Tandem catalytic C(sp3)-H amination/sila-sonogashira-hagihara coupling reactions with iodine reagents

Article abstract of DOI:10.1002/anie.201412364

A new tandem C-N and C-C bond-forming reaction has been achieved through Rh^II/Pd⁰ catalysis. The sequence first involves an iodine(III) oxidant, then the in situ generated iodine(I) by-product is used as a coupling partner. The overall process demonstrates the synthetic value of iodoarenes produced in trivalent iodine reagent mediated oxidations. I(003) is a double agent: A tandem C-N and C-C bond-forming reaction has been achieved through Rh^II/Pd⁰ catalysis. The sequence first involves an iodine(III) oxidant, then the in situ generated iodine(I) by-product is used as a coupling partner. The overall process affords complex building blocks with high yields, and demonstrates the synthetic value of iodoarenes produced in trivalent iodine reagent mediated oxidations.

Full text of DOI:10.1002/anie.201412364

Angewandte
Chemie
DOI: 10.1002/anie.201412364
Hypervalent Compounds
3
À
Tandem Catalytic C(sp ) H Amination/Sila-Sonogashira–Hagihara
Coupling Reactions with Iodine Reagents**
Julien Buendia, Benjamin Darses, and Philippe Dauban*
À
À
Abstract: A new tandem C N and C C bond-forming
reaction has been achieved through RhII/Pd0 catalysis. The
sequence first involves an iodine(III) oxidant, then the in situ
generated iodine(I) by-product is used as a coupling partner.
The overall process demonstrates the synthetic value of
iodoarenes produced in trivalent iodine reagent mediated
oxidations.
of PhI-catalyzed reactions, studies were aimed at searching
for nitrene additions with catalytic amounts of iodine, but
these were unsuccessful.[13] Accordingly, we have envisaged
an alternate solution which relies on the design of new
tandem catalytic reactions. We therefore report herein a
3
À
C(sp ) H amination/sila-Sonogashira–Hagihara coupling
sequence which enhances the synthetic value of ArI-based
iodine(III) oxidants (Scheme 1).
C
atalytic tandem reactions are efficient synthetic tools to
address the issues of molecular diversity.[1] Their development
challenges the creativity of organic chemists, such that new
functionalized molecular architectures can be accessed by
À
À
appropriate sequences of C C and C X bond-forming
reactions.[2] Tandem reactions are also relevant in the context
of sustainable chemistry because their application can offer
the opportunity to convert side-products, generated during
the first step, in a subsequent transformation of the sequen-
ce.[2b,c,3]
The last two decades have witnessed major developments
in the chemistry of hypervalent iodine compounds.[4] These
compounds are nontoxic reagents, mostly derived from
iodobenzene (PhI), which can perform selective transforma-
tions.[5] However, a major issue often pointed out in hyper-
valent iodine chemistry is the low atom economy resulting
from the generation of PhI in stoichiometric amounts. To
circumvent this drawback, processes involving either catalytic
amounts of iodine reagents[5d,6,7] or recyclable iodine com-
pounds[7a,8] have been designed. In the context of sustain-
ability, however, using the iodoarene side-products in tandem
catalysis could also be envisioned. This approach could
provide rapid access to new molecular building blocks while
reducing the production of waste.
3
À
Scheme 1. Tandem C(sp ) H amination/sila-Sonogashira–Hagihara
coupling. TMS=trimethylsilyl.
3
À
We have recently described a stereoselective C(sp ) H
amination of hydrocarbons, and it involves the chiral rhod-
ium(II) complex 1 as the catalyst and an iodine(III) reagent as
the oxidant.[14] Thus, we hypothesized that the iodobenzene
generated from our effective amination reaction could be
subsequently used in a metal-catalyzed cross-coupling. We
took inspiration from the sila-Sonogashira–Hagihara reaction
conditions[15] to investigate the one-pot combination with
Efficient atom-transfer reactions have also been achieved
with hypervalent iodine reagents.[9] Of particular relevance is
the use of iminoiodinanes as nitrene precursors in the
presence of metal complexes.[10] Recent investigations have
a catalytic nitrene transfer (Table 1). After the initial step of
C(sp ) H amination from 3a, application of the reaction
3
3
À
À
led to the discovery of efficient catalytic C(sp ) H amina-
tion[11] and alkene aziridination.[12] In line with the emergence
conditions reported by Nagasaka et al.,[15a] however, did not
prove successful (entry 1). Pleasingly, by replacing nBu4NCl
by nBu4NF (TBAF) and increasing the amount of silver
carbonate, the tandem reaction proceeded in a one-pot
manner to give the expected product 4aa in 49% yield
(entry 2). Further improvement was obtained with the
addition of a base in the reaction mixture. A rapid screening
determined that K2CO3 was the most suitable base (see
Table S1 in the Supporting Information). Thus, adding
3 equivalents of K2CO3 generated compound 4aa in 65%
yield (Table 1, entry 3). This result was improved by adjusting
the amount of TBAF to 2 equivalents (entry 4). A screening
of silver salts and palladium complexes revealed that Ag2CO3
[*] Dr. J. Buendia, Dr. B. Darses, Dr. P. Dauban
Centre de Recherche de Gif-sur-Yvette, Institut de Chimie des
Substances Naturelles, UPR 2301 CNRS
Avenue de la Terrasse, F-91198 Gif-sur-Yvette (France)
E-mail: philippe.dauban@cnrs.fr
[**] We wish to thank the French National Research Agency (program n8
ANR - 11- IDEX-0003-02 and CHARMMMAT ANR - 11-LABX-0039)
for financial support and a fellowship (J.B.). We warmly thank Dr.
Frꢀdꢀric Taran and Dr. Gael Zucchi for fruitful discussions.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201412364.
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and [Pd(PPh3)4] were the most efficient (Table S1). Interest-
ingly, decreasing the amount of palladium catalyst to 5 mol%
did not affect the yield (Table 1, entry 5). We then decided to
study the effect of copper salts in the sila-Sonogashira–
Hagihara reaction.[16] As revealed by the screening of various
copper(I) sources, their use has a beneficial effect on the yield
and copper(I) chloride proved to be the most effective (see
Table S2).[17,18] Replacing Ag2CO3 by CuCl generated 4aa in
82% yield (Table 1, entry 6). We then found that the use of an
organic base, such as DABCO, afforded 4aa in higher purity
and yields (entries 7–9). Finally, an optimal yield of 89% was
reached by running the reaction in THF at 708C (entry 10).
Additionally, application of these reaction conditions pre-
vents the formation of side-products which were observed in
the previous experiments with CuCl.[19,20]
Moreover, in all cases, the alkynes proved inert towards the
3
C(sp ) H amination reaction conditions.[24] The overall trans-
À
formation can be performed on a 2 mmol scale with equal
efficiency, even using only 0.3 mol% of the rhodium complex,
as shown in the case of 4ia.
The scope of the tandem reaction was extended to alkenes
and adamantane derivatives (Scheme 3). The reaction pro-
ceeded with excellent chemo-, regio-, and stereoselectivity to
provide the expected products with yields ranging from 62 to
82%. Importantly, the examples displayed in Schemes 2 and 3
show that the presence of a propargyl ether, a vinyl chloride
moiety, and even an ester group is well tolerated under these
reaction conditions.
Finally, we can improve the molecular diversity accessible
through this process by running the reaction with (diacetoxy)-
iodoarenes, thus, allowing the introduction of various
aromatic rings on the substrate. The iodine(III)
oxidants, substituted either by an electron-withdraw-
ing or electron-donating group, were prepared from
the corresponding iodoarenes by a simple reaction
with sodium perborate.[25] We were very pleased to
Table 1: Screening of reaction conditions for the tandem reactions.[a]
observe that the nature of these reagents do not
3
À
influence the efficiency of the C(sp ) H amination
and the palladium-catalyzed coupling. The expected
products were isolated with comparable yields in
Entry
Pd catalyst
(mol%)
Metal salt
(equiv)
Base
(equiv)
FÀ source
(equiv)
Yield
the 54–86% range (Scheme 4). Of particular interest
is the introduction of a wide range of ortho-, meta-,
[%][b]
1
2
3
4
5
6
7
8
[Pd(PPh3)4] (10)
[Pd(PPh3)4] (10)
[Pd(PPh3)4] (10)
[Pd(PPh3)4] (10)
[Pd(PPh3)4] (5)
[Pd(PPh3)4] (10)
[Pd(PPh3)4] (10)
[Pd(PPh3)4] (10)
[Pd(PPh3)4] (5)
[Pd(PPh3)4] (10)
Ag2CO3 (0.5)
Ag2CO3 (1)
Ag2CO3 (1)
Ag2CO3 (1)
Ag2CO3 (1)
CuCl (1)
CuCl (1)
CuCl (1)
CuCl (1)
CuCl (1)
–
nBu4NCl (1.5)
nBu4NF (1.5)
nBu4NF (1.5)
nBu4NF (2)
nBu4NF (2)
nBu4NF (2)
nBu4NF (2)
nBu4NF (2)
nBu4NF (2)
nBu4NF (2)
<5
49
65
74
75
and para-substituted aromatic rings as well as
a naphthyl and a thienyl ring. Thus, this methodology
highlights, for the first time, the value of iodoarene-
derived oxidants as versatile building blocks in
synthesis.[26]
In terms of the mechanism, it is worth mention-
ing that each step of the tandem process involves
iodine reagents which differ by their respective
K2CO3 (3)
K2CO3 (3)
K2CO3 (3)
K2CO3 (3)
K2CO3 (3)
DABCO (3)
DABCO (4)
DABCO (4)
DABCO (4)
82[c]
82[d]
86[d]
84[c]
89[f]
9
10[e]
3
À
valences (Scheme 5). The catalytic C(sp ) H amina-
tion, thus, relies on the generation of the metal-
lanitrene A through the reaction between the amide
2 and the iodine(III) oxidant, in the presence of the
rhodium(II) complex 1. One equivalent of the
[a] Reaction conditions: a mixture of 3a (0.2 mmol), 2 (0.24 mmol), 1 (3 mol%),
and PhI(OPiv)2 (0.28 mmol) is stirred at À358C for 72 h. A base (0.6 to 0.8 mmol),
[Pd(PPh3)4] (5 to 10 mol%), THF (1 mL), TBAF (0.6 mmol) and the silver or copper
salt (0.2 mmol) are added. The mixture is stirred at 608C. [b] After flash
chromatography. [c] Isolated in mixture with 6% of the side products. [d] Isolated in
mixture with 3% of the side products. [e] Run at 708C. [f]<1% of the side products.
DABCO=l,4-diazabicyclo[2.2.2]octane.
monovalent iodoarene is then released whereas
3
À
nitrene C(sp ) H insertion affords the compound 6.
The latter undergoes desilylation to deliver the
alkynylcopper species 7 in the presence of TBAF,
The optimized reaction conditions were applied to various
CuCl, and DABCO. The compound 7 enters the second
catalytic cycle through a transmetalation step with the
arylpalladium(II) intermediate B generated by the oxidative
addition of the palladium(0) complex to ArI. Isomerization of
C into D followed by reductive elimination, finally leads to
the expected product 4.
aromatic substrates to investigate the scope of the tandem
3
À
benzylic C(sp ) H amination/palladium-catalyzed coupling
reaction (Scheme 2). This method allows the stereoselective
preparation of functionalized conjugated systems of potential
interest for the development of optoelectronic devices such as
organic field effect transistors and organic light-emitting
diodes.[21] The expected products 4 were generally obtained as
a single isomer with yields in the 64–89% range, except in the
case of the meta-substituted derivative 4c which was isolated
in 34% yield.[22] This result, however, is in line with the 4:1
ratio of para/meta regioisomers observed with the 5-substi-
tuted indan 4b. Worthy of note is the complete chemo-
selectivity observed for the formation of 4d despite the
presence of two benzylic sites in the starting material.[23]
In conclusion, we have described a new tandem catalytic
reaction which provides an efficient solution to use the ArI
moiety generated in iodine(III)-oxidant-based processes.[27]
3
À
The sequence combines a catalytic C(sp ) H nitrene insertion
À
with a palladium-catalyzed C C cross-coupling to afford
complex nitrogenous molecules with very good yields and
complete stereoselectivity. This work highlights the value of
the iodoarene part of iodine(III) oxidants as a relevant
building block in synthesis. In addition, the process is a rare
2
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Scheme 2. Tandem reaction with aromatic substrates.
Scheme 4. Tandem reaction with various iodoarene-derived reagents.
concept of hypervalent iodine compounds as double reagents
to other types of tandem reactions.
Experimental Section
General procedure for the catalytic tandem reaction: In an oven-
dried sealable tube were introduced activated 4 ꢀ molecular sieves
(100 mg), Rh2[(S)-nta]4 (1; 0.006 mmol, 3 mol%), the S-sulfonimida-
mide 2 (0.24 mmol, 1.2 equiv) and the substrate (0.2 mmol, 1 equiv).
1,1,2,2-Tetrachloroethane (0.75 mL) and methanol (0.25 mL) were
added under argon. The tube was cooled to À788C, and PhI(OPiv)2
(0.28 mmol, 1.4 equiv) was added in one portion. The mixture was
stirred at À358C for 72 h. The tube was then allowed to warm at room
temperature. DABCO (0.8 mmol, 4 equiv), [Pd(PPh3)4] (0.02 mmol,
10 mol%), THF (1 mL) and TBAF (c = 1m in THF, 0.4 mmol,
2 equiv) were added, followed by CuCl (0.2 mmol, 1 equiv). The
solution was stirred at 708C overnight. After cooling to RT, the
resulting mixture was filtered over celite and the filtrate was
evaporated under reduced pressure. The oily residue was purified
by flash chromatography (CH2Cl2/EtOAc).
Scheme 3. Tandem reaction with alkenes and alkanes.
example of rhodium(II)/palladium(0) tandem catalysis which
is complementary to those reported with either rhodium(I) or
rhodium(III) complexes.[28] We are currently extending the
Received: December 25, 2014
Revised: February 18, 2015
Published online: && &&, &&&&
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Chemie
[22] Application of the tandem reaction to the ortho-substituted
[26] ortho-Substituted phenyliminoiodinanes have been previously
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3
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À
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3
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Communications
Hypervalent Compounds
J. Buendia, B. Darses,
P. Dauban*
&&&& — &&&&
3
À
Tandem Catalytic C(sp ) H Amination/
Sila-Sonogashira–Hagihara Coupling
Reactions with Iodine Reagents
À
I(003) is a double agent: A tandem C N
partner. The overall process affords
complex building blocks with high yields,
and demonstrates the synthetic value of
iodoarenes produced in trivalent iodine
reagent mediated oxidations.
À
and C C bond-forming reaction has been
achieved through RhII/Pd0 catalysis. The
sequence first involves an iodine(III)
oxidant, then the in situ generated iodi-
ne(I) by-product is used as a coupling
6
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