Photoinduced radical-initiated carboxylative cyclization of allyl amines with carbon dioxide

Article abstract of DOI:10.1039/c6gc03200a

Visible light-promoted CO₂ upgrading: a highly efficient and metal-free photochemical method for the carboxylative cyclization of allyl amines with CO₂ is reported to prepare perfluoroalkylated oxazolidinones with high efficiency under ambient conditions by using perfluoroalkyl iodides as radical sources.

Full text of DOI:10.1039/c6gc03200a

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COMMUNICATION
Photoinduced radical-initiated carboxylative cyclization of allyl
amines with carbon dioxide†
Received 00th January 20xx,
Accepted 00th January 20xx
a
a
a
a
a,b
a
Mei-Yan Wang, Yu Cao, Xi Liu, Ning Wang, Liang-Nian He* and Si-Han Li
DOI: 10.1039/x0xx00000x
www.rsc.org/
t
Visible light-promoted CO upgrading: A highly efficient and equivalent tert-butyl hypoiodite ( BuOI) could efficiently
2
metal-free photochemical method for the carboxylative promote the carboxylative cyclization of CO with allyl
2
6
b
+
cyclization of allyl amines with CO2 is reported to prepare amines. As a result, the active iodine reagent (electrophilic I
perfluoroalkylated oxazolidinones with high efficiency at as key species) as promoter is crucial for this reaction. To date,
ambient conditions by using perfluoroalkyl iodides as radical the development of this kind of carboxylative cyclization is still
t
sources.
limited with using active iodine reagents (i.e. I , BuOI, N-
2
o
iodosuccinimide) at a low temperature (-20 – 0 C), presumably
The development of sustainable strategies for organic synthesis
going through activation of the C=C bond of allyl amines by
electrophilic monovalent iodine (I ). Accordingly, the
development of effective strategies for the carboxylative
cyclization of allyl amines with CO2 at ambient conditions
remains attractive and challenging.
+
has received increasing attention. In this context, utilizing CO2
1
as a synthon for the synthesis of heterocycles is attractive,
b
e
c
a
u
s
e
C
O
i
s
a
u
b
i
q
u
i
t
o
u
s
n
o
n
t
o
x
i
c
a
n
d
r
e
n
e
w
a
b
l
e
C
-
2
1
building block. Commonly, CO conversion requires energy
2
input due to its thermodynamically stable and kinetically inert.
As well-known, the C=C bond easily reacts with a radical
generated through photocatalysis. In this aspect, photoinduced
perfluoroalkylation of alkenes is attractive, because the
Solar energy as an initiator or promoter for CO transformation
2
8
is undoubtedly appealing because of its natural abundance, ease
2
of use and potential applications on an industrial scale. In
introduction of a perfluoroalkyl substituent into the organic
motifs can significantly alter physical, chemical and biological
recent years, much attention has been paid to photocatalytic
9
reduction of CO to produce energy-related products such as
2
properties of the resultant molecules. In this context, we
3
formic acid, methanol, methane or hydrocarbons. To the best
hypothesized that a photoinduced perfluoroalkyl radical could
react with the C=C bond of allyl amines, thus in situ generating
an active intermediate, which subsequently reacts with CO2.
Herein, we presented an efficient photoinduced radical-initiated
protocol for the carboxylative cyclization of allyl amines with
CO2 under mild conditions using perfluoroalkyl iodides as
radical and fluorine sources, which simultaneously achieves the
incorporation of perfluoroalkyl moiety into 2-oxazolidinones as
shown in Scheme 1.
of our knowledge, the work towards the light-driven
incorporation of CO into value-added heterocycles has rarely
2
4
been reported. Excitingly, Murakami group developed the
solar-driven/UV light-driven strategy for chemical fixation of
CO2 into organic componnds e.g. amino-substituted cyclic
carbonates and carboxylic acids from α-methylamino ketones
5
and o-alkylphenyl ketones, seperately. To extend the
application of photochemical synthesis to CO2 fixation is
urgently required, and represents a promising field.
We began our study by examining the reaction of N-
On the other hand, the carboxylative cyclization of allyl
benzylprop-2-en-1-amine (1a) and CO , with perfluorobutyl
iodide ( C F I) as the • C F radical source, in acetonitrile
4 9 4 9
2
6
n
n
amines with CO is a promising example for CO utilization,
2
2
because the products i.e. 2-oxazolidones are of significant
pharmaceutical scaffolds that widely exist in drugs and organic
synthesis. In 2012, Minakata group demonstrated that
under a 300 W xenon lamp (420-700 nm). Delightedly, the
7
a.
State Key Laboratory and Institute of Elemento-Organic Chemistry, Nankai
University, P. R. China
Collaborative Innovation Centre of Chemical Science and Engineering, Nankai
b.
University, 94 Weijin Road, Tianjin 300071, P. R. China
E-mail: heln@nankai.edu.cn, Fax: +86 22-23503878, Tel: +86 22-23503878
†
Electronic Supplementary Information (ESI) available
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
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n
n
Scheme 1 Photoinduced radical-initiated carboxylative cyclization of allyl amines with
CO
yields under the identical conditions, with C F I, C F I and
3
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7 6 13
2
.
DOI: 10.1039/C6GC03200A
CF I as radical source respectively. Interestingly, this protocol
3
a
Table 2 Scope of allyl amines and perfluoroalkyl iodides
a
2
Table 1 Visible-light induced carboxylative cyclization of allyl amines with CO
n
b
Entry
Allyl amine 1
C
n
F
2n+1
I
Product 2
Yield (%)
b
Entry
1
Base (equiv.)
Solvent
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
THF
Yield (%)
n
—
21
0
4 9
C F I
c
2
K
2
CO
CO
3
(2.0)
(2.0)
(2.0)
1
2
3
4
R = Bn, 1a
R = Cy, 1b
R = Me, 1c
R = Bn, 2a
R = Cy, 2b
R = Me, 2c
91
80
99
88
3
4
5
6
7
8
9
K
2
3
70
12
72
85
89
85
92
84
91
83
47
65
90
trace
Li
Cs
2
CO
CO
3
2
3
(2.0)
t
t
R = Bu, 1d
R = Bu, 2d
DBU (2.0)
TBD (2.0)
TBD (2.5)
TBD (1.5)
TBD (1.2)
TBD (1.5)
TBD (1.5)
TBD (1.5)
TBD (1.5)
TBD (1.5)
TBD (1.5)
n
C
4
F
9
I
1
1
1
1
1
1
1
0
1
2
3
4
5
6
5
6
7
X = F, 1e
X = Cl, 1f
X = Br, 1g
X = F, 2e
X = Cl, 2f
X = Br, 2g
82
90
90
82
d
e
8
9
3
X = OCH , 1h
3
X = OCH , 2h
DMF
n
C
4
F
9
I
I
DMSO
8
7
3
CH Cl
1
i
2
i
a
n
Reaction conditions: 1a (73.2 mg, 0.5 mmol),
4 9
C F I (172 µL, 1.0 mmol), MeCN
b
c
d n
(
2 mL), CO
2
(1 bar), room temperature. Isolated yield. No light.
4 9
C F I (1.25
e n
1a
mmol).
4 9
C F I (0.75 mmol).
n
1
1
1
0
1
2
C
3
F
7
n = 3, 2j
n = 6, 2k
n = 1, 2l
94
73
96
n
6 13
C F I
product i.e. 3-benzyl-5-nonafluoropentyl oxazolidin-2-one (2a
of the carboxylative cyclization was obtained in 21% yield after
2 h (Table 1, entry 1) which demonstrated that our hypothesis
)
3
CF I
a
n
Reaction conditions: allyl amine 1 (0.5 mmol),
mmol), MeCN (2 mL), CO
Isolated yield. Cy = cyclohexyl.
C
n
F
2n+1I (1.0 mmol), TBD (0.75
1
b
2
(1 bar, closed), visible light (420-700 nm), r.t., 12 h.
is feasible. Notably, control experiment showed that visible
light was required (entry 2). These results inspired us to further
optimize the reaction conditions. We speculated that the
addition of a base could stabilize the carbamate anion generated
1
0
from 1a and CO2. Gratifyingly, the target product 2a was
produced in 70% yield by adding two equivalents of K CO3
2
(
entry 3). Then several other bases were tested (entries 4–7),
and 1,5,7-triazabicyclo[4,4,0]dec-5-ene (TBD) was identified
as the best choice, thus providing 2a in 89% yield (entry 7).
Next, we investigated the effects of the stoichiometry of
reagents including perfluorobutyl iodide and TBD on the
Scheme 2 Carboxylative cyclization of allyl alcohols with CO
2
is also applicable to the allyl alcohol (Scheme 2), producing the
perfluoroalkylated cyclic carbonates (2m and 2n), of which, 2m
is a promising co-solvent of lithium battery electrolytes.
As an attractive set of this work, the mechanism of this
visible light-driven carboxylative cyclization was strictly
explored. In the course of initial study on the reaction of N-
reaction outcome (entries 8–12). An excess amount of TBD
1
1
n
(
1.5 equiv.) and C F I (2 equiv.) was needed for obtaining the
4
9
maximum yield (92%) (entry 9). In addition, among the
solvents we investigated (entries 13–16), besides MeCN,
DMSO could also give a comparable yield of product 2a (entry
benzylprop-2-en-1-amine 1a, CO and perfluorobutyl iodide in the
2
15 vs 9).
absence of base, besides the product 2a, an aziridine i.e. 1-benzyl-2-
nonafluoropentyl-aziridine 3a was isolated with a 35% yield (Table
S1, entry 1, ESI†). When a base like TBD existed, most of reactants
were converted into 2a (Table S1, entry 2, ESI†). These results
corroborated our initial hypothesis that the base is vital to efficient
generation of a carbamate intermediate with subsequent formation of
C–O bond rather than C–N bond formation. Indeed, treatment of the
allyl amine 1a and perfluorobutyl iodide with two equivalents of
TBD under argon and visible light, the aziridine 3a was obtained as
the sole product in excellent yield (Table S1, entry 3, ESI†). When
Having established the method of radical-initiated
carboxylative cyclization of allyl amines with CO , we then
2
examined the reactivity of various allyl amines to further
explore the utility of this protocol as listed in Table 2. Both N-
benzyl- and N-alkyl-allyl amines gave the corresponding
products (2a
fluoro, chloro, bromo, methoxyl and methylal on the aromatic
ring were tolerated with the present protocol 2e−2i).
–2d) in excellent yields. Functional groups like
(
Heptafluorobutyl, tridecafluoroheptyl and trifluoroethyl 2-
oxazolidinones (2j−2l) were also successfully attained in good
2
| J. Name., 2012, 00, 1-3
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the resultant in above experiment was further treated with CO , only
COMMUNICATION
D
is an intermediate in the carboxylative cyclizaVtieiwonArtioclfe Oanllliynel
2
DOI: 10.1039/C6GC03200A
3
a recovered (Scheme 3a). In addition, when 3a was subjected to the alcohol and CO . As such, an iodo-perfluoroalkylated
2
Scheme 3 Exclusion experiment of the aziridine intermediate.
+
-
standard reaction conditions or treated with [TBDH] I , the
1
carboxylative cyclization was not observed (Scheme 3b). On Fig. 1 H NMR spectra for the visible light-driven carboxylative cyclization of allyl
2
alcohol 1m (14.5 mg, 0.25 mmol), TBD (52.2 mg, 0.375 mmol), CO (1 bar, closed) and
the basis of these observations and previous reports about the
iodo-perfluoroalkylation of alkene, it is strongly suggested that
n
8
4 9 3
C F I (86 µL, 0.5 mmol) in CD CN.
2
a
is not generated from 3a but may be from an iodo-
perfluoroalkylated intermediate , which can be converted into
facilely under basic conditions through intramolecular
nucleophilic cyclization due to the good leaving ability of
iodide ion (Scheme 4). In contrary, the intermediate under
neutral conditions tends to release CO , leading to afford β-
carbamate species
carboxylative cyclization of allyl amines with CO2.
Since the visible light is indispensable to smooth conversion
A could presumably be involved in the
A
2
a
of 1a
,
we speculated that the formation of iodo-
may go through
the visible light-driven radical addition of C F I to allyl amines.
A
perfluoroalkylated carbamate intermediate
A
2
n
4
9
halogenated amine species
byproduct 3a
B, further the formation of
To further gain insight into the reaction mechanism, the radical-
trapping experiment was carried out by employing two
equivalents of 4-OH-TEMPO under the standard conditions
.
(
Scheme 5a). As expected, 1a was completely recovered,
hinting that this carboxylative cyclization proceeded via a
n
radical path. Furthermore, the reaction of C F I with allyl ether
4
9
4
under standard conditions gave the cyclic product 5 in 61%
yield (dr = 50:11), also implicating the involvement of the
radical propagation (Scheme 5b).
Scheme 4 Competitive reactions between the formation of oxazolidinone 2a and
aziridine 3a.
To confirm that an iodo-perfluoroalkylated intermediate is
involved in the overall reaction, we monitored the
carboxylative cyclization reaction of allyl alcohol 1m, CO and
2
n
1
C F I in deuterated acetonitrile by H NMR technique in
4
9
consideration of the relative stability of β-halogenated alcohol
to β-halogenated amine. Within 1 h, the solubility of the allyl
carbonate precipitated from allyl alcohol, CO2 and TBD is
increasing, probably due to a little increase in reaction
temperature caused by light input. Thus, an enhancement in the
intensity of signal centred at 4.36 ppm was observed (Fig. 1).
Meanwhile, a group of weak signals corresponding to 4-
nonafluoropentyl-ethylene carbonate 2m (diamonds in Fig. 1)
appeared, indicating the start of this carboxylative cyclization
reaction. As the reaction progressed at 4 h, a new set of signals
emerged at δ = 4.31, 3.82, 3.67 ppm (triangles in Fig. 1),
Scheme 5 Radical-trapping experiments.
On the basis of above observations, a plausible mechanism
for the present metal-free and visible light-driven carboxylative
cyclization of allyl amines
taking 1a for an example. Initially, the carbamate
characterizations of carbamate , see ESI†) is formed readily
1 with CO is depicted in Scheme 6,
2
E
(Detailed
E
12
from 1a and CO promoted by TBD. Initiated by visible light,
2
n
C F I occurs to homolytic cleavage of carbon-iodine bond,
generating • C F and I• radical species. Addition of • C F
4 9
4
9
n
n
4
9
assigned to the iodo-perfluoroalkylated carbonate
D, which was
radical to the π-bond of carbamate
perfluoroalkylated secondary carbon radical species F, which is
trapped by I• radical to produce the iodo-perfluoroalkylated
E furnishes the
indirectly corroborated by GC-MS (see Fig. S1, ESI†). From 6
1
h to 6.2 h, the carbonate
D was fully converted into 2m. The H
NMR study confirms that the iodo-perfluoroalkylated carbonate
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carbamate intermediate A-1 (Path I). Alternatively, the
He, ChemSusChem, 2015,
8
, 52; (g) J. Hu, J. Ma, Q. Zhu, Z.
View Article Online
DOI: 10.1039/C6GC03200A
intermediate A-1 might be formed via a radical propagation of
Zhang, C. Wu and B. Han, Angew. Chem., Int. Ed., 2015, 54,
n
F
with C F I (Path II). Finally, intramolecular nucleophilic
5399; (h) D. Adhikari, A. W. Miller, M.-H. Baik and S. T.
Nguyen, Chem. Sci., 2015, , 1293; (i) Z. Zhang, L.-L. Liao,
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Wang, Q.-W. Song, R. Ma, J.-N. Xie and L.-N. He, Green
Chem., 2016, 18, 282.
4
9
cyclization of A-1 gives the perfluoroalkylated 2-oxazolidinone
6
+
-
2
a
with release of [TBDH] I .
2
3
G. Ciamician, Science, 1912, 36, 385.
(a) T. W. Woolerton, S. Sheard, E. Reisner, E. Pierce, S. W.
Ragsdale and F. A. Armstrong, J. Am. Chem. Soc., 2010, 132
,
2
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5969; (f) W.-H. Wang, Y. Himeda, J. T. Muckerman, G. F.
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promoted by visible light irradiation with high efficiency under
ambient conditions. By using perfluoroalkyl iodides as radical
and fluorine sources, this strategy achieves concurrent and
2
016, 138, 6292.
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4
,
2
direct incorporation of both CO and perfluoroalkyl moiety into
2
1
oxazolidinones in excellent yields. Control experiments and H
,
NMR study show that the iodo-perfluoroalkylated carbamate
6
generated through the visible light-driven radical addition of
and W. Macyk, ChemPlusChem., 2014, 79, 708; (e) N. Ishida,
Y. Masuda, S. Uemoto and M. Murakami, Chem. Eur. J.,
n
C F I to allyl amines could be the intermediate of this reaction.
4
9
Notably, the perfluoroalkylated cyclic carbonate is also
obtained successfully via this protocol from allyl alcohol and
2
016, 22, 6524.
5
6
(a) Y. Masuda, N. Ishida and M. Murakami, J. Am. Chem.
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CO . This protocol also offers a sustainable and promising
2
approach for incorporating CO2 into heterocycles through
efficient usage of solar energy.
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2
006, 17, 2548; (b) Y. Takeda, S. Okumura, S. Tone, I.
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Acknowledgements
We are grateful to the National Key Research and
Development Program (2016YFA0602900), the National
Natural Science Foundation of China, the Natural Science
Foundation of Tianjin Municipality (16JCZDJC39900),
Specialized Research Fund for the Doctoral Program of Higher
Education (20130031110013), NFFTBS (J1103306), Research
Found for the Doctoral Innovation Project of Nankai University
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1
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DOI: 10.1039/C6GC03200A
A highly efficient photoinduced radical-initiated strategy for the carboxylative
cyclization of allyl amines with CO was developed firstly.
2