Sodium pyruvate as a peroxide scavenger in aerobic oxidation under carbene catalysis

Article abstract of DOI:10.1039/d0gc02555k

NHC-Catalyzed aerobic oxidative reactions of imines and aldehydes have been developed by using sodium pyruvate as a novel and efficient peroxide scavenger. A structurally diverse set of imidates and amidines has been prepared from imines using this strategy. This general and efficient strategy features the use of sodium pyruvate as a novel and efficient peroxide scavenger and ambient air as the sole oxidant to efficiently control the NHC-catalyzed aerobic reaction pathway (selective realization of the oxidative pathway) under mild and green conditions. This journal is

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Sodium Pyruvate as a Peroxide Scavenger in Aerobic Oxidation
under Carbene Catalysis
Guanjie Wang,a Chenlong Wei,a Xianfang Hong,a Zhenqian Fu,*a and Wei Huang,a,b
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
NHC-catalyzed aerobic oxidative reaction of imines or aldehydes has been developed by using sodium pyruvate as a novel
and efficient peroxide scavenger. A structurally diverse set of imidates and amidines has been prepared from imines by
this strategy. This general and efficient strategy features using sodium pyruvate as a novel and efficient peroxide
scavenger and ambient air as the sole oxidant, efficiently controls NHC-catalyzed aerobic reaction pathway (selective
realization of oxidative pathway), mild and green conditions.
www.rsc.org/
important intermediates in NHC-catalyzed reactions. As shown in
Figure 2, intermediate III with peroxyl moiety often undergoes
oxygenative and oxidative pathways at the same time when
Introduction
Oxidation represents as one of the most important and
fundamental reactions, plays an essential role in organic functional
group transformations. Molecular dioxygen (or ambient air) is
recognized as the ideal oxidant due to its nearly no-cost, abundant,
and environmentally benign. However, oxidative reactions with the
direct use of molecular dioxygen (in particular, ambient air) as the
sole oxidant, actually remain among the most critical challenges
and have received continuous attentions to academic research and
industrial application.1 Notably, transition-metal (such as Pd, Cu)
catalyzed aerobic oxidation has made impressive progress in the
last decade.1 In contrast, organocatalyzed aerobic reactions are less
far developed. Few successful examples in this area mainly
undergoes an oxygenative pathway, resulting in peroxyl products,
or doing further treatment with a reductant (such as phosphine) to
give the hydroxyl-containing products.2 Despite the impressive
progress, organocatalyzed aerobic reactions via an oxidative
pathway remain elusive and are still highly desirable.
molecular dioxygen (or ambient air) was used as the sole oxidant.15
Intermediate III was reduced by aldehydes (or Breslow intermediate
II) to give carboxylic acids as side products via an oxygenative
pathway under the reaction conditions. The other possible
oxidative pathway undergoes removement of the peroxyl moiety of
intermediate IV to give desired oxidative intermediate VII, which
further reacts with nucleophiles to give oxidative products. Notably,
the above two pathways usually exist simultaneously, resulting in
poor atom economy and reaction efficiency. Although much effort
has been devoted in NHC-catalyzed aerobic oxidative reactions,15
a
general and efficient strategy for making the reaction pathway
dominatedly undergo desired oxidative pathway by using ambient
air as the sole oxidant largely remains underdeveloped.
OH
reductant
R
X
Oxygenative products
O
X
O
Organocatalyst
O2
Well developed
R
X
R
N-heterocyclic carbene (NHC) has proven as one of the most
privileged organocatalysts, enabling construction of a structurally
diverse set of important molecules from simple raw materials under
mild conditions.3 In this area, NHC/aldehyde(or enal)-derived
Breslow intermediates,4 which could be oxidized by various
oxidants5-15 via an oxidative pathway to generate the corresponding
(unsaturated) acyl azoliums,16 are proven to be one of the most
Nu
Nu
H
R
X
R
X
_
HOO
Oxidative products
Scare
Figure 1 Organocatalyzed aerobic reactions.
New organic reaction modes are often inspired by biological
processes in nature. Pyruvic acid and its salts (such as sodium
pyruvate), as among endogenous small molecules, not only an
important intermediate of glucose metabolism in all biological cells,
but also a natural antioxidant associated with protection of
different cells against oxidative damage through non-enzymatic
scavenging of reactive oxygen species (ROS) including H2O2 to
produce acetate, water and carbon dioxide.17 Inspired by this
biological process, we envisioned that sodium pyruvate might be an
a. Key Laboratory of Flexible Electronics & Institute of Advanced Materials, Jiangsu
National Synergetic Innovation Center for Advanced Materials, Nanjing Tech
University, 30 South Puzhu Road, Nanjing, 211816, China. E-mail:
iamzqfu@njtech.edu.cn.
b. Shaanxi Institute of Flexible Electronics (SIFE), Northwestern Polytechnical
University (NPU), 127 West Youyi Road, Xi'an, 710072, China.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
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efficient reductant, which could remove entire peroxyl moiety to Table 1. Optimization of reaction conditionsa
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DOI: 10.1039/D0GC02555K
undergo aerobic oxidative pathway under carbene organocatalysis.
According to our understanding of organocatalysis,18 we herein
present a novel strategy for the use of sodium pyruvate as a
peroxide scavenger to realize carbene-catalyzed aerobic oxidation,
meanwhile a series of imidates and amidines were prepared from
imines under mild and green conditions. Importantly, imidates and
amidines as core structural motifs are frequently found in synthetic
intermediates19 and pharmaceutically important molecules.20
S
S
S
Standard
conditions
N
N
N
N
HN
+
N
O
OMe
2a
H
Ph
Ph
Ph
2a'
1a
Standard conditions:
BF4
A
Ar = Mes,
N
N
A
NHC precursor (20 mol %), K2CO3 (1.5 equiv),
B
= Ph,
= C6F5,
o
N
Ar
Air
MeOH (0.1 M), MgSO4 (50 mg), 25 C,
, 6 h.
C
Entrya
Variation from standard conditions
Yield(%)b
a) Two competitive pathways for NHC-catalyzed aerobic reactions
3a
3a
30
<5
<5
11
10
20
N
1
2
3
4
5
6
none
34
92
36
48
35
62
N
N
R
N
N
XH
R
X
N
N
II
R
N
N
1.0 equiv “SP” was used
1.0 equiv DPPE was used
1.0 equiv P(OEt)3 was used
1.0 equiv PPh3 was used
0.5 equiv instead of 1.0 equiv SP
variation in conditions from entry 2
B instead of A
C instead of A
15 mol % instead of 20% mol A
No A
base = DBU
base = Cs2CO3
base = NaOAc or Et3N
1.0 equiv instead of 1.5 equiv K2CO3
Without MgSO4
O2
X
N
N
N
O
X
R
H
O
H
O
X= O, NAr
HO
I
III
IV
I
_
HOO
X
OH
X
N
N
R
R
OH
or
XH
7
8
9
78
30
76
n.d.
83
68
<5
71
83
<10
90
<5
<5
<5
n.d.
<5
<5
n.d.
<5
<5
n.d.
<5
X
X
N
O
-NHC
NuH
O
N
R
Nu
VIII
N
N
-NHC
R
R
R
VII
V
O
oxygenative
path
oxidative
path
10
11
12
13
14
15
16
17
VI
This work:
b)
S
S
S
20 mol % NHC
N
N
N
N
K2CO3(1.5 equiv)
HN
N
+
Under N2 atmosphere
Under O2 atmosphere
O
MeOH, MgSO4
OMe
H
Ph
Ph
Ph
Ambient air, 25oC, 6h
1a
Oxygenative
product
Oxidative
product
a
b
Reactions were conducted on a 0.1 mmol scale of 1a. Isolated yields after
with SP 92% yield
w/o SP
<5% yield
column chromatography. DPPE = 1,2-bis(diphenylphosphino)ethane, “SP” =
Sodium pyruvate, DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene. n.d. = not detected.
"SP" =
Sodium Pyruvate
34%
30%
Figure 2 Our proposed oxidative pathway using air as oxidant.
entries 7 and 8). When the catalyst loading was lowered to 15
mol %, the product yield decreased considerably (Table 1, entry 9).
Without NHC, neither product 2a nor 2a’ was found (Table 1, entry
10). Base screening revealed that K2CO3 was proven to be the most
effective (Table 1, entries 11-14). In the absence of the drying agent,
the product yield was decreased considerably (Table 1, entry 15).
The generation of product 2a in trace amount under nitrogen
atmosphere and in excellent yield under oxygen atmosphere
indicated that dioxygen in ambient air is necessary and effective
enough to promote this reaction (Table 1, entries 16, and 17).
Results and discussion
The present study was initiated by treating the aldimine 1a with
the triazolium NHC precatalyst A, using K2CO3 as the base, MeOH as
the nucleophile and solvent under ambient air. The desired
oxidative product imidate 2a was obtained in 34% yield.
Simultaneously, the oxygenative product amide 2a’18a was also
found in similar yield (Table 1, entry 1). Then, the additive was
introduced into reaction system in order to control the reaction
pathway. Impressively, when sodium pyruvate in an amount of 1.0
equiv was employed, the yield of oxidative product imidate 2a was
significantly increased to 92% yield. And the yield of amide 2a’ was
suppressed into less than 5% (Table 1, entry 2). This result indicated
that the aerobic oxidative pathway can be controlled excellently
through the addition of peroxide scavenger. Subsequently,
phosphines (such as DPPE, P(OEt)3 and PPh3) which have proven to
be efficient reductants in aerobic reactions,2k,21 cannot deliver
satisfactory results (Table 1, entries 3-5). Notably, the reaction got
worse in both yield and selectivity when the amount of sodium
pyruvate was reduced to 0.5 equivalents (Table 1, entry 6). NHC
precatalyst B and C are inferior to A in terms of yield (Table 1,
With optimized reaction conditions in hand (Table 1, entry 2), the
scope of the reaction was explored (Table 2). Various aldimine
substrates were first evaluated by using methanol as the other
reactant and solvent. As shown in Scheme 1, the benzaldehyde
moieties of aldimines bearing an electron-donating (Me, MeO) and
an electron-withdrawing group (Cl, NO2, CF3, Br, CO2Me) at
different positions (para, meta and ortho) are compatible with the
reaction conditions (2a-2k). Among these cases, strong electron
withdrawing groups such as nitro and trifluoromethyl led a reduced
yields comparison to other substituent groups probably due to their
easy hydrolysis. The phenyl unit can be replaced successfully by
2 | J. Name., 2012, 00, 1-3
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heteroaryl unit (such as 2-furyl, 2-thienyl and 3-pyridinyl) to afford from non-commercially aldehydes, which were easilVyieowbAtraticinleeOdnlibnye
the desired products (2l-2n). It’s worth mentioning that enal- installation a formyl group into electron-DriOchI: 1h0e.1t0e3r9o/aDr0eGnCe0s25(i5.e5K.,
derived aldimine also gave imidate 2o in an acceptable yield. Imines indole and carbazole) via Vilsmeier–Haack reaction, gave the
desired products 2p and 2q in excellent yields. Notably, the
presence of 2-aminobenzoxazole is not an obligation since a variety
Table 2. Reaction Scopea
of heteroaryl amine-derived imines such as 2-aminobenzimidazole
1r, 2-aminobenzoxazole 1s, 2-aminothiazole 1t, 2-aminopyridine 1u,
20 mol % NHC
K2CO3 (1.5 equiv)
RO
X
N
R
5-methyl-3-aminoisoxazole 1v and substituted 2-benzothiazolamine
(1w-1y) were also capable of enabling the preparation of the
imidates 2r-2y with moderate to excellent yields. It is worth
mentioning that compound 2z which has the mortality of 100%
against psedualetia separate based on the known biological activity
test report,22 could be obtained in 68% yield. Replacement of
methanol with ethanol or isopropanol led to give imidates 2aa and
2ab. Furthermore, other alcohols that are not economy as solvents
like benzyl alcohol, propargyl alcohol, and cyclohexanol were also
suitable nucleophiles in our modified reaction conditions (2ac-2ae)
(see SI for details).
N
X
R
N
N
SP (1.0 equiv)
MgSO4, MeOH, 25oC, air, 6h
H
2
1
2a
2b
2c
2d
2e
2f
2g
2h
; R = H, 92% yield
; R = o-Cl, 85% yield
; R = m-Cl, 73% yield
; R = p-Cl, 76% yield
; R = p-NO2, 42% yield
; R = p-CF3, 56% yield
; R = p-Br, 81% yield
; R = p-OMe, 92% yield
; R = p-Me, 93% yield
S
S
N
N
N
N
OMe
OMe
R
2k
; 88% yield
2i
2j;
R = p-CO2Me, 71% yield
S
S
S
Table 3. Reaction Scopea
N
OMe
N
N
N
N
N
N
OMe
OMe
X
R3
R2
N
Ph
2l
; X = S, 67% yield
X
20 mol % NHC
NaOAc (1.5 equiv)
N
R2
R3
2m
; X = O, 42% yield
2n
; 56% yield
R
N
X
2o
; 61% yield
R
NH
+
N
N
SP (1.0 equiv)
4 Å MS, THF, 25oC, 6h
H
S
3
1
S
X
N
N
N
N
N
N
S
S
N
OMe
S
OMe
OMe
N
Bn
N
N
N
N
N
N
Cl
Ph
3a
N
N
H
Ph
Ph
3c
N
H
H
2r
; X = NH, 63% yield
2s
3b
; 78% yield
; 77% yield
; 72% yield
2q
; X = O, 65% yield
; 91% yield
2p
; 96% yield
S
S
S
N
S
O
N
N
N
N
NH
N
N
N
N
N
N
N
N
Ph
Ph
N
H
OMe
Ph
OMe
NHBn
Ph
2v
OMe
Cl
Cl
3d
; 92% yield
S
3e
; 60% yield
3f
; 82% yield
; 81% yield
2u
; 40% yield
2t
; 92% yield
S
S
S
F3C
R
N
N
N
N
N
N
OMe
N
N
2w
; R = Cl, 83% yield
; R = Me, 82% yield
R = MeO, 85% yield
Cl
Ph
N
Ph
NH
CF3
S
NH
2x
2Y:
S
NH
N
OMe
R
Against Psedualetia separata
R
2z
; 68% yield
3g
3h
3i;
3j;
; R = H, 68% yield
3k
; R = Br, 82% yield
3m
; 66% yield
; R = Me, 76% yield
R = MeO, 78% yield
R = Cl, 57% yield
3l
; R = Me, 54% yield
S
S
N
S
N
N
N
Ph
N
N
Ph
Ph
OEt
Cl
O Pr
i-
OBn
O
b
2ab
; 45% yield
2aa
; 81% yield
2ac
; 66% yield
N
N
S
NH
N
N
S
S
Cl
NH
N
N
Ph
N
N
O
O
Ph
Ph
3o
; 70% yield
3n
b
3n; 66% yield
b
ccdc: 2014118
2ad
; 70% yield
2ae
; 68% yield
a
aStandard conditions as in Table 1, entry 2; yields (after SiO2 chromatography
purification) were based on aldimines 1. aldimine 1a (0.1 mmol), 20 mol % NHC-
Reaction conditions: aldimines 1 (0.1 mmol), 20 mol % NHC-precursor A, amines (2.0
equiv), 1.0 equiv SP, 1.5 equiv NaOAc, 100mg 4Å MS, 0.1M THF, 25oC, 6h, air.
b
precursor A, alcohols (2.0 equiv), 1.0 equiv SP, 1.5 equiv NaOAc, 100 mg 4Å MS, 0.1M
We next turned our attention to use amines as nucleophiles in
NHC-catalyzed aerobic oxidation by using sodium pyruvate as a
peroxide scavenger (Table 3). Primary alkyl amines are well
THF, 25oC, 6h, air.
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tolerated and the corresponding amidines were obtained in good to material decomposed for 6, or remained for 7 and 8, respectively
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DOI: 10.1039/D0GC02555K
high yields (3a–3e). The secondary amine, such as piperidine, (Scheme 1a). Other pyruvates were investigated. The use of
worked well to form 3f in good yield. Pleasingly, the imidoyl azolium Sodium phenylpyruvate instead of Sodium pyruvate as a peroxide
intermediates also exhibits good reactivity towards weaker nitrogen scavenger led to decrease the selectivity (Scheme 1b). Replacement
nucleophiles anilines (3g–3j). Finally, we further examined several of Sodium pyruvate with Ethyl pyruvate could not improve the
aldimines with different substituents and electronic properties by selectivity obviously. This results indicated that salt moiety plays a
using p-methylaniline as the nucleophile. In all these cases, the crucial role in this transformation.
desired amidines 3k–3o were successfully obtained in moderate to
good yields.
(a)
N
Ph
optimal conditions
N
Ph
OMe
n. d.
To further demonstrate the generality of NHC-catalyzed aero-bic
oxidative approach by using sodium pyruvate as a peroxide
scavenger, we investigated NHC-catalyzed aerobic oxidation of
aldehydes for synthesis carboxylic esters (Table 4). Gratifyingly,
substituted aromatic aldehydes were suitable substrates under
optimal reaction conditions to give corresponding oxidative
products 5 in excellent yields. In sharp contrast, poor selectivity was
observed in absence of sodium pyruvate under otherwise identical
conditions. As expected, excellent results could be obtained for
substituted enals under optimal conditions (5h-5l). These results
further indicated that sodium pyruvate could be an efficient
peroxide scavenger in NHC-catalyzed aerobic oxidation.
R
R
H
6
R = Ts,
R = PMP,
R = Bn,
7
8
(b)
S
S
S
20 mol % NHC
N
N
N
K2CO3 (1.5 equiv)
HN
N
N
+
O
OMe
2a
MeOH, MgSO4
Ph
Ph
H
Ph
Ph
Ambient air, 25oC, 6h
O
2a'
1a
O
Table 4. Sodium pyruvate as a peroxide scavenger in NHC-catalyzed aerobic
9
with
56% yield
41% yield
21% yield
32% yield
ONa
OEt
oxidation of aldehydes.a
10
with
O
O
9
10
A
20 mol % NHC
O
K2CO3(1.5 equiv)
O
R
OMe
Scheme 1 Mechanistic study. n.d=not detected.
R
H
SP (1.0 equiv)
MeOH, 25oC, air, 24h
4
5
N
H
O
O
O
Ph
N
N
N
OMe
OMe
OMe
S
N
S
N
N
Me
Br
Ph
H
IX
5a
5b
, 92% yield
, 85% yield
5c
, 89% yield
63% yield (w/o SP)
48% yield (w/o SP)
52% yield (w/o SP)
N
X
N
1a
N
O
Base
O
O
Me
Me
OMe
OMe
OMe
Cl
N
Ph
N
N
N
N
5e
, 90% yield
5f
N
, 89% yield
5d
, 91% yield
43% yield (w/o SP)
S
N
42% yield (w/o SP)
66% yield (w/o SP)
NH
XI
(NHC)
O
O
O
aza-Breslow intermediate
2a
OMe
OMe
OMe
Cl
O2
Ph
5h
, 89% yield
5i
, 66% yield
15% yield (w/o SP)
5g
, 96% yield
N
MeOH
35% yield (w/o SP)
S
45% yield (w/o SP)
N
N
N
Ph
S
N
N
N
O
N
O
OMe
O
N
N
O
H
XIII
OMe
O
OMe
Me
OMe
SP
XII
CO2
MeO
H2O
5l
, 82% yield
5j
, 86% yield
31% yield (w/o SP)
5k
, 83% yield
33% yield (w/o SP)
MeCO2
52% yield (w/o SP)
Reactions were conducted on 0.1 mmol scale of 4. The yield of 5 was estimated
via 1H NMR analysis with 1, 3, 5-trimethoxybenzene as an internal standard. The
yield for the reaction without the presence of the sodium pyruvate under
otherwise identical conditions is also given. For reaction of enal substrates 4h-4l,
50 mg MgSO4 was added as drying agent.
Scheme 2 Proposed mechanism.
Based on previous work and the current results, the proposed
mechanism is shown in Scheme 2. The addition of NHC to imine 1a
generates intermediate IX. The electron-donating nitrogen anion of
intermediate IX is converted into electron-withdrawing nitrogen
To probe the reaction pathway, control experiments were
performed as shown in Scheme 1. Both N-Ts aldimine 6, and simple
aromatic (7) or aliphatic imines (8) were not effective, and the raw
(C=N) of intermediate
X through the dearomatization of
benzothiazole ring, which could significantly increase the acidity of
4 | J. Name., 2012, 00, 1-3
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hydrogen on the carbon bounded to NHC. Subsequently,
In summary, we have addressed NHC-catalyzed aerobic oxidative
View Article Online
DOI: 10.1039/D0GC02555K
deprotonation of Intermediate X under basic conditions led to reaction of imines or aldehydes by using sodium pyruvate as a novel
produce an aza-Breslow intermediate XI, which adds to dioxygen and efficient peroxide scavenger. Various imidates and amidines
from the air to generate intermediate XII. Then, sodium pyruvate were prepared from imines with acohols and amines in good to
could remove peroxide moiety to give intermediate XIII and form excellent yields, respectively. Furthermore, aldehydes underwent
acetate, water and carbon dioxide in the meantime. Intermediate oxidative pathway to form carboxylic esters by this strategy. This
XIII further reacts with methanol to result in the formation of general and efficient strategy features using sodium pyruvate as a
product 2a and regeneration of the free carbene.
novel and efficient peroxide scavenger and ambient air as the sole
oxidant, efficiently controls NHC-catalyzed aerobic reaction
pathway (selective realization of oxidative pathway). Exploration of
this strategy in other NHC-catalyzed aerobic oxidative reactions is
currently in progress.
To demonstrate the practicality of this catalytic system, large-
scale synthesis of products 2a, 3d,and 5b was conducted (Scheme
3a). Reduce the amount of catalyst to 10 mol %, the reaction of 1a
(2 mmol) worked smoothly to give 2a in 68% yield. Compound 3d
can be obtained in 61% yield from 1a in a 2 mmol scale.
Furthermore, in the absence of drying agent MgSO4, benzaldehyde
(2 mmol) can be converted to ester product in 65% yield.
Acknowledgements
We acknowledge financial support by National Key R&D Program
of China (2017YFA0204704), National Natural Science Foundation of
China (21602105), and Natural Science Foundation of Jiangsu
Province (BK20171460). G. Wang is grateful to Postgraduate
Research & Practice Innovation Program of Jiangsu Province
(KYCX20_0988) for financial support.
Benzothiazole and their derivatives are crucial structural motifs in
natural products,23 synthetic molecules,24 and functional material.25
Imidates and amidines bearing an benzothiazole or thiazole moiety
have exhibited potential applications as ligands in metal catalysis
and fluorescent dyes owing to their unique electronic and structural
properties.26 The amidines 3 (such as 3g) could react with acyl
chlorides to access various heteroaromatic compounds 12 with
good yields via a known procedure (Scheme 3b).
Notes and references
1
For selected reviews, see: (a) T. Punniyamurthy, S. Velusamy,
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a) The large-scale reaction.
S
10 mol % NHC
S
K2CO3 (1.5 equiv)
N
N
N
N
SP (1.0 equiv), MgSO4
MeOH, 25oC, air
H
Ph
OMe
Ph
2a,
1a
68% yield
2 mmol
BnNH2 (1.5 equiv)
10 mol % NHC
S
S
N
NaOAc (1.5 equiv)
N
N
N
SP (1.0 equiv), 4 Å MS
THF, 25oC, air
H
Ph
Ph
3d,
NHBn
1a
61% yield
2 mmol
O
10 mol % NHC
O
K2CO3 (1.5 equiv)
H
OMe
SP (1.0 equiv)
MeOH, 25oC, air
Br
Br
4b
5b
, 65% yield
34% yield (w/o SP)
2 mmol
3g
b) Synthesis of heteroaromatic compounds from
.
O
N
S
O
R
known process
N
N
+
R
Cl
S
Ph
12
N
NHPh
Ph
72-78% yield
R = Aryl, alkyl
3g
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11
Scheme 3 Large-scale reaction and synthesis of heteroaromatic
compounds from 3g.
Conclusions
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ARTICLE
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Journal Name
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Graphic Abstract
X
X
NHC
+
Nu-H
R
H
R
Nu
SP, Ambient air
58 examples
up to 96% yield
X = O, NAr
(Nu: -OR, -NRR')
O2
NHC
Nu-H
Oxidative
pathway
XH
O
R
N
X
N
O
N
N
N
N
R
CO2
SP
H2O
MeCO2
SP: Sodium pyruvate
Aerobic oxidative pathway
Ambient air as the sole oxidant


Sodium pyruvate as a peroxide scavenger


Access to imidates amidines and esters
,
NHC-catalyzed aerobic oxidative reaction of imines or aldehydes
has been developed by using sodium pyruvate as a novel and
efficient peroxide scavenger.
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