Catalytic Intramolecular C(sp3)–H Amination of Carbamimidates

Article abstract of DOI:10.1002/ejoc.201700263

The Rh^II-catalyzed intramolecular C(sp³)–H amination of carbamimidates allowed new nitrogen heterocycles to be isolated in yields up to 99 %. The reaction was best performed in the presence of the Rh₂(esp)₂ (esp = α,α,α′,α′-tetramethyl-1,3-benzenedipropionic acid) complex by using 2,2,2-trichloroethoxysulfonyl-protected compounds. The reaction could be applied to substrates possessing a benzylic, an allylic, a propargylic, or a tertiary C(sp³)–H bond.

Full text of DOI:10.1002/ejoc.201700263

DOI: 10.1002/ejoc.201700263
Communication
C-H Amination
Catalytic Intramolecular C(sp3)–H Amination of Carbamimidates
Gwendal Grelier,[a] Romain Rey-Rodriguez,[a] Benjamin Darses,[a] Pascal Retailleau,[a] and
Philippe Dauban*[a]
Abstract: The RhII-catalyzed intramolecular C(sp3)–H amination 1,3-benzenedipropionic acid) complex by using 2,2,2-tri-
of carbamimidates allowed new nitrogen heterocycles to be chloroethoxysulfonyl-protected compounds. The reaction could
isolated in yields up to 99 %. The reaction was best performed be applied to substrates possessing a benzylic, an allylic, a
in the presence of the Rh2(esp)2 (esp = α,α,α′,α′-tetramethyl- propargylic, or a tertiary C(sp3)–H bond.
Introduction
ment of rhodium(II)-catalyzed intramolecular C(sp3)–H amin-
ation reactions. The design of the Rh2(esp)2 complex (esp =
α,α,α′,α′-tetramethyl-1,3-benzenedipropionic acid) has allowed
expansion of the scope to various substrates such as ureas,
guanidines, O-sulfamoyl-hydroxylamine derivatives, and sulf-
amides, which thereby gives rapid access to various new nitro-
gen heterocycles (Scheme 1a).[16] In the context of molecular
diversity, we decided to investigate the reactivity of carb-
amimidates as nitrene precursors (Scheme 1b). The use of
carbamimidates in catalytic intramolecular C(sp3)–H amination
has never been reported,[17,18] and it was hypothesized that
the reaction would afford cyclic compounds that were recently
described[19] and which are of potential value for medicinal
chemistry.[20] In this communication, we therefore wish to report
the rhodium(II)-catalyzed intramolecular C(sp3)–H amination of
carbamimidates to provide new heterocyclic structures in very
good yields.
A recent study of the drugs approved by the US FDA has show-
cased the paramount importance of nitrogen in organic chem-
istry. More than 80 % of small-molecule drugs contain at least
one nitrogen atom, and 59 % of them possess a nitrogen het-
erocycle.[1] Future drugs will also rely on the unique properties
of nitrogen, as suggested by the new building blocks that are
incorporated into final screening compounds.[2] The ubiquity of
nitrogen in life sciences, accordingly, remains a driving force for
organic chemists to design new amination methods.[3] Much
attention has been paid to the development of improved cata-
lytic methods for the synthesis of heterocycles that take into
account the notions of step economy, selectivity, and molecular
diversity.
The catalytic amination of C(sp3)–H bonds has emerged as a
new powerful synthetic method for the preparation of nitro-
gen-containing compounds.[4] The direct conversion of a C–H
bond into a C–N bond shortens synthetic schemes and gives
access to molecular diversity likely to open a new space for
intellectual property. In this context, much progress has been
made with the application of catalytic nitrene C(sp3)–H inser-
tions.[5] These C(sp3)–H amination reactions have been shown
to be efficiently performed with Ru,[6] Cu,[7] Ag,[8] Co,[9] Fe,[10]
Mn,[11] and Ir[12] complexes, but the most significant achieve-
ments have been reported with the use of dirhodium(II) com-
plexes.[13] Several examples of the total syntheses of complex
molecules demonstrate the unique capacity of these dinuclear
species to mediate nitrene insertions with very high levels of
efficiency and selectivity.[14]
Since Du Bois reported seminal studies with carbamates and
sulfamates for the synthesis of 1,2- and 1,3-amino alcohols, re-
spectively,[15] particular attention has been paid to the develop-
Scheme 1. Extension of the scope of the intramolecular C(sp3)–H amination
reaction.
[a] Institut de Chimie des Substances Naturelles, CNRS UPR 2301,
Univ. Paris-Sud, Université Paris-Saclay,
1, av. de la Terrasse, 91198 Gif-sur-Yvette, France
E-mail: philippe.dauban@cnrs.fr
http://www.icsn.cnrs-gif.fr/spip.php?article666&lang=en
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under http://dx.doi.org/10.1002/ejoc.201700263.
Results and Discussion
The starting carbamimidates were prepared according to a pro-
tocol inspired by the method reported by Du Bois for the syn-
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thesis of guanidines.[16b] On the basis of that study, we initially could be obtained after only 4 h of heating at 80 °C (Table 1,
focused on the use of 2,2,2-trichloroethoxysulfonyl (Tces)-pro- entry 11).
tected carbamimidates, which could be readily accessed from
chloroimidothionate 1 obtained in two steps from trichloro-
ethylsulfamate (Scheme 2). Reference substrate 2a, which was
used for our initial screening of the reaction conditions, was
isolated in 49 % yield.
We tested the reactivity of other N-protected carb-
amimidates, albeit unsuccessfully, as the N-sulfonyl- and N-alk-
oxycarbonyl derivatives proved either unstable or unreactive
under the oxidizing conditions of the intramolecular reaction
(Figure 1). The best conditions reported in Table 1 (entry 11)
were then applied to study the scope of the reaction with respect
to the alkyl side chain of N-Tces-carbamimidates 2 (Table 2).
Table 2. Catalytic intramolecular C(sp3)–H amination of carbamimidates 2.[a]
Scheme 2. Synthesis of Tces-protected carbamimidate 2a.
The first experiment in the presence of Rh2(OAc)4 (2 mol-%),
PhI(OAc)2 (1.5 equiv.), and MgO (2.5 equiv.) in benzene allowed
us to isolate the expected cyclic carbamimidate 3a in 15 % yield
(Table 1, entry 1). A rapid screening of rhodium(II) complexes
then revealed the superior reactivity of Rh2(esp)2, as cyclic prod-
uct 3a was isolated in 80 % yield after 20 h at 80 °C (Table 1,
entries 1–3).[21] With respect to the solvent, the best result was
obtained if the reaction was performed in benzene, but toluene
could provide a safer alternative, as its use allowed compound
3a to be isolated in 74 % yield (Table 1, entries 3–6). Replacing
PhI(OAc)2 by PhI(OPiv)2 (OPiv = OCOtBu) proved detrimental to
the yield (Table 1, entry 7), whereas lowering the amount of
the iodine(III) oxidant significantly decreased the overall reac-
tivity; in this case, the expected product 3a was isolated in 72 %
yield after 3 days (Table 1, entry 8). The presence of magnesium
oxide was also required to ensure optimal conversion (Table 1,
entry 9). Finally, though the intramolecular C(sp3)–H amination
could also be performed at room temperature with similar effi-
ciency (Table 1, entry 10), we found that a very similar yield
Table 1. Catalytic intramolecular C(sp3)–H amination of 2a.[a]
Entry
Catalyst
Solvent
Oxidant
(equiv.)
Yield[b]
[%]
1
2
3
4
5
6
7
8
Rh2(OAc)4
Rh2(CF3CONH)4
Rh2(esp)2
Rh2(esp)2
Rh2(esp)2
Rh2(esp)2
Rh2(esp)2
Rh2(esp)2
Rh2(esp)2
Rh2(esp)2
Rh2(esp)2
benzene
benzene
benzene
CH2Cl2
Cl2CHCHCl2
toluene
benzene
benzene
benzene
benzene
benzene
PhI(OAc)2 (1.5)
PhI(OAc)2 (1.5)
PhI(OAc)2 (1.5)
PhI(OAc)2 (1.5)
PhI(OAc)2 (1.5)
PhI(OAc)2 (1.5)
PhI(OPiv)2 (1.5)
PhI(OAc)2 (1.2)
PhI(OAc)2 (1.5)
PhI(OAc)2 (1.5)
PhI(OAc)2 (1.5)
15
48
80
48
32
74
61
72[c]
69[d]
80[e]
79[f]
9
10
11
[a] Reaction conditions, unless otherwise mentioned: 2a (1.0 equiv.), iod-
ine(III) oxidant (1.5 equiv.), RhII catalyst (2 mol-%), MgO (2.5 equiv.), solvent
(0.12
M
), 80 °C, 20 h. [b] Yield of isolated product. [c] After 3 days of reaction.
[a] Reaction conditions: 2 (1.0 equiv.), PhI(OAc)2 (1.5 equiv.), Rh2(esp)2 (2 mol-
%), MgO (2.5 equiv.), benzene (0.12 ), 80 °C, 4 h. [b] Yield of isolated product.
[d] Without MgO. [e] After 18 h at r.t. [f] After 4 h at 80 °C.
M
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Communication
which is the product of alkene oxyamination, was isolated in
54 % yield.[24] We were pleased to notice that the homoallylic
derivative 2p gave the expected allylic amine 3p, though only
in 34 % yield.[25] By contrast, the nopol-derived carbamimidate
2p afforded a ≈1:1.6 mixture of allylic amine 3q and aziridine 5.
Figure 1. Other N-protected carbamimidates.
Conclusions
We found that the rhodium-catalyzed intramolecular C(sp3)–
H amination reaction could be applied to various classes of
carbamimidates. Several aromatic substrates substituted by ei-
ther an electron-donating or an electron-withdrawing group at
the ortho or para position were converted into the correspond-
ing cyclic carbamimidates 3 with yields ranging from 32 to
80 %, following reaction at the secondary benzylic position
(Table 2, entries 1–6). In the case of substrates displaying a
tertiary site, the reaction was even more efficient, and products
3g–i were obtained in excellent yields (Table 2, entries 7–9).
Worthy of note is the stereospecificity of the intramolecular
C(sp3)–H amination with optically pure substrate 2i (see the
Supporting Information for the X-ray structure), which is in line
with that demonstrated for carbamates, sulfamates, and
other nitrene precursors.[15,16,22] The high capacity of the carb-
amimidates to undergo reaction at tertiary centers was applied
to the formation of azaspirocycles, which are currently receiving
growing attention in medicinal chemistry.[23] Spirocyclic carb-
amimidates 3j–l were thus isolated in 84–99 % yield (Table 2,
entries 10–12). Compound 3l highlights the propensity of
carbamimidate-derived nitrenes to undergo C(sp3)–H insertion
α to a heteroatom. However, the analogous reaction from sub-
strate 2m only led to 2-aminooxazole 3m, which was isolated
in 63 % yield (Table 2, entry 13). This compound is believed to
result from a first intramolecular C(sp3)–H amination step α to
the methoxy group followed by elimination of the methoxy
group. Product 3n demonstrates that carbamimidates can un-
dergo propargylic C(sp3)–H amination, though with moderate
efficiency (Table 2, entry 14).[11,13j,13n]
In conclusion, this study demonstrated that carbamimidates are
relevant nitrene precursors that allow the scope of the
rhodium(II)-catalyzed intramolecular C(sp3)–H amination reac-
tion to be enhanced. Their reaction in the presence of PhI(OAc)2
and the highly active Rh2(esp)2 (2 mol-%) complex afforded
new heterocyclic structures in yields up to 99 %. Relative to the
yields obtained with analogous carbamates, the slightly higher
yields observed with carbamimidates suggest a beneficial effect
of the imidoyl group on the reactivity of the nitrene, as previ-
ously shown with sulfonimidamides.[18] Work is in progress to
increase the molecular diversity accessible through the applica-
tion of catalytic C(sp3)–H amination.
Experimental Section
General Procedure: An oven-dried sealable tube equipped with a
stirring bar and flushed with argon was charged with acyclic carb-
amimidate 2 (1.0 equiv.), Rh2(esp)2 (2 mol-%), MgO (2.5 equiv.),
benzene, and PhI(OAc)2 (1.5 equiv.). The mixture was stirred at 80 °C
for 4 h before it was filtered through a Celite pad (CH2Cl2). The
filtrate was then concentrated under reduced pressure to afford
the crude product, which was purified by flash chromatography
(petroleum ether/EtOAc).
Acknowledgments
We wish to thank the French National Research Agency (pro-
gram no. ANR-11-IDEX-0003-02, CHARMMMAT ANR-11-LABX-
0039, and ANR-15-CE29-0014-01; fellowship to R.R.-R.), the Min-
istère de l'Enseignement Supérieur et de la Recherche (fellow-
ship to G.G.), and the Institut de Chimie des Substances Natu-
relles for their support. Support of the COST Action CA15106
“C-H Activation in Organic Synthesis” is kindly acknowledged.
We also investigated the reactivity of unsaturated substrates,
as these raise the key issue of chemoselectivity, that is, the re-
activity of the allylic C(sp3)–H bond versus that of the π bond.
However, as previously observed with various nitrene precur-
sors in the presence of dirhodium(II) tetracarboxylates,[15,16b]
low levels of chemoselectivity were observed (Scheme 3). We
first checked that the alkene of allylic substrate 2o could react
under the optimized conditions. Not surprisingly, compound 4,
Keywords: Amination · Nitrenes · Homogeneous catalysis ·
Rhodium · Nitrogen heterocycles
[1] E. Vitaku, D. T. Smith, J. T. Njardarson, J. Med. Chem. 2014, 57, 10257.
[2] F. W. Goldberg, J. G. Kettle, T. Kogej, M. W. D. Perry, N. P. Tomkinson, Drug
Discovery Today 2015, 20, 11.
[3] a) A. Ricci (Ed.), Amino Group Chemistry: From Synthesis to the Life Scien-
ces, Wiley-VCH, Weinheim, 2008; b) A. K. Yudin (Ed.), Catalyzed Carbon–
Heteroatom Bond Formation, Wiley-VCH, Weinheim, 2011.
[4] For reviews on C–H amination, see: a) H. M. L. Davies, J. R. Manning,
Nature 2008, 451, 417; b) F. Collet, R. H. Dodd, P. Dauban, Chem. Com-
mun. 2009, 5061; c) D. N. Zalatan, J. Du Bois, Top. Curr. Chem. 2010, 292,
347; d) J. L. Jeffrey, R. Sarpong, Chem. Sci. 2013, 4, 4092; e) M.-L. Louillat,
F. W. Patureau, Chem. Soc. Rev. 2014, 43, 901; f) Y. Park, Y. Kim, S. Chang,
Chem. Rev. 2017, DOI: 10.1021/acs.chemrev.6b00644.
[5] For reviews on C–H amination with nitrenes, see: a) P. Müller, C. Fruit,
Chem. Rev. 2003, 103, 2905; b) M. M. Díaz-Requejo, P. J. Pérez, Chem. Rev.
Scheme 3. Intramolecular C(sp3)–H amination of unsaturated carbamimidates.
Eur. J. Org. Chem. 2017, 1880–1883
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2008, 108, 3379; c) S. Fantauzzi, A. Caselli, E. Gallo, Dalton Trans. 2009,
5434; d) T. G. Driver, Org. Biomol. Chem. 2010, 8, 3831; e) J. Du Bois, Org.
Process Res. Dev. 2011, 15, 758; f) F. Collet, C. Lescot, P. Dauban, Chem.
Soc. Rev. 2011, 40, 1926; g) J. W. W. Chang, T. M. U. Ton, P. W. H. Chan,
Chem. Rec. 2011, 11, 331; h) J. L. Roizen, M. E. Harvey, J. Du Bois, Acc.
Chem. Res. 2012, 45, 911; i) T. Uchida, T. Katsuki, Chem. Rec. 2014, 14,
117; j) R. J. Scamp, J. W. Rigoli, J. M. Schomaker, Pure Appl. Chem. 2014,
86, 381; k) J. Buendia, G. Grelier, P. Dauban, Adv. Organomet. Chem. 2015,
64, 77.
Lebel, Chem. Eur. J. 2008, 14, 6222; i) H. Lebel, C. Spitz, O. Leogane, C.
Trudel, M. Parmentier, Org. Lett. 2011, 13, 5460; j) H. Lebel, C. Trudel, C.
Spitz, Chem. Commun. 2012, 48, 7799; k) M. Anada, M. Tanaka, N.
Shimada, H. Nambu, M. Yamawaki, S. Hashimoto, Tetrahedron 2009, 65,
3069; l) A. Nörder, P. Hermann, E. Herdtweck, T. Bach, Org. Lett. 2010, 12,
3690; m) A. Nörder, S. A. Warren, E. Herdtweck, S. M. Huber, T. Bach, J.
Am. Chem. Soc. 2012, 134, 13524; n) R. D. Grigg, J. W. Rigoli, S. D. Pearce,
J. M. Schomaker, Org. Lett. 2012, 14, 280; o) C. Liang, F. Collet, F. Robert-
Peillard, P. Müller, R. H. Dodd, P. Dauban, J. Am. Chem. Soc. 2008, 130,
343; p) C. Lescot, B. Darses, F. Collet, P. Retailleau, P. Dauban, J. Org. Chem.
2012, 77, 7232; q) J. Buendia, B. Darses, P. Dauban, Angew. Chem. Int. Ed.
2015, 54, 5697; Angew. Chem. 2015, 127, 5789; r) J. Buendia, G. Grelier,
B. Darses, A. G. Jarvis, F. Taran, P. Dauban, Angew. Chem. Int. Ed. 2016,
55, 7530; Angew. Chem. 2016, 128, 7656.
[6]
[7]
[8]
Ru complexes: a) E. Milczek, N. Boudet, S. Blakey, Angew. Chem. Int. Ed.
2008, 47, 6825; Angew. Chem. 2008, 120, 6931; b) M. E. Harvey, D. G.
Musaev, J. Du Bois, J. Am. Chem. Soc. 2011, 133, 17207; c) Y. Nishioka, T.
Uchida, T. Katsuki, Angew. Chem. Int. Ed. 2013, 52, 1739; Angew. Chem.
2013, 125, 1783.
Cu complexes: a) M. R. Fructos, S. Trofimenko, M. M. Díaz-Requejo, P. J.
Pérez, J. Am. Chem. Soc. 2006, 128, 11784; b) R. Bhuyan, K. M. Nicholas,
Org. Lett. 2007, 9, 3957; c) S. Wiese, Y. M. Badiei, R. T. Gephart, S. Mossin,
M. S. Varonka, M. M. Melzer, K. Meyer, T. R. Cundari, T. H. Warren, Angew.
Chem. Int. Ed. 2010, 49, 8850; Angew. Chem. 2010, 122, 9034.
Ag complexes: a) Z. Li, D. A. Capretto, R. Rahaman, C. He, Angew. Chem.
Int. Ed. 2007, 46, 5184; Angew. Chem. 2007, 119, 5276; b) B. P. Gòmez-
Emeterio, J. Urbano, M. M. Díaz-Requejo, P. J. Pérez, Organometallics
2008, 27, 4126; c) J. W. Rigoli, C. D. Weatherly, J. M. Alderson, B. T. Vo,
J. M. Schomaker, J. Am. Chem. Soc. 2013, 135, 17238; d) R. J. Scamp, J. G.
Jirak, N. S. Dolan, I. A. Guzei, J. M. Schomaker, Org. Lett. 2016, 18, 3014;
e) N. S. Dolan, R. J. Scamp, T. Yang, J. F. Berry, J. M. Schomaker, J. Am.
Chem. Soc. 2016, 138, 14658.
Co complexes: a) H. Lu, J. Tao, J. E. Jones, L. Wojtas, X. P. Zhang, Org. Lett.
2010, 12, 1248; b) H. Lu, H. Jiang, L. Wojtas, X. P. Zhang, Angew. Chem.
Int. Ed. 2010, 49, 10192; Angew. Chem. 2010, 122, 10390; c) H. Lu, H.
Jiang, Y. Hu, L. Wojtas, X. P. Zhang, Chem. Sci. 2011, 2, 2361; d) H. Lu, K.
Lang, H. Jiang, L. Wojtas, X. P. Zhang, Chem. Sci. 2016, 7, 6934; e) O.
Villanueva, N. Mace Weldy, S. B. Blakey, C. E. MacBeth, Chem. Sci. 2015,
6, 6672.
[14] B. Darses, R. Rodrigues, L. Neuville, M. Mazurais, P. Dauban, Chem. Com-
mun. 2017, 53, 493.
[15] a) C. G. Espino, J. Du Bois, Angew. Chem. Int. Ed. 2001, 40, 598; Angew.
Chem. 2001, 113, 618; b) C. G. Espino, P. M. Wehn, J. Chow, J. Du Bois, J.
Am. Chem. Soc. 2001, 123, 6935.
[16] a) C. G. Espino, K. W. Fiori, M. Kim, J. Du Bois, J. Am. Chem. Soc. 2004,
126, 15378; b) M. Kim, J. V. Mulcahy, C. G. Espino, J. Du Bois, Org. Lett.
2006, 8, 1073; c) D. E. Olson, J. Du Bois, J. Am. Chem. Soc. 2008, 130,
11248; d) T. Kurokawa, M. Kim, J. Du Bois, Angew. Chem. Int. Ed. 2009,
48, 2777; Angew. Chem. 2009, 121, 2815.
[17] For previous studies of alkoxyimidoylnitrenes with alkenes and arenes,
see: a) A. Subbaraj, O. Subba Rao, W. Lwowski, J. Org. Chem. 1989, 54,
3945; b) H. A. Dabbagh, W. Lwowski, J. Org. Chem. 1989, 54, 3952.
[18] Our previous studies on catalytic nitrene transfers with sulfonimidamides
revealed that they have higher reactivity than sulfonamides. See: P. H.
Di Chenna, F. Robert-Peillard, P. Dauban, R. H. Dodd, Org. Lett. 2004, 6,
4503. This observation led us to hypothesize that the imidoyl group of
sulfonimidamides could be responsible for the improved reactivity. On
the basis of this hypothesis, we supposed that we could observe the
same trend in reactivity by switching from carbamates to carbamimid-
ates.
[9]
[10] Fe complexes: a) Y. Liu, C.-M. Che, Chem. Eur. J. 2010, 16, 10494; b) S. M.
Paradine, M. C. White, J. Am. Chem. Soc. 2012, 134, 2036; c) E. T. Hen-
nessy, T. A. Betley, Science 2013, 340, 591.
[19] M. J. Campbell, F. D. Toste, Chem. Sci. 2011, 2, 1369.
[20] D. L. Boger (The Scripps Research Institute, La Jolla), PCT/US2013/
033809, 2013.
[11] Mn complexes: S. M. Paradine, J. R. Griffin, J. Zhao, A. L. Petronico, S. M.
Miller, M. C. White, Nat. Chem. 2015, 7, 987.
[21] A blank experiment showed a lack of reactivity in the absence of a
rhodium(II) complex.
[12] Ir complexes: a) M. Ichinose, H. Suematsu, Y. Yasutomi, Y. Nishioka, T.
Uchida, T. Katsuki, Angew. Chem. Int. Ed. 2011, 50, 9884; Angew. Chem.
2011, 123, 10058; b) T. Kang, Y. Kim, D. Lee, Z. Wang, S. Chang, J. Am.
Chem. Soc. 2014, 136, 4141; c) X. Xiao, C. Hou, Z. Zhang, Z. Ke, J. Lan, H.
Jiang, W. Zeng, Angew. Chem. Int. Ed. 2016, 55, 11897; Angew. Chem.
2016, 128, 12076.
[22] The stereospecific insertion of the rhodium-bound nitrene species into
the C(sp3)–H bond is in line with a concerted asynchronous mechanism
that is widely acknowledged for the intramolecular C–H amination. See
also refs.[4b,4c,5h,5k]
[23] a) G. Müller, T. Berkenbosch, J. C. J. Benningshof, D. Stumpfe, J. Bajorath,
Chem. Eur. J. 2017, 23, 703; b) K. Undheim, Synthesis 2014, 46, 1957;
c) C. M. Marson, Chem. Soc. Rev. 2011, 40, 5514.
[24] a) G. Dequirez, J. Ciesielski, P. Retailleau, P. Dauban, Chem. Eur. J. 2014,
20, 8929; b) J. Ciesielski, G. Dequirez, P. Retailleau, V. Gandon, P. Dauban,
Chem. Eur. J. 2016, 22, 9338.
[13] RhII complexes: a) K. W. Fiori, J. Du Bois, J. Am. Chem. Soc. 2007, 129,
562; b) D. N. Zalatan, J. Du Bois, J. Am. Chem. Soc. 2008, 130, 9220;
c) K. W. Fiori, C. G. Espino, B. H. Brodsky, J. Du Bois, Tetrahedron 2009,
65, 3042; d) J. L. Roizen, D. N. Zalatan, J. Du Bois, Angew. Chem. Int. Ed.
2013, 52, 11343; Angew. Chem. 2013, 125, 11553; e) R. P. Reddy, H. M. L.
Davies, Org. Lett. 2006, 8, 5013; f) B. J. Stokes, H. Dong, B. E. Leslie, A. L.
Pumphrey, T. G. Driver, J. Am. Chem. Soc. 2007, 129, 7500; g) Q. Nguyen,
K. Sun, T. G. Driver, J. Am. Chem. Soc. 2012, 134, 7262; h) K. Huard, H.
[25] Trace amounts of the aziridine were also observed, but it degraded dur-
ing purification by column chromatography on silica gel.
Received: February 21, 2017
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