Synthesis and Structure of Hypervalent Iodine(III) Reagents Containing Phthalimidate and Application to Oxidative Amination Reactions

Article abstract of DOI:10.1002/anie.201506805

A new class of hypervalent iodine reagents containing phthalimidate was synthesized, and structurally characterized by X-ray analysis. The benziodoxole-based reagent displays satisfactory solubility in common organic solvents and is reasonably stable in solution as well as in the solid state. The reagent was used for the oxidative amination of the C(sp³)-H bond of N,N-dimethylanilines. In addition, the reagent was also applicable to oxidative amination with rearrangement of trialkylamines as well as enamines that were prepared in situ from secondary amines and aldehydes.

Full text of DOI:10.1002/anie.201506805

Angewandte
Chemie
International Edition: DOI: 10.1002/anie.201506805
German Edition: DOI: 10.1002/ange.201506805
Amination Reactions
Synthesis and Structure of Hypervalent Iodine(III) Reagents
Containing Phthalimidate and Application to Oxidative Amination
Reactions
Kensuke Kiyokawa,* Tomoki Kosaka, Takumi Kojima, and Satoshi Minakata*
À
Abstract: A new class of hypervalent iodine reagents contain-
ing phthalimidate was synthesized, and structurally character-
ized by X-ray analysis. The benziodoxole-based reagent
displays satisfactory solubility in common organic solvents
and is reasonably stable in solution as well as in the solid state.
carbons, including the diamination of alkenes, allylic C H
[7]
À
amination, and the C H amination of acetylenes. Despite
these advances, the use of a hypervalent iodine reagent
containing phthalimidate is still very limited, even though it
has the potential to introduce a phthalimide moiety into an
organic molecule. In 1983, Varvoglis and co-workers synthe-
sized PhI(NPhth)2 (Phth = phthaloyl) by treating PhI-
(OCOCF3)2 with potassium phthalimide.[8,9] However, it is
thermally stable but undergoes rapid hydrolysis in the
presence of moisture in solution, and only a few examples
of synthetic applications have been reported so far.[10]
Although the formation of N-(phenylacetoxyiodo)imido
The reagent was used for the oxidative amination of the
3
À
C(sp ) H bond of N,N-dimethylanilines. In addition, the
reagent was also applicable to oxidative amination with
rearrangement of trialkylamines as well as enamines that
were prepared in situ from secondary amines and aldehydes.
T
he incorporation of an amino functional group into an
organic molecule by oxidative amination is a powerful
strategy for preparing various types of nitrogen-containing
compounds, which are promising candidates for use in the
synthesis of various biologically active and medicinally
important compounds. Recently, hypervalent iodine reagents
containing an iodine–nitrogen bond have been reported to be
potentially useful for oxidative amination reactions.[1,2] To
date, several examples of defined hypervalent iodine reagents
containing transferable nitrogen functional groups such as
imino, azido, and imido groups have been reported, and they
have been used in various oxidative amination reactions.
species (PhI(OAc)(NPhth)) was recently proposed for the
metal-free oxidative amination of aryl C(sp ) and benzylic
C(sp ) H bonds using PhI(OAc)2 with phthalimide, precise
2
À
3
À
structural proof of the intermediate was not obtained.[11] In
this context, we recognized that the synthesis of a structurally
defined hypervalent iodine reagent containing phthalimidate,
which is both stable but reactive under the desired conditions,
would be highly desirable for the direct investigation of the
reactivity of an iodine(III) reagent containing phthalimidate
and for further expanding its synthetic utility. Herein, we
report on the synthesis and X-ray structural characterization
of benziodoxole-based hypervalent iodine reagents contain-
ing phthalimidate, and their use in oxidative amination
reactions.
=
Among them, iminoiodanes (PhI NTs; Ts = p-toluenesul-
fonyl), a class of compounds that are useful precursors of
nitrene in the presence of transition metals, have been the
most widely used reagents for the aziridination of alkenes and
Our initial efforts focused on the synthesis of the hyper-
valent iodine reagents 1 and 2 (Scheme 1). First, following
a known method, chloroiodane 3 was prepared by treating 2-
iodobenzoic acid with trichloroisocyanuric acid (TCICA).[12]
Subsequently, the reaction of 3 with potassium phthalimide
afforded 1 in 85% yield. In addition, 2 was also synthesized by
treating potassium phthalimide with chloroiodane 4, which
was also prepared by a previously reported method.[13] Both
1 and 2 were found to be reasonably stable under ambient
[3]
À
amination of C H bonds. Oxidative amination using
À
a hypervalent iodine reagent containing an I N single bond
has received considerable attention in recent decades. In
1994, Zhdankin et al. reported the preparation of isolable
azidoiodanes that are stabilized by the formation of five-
membered heterocycles, including an iodine(III) center, and
demonstrated that they were sufficiently reactive to permit
À
their use in the C H azidation of dimethylanilines and
alkanes.[4–6] Recently, MuÇiz and co-workers successfully
prepared a new class of hypervalent iodine reagents bearing
a bissulfonimide group as a ligand. These compounds have
a highly electrophilic iodine(III) center and were applicable
for use in the oxidative amination of unsaturated hydro-
[*] Dr. K. Kiyokawa, T. Kosaka, T. Kojima, 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
Scheme 1. Syntheses of hypervalent iodine reagents 1 and 2. a) TCICA,
MeCN, 758C, 10 min; b) potassium phthalimide, MeCN, RT, 1 h;
c) MeMgI, Et2O, 08C to RT, 15 h; then reflux, 1.5 h; d) tBuOCl, CH2Cl2,
08C, 22 h; e) potassium phthalimide, MeCN, RT, 2 h.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201506805.
Angew. Chem. Int. Ed. 2015, 54, 13719 –13723
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
13719

.
Angewandte
Communications
conditions in the solid state and even in solution. Reagent 1 is
soluble only in a highly polar solvent such as dimethylsulf-
oxide, while 2 displayed satisfactory solubility in common
organic solvents such as chloroform, dichloromethane, and
acetonitrile.[14] Single crystals of 2 suitable for X-ray crystallo-
graphic analysis were obtained from a solution of 2 in
acetonitrile at ambient temperature. The structural data for 2
clearly revealed that the phthalimidate was bound through its
N atom to the hypervalent iodine(III) center, which shows
a distorted T-shaped geometry (Figure 1). The length of the
yield of 5a was dramatically decreased to 13%, thus indicat-
ing that the reaction proceeds through a radical pathway
involving a one-electron oxidation of the substrate by 2
(Table 1, entry 4).[17] Low yields were obtained when the
reaction was performed with PhI(NPhth)2 or a combination of
PhI(OAc)2 and phthalimide (Table 1, entries 5 and 6).
À
Oxidative C H amination using 2 was investigated for
a range of N,N-dialkylaniline derivitives (Scheme 2, reac-
Figure 1. Crystal structure of 2 (hydrogen atoms are omitted for
clarity). Thermal ellipsoids are shown at the 30% probability level.
Selected bond lengths [Š] and angles [8]: I1-N1 2.197(4), I1-O1
2.064(3), I1-C1 2.113(5), O1-I1-N1 168.04(14); N1-I1-C1 89.13(16),
O1-I1-C1 78.91(15), I1-O1-C7 111.1(3).
À
Scheme 2. Oxidative C H amination of N,N-dialkylanilines.
tion i). The reaction of p-toluidine afforded the corresponding
product 5b in high yield. A substrate bearing a methoxy
group on the phenyl ring also reacted readily, and a bromo
substituent was tolerated to give the product 5d. Interestingly,
the use of N,N-diethylaniline as a substrate for the reaction
with 2 in toluene afforded 6, which has two phthalimide
moieties at the b-position to the nitrogen atom (Scheme 2,
reaction ii).[18,19]
À
I1 N1 bond of 2.197(4) is shorter than that observed in the
saccharinylbenziodoxole derivative reported by Zhdankin
and co-workers.[15] In the solid state, 2 exists as a monomer
without any intermolecular secondary bonding interactions
around the iodine center.
To illustrate the synthetic utility of these reagents, we
investigated the reactivity of 1 and 2 in an oxidative amination
reaction (Table 1). When N,N-dimethylaniline was employed
To further investigate the applicability of the double
imidation reaction to give a product such as 6, we examined
reactions with trialkylamines (Table 2). Treatment of triethyl-
amine with 2 equiv of 2 in acetonitrile at 608C for 6 h afforded
7a containing two phthalimide moieties in 36% yield
(Table 2, entry 1), similar to the result of the reaction of
N,N-diethylaniline described above. The reaction of tri-n-
propylamine provided 7b, the structure of which was
confirmed by NMR spectroscopy and X-ray structural
analysis.[20] This result clearly indicates that the reaction
includes a rearrangement step (Table 2, entry 2).[18,21] More-
over, the same transformation was observed in reactions using
trialkylamines that have a longer alkyl chain (Table 2,
entries 3 and 4). The more sterically hindered triisobutyl-
amine also underwent the rearrangement to provide the
corresponding amine 7e with a quarternary carbon atom,
albeit in low yield (Table 2, entry 5). The reaction of
dicyclohexylpropylamine proceeded selectively at the propyl
chain to give 7 f (Table 2, entry 6). Although Tian and Loh
reported the copper-catalyzed oxidative rearrangement of
tertiary amines under aerobic conditions to provide a-amino
acetals,[22] our oxidative amination with rearrangement pro-
ceeded under metal-free conditions to provide products that
contain amino functional groups.
as a model substrate in the reaction with 1 in MeCN at 708C,
3
À
C(sp ) H amination occurred to provide 5a in 62% yield
(Table 1, entry 1).[16] Reagent 2 was found to be more efficient
than 1, and 5a was produced in a high yield when a small
excess of 2 was used (Table 1, entries 2 and 3). When the
reaction was conducted in the presence of 2,2,6,6-tetrame-
thylpiperidine-N-oxyl (TEMPO) as a radical inhibitor, the
[a]
À
Table 1: Oxidative C H amination of N,N-dimethylaniline.
Entry
Hypervalent iodine reagent
Yield [%][b]
1
2
3
1 (1 equiv)
2 (1 equiv)
2 (1.3 equiv)
2 (1.3 equiv)
PhI(NPhth)2 (1 equiv)
PhI(OAc)2 (1 equiv)
Phthalimide (1 equiv)
62
74
83[c]
13
28
38
4[d]
5
6
[a] Reaction conditions: N,N-dimethylaniline (0.1 mmol), hypervalent
iodine reagent (0.1 or 0.13 mmol), MeCN (1 mL), 708C, 12 h.
[b] Determined by 1H NMR analysis of crude product using 1,1,2,2-
tetrachloroethane as an internal standard. [c] Yield of isolated product.
[d] TEMPO (1 equiv) was added.
In this oxidative amination with rearrangement of tri-
alkylamines, an enamine that is generated in situ by the
oxidation of an amine was predicted to be a reactive
intermediate according to a previous report.[22] In addition,
13720 www.angewandte.org
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2015, 54, 13719 –13723

Angewandte
Chemie
Table 2: Oxidative amination with rearrangement of trialkylamines.[a]
the regioselective opening of 11 probably occurred through
the formation of an N-phthaloyliminium ion followed by the
nucleophilic attack of a phthalimidate, to afford the product
7.[25] Indeed, when the enamine 9a (which was prepared
separately by reacting hexanal with di-n-butylamine) was
treated with 1 equiv of 2 and 1 equiv of phthalimide as an
additional aminating reagent in MeCN at 508C, the corre-
sponding product 7g was produced in 70% yield (Scheme 4).
This result provides strong support for the mechanism shown
in Scheme 3.
Entry
1
Trialkylamine
Product
Yield [%][b]
36
7a
7b
7c
7d
7e
7 f
2
59
52
58
20
38
3
4
Scheme 4. Reaction of an enamine with 2.
5
The oxidative amination was also applicable to reactions
in which various types of secondary amines and aldehydes
were used as starting materials. These reactions involve the
formation of an enamine in situ (Scheme 5).[26] When the
6[c]
[a] Reaction conditions: trialkylamine (0.1 mmol), 2 (0.2 mmol), MeCN
(1 mL), 608C, 6 h. [b] Yield of isolated product. [c] The reaction was
conducted at 708C.
when the reaction of tri-n-propylamine with 2 was examined
in the presence of TEMPO (a radical inhibitor) the yield of 7b
remained essentially the same, thereby indicating that the
reaction does not involve the formation of a radical inter-
mediate.[20] A proposed mechanism for the reaction is
depicted in Scheme 3. The reaction is initiated by an attack
Scheme 5. Oxidative amination with rearrangement of enamines gen-
erated in situ from amines and aldehydes. Unless otherwise noted,
reaction conditions: amines (0.15 mmol), aldehydes (0.1 mmol), 2
(0.1 mmol), phthalimide (0.1 mmol), MeCN (1 mL), 508C, 12 h. Yields
are for the isolated products. [a] The reaction was conducted at 608C.
[b] The d.r. value was determined by 1H NMR analysis.
Scheme 3. Plausible reaction mechanism.
of an amine on an electrophilic iodine center of 2 to form the
ammonium intermediate 8. Proton abstraction by the result-
ing phthalimidate gives an imminium ion, which is followed
by proton abstraction by an alkoxide (R’’OÀ) to provide
enamine 9.[23] Subsequently, the enamine 9 participates in the
reaction of dibenzylamine, hexanal, and 2 in the presence of
phthalimide was examined, the corresponding product 7h was
obtained in 78% yield.[18,27] The use of diallylamine and
a bulkier allylcyclohexylamine also provided the correspond-
ing products (7i and 7j) in 77% and 61% yield, respectively.
A simple aliphatic amine, diethylamine, resulted in a moder-
ate yield of 7k. Moreover, cyclic secondary amines such as
1,2,3,4-tetrahydroisoquinoline, morpholine, and thiomorpho-
[24]
À
reaction with 2 to form the C I bond.
The resulting
iminium 10 reacts with the phthalimidate, and a subsequent
intramolecular cyclization with reductive elimination of the
iodobenzene derivative affords the aziridinium intermediate
11, which would lead to the rearrangement product. Finally,
Angew. Chem. Int. Ed. 2015, 54, 13719 –13723
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org 13721

.
Angewandte
Communications
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) V. V. Zhdankin, R. M. Arbit, M. McSherry,
B. Mismash, V. G. Young, Jr., J. Am. Chem. Soc. 1997, 119,
7408 – 7409.
line were suitable for this transformation to give the products
(7l–7n, respectively) in moderate to good yields.[28] We
further investigated the scope of this reaction by using
a series of aldehydes.[29] The aldehyde containing a phenyl
group at the terminal position provided 7o, while a b-
branched aldehyde provided 7p in good yield at a higher
temperature. The substrate bearing a double bond was well-
tolerated in this oxidative rearrangement. In addition, (S)-
(À)-b-citronellol, derived from natural sources, was also
smoothly converted into the product 7r as a diastereomeric
mixture.
[5] S. Akai, T. Okuno, M. Egi, T. Takada, H. Tohma, Y. Kita,
Heterocycles 1996, 42, 47 – 51.
[6] For selected recent examples of azidation using isolable
azidoiodanes, see a) D. Lubriks, I. Sokolovs, E. Suna, J. Am.
Chem. Soc. 2012, 134, 15436 – 15442; b) M. V. Vita, J. Waser,
Org. Lett. 2013, 15, 3246 – 3249; c) Q.-H. Deng, T. Bleith, H.
Wadepohl, L. H. Gade, J. Am. Chem. Soc. 2013, 135, 5356 – 5359;
d) B. Zhang, A. Studer, Org. Lett. 2013, 15, 4548 – 4551; e) H.
Yin, T. Wang, N. Jiao, Org. Lett. 2014, 16, 2302 – 2305; f) Y. Fan,
W. Wan, G. Ma, W. Gao, H. Jiang, S. Zhu, J. Hao, Chem.
Commun. 2014, 50, 5733 – 5736; g) A. Sharma, J. F. Hartwig,
Nature 2015, 517, 600 – 604.
[7] a) C. Rçben, J. A. Souto, Y. Gonzµlez, A. Lishchynskyi, K.
MuÇiz, Angew. Chem. Int. Ed. 2011, 50, 9478 – 9482; Angew.
Chem. 2011, 123, 9650 – 9654; b) J. A. Souto, D. Zian, K. MuÇiz,
J. Am. Chem. Soc. 2012, 134, 7242 – 7245; c) J. A. Souto, Y.
Gonzµlez, A. Iglesias, D. Zian, A. Lishchynskyi, K. MuÇiz,
Chem. Asian J. 2012, 7, 1103 – 1111; d) J. A. Souto, P. Becker, A.
Iglesias, K. MuÇiz, J. Am. Chem. Soc. 2012, 134, 15505 – 15511;
e) A. Lishchynskyi, K. MuÇiz, Chem. Eur. J. 2012, 18, 2212 –
2216; f) J. A. Souto, C. Martínez, I. Velilla, K. MuÇiz, Angew.
Chem. Int. Ed. 2013, 52, 1324 – 1328; Angew. Chem. 2013, 125,
1363 – 1367; g) C. Rçben, J. A. Souto, E. C. Escudero-Adµn, K.
MuÇiz, Org. Lett. 2013, 15, 1008 – 1011.
In conclusion, novel benziodoxole-based hypervalent
iodine reagents containing phthalimidate were prepared and
were found to be reasonably stable under ambient conditions
in both the solid and solution states. The use of these reagents
3
À
allowed oxidative amination reactions, including the C(sp )
H amination of N,N-dimethylanilines and oxidative amina-
tion with the rearrangement of trialkylamines as well as
enamines prepared in situ from secondary amines and
aldehydes, to be carried out. Further investigations focused
on expanding the utility of the iodine reagents is currently in
progress.
Acknowledgements
[8] L. Hadjiarapoglou, S. Spyroudis, A. Varvoglis, Synthesis 1983,
207 – 208.
[9] For related studies on hypervalent iodine reagents with imidates,
see a) M. Papadopoulou, A. Varvoglis, J. Chem. Res. 1983, 66 –
67; b) M. Papa dopoulou, A. Varvoglis, J. Chem. Res. 1984, 166 –
167.
This work was supported by Grants-in-Aid for Scientific
Research (No. 25288047 and No. 26105735) from MEXT and
by a research Grant from the Society of Iodine Science. We
thank Dr. Nobuko Kanehisa (Osaka University) for valuable
advice regarding X-ray crystallography.
[10] a) K. Moriyama, K. Ishida, H. Togo, Org. Lett. 2012, 14, 946 –
949; b) K. Kiyokawa, S. Yahata, T. Kojima, S. Minakata, Org.
Lett. 2014, 16, 4646 – 4649; c) L. Marchetti, A. Kantak, R. Davis,
B. DeBoef, Org. Lett. 2015, 17, 358 – 361; d) A. A. Kantak, L.
Marchetti, B. DeBoef, Chem. Commun. 2015, 51, 3574 – 3577.
[11] a) A. A. Kantak, S. Potavathri, R. A. Barham, K. M. Romano, B.
DeBoef, J. Am. Chem. Soc. 2011, 133, 19960 – 19965; b) H. J.
Kim, J. Kim, S. H. Cho, S. Chang, J. Am. Chem. Soc. 2011, 133,
16382 – 16385.
Keywords: amination · amines · hypervalent iodine reagents ·
phthalimides · rearrangement
How to cite: Angew. Chem. Int. Ed. 2015, 54, 13719–13723
Angew. Chem. 2015, 127, 13923–13927
[1] V. V. Zhdankin, Hypervalent Iodine Chemistry: Preparation,
Structure and Synthetic Application of Polyvalent Iodine Com-
pounds, Wiley, New York, 2013.
ˇ
[12] V. Matousek, E. Pietrasiak, R. Schwenk, A. Togni, J. Org. Chem.
2013, 78, 6763 – 6768.
[2] For selected reviews on chemistry of hypervalent iodine, see
a) R. D. Richardson, T. Wirth, Angew. Chem. Int. Ed. 2006, 45,
4402 – 4404; Angew. Chem. 2006, 118, 4510 – 4512; 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) H. Liang,
M. A. Ciufolini, Angew. Chem. Int. Ed. 2011, 50, 11849 – 11851;
Angew. Chem. 2011, 123, 12051 – 12053; e) M. Uyanik, K.
Ishihara, ChemCatChem 2012, 4, 177 – 185; f) R. Samanta,
A. P. Antonchick, Synlett 2012, 809 – 813; g) M. Brown, U.
Farid, T. Wirth, Synlett 2013, 424 – 431; h) R. Samanta, K.
Matcha, A. P. Antonchick, Eur. J. Org. Chem. 2013, 5769 – 5804.
[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.
[13] P. Eisenberger, I. Kieltsch, R. Koller, K. Stanek, A. Togni, Org.
Synth. 2011, 88, 168 – 180.
[14] Solubility of 2: 242 mgmLÀ1 in chloroform, 115 mgmLÀ1 in
dichloromethane, and 6 mgmLÀ1 (21 mgmLÀ1 at 508C) in
acetonitrile.
[15] A. Yoshimura, S. R. Koski, J. M. Fuchs, A. Saito, V. N. Nemykin,
V. V. Zhdankin, Chem. Eur. J. 2015, 21, 5328 – 5331.
3
À
[16] KI-catalyzed imidation of the C(sp ) H bond of N,N-dimethyl-
aniline has been reported, see Z.-Q. Lao, W.-H. Zhong, Q.-H.
Lou, Z.-J. Li, X.-B. Meng, Org. Biomol. Chem. 2012, 10, 7869 –
7871.
[17] Cyclic voltammetry (CV) of 1 and 2 in MeCN showed an
irreversible reduction wave at Epc1 = À1.36 V (1) and À1.95 V
(2) versus Fc/Fc+. See the Supporting Information for details.
[18] For details of the optimization of the reaction conditions, see the
Supporting Information.
[19] When the reaction of N-ethyl-N-methylaniline with 2 equiv of 2
was conducted for a competition experiment, the monoaminated
product (generated by the reaction at methyl group) and the
diaminated product (generated by the reaction at ethyl group)
[4] a) V. V. Zhdankin, C. J. Kuehl, A. P. Krasutsky, M. S. Forma-
neck, J. T. Bolz, Tetrahedron Lett. 1994, 35, 9677 – 9680; b) A. P.
Krasutsky, C. J. Kuehl, V. V. Zhdankin, Synlett 1995, 1081 – 1082;
13722 www.angewandte.org
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2015, 54, 13719 –13723

Angewandte
Chemie
were obtained in 51% and 7% yields, respectively. See the
Supporting Information for details.
Int. Ed. 2012, 51, 9105 – 9109; Angew. Chem. 2012, 124, 9239 –
9243.
[20] See the Supporting Information for details.
[27] When the reaction was conducted in the presence of TEMPO,
the yield of 7h remained essentially the same. See the Support-
ing Information for details.
[28] When the reaction using trimethylsilyl-protected diphenylproli-
nol was carried out, the corresponding product was obtained in
53% yield in a diastereomeric ratio of 86:14. See the Supporting
Information for details.
[29] Reactions using a-branched aldehydes, such as isobutyraldehyde
and cyclohexanecarbaldehyde, failed to provide the desired
products.
[21] When the reaction of tri-n-propylamine with 1 equiv of reagent 2
was conducted, 7b was obtained as the sole product.
[22] J. S. Tian, T. P. Loh, Angew. Chem. Int. Ed. 2010, 49, 8417 – 8420;
Angew. Chem. 2010, 122, 8595 – 8598.
[23] a) W. Muramatsu, K. Nakano, C.-J. Li, Org. Biomol. Chem. 2014,
12, 2189 – 2192; b) N. Zhang, R. Cheng, D. Zhang-Negrerie, Y.
Du, K. Zhao, J. Org. Chem. 2014, 79, 10581 – 10587.
[24] A. E. Allen, D. W. C. MacMillan, J. Am. Chem. Soc. 2010, 132,
4986 – 4987.
[25] For examples of reactions involving N-phthaloyliminium ions,
see a) P. Renaud, A. Stojanovic, Tetrahedron Lett. 1996, 37,
2569 – 2572; b) A. Stojanovic, P. Renaud, K. Schenk, Helv. Chim.
Acta 1998, 81, 268 – 284.
[26] a) J. S. Tian, T. P. Loh, Chem. Commun. 2011, 47, 5458 – 5460;
b) J. S. Tian, K. W. J. Ng, J. R. Wong, T. P. Loh, Angew. Chem.
Received: July 23, 2015
Published online: September 18, 2015
Angew. Chem. Int. Ed. 2015, 54, 13719 –13723
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org 13723