Visible-Light-Mediated Hydroxycarbonylation of Diazonium Salts

Article abstract of DOI:10.1002/adsc.201800532

A visible light-promoted catalytic photoredox hydroxycarbonylation was achieved on aryl diazonium salts whether preformed or generated in situ from the corresponding anilines. This strategy allows a straightforward access to a variety of carboxylic acids under mild conditions. (Figure presented.).

Full text of DOI:10.1002/adsc.201800532

Title: Visible-Light-Mediated Hydroxycarbonylation of Diazonium Salts
Authors: Cyrille Gosset, Sylvain Pellegrini, Romain Jooris, Till
Bousquet, and Lydie Pélinski
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10.1002/adsc.201800532
Advanced Synthesis & Catalysis
UPDATE
DOI: 10.1002/adsc.201((will be filled in by the editorial staff))
Visible-Light-Mediated Hydroxycarbonylation of Diazonium
Salts
Cyrille Gosset, Sylvain Pellegrini, Romain Jooris, Till Bousquet* and Lydie Pelinski
Univ. Lille, CNRS, Centrale Lille, ENSCL, Univ. Artois, UMR 8181, Unité de Catalyse et Chimie du Solide, 59000 Lille,
France
Tel: (+33) 3 20 43 48 93. 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))
chemistry, it remains a highly attractive C1 building
block.[7] Keeping in mind that it can be safely handled
Abstract. A visible light-promoted catalytic photoredox
hydroxycarbonylation was achieved on aryl diazonium
salts whether preformed or generated in situ from the
both
at
the
laboratory
and
corresponding anilines. This strategy allows
a
straightforward access to a variety of carboxylic acids
under mild conditions.
Keywords:
Visible-light-promoted
photocatalysis;
Carbonylation; Diazonium salts; Carboxylic acids
Over the past decade, visible light photoredox
catalysis has continued to generate an impressive
interest.[1] In an international context oriented
towards the development of sustainable processes, the
use of visible light as an inexhaustible source of
energy to promote reactions represents a very
promising alternative. Since the revival of this field,[2]
a
great
number
of
photoredox
organic
transformations has been highlighted including
catalytic carbonylation reactions.[3] In 2015, the
groups of Jacobi von Wangelin and Xiao reported
independently the first alkoxycarbonylation catalyzed
by eosin or fluorescein respectively[3a,b] while few
months later, Gu described the eosin-catalyzed
preparation of diarylketones (Scheme 1).[3c] In
addition to these works, although not photocatalytic,
an interesting alkoxycarbonylation initiated by a
weak base was developed and described in 2017.[4]
All these processes were performed under 50 to 80
atm. of carbon monoxide starting from diazonium
salts.
Scheme 1. Visible-light-promoted carbonylations
Apart from this, aryl carboxylic acids are
ubiquitous motifs in a good number of natural
products, dyes, biologically active molecules as well
as polymers.[5] Additionally, as common key building
blocks to easily access a variety of synthetic products,
these moieties are of particular interest. Consequently,
a wide range of methods were developed for their
preparation including the direct oxidation of methyl
arenes, aromatic aldehydes and alcohol derivatives[6]
and the palladium-catalyzed hydroxycarbonylation.[7]
Although carbon monoxide is a toxic and hazardous
gas and therefore does not fulfill the criteria of green
Figure 1. Xanthene photocatalysts
particularly at the industrial scale, carbon monoxide
is as well inexpensive and readily available notably
1
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10.1002/adsc.201800532
Advanced Synthesis & Catalysis
from low-cost biomass sources, such as biorenewable
agricultural wastes.
fluorescein or eosin Y were evaluated remain
surprising.
In this context and given our recent interest in the
synthesis of carboxylic acid derivatives,[8] we wish to
report herein a visible light-driven photocatalytic
hydroxycarbonylation from aryl diazonium salts.
Thus keeping the Ru(bpy)3Cl2 as a promoter, the
pressure of carbon monoxide was decreased and the
reaction time was adjusted (entries 9-11). It was
found that a minimum of 10 bar pressure was
required during 3 h for a full conversion into the
benzoic acid 2a. Although the reaction proceeded
faster with 50 bar of CO, it seems to us that lowering
the pressure of CO
Table 1. Optimization of the reaction conditionsa)
Entry Catalyst
CO
Reaction
Yield
(%)b)
>99
>99
>99
Tracec)
16c)
(65)d)
7c)
(bar) time (h)
1
2
3
4
5
Ru(bpy)3Cl2
50
50
50
50
50
16
3
0.5
0.5
0.5
Ru(bpy)3Cl2
Ru(bpy)3Cl2
Fluoresceine
Eosin Y
6
7
8
9
Rose bengal
Rhodamine B
Rhodamine 6G
Ru(bpy)3Cl2
Ru(bpy)3Cl2
50
50
50
10
10
0.5
0.5
0.5
0.5
3
Tracec)
18c)
80
10
>99
(91)e)
16
Scheme
2.
Putative
mechanism
of
the
hydroxycarbonylation reaction
11
12
13
14
15
16
17
Ru(bpy)3Cl2
Ru(bpy)3Cl2
Ru(bpy)3Cl2
Ru(bpy)3Cl2
Ru(bpy)3Cl2
none
1
3
0.5
3
3
16
3
10
10
10
10
10
10
70f)
87g)
35h)
>99i)
0
was more beneficial. Asides from this, adding 40
equivalents of water instead of 20 equivalents led to
significantly reduce the yield (entry 9 vs 12).
Additionally, the yield was dramatically affected
when lowering the catalyst loading to 0.5 mol %
(entries 13-14).
Interestingly, it is convenient to note that the
reaction can be performed with a less powerful light
source without loss of yield, albeit a longer reaction
time was required (1W entry 15 vs 11W entry 10).
Last but not least, control experiments
demonstrated the strict requirement of both catalyst
and light for the reaction to occur (entries 16-17).
Following this preliminary study, the optimized
conditions for the hydroxycarbonylation were 1
mol % of Ru(bpy)3Cl2, 20 equiv. of water, 10 bar of
CO and blue LED irradiation (LED λmax = 447 nm,
11W).
Ru(bpy)3Cl2
3
0j)
a)General conditions: 1a (0.225 mmol, 1 equiv.), H2O (20
equiv.), photocatalyst (1 mol %), MeCN (1 mL),
irradiation (LED λmax = 447 nm, 11W). b)NMR yields
using 1,3,5-trimethoxybenzene as internal standard.
c)Irradiation (LED λmax = 530 nm, 11W). d)16 h reaction
f)
time. e)Isolated yield. 40 equiv. of H2O was added. g)0.5
mol % catalyst loading. h)0.1 mol % catalyst loading.
i)Irradiation (LED λmax = 447 nm, 1W). j)In the dark.
The feasibility of the reaction was first evaluated
on the 4-methoxybenzenediazonium tetrafluoroborate
salt 1a, in the presence of 20 equivalents of water and
1 mol % of Ru(bpy)3Cl2 under 50 bar of carbon
monoxide. After 16 h, we were glad to observe the
formation of the desired 4-methoxybenzoic acid in a
quantitative yield (Table 1, entry 1). From this result,
the reaction time was decreased to 30 mn without loss
of yield (entries 2 and 3).
Inspiring by the previous photocatalytic
alkoxycarbonylations and recognizing the importance
and advantage of organic photoredox catalysis, we
turned our next investigation on the assessment of
various xanthene dyes as photocatalysts (Figure 1,
Table 1, entries 4-8). In regard to the literature,[3]
while lower reactivies with rose bengal, rhodamine B
and 6G were expected, such low yields when
The putative mechanism for this transformation is
outlined in Scheme 2. In a first step, the photocatalyst
is excited by irradiation into the reductive specie
2+*
Ru(bpy)3
which further proceeds to a single
electron transfer with the diazonium salt. It results the
formation of the aryl radical. Since the oxidation
potential of this radical is too low to be oxidized by
the Ru(III) complex,[3] it first reacts with carbon
monoxide leading thus to the more oxidisable radical
acyl. The oxidation of this latter into an acylium ion
led upon addition of water to the expected aryl
carboxylic acid.
The scope of the reaction was then extended and
evaluated on diversely substituted aryl diazonium
tetrafluoroborate salts (Table 2).
2
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10.1002/adsc.201800532
Advanced Synthesis & Catalysis
From this screening, it appears that a good variety
from the methyl 4-benzoate diazonium salt 1o is
mainly due to the side formation of the terephthalic
acid by saponification (47 % NMR yield).
Following this scope exploration, we wondered
whether the in-situ generation of aryl diazonium salts
from anilines would be compatible with our
hydroxycarbonylation conditions.
of electron-rich or poor substituents (methoxy,
phenoxy, amide, alkyl, bromide, fluoride, nitro and
ester) are tolerated during the process.
In accordance with the previously reported
photocatalytic carbonylation reactions of aryl
diazonium salts, electron donating groups are
beneficial for the reaction while electron withdrawing
group are less so. Interestingly, while the yield of 2b
was dramatically affected by the presence of methoxy
substituent on the position 3 of the benzene ring, a
good conversion into the desired carboxylic acids 2c
was observed when similar substituent was present in
Inspired by previous work on the purpose,[11] we
decided to achieve the reaction by adding 20 mol %
of methanesulfonic acid and 1.5 equiv. tert-butyl
nitrite to an acetonitrile solution containing 1 equiv.
of p-anisidine, 1 mol % of Ru(bpy)3Cl2, 20 equiv. of
water under 11W blue LED irradiation. In order to
slightly increase the yield of 2a, it was found that the
reaction has to be carried out preferentially for 16 h
(Table 3).
Table 2. Scope of the hydroxycarbonylation of various
aryl diazonium saltsa),b)
Table 3. Scope of the in situ-generated diazonium salts
hydroxycarbonylationa),b)
a)General conditions: 1a (0.225 mmol, 1 equiv.), H2O (20
equiv.), Ru(bpy)3Cl2 (1 mol %), CO (10 bar), MeCN (1
mL), 16 h reaction time, irradiation (LED λmax = 447 nm,
11W). b)Isolated yields.c)3 h reaction time.
a)General conditions: 1a (0.225 mmol, 1 equiv.), H2O (20
equiv.), Ru(bpy)3Cl2 (1 mol %), CO (10 bar), MeCN (1
mL), 3 h reaction time, irradiation (LED λmax = 447 nm,
c)
11W). b)Isolated yields. CO (50 bar), 16 h reaction time.
The one pot procedure was then successfully
extended to various anilines. Unfortunately, no
improvement was observed for the formation of 2b,
2k and 2m. Nevertheless, knowing that this is a one
pot procedure, the yields of the desired products were
mostly very satisfactory.
In summary, a visible light-driven photocatalytic
hydroxycarbonylation was developed for the
synthesis of diversely substituted aryl carboxylic
acids. This reaction was achieved under mild
conditions from either pre-isolated or in situ-
generated diazonium salts. Avoiding the preparation
d)NMR yield of terephthalic acid using 1,3,5-
trimethoxybenzene as internal standard.
both positions 3 and 4. Although, most substrates are
well converted, the yields of some carboxylic acids
were altered by the competitive Sandmeyer reaction,
thus leading to the aryl acetanilide.[10] In those cases,
excepted for compound 2b, increasing both the
pressure of carbon monoxide to 50 bar and the
reaction time to 16 h has helped to improve the yields.
It is worth noting that the 42 % modest yield of 2o
3
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10.1002/adsc.201800532
Advanced Synthesis & Catalysis
and isolation of the latter is a significant step forward
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Experimental Section
Typical procedure hydroxycarbonylation from diazonium
salts
A solution containing 0.225 mmol of diazonium
salt 1 (1 eq.), 0.002 mmol of Ru(bpy)3Cl2.6H2O (1
mol %) and 4.5 mmol of H2O (20 eq.) in acetonitrile
(1 mL) was prepared in an autoclave equipped with
quartz-glass windows. After the reactor was flushed
three times, it was pressurised with 10 bar of carbon
monoxide. After 3 h reaction at room temperature
under stirring and blue LEDs irradiation (11W), the
pressure was carefully released, and acetonitrile was
removed under reduced pressure. The residue was
dissolved in 20 mL of ethyl acetate and extracted 3
times with 20 mL of NaHCO3 saturated solution (20
mL). After being acidified to pH 1, the combined
aqueous phases were extracted 3 times with 50 mL of
dichloromethane. The organic phases were dried over
MgSO4, filtrated and the solvent was removed under
vacuum to afford the pure product 2.
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anilines
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To solution containing 0.225 mmol of aniline
derivative
3
(1 eq.) and 0.002 mmol of
Ru(bpy)3Cl2.6H2O (1 mol %) in acetonitrile (1 mL),
in an autoclave equipped with quartz-glass windows,
was successively added 0.045 mmol of
methanesulfonic acid (0.2 eq.), 0.34 mmol of tert-
butyl nitrite (1.5 eq.) and 4.5 mmol of water (20 eq.).
After the reactor was flushed three times, it was
pressurised with 10 bar of carbon monoxide. After 16
h reaction at room temperature under stirring and
blue LEDs irradiation (11W), the product 2 was
isolated following the work-up previously described.
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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.
We also would like to thank Céline Delabre for her technical
support.
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10.1002/adsc.201800532
Advanced Synthesis & Catalysis
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5
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10.1002/adsc.201800532
Advanced Synthesis & Catalysis
UPDATE
Visible-Light-Mediated Hydroxycarbonylation of
Diazonium Salts
Adv. Synth. Catal. Year, Volume, Page – Page
Cyrille Gosset, Sylvain Pellegrini, Romain Jooris,
Till Bousquet* and Lydie Pelinski
6
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