Photocatalyzed Amidoarylation of 1,3-Butadiene

Article abstract of DOI:10.1002/adsc.202000071

1,3-Butadiene is involved in a photocatalyzed amidoarylation reaction that allows the synthesis of N-allyl amides. The reaction was evaluated on a wide range of aryl diazonium salts and nitriles as co-reactants. Selectivity issues were studied from the help of a computational approach. (Figure presented.).

Full text of DOI:10.1002/adsc.202000071

Title: Photocatalyzed Amidoarylation of 1,3-Butadiene
Authors: Cyrille Gosset, Aurélien Moncomble, Clément Dumont,
Sylvain Pellegrini, Till Bousquet, Mathieu Sauthier, and Lydie
Pelinski
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10.1002/adsc.202000071
Advanced Synthesis & Catalysis
UPDATE
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
Photocatalyzed Amidoarylation of 1,3-Butadiene
Cyrille Gosset,† Aurélien Moncomble,‡ Clément Dumont,† Sylvain Pellegrini,† Till
Bousquet,†* Mathieu Sauthier† and Lydie Pélinski†
†
Univ. Lille, CNRS, Centrale Lille, ENSCL, Univ. Artois, UMR 8181, Unité de Catalyse et Chimie du Solide, F-59000 Lille,
France
‡ Univ. Lille, CNRS, UMR 8516 – LASIR – Laboratoire de Spectrochimie Infrarouge et Raman, F-59000 Lille, France
Tel: (+33) 3 74 95 13 19. Fax: (+33) 3 20 43 65 85; email: till.bousquet@univ-lille1.fr
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.((Please
delete if not appropriate))
Abstract. 1,3-Butadiene is involved in a photocatalyzed
Table 1. Optimization of the Reaction Conditions
amidoarylation reaction that allows the synthesis of N-
allyl amides. The reaction was evaluated on a wide range
of aryl diazonium salts and nitriles as co-reactants.
Selectivity issues were studied from the help of a
computational approach.
Keywords: Visible-light-promoted photocatalysis; 1,3-
butadiene; Diazonium salts;
Entry Variation from the standard
conditions
Yield (%)a
(l:b ratio)
75 (1:2.8)
51 (1:3.5)
1b
2
None
[Ir(dtbbpy)(ppy)2]PF6 as
photocatalyst
Catalytic functionalization of 1,3-dienes has
provided a wide range of chemical building blocks of
great importance in organic chemistry. 1,3-Butadiene
is the simplest member of the series of conjugated
dienes. Its annual production of over 12Mt is
essentially dedicated to the production of synthetic
rubbers and high-added value fine chemicals. This
diene is currently obtained as a side product of
ethylene production by oil cracking. Alternatively, in
a global context oriented towards the valorization of
bio-based chemicals, it has long been established that
1,3-butadiene could be formed by biomass conversion.
In particular, the two main industrially proven
technology known as Lebedev and Ostromislensky
processes are based on the conversion of ethanol.
1,3-Butadiene is a versatile and remarkable C4
platform molecule for a large number of catalytic
transformations.[1-21] Among those, metal-catalyzed
3c
4c
5c
6c
7
Eosin Y as photocatalyst
Fluorescein as photocatalyst
Rhodamine B as photocatalyst
Rhodamine 6G as photocatalyst
0.5 mol % Ru(bpy)3Cl2
0.2 mol % Ru(bpy)3Cl2
0.1 mol % Ru(bpy)3Cl2
2 equiv. of H2O
traces
traces
traces
traces
73 (1:2.8)
57 (1:2.2)
50 (1:2.7)
64 (1:3.5)
46 (1:4.6)
51 (1:3.2)
66 (1:2.4)
59 (1:2.8)
60 (1:3.5)
46 (1:4.3)
0
8
9
10
11
12
13
14
15
16
17
18
5 equiv. of H2O
25.4 equiv of 1,3-butadiene
6.4 equiv of 1,3-butadiene
3.8 equiv of 1,3-butadiene
5 h reaction time
40 h reaction time
In absence of catalyst
In absence of light
0
aIsolated yields. bReaction conditions: 1a (0.45 mmol), 1,3-
multicomponent
reactions
are
useful
and
butadiene
(5.7
mmol),
H2O
(0.45
mmol),
straightforward synthetic approaches to provide
difunctionnalized diene derivatives, in particular for
arylative transformations.[22-28] Besides, over the past
decade, visible light photoredox catalysis has
continued to generate an impressive interest. The use
of visible light to promote reactions represents a very
promising alternative. Since the revival of this field in
2008, various photoredox organic transformations
have been highlighted. Surprisingly, only two articles
have scarcely described the use of 1,3-butadiene
under photocatalytic initiation.
Ru(bpy)3Cl2.6H2O (1 mol %) in acetonitrile (2 mL) were
irradiated using a 11 W LED (λmax = 447 nm). Irradiation
(LED λmax = 530 nm).
c
In 2017, T. Rovis has thus reported the
hydroaminoalkylation of conjugated dienes using a
unified cobalt and photoredox catalytic system.[29] In
2018, T. Yoon has performed [3+2] cycloaddition
with various alkenes including 1,3-butadiene by a
1
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10.1002/adsc.202000071
Advanced Synthesis & Catalysis
tandem Lewis acid / photoredox catalysis.[30] As such,
the transformation of 1,3-butadiene in a context of
photocatalysis is, to date, limited to scope studies in
organic chemistry. Photocatalytic transformations of
1,3-butadiene would open new valorization pathways
for this industrially relevant molecule.
Despite of the steric hindrance, iPrCN and tBuCN
were also efficiently reacted thus affording 2ac and
2ad with respectively 55% and 33% yield. Finally,
whereas monochloroacetonitrile was converted in 2af
with 60% yield, the trichlorinated derivative proved to
be inert.
In this context and inspired by a tandem
photoredox Meerwein-Ritter reaction described by B.
König on styrene derivatives,[31] we now describe
herein a photocatalyzed amidoarylation of 1,3-
butadiene.
Table 2. Scope of the Amidoarylation Reactiona
The 4-methoxybenzenediazonium tetrafluoroborate
1a was chosen as model substrate to explore the
feasibility of the reaction in the presence of 1,3-
butadiene and water in acetonitrile as solvent (Table
1). Satisfyingly, in the presence of 1 mol % of
Ru(bpy)3Cl2, the reaction led to the linear/branched-
adducts l-2a/b-2a with 75 % yield and a 1:2.8 ratio
(entry 1). The yield in 2a decreased to 51% when the
reaction was catalyzed with [Ir(dtbbpy)(ppy)2]PF6
(entry 2). Only traces of product were observed when
the transformation was initiated with various xanthene
dyes as organophotocatalysts (entries 3-6). Although
the yield remained stable in the presence of 0.5 mol %
of Ru(bpy)3Cl2 (entry 7), lower catalyst loadings led
Entry Reagent
R
Product Yield (%)
(l:b-ratio)
1
2
3
75 (1:2.8)
77 (1:2.4)
57 (1:1.6)
1a
1b
1c
4-OMe
4-OPh
3,4-
OCH2O
4-Ph
4-Me
3,4-Me
4-iPr
H
4-F
4-Br
4-NO2
4-CO2Me
3-NO2
3-OMe
2a
2b
2c
4
4
5
70 (1:1.9)
72 (1:2.4)
60 (1:2.4)
61 (1:1.9)
61 (1:1.8)
70 (1:1.9)
70 (1:1.3)
61 (1:1.7)
60 (1:1.2)
31 (1:1.9)
37 (1:1.1)
1d
1e
1f
2d
2e
2f
2g
2h
2i
2j
2k
2l
6
7
8
1g
1h
1i
to
a
significantly reduced efficiency of the
9
1j
transformation (entries 8, 9). In addition, the yield
was affected when the amount of water was increased
(entries 10, 11). To conclude this optimization set of
experiments, it was found that 12.7 equivalents of
1,3-butadiene was optimal for the transformation
(entry 1 vs entries 12-14) and the reaction has to run
for 16 h (entry 1 vs entries 15, 16). It is worth
noticing that no Z-isomer was observed on the linear
product linear-2a. Last but not least, control
experiments demonstrated the strict requirement of
both catalyst and light for the reaction to occur
(entries 17-18).
Following this preliminary study, the optimized
conditions for the photocatalyzed amidoarylation
were 1 mol % of Ru(bpy)3Cl2, 12.7 equivalent of 1,3-
butadiene, 1 equivalent of water, a 0.23 M
concentration of aryldiazonium salt and irradiation
during 16 h with a blue LED (λmax = 447 nm, 11W).
The scope of the reaction was then extended and
evaluated on diversely substituted aryl diazonium
tetrafluoroborate salts (Table 2). From this study, it
was observed that electron withdrawing as well as
donating groups are tolerated in this photoredox
process and variously meta- or para-substituted
phenyl diazonium salts allowed the synthesis of
allylic N-allylamides with 57-77% yields. Two
exceptions are the meta-nitro and the meta-methoxy
phenyldiazonium salts with lead to the formation of
compounds 2m and 2n with 31 and 37% yields
respectively.
10
11
12
13
1k
1l
1m
1n
2m
2n
aReaction conditions: 1 (0.45 mmol), 1,3-butadiene (5.7
mmol), H2O (0.45 mmol), Ru(bpy)3Cl2.6H2O (1 mol %) in
acetonitrile (2 mL) were irradiated using a blue 11 W LED
(λmax = 447 nm).
Table 3. Screening of Nitrilesa
Entry Nitrile
Product
Yield (%)b
(l:b-ratio)
75 (1:2.8)
57 (1:4.5)
55 (1:4)
33 (1:3.8)
0 (-)
60 (1:3.8)
46 (1:4.3)
1
2
3
4
5
6
7
MeCN
EtCN
iPrCN
tBuCN
CCl3CN
CH2ClCN
PhCN
2a
2ab
2ac
2ad
2ae
2af
2ag
aReaction conditions: 1a (0.45 mmol), 1,3-butadiene (5.7
mmol), H2O (0.45 mmol), Ru(bpy)3Cl2.6H2O (1 mol %) in
nitrile (2 mL) were irradiated using a blue 11 W LED
(λmax = 447 nm). bIsolated yields.
The mechanism proposed for this reaction is
described in the scheme 1 with the aryl diazonium salt
1a. The absorption of a photon promotes the
2+
Furthermore, starting from diazonium 1a, various
nitriles were evaluated in the reaction (Table 3).
Propionitrile and benzonitrile were respectively
converted in 2ab and 2ag with 57% and 46% yield.
photocatalyst Ru(bpy)3
into an excited state
Ru(bpy)32+* able to reduce the aryl diazonium into the
corresponding aryl radical. Addition of the latter onto
2
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10.1002/adsc.202000071
Advanced Synthesis & Catalysis
1,3-butadiene leads to the allylic radical which upon
intermediate. Further experiments are ongoing to
improve the yield of this relevant reaction.
3+
oxidation with Ru(bpy)3
provides the allylic
carbocation. Addition of the acetonitrile onto the
primary or secondary carbocation followed by a Ritter
reaction in presence of water furnished the linear or
branched acetamides. Mechanistically, it is of interest
to note that aside from the expected product, in some
cases, trace amounts of side products were identified
by mass spectroscopy (scheme 2).[32] As such, the
allylic
From the amidoarylation process, it was observed
that the branched isomer was always favored over the
linear one. To rationalize this selectivity issue, a
computational study was undertaken on the formation
of 2a, 2h and 2l. These products formation were
selected to cover the whole electronic span from
electron-donating to electron-withdrawing groups. As
a first postulate, we assumed that the reactivity of the
allylic cationic intermediate toward a nucleophile
such
aReaction conditions: 1c (0.45 mmol), 1,3-butadiene (5.7
mmol), Ru(bpy)3Cl2.6H2O (1 mol %) in acetonitrile (2 mL)
were irradiated using a blue 11 W LED (λmax = 447 nm).
Scheme 3. Dihydroisoquinoline formationa
Scheme 1. Proposed Mechanism
Scheme 2. Side products formation
Figure 1. Relative energy calculated against the value of
the bond angle Ar-C-C+
alcohol derivative 3 and diaryl adduct 5 would result
from the addition of a molecule of water or anisole[33]
respectively onto the allylic carbocation. Furthermore,
trace amounts of C-8 products 4 and 6 resulting from
the addition of one molecule of butadiene to the
allylic carbocation were observed. It is worth noticing
that neither polybutadienes nor higher oligomers were
obtained during this process. This is consistent with a
fast reaction of the cation with the nitrile.
Interestingly, when the reaction was performed
with the methylenedioxy-containing adduct 1c,
besides the formation of 2c (Table 2, entry 3), 25 %
of 3,4-dihydroisoquinoline 7 was isolated as well.
Conducting the reaction in absence of water led to
increase the yield of 7 to 50 % (Scheme 3). This
product results from the Friedel-Crafts addition of the
electron rich aromatic ring to the nitrilium
Figure 2: Fukui function (isovalue = 0.0015 au) for the
intermediate originating from 1e
as acetonitrile can be a clue of the regioselectivity.
However, during the geometry optimization of these
three structures, an interesting issue was encountered
as several computations led to the formation of a
3
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10.1002/adsc.202000071
Advanced Synthesis & Catalysis
bridge arylium intermediate. This surprising result
was not confirmed by experimental results.[34]
Therefore, a more careful examination of the
geometries was processed and the energy of the
intermediate molecule was computed against the
value of the bond angle Ar-C-C+. The obtained curves
are depicted in Figure 1.
An interesting trend is observed where the optimal
angle decreases with the increase of the electron-
donating nature of the aryl substituent. This
observation is consistent as the electron donating
character increases the electron density on the ipso
carbon (Cipso) of the benzene ring. This is supported
by the span of computed AIM charges on this atom,
ranging from ‒0.026 for the intermediate originating
from 2a to ‒0.019 for the one from 2l (see Supporting
information for more details). Thus, the Coulomb
interaction between this latter and allylic carbocation
(C+) drives the value of the angle. This interaction
could be a first explanation to the aforementioned
regioselectivity of the reaction. Indeed, to enhance the
Cipso–C+ interaction, the cationic character of C+ could
be enforced, that would lead to an increased
significance of the related mesomer form.
With the aim to confirm this assumption, the
electrophilic Fukui function f+(r) for the cationic
intermediates was calculated.[35] It has been computed
using a finite difference method, and the result of this
computational analysis in the case of the intermediate
originating from 1h is depicted in Figure 2.[36]
As result of this computation study, the Fukui
function is in line with the stabilizing Coulomb
interaction formulated above. Indeed, the lobe of non-
terminal allylic carbocation is oriented towards the
ipso carbon of the benzene moiety. Consequently, the
volume of the lobe and thus the cationic character of
this carbocation is confirmed to be higher than the
terminal allylic carbocation.
salt (1 eq, 0.45 mmol), Ru(bpy)3Cl2 (3.3 mg, 1 mol%,
0.005 mmol), acetonitrile (2 mL) and water (8.5 µL, 1
eq, 0.45 mmol). After 16h under 11 W blue light
irradiation, the crude product was transfered into a
round-bottom flask and concentred by evaporation.
Both linear and branched product were separated and
isolated by column chromatography on silica gel
(from DCM to DCM/AcOEt 80/20).
Acknowledgements
Chevreul institute (FR 2638), Ministère de l’Enseignement
Supérieur et de la Recherche, Région Nord – Pas de Calais and
FEDER are acknowledged for supporting and funding this work.
This work was granted access to the HPC resources of CINES
(Centre Informatique National de l’Enseignement Superieur) and
IDRIS (Institut du Developpement et des Ressources en
Informatique Scientifique) under the allocations A0050806933
made by GENCI (Grand Equipement National de Calcul Intensif).
We also would like to thank Romain Jooris and Céline Delabre
for their technical support.
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In conclusion, we have developed a straightforward
visible light photoinduced amidoarylation reaction
of 1,3-butadiene. This multicomponent reaction yields
-allylamides from a good range of aryl diazonium
salts and nitriles. We believe that this process
represents an opening wedge in the valorization of
1,3-butadiene through photocatalyzed transformation.
Interestingly,
it
was
found
that
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(at -20 °C) Schlenk flask containing the diazonium
4
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10.1002/adsc.202000071
Advanced Synthesis & Catalysis
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[32] For clarity, only the linear products were represented.
[33] Anisole was supposedly formed from the hydrogen
atom transfer reaction between the solvent and the aryl
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[34] No product resulted from this intermediate was
observed.
[35] This function localizes the electrophilic part of the
molecules (e.g. those that bear the most important part
of the increase of the electron density if the number of
electron increases). For this purpose, this function is
defined for each point of the space from the electron
density ρ(r) and from the number of electrons N
휕휌(푟⃗)
+( )
according to the equation: 푓 푟⃗ = (
)
휕푁
푣,푁>푁
0
[36] A similar representation was obtained for the
intermediate originating from 1d (see supporting
information).
5
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10.1002/adsc.202000071
Advanced Synthesis & Catalysis
COMMUNICATION
Photocatalyzed Amidoarylation of 1,3-Butadiene
Adv. Synth. Catal. Year, Volume, Page – Page
Cyrille Gosset, Aurélien Moncomble, Clément
Dumont, Sylvain Pellegrini, Till Bousquet,*
Mathieu Sauthier and Lydie Pélinski
This article is protected by copyright. All rights reserved.
6