Generation and cross-coupling of benzyl and phthalimide-N-oxyl radicals in a cerium(IV) ammonium nitrate/N-hydroxyphthalimide/ArCH2R system

Article abstract of DOI:10.1016/j.tet.2012.10.018

A method was developed for the cross-dehydrogenative coupling of alkylarenes and related compounds with N-hydroxyphthalimide (NHPI) using cerium(IV) ammonium nitrate (CAN) to prepare O-substituted NHPI derivatives. The characteristic feature of the reaction is that NHPI plays a dual role. Thus, in the presence of CAN, NHPI generates the phthalimide-N-oxyl (PINO) radical, which abstracts a hydrogen atom from the benzyl position to form a C-centered radical. The target oxidative cross-coupling product is formed mainly through the recombination of PINO with the C-centered radical. Therefore, NHPI serves as a mediator for the radical process and a reagent for the radical cross-coupling. The target products were obtained in yields from 35 to 80%.

Full text of DOI:10.1016/j.tet.2012.10.018

Tetrahedron 68 (2012) 10263e10271
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Generation and cross-coupling of benzyl and phthalimide-N-oxyl radicals
in a cerium(IV) ammonium nitrate/N-hydroxyphthalimide/ArCH2R system
*
Alexander O. Terent’ev , Igor B. Krylov, Mikhail Y. Sharipov, Zoya M. Kazanskaya, Gennady I. Nikishin
N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Leninsky Prospekt 47, Moscow 119991, Russian Federation
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 12 June 2012
Received in revised form 19 September 2012
Accepted 5 October 2012
Available online 12 October 2012
A method was developed for the cross-dehydrogenative coupling of alkylarenes and related compounds
with N-hydroxyphthalimide (NHPI) using cerium(IV) ammonium nitrate (CAN) to prepare O-substituted
NHPI derivatives. The characteristic feature of the reaction is that NHPI plays a dual role. Thus, in the
presence of CAN, NHPI generates the phthalimide-N-oxyl (PINO) radical, which abstracts a hydrogen
atom from the benzyl position to form a C-centered radical. The target oxidative cross-coupling product
is formed mainly through the recombination of PINO with the C-centered radical. Therefore, NHPI serves
as a mediator for the radical process and a reagent for the radical cross-coupling. The target products
were obtained in yields from 35 to 80%.
Keywords:
N-Hydroxyphthalimide
Cerium(IV) ammonium nitrate
Alkylarenes
Ó 2012 Elsevier Ltd. All rights reserved.
Oxidation
Coupling
Free radicals
1. Introduction
alkenes,27,28 alkynes,31 ethers,25,27,34 alcohols,25,40,41 amides,42 and
alkanes32,36,43 thus generating radicals, which are transformed into
Radical reactions occupy an important place in both laboratory
synthesis1e3 and industrial processes (such as oxidation by oxygen,
halogenation, sulfochlorination, sulfoxidation, nitration, and poly-
merization).4,5 These reactions also play a significant role in oxi-
dation reactions in metabolism of living organisms.6,7
Radical oxidation reactions involving oxygen or its compounds
have gained wide acceptance. These reactions result in the addition
of one or several oxygen atoms to the starting molecule to give
alcohols and ketones,8e10 peroxides,11,12 or carboxylic acids.13
Cross-coupling reactions of C-centered and O-centered (bound
to an organic moiety) radicals accompanied by the formation of the
CeO bond have been less well-studied.14e18
target products.
NHPI can be considered as a promising mediator for industrial
radical processes, for example, for the production of hydro-
peroxides,44e47 alcohols,48,49 ketones,48,50,51 aldehydes,48 carbox-
ylic acids,49,52,53 and nitro derivatives49 from hydrocarbons and
compounds containing alkyl groups, as well as for the oxidation of
ethers54,55 and in more complex oxidation reactions involving CeC
cross-coupling.49,56 The Daicel Company has developed environ-
mentally friendly oxidation methods with the use of NHPI, for ex-
ample, for the oxidation of 3-picoline,57 p-xylene, and cyclohexane58
to nicotinic, terephthalic, and adipic acids, respectively.
The second key reagent used in the present study is the strong
one-electron oxidizer CAN (standard reduction potential of Ceþ4 is
þ1.61 V vs normal hydrogen electrode).59 This reactant is low-toxic,
convenient to handle, and hydrolytically stable. It is used for the
generation of radicals from tertiary alcohols,60 ketones,61 1,3-
dicarbonyl compounds,62e65 enol ethers,66 thiophenols,67 al-
kenes,68,69 and halide,70e74 thiocyanate,75,76 and azide anions.76e79
The thus synthesized radicals can add at double bonds to form new
CeC and C-heteroatom bonds, abstract a hydrogen atom from or-
ganic substrates, or participate in other transformations.
In the present study, we performed the cross-dehydrogenative
coupling of N-hydroxyphthalimide (NHPI) with alkylarenes and
related compounds using cerium(IV) ammonium nitrate (CAN,
(NH4)2Ce(NO3)6).
NHPI19e23 serves as an efficient mediator for reactions resulting in
the cleavage of CeH bonds to form CeO,24e31 CeN,32,33 CeC,34e36 C-
Hal,37,38 and CeS39 bonds. In the presence of oxidizing agents, NHPI is
transformed into the nitroxide radical (pthalimide N-oxyl, PINO) ca-
pable of abstracting a hydrogen atom from alkylarenes,24,25,27,30,32
In the presence of CAN, NHPI is oxidized to the PINO radical.80
The NHPIeCAN system was used for the oxidation of alcohols
* Corresponding author. E-mail address: terentev@ioc.ac.ru (A.O. Terent’ev).
containing an aryl substituent in the a position to form ketones
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.10.018

10264
A.O. Terent’ev et al. / Tetrahedron 68 (2012) 10263e10271
O
OH
CAN cat.
NHPI cat.
O2
MeCN,
reflux
(A)
O
HN
R1
NHPI cat.
O
R1CN, 80 o
(B)
C
N
1 eq. NHPI
O
+ CAN
solvent,
rt
O
ONO2
NHPI cat.
(D)
(E)
MeCN, rt
present study
(C)
O
Scheme 1. Use of CAN for transformations of alkylarenes.
(Scheme 1, A),41 for the amidation of alkanes and alkylarenes
(Scheme 1, B),33 and for the introduction of the nitrate group in the
benzyl position (Scheme 1, C).30
O-substituted hydroxylamines, which are employed as intermediates
in the synthesis of compounds having specific antagonistic,91 in-
hibitory,87,92 antiprotozoal,93,94 and fungicidal88e90 activity.
In the present study, we discovered the cross-dehydrogenative
coupling of alkylarenes and their derivatives with NHPI under the ac-
tion of CAN as oxidant giving O-substituted NHPI (Scheme 1, D). This
reaction was somewhat unexpected, because it is known that CAN
oxidizes alkylarenes to ketones and aldehydes in preparative yields
(Scheme 1, E),81 and the introduction of NHPI as an additional oxidation
mediator could lead to an increase in the yield of carbonyl compounds.
Recently, oxidative cross-coupling reactions with the use of
2. Results and discussion
Taking into account the growing field of application of O-
substituted NHPI derivatives and the practical importance of oxi-
dation reactions with the use of NHPI, we turned our attention to
the oxidative cross-coupling reactions of alkylarenes and their
derivatives 1aem with NHPI under the action of CAN giving
products 2aem (Scheme 2).
84
NHPI/CuCl/PhI(OAc)2,82 NHPI/NaIO4/SiO2,83 and NHPI/Pb(OAc)4
systems were proposed, which are similar to reaction D. The
drawbacks of the first reaction are that it requires high temperature
(70 ꢀC) and that it is necessary to separate phenyl iodide, which is
formed as a by-product from (diacetoxyiodo)benzene, to obtain the
target product. The second reaction is performed with the use of
the complex multicomponent heterogeneous system CH2Cl2/SiO2/
(H2OþNaIO4)/NHPI, whose properties substantially depend on the
ratio of the phases and the type of silica gel; cyclohexene and
cyclooctene were used for the cross-coupling (the yields of the
products were not reported). In the study,84 PINO was generated
from NHPI in the presence of Pb(OAc)4, and then it was used in the
reactions with arylmethanes, benzyl alcohols, and benzaldehydes;
the yields of oxidative cross-coupling products were not reported.
The related oxidative cross-coupling of primary alcohols and
aldehydes with N-hydroxysuccinimide (analogue of NHPI) affords
N-hydroxysuccinimide esters. The oxidant in the reaction is 2-
iodoxybenzoic acid (IBX). The authors proposed the reaction
mechanism without the participation of the nitroxide radical.85
O-Substituted NHPI derivatives can also be prepared by the
nucleophilic substitution reaction between the NHPI anion and
halide86e90 or by the Mitsunobu reaction of NHPI with alcohols.91,92
The method developed in the present study is based on the
oxidative cross-coupling with the use of more readily available
starting reactants compared to halides and alcohols, whose syn-
thesis requires additional halogenation or oxidation of alkylarenes.
In addition, the nucleophilic substitution of halogens is accompa-
nied by elimination side reactions.
To optimize the reaction conditions, we investigated the cross-
coupling of NHPI with toluene 1a to elucidate the influence of the
nature of the solvent, the reagent ratio, the temperature, and the
synthesis procedure on the yield of the target product 2a (Table 1).
The solvents used in this study can be divided into the following
two groups: low-polarity solvents, such as CH2Cl2, CHCl3, CCl4,
benzene, and hexane, which form two-phase systems with water,
and polar, water-miscible solvents, such as acetone, DMSO, MeCN,
CH3COOH, CF3COOH, and MeOH; EtOAc occupies an intermediate
place. The solvents belonging to the first group weakly dissolve
CAN and NHPI; however, despite low solubility of NHPI, the target
product 2a was obtained in runs 1e8 in yields from 50 to 69%. A
much lower yield of 2a was observed in the experiments with CCl4
(run 9, 34%) and hexane (run 10, 6%). The characteristic feature of
the solvents belonging to the first group is that CAN is present in
the aqueous phase, whereas toluene, product 2a, and, apparently,
the intermediate benzyl radical, are in the organic phase.
The results of the synthesis in EtOAc (run 11), which is moder-
ately miscible with the aqueous phase, are similar to those of runs
1e8.
In acetone, DMSO, MeCN, CH3COOH, CF3COOH, and MeOH (runs
12e27), which are unlimitedly miscible with water, the reaction
mixture is a single phase or consists of two liquid phases with
closer compositions than in the case of low-polarity solvents. In
runs 12e25, product 2a was obtained in a yield from 35% to 80%.
The strong acid CF3COOH, (run 26) and easily oxidizable MeOH (run
27) are inefficient solvents.
O-Substituted NHPI derivatives are used in medicinal chemistry.
The treatment of these compounds with hydrazine affords
In runs 4, 5, 15, 16, 18, and 25, the influence of the change in the
reagent ratio 1a:NHPI:CAN compared to the stoichiometric ratio of

A.O. Terent’ev et al. / Tetrahedron 68 (2012) 10263e10271
10265
R''
i
R
R
R'
R'
2a-k
1a-k
t
a
b
c
d
: R = H, R' = H; : R = H, R' = 4-Bu ; : R = H, R' = 2-Me; : R = H, R' = 4-Me;
e
f
g
h
: R = H, R' = 4-OMe; : R = H, R' = 4-Ac; : R = H, R' = 4-COOEt; : R = H, R' = 4-Br;
i: R = Me, R' = H; j: R = COEt, R' = H; k: R = CH2COOEt, R' = H
OEt
OEt
R''
R''
O
O
i
i
1l
2l
1m
2m
O
R'' =
i: CAN aq., NHPI, solvent, 20-25 °C
N
O
O
Scheme 2. Synthesis of O-substituted NHPI derivatives 2aem by oxidative cross-coupling of NHPI with alkylarenes and related compounds 1aem.
1:1:2 was investigated. A 5e10 fold excess of 1a results in an in-
crease in the yield of 2a by 10e15%. An increase in the amount of
NHPI to a twofold excess (run 18 vs run 16) has almost no effect on
the yield. An increase in the excess of CAN in run 15 compared to
run 12 leads to a decrease in the yield of 2a due, apparently, to
oxidation side reactions.
Compared to runs 1 and 12, the time of the addition of a CAN
solution to the reaction mixture in runs 2 and 13, was reduced from
10 min to 15 s. The synthesis in CH2Cl2 (run 2 vs run 1) gave
a similar result, whereas the synthesis in acetone (run 13 vs run 12)
afforded the target product in lower yield and produced benzyl
nitrate (5% yield). Apparently, benzyl nitrate is formed as a result of
the reaction of the benzyl radical with CAN, which has no time to be
consumed in the oxidation of NHPI.30
In runs 19 and 20, the first step involved the generation of PINO
from NHPI and CAN followed by the addition of the toluene after 1.5
(run 19) or 7 (run 20) min. In both cases, the results were similar to
those obtained according to the standard procedure (run 18). This
fact is indicative of high stability of PINO in the reaction system.
The yield of the target product in runs 3 and 14 performed in air
differs only slightly from that obtained under argon (runs 1 and 13,
respectively). Nevertheless, the syntheses were performed under ar-
gon to exclude anyoxidationwith atmospheric oxygen as side reaction.
Taking into account the optimized reaction conditions of runs 4,
5, and 16, we synthesized O-substituted NHPI derivatives 2aem.
Most of experiments were performed in acetone (Table 2).
Based on the results presented in Table 2, it can be concluded
that the above-described method for the synthesis of cross-
coupling products 2aem enables the use of alkylarenes and their
derivatives 1aem of substantially different nature as the starting
reagents. Compounds 2aem were synthesized in yields from 35 to
37% (runs 9 and 11) to 70e80% (runs 1, 3, 6, and 7) from toluene or
substituted methylarenes ArCH3 containing both electron-donating
and electron-withdrawing substituents in the arene moiety. Steri-
cally more hindered ArCH2R can also be involved in cross-coupling
reaction (runs 9e13).
Table 1
Influence of the nature of the solvent, the reagent ratio (toluene 1a:NHPI:CAN), and
the reaction conditions on the yield of N-benzyloxyphthalimide 2aa
Run
Solvent
Molar ratio 1a:NHPI:CAN
Yield of 2a, %
1
2
3
4
5
6
7
8
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CHCl3
1:1:2
1:1:2
1:1:2
5:1:2
10:1:2
1:1:2
1:1:2
1:1:2
1:1:2
1:1:2
1:1:2
1:1:2
1:1:2
1:1:2
1:1:3
5:1:2
5:1:2
5:2:2
5:2:2
5:2:2
5:1:2
1:1:2
1:1:2
1:1:2
5:1:2
1:1:2
1:1:2
63
62b
59c
65
69
59
Benzene
Benzene
CCl4
Hexane
EtOAc
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
Acetone
DMSO
56
50d
34
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
6
56
64
55b,e
63c
34
80
77d
78
77f
77g
62e,f
35
MeCN
35
70
80
9
CH3COOH
CH3COOH
CF3COOH
CH3OH
13
a
General reaction conditions:
a
mixture of toluene 1a (0.15e1.50 g,
1.63e16.3 mmol), N-hydroxyphthalimide (266e532 mg, 1.63e3.26 mmol), and
a solvent (5 mL) was purged with argon. Then a solution of CAN (1.79e2.68 g,
3.26e4.89 mmol) in water (3 mL) was added with vigorous stirring under argon for
10 min, and the reaction mixture was stirred at 20e25 ꢀC for 30 min.
b
A solution of CAN was added for 15 s.
The experiment was performed without argon.
The reaction temperature was 50 ꢀC.
Approximately 5% of benzyl nitrate was formed as a by-product.
A suspension of NHPI (532 mg or 266 mg; 1 or 0.5 mol per mole of CAN) in acetone
c
d
e
f
(4 mL) was purged with argon. Then a solution of CAN (1.79 g, 3.26 mmol) in water
(3 mL)wasaddedwith vigorousstirring for30 s, andafter1.5 mina solutionof toluene
(751 mg, 8.16 mmol, 2.5 mol per mole of CAN) in acetone (3 mL) was added for 30 s.
According to the results of the optimization of reaction condi-
tions, the presence of an excess of arene 1a facilitates an increase in
the yield of oxidative cross-coupling product 2a (Table 1). The
g
The experiment was performed as described in the note f, but a toluene solution
was added 7 min after the addition of CAN.

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A.O. Terent’ev et al. / Tetrahedron 68 (2012) 10263e10271
Table 2
Synthesis of O-substituted derivatives of N-hydroxyphthalimide 2aema
Run
Substituted arene 1aem
Cross-coupling product 2aem
Molar ratio 1aem/NHPI
Yield of 2aem, %
1
5
80
78b
1a
2a
2
3
10
10
52
70
63
1b
2b
3
1c
2c
4
1d
2d
5
5
5
39
56c
1e
2e
6
7
8
3
3
3
75
76
53
1f
2f
1g
2g
1h
2h

A.O. Terent’ev et al. / Tetrahedron 68 (2012) 10263e10271
Cross-coupling product 2aem
10267
Table 2 (continued )
Run Substituted arene 1aem
Molar ratio 1aem/NHPI
Yield of 2aem, %
9
3
35
1i
2i
10
3
65
1j
2j
11
3
37
1k
2k
12
13
3
3
50
51
1l
2l
1m
2m
a
General reaction conditions: a mixture of NHPI (266 mg, 1.63 mmol), arene 1aem (0.52e1.73 g, 3e10 mol per mole of NHPI), and acetone (5 mL) was purged with argon for
5 min, and then a solution of CAN (1.79 g, 3.26 mmol) in water (3 mL) was added with vigorous stirring for 10 min. Then the reaction mixture was stirred at 20e25 ꢀC for 30 min.
b
The synthesis was scaled up with an increase in the amounts of the reagents by a factor of 10.
CH2Cl2 as the solvent.
c

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A.O. Terent’ev et al. / Tetrahedron 68 (2012) 10263e10271
synthesis of 2aem (Table 2) was performed with the use of a 3e10-
fold excess of 1aem, the excess being limited by the problems with
the separation of the target products 2aem from unconsumed
1aem.
4. Experimental section
4.1. General
Taking into account the data published in the literature,23,30,33,80
two pathways for the formation of oxidative cross-coupling prod-
ucts 2 may be proposed (A and B, Scheme 3).
The NMR spectra were recorded on a Bruker AM-300
(300.13 MHz for 1H and 75.48 MHz for 13C) spectrometer in
CDCl3. IR spectra were recorded on a Bruker ALPHA FT-IR spec-
Scheme 3. Proposed mechanism of the reaction of alkylarenes 1aem with the NHPIeCAN system.
Initially, the reaction of AreCH2eR with PINO, which is gener-
ated from NHPI in the presence of CAN, results in formation of a C-
centered radical Are(CHꢁ)eR. The latter either recombines with the
PINO radical (pathway A) or is oxidized by CAN to the Are(CHþ)eR
cation, which reacts with NHPI (pathway B). The pathway A seems
to be the major one. This is supported by the following facts. First, in
runs 19 and 20 (Table 1), where PINO is generated and CAN is
completely consumed before the addition of the toluene (in this
case, the Are(CHþ)eR cation is not formed), the target cross-
coupling product 2a is formed in good yield.
trometer. The melting points were determined on a Kofler hot stage
and are uncorrected. Column chromatography was performed with
the use of SiO2 (0.060e0.200 mm, 60 A, Acros).
Toluene, 4-tert-butyltoluene, o-xylene, p-xylene, p-methylanisole,
40-methylacetophenone, ethyl 4-methylbenzoate, 4-bromotoluene,
etylbenzene, 1-phenyl-2-butanone, fluorene, N-hydroxyphthalimide,
and cerium(IV)ammonium nitrate were commercialreagents (Acros).
Hydrocinnamic acid and 1-naphthylacetic acid ethyl esters
were synthesized by esterification of hydrocinnamic acid and
1-naphthylacetic acid with ethanol.
Second, the reactions in a solution in acetic acid (runs 24 and 25)
do not give benzyl acetate, which is the expected product in the
case of generation of AreCHþ2 in the reaction mixture. In these re-
actions only 2a was isolated as the reaction product.
CH2Cl2, CHCl3, CCl4, benzene, hexane, ethyl acetate, acetone, di-
methyl sulfoxide, MeCN, acetic acid, trifluoroacetic acid, and meth-
anol of high purity grade were used as is from commercial sources.
The pathway A is additionally supported by the results of the
special experiment, in which benzyl alcohol (a source of AreCH2þ
cations), NHPI, acetic acid, water, and hydrochloric acid were mixed
(conditions similar to those used in runs 24 and 25 in Table 1). The
resulting suspension was stirred at room temperature for 7 h. In
this experiment, we isolated the starting benzyl alcohol (45%) and
benzyl acetate (24%) as the reaction product of AreCHþ2 and AcOH,
whereas product 2a was not detected. Hence, it can be concluded
that NHPI shows low reactivity toward AreCHþ2 in this system.
4.2. Experiment to Table 1 (runs 1e18, 22e27)
Toluene 1a (0.15e1.50 g, 1.63e16.3 mmol), N-hydroxyph-
thalimide (266e532 mg, 1.63e3.26 mmol), and the solvent (5 mL)
were mixed, and the mixture was purged with argon for 5 min
(except for runs 3 and 14, which were performed in air). Then
a solution of CAN (1.79e2.68 g, 3.26e4.89 mmol) in water (3 mL)
was added with vigorous stirring under argon for 10 min (except
for runs 2 and 13, where a CAN solution was added for 15 s), after
which the mixture turned dark red. The reaction mixture was
stirred at 20e25 ꢀC for 30 min (the mixture turned colorless within
7e15 min, except for runs 9 and 10). Then water (20 mL) was added
to the reaction mixture. The extraction was performed with CHCl3
(2ꢂ10 mL), and the combined organic extracts were successively
washed with a saturated aqueous NaHCO3 solution (10 mL) and
water (20 mL). The mixture was dried over MgSO4, and the solvent
was removed using a water-jet vacuum pump. The yield of 2a was
determined by 1H NMR spectroscopy based on the comparison of
3. Conclusion
A method was developed for the synthesis of O-substituted
NHPI derivatives by the oxidative cross-coupling of alkylarenes and
related compounds with NHPI under action of CAN. The successful
synthesis of cross-coupling products was a priori unlikely due to
the simultaneous presence of reactive species of different nature in
the reaction mixture, several competitive reactions, and the pos-
sible formation of carbonyl compounds as products of further ox-
idation. The experimental data suggest that the preferred
mechanism involves the generation of PINO radicals from NHPI and
CAN followed by the abstraction of a hydrogen atom from the
benzyl position of alkylarene by these radicals to form C-centered
radicals. The cross-coupling product is formed through the re-
combination of PINO with a C-centered radical. The synthesis
proceeds under mild conditions at room temperature with the use
of readily available reagents. The target products were prepared in
yields from 35 to 80%. The procedure is scalable to gram amounts.
the intensity of the characteristic signal of 2a at
d 5.22 (CH2) and the
signal of dioxane (as the reference) at 3.75 (CH2).
d
In runs 13 (12.0 mg, 0.078 mmol) and 21 (13.1 mg, 0.087 mmol)
benzyl nitrate was isolated by column chromatography on SiO2
using CH2Cl2 as the eluent.
4.3. Experiment to Table 1 (runs 19e21)
A suspension of NHPI (266e532 mg, 0.5 or 1 mol per mole of
CAN, 1.63e3.26 mmol) in acetone (4 mL) was purged with argon for

A.O. Terent’ev et al. / Tetrahedron 68 (2012) 10263e10271
10269
5 min. Then a solution of CAN (1.79 g, 3.26 mmol) in water (3 mL)
was added with vigorous stirring for 30 s. After 1.5 min in runs 19
and 21 and after 7 min in run 20, a solution of toluene (751 mg,
8.16 mmol, 2.5 mol per mole of CAN) in acetone (3 mL) was added
during 30 s. The reaction mixture was stirred at 20e25 ꢀC for
30 min. The isolation of the products and the estimation of the
yields were performed as described above.
CDCl3) 2.34 (s, 3H, CH3), 5.17 (s, 2H, CH2ON), 7.18 (d, J¼8.07 Hz,
2H, ArH), 7.42 (d, J, 2H, ArH), 7.64e7.86 (m, 4H, ArH); dC
(75.47 MHz, CDCl3) 21.4, 79.8, 123.6, 129.0, 129.3, 130.1, 130.9,
134.5, 139.4, 163.6.
4.6.5. N-(4-Methoxybenzyloxy)phthalimide (2e).86,87 White crys-
tals; mp¼135e136 ꢀC (lit.87 mp 109e122 ꢀC); dH (300.13 MHz,
CDCl3) 3.79 (s, 3H, CH3), 5.14 (s, 2H, CH2) 6.88 (m, 2H, ArH), 7.44 (m,
2H, ArH), 7.68e7.84 (m, 4H, ArH); dC (75.47 MHz, CDCl3) 55.3
(OCH3), 79.6 (CH2) 114.0, 123.5, 126.0, 129.0, 131.7, 134.5 (Ar), 160.5
(COMe), 163.6 (C]O).
4.4. Experiment to Table 2 (runs 1e13)
A
mixture of NHPI (266 mg, 1.63 mmol), arene 1aem
(0.52e1.73 g, 3e10 mol per mole of NHPI), and acetone or CH2Cl2
(5 mL) (run 5) was purged with argon for 5 min. Then a solution of
CAN (1.79 g, 3.26 mmol) in water (3 mL) was added with vigorous
stirring for 10 min. The reaction mixture was stirred at 20e25 ꢀC for
30 min. Then water (20 mL) was added to the reaction mixture, the
mixture was extracted with CHCl3 (2ꢂ10 mL), and the combined
organic extracts were successively washed with a saturated aque-
ous NaHCO3 solution (10 mL) and water (20 mL). The mixture was
dried over MgSO4, and the solvent was removed using a water-jet
vacuum pump. Products 2aem were isolated by column chroma-
tography on SiO2 using CH2Cl2/EtOAc as the eluent with an in-
creasing gradient of the latter from 0 to 20%.
4.6.6. N-(4-Acetylbenzyloxy)phthalimide
(2f). White
crystals;
Mp¼148e149 ꢀC; [found: C, 69.01; H, 4.57; N, 4.69. C17H13NO4 re-
quires: C, 69.15; H, 4.44; N, 4.74%]; nmax (KBr) 1723, 1688, 1675,
1390, 1357, 1263, 1184, 1126, 966, 875, 822, 701 cmꢃ1
; dH
(300.13 MHz, CDCl3) 2.61 (s, 3H, CH3), 5.27 (s, 2H, CH2O), 7.61e7.69
(m, 2H, ArH), 7.68e7.88 (m, 4H, ArH), 7.92e8.02 (m, 2H, ArH); dC
(75.47 MHz, CDCl3) 26.8 (CH3), 79.1 (CH2O), 123.7, 128.7, 129.0,
129.8, 134.7, 137.8, 138.9, 163.5, 197.7 (C]O).
4.6.7. N-(4-Carbethoxybenzyloxy)phthalimide (2g). White crystals;
mp¼151e152 ꢀC; [found: C, 66.48; H, 4.89; N, 4.29. C18H15NO5 re-
quires: C, 66.46; H, 4.65; N, 4.31%]; nmax (KBr) 1738, 1726, 1393,
The experiment on the synthesis of 2a was performed also with
the amounts of the reagents increased tenfold.
1275, 1186, 1140, 1101, 974, 761, 699 cmꢃ1
; dH (300.13 MHz, CDCl3)
1.39 (t, J1¼7.33 Hz, 3H, CH3), 4.38 (q, J1, 2H, CH2), 5.26 (s, 2H,
CH2ON), 7.61 (d, J2¼8.07 Hz, 2H, ArH), 7.68e7.87 (m, 4H, ArH), 8.06
(d, J2, 2H, ArH); dC (75.47 MHz, CDCl3) 14.4, 61.2, 79.2, 123.7, 128.9,
129.5, 129.9, 131.4, 134.6, 138.6, 163.5, 166.3.
4.5. Additional experiment on the determination of the pre-
ferred mechanism of the formation of 2a
Benzyl alcohol (176 mg, 1.63 mmol), NHPI (266 mg, 1.63 mmol),
acetic acid (5 mL), water (3 mL), and 34% aqueous HCl (175 mg,
1.63 mmol) were mixed. The resulting suspension was stirred at
room temperature for 7 h. The products were isolated as described
in the experiment to Table 2 using CH2Cl2 as the eluent for column
chromatography. Benzyl alcohol (79 mg, 0.73 mmol, 45%) and
benzyl acetate (59 mg, 0.39 mmol, 24%) were obtained.
4.6.8. N-(4-Bromobenzyl)phthalimide
(2h).88 White
crystals;
mp¼133e136 ꢀC (lit.88 mp¼143e145 ꢀC); dH (300.13 MHz, CDCl3)
5.15 (s, 2H, CH2), 7.36e7.45 (m, 2H, ArH), 7.46e7.54 (m, 2H, ArH),
7.65e7.83 (m, 4H, ArH); dC (75.47 MHz, CDCl3) 79.1 (CH2), 123.6,
123.7, 128.9, 131.5, 131.8, 132.9, 134.6 (Ar), 163.5 (C]O).
4.6.9. N-(1-Phenylethoxy)phthalimide
(2i).82 White
crystals;
4.6. Analytical data for obtained compounds
mp¼93e95 ꢀC (lit.82 mp¼93e95 ꢀC) dH (300.13 MHz, CDCl3) 1.73
(d, J1¼6.5 Hz, 3H, CH3), 5.51 (q, J1, 1H, CHO), 7.34 (m, 3H, ArH), 7.52
(d, J2¼7.9 Hz, 2H, ArH), 7.62e7.81 (m, 4H, ArH); dC (75.47 MHz,
CDCl3) 20.6 (CH3), 85.3 (CHO), 123.5, 127.8, 128.5, 129.0, 129.1, 134.4,
139.2, 163.9 (Ar).
4.6.1. N-Benzyloxyphthalimide
(2a).82 White
crystals;
mp¼144e146 ꢀC (lit.82 mp 143e146 ꢀC); dH (300.13 MHz, CDCl3)
5.22 (s, 2H, CH2), 7.33e7.44 (m, 3H, ArH), 7.49e7.59 (m, 2H, ArH),
7.68e7.85 (m, 4H, ArH); dC (75.47 MHz, CDCl3) 79.9 (CH2), 123.5,
128.6, 129.0, 129.4, 129.9, 133.8, 134.5 (Ar), 163.5 (C]O).
4.6.10. 1-Phenyl-1-(phthalimide-N-oxy)-butane-2-one (2j). White
crystals; Mp¼113e114 ꢀC; [found: C, 69.97; H, 5.06; N, 4.61.
C18H15NO4 requires: C, 69.89; H, 4.89; N, 4.53%]; nmax (KBr) 1794,
4.6.2. N-(4-tert-Butylbenzyloxy)phthalimide (2b).95 White crystals;
mp¼107e107.5 ꢀC; [found: C, 73.98; H, 6.03; N, 4.39. C19H19NO3
requires: C, 73.77; H, 6.19; N, 4.53%]; nmax (KBr) 1725, 1387, 1185,
1729, 1355, 1187, 1127, 1114, 984, 972, 876, 702 cmꢃ1
; dH
(300.13 MHz, CDCl3) 1.07 (t, J¼7.33 Hz, 3H), 2.55e2.74 (m, 1H, CH2),
2.75e2.94 (m, 1H, CH2), 5.79 (s, 1H, CHON), 7.32e7.46 (m, 3H, ArH),
7.46e7.60 (m, 2H, ArH), 7.66e7.86 (m, 4H, ArH); dC (75.47 MHz,
CDCl3) 7.4 (CH3), 32.1 (CH2), 92.0 (CHON), 123.7, 128.3, 128.8, 128.9,
129.8, 133.1, 134.7 (Ar), 163.3, 205.4 (C]O).
1133, 1122, 969, 875, 818, 711, 702, 516 cmꢃ1
; dH (300.13 MHz,
CDCl3) 1.32 (s, 9H, 3CH3), 5.19 (s, 2H, CH2), 7.42 (m, 2H, ArH), 7.49
(m, 2H, ArH), 7.71e7.87 (m, 4H, ArH); dC (75.47 MHz, CDCl3) 31.4
(CH3), 34.8 (C(CH3)3) 79.9 (CH2), 123.6, 125.6, 129.1, 129.8, 130.8,
134.5, 152.6 (Ar), 163.6 (C]O).
4.6.11. Ethyl 3-phenyl-3-(phthalimide-N-oxy)-propanoate (2k). White
crystals; mp¼66e68 ꢀC; [found: C, 67.14; H, 4.99; N, 4.03. C19H17NO5
requires: C, 67.25; H, 5.05; N, 4.13%]; nmax (CHCl3) 1792, 1741, 1373,
4.6.3. N-((2-Methylphenyl)methoxy)phthalimide
(2c).91 White
crystals; Mp¼132.5e133.5 ꢀC; [found: C, 71.87; H, 4.92; N, 5.19.
C16H13NO3 requires: C, 71.90; H, 4.90; N, 5.24%]; nmax (KBr) 1788,
1225, 1207, 1188, 976, 878, 702 cmꢃ1
; dH (300.13 MHz, CDCl3) 1.19 (m,
1726, 1375, 1364, 1185, 1130, 978, 875, 780, 703 cmꢃ1
;
dH
3H, CH3), 2.96 (dd, J1¼16.1 Hz, J2¼6.6 Hz, 1H, CH2), 3.28 (dd, J1,
J3¼7.3 Hz, 1H, CH2), 4.09 (m, 2H, CH2O), 5.81 (m, 1H, CHON),
7.29e7.40 (m, 3H, ArH), 7.49e7.57 (m, 2H, ArH), 7.65e7.79 (m, 4H,
ArH); dC (75.47 MHz, CDCl3) 14.2 (CH3), 40.4 (CH2), 61.0 (CH2O), 85.2
(CHON), 123.5,128.2,128.6,128.9,129.5,134.5, 136.8 (Ar), 163.6, 169.7
(C]O).
(300.13 MHz, CDCl3) 2.61 (s, 3H, CH3), 5.25 (s, 2H, CH2O), 7.13e7.21
(m, 1H, ArH), 7.22e7.32 (m, 2H, ArH), 7.34e7.42 (m, 1H, ArH),
7.68e7.88 (m, 4H, ArH); dC (75.47 MHz, CDCl3) 19.1 (CH3), 78.2
(CH2O), 123.5, 126.0, 129.1, 129.9, 130.7, 131.4, 131.9, 134.5, 139.2,
163.6 (C]O).
4.6.4. N-((4-Methylphenyl)methoxy)phthalimide
(2d).82 White
4.6.12. Ethyl 2-(1-naphthyl)-2-(phthalimide-N-oxy)-ethanoate (2l). Sli-
ghtly yellow crystals; mp¼125e126 ꢀC; [found: C, 70.17; H, 4.52; N,
crystals, mp¼141.5 ꢀC (lit.82 mp 134e136); dH (300.13 MHz,

10270
A.O. Terent’ev et al. / Tetrahedron 68 (2012) 10263e10271
24. Yoshino, Y.; Hayashi, Y.; Iwahama, T.; Sakaguchi, S.; Ishii, Y. J. Org. Chem. 1997,
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3.83. C22H17NO5 requires: C, 70.39; H, 4.56; N, 3.73%]; nmax (KBr) 1795,
1755, 1735, 1368, 1337, 1187, 1031, 960, 874, 801, 780, 697 cmꢃ1
dH
;
25. Einhorn, C.; Einhorn, J.; Marcadal, C.; Pierre, J.-L. Chem. Commun. 1997, 447e448.
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(300.13 MHz, CDCl3) 1.19 (m, 3H, CH3), 4.16e4.32 (m, 2H, CH2O), 6.67
(s, 1H, CHON), 7.44e7.96 (m,10H, ArH), 8.50 (d, J¼8.81 Hz,1H, ArH); dC
(75.47 MHz, CDCl3) 14.0 (CH3), 62.0 (CH2O), 83.1 (CHON), 123.7, 123.9,
125.2, 126.2, 127.2, 128.1, 128.8, 128.9, 130.8, 131.7, 133.9, 134.3, 134.6
(Ar), 163.3, 168.4 (C]O).
4.6.13. N-(9H-Fluorene-9-yloxy)phthalimide (2m).82 White crys-
tals; mp¼189e190 ꢀC (lit.82 mp¼189e191 ꢀC); dH (300.13 MHz,
CDCl3) 6.12 (s, 1H, CHO), 7.32 (t, J¼7.0 Hz, 2H, ArH), 7.41 (t, J¼7.1 Hz,
2H, ArH), 7.61 (d, J¼7.5 Hz, 2H, ArH), 7.73 (m, 2H, ArH), 7.82 (m, 4H,
ArH); dC (75.47 MHz, CDCl3) 88.5, 120.0, 123.7, 127.1, 127.9, 129.0,
130.2, 134.6, 140.1, 141.3, 164.0.
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4.6.14. Benzylnitrate.96 Colorless oil; dH (300.13 MHz, CDCl3) 5.45
(s, 2H, CH2), 7.43 (m, 5H, ArH); dC (75.47 MHz, CDCl3) 75.0 (CH2),
129.0, 129.2, 129.6, 132.4 (Ar).
4.6.15. Benzyl alcohol. Colorless oil; dH (300.13 MHz, CDCl3) 2.66
(brs, 1H, OH), 4.63 (s, 2H, CH2), 7.36 (m, 5H, ArH); dC (75.47 MHz,
CDCl3) 65.1 (CH2), 127.0, 127.6, 128.5, 140.9 (Ar).
43. Ishii, Y.; Iwahama, T.; Sakaguchi, S.; Nakayama, K.; Nishiyama, Y. J. Org. Chem.
1996, 61, 4520e4526.
44. Kuhnle, A.; Duda, M.; Jost, C.; Fries, G.; Kirchhoff, J.; Schiffer, T.; Sheldon, R. A.;
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4.6.16. Benzyl acetate.97 Colorless oil; dH (300.13 MHz, CDCl3) 2.11
(s, 3H, CH3), 5.12 (s, 2H, CH2), 7.37 (m, 5H, ArH); dC (75.47 MHz,
CDCl3) 21.1 (CH3), 66.4 (CH2), 128.4, 128.7, 136.1, 171.0 (C]O).
47. Kuhnle, A.; Duda, M.; Tanger, U.; Sheldon, R. A.; Manickam, S.; Arends, I. W. C. E.
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Acknowledgements
49. Ishii, Y.; Nakano, T.; Hirai, N. U.S. Reissued Patent RE39744 E, 2007.
50. Marhold, A.; Joschek, J. P. U.S. Patent 7,148,384 B2, 2006.
51. Ishii, Y.; Nakano, T. U.S. Patent 6,232,258 B1, 2001.
52. Hirai, N.; Terada, M. U.S. Patent 7,524,986 B2, 2009.
53. Ishii, Y.; Nakano, T. U.S. Patent 6,020,522, 2000.
This work is supported by the Grant of the Russian Foundation
for Basic Research (Grant 12-03-31876) and by the Program for
Basic Research of the Presidium of the Russian Academy of Sciences
and the Ministry of Education and Science of the Russian Federation
(Grant 8651).
54. Ishii, Y.; Nakano, T. U.S. Patent 6,037,477, 2000.
55. Hanselmann, P.; Hildbrand, S. U.S. Patent 6700010 B1, 2004.
56. Ishii, Y.; Iwahama, T.; Nakano, T. U.S. Patent 7,183,423 B1, 2007.
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Supplementary data
59. Nair, V.; Deepthi, A. Chem. Rev. 2007, 107, 1862e1891.
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The supplementary data containing NMR spectra of the reaction
products is available on http://www.sciencedirect.com. Supple-
mentary data related to this article can be found online at http://
dx.doi.org/10.1016/j.tet.2012.10.018.
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