Synthesis of Hypervalent Iodine(III) Reagents Containing a Transferable (Diarylmethylene)amino Group and Their Use in the Oxidative Amination of Silyl Ketene Acetals

Article abstract of DOI:10.1002/anie.201904971

The preparation of some hypervalent iodine reagents containing a transferable amino group derived from benzophenone imine derivatives is reported. The reagents can be readily prepared and stored as a bench-stable solid, and were successfully used in the transition-metal-free oxidative amination of silyl ketene acetals to afford the corresponding α-amino esters, the benzophenone imine moieties of which could be easily hydrolyzed, thereby leading to the formation of primary amines.

Full text of DOI:10.1002/anie.201904971

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Accepted Article
Title: Synthesis of Hypervalent Iodine(III) Reagents Containing a
Transferable (Diarylmethylene)amino Group and Their Use in the
Oxidative Amination of Silyl Ketene Acetals
Authors: Kensuke Kiyokawa, Daichi Okumatsu, and Satoshi Minakata
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201904971
Angew. Chem. 10.1002/ange.201904971
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10.1002/anie.201904971
Angewandte Chemie International Edition
COMMUNICATION
Synthesis of Hypervalent Iodine(III) Reagents Containing a
Transferable (Diarylmethylene)amino Group and Their Use in the
Oxidative Amination of Silyl Ketene Acetals
Kensuke Kiyokawa,* Daichi Okumatsu, and Satoshi Minakata*
Abstract: The preparation of some hypervalent iodine reagents
containing a transferable amino group derived from benzophenone
O
imine derivatives are reported. The reagents could be readily
prepared, stored as a bench-stable solid, and were successfully
used in the transition-metal-free oxidative amination of silyl ketene
acetals to afford the corresponding α-amino esters, whose
benzophenone imine moieties could be easily hydrolyzed, leading to
the formation of primary amines.
R1
TsN
I
Ts2N
I
X
N3
I
X
PhthN
I
X
S
N
I
X
R2
I
II
III
IV
V
Figure 1. Representative examples of hypervalent iodine reagents that
contain transferable nitrogen functional groups.
Oxidative amination is one of the most attractive
transformations to access various types of nitrogen containing
compounds, which are promising building blocks that can be
used to prepare biologically active and medicinally important
compounds. Hypervalent iodine reagents have emerged as a
powerful tool in oxidative transformations,[1,2] and in the past
decades, several examples of reagents containing transferable
nitrogen functional groups such as imino (I),[3] bissulfonimido
(II),[4,5] azido (III),[6] phthalimido (IV),[7,8] and sulfoximido (V)[9]
groups have been developed for use in some unique oxidative
amination reactions. However, despite recent advances, there
continue to be problems associated with preparing amines
utilizing those reagents. Indeed, although iminoiodane I and
bisimidoiodane II are extensively used in the oxidative amination
of unsaturated hydrocarbons and C–H bond amination,[3,4] it is
frequently difficult to deprotect the amino group in the products,
thus hampering the synthesis of primary amines and further
elaboration of the amine products. Azidoiodane III has recently
been recognized as a useful reagent for preparing organic
azides in an oxidative manner.[6] Neverthless, it is well known
that azides are hazardous substances and the fact that a
laborious reduction process is needed is a disadvantage in
amine synthesis. Synthetic application of IV in oxidative
amination has remained limited even though a phthaloyl group
can be easily removed to provide a primary amine.[7] Thus, the
development of a new method that enables the introduction of a
readily modifiable nitrogen-containing functional group into an
organic molecule utilizing hypervalent iodine reagents continues
to be a challenging task.[10]
Benzophenone imine has been used as an aminating
reagent in transition-metal catalyzed amination[11] and catalytic
C–H amination,[12] and the resulting aminated products can be
easily hydrolyzed to give primary amines. In addition, N-stannyl
benzophenone imine has been applied to a radical alkylation
reaction.[13] Meanwhile, benzophenone imine-derived oxime
derivatives function as an electrophilic aminating reagent, which
enables the amination of alkynyl copper reagents,[14a] Grignard
reagents,[14b] and organoboron compounds with
a copper
catalyst.[14c] In this context, we hypothesized that hypervalent
iodine reagents combined with benzophenone imine would offer
a promising tool for oxidative amination to deliver modifiable
amine products. Herein, we report on the development of some
hypervalent iodine reagents that contain a benzophenone imine-
derived nitrogen functional group and their use in the oxidative
amination of silyl ketene acetals to provide α-amino acid
derivatives.
Our initial efforts focused on the synthesis of the hypervalent
iodine reagent 2 having a benziodoxolone skeleton along with
the stability of the product (Scheme 1).[15] Gratifyingly, the
synthesis of the desired 2 was achieved by a simple ligand
exchange process. Indeed, acetoxyiodane 1 reacted smoothly
with benzophenone imine in dichloromethane at room
temperature to furnish the desired 2 in high yield, even in the
case of a gram-scale synthesis (3.9 g, 91%). This simple
process was successfully applied to the synthesis of derivatives
containing electron-donating methoxy (3) and electron-
withdrawing trifluoromethyl (4) groups. The synthesized
reagents were reasonably stable under ambient conditions in the
solid state as well as in solution. Single crystals of
a
representative sample of 2 suitable for X-ray crystallographic
analysis were grown by the slow diffusion of an acetonitrile
solution.[16,17] Structural data for
2
revealed that the
benzophenone imine moiety was N-bound to the hypervalent
iodine(III) center, which shows a typical distorted T-shaped
geometry (Figure 2). The length of the I–N bond of 2.083(3) Å is
somewhat longer than that observed for the sulfoximidoyl-
containing hypervalent iodine reagent reported by Bolm and co-
workers.[9a] In the solid state, 2 exists as a monomer with no
intermolecular secondary bonding interactions around the iodine
center, which is consistent with the fact that it is soluble in
organic solvents, such as chloroform and dichloromethane.
Dr. K. Kiyokawa, D. Okumatsu, Prof. Dr. S. Minakata
Department of Applied Chemistry, Graduate School of Engineering,
Osaka University, Yamadaoka 2-1, Suita, Osaka 565-0871 (Japan)
E-mail: kiyokawa@chem.eng.osaka-u.ac.jp
minakata@chem.eng.osaka-u.ac.jp
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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10.1002/anie.201904971
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COMMUNICATION
Ar
N
NH
were also applicable to this amination but their reactivity was
lower than that of 5a (Entries 11 and 12). No reaction was
observed with benzophenone imine-derived oxime derivatives
that can function as electrophilic aminating reagents (Entries 13
and 14).[14] Conducting the reaction at room temperature
Ar
Ar
Ar
I
O
AcO
I
O
(1‒1.5 equiv)
CH2Cl2, RT, 24 h
O
O
1
2, 91% [3.9 g]
Ar = 4-MeOC6H4 3, 70%
Ar = 3-CF3C6H4 4, 98%
Ar = Ph
resulted in
a lower yield of 5a (Entry 15). The reaction
proceeded with comparable efficiency, even in the dark,
demonstrating that the reaction is a thermal process (Entry 16).
Scheme 1. Syntheses of hypervalent iodine reagents containing
a
benzophenone imine-derived nitrogen functional group.
Table 1. Effect of solvents and reaction parameters on the oxidative amination
of the silyl ketene acetal 5a and control experiments.[a]
SiMe3
O
O
O1
C7
Ph
N
+
2
OMe
OMe
solvent
60 °C, 2 h
Ph
Ph Ph
I1
O2
6a
5a (E/Z = 71:29)
(1 equiv)
C8
C1
Entry
Solvent
Yield [%][b]
N1
1
2
3
4
5
6
7
1,2-Dichloroethane
MeCN
42
70
45
39
12
0
DMF
THF
Figure 2. Crystal structure of 2 (hydrogen atoms are omitted for clarity).
Thermal ellipsoids are shown at the 50% probability level. Selected bond
lengths [Å] and angles [°]: I1−N1 2.083(3), I1−O1 2.312(3), I1−C1 2.114(4),
N1−C8 1.291(5), O1−I1−N1 165.16(10); N1−I1−C1 88.90(13), O1−I1−C1
76.56(12), I1−O1−C7 114.7(2), I1−N1−C8 115.7(2).
MeNO2
HFIP
Toluene
0
Entry
8
Deviation from the conditions of Entry 2
2 (1.5 equiv)
Yield [%][b]
74
82
70
58
52
0
We next turned our attention to exploring the reactivity of the
synthesized hypervalent iodine reagents. The direct oxidative α-
amination of carbonyl compounds in the carboxylic acid
oxidation state is one of the most straightforward methods for
preparing unnatural α-amino acid derivatives,[18] which are
promising structural motifs for the preparation of biologically
active molecules. In addition to direct methods, the oxidative
amination of silyl ketene acetals is also a practical and reliable
strategy, and several transition metal-catalyzed approaches
have been reported to date, in which iminoiodanes,[19a,b]
hydroxyamines,[19c] and chloramines[19d] were used as a nitrogen
source. However, a remaining issue is the need for transition-
metal catalysts to be used and difficulties associated with the
further elaboration of an amino group in the products. In this
context, we were pleased to find that the hypervalent iodine
reagent 2 was capable of aminating silyl ketene acetals without
the addition of any catalyst or additive.
9
5a (1.5 equiv)
10
11
12
13
14
15
16
(Z)-5a (E/Z = 9:91) instead of 5a (E/Z = 71:29)
7 instead of 5a, 12 h
8 instead of 5a, 12 h
9 instead of 2, 12 h
10 instead of 2, 12 h
RT
0
48
66
In the dark
[a] Reactions were performed on a 0.2 mmol scale. [b] Determined by 1H NMR
analysis of the crude product using 1,1,2,2-tetrachloroethane as an internal
standard.
SiMe2tBu
Si(iPr)3
O
O
OAc
Ph
OBz
N
N
OMe
OMe
Ph
Ph
Ph
Ph
7 (E/Z = 71:29)
Ph
8 (E/Z = 89:11)
9
10
When the silyl ketene acetal 5a (E/Z = 71:29) derived from
methyl phenylacetate was employed in the reaction with 2 in 1,2-
dichloroethane at 60 °C, oxidative amination occurred to give the
desired 6a in 42% yield (Table 1, Entry 1). The results of a
solvent screening revealed that the yield of 6a could be
increased to 70% when MeCN was used (Entry 2). Reactions in
other polar solvents, such as DMF, THF, and MeNO2, resulted in
lower yields of 6a than that in MeCN (Entries 3–5) while no
desired product was formed when HFIP and toluene were used
as the solvent (Entries 6 and 7). Increasing the amounts of
reagents used were effective, and the use of 1.5 equivalents of
5a gave the best result (Entries 8 and 9). The E/Z configuration
of a silyl ketene acetal would little affect the efficiency of the
reaction because (Z)-5a (E/Z = 9:91) provided the same yield
(Entry 2 vs. 10). Silyl ketene acetals bearing a bulky silyl group,
such as tert-butyldimethylsilyl (7) and triisopropylsilyl (8) groups,
With the optimized reaction conditions in hand (Table 1,
Entry 9), the substrate scope of the amination was investigated
(Table 2). A series of silyl ketene acetals containing electron-rich
and -deficient aryl groups at the 2-position were subjected to
amination with 2, and all of the reactions proceeded successfully
to afford the corresponding α-amino esters in good to high yields
(Entries 1–6). The presence of a methyl substituent on the o- or
m-positions did not affect the reactivity (Entries 7 and 8). An
electron-rich N-methyl indolyl group was well tolerated under the
oxidative conditions to provide the desired 6i (Entry 9). In
addition, silyl ketene acetals containing aliphatic substituents at
the 2-position were also suitable for this amination. For example,
substrates containing n-butyl (5j) and sterically hindered
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10.1002/anie.201904971
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COMMUNICATION
isopropyl (5k) groups were smoothly converted into the
corresponding α-amino esters (Entries 10 and 11). Furthermore,
the sterically demanding dimethyl-substituted 5l was also
transformed into 6l containing an α-tertiary amine moiety in
moderate yield (Entry 12). However, unfortunately, the present
method could not be applied to the amination of a silyl enol ether
derived from acetophenone (not shown).
reaction using 2, indicating that the amination was not
significantly influenced by the electronic property of the imine
moiety of the hypervalent iodine reagent.
SiMe3
O
O
Ar
N
+
3 or 4
OMe
OMe
MeCN, 60 °C, 2 h
Ph
Ar Ph
5a (E/Z = 71:29)
(1.5 equiv)
using 3: 11, 72% (Ar = 4-MeOC6H4)
using 4: 12, 70% (Ar = 3-CF3C6H4)
Table 2. Substrate scope.[a]
Scheme 2. Oxidative amination using hypervalent iodine reagents 3 and 4.
SiMe3
O
O
R1
Ph
N
+
2
OMe
OMe
MeCN, 60 °C, 2 h
R1 R2
R2
Ph
It is well known that a benzophenone imine moiety is be
easily hydrolyzed, and this allowed us to carry out a one-pot
synthesis of the unprotected α-amino ester 13 (Scheme 3). A
sequential one-pot protocol consisting of the oxidative amination
of 5a with 2, removal of the volatiles under reduced pressure,
and acid hydrolysis at room temperature followed by a simple
basic workup, afforded desired 13 in good yield. This quite
simple method offers a useful and practical process for the
synthesis of α-amino acid derivatives.
5 (1.25−2 equiv)
6
Entry
5
6
Yield [%]
SiMe3
O
O
Ph
N
X
OMe
OMe
Ph
X
5a, X = H (E/Z = 71:29)
1
2
3
4
5
6
7
8
6a
78
73
73
83
76
84
75
75
5b, X = 4-OMe (E/Z = 93:7)
5c, X = 4-Me (E/Z = 74:26)
5d, X = 4-Cl (E/Z = 64:36)
5e, X = 4-Br (E/Z = 63:37)
5f, X = 4-CF3 (E/Z = 40:60)
5g, X = 2-Me (E/Z = 60:40)
5h, X = 3-Me (E/Z = 74:26)
6b
6c
6d
6e
6f
SiMe3
O
O
H2N
+
2
OMe
OMe
MeCN
60 °C, 2 h
acid
hydrolysis
Ph
Ph
13, 76%
5a (E/Z = 71:29)
(1.5 equiv)
one-pot
6g
6h
Scheme 3. Synthesis of a primary amine via a one-pot procedure.
SiMe3
O
O
Mechanistic aspects of the oxidative amination were also
investigated. Both 1H NMR and GC-MS analysis of byproducts in
the amination of 5a (Table 1, Entry 9) revealed that a small
amount of 14 and benzophenone azine (15) were generated,
which were likely formed through the homocoupling of the
corresponding α-carbonyl radicals and iminyl radicals,
respectively (Scheme 4a).[20,21] To examine this issue further, we
Ph
N
OMe
OMe
9[b]
55
Ph
MeN
MeN
5i[c]
6i
SiMe3
O
O
O
O
Ph
Ph
Ph
N
10
51
OMe
OMe
OMe
OMe
carried out
a radical trapping experiment using 2,2,6,6-
Ph
tetramethyl-piperidin-1-oxyl (TEMPO). When TEMPO was added
to the amination reaction of 5a, the formation of 6a was
suppressed (19%), and 16 was produced as the main product
through the trapping of an α-carbonyl radical derived from 5a by
TEMPO (Scheme 4b).[22] These results clearly indicate that an α-
carbonyl radical 17 as well as an iminyl radical 18 (in Scheme 5)
are generated in situ and both participate in the amination step.
A radical mechanism was further confirmed by a radical clock
experiment using the silyl ketene acetal 5m containing a
cyclopropyl substituent (Scheme 4c).[23] When 5m was subjected
to the amination reaction conditions, the cyclopropane-contining
6m was formed in low yield, and some ring-opening products
(not fully characterized) were observed, one of which was
determined to be 6m'.[24]
5j[c]
6j
SiMe3
O
N
11
12
63
58
OMe
Ph
5k (E/Z = >95:5)
SiMe3
6k
6l
O
N
OMe
Ph
5l
[a] Reactions were performed on a 0.4 mmol scale. Yields are isolated yields.
The isolated products contained a small amount of dimers of 5. See the
Supporting Information for details. [b] Reaction was conducted at RT. [c] E/Z
ratios were not determined.
Oxidative amination was also examined using derivatives 3
and 4 that contain electron-rich and -deficient imine moieties,
respectively (Scheme 2). Both reagents could be used to deliver
the corresponding products in yields comparable to those for the
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10.1002/anie.201904971
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COMMUNICATION
a)
ketene acetals was developed to afford α-amino acid derivatives.
These preliminary studies demonstrate that these new types of
hypervalent iodine reagents can function as useful aminating
reagents for the synthesis of primary amines. Further
investigations focused on expanding the utility of iodine reagents
such as these for organic synthesis are currently in progress.
Ph
Ph
N
SiMe3
Ph
O
O
2
MeO
N
+
+
6a
OMe
OMe
MeCN
60 °C, 2 h
82%
O
Ph
Ph
Ph
Ph
5a (E/Z = 71:29)
(1.5 equiv)
14, 7%
(d.r. = 1:1)
15, <10%
b)
2
SiMe3
O
TEMPO
(1 equiv)
O
O
Ph
N
O
+
Acknowledgements
OMe
N
OMe
OMe
Ph
MeCN
60 °C, 2 h
Ph Ph
Ph
16, 73%
5a (E/Z = 71:29)
(1 equiv)
This work was supported by JSPS KAKENHI Grant Numbers
19H02716 (S.M.) and 18K14217 (K.K.). We thank Dr. Norimitsu
Tohnai (Osaka University) for assistance with X-ray
crystallographic analysis.
6a, 19%
c)
SiMe3
O
O
Ph
O
2
Ph
N
+
OEt
OEt
Ph
N
OEt
MeCN
60 °C, 2 h
Ph
6m, 17%
Keywords: amination • amino acids • iodine • radical • synthetic
methods
5m (E/Z = 76:24)
(2 equiv)
6m’, <5%
[1]
[2]
a) V. V. Zhdankin, Hypervalent Iodine Chemistry: Preparation, Structure
and Synthetic Application of Polyvalent Iodine Compounds, Wiley, New
York, 2014; b) Hypervalent Iodine Chemistry, (Ed.: T. Wirth), in: Topics
in Current Chemistry, Vol. 373, Springer, Berlin, 2016.
Scheme 4. Mechanistic investigations into the oxidaitve amination reaction. a)
Byproducts in the standard amination reaction. b) Radical trapping experiment
with TEMPO. c) Reaction of cyclopropane-containing 5m. Yields are
determined by 1H NMR analysis of the crude product.
For selected reviews on chemistry of hypervalent iodine compounds,
see: a) T. Wirth, Angew. Chem. Int. Ed. 2005, 44, 3656–3665; Angew.
Chem. 2005, 117, 3722–3731; b) V. V. Zhdankin, P. J. Stang, Chem.
Rev. 2008, 108, 5299–5358; c) E. A. Merritt, B. Olofsson, Angew.
Chem. Int. Ed. 2009, 48, 9052–9070; Angew. Chem. 2009, 121, 9214–
9234; d) M. Uyanik, K. Ishihara, ChemCatChem 2012, 4, 177–185; e) R.
Samanta, K. Matcha, A. P. Antonchick, Eur. J. Org. Chem. 2013, 5769–
5804; f) F. V. Singh, T. Wirth, Chem. Asian J. 2014, 9, 950–971; g) A.
Yoshimura, V. V. Zhdankin, Chem. Rev. 2016, 116, 3328–3435; h) Y. Li,
D. P. Hari, M. V. Vita, J. Waser, Angew. Chem. Int. Ed. 2016, 55,
4436–4454; Angew. Chem. 2016, 128, 4512–4531.
Based on these experimental results, a proposed reaction
pathway is depicted in Scheme 5. The reaction is initiated
through a single electron transfer (SET) from the silyl ketene
acetal 5 to the hypervalent iodine reagent 2.[25,26] The resulting
radical cation and anion species are then quickly decomposed to
form the α-carbonyl radical 17 and the iminyl radical 18,
respectively, which are then rapidly coupled to produce the α-
amino ester 6. In addition, given the fact that the formation of a
certain amount of 6a, even in the presence of TEMPO (Scheme
4b) and that the cyclopropane-containing product 6m is formed
(Scheme 4c), an alternative pathway including a radical addition
of 18 to 5 followed by single-electron oxidation of the resulting
19 by 2, is also a possible pathway.[25,27,28]
[3]
a) S. Minakata, Y. Takeda, K. Kiyokawa in Methods and Applications of
Cycloaddition Reactions in Organic Syntheses (Eds.: N. Nishiwaki),
Wiley-VCH, Weinheim, 2013, chap. 2. For selected reviews, see: b) P.
Müller, C. Fruit, Chem. Rev. 2003, 103, 2905–2920; c) J. W. W. Chang,
T. M. U. Ton, P. W. H. Chan, Chem. Rec. 2011, 11, 331–357. For
selected examples, see: d) D. Macikenas, E. Skrzypczak-Jankun, J. D.
Protasiewicz, J. Am. Chem. Soc. 1999, 121, 7164–7165; e) A.
Yoshimura, V. N. Nemykin, V. V. Zhdankin, Chem. Eur. J. 2011, 17,
10538–10541; f) Y. Kobayashi, S. Masakado, Y. Takemoto, Angew.
Chem. Int. Ed. 2018, 57, 693–697; Angew. Chem. 2018, 130, 701–705.
a) C. Röben, J. A. Souto, Y. González, A. Lishchynskyi, K. Muñiz,
Angew. Chem. Int. Ed. 2011, 50, 9478–9482; Angew. Chem. 2011, 123,
9650–9654; b) J. A. Souto, D. Zian, K. Muñiz, J. Am. Chem. Soc. 2012,
134, 7242–7245; c) J. A. Souto, P. Becker, A. Iglesias, K. Muñiz, J. Am.
Chem. Soc. 2012, 134, 15505–15511; d) J. A. Souto, C. Martínez, I.
Velilla, K. Muñiz, Angew. Chem. Int. Ed. 2013, 52, 1324–1328; Angew.
Chem. 2013, 125, 1363–1367; e) C. Röben, J. A. Souto, E. C.
Escudero-Adán, K. Muñiz, Org. Lett. 2013, 15, 1008–1011; f) K. Muñiz,
Acc. Chem. Res. 2018, 51, 1507–1519.
+
ArCO2SiMe3
SiMe3
SiMe3
OMe
O
O
O
[4]
OMe
+
OMe
17
R
R
R
5
5
−
ArCO2
SET
Ph
N
−
2
2
(Ar = 2-IC6H4)
Ph
18
[5]
[6]
a) K. Moriyama, K. Ishida, H. Togo, Org. Lett. 2012, 14, 946–949; b) K.
Ishida, H. Togo, K. Moriyama, Chem. Asian J. 2016, 11, 3583–3588.
a) V. V. Zhdankin, C. J. Kuehl, A. P. Krasutsky, M. S. Formaneck, J. T.
Bolz, Tetrahedron Lett. 1994, 35, 9677–9680; b) S. Akai, T. Okuno, M.
Egi, T. Takada, H. Tohma, Y. Kita, Heterocycles 1996, 42, 47–51; c) V.
V. Zhdankin, A. P. Krasutsky, C. J. Kuehl, A. J. Simonsen, J. K.
Woodward, B. Mismash, J. T. Bolz, J. Am. Chem. Soc. 1996, 118,
5192–5197; d) S. Alazet, J. Preindl, R. Simonet-Davin, S. Nicolai, A.
Nanchen, T. Meyer, J. Waser, J. Org. Chem. 2018, 83, 12334–12356
and references therein.
−
SiMe3
SiMe3
O
2
2
O
O
18
Ph
N
Ph
N
OMe
OMe
OMe
R
Ph
R
Ph
R
5
19
6
Scheme 5. Proposed reaction pathway.
In conclusion, benziodoxolone-based hypervalent iodine
reagents containing a transferable (diarylmethylene)amino group
were prepared and found to be reasonably stable under ambient
representative compound was structurally
characterized by X-ray analysis. In addition, using these
reagents, the transition-metal-free oxidative amination of silyl
[7]
a) M. Papadopoulou, A. Varvoglis, J. Chem. Res. 1983, 66–67; b) L.
Hadjiarapoglou, S. Spyroudis, A. Varvoglis, Synthesis 1983, 207–208;
c) K. Kiyokawa, S. Yahata, T. Kojima, S. Minakata, Org. Lett. 2014, 16,
4646–4649; d) L. Marchetti, A. Kantak, R. Davis, B. DeBoef, Org. Lett.
2015, 17, 358–361; e) A. A. Kantak, L. Marchetti, B. DeBoef, Chem.
Commun. 2015, 51, 3574–3577; f) K. Kiyokawa, T. Kosaka, T. Kojima,
conditions.
A
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10.1002/anie.201904971
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Entry for the Table of Contents (Please choose one layout)
Layout 2:
COMMUNICATION
Kensuke Kiyokawa,* Daichi Okumatsu,
and Satoshi Minakata*
Ar
SiMe3
O
Ar
O
I III
N
R1
Ar
N
OR3
OR3
Page No. – Page No.
R1 R2
Ar
R2
transition-metal-free
Synthesis of Hypervalent Iodine(III)
Reagents Containing a Transferable
(Diarylmethylene)amino Group and
Their Use in the Oxidative Amination
of Silyl Ketene Acetals
The preparation of some hypervalent iodine reagents containing a transferable
amino group derived from benzophenone imine derivatives are reported. The
reagents could be readily prepared, stored as a bench-stable solid, and were
successfully used in the transition-metal-free oxidative amination of silyl ketene
acetals to afford the corresponding α-amino esters, whose benzophenone imine
moieties could be easily hydrolyzed, leading to the formation of primary amines.
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