Nickel catalyzed hydrosilane reduction of (het)arenecarboxylic acids into aldehydes

Article abstract of DOI:10.1016/j.mencom.2021.03.043

Nickel-catalyzed reduction of (het)arenecarboxylic acids with hydrosilanes in the presence of dimethyl dicarbonate as the activator affords the corresponding aldehydes. The role of the activator is the conversion of the acids into their anhydrides undergoing C–O cleavage. The good yields were achieved in case of substrates bearing electron-donating and electron-neutral groups.

Full text of DOI:10.1016/j.mencom.2021.03.043

Mendeleev
Communications
Mendeleev Commun., 2021, 31, 271–273
Nickel catalyzed hydrosilane reduction
of (het)arenecarboxylic acids into aldehydes
Liang Wang,a Yaoyao Wang,b Yu Tao,a Nana Zhanga and Shubai Li*a
a School of Chemical and Pharmaceutical Engineering, Changzhou Vocational Institute of Engineering,
213164 Changzhou, P. R. China. Fax: +86 5198 633 2059; e-mail: lwcczu@126.com, lsbcz88@126.com
b School of Petrochemical Engineering, Jiangsu Key Laboratory of Advanced Catalytic Materials &
Technology, Changzhou University, 213164 Changzhou, China
DOI: 10.1016/j.mencom.2021.03.043
Nickel-catalyzed reduction of (het)arenecarboxylic acids
with hydrosilanes in the presence of dimethyl dicarbonate as
the activator affords the corresponding aldehydes. The role
of the activator is the conversion of the acids into their
anhydrides undergoing C–O cleavage. The good yields were
achieved in case of substrates bearing electron-donating and
electron-neutral groups.
H
O
O
Si
O
O
O
O
H
MeO
O
OMe
[Ni] (cat.)
Ar
OH
Ar
O
R
Ar
H
in situ
R = Ar or OMe
Keywords: nickel catalysis, C–O cleavage, arenecarboxylic acids, aldehydes, hydrosilanes, dimethyl dicarbonate.
Aldehydes are most commonly prepared through the oxidation
of the corresponding alcohols or selective reduction of
carboxylic derivatives. The direct reduction of carboxylic acid
derivatives is generally difficult since aldehydes are more easily
reduced to alcohols than the starting reactants.1 In this context,
the Rosenmund reduction shows good application while
some hydride reagents,2 catalysts3–6 as well as synthetic
methodologies7,8 have been developed. Despite these important
advances, the reported methods still have some limitations
including the limited substrate scope or practicality.9
The use of acid derivatives such as their halides, anhydrides,
esters, etc. instead of the very acids to prepare aldehydes attracted
much attention. For example, Yamamoto and co-workers
reported the synthesis of aldehydes from carboxylic acids via
hydrogenation of the in situ generated anhydrides under the
action of pivalic anhydride.10,11 Gooßen and co-workers
employed hydrophosphite salts as the reductants to achieve the
similar process.12 Later, Tsuji and co-workers developed a Pd-
catalyzed reduction of carboxylic acids to aldehydes with
hydrosilanes in the presence of pivalic anhydride.13 Inspired by
the success of Ni catalysis in cross-coupling reactions,14–24 just
recently, Bergman and co-workers reported a nickel-catalyzed
selective reduction of carboxylic acids to aldehydes.25 However,
limited arenecarboxylic acid substrates were reported for their
process. Inspired by the above contributions, herein we report an
efficient protocol for the selective reduction of arenecarboxylic
acids to aldehydes in detail.
Table 1 Optimization of the reaction conditions for reduction of benzoic
acid 1a into bezaldehyde 2a.a
Hydro-
silane
Entry [Ni] source
Ligand
Base
Yield (%)b
1
2
3
4
5
6
7
8
9
Ni(COD)2
dtbbpy PhSiH3
2,6-lutidine
2,6-lutidine
2,6-lutidine
2,6-lutidine
2,6-lutidine
12
NiCl2(dme) dtbbpy PhSiH3
NiBr2 ·3H2O dtbbpy PhSiH3
39
45, 38,c 51d
NiBr2 ·3H2O bpy
NiBr2 ·3H2O phen
PhSiH3
PhSiH3
20
14
NiBr2 ·3H2O dtbbpy PhSiH3
NiBr2 ·3H2O dtbbpy PhSiH3
NiBr2 ·3H2O dtbbpy PhSiH3
NiBr2 ·3H2O dtbbpy Ph2SiH2
2,4,6-collidine 31
DBU
11
DIPEA
2,6-lutidine
24
65,d 69,d,e
77,d,f 75d,g
52d
10
NiBr2 ·3H2O dtbbpy MePhSiH2 2,6-lutidine
a Reaction conditions: 1a (0.2 mmol), [Ni] (10 mol%), ligand (20 mol%),
Zn (20 mol%), hydrosilane (1.5 equiv.), DMDC (2 equiv.), base (1.2 equiv.),
EtOAc (4 ml), 60 °C, 24 h. b GC yield using n-dodecane as the internal
standard. c 5 mol% catalyst. d 20 mol% catalyst. e 2.0 equiv. Ph2SiH2.
f 2.25 equiv. Ph2SiH2. g 2.5 equiv. Ph2SiH2. For more optimization
experiments (e.g., solvent, temperature and reagent variation), see Online
Supplementary Materials, Tables S1 and S2.
yields of product 2a as 39 and 45%, respectively (entries 2
and 3). Switching the ligand to 2,2'-bipyridyl (bpy) or
1,10-phenanthroline (phen) led to lower yields (entries 4
and 5). The use of other organic or inorganic bases instead of
2,6-lutidine provided 2a in lower yields (entries 6–8 as well as
Table S1, entries 14–18). Lowering the catalyst loading to 5%
still gave 2a in 38% yield which was increased to 51% with
20% loading of the catalyst (see Table 1, entry 3, footnotes c, d).
While screening hydrosilanes and their amount (entries 9, 10),
we found the use of 2.25 equiv. Ph2SiH2 to be superior providing
77% yield of benzaldehyde 2a. Variation of some other
parameters (solvent, temperature, activator and reducing metal
nature, see Online Supplementary Materials, Table S2) did not
lead to improvement of the reaction outcome.
Initially, we started to optimize the reaction conditions by
employing those similar to other published Ni-hydrosilane
reductive methods (Table 1; Tables S1 and S2 in Online
Supplementary Materials) using benzoic acid 1a as the
substrate.25–27 Briefly, reduction of benzoic acid 1a in the
presence of Ni(COD)2, 4,4'-di-tert-butyl-2,2'-bipyridine
(dtbbpy), zinc, dimethyl dicarbonate (DMDC), phenylsilane
and 2,6-lutidine in ethyl acetate provided the desired
benzaldehyde 2a in 12% yield (Table 1, entry 1). Other nickel
sources such as NiCl2(dme) or NiBr2·3H2O provided better
© 2021 Mendeleev Communications. Published by ELSEVIER B.V.
on behalf of the N. D. Zelinsky Institute of Organic Chemistry of the
Russian Academy of Sciences.
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Mendeleev Commun., 2021, 31, 271–273
O
O
O
O
O
i
Ph
H
Ph
O
Ph
Ar
OH
1a–p
Ar
2a–p
H
2a
LnNi0
B
O
– CO2
– MeO–
Zn
dtbbpy
i
j
Ar = 2-MeC6H4, 74%
Ar = 3-MeC6H4, 75%
Ph
OH
a Ar = Ph, 77%
b Ar = 4-MeC6H4, 78%
c Ar = 4-EtC6H4, 76%
d Ar = 4-MeOC6H4, 80%
e Ar = 4-ButC6H4, 74%
f Ar = 4-Me2NC6H4, 81%
g Ar = 4-MeSC6H4, 72%
h Ar = 2-MeOC6H4, 75%
k Ar = 3,4-(MeO)2C6H3, 79%
Ar = 2-naphthyl, 71%
NiBr2·3H2O
l
O
O
O
m Ar = 4-MeO2CC6H4, 42%
n Ar = 1-methylindol-3-yl, 54%
o Ar = 2-furyl, 39%
Ph
NiIILn
O
Ph
O
OMe
O
A
Ph
Ph
NiIILn
p ‘Ar’ = PhCH=CH, 31%
O
O
O
H
C
Scheme 1 Reagents and optimized conditions: i,
1 (0.2 mmol),
MeO
O
+
OMe
D
NiBr2 ·3H2O (20 mol%), dtbbpy (20 mol%), Zn (20 mol%), Ph2SiH2
(2.25 equiv.), (MeO)2C2O3 (2 equiv.), 2,6-lutidine (1.2 equiv.), EtOAc
(4 ml), 60 °C, 24 h, GC yields. For Ar = 4-F3CC6H4, 4-O2NC6H4 and
3-pyridyl, trace yields; for Ar = 4-BrC6H4, product mixture was formed.
Ph2SiH2
MeO–
O
O
2,6-lutidine
– O
Ph
Ph
OH
1a
Ph2Si(OMe)H
Ph2Si(OMe)2
A series of aromatic acids 1a–p were then tested under the
optimized reaction conditions (Scheme 1).† In general, most of
the reactions proceeded smoothly to afford the corresponding
aldehydes 2a–p in moderate to good yields. Aromatic acids
bearing electron-donating and electron-neutral groups such as
alkyl, methoxy, dimethylamino and methylthio were found to be
good substrates. However, reduction of benzoic acids bearing
strong electron-withdrawing groups gave trace amounts of the
desired products. Similarly, electron-deficient monomethyl
terephthalate 1m afforded product 2m in 42% yield. It was also
worth noting that the reduction of 4-bromobenzoic acid was not
selective to produce a mixture of 4-bromobenzaldehyde, benzoic
Scheme 3
acid and benzaldehyde. Reduction of 2-naphthoic acid 1l also
proceeded well, giving 2-naphthaldehyde 2l in 71% yield.
Heterocyclic aromatic acids such as 1-methyl-1H-indole-3-
carboxylic acid 1n and furan-2-carboxylic acid 1o gave the
corresponding products 2n,o in relatively moderate yields
(54 and 39%, respectively). Finally, cinnamic acid 1p was
converted into cinnamaldehyde 2p in 31% yield.
Some control experiments were performed to gain insight
into the mechanism. Bergman and co-workers previously showed
that both mixed and symmetrical anhydrides were generated
during the reaction in the presence of the base and the Ni
catalyst.25 Importantly, formation of symmetrical anhydride is
more prevalent than mixed anhydride in the presence of Ni
catalyst (Scheme 2, experiments a and b). These results suggested
that the anhydride may be the active intermediate in this reaction.
Next, the benzoic anhydride was tested as the substrate under the
standard reaction conditions in the absence of DMDC. However,
only trace amounts of the desired product 2a were formed
(see Scheme 2, experiment c). When 1 equiv. of NaOMe was
added to mimic our catalytic conditions, aldehyde 2a was
obtained in 31% yield (experiment d). These results indicate that
methoxide anion (MeO–) is indispensable for this transformation.
A mechanism outlined in Scheme 3 is proposed based on the
control experiments and the literature data. Initially, benzoic acid
1a reacts with DMDC in the presence of 2,6-lutidine to generate
non-symmetrical anhydride A, which reacts with another
molecule of 1a in the presence of Ni catalyst to give symmetrical
anhydride B.25 Then, compound B undergoes oxidative addition
to a Ni0 species,28 which are formed in situ by the reduction of
Niii with Zn, to deliver the intermediate C. Under the assistance
of methoxide, transmetalation with diphenylsilane occurs and
hydrometallide intermediate D is generated.29 Finally, reductive
elimination within D provides product 2a and the Ni0 species are
regenerated.30
(a)
O
+ DMDC
+
Ph
OH
O
O
O
O
2,6-lutidine
Ph
O
OMe
Ph
O
Ph
EtOAc
ref. 25
(b)
O
O
+ DMDC
Ph
O
OH
O
2,6-lutidine
Ni catalyst
O
O
+
Ph
O
O
OMe
Ph
O
Ph
EtOAc
ref. 25
dominant
(c)
O
Standard conditions
without DMDC
Ph
O
Ph
Ph
H
2a, trace
(d)
O
O
O
Standard conditions
NaOMe instead of DMDC
Ph
O
Ph
Ph
H
2a, 31%
Scheme 2
†
In summary, we have accomplished a Ni-catalyzed selective
reduction of (het)arenecarboxylic acids to aldehydes in the
presence of hydrosilane and DMDC as the activator. Aromatic
carboxylic acids containing electron-donating and electron-
neutral groups showed good reactivities. Some heterocyclic
aromatic acids were also successfully converted to the
corresponding aldehydes albeit with moderate reactivities. This
procedure provided a direct way for the selective reduction of
(het)arenecarboxylic acids.
General procedure for the synthesis of aldehydes 2. In an oven-dried
10 ml vial, NiBr2 ·3H2O (11 mg, 0.04 mmol) was stirred vigorously with
ligand dtbbpy (11 mg, 0.04 mmol) in a dry solvent (4 ml) for 10 min.
Then acid 1 (0.2 mmol) and Zn (3 mg, 0.04 mmol) were added to a 10 ml
Schlenk flask with a magnetic stir bar. The flask was evacuated and
backfilled with nitrogen three times. To this the solution of the Ni/ligand
prepared above, 2,6-lutidine (0.24 mmol) and DMDC (0.4 mmol) were
added. Then, Ph2SiH2 (0.45 mmol) was added via microsyringe, and the
reaction mixture was stirred at 60 °C for 24 h. After cooling to room
temperature, the mixture was diluted with diethyl ether (5.0 ml) and
n-dodecane as an internal standard was added. The yield of product 2 was
analyzed by gas chromatography using n-dodecane as the internal
standard.
This project was financially supported by the Research
Fund of Changzhou Vocational Institute of Engineering
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Mendeleev Commun., 2021, 31, 271–273
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Online Supplementary Materials
Supplementary data associated with this article can be found
in the online version at doi: 10.1016/j.mencom.2021.03.043.
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Received: 5th November 2020; Com. 20/6356
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