Visible-light photocatalyzed oxidative decarboxylation of oxamic acids: a green route to urethanes and ureas

Article abstract of DOI:10.1039/c8cc05462b

A sustainable metal-free route to urethanes and ureas based on a photocatalyzed oxidative decarboxylation of oxamic acids is described. The reaction includes in situ generation of an isocyanate from the oxamic acid, using an organic dye as a photocatalyst, a hypervalent iodine reagent as an oxidant and a light source, which trigger the free-radical decarboxylation. This protocol successfully avoids the isolation, purification and storage of carcinogenic isocyanates and allows elaboration of urethanes and ureas in a one-pot process from commercially available sources.

Full text of DOI:10.1039/c8cc05462b

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Marilyn M. Olmstead, Alan L. Balch, Josep M. Poblet, Luis Echegoyenet al.
Reactivity differences of Sc3N@C2n (2n 68 and 80). Synthesis of the
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DOI: 10.1039/C8CC05462B
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Visible-Light Photocatalyzed Oxidative Decarboxylation of Oxamic
Acids: A Green Route to Urethanes and Ureas
Govind Goroba Pawar,a Frédéric Robert,a Etienne Grau,b Henri Cramail,*b and Yannick Landais*a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
A sustainable metal-free route to urethanes and ureas based on a been reviewed recently.11,12 Oxamic acids prepared through the
photocatalyzed oxidative decarboxylation of oxamic acids is coupling between amines and oxalic acid derivatives are potent
described. The reaction includes in situ generation of an isocyanate precursors of isocyanates. Minisci originally oxidized such
α-
from the oxamic acid, using an organic dye as a photocatalyst, a amidoacid derivatives into isocyanates using Ag(I) and Cu(II)
hypervalent iodine reagent as an oxidant and a light source, which salts as catalysts and stoichiometric amount of K2S2O8 as an
trigger the free-radical decarboxylation. This protocol successfully oxidant in a water-CH3CN medium.13 Although the reaction led
avoids the isolation, purification and storage of carcinogenic to the desired isocyanates, yields were moderate and large
isocyanates and allows elaboration of urethanes and ureas in a one- amount of amine was also observed due to partial hydrolysis of
pot process from commercially available sources.
the isocyanate in the reaction medium. We propose here to
investigate a metal-free catalytic system to overcome these
problems, developing an environmentally friendly synthetic
route to isocyanates and urethanes, which may also be
extended to ureas. Our strategy includes the in situ generation
of isocyanates using a photocatalyst (PC) and a visible light
source,14 which trigger the free-radical decarboxylation of
oxamic acids in the presence of an organic oxidant (Figure 1).15
This protocol avoids the isolation, purification and storage of
the carcinogenic isocyanates and allows elaboration of
urethanes and ureas in a one-pot process from readily available
starting material.
Urethanes display attractive biological activities and constitute
key structural motifs in many targets having clinical potential,
being present in many FDA approved drugs.1 This functional
group shows, as amides, bond resonance, albeit to a smaller
extent.2 Urethanes exhibit excellent proteolytic stabilities,3 and
as a consequence, are often used as peptide bond surrogates.4
They are also widely used as amine protecting groups,5 showing
orthogonality and stability towards acids, bases or
hydrogenation. Numerous methods have been developed to
access urethanes, and among the best known, the Hofmann
amide rearrangement,6 the Curtius rearrangement from acyl
azide,7 or the addition of amines to mixed carbonates.8
Sustainable procedures using CO2 as a phosgene surrogate have
been described recently.9 Finally, the addition of alcohols to
isocyanates is probably the most reliable method to access
urethanes.10 This strategy is commonly employed to access
polyurethanes (PUs), an important class of polymers with a wide
range of applications.11 However, this approach suffers from the
use of highly hazardous phosgene as a precursor during the
preparation of carcinogenic isocyanates. Strategies to avoid
such toxic activated carbonyl species have flourished and have
O
R
R'OH
N
OR'
H
O
R
urethane
R
N
C O
N
O
H
* carcinogenic
R
R'
*
from
phosgene
prepared
PC, oxidant
N
N
H
R'NH2
toxic
H
visible-light
urea
O
-
Metal-free
Organic photocatalyst (PC)
No isolation of
isocyanate
R
OH
N
-
-
-
H
O
acid
as
iodine
oxidant
oxamic
I
Hypervalent
Figure 1 Visible-light mediated access to urethanes and ureas from oxamic acids
Reaction conditions were first optimized as to access in a one-
pot process urethane 3a from oxamic acid 1a (Table 1). The
transformation was first carried out in the presence of
photoredox catalyst (PC) Ru(bpy)3Cl2H2O and (NH4)2S2O8 as an
oxidant in CH2Cl2/H2O (1:1) at rt under visible light irradiation
(Blue LEDs, λmax = 452 nm, SI). Pleasingly, in our first attempt the
a.University of Bordeaux, Institute of Molecular sciences (ISM), UMR-CNRS 5255,
351, Course de la Libération, 33405 Talence Cedex, France. E-mail :
yannick.landais@u-bordeaux.fr
b.University of Bordeaux, Laboratory of Organic Polymer Chemistry (LCPO), UMR-
CNRS 5629, 16 Avenue Pey-Berland, 33600 Pessac, France. E-mail:
cramail@enscbp.fr
Electronic Supplementary Information (ESI) available: See DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
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corresponding carbamate 3a was isolated in 30% yield (entry 1). well as light were necessary for this transformation, as no
View Article Online
DOI: 10.1039/C8CC05462B
The use of water-soluble oxidants such as K2S2O8 or Na2S2O8 desired product was observed in their absence (entries 14-16).
provided poor results (yields <15%). Removal of water from the With these optimal conditions in hand, the scope of the reaction
reaction medium and use of (nBu4N)2S2O8 in CH2Cl2 led only to was then established, varying the nature of oxamic acids
1
and
trace amounts of 3a, due to the low solubility of the persulfate alcohols
2 (Conditions A, Scheme 1). The one-pot process was
(entry 2). When more lipophilic hypervalent iodine (BI-OH)16 shown to be rather general, with yields ranging between 30%
was introduced as an oxidant, 3a was formed in good yield and 90%. Primary, secondary and tertiary alcohols react
(entry 3). Changing BI-OH for acetoxybenziodoxole (BI-OAc) led smoothly even with hindered isocyanates (i.e. 3r-u, 3aa, 3ab),
to improved yield, likely as a result of the better leaving group although reaction time needs to be increased with steric bulk of
ability of OAc (entry 4). Gratifyingly, the reaction proceeded the alcohol. Using diols, only monofunctionalization occurs as
readily in DCE using 1.0 mol% of photocatalyst affording 3a in shown with 3f and 3h. The reaction conditions are mild,
91% isolated yield (entry 5).
allowing functional groups on both partners, including alcohols,
halides, alkynes, strained rings, heteroarenes or esters.
Table 1 Oxidative decarboxylation of oxamic acids. Optimization studies.
O
O
4CzIPN, BI-OAc
R
R'
+
R' OH
R
N
CO2H
N
O
rt
DCE, 24-48
h,
H
H
Blue LED
1
2
3
2a
N
N
EtOH
Me
O
Me
O
CN
O
Me
O
PC, oxidant
H
H
N
N
N
N
OEt
O
CF3
Me
4
N
OEt
N
CO2H
N
O
solvent, time
LED
H
N
OEt
H
H
H
CN
4CzIPN
O
80%
O
3a
3b
3c
48%
,
3d 77%
86%
O
,
,
,
1a
3a
Me
Me
O
O
O
Me
Me
OH
N
O
N
H
O
N
O
OH
entrya
PC
(mol%)
Oxidant
(1.5 eq.)
(NH4)2S2O8
(nBu4)2S2O8
BI-OH
BI-OAc
BI-OAc
BI-OAc
BI-OAc
BI-OAc
BI-OAc
BI-OAc
BI-OAc
BI-OAc
BI-OAc
BI-OAc
-
solvent
t (h)
Yield
4
2
N
OEt
H
2
4
H
H
3f 74%b
3g
3h
68%
,
(%)b
30
3e
58%
90%
,
,
,
O
O
CH2Cl2/H2Oc
CH2Cl2
CH2Cl2
CH2Cl2
DCE
DCE
DCE
DCE
CH2Cl2
THF
MeCN
DMF
DMSO
DCE
DCE
DCE
15
15
15
15
15
15
24
24
24
24
24
24
24
24
24
24
H
1
2
3
4
5
6
7
8
Ru(bpy)3Cl2 (2)
Ru(bpy)3Cl2 (2)
Ru(bpy)3Cl2 (2)
Ru(bpy)3Cl2 (2)
Ru(bpy)3Cl2 (1)
4CzIPN (2)
N
O
Ph
N
H
O
N
H
O
Me
Trace
75
86
94(91)d
76
80
91(86)d
84
46
52
30
NA
NA
NA
NAe
O
30%
F
Me
3i
3j 72%
3k 42%
,
,
,
O
Me
O
H
N
Ph
O
Ph
O
N
H
O
N
H
O
Ph
O
O
3m 75%b
3n 42%
3l 74%b
,
,
Cl
,
Me
AcrMes+ClO4 (1)
-
O
O
Ph
HN
O
Ph
4CzIPN (1)
4CzIPN (1)
4CzIPN (1)
4CzIPN (1)
4CzIPN (1)
4CzIPN (1)
-
N
H
O
Me
N
O
H
O
S
9
56%b
Me
52%b
3q
,
3p
40%
,
3o
,
10
11
12
13
14
15
16
Me
Me
Me
O
O
O
O
Ph
O
O
O
O
HN
HN
HN
HN
3r
3s 85%b
3t
3u
35%
,
68%
,
81%
,
,
4CzIPN (1)
4CzIPN (1)
Me
BI-OAc
Me
Me
a Unless otherwise mentioned, all reactions were performed with 1a (1 eq.), 2a (3
Me
O
O
eq.), PC (1-2 mol%) and oxidant (1.5 eq.) in the indicated solvent (0.2 M), in a sealed
Ph
N
H
O
3w 71%b
N
H
O
3v
,
79%
,
b
tube. Yields of 3a determined by 1H NMR with external standard 1,3,5-
O
trimethylbenzene c 1:1 mixture. d Isolated yields of 3a. e Absence of blue LED.
O
Me
HN
O
O
O
OEt
N
H
O
N
H
O
Encouraged by these results, replacement of non-sustainable
metal photoredox catalyst with cheaper organic dyes was then
investigated, using BI-OAc as the oxidant and DCE as a solvent.
While Eosin-Y, rose-Bengal led only to traces of 3a, 4CzIPN17
showed efficiency comparable to that of metal photocatalysts
(entry 6). Similarly, acridinium salt18 provided 80% of conversion
(entry 7). Remarkably, decreasing the amount of 4CzIPN to 1.0
mol % and increasing the reaction time up to 24 h finally offered
optimal conditions with 91% yield (entry 8). Among hypervalent
iodine reagents examined, BI-OAc was the most effective
oxidant for this reaction as compared to BI-OH, BI-OMe,
PhI(OAc)2, and PhI(TFA)2. An evaluation of solvents showed that
reaction proceeds more efficiently with DCE or CH2Cl2 (entries 8
and 9), as use of THF, MeCN, DMF, or DMSO, significantly
decreased the yields (entries 10-13). Finally, control
experiments indicated that both photocatalyst and oxidant, as
O
b
3x,
3y
3z
62%
82%b
60%b
,
,
O
Me Me
Me
Me
O
N
H
O
Cl
Ph
b (brsm)
N
O
H
66%b
3ab
,
3aa
,78%
a Conditions A: The reaction was carried out with oxamic acid (1 eq.), R’OH (2-3
eq.), PC (1 mol%) and oxidant (1.5 eq.) in DCE (0.2 M) in a sealed tube. b Conditions
B: The reaction was conducted with oxamic acid (3 eq.), R’OH (1 eq.), PC (1 mol%)
and oxidant (2 eq.) in DCE (0.1 M), in a sealed tube.
Scheme 1 Oxidative decarboxylation of oxamic acids. Substrate scope.
Two main limitations were however observed; (1) reaction
using benzyl alcohols did not provide the desired compounds
due to the oxidation of the alcohol under the reaction
conditions A. Similarly, oxamic acids from benzylamines tend to
oxidize at the benzylic position to form the corresponding
2 | J. Name., 2012, 00, 1-3
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aldehyde; (2) somewhat lower yields were observed with Finally, a series of intermediate trapping experVimieweAnrttisclewOnelirnee
oxamic acids derived from anilines due to the known carried out as to establish the DmOeI:c1h0.a1n03is9m/C8CoCf054t6h2iBs
decarbonylation of the putative carbamoyl radical intermediate photocatalyzed oxidative decarboxylation of oxamic acids. First,
(vide infra).13b These limitations were however overcome using 1b was treated under the standard conditions, but in the
an excess of oxamic acid (Conditions B), leading to improved presence of TEMPO, which led to the formation of compound 7,
yields of the corresponding urethanes (i.e. 3w-z). Bis-oxamic albeit in low yield, supporting the radical nature of the process
acids 4a-b were also shown to react cleanly with alcohols to (Scheme 4). According to the seminal mechanistic proposal by
afford the corresponding bis-carbamates 5a-d in good yields Minisci,13b decarboxylation of oxamic acid under oxidative
(Scheme 2). This result is noteworthy as it opens the way to the conditions proceeds through the formation of a carbamoyl
synthesis of polyurethanes using diols.
radical intermediate (RNHCO.),19 which further oxidation
generates the corresponding cation or protonated isocyanate
O
O
O
O
(RNHC+=O
↔
RHN+=C=O). When oxamic acid 1a was treated
4CzIPN, BI-OAc
X
R
X
R
+
R
OH
HO2C
N
N
CO2H
O
N
H
N
O
rt
DCE, 36-48
h,
under conditions above, replacing R’OH with alkynylsulfone
amide
was detected (1H NMR, MS), supporting the presence
of a carbamoyl radical intermediate, reacting onto through an
addition-elimination process20 to form
. The same reaction was
8,
H
H
H
Blue LED
5a-d
4a-b
9
O
O
8
Ph
N
H
OEt
N
H
O
H
H
9
EtO
N
O
N
Ph
repeated using oxamic acid 1a and allylsilane 10, which led to
the formation of amide 11 in 22% yield. Although this
experiment was originally intended to support the presence of
the cationic species (RNHC+=O), we cannot rule out at this stage
that allylsilane 10 may also trap the carbamoyl radical, to form
5a
5b
72%
58%
,
,
O
O
O
O
O
H
N
OEt
Me
Me
EtO
N
O
N
N
O
4
4
H
4
H
H
O
5c
,
5d
,
62%
68%
a Conditions C: the reactions were carried out with oxamic acid (1 eq.), ROH (3
eq.), PC (2 mol%) and oxidant (2 eq.) in DCE (0.2 M), in a sealed tube.
a
β
-silyl radical, the oxidation of which (possibly by 4CzIPN.+, the
semi-oxidized form of the photocatalyst) would lead to a -silyl
β
Scheme 2 Bis-oxamic acids as bis-urethane precursors
cation collapsing to afford 11 (vide infra). Finally, it was
envisioned that decarboxylation of oxamic acid would proceed
through the intermediary of a benziodoxole-oxamic acid
complex such as 12 (having a weak O-I bond) as recently
The results obtained in the carbamate series then prompted us
to extend the methodology to the preparation of
unsymmetrical ureas. The one-pot protocol established for the
carbamate was however not found suitable for a direct access
proposed for the related oxidative decarboxylation of
α-
ketoacids.16c However, all our efforts to prepare 12 through
coupling between oxamic acid 1a and BIOAc unfortunately met
with failure.
O
O
rt
4CzIPN, BI-OAc, DCE, Blue LED, 24
h,
R
R
R'
N
CO2H
N
N
H
H
H
then Et N
(3.0 equiv.)
30o 4-6 h
3
1a-f
6a-i
R'-NH
,
equiv)
C,
2 (1.0
OMe
OMe
O
O
H
N
H
O
4CzIPN, BI-OAc
TEMPO
N
H
N
H
O
HN
N
HN
N
N
O
OH
H
H
N
O
O
O
rt, LED
DCE, 24
h,
1b
6a
6b
6c
68%
,
70%
78%
,
,
1H NMR)
7
(
4CzIPN, BI-OAc
O
O
Me3Si
SO2Ph
8
O
N
HN
N
H
O
Cl
HN
Me Me
H
DCE, 24 rt, LED
h,
N
H
N
H
O
N
H
6d
6e
6f 74%
,
69%
82%
,
,
SiMe3
O
9
1H NMR,
MS)
(
H
N
H
N
H
H
N
N
OMe
OMe
O
N
N
N
H
N
H
Me
O
O
Me
O
O
O
4CzIPN,
BI-OAc
I
SiMe3
O
10
6g
6h
6i
64%
78%
52%
,
,
,
X OAc
N
I
N
1a
H
H
O
O
rt, LED
DCE, 24
h,
a Conditions D: the reactions were carried out with oxamic acid (2.0 eq.), PC (1
mol%) and oxidant (1.5 eq.) in DCE (0.1 M), then Et3N (3 eq.), R’NH2 (1.0 eq.), under
Ar atm, 30oC , 4-6 h.
O
,
11
12
22%
Scheme 4 Intermediate trapping experiments.
Scheme 3 Synthesis of unsymmetrical ureas.
to ureas, likely due to the oxidation of the amine partner under
the reaction conditions. Moreover, the presence of benzoic acid
residue resulting from the reaction of the oxidant BI-OAc clearly
obstructed the formation of ureas. These drawbacks could
however be circumvented adding, in the same pot, after
completion of the decarboxylation process, 3.0 equiv. of Et3N
prior to the addition of the amine (Conditions D). This two-steps
one-pot protocol proved its efficiency affording a variety of
ureas 6a-i in satisfying yields (Scheme 3).
On the basis of these trapping experiments and related
literature,15,16 a plausible mechanism was proposed, starting
with the quenching of photocatalyst (PC: 4CzIPN) in its excited
state by an intermediate of type
I formed through ligand
exchange at the iodine center (Figure 2).16c This would generate
the resulting radical-anion II, then collapsing to afford the
corresponding amidocarboxyl radical. Decarboxylation of the
latter would form carbamoyl radical III, along with the o-
iodobenzoic acid anion. III would then be oxidized further by the
photocatalyst radical cation PC.+ into the corresponding
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8879; (c) X. C. Huang, J. W. Keillor, Tetrahedron LVeitetw.,A1rt9ic9le7O,n3lin8e
,
protonated isocyanate IV, returning PC in its ground state. IV
would finally loose a proton to afford the desired isocyanate,21
or react in situ with alcohols and amines to give urethanes and
ureas respectively.
313; (d) P. Radlick, L. R. Brown, SyntheDsOisI,: 1109.17043,94/C, 82C9C00;5(4e6)2SB.
R. Manne, K. Thalluri, R. R. Giri, J. Chandra, B. Mandal, Adv.
Synth. Catal., 2017, 359, 168.
(a) T. Curtius, J. Prakt. Chem., 1894, 50, 275; (b) E. F. V.
Scriven, K. Turnbull, Chem. Rev., 1988, 88, 297.
7
8
O
O
(a) N. Kornblum, A. Scott, J. Org. Chem., 1977, 42, 399; (b) K.
Takeda, K. Tsuboyama, M. Hoshino, M. Kishino, H. A. Ogura,
Synthesis, 1987, 557; (c) R. E. Shute, D. H. Rich, Synthesis,
1987, 346.
(a) D. Chaturvedi, S. Ray, Monatsh. Chem., 2006, 137, 127; (b)
T. Sakakura, Y. Saito, M. Okano, J. Choi, T. Sako, J. Org. Chem.,
1998, 63, 7095; (c) M. Abla, J. C. Chol, T. Sakakura, Chem.
Commun., 2001, 2238; (d) Y. Yoshida, S. Ishii, T. Yamashita,
Chem. Lett., 1984, 13, 1571; (e) S. Cenini, C. Crotti, M. Pizzotti,
F. Porta, J. Org. Chem., 1988, 53, 1243; (f) R. N. Salvatore, J. A.
Ledger, K. W. Jung, Tetrahedron Lett., 2001, 42, 6023; (g) T. E.
Waldman, W. D. Mcghee, J. Chem. Soc., Chem. Commun.,
1994, 957; (h) M. Yoshida, N. Hara, S. Okuyama, Chem.
Commun., 2000, 151.
+
-
R'XH
+
H
C
R
R
R
N
C
O
N
XR'
PC
N
-
H
H
IV
H
υ
h
O
9
R
N
III
H
O
PC
R
I
PC*
AcO
-
-
CO2
O
CO2
I
O
O
O
O
R
O
O
R
N
N
N
CO2H
-
BI
BI
AcOH
H
H
H
O
I
II
Figure 2 Mechanism of the oxidative decarboxylation of oxamic acids.
10 (a) S. Ozaki, Chem. Rev., 1972, 72, 457; (b) O. Bayer, Angew.
Chem., 1947, 59, 257; (c) O. Bayer, E. Müller, Angew. Chem.,
1960, 72, 934.
11 L. Maisonneuve, O. Lamarzelle, E. Rix, E. Grau, H. Cramail,
Chem. Rev., 2015, 115, 12407.
12 (a) H. Eckert, B. Forster, Angew. Chem., Int. Ed. Engl., 1987,
26, 894; (b) M. Denarié, D. Grehouillat, T. Malfroot, J. P.
Senet, G. Sennyey, P. Wolf, Tetrahedron Lett., 1987, 28, 5823;
(c) K. Takeda, K. Tsuboyama, K. Yamaguchi, H. Ogura, J. Org.
Chem., 1985, 50, 273.
13 (a) F. Minisci, F. Coppa, F. Fontana, J. Chem. Soc., Chem.
Commun., 1994, 679; (b) F. Minisci, F. Fontana, F. Coppa, Y. M.
Yan, J. Org. Chem., 1995, 60, 5430.
14 For selected reviews on visible-light photoredox catalysis, see:
(a) C. K. Prier, D. A. Rankic, D. W. C. MacMillan, Chem. Rev.
2013, 113, 5322; (b) J. M. R. Narayanam, C. R. J. Stephenson,
Chem. Soc. Rev., 2011, 40, 102; (c) N. A. Romero, D. A.
Nicewicz, Chem. Rev. 2016, 116, 1007; (d) L. Marzo, S. K.
Pagire, O. Reiser, B. König, Angew. Chem. Int. Ed. 2018,
DOI.org/10.1002/anie.201709766n.
15 (a) W. F. Petersen, R. J. K. Taylor, J. R. Donald, Org.
Lett., 2017, 19, 874; (b) Q.-F. Bai, C. Jin, J.-Y. He, G. Feng, Org.
Lett., 2018, 20, 2172.
In summary, we reported a “metal-free” photocatalyzed
oxidative decarboxylation of oxamic acids, which provides a
straightforward and environmentally benign entry toward
urethanes and ureas. The methodology uses readily available
starting material as well as standard photocatalyst and organic
oxidant sources. Intermediate trapping experiments suggest
that BIOAc used as terminal oxidant reacts with the oxamic acid
to generate an instable benziodoxole-oxamic acid complex, the
source of the amidocarboxyl radical. Decarboxylation of the
latter and further oxidation lead to the desired isocyanate.
Work is actively pursued in our laboratories to apply this
strategy to the synthesis of bio-sourced polyurethanes, which
will be reported soon.
We are grateful to the University of Bordeaux (UBx) for financial
support through the 2017 IdEx Bordeaux Post-doctoral
Program. We acknowledge C. Absalon for mass spectrometry
analysis (Cesamo, UBx) and the CNRS for financial help.
16 (a) H. Tan, H. Li, W. Ji, L. Wang, Angew. Chem. Int. Ed., 2015,
54, 8374; (b) H. Huang, G. Zhang, L. Gong, S. Zhang, Y. Chen, J.
Am. Chem. Soc., 2014, 136, 2280; (c) H. Huang, K. Jia, Y. Chen,
Angew. Chem. Int. Ed., 2015, 54, 1881; (d) H. Huang, K. Jia, Y.
Conflicts of interest
“There are no conflicts to declare”.
Chen, ACS Catal., 2016, 6, 4983 and references cited therein.
17 H. Uoyama, K. Goushi, K. Shizu, H. Nomura, C. Adachi, Nature,
2012, 492, 234.
Notes and references
1
A. K. Ghosh, M. Brindisi, J. Med. Chem., 2015, 58, 2895 and
references therein.
(a) C. Dugave, L. Demange, Chem. Rev., 2003, 103, 2475; (b)
C. Cox, T. Lectka, J. Org. Chem., 1998, 63, 2426; (c) P. R.
Rablen, J. Org. Chem., 2000, 65, 7930; (d) M. J. Deetz, C. C.
Forbes, M. Jonas, J. P. Malerich, B. D. Smith, O. Wiest, J. Org.
Chem., 2002, 67, 3949.
18 S. S. Fukuzumi, H. Kotani, K. Ohkubo, S. Ogo, N. V. Tkachenko,
H. Lemmetyinen, J. Am. Chem. Soc., 2004, 126, 1600.
19 (a) For a review on acyl and carbamoyl radical chemistry, see:
C. Chatgilialoglu, D. Crich, M. Komatsu, I. Ryu, Chem. Rev.,
1999, 99, 1991; (b) W. F. Petersen, R. J. K. Taylor, J. R. Donald,
Org. Biomol. Chem., 2017, 15, 5831; (c) M. Li, C. Wang, P. Fang,
H. Ge, Chem. Commun., 2011, 47, 6587; (d) M. Yuan, L. Chen,
J. Wang, S. Chen, K. Wang, Y. Xue, G. Yao, Z. Luo, Y. Zhang,
Org. Lett., 2015, 17, 346.
20 (a) M. Nagatomo, S. Yoshida, M. Inoue, Chem. Asian J., 2015,
10, 120; (b) S. Zhou, T. Song, H. Chen, Z. Liu, H. Shen, C. Li, Org.
Lett., 2017, 4819, 698; (c) J. Xiang, W. Jiang, P. L. Fuchs,
Tetrahedron Lett., 1997, 38, 6635; (d) A.-P. Schaffner, V.
Darmency, P. Renaud, Angew. Chem., Int. Ed., 2006, 45, 5847;
(e) V. Liautard, F. Robert, Y. Landais, Org. Lett., 2011, 13, 2658.
21 When the oxidation was carried out in the absence of R’OH
(Scheme 1), corresponding isocyanates were formed in good
yields.
2
3
4
(a) F. Vacondio, C. Silva, M. Mor, B. Testa, Drug Metab. Rev.,
2010, 42, 551; (b) B. Testa, J. M. Mayer, Hydrolysis in Drug and
Prodrug Metabolism
–
Chemistry, Biochemistry, and
Enzymology; Wiley-VCH: Weinheim, Germany, 2003.
C. Y. Cho, E. J. Moran, S. R. Cherry, J. C. Stephans, S. P. Fodor,
C. L. Adams, A. Sundaram, J. W. Jacobs, P. G. Shultz, Science,
1993, 261, 1303.
5
6
T. W. Greene, P. G. M. Wuts, Protecting Groups in Organic
Synthesis, 3rd Ed. J. Wiley & Sons, New York, (1999), 503.
(a) P. Gogoi, D. Konwar, Tetrahedron Lett., 2007, 48, 531; (b)
Y. Matsumura, T. Maki, Y. Satoh, Tetrahedron Lett., 1997, 38
,
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Graphical Abstract
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DOI: 10.1039/C8CC05462B
Visible‐Light Photocatalyzed Oxidative Decarboxylation of
Oxamic Acids: A Green Route to Urethanes and Ureas
Oxidative decarboxylation of oxamic acids under visible‐
light irradiation in the presence of alcohols or amines
provides urethanes or ureas.