Enantioselective Synthesis of trans-2,3-Dihydro-1H-indoles Through C–H Insertion of α-Diazocarbonyl Compounds

Article abstract of DOI:10.1002/ejoc.201700412

A stereoselective synthesis of 2,3-dihydro-1H-indoles with a Rh^II-catalyzed C–H insertion is reported. The α-diazo carbonyl intermediates can be obtained by a diazo-transfer reaction of 2-aminophenylacetic acids. Optimization and kinetic studie

Full text of DOI:10.1002/ejoc.201700412

A Journal of
Accepted Article
Title: Enantioselective Synthesis of trans-2,3-Dihydro-1H-indoles
through C-H Insertion of α-Diazocarbonyl Compounds
Authors: Micol Santi, Simon T. R. Müller, Ana A. Folgueiras-Amador,
Alexander Uttry, Paul Hellier, and Thomas Wirth
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201700412
Link to VoR: http://dx.doi.org/10.1002/ejoc.201700412
Supported by

10.1002/ejoc.201700412
European Journal of Organic Chemistry
COMMUNICATION
Enantioselective Synthesis of trans-2,3-Dihydro-1H-indoles
through C–H Insertion of α-Diazocarbonyl Compounds
Micol Santi,[a] Simon T. R. Müller,[a] Ana A. Folgueiras-Amador,[a] Alexander Uttry,[a] Paul Hellier[b] and
Thomas Wirth*[a]
Abstract: A stereoselective synthesis of 2,3-dihydro-1H-indoles with
a Rh(II) catalyzed C–H insertion is reported. The α-diazo carbonyl
intermediates are obtained via a diazo-transfer reaction on 2-
aminophenylacetic acids. Optimizations and kinetic studies were
performed leading to increased yields of the diazo-transfer after
mechanistic evaluation of the side product formation. trans-2,3-
Dihydro-1H-indoles were obtained in high diasteromeric excesses
(up to 94% de) and enantioselectivites (up to 94% ee).
using Rh2(S-DOSP)4 and Rh2(S-PTTL)4 as catalysts (Scheme
1b). In both cases, the cis-products were produced in high yields
and with excellent diastereomeric and enantiomeric excesses.[10]
We report herein an efficient stereoselective synthesis for trans-
2,3-dihydro-1H-indoles from α-diazo carbonyl compounds using
Rh(II)-catalyzed intramolecular C–H insertions (Scheme 1c).
Previous work:
Buchwald et al.
R
L*CuH (4 mol%)
R
up to 94% yield
up to 98% de
up to 97% ee
Dihydroindoles (indolines) are constituents of many natural
products and biologically active compounds, such as
vinblastine,[1] physostigmine[2] and pentopril[3] (Figure 1).
a
Ar
N
Ar
N
H
CO2Me
R
Davies et al.
72% yield
94% de
Rh2(S-DOSP)4
1 mol%
Me
MeHN
O
OH
O
63% ee
N
N
Me
CO2Me
N2
O
R = c-C6H11
N
Me
H
H
N
H
b
Physostigmine
NH
MeO2C
MeO
O
R
Hashimoto et al.
CO2Me
86% yield
98% de
94% ee
OAc
OH
CO2H
N
Rh2(S-PTTL)4
1 mol%
R
CO2H
Me
H
N
O
Me CO2Me
R = Ph
O
Me
Pentopril
Vinblastine
This work:
Figure 1. Examples of natural products and synthetic drugs containing the
dihydroindole framework.
CO2R1
N2
CO2R1
R2
Rh2(R-DOSP)4
0.5 mol%
up to 92% yield
up to 94% de
up to 94% ee
c
R2
N
N
Ts
Ts
In the standard repertoire for the preparation of indolines are
4
]
metal-catalyzed aryl aminations,[
intramolecular radical-
as well as intramolecular
Scheme 1. Examples of asymmetric synthesis of heterocycles: a: Buchwald’s
asymmetric synthesis to cis-dihydroindoles; b: Rh(II)-catalyzed C–H insertion
from α-diazo carbonyl compounds to dihydrobenzofuran; c: This work on the
asymmetric synthesis of trans-dihydroindoles via C–H insertion.
5
]
mediated aryl aminations,[
carbolithiations.[6]
A
very efficient and highly stereoselective Cu-catalyzed
synthesis of cis-2,3-disubstituted indolines was recently reported
by Ascic and Buchwald (Scheme 1a).[7] Davies et al.[8] as well as
Hashimoto and co-workers[9] optimized the rhodium-catalyzed
C–H insertion for the formation of chiral dihydrobenzofurans
Diazo, and particularly α-diazo carbonyl compounds, are well
established as versatile intermediates in many chemical
transformations,[ 11 ] including C–C bond formation from the
catalytic activation of C(sp3)-H bonds.[12] The metal-catalyzed C–
H
insertion from aryl diazo acetates has been widely
[a]
M. Santi, Dr. S. T. R. Müller, A. A. Folgueiras-Amador, A. Uttry, Prof.
Dr. T. Wirth
School of Chemistry
Cardiff University
Park Place, Main Building, Cardiff CF10 3AT (UK)
E-Mail: wirth@cf.ac.uk
investigated in the last decade where chiral dirhodium(II)
complexes have been shown to be the most efficient catalysts
for the synthesis of optically active heterocycles.[13] However,
only a few reports describe indoline formation via carbene C–H
insertions.[14]
Homepage: http://blogs.cardiff.ac.uk/wirth/
We describe here the efficient synthesis of trans-dihydroindoles
starting from the commercially available 2-nitrophenylacetic acid
1 (Scheme 3). The nitro group was chemoselectively reduced
with hydrogen and Pd/C as with other reduction protocols side
products were observed. The N-tosyl group was found to more
stable than N-acetyl and N-boc derivatives (see supporting
information). Subsequently, the optimization of the diazo transfer
[b]
Dr. P. Hellier
Pierre Fabre Médicament
Parc Industriel de la Chartreuse
81106 Castres CEDEX (France)
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201700412
European Journal of Organic Chemistry
COMMUNICATION
reaction using 2a as model substrate to obtain the diazo
intermediate 3a was investigated in detail (Table 1).
reaction yielding 3a in comparable yields (Table 1, entries 6-7),
but at 65 ºC there is some decomposition of 3a and of p-NBSA
in the presence of DBU.
The solid-state structures of the product 3a and the side product
4a were also determined by X-ray diffraction analysis (Figure
2).[17] The complex 1H NMR spectrum of 4a suggests a 1:1
mixture of two rotamers due to the sterically encumbered amine
nitrogen (see supporting information).
1. AcCl, MeOH
2. H2, Pd/C
CO2Me
CO2H
NO2
3. TsCl, pyridine
4. RCH2Br, NEt3
N
R
Ts
2
1
2a: R = Ph, 69%
Scheme 2. Synthesis of starting materials 2.
Table 1. Optimization of the diazo transfer conditions.[a]
CO2Me
CO2Me
N2
CO2Me
N3
sulfonyl azide
+
N
Ph
N
Ph
N
Ph
Ts
Ts
Ts
2a
3a
4a
Figure 2. Solid state X-ray crystal structures of diazo compound 3a (left) and
of the azide 4a (right).
Sulfonyl azide
Base
(equiv.)
Reaction
conditions
3a
4a
Entry
(equiv.)
[%][b]
[%][b]
To explain better the different behaviour of 2a compared to other
aryl acetate derivatives under similar diazo transfer conditions,
the reaction progress for 2a and methyl phenylacetate 5 was
monitored by NMR spectroscopy (Scheme 3). These experi-
ments show that 2a and 5 are converted into intermediates 6
and 8, whose decomposition lead to the diazo compounds 7 and
3a, according to the mechanism reported in literature.[ 18 ]
Compared to 2a, methyl phenylacetate 5 takes longer to form
the triazene intermediate 6 with full conversion into 7 after 24 h.
As soon as 6 is formed, a rapid cleavage to the diazo compound
7 occurs. We have not isolated intermediates 6 and 8, but
similar compounds have been shown to be useful precursors for
the generation of diazo compounds under mild conditions.[19]
DBU
(1.7)
MeCN
22 °C, 24 h
1
2
p-ABSA (1.2)
36
45
0
mesyl azide
(1.2)
DBU
(1.7)
MeCN
22 °C, 24 h
0
DBU
(2.5)
MeCN
22 °C, 48 h
3
p-NBSA (2)
p-NBSA (2)
p-NBSA (2)
p-NBSA (2)
p-NBSA (2)
50
63
53
65
63
18
13
29
0
DBU
(2.5)
MeCN
22°C, 48 h
4[c]
5[d]
6[c]
7[c]
DBU
(2.5)
MeCN
22°C, 48 h
DBU
(2.5)
MeCN
45°C, 48 h
CO2Me
N2
CO2Me
p-ABSA, DBU, CD3CN
DBU
(2.5)
MeCN
65°C, 24 h
0
CO2Me
O2
S
N
5
N
N
7
[a] DBU was added to a solution of 2a and sulfonyl azide. The reaction
was quenched with sat. aq. NH4Cl. [b] Isolated yield after column
chromatography. [c] The reaction was quenched with a pH 7 phosphate
buffer solution. [d] The reaction was quenched with a sat. aq. NaHCO3.
NHAc
6
CO2Me
N2
CO2Me
p-ABSA or p-NBSA, DBU, CD3CN
3a
4a
Initially, p-acetamidobenzenesulfonyl azide (p-ABSA) was used
as transfer reagent and 1,8-diazabicyclo[5.4.0]undec-7-ene
(DBU) as base in acetonitrile since this combination has
previously been reported in the efficient synthesis of aryl diazo
acetates.[15] We also have used the same combination for the
generation of diazo compounds in flow systems.[16] However,
these conditions led to low yields and to the formation of azide
4a as unexpected side product (Table 1, entry 1). The
employment of different solvents, stronger bases such as
LiHMDS or more reactive diazo transfer reagents such as mesyl
azide (Table 1, entry 2) did not lead to any reaction (see
supporting information). However, when p-nitrobenzenesulfonyl
azide (p-NBSA) was used the product yield increased to 63%,
especially when the reaction was quenched with a pH 7
phosphate buffer rather than with ammonium chloride (Table 1,
entry 4). Higher temperatures appeared to avoid the side
N
Ph
CO2Me
O2
Ts
+
S
N
Ph
N
CO2Me
N3
N
N
Ts
2a
N
Ph
R
Ts
N
Ph
8a: R = NHAc
8b: R = NO2
Ts
Scheme 3. The kinetic experiments were performed using a 300 MHz NMR
spectrometer in CD3CN (0.5 mL).
On the contrary, 2a is completely converted into 8 within 60 min
(8a) or 10 min (8b). Due to the higher stability of the
intermediates 8, their cleavage into the diazo product 3a is slow.
The diazo derivative 3a becomes detectable only after 22 h and
is formed slowly (over 168 h), while a small amount of the azide
4a can be detected after just 1 h.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201700412
European Journal of Organic Chemistry
COMMUNICATION
Table 2. Stereoselective C–H insertion of 3a using rhodium(II) catalysts.[a]
The competition between the formation of 3a and 4a is attributed
to the decomposition of the triazene during the work-up as
previously described by Evans,[20] as the triazene intermediate
can be cleaved in two different pathways depending on the
quenching agent.
CO2Me
N2
rhodium(II)
catalyst
CO2Me
CO2Me
+
Ph
Ph
12 h
N
N
N
Ph
Ts
Ts
Ts
3a
9a
10a
In the synthesis of the starting materials 2 as shown in Scheme
2, it was possible to carry forward crude reaction mixtures with
only final column purifications. Products 2 were obtained in
moderate to good overall yields (37-82%). Most N-benzyl
derivatives (2a-k) showed very good yields (>50%) compared to
N-alkyl substrates (2l-n), which have been prepared using a
Mitsunobu reaction in the alkylation step. With the optimized
reaction conditions, the substrate scope of the diazo transfer
reaction was examined and a series of compounds 3 was
synthesized as shown in Scheme 4. Electron-donating and -
withdrawing groups are tolerated except for the nitro-substituted
derivatives (2e and 2j) which gave complex product mixtures.
ee
9a[d]
[%]
ee
10a[d]
[%]
Yield
[%][b]
9a:10a
Entry
Rh(II) catalyst
Conditions
[c]
Rh2(OAc)4
1 mol%
CH2Cl2
22 °C, 12 h
1
2
92
77
81
48
4:1
3.5:1
13:1
9:1
-
-
60
0
Rh2(S-DOSP)4
CH2Cl2
22 °C, 12 h
41
83
75
72
58
11
86
73
1 mol%
Rh2(R-DOSP)4
n-C6H14
22 °C, 12 h
3
1 mol%
Rh2(R-DOSP)4
n-C6H14
0 °C, 12 h
4
0
1 mol%
CO2R1
CO2R1
N2
p-NBSA, DBU
Rh2(S-DOSP)4
cyclohexane
22 °C, 12 h
full
conv.
5[e]
9.3:1
1:1.1
1:4
7
1 mol%
MeCN, 45 °C, 24 h
N
R2
N
R2
Ts
Ts
Rh2(R-PTAD)4
n-C6H14
22 °C, 12 h
6
18
63
82
82
40
4
1 mol%
2
3
3c: X = 4-OMe, 52%
3d: X = 4-CF3, 37%
3e: X = 4-NO2, 0%
3f: X = 4-Me, 39%
3g: X = 3-Me, 55%
3h: X = 2-Ph, 75%
3i: X = 2-Me, 42%
3j: X = 2-NO2, traces
CO2Me
N2
CO2Me
N2
CO2iPr
Rh2(S-PTTL)4
1 mol%
n-C6H14
22 °C, 12 h
7
N2
N
N
Ph
N
Ph
Rh2(R-DOSP)4
0.5 mol%
n-C6H14
22 °C, 24 h
Ts
8
11:1
48:1
0
Ts
Ts
X
3a: 69%
3b: 42%
Rh2(R-DOSP)4
0.5 mol%
n-C6H14
0 °C, 24 h
9
n.d.
CO2Me
CO2Me
N2
CO2Me
N2
N2 Br
[a] The reactions were performed on 0.12 mmol scale. [b] 9a + 10a isolated
yield. [c] Determined by 1H NMR. [d] Determined by HPLC. [e] Performed on
0.02 mmol scale, yield determined by 1H NMR.
N
N
Ph
N
X
Ts
Ts
Ts
3k: 50%
3m: X = C5H11, 41%[a]
3n: X = sec-butyl, 33%[a]
3l: 24%[a]
Table 3. Substrate scope of 1,2-dihydro-1H-indoles.[a]
Scheme 4. Scope of the diazo-transfer reaction. [a] Yield determined by 1H
NMR.
CO2R1
CO2R1
R2
Rh2(R-DOSP)4
0.5 mol%
N2
R2
n-hexane
N
N
22 ºC, 12 h
Ts
Ts
Reasonable yields of the diazo compounds 3 have been
obtained and the best conditions for the subsequent
enantioselective C–H insertions to obtain the dihydroindole
target compounds were then evaluated. Initial screening of
catalysts and reaction conditions was performed with substrate
3a using Rh2(DOSP)4, Rh2(PTAD)4 and Rh2(PTTL)4 as well-
known catalysts for this type of C–H insertions.
Among all the screened conditions, the highest ee was achieved
using Rh2(DOSP)4 as chiral catalyst at room temperature in n-
hexane giving 11:1 dr, 86% ee (Table 2, entry 8). Surprisingly,
3
9
Yield
(%)[b]
Entry
1
9
9:10[c]
ee% [d]
CO2Me
Ph
9a
82
62
11:1
86
N
Ts
CO2iPr
Ph
9b
2
3
2.2:1
35:1
35
66
performing the reaction at lower temperature showed
a
N
Ts
decrease in enantioselectivity, despite a significant improvement
on the diastereomeric ratio (Table 2, entry 9).
The optimized reaction conditions were then used to synthesize
9a-k. The dihydroindoles 9 were typically obtained in good yields
and in good to excellent enantiomeric excesses. (Table 3).
CO2Me
80[e]
9c
OMe
N
Ts
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201700412
European Journal of Organic Chemistry
COMMUNICATION
the crude reaction mixture purified via flash column chromatography to
afford product 3.
CO2Me
9d
4
5
82
37
5:1
80
94
CF3
N
Ts
Molecular sieves (3 Å, 1.2 g), Rh2(R-DOSP)4 (4.4 mg, 0.002 mmol, 1
mol%) were dissolved in dry n-hexane (10 mL). Diazo compound 3 (0.23
mmol) was added and the reaction mixture was stirred at 22 °C under
argon until all diazo compound was consumed (TLC). The reaction
mixture was passed through a short silica plug which was washed with
CH2Cl2 (3 x 5 mL). The reaction mixture was concentrated in vacuo and
purified via column chromatography to afford dihydroindole 9.
CO2Me
9e
13:1
N
Ts
Ph
CO2Me
9f
9g
9h
9i
6
7
8
9
86
73
92
48
8:1
8:1
64
71
42
75
N
Ts
Acknowledgements
CO2Me
Financial support by Pierre Fabre, France, and the School of
Chemistry, Cardiff University, is gratefully acknowledged. We
thank the EPSRC National Mass Spectrometry Facility,
Swansea, for mass spectrometric data.
N
Ts
CO2Me
14:1
6:1
N
Ts
Keywords: Diazo compounds • azide • dihydroindole • C–H
CO2Me
insertion • rhodium
N
Ts
Br
[1] a) H. Ishikawa, D. A. Colby, S. Seto, P. Va, A. Tam, H. Kakei, T. J. Rayl, I.
Hwang, D. L. Boger, J. Am. Chem. Soc. 2009, 131, 4904-4916; b) S.
Yokoshima, H. Tokuyama, T. Fukuyama, Chem. Rec. 2010, 10, 101-118.
[2] a) T. Bui, S. Syed, C. F. Barbas III, J. Am. Chem. Soc. 2009, 131, 8758-
8759; b) G. Pandey, J. Khamrai, A. Mishra, Org. Lett. 2015, 17, 952-955.
[3] A. Rakhit, M. E. Hurley, V. Tipnis, J. Coleman, A. Rommel, H. R. Brunner,
J. Clin. Pharmacol. 1986, 26, 156-164.
[4] a) G. Evano, N. Blanchard, M. Toumi, Chem. Rev. 2008, 108, 3054-3131;
b) J. P. Wolfe, R. A. Rennels, S. L. Buchwald, Tetrahedron 1996, 52,
7525-7546; c) B. H. Yang, S. L. Buchwald, Org. Lett. 1999, 1, 35-38.
[5] J. N. Johnston, M. A. Plotkin, R. Viswanathan, E. N. Prabhakaran, Org.
Lett. 2001, 3, 1009-1011.
CO2Me
Ph
10
11
53
7:1
33
48
9j
N
Ts
CO2Me
64
>99:1
9k
N
Ts
[6] a) D. W. Zhang, L. S. Liebeskind, J. Org. Chem. 1996, 61, 2594-2595; b)
W. F. Bailey, X. L. Jiang, J. Org. Chem. 1996, 61, 2596-2597; c) S. Anas,
H. B. Kagan, Tetrahedron: Asymmetry 2009, 20, 2193-2199; d) D. Liu, G.
Zhao, L. Xiang, Eur. J. Org. Chem. 2010, 3975-3982.
[a] Reactions performed according to the conditions shown in
Table 2, entry 8. [b] Combined yield of 9 + 10. [c] Determined by 1H
NMR. [d] Determined by HPLC. [e] 1 mol% catalyst used.
[7] E. Ascic, S. L. Buchwald, J. Am. Chem. Soc. 2015, 137, 4666-4669.
[8] H. M. L. Davies, M. V. A. Grazini, E. Aouad, Org. Lett. 2001, 3, 1475-
1477.
[9] H. Saito, H. Oishi, S. Kitagaki, S. Nakamura, M. Anada, S. Hashimoto,
Org. Lett. 2002, 4, 3887-3890.
A bulkier ester seemed to have a negative impact on the
asymmetric cyclization with a drop of both de and ee (9b). Both
electron-donating and electron-withdrawing groups showed
good conversion and stereoselectivity affording 9c-h in good ee
under the optimized reaction conditions. On the other hand, 2-
substituted aryl derivatives 9e and 9i were obtained with 72% de
and >75% ee, but a slower conversion was observed.
[10] R. P. Reddy, G. H. Lee, H. M. L. Davies, Org. Lett. 2006, 8, 3437-3440.
[11] G. Maas, Angew. Chem. Int. Ed. 2009, 48, 8186-8195.
[12] a) S. M. Nicolle, W. Lewis, C. J. Hayes, C. J. Moody, Angew. Chem. Int.
Ed. 2016, 55, 3749-3753; b) M. Peña-López, M. Beller, Angew. Chem.
Int. Ed. 2017, 56, 46-48.
[13] a) T. Ye, M. A. McKervey, Chem. Rev. 1994, 94, 1091-1160; b) M. P.
Doyle, M. A. McKervey, T. Ye, in Modern Catalytic Methods for Organic
Synthesys with Diazo Compouds: From Cyclopropanes to Ylides, Wiley,
New York, 1998; c) H. M. L. Davies, A. M. Walji in Modern Rhodium-
Catalyzed Organic Reactions, Wiley-VCH, Weinheim, 2005, pp. 301-340.
[14] a) S. Lee, H.-J. Lim, K. L. Cha, G. A. Sulikowski, Tetrahedron 1997, 53,
16521-16532; b) G. Sulikowski, S. Lee, Tetrahedron Lett. 1999, 40, 8035-
8038.
In conclusion, we have developed a new synthetic pathway
to afford trans-2,3-dihydro-1H-indoles from α-diazocarbonyl
precursors in good yields and with high enantioselective
excesses using a stereoselective Rh(II)-catalyzed C–H insertion.
[15] a) H. M. L. Davies, W. R. Cantrell, K. R. Romines, J. S. Baum, Org.
Synth. 1991, 70, 93; b) H. M. L. Davies, M. V. A. Grazini, E. Aouad, Org.
Lett. 2001, 3, 1475-1477; c) D. F. Taber, R. B. Sheth, P. V. Josh, J. Org.
Chem. 2005, 70, 2851-2854.
Experimental Section
[16] a) S. T. R. Müller, A. Murat, D. Maillos, P. Lesimple, P. Hellier, T. Wirth,
Chem. Eur. J. 2015, 21, 7016-7020; b) S. T. R. Müller, A. Murat, P.
Hellier, T. Wirth, Org. Process Res. Chem. 2016, 20, 495-502.
[17] CCDC-1441276 (3a), CCDC-1441277 (4a) and CCDC-1441275 (9a)
contain the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
A solution containing the ester 2 (1 mmol) and p-NBSA (456 mg, 2 mmol)
in CH3CN (4 mL) was cooled to 0 °C. DBU (374 µL, 2.5 mmol) was
added dropwise. The reaction was stirred for 48 h at room temperature
(or 45 °C). After completion (TLC), the reaction mixture was cooled to
0 °C and a pH 7 phosphate buffer (10 mL) was added. The mixture was
extracted with CH2Cl2 (2 x 20 mL) and the combined organic fractions
were washed with pH 7 phosphate buffer (10 mL) and brine (15 mL) and
dried over MgSO4. The solvent was evaporated in vacuo at 30 °C and
[18] M. Regitz, Angew. Chem. Int. Ed. 1966, 5, 681-682.
[19] a) M. Schroen, S. Bräse, Tetrahedron 2005, 61, 12186-12192; b) E. L.
Myers, R. T. Raines, Angew. Chem. Int. Ed. 2009, 48, 2359-2363.
[20] D. A. Evans, T. C. Britton, J. A. Ellman, R. L. Dorow, J. Am. Chem. Soc.
1990, 112, 4011-4030.
This article is protected by copyright. All rights reserved.

10.1002/ejoc.201700412
European Journal of Organic Chemistry
COMMUNICATION
Entry for the Table of Contents
COMMUNICATION
M. Santi, S. T. R. Müller, A. A.
Folgueiras-Amador, A. Uttry, P. Hellier,
T. Wirth*
Page No. – Page No.
Enantioselective Synthesis of trans-
2,3-Dihydro-1H-indoles through C–H
Insertion of α-Diazocarbonyl
Compounds
Azides vs. Diazos: The competition in the diazo-transfer was resolved which
allowed the development of a highly selective synthesis of trans-indolines.
This article is protected by copyright. All rights reserved.