of olefn (Khara-
sch–Sosnovsky reaction) have presented lots of limitations such as low chemical
1 3

2‑Aminopyrazine‑functionalized MCM‑41 nanoporous silica…
yields, long reaction time, large amount of catalyst and use a large ratio of olefn
(5–10 mmol) to perester (1 mmol) (Scheme 2).
This large ratio limits spatially using the expensive olefns or olefns com-
ing from a multi-step synthesis [8, 10, 16, 24, 25, 27]. To overcome these limi-
tations, we evaluated the catalytic potential of new synthesized heterogeneous
ligand Pyr-MCM-41 in the presence of copper salts with diferent peresters
in a smaller ratio of alkene to perseter. So, in a typical procedure, the reac-
tion was performed using cyclohexene (2 mmol) and perester 3d as an oxidant
(0.85 mmol) in the presence of Pyr-MCM-41 (10 mg) and CuOTf (2.5 mol%)
at room temperature in acetonitrile [8, 10, 26–28]. The optimization reaction
conditions were obtained by varying diferent copper salts, solvents, tempera-
tures, amounts of heterogeneous ligand and copper loading which the opti-
mized results are presented in Table 2. The efect of diferent Cu salts includ-
ing, CuOTf, Cu(CH3CN)4PF6, Cu(NO3)2, CuSO4, Cu(OAc)2, CuO and CuI on
the model reaction was given in entries 2–7. As observed in Table 2, the in situ
immbolization of copper salts on Pyr-MCM-41 improved the chemical yield
(up to 97%) and rate of reactions (Entries 10–16), which the highest catalytic
activity was achieved by Cu(OTf) (Entry 16). The examination of the reaction
solvent showed that acetonitrile had the best efect in terms of yield and reac-
tivity (Entries 16–21). On the other hand, as expected, the yield and rate of reac-
tion decreased in lower temperatures (0 and 10 °C), while in high temperatures
(45 and 80 °C) the time of reaction did not change signifcantly but the yield
decreased (Entries 22–25). For comparison, the reaction which accomplished
under the homogeneous catalytic infuence of 2-aminopyrazine yielded 77% of
cyclohex-2-en-1-yl 4-nitrobenzoate 5d after 30 h at room temperature (Entry 28,
Table 2).
By varying the loading of heterogeneous ligand and Cu(OTf), the best results
were aforded with 10 mg of heterogeneous ligand and 2.5 mol% of Cu(OTf)
(Entry 3, Table 3) [8, 10, 26–28].
After obtaining the optimal reaction conditions, we explored the scope of this
protocol with a range of olefns. To our delight, cycloolefns were in accordance
with optimal conditions giving the corresponding allylic esters 4–7 in moder-
ate to good yields and less time (Entries 1, 5, 7, 8, Table 4) [8, 10, 26–28].
Due to the conformational efect, in the case of cyclopentene, cycloheptene and
cyclooctene, the reactions performed with lower rate than cyclohexene. Appli-
cation of this protocol on 1, 5-cyclooctadiene confrmed this protocol could be
generalized to the nonconjugated dienes (Entry 9, Table 4). In addition, lin-
ear alkenes were also evaluated under the optimal protocol that the reactions
produced the products in long-time reaction with low yield (Entries 10–11,
Table 4). The efect of diferent synthesized peresters on the efciency of this
reaction was evaluated using diferent peresters such as tert-butyl benzoperox-
oate 3a, tert-butyl p-methylbenzoperoxoate 3b, tert-butyl p-chlorobenzoperox-
oate 3c and tert-butyl 2-chloro-5-nitrobenzoperoxoate 3e, which indicated the
presence of withdrawing groups on phenyl weaken the oxygen–oxygen bond of
peresters, and thus the rate of tert-butoxy radical formation was increased [9,
33] (Entries 2–6, Table 4).
1 3

S. Samadi et al.
Table 2 Efect of copper salts, Pyr-MCM-41, solvent and temperature on the allylic C–H bonds oxida-
tion of cyclohexene at diferent temperatures
O
O
O
O
O
Pyr-MCM-41 (10 mg)
Cu salt
(2.5 mol%)
T
°
NO2
+
5d
3d
CH CN
(3 mL), ( C)
3
NO2
Entry
Catalyst
–
Cu(OAc)2
Cu(NO3)2
CuSO4
CuO
Solvent
Tempera- Time (h)
ture (°C)
Yield (%)a
1
2
3
4
5
6
7
8
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetone
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
r.t.
10
0
>200
120
110
>200
>200
150
30
33
–
85
72
144
124
96
17
6
10
28
73
80
<10
62
65
55
45
60
75
78
–
66
70
60
52
70
83
97
93
74
40
65
40
71
55
87
90
82
86
77
CuI
Cu(CH3CN)4PF6
CuOTf
Pyr-MCM-41
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
Cu(OAc)2, Pyr-MCM-41
Cu(NO3)2, Pyr-MCM-41
CuSO4, Pyr-MCM-41
CuO, Pyr-MCM-41
CuI, Pyr-MCM-41
Cu(CH3CN)4PF6, Pyr-MCM-41
CuOTf, Pyr-MCM-41
CuOTf, Pyr-MCM-41
CuOTf, Pyr-MCM-41
CuOTf, Pyr-MCM-41
CuOTf, Pyr-MCM-41
CuOTf, Pyr-MCM-41
CuOTf, Pyr-MCM-41
CuOTf, Pyr-MCM-41
CuOTf, Pyr-MCM-41
CuOTf, Pyr-MCM-41
CuOTf
Dichloromethane
Chloroform
Benzene
n-Hexane
110
36
100
8
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
40
80
40
80
r.t
6
29
24
30
CuOTf
CuOTf, 2-Aminopyrazine
Reaction conditions: cyclohexene (2 mmol), perester 3d (0.85 mmol), Pyr-MCM-41 (10 mg), Cu Salt
(2.5 mol%), Solvent (3 mL)
aIsolated yield
1 3

2‑Aminopyrazine‑functionalized MCM‑41 nanoporous silica…
Table 3 Efects of Pyr-MCM-41 and Cu(CH3CN)4PF6 loading on the allylic C–H bonds oxidation of
cyclohexene
O
O
O
O
Pyr-MCM-41 (mg)
Cu(OTf) (mol%)
O
+
NO2
r. t.
CH CN
(3 mL),
3
5d
3d
NO2
Entry
Cu(OTf) (mol%)
Pyr-MCM-41 (mg)
Time (h)
Yield (%)a
1
2
3
4
5
6
7
2.5
2.5
2.5
5
10
2.5
2.5
5
40
25
6
4
9
10
50
77
85
97
93
92
83
70
10
10
10
15
20
2.5
Reaction conditions: cyclohexene (2 mmol), perester 3d (0.85 mmol), Pyr-MCM-41 (mg), CuOTf
(mol%), CH3CN (3 mL)
aIsolated yield
Reaction mechanism
Proposed mechanism for allylic C–H bonds oxidation of cyclohexene [34–41]
in the presence of heterogeneous ligand Pyr-MCM-41 [8] was presented in
scheme 3. Cleavaging the oxygen–oxygen bond in tert-butyl 4-nitrobenzop-
eroxoate by Cu (I) species led to the formation of Cu (II) p-nitrobenzoate and
tert-butoxy radical. Afterward, tert-butyl alcohol and cylohexenyl radical were
formed by abstracting the hydrogen atom from the allylic position of cyclohexene
with tert-butoxy radical [40, 41]. Addition of cylohexenyl radical to the Cu (II)
p-nitro benzoate produced [42, 43] Cu(III) p-nitrobenzoate, which rearranged via
a seven-membered cyclic transition state to give cyclohex-2-en-1-yl 4-nitroben-
zoate and Cu (I) catalyst [29, 40] (Scheme 3).
Catalyst recyclability
The recyclability of the prepared catalyst was examined in the allylic C–H bonds
oxidation of olefns. For this purpose, the catalyst was separated from the mixture
of the model reaction via fltration, washed with methylene chloride and water
and then dried at 40 °C for 2 h under vacuum. The recovered catalyst was applied
for other runs of the reaction. The catalyst was able to perform the reaction for
1 3

S. Samadi et al.
Table 4 Synthesis of allylic esters 4–10 in the presence of a homogeneous (Pyr, CuOTf) and heterogene-
ous catalyst (CuOTf on Pyr-MCM-41)
Reaction conditions: olefn (2 mmol), perester 3a–e (0.85 mmol), Pyr-MCM-41 (10 mg), Cu(OTf)
(2.5 mol%), CH3CN (3 mL)
aIsolated yield
1 3

2‑Aminopyrazine‑functionalized MCM‑41 nanoporous silica…
Scheme 3 Proposed pathway for allylic oxidation of cyclohexene in the presence of heterogeneous
ligand Pyr-MCM-41 and Cu(OTf)
1 3

S. Samadi et al.
Time(h)
Yield(%)
1
2
3
4
5
6
7
Fig. 5 Correlation between recyclability of the catalyst with time and yield
six consecutive runs, without signifcant efect on the reaction times and product
yields; after that highest decrease was observed (Fig. 5).
Conclusion
A novel catalytic system has been synthesized via reaction of Cl-MCM-41 with
2-aminopyrazine, then in situ immobilization of CuOTf. The catalytic activity of
this catalyst was examined in allylic C–H bond oxidation of olefns by using difer-
ent synthesized perester for the frst time. The low amount of the catalyst, mild reac-
tion condition, a small ratio of alkene to perseter (2:0.85), shorter reaction times and
good yields of allylic esters were highlighted in this method compared to the most
previous reports.
Acknowledgements We are grateful to the University of Kurdistan Research Councils and the Iranian
National Science Foundation (Proposal No: 95838133) for the partial support of this work.
References
1. G. Chuah, X. Hu, P. Zhan, S. Jaenicke, J. Mol. Catal. A Chem. 181, 25 (2002)
2. T. Conesa, J. Hidalgo, R. Luque, J. Campelo, A. Romero, Appl. Catal. A Gen. 299, 224 (2006)
3. I. Dı́ az, C. Márquez-Alvarez, F. Mohino, J.N. Pérez-Pariente, E. Sastre, Microporous Mesoporous
Mater 44, 295 (2001)
4. I. Dı
́
az, F. Mohino, J.N. Pérez-Pariente, E. Sastre, Appl. Catal. A Gen. 205, 19 (2001)
5. T. Yanagisawa, K. Kuroda, C. Kato, React. Solid 5, 167 (1988)
6. Y.V.S. Rao, D.E. De Vos, P.A. Jacobs, Angew. Chem. Int. Ed. 36, 2661 (1997)
7. A. Cauvel, G. Renard, D. Brunel, J. Org. Chem. 62, 749 (1997)
8. S. Samadi, K. Jadidi, B. Khanmohammadi, N. Tavakoli, J. Catal. 340, 344 (2016)
9. J. Eames, M. Watkinson, Angew. Chem. Int. Ed. 40, 3567 (2001)
10. S. Samadi, A. Ashouri, M. Ghambarian, RSC Adv. 7, 19330 (2017)
11. R. Hayes, T.W. Wallace, Tetrahedron Lett. 31, 3355 (1990)
12. R.E. Claus, S.L. Schreiber, Org. Synth. 64, 150 (1986)
1 3

2‑Aminopyrazine‑functionalized MCM‑41 nanoporous silica…
13. J. Ficini, J. d’Angelo, Tetrahedron Lett. 17, 2441 (1976)
14. E. Alvarez, M.T. Diaz, R. Perez, J.L. Ravelo, A. Regueiro, J.A. Vera, D. Zurita, J.D. Martin, J. Org.
Chem. 59, 2848 (1994)
15. E. Corey, J. Lee, J. Am. Chem. Soc. 115, 8873 (1993)
16. M.B. Andrus, J.C. Lashley, Tetrahedron 58, 845 (2002)
17. M. Kharasch, G. Sosnovsky, N. Yang, J. Am. Chem. Soc. 81, 5819 (1959)
18. A.L. García-Cabeza, R. Marín-Barrios, F.J. Moreno-Dorado, M.J. Ortega, G.M. Massanet, F.M.
Guerra, Org. Lett. 16, 1598 (2014)
19. J.F. Hartwig, M.A. Larsen, ACS Cent. Sci. 2, 281 (2016)
20. E. Shi, Y. Shao, S. Chen, H. Hu, Z. Liu, J. Zhang, X. Wan, Org. Lett. 14, 3384 (2012)
21. B.L. Tran, M. Driess, J.F. Hartwig, J. Am. Chem. Soc. 136, 17292 (2014)
22. C.-Y. Wang, R.-J. Song, W.-T. Wei, J.-H. Fan, J.-H. Li, Chem. Commun. 51, 2361 (2015)
23. S. Sadjadi, S. Samadi, M. Samadi, Res. Chem. Intermed. 45, 2441 (2019)
24. M.B. Andrus, D. Asgari, Tetrahedron 56, 5775 (2000)
25. M.B. Andrus, B. Sekhar, J. Heterocycl. Chem. 38, 1265 (2001)
26. L. Faraji, S. Samadi, K. Jadidi, B. Notash, Bull. Korean Chem. Soc. 35, 1989 (2014)
27. S. Samadi, K. Jadidi, B. Notash, Tetrahedron: Asymmetry 24, 269 (2013)
28. S. Samadi, S. Nazari, H. Arvinnezhad, K. Jadidi, B. Notash, Tetrahedron 69, 6679 (2013)
29. N. Zhu, B. Qian, H. Xiong, H. Bao, Tetrahedron Lett. 58, 4125 (2017)
30. M.B. Andrus, Z. Zhou, J. Am. Chem. Soc. 124, 8806 (2002)
31. S. Samadi, K. Jadidi, M. Samadi, A. Ashouri, B. Notash, Tetrahedron 75, 862 (2019)
32. D. Kumar, K. Schumacher, C.D.F. von Hohenesche, M. Grün, K. Unger, Colloids Surf. A 187, 109
(2001)
33. M.B. Andrus, X. Chen, Tetrahedron 53, 16229 (1997)
34. A.L. Beckwith, A.A. Zavitsas, J. Am. Chem. Soc. 108, 8230 (1986)
35. J. Kochi, Tetrahedron 18, 483 (1962)
36. J. Kochi, R. Subramanian, J. Am. Chem. Soc. 87, 4855 (1965)
37. J.K. Kochi, J. Am. Chem. Soc. 84, 774 (1962)
38. J.K. Kochi, P.J. Krusic, J. Am. Chem. Soc. 90, 7157 (1968)
39. J.A. Mayoral, S. Rodríguez-Rodríguez, L. Salvatella, Chem. Eur. J. 14, 9274 (2008)
40. C. Walling, W. Thaler, J. Am. Chem. Soc. 83, 3877 (1961)
41. C. Walling, A.A. Zavitsas, J. Am. Chem. Soc. 85, 2084 (1963)
42. S.H. Bertz, S. Cope, M. Murphy, C.A. Ogle, B.J. Taylor, J. Am. Chem. Soc. 129, 7208 (2007)
43. A. Casitas, X. Ribas, Chem. Sci. 4, 2301 (2013)
Publisher’s Note Springer Nature remains neutral with regard to jurisdictional claims in published
maps and institutional afliations.
1 3