Rhodium(III)-Catalyzed Oxidative Intramolecular 1,1-Oxyamination of Alkenes with Protected Amino Acids to Produce Oxazoloisoindole-2,5-diones

Article abstract of DOI:10.1002/ejoc.202100143

It has been established that an electron-deficient bis(ethoxycarbonyl)-substituted cyclopentadienyl (Cp^E) rhodium(III) complex catalyzes the oxidative intramolecular 1,1-oxyamination of alkenes with N-benzoyl amino acids to produce oxazoloisoindole-2,5-diones. Experimental and theoretical mechanistic studies revealed that this oxidative 1,1-oxyamination proceeds via not the aza-Wacker reaction but the formation of a rhoda(III)oxazolidine initiated by the carboxylic acid-directed N?H bond cleavage.

Full text of DOI:10.1002/ejoc.202100143

Communications
doi.org/10.1002/ejoc.202100143
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Rhodium(III)-Catalyzed Oxidative Intramolecular 1,1-
Oxyamination of Alkenes with Protected Amino Acids to
Produce Oxazoloisoindole-2,5-diones
Hiroto Takahashi,[a] Yuki Nagashima,[a] and Ken Tanaka*[a]
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It has been established that an electron-deficient bis
(ethoxycarbonyl)-substituted cyclopentadienyl (CpE) rhodium(III)
complex catalyzes the oxidative intramolecular 1,1-oxyamina-
tion of alkenes with N-benzoyl amino acids to produce
oxazoloisoindole-2,5-diones. Experimental and theoretical
mechanistic studies revealed that this oxidative 1,1-oxyamina-
tion proceeds via not the aza-Wacker reaction but the formation
of a rhoda(III)oxazolidine initiated by the carboxylic acid-
directed NÀ H bond cleavage.
The transition-metal-catalyzed oxidative oxyamination of al-
kenes is a valuable transformation in organic synthesis.[1,2] This
transformation is classified into 1,2-oxyamination[1] and 1,1-
oxyamination.[2] For example, Wang reported the copper(II)-
catalyzed 1,2-oxyamination of alkenes in the amino lactoniza-
tion of alkenyl carboxylic acids with O-benzoylhydroxylamines.[3]
Rovis reported the iridium(III)-catalyzed 1,2-oxyamination of
alkenes in the regiodivergent oxy lactamization of alkenyl
carboxamides with carboxylic acids.[4] Besides, the oxyamination
of alkenes with amino alcohols or amino acids can furnish
heterocycles containing both oxygen and nitrogen, which are
basic skeletons of bioactive substances.[5] As an example using
the amino alcohols, Lloyd-Jones and Booker-Milburn reported
the palladium(II)-catalyzed 1,1-oxyamination of alkenes with N-
protected amino alcohols (Figure 1a).[6] Roland and Kadouri-
Puchot reported an intramolecular variant producing bicyclic
oxazolidines (Figure 1b).[7] These 1,1-oxyamination reactions
proceed via the aza-Wacker reaction giving enamine intermedi-
ates. Recently, in 2018, Zhang reported the palladium(II)-
catalyzed oxidative 1,2-oxyamination of 1,3-dienes with amino
alcohols or amino acids giving morpholine and morpholin-2-
one derivatives.[8] The annulation of amino acid derivatives
proceeds via the formation of five-membered palladacycle A
followed by alkene insertion giving π-allyl intermediate B, and
thus monoenes cannot be used for this reaction (Figure 1c). In
Figure 1. Research backgrounds.
this paper, we have established that electron-deficient bis
(ethoxycarbonyl)-substituted cyclopentadienyl (CpE) rhodium(III)
complex 1[9] catalyzes the oxidative intramolecular 1,1-oxy-
amination of alkenes with N-protected amino acids in (2-
vinylbenzoyl)glycine derivatives 2 via rhodacycle intermediates
C and D producing oxazoloisoindole-2,5-diones 3, which are
[a] H. Takahashi, Dr. Y. Nagashima, Prof. Dr. K. Tanaka
Department of Chemical Science and Engineering
Tokyo Institute of Technology
O-okayama, Meguro-ku, 152-8550 Tokyo, Japan
E-mail: ktanaka@apc.titech.ac.jp
http://www.apc.titech.ac.jp/~ktanaka/
found in the core structure of pharmaceuticals, such as an
antidiabetic agent (Figure 1d).[10,11]
We previously reported that complex 1 is a highly active
catalyst for the oxidative [4+2][12] and [2+2+2][13] annulation
reactions of benzoic acids with alkynes, which proceed via the
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/ejoc.202100143
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formation of five-membered rhodacycles by carboxylic acid-
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directed CÀ H bond cleavage.[14] We anticipated that 1 reacts
with 2 to form five-membered rhodacycle C by carboxylic acid-
directed NÀ H bond cleavage, which would afford some
cyclization products. Thus, we first examined the reaction of (2-
vinylbenzoyl)phenylglycine (2a) in the presence of a catalytic
amount of
1
(10 mol% Rh), AgOAc (20 mol%), and
Cu(OAc)2·H2O (20 mol%), which were used for the CpERhIII-
catalyzed oxidative [2+2+2] annulation of benzoic acids with
alkynes. Pleasingly, the oxidative annulation to form oxazoloi-
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°
soindole-2,5-dione 3a proceeded at 80 C in 29% yield (Table 1,
entry 1). To improve the yield of 3a, various silver(I) salts were
screened (entries 1–5), which revealed that the use of AgOTf
afforded 3a in the highest yield of 43% (entry 5). In the absence
of the silver(I) salt, the yield of 3a could be improved further to
45% (entry 6).[15] Solvents were also surveyed, but neither the
less polar solvent (toluene) nor more polar solvents [1,4-
dioxane, (CH2OMe)2, and CH3CN] were ineffective (entries 7–10).
Under this condition, various RhIII and IrIII complexes were tested
(entries 7–9), but the yields did not exceed that of entry 6.
Finally, PdCl2(CH3CN)2/benzoquinone/LiCl system, which was
used in the reaction shown in Figure 1b,[7] was also tested, but
3a was not obtained at all (entry 10).
With the optimized reaction conditions in hand, the
substrate scope was examined as shown in Figure 2a. With
respect to substituents on the benzoyl group, the reactions of
fluoro-, chloro-, trifluoromethyl-, methoxy-, and methyl-substi-
tuted (2-vinylbenzoyl)phenylglycines 2b–h at the ortho-, meta-,
or para-position gave the corresponding oxazoloisoindole-2,5-
dioness 3b–h. In general, electron-deficient products 3b, 3c,
Table 1. Optimization of reaction conditions.[a]
Entry
Metal complex
AgX
Solvent
Yield [%][b]
Figure 2. Substrate scope. 2 (0.10 mmol), 1 (0.0050 mmol), Cu(OAc)2·H2O
(0.020 mmol), and (CH2Cl)2 (2.0 mL) were used. The cited yields were of
isolated products. [a] [CpRhI2]n (0.010 mmol Rh) was used. [b] [Cp*RhCl2]2
(0.0050 mmol) was used. [c] 2i (1.0 mmol), 1 (0.050 mmol), Cu(OAc)2·H2O
(0.20 mmol), and (CH2Cl)2 (10 mL) were used.
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1
1
1
1
1
1
1
1
AgOAc
Ag2CO3
AgSbF6
AgNTf2
AgOTf
none
none
none
none
none
(CH2Cl)2
(CH2Cl)2
(CH2Cl)2
(CH2Cl)2
(CH2Cl)2
(CH2Cl)2
toluene
1,4-dioxane
(CH2OMe)2
CH3CN
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0
3d, 3f, and 3h were obtained in higher yields than electron-
rich products 3e and 3g. With respect to substituents on the
glycine unit, substituted phenylglycine (2i and 2j), phenyl-
alanine (2k), and α-ethyl-phenylglycine (2l) derivatives could
participate in this transformation, although the yields of the
corresponding oxazoloisoindole-2,5-diones 3i, 3j, 3k, and 3l
were lower than that of 3a. In the reaction of 1a, the difference
in catalytic activity between 1, [CpRhI2]n, [Cp*RhCl2]2 was small,
but in the reaction of less reactive substrate 2k, 1 and [CpRhI2]n
showed significantly higher activity than [Cp*RhCl2]2. We have
attempted the 1,1- and 1,2-disubstituted olefin substrates, but
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1
1
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14[c]
[CpRhI2]n
[Cp*RhCl2]2
[Cp*IrCl2]2
PdCl2(CH3CN)2
benzoquinone, LiCl
none
none
none
none
(CH2Cl)2
(CH2Cl)2
(CH2Cl)2
(CH2Cl)2
[a] 2a (0.10 mmol), metal complex (0.010 mmol metal), AgX (none or
0.020 mmol Ag), Cu(OAc)2·H2O (0.020 mmol), and (CH2Cl)2 (2.0 mL) were
used. [b] Determined by 1H NMR using dimethyl sulfone or dimethyl
terephthalate as an internal standard. [c] Reaction was conducted using 2a
(0.10 mmol), PdCl2(CH3CN)2 (0.010 mmol), benzoquinone (0.10 mmol), LiCl
(1.0 mmol), and THF (2.0 mL) at reflux for 4 h.
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the corresponding cyclization products were not obtained. Not
A plausible reaction mechanism is shown in Figure 3c. First,
CpERhIII acetate E, generated from [CpERhCl2]2 and Cu(OAc)2,
reacts with 2a to form five-membered rhodacycle C [rhoda(III)
oxazolidine] via carboxylic acid-directed NÀ H bond cleavage.
Subsequent alkene insertion gives seven-membered rhodacycle
D.[16] β-Hydrogen elimination affords rhodium(III) hydride F and
reductive elimination affords enamine G (path A). Protonation
of the enamine moiety with the carboxylic acid affords
zwitterionic intermediate H and the subsequent oxycyclization
affords syn-product 3a.[17,18] Reductive elimination of D would
afford oxazinoisoindole-3,6-dione 6a (path B), but 6a was not
generated at all. Alternatively, cleavage of the vinylic CÀ H bond
affords azarhodacycle I.[19] The subsequent reductive elimination
can also afford the same enamine intermediate G along with
CpERhI complex J, which is oxidized to regenerate CpERhIII
complex E (path C).
To identify the possible reaction pathways and structures,
we performed density functional theory (DFT) calculations using
a model substrate and catalyst, (R)-2a and CpE(CO2Me)Rh(OAc)2,
respectively (Figure 4, paths A–C). A carboxylic acid on (R)-2a is
deprotonated by the rhodium catalyst to form the initial
complex IM1a with an energy gain of 6.7 kcalmolÀ 1. The
formation of a five-membered rhodacycle by an additional
coordination of the lone pair on the nitrogen atom of the
amide moiety (RhÀ N=2.23 Å, RhÀ O=2.05 Å) stabilizes this
complex. Subsequently, chelation-assistance of the carboxyl
group allows NÀ H bond cleavage to give more compact five-
membered rhodacycle IM2a [rhoda(III)oxazolidine, RhÀ N=
2.16 Å, RhÀ O=2.04 Å] than IM1a without large endothermicity
(only 1.2 kcalmolÀ 1 unstable from RT1). Intramolecular insertion
of the alkene unit (IM3a to IM4a, path A) proceeds smoothly
with an activation energy of 8.7 kcalmolÀ 1 and a large energy
gain of 16.9 kcalmolÀ 1, probably due to the strain release from
the five-membered compact rhodacycle to the seven-mem-
bered one. On the other hand, the CÀ H bond cleavage of the
alkene unit (IM3c to IM4c, path C) requires extremely high
activation energy (37.2 kcalmolÀ 1) and the thus generated
rhodacycle IM4c is unstable (ΔG=13.7 kcalmolÀ 1). This is
because this configuration (six-membered rhodacycle) involves
a large steric hindrance around rhodium(III) atom. The low
activation energy (4.1 kcalmolÀ 1) is calculated for β-hydrogen
elimination (IM5a to IM6a, path A), despite an energy loss of
19.1 kcalmolÀ 1 for conformation change by the free rotation of
the CÀ C bond (IM4a to IM5a). However, reductive elimination
from seven-membered rhodacycle (IM5b to IM6b, path B)
requires the highest activation energy of 59.3 kcalmolÀ 1 and is
thermodynamically unfavorable. Therefore, path A is considered
to be the most favorable pathway.
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only α-amino acid derivatives but also 2-aminobenzoic acid
derivative 2m could participate in this annulation to give 1,1-
oxyamination product 3m, although the yield was low (Fig-
ure 2b). Finally, the oxidative annulation of 2i could be
conducted in a preparative-scale (1.0 mmol) to give 3i in 37%
yield, which is comparable to that on a small scale (Figure 2c).
To investigate whether the present intramolecular 1,1-
oxyamination involves the aza-Wacker process, the reaction of
phenylglycine methyl ester derivative 4a was examined (Fig-
ure 3a). No conversion of 4a was observed under the optimized
conditions, and thus this reaction may involve five-membered
rhodacycle C, generated through carboxylic acid-directed NÀ H
bond cleavage. Additionally, the reaction of 2a was conducted
in the presence of an external deuterium source (AcOD) to give
deuterated product D-3a with high deuterium content of 89%
(Figure 3b). Therefore, this reaction may involve protonation in
the vinyl group.
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Furthermore, for the identification of the role of directing
groups, DFT calculations using methyl ester (R)-4a instead of
carboxylic acid (R)-2a (Figure 4, path D) were conducted. Under
neutral conditions, weak coordination of lone pair on the
nitrogen atom to rhodium(III) (RhÀ N=2.42 Å) results in the
endothermic formation of IM1d with a large energy loss of
9.5 kcalmolÀ 1 from RT2. The sequential deprotonation of NÀ H
bond to form RhÀ N bond (2.17 Å) also fails to produce the
energy gain (ΔGtotal =12.3 kcalmolÀ 1), whereas the latter proc-
Figure 3. Experimental mechanistic studies.
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Figure 4. Theoretical mechanistic studies. The changes of the relative free energies calculated at the M06/6-31g* (C, H, O, and N) and LANL2DZ (Rh) levels are
shown in kilocalories per mole.
esses (insertion and β-hydrogen elimination) are still allowed Acknowledgments
with CpERh catalyst. Therefore, the key to the success of the
present 1,1-oxyamination is the formation of stable five-
membered rhodacycle [rhoda(III)oxazolidine] IM2a. These re-
sults support the experimental finding that 4a failed to afford
5a (Figure 3a).
This work was supported partly by a Grant-in-Aid for Scientific
Research (No. JP19H00893) from JSPS (Japan). We thank Umicore
for generous support in supplying RhCl3·nH2O. A generous allot-
ment of computational resources from TSUBAME (Tokyo Institute
of Technology) is gratefully acknowledged.
In conclusion, we have established that the oxidative
intramolecular 1,1-oxyamination of alkenes with N-benzoyl
amino acids giving oxazoloisoindole-2,5-dione derivatives is
catalyzed by an electron-deficient CpERhIII complex. Experimen- Conflict of Interest
tal mechanistic studies suggested that this oxidative intra-
molecular 1,1-oxyamination proceeds through the five-mem-
bered rhodacycle [rhoda(III)oxazolidine] via carboxylic acid-
directed NÀ H bond cleavage, and the DFT calculations revealed
that the alkene insertion to this five-membered rhodacycle
followed by β-hydrogen elimination is favorable than the CÀ H
bond cleavage of the alkene unit followed by reductive
elimination.
The authors declare no conflict of interest.
Keywords: Alkenes · Amino acids · Cyclization · Oxyamination ·
Rhodium
[1] For a review involving the 1,2-oxyamination of alkenes, see: B. N.
Hemric, Org. Biomol. Chem. 2021, 19, 46–81.
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[2] For e review involving the 1,1-oxyamination of alkenes, see: S. Yang, Y.
Satoh, Y. Shibata, K. Tanaka, M. Miura, J. Org. Chem. 2013, 78, 1365–
1370; c) Y. Hoshino, Y. Shibata, K. Tanaka, Adv. Synth. Catal. 2014, 356,
1577–1585; d) H. Baars, Y. Unoh, T. Okada, K. Hirano, T. Satoh, K. Tanaka,
C. Bolm, M. Miura, Chem. Lett. 2014, 43, 1782–1784; e) Y. Takahama, Y.
Shibata, K. Tanaka, Chem. Eur. J. 2015, 21, 9053–9056; f) Y. Shibata, E.
Kudo, H. Sugiyama, H. Uekusa, K. Tanaka, Organometallics 2016, 35,
1547–1552; g) Y. Takahama, Y. Shibata, K. Tanaka, Org. Lett. 2016, 18,
2934–2937; h) Y. Takahama, Y. Shibata, K. Tanaka, Chem. Lett. 2016, 45,
1177–1179; i) R. Yoshimura, Y. Shibata, K. Tanaka, J. Org. Chem. 2018, 84,
13164–13171; j) Y. Honjo, Y. Shibata, K. Tanaka, Chem. Eur. J. 2019, 25,
9427–9432; k) R. Yoshimoto, H. Morisaka, Y. Usuki, Y. Shibata, K. Tanaka,
T. Satoh, Chem. Lett. 2020, 49, 1481–1483; l) H. Takahashi, Y. Honjo, Y.
Shibata, Y. Nagashima, K. Tanaka, Synthesis 2021, 53, ASAP, DOI:
10.1055/a-1328-6436.
1
2
3
4
5
6
7
8
9
Chen, Z. Ding, Org. Biomol. Chem. 2020, 18, 6983–7001.
[3] a) B. N. Hemric, K. Shen, Q. Wang, J. Am. Chem. Soc. 2016, 138, 5813–
5816; b) B. N. Hemric, A. W. Chen, Q. Wang, J. Org. Chem. Soc. 2019, 84,
1468–1488.
[4] H. Lei, J. H. Conway, J. Caleb, C. Cook, T. Rovis, J. Am. Chem. Soc. 2019,
141, 11864–11869.
[5] For selected reviews, see: a) G. Kaur, A. Sharma, B. Banerjee, J. Serb.
Chem. Soc. 2018, 83, 1071–1097; b) B. Banerjee, Ultrason. Sonochem.
2017, 35, 15–35; c) N. Krause, O. Aksin-Artok, M. Asikainen, V. Breker, C.
Deutsch, J. Erdsack, H.-T. Fan, B. Gockel, S. Minkler, M. Poonoth, Y.
Sawama, Y. Sawama, T. Sun, F. Volz, C. Winter, J. Organomet. Chem.
2012, 704, 1–8; d) D. J. Newman, G. M. Cragg, J. Nat. Prod. 2007, 70,
461–477.
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[6] L. D. Elliott, J. W. Wrigglesworth, B. Cox, G. C. Lloyd-Jones, K. I. Booker-
[15] Substrate 2a was converted to unidentified oligomeric products other
Milburn, Org. Lett. 2011, 13, 728–731.
[7] J. Alladoum, E. Vrancken, P. Mangeney, S. Roland, C. Kadouri-Puchot,
Org. Lett. 2009, 11, 3746–3749.
than product 3a.
[16] For examples of the intramolecular alkene insertion into the electron-
deficient (CO)NÀ RhIII bond, see: a) R. T. Yu, T. Rovis, J. Am. Chem. Soc.
2006, 128, 12370–12371; b) T. J. Martin, T. Rovis, Angew. Chem. Int. Ed.
2013, 52, 5368–5371; Angew. Chem. 2013, 125, 5476–5479; Angew.
Chem. 2013, 125, 5476–5479; Angew. Chem. Int. Ed. 2013, 52, 5368–
5371. For insertion into the (CO)NÀ IrIII bond, see: c) H. J. Conway, T.
Rovis, J. Am. Chem. Soc. 2018, 140, 135–138.
[17] This oxycyclization through the zwitterionic intermediate proceeds
diastereoselectively to afford syn-isomer. See ref 7.
[18] The NOESY experiments revealed that syn-isomers of 3j, 3k, and 3l are
[8] K. Wen, Z. Wu, B. Chen, J. Chen, W. Zhang, Org. Biomol. Chem. 2018, 16,
5618–5625.
[9] Y. Shibata, K. Tanaka, Angew. Chem. Int. Ed. 2011, 50, 10917–10921;
Angew. Chem. 2011, 123, 11109–11113; Angew. Chem. 2011, 123,
11109–11113; Angew. Chem. Int. Ed. 2011, 50, 10917–10921.
[10] For examples, see: a) T. Nagase, T. Iino, Y. Sato, T. Nishimura, Eiki, J. WO
2001014386, Mar 1, 2001; b) T. Iino, Y. Sato, T. Nishimura, M. Banba, J.
Eiki, T. Nagase, JP 2002255967, Sep 11, 2002.
[11] For an example of the palladium-catalyzed synthesis of this antidiabetic
agent, see: K. Jing, X.-N. Wang, G.-W. Wang, J. Org. Chem. 2019, 84, 161–
172.
[12] a) E. Kudo, Y. Shibata, M. Yamazaki, K. Masutomi, Y. Miyauchi, M. Fukui,
H. Sugiyama, H. Uekusa, T. Satoh, M. Miura, K. Tanaka, Chem. Eur. J.
2016, 22, 14190–14194. For a related [4+2] annulation of benzyl
alcohols with alkynes, see: b) M. Fukui, Y. Hoshino, T. Satoh, M. Miura, K.
Tanaka, Adv. Synth. Catal. 2014, 356, 1638–1644.
[13] a) Y. Honjo, Y. Shibata, E. Kudo, T. Namba, K. Tanaka, Chem. Eur. J. 2018,
24, 317–321; For related [4+2] annulations of anilides and N-(1-
Naphthyl)acetamide with alkynes, see: b) M. Fukui, Y. Shibata, Y.
Hoshino, H. Sugiyama, H. Uekusa, K. Noguchi, K. Tanaka, Chem. Asian J.
2016, 11, 2260–2264; c) J. Terasawa, Y. Shibata, M. Fukui, K. Tanaka,
Molecules 2019, 23, 3325–3336.
obtained. See the Supporting Information.
[19] For examples of the intramolecular cleavage of the vinylic CÀ H bond
with the rhodium(III) amide, see: a) S.-S. Zhang, J.-Q. Wu, X. Liu, H.
Wang, ACS Catal. 2015, 5, 210–214; b) I. S. Hassan, A. N. Ta, M. W.
Danneman, N. Semakul, M. Burns, C. H. Basch, V. N. Dippon, B. R.
McNaughton, T. Rovis, J. Am. Chem. Soc. 2019, 141, 4815–4819; c) S. Lee,
N. Semakul, T. Rovis, Angew. Chem. Int. Ed. 2020, 59, 4965–4969; Angew.
Chem. 2020, 132, 4995–4999. For the iridium(III) amide, see: d) K.
Murakami, M. Nagamoto, T. Nishimura, Chem. Lett. 2020, 49, 732–735.
For the cobalt(II) amide, see: e) L. Grigorjeva, O. Daugulis, Org. Lett.
2014, 16, 4684–4687; f) S. Tang, D. Wang, Y. Liu, L. Zeng, A. Lei, Nat.
Commun. 2018, 9, 798–804.
[14] For other examples of the CÀ H bond functionalization reactions using
complex 1, see: a) K. Morimoto, M. Itoh, K. Hirano, T. Satoh, Y. Shibata,
K. Tanaka, M. Miura, Angew. Chem. Int. Ed. 2012, 51, 5359–5362; Angew.
Chem. 2012, 124, 5455–5458; Angew. Chem. 2012, 124, 5455–5458;
Angew. Chem. Int. Ed. 2012, 51, 5359–5362; b) M. Itoh, K. Hirano, T.
Manuscript received: February 6, 2021
Revised manuscript received: March 6, 2021
Accepted manuscript online: March 9, 2021
Eur. J. Org. Chem. 2021, 1891–1895
www.eurjoc.org
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