Metal-Free Fast Azidation by Using Tetrabutylammonium Azide: Effective Synthesis of Alkyl Azides and Well-Defined Azido-End Polymethacrylates

Article abstract of DOI:10.1002/chem.201903188

An effective method to synthesize azido-end polymethacrylates from tetrabutylammonium azide (BNN₃) in a nonpolar solvent (toluene) was developed. Several low-mass alkyl halides were reacted with BNN₃ in toluene as model reactions and

Full text of DOI:10.1002/chem.201903188

A Journal of
Accepted Article
Title: Metal-Free Fast Azidation Using Tetrabutylammonium Azide:
Effective Synthesis of Alkyl Azides and Well-defined Azido-end
Polymethacrylates
Authors: Chen-Gang Wang, Amerlyn Ming Liing Chong, Yunpeng Lu,
Xu Liu, and Atsushi Goto
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
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to this Accepted Article as a result of editing. Readers should obtain
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content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201903188
Link to VoR: http://dx.doi.org/10.1002/chem.201903188
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FULL PAPER
Metal-Free Fast Azidation Using Tetrabutylammonium Azide:
Effective Synthesis of Alkyl Azides and Well-defined Azido-end
Polymethacrylates
Chen-Gang Wang, Amerlyn Ming Liing Chong, Yunpeng Lu, Xu Liu and Atsushi Goto*
Abstract: An effective method to synthesize azido-end
polymethacrylates using tetrabutylammonium azide (BNN ) in a non-
polar solvent (toluene) was developed. Several low-mass alkyl
halides were reacted with BNN in toluene as model reactions and
the rate constants of these reactions were determined, confirming
fast BNN -azidation for tertiary and secondary halides. The end-
However, the use of copper brings about time-consuming post-
purification steps and limits the biomedical and other
applications. Han and Tsarevsky generated azide radicals using
hypervalent iodine compounds and used the azide radicals to
3
3
[
13]
initiate and terminate conventional radical polymerizations.
3
This method elegantly yielded azido-end polymethacrylates in a
metal-free manner, while the polymer structures were not aimed
to control because of conventional radical polymerization.
Our research group has synthesized iodo-end polymers
(polymer–I) via reversible complexation mediated polymerization
(RCMP), which is an organocatalyzed living (or reversible
deactivation) radical polymerization. RCMP uses an alkyl iodide
group transformation of halide-end polymethacrylates was effective
and nearly quantitative. Notably, the combination of organocatalyzed
living (or reversible deactivation) radical polymerization and BNN
3
-
azidation enabled metal-free synthesis of azido-end
polymethacrylates, including single-azido-end and multi-azido-end
functional homopolymers and block copolymer. The rapid and
[
14–18]
quantitative reaction without using a large excess of BNN
3
metal-free
as an initiator and an organic molecule as a catalyst.
The
and polar-solvent-free nature, and broad polymer scope are
attractive feature of this azidation.
weak C–I bond at the polymer–I chain-end facilitates end-group
[
19,20]
modification.
polymethacrylate–I to azido-end polymethacrylate–N
a small excess of NaN
use of iodide instead of bromide enabled the reduction of NaN
We
recently
successfully
converted
3
using only
[
21]
3
(1.1 eq) in a polar solvent (DMF). The
3
Introduction
(1.1 eq (I) vs 10 eq (Br)).
A metallic azide salt NaN
3
is soluble only in polar solvents.
Alkyl azides are important precursors in organic chemistry,
In sharp contrast, tetrabutylammonium azide (BNN
organic azide salt, is soluble in both polar and nonpolar solvents.
In the present work, we used BNN as an azidation reagent in a
nonpolar solvent, i.e., toluene (Scheme 1c). BNN was
3
), which is an
e.g., in the synthesis of heterocycles, functional peptides, and
[
1–3]
biomedical molecules.
Because of the high reactivity, azide
3
chemistry is also extensively utilized in polymer chemistry.
Azido-chain-end functionalized polymers are enabling building
blocks to construct structurally complex macromolecules via 1,3-
dipolar cycloadditions, particularly copper(I)-catalyzed azide-
3
successfully used to initiate anionic polymerization of oxiranes
and vinyl monomers to give polymers with an azido group at the
[22,23]
initiating chain end.
However, the stringent moisture-free
[
4–8]
alkyne “click” cycloaddition (CuAAC).
Sodium azide (NaN ) is widely used as an azidation agent
condition required in anionic polymerizations limits the synthetic
accessibility.
3
of alkyl halides and halide-end polymers in polar solvents such
as dimethylformamide (DMF) and dimethyl sulfoxide (DMSO).
Azido-end polystyrenes and polyacrylates were thereby
efficiently synthesized. However, the NaN
3
-azidation was
relatively slow for polymethacrylates because of the difficulty of
[
9,10]
SN
2
displacement for generating tertiary alkyl azides.
A 10-
fold excess of NaN
3
with long reaction time (≥ 12 h) was
generally required for quantitative azidation of bromo-end
polymethacrylates due to the tertiary alkyl chain end (Scheme
[
11]
1
a). Because of its explosive nature, the use of a large excess
of NaN poses a potential safety concern in a scale-up synthesis.
Besides this conventional NaN -azidation, Vermonden and
coworkers reported a fast NaN -azidation using a copper
catalyst, attaining a quantitative conversion of a tertiary alkyl
3
3
3
[
12]
3
bromide in 20 min with 1.2 equivalence of NaN (Scheme 1b).
Dr. C-G. Wang, A. M. L. Chong, Dr. Y. Lu, Dr. X. Liu, Prof. Dr. A. Goto
Institution Division of Chemistry and Biological Chemistry, School of
Physical and Mathematical Sciences, Nanyang Technological University,
21 Nanyang Link, 637371 Singapore
E-mail: agoto@ntu.edu.sg
Scheme 1. Azidation of Polymethacrylates: (a) Conventional Approach, (b)
Copper-catalyzed Approach, and (c) This Work.
Supporting information for this article is given via a link at the end of the
document.
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Chemistry - A European Journal
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A significant finding in the present work was that the BNN
azidation in toluene was as efficient as the conventional NaN
3
-
-
removal of BNI in the post-purification of the obtained alkyl
azides.
3
azidation in polar solvents. The BNN
quantitative without using a large excess of BNN
catalysts, or polar solvents. We systematically studied the BNN
azidation using different alkyl halides (I, Br and Cl) at different
temperatures in low-mass systems. We also experimentally
determined the azidation rate constant in several systems. We
subsequently applied the BNN -azidation to polymer systems.
3
We synthesized iodo-end polymethacrylates via RCMP and
converted them to the azido-end polymethacrylates. The
combination of RCMP with the BNN -azidation offers a
3
3
-azidation was rapid and
For comparison, NaN
Crown-6-ether was added to dissolve NaN
mM), NaN (1.5 eq), and 18-crown-6-ether (1.5 eq) were heated
at 50 °C in toluene-d , resulting in only 3% azido conversion
even after 2 h (Table 1, Entry C1). This result is consistent with
our previous finding that the reaction of EMA–I with NaN in
toluene predominantly generates EMA radical rather than EMA–
3
was used instead of BNN
3
in toluene. 18-
3
, metallic
3
. EMA–I (1.0 eq, 40
3
-
3
8
3
•
[
21]
N
3
.
Although the reason for the predominant radical
generation by NaN and the predominant azidation by BNN is
unclear at the moment, this result means that the observed rapid
azidation is unique to BNN . No requirement of expensive 18-
3
3
completely metal-free synthetic route of azido-end polymers.
The use of the non-polar solvent further uniquely enabled the
azidation of hydrophobic polymers that are insoluble in polar
solvents.
3
3
crown-6-ether to dissolve BNN is also beneficial in the practical
use.
Results and Discussion
We first studied the BNN
systems. For tertiary alkyl halides, we used ethyl 2-iodo-2-
methylpropionate (EMA–I) and ethyl 2-bromo-2-
3
-azidation in low molar mass
methylpropionate (EMA–Br) (Figure 1), which are unimer models
of polymethacrylate–iodide and polymethacrylate–bromide,
respectively. A mixture of EMA–I (40 mM) and BNN
3
(60 mM)
. As
was heated at 50 °C in a nonpolar solvent, i.e., toluene-d
8
1
the H NMR spectra show (Figure 2), the azidation was very fast
and completed within 20 min (Table 1, Entry 2).
1
Figure 2. H NMR (300 MHz) spectra of (a) pure EMA−I, (b) pure EMA−N
3
,
3 8
and (c−f) a mixture of EMA−I (40 mM) and BNN (60 mM) heated in toluene-d
at 50 °C for 2, 5, 10 and 20 min, respectively (Table 1, entry 2).
Figure 1. Structures of alkyl halides, poly(methyl methacrylate)-halides, and
azidation agents used in this work.
3
A reduced amount of BNN from 1.5 eq to 1.2 eq still gave
Density functional theory (DFT) calculation suggested that
the total energy change from the reactants (EMA–X and
a fast azidation with an almost quantitative (96%) conversion
after 45 min at 50 °C (Table 1, Entry 3). Lowering the
temperature from 50 °C to room temperature (rt) (20±2 °C)
slowed down the reaction but still attained a 96% conversion
tetramethylammonium azide (Me
BNN for the calculation) to the corresponding products (EMA–
and Me NX) is negative (–91.10 kJ/mol for X = I and –91.63
kJ/mol for X = Br), rationalizing the favorable formation of EMA–
from EMA–Br and EMA–I (Figure S2, Supporting information). than that of the alkyl iodide EMA–I but was still fast. With 1.5 eq
4 3
NN ) as a simplified model of
3
N
3
4
after 3 h with 1.5 eq of BNN
3
(Table 1, Entry 1).
The azidation of the alkyl bromide EMA–Br was slower
N
3
Despite the large energy change, the reverse reaction may
slowly occur. In the present system, tetrabutylammonium iodide
3
of BNN , the conversion reached 96% after 1 h at 50 °C and
90% after 6 h at rt (Table 1, Entries 4 and 5), showing the
effective azidation of the alkyl bromide.
3 8
(BNI) (generated from BNN ) precipitated in toluene-d . The
poor solubility of BNI in toluene prevents the reverse reaction
from occurring, driving the azidation reaction (a Finkelstein-type
[
24]
reaction). The poor solubility of BNI is also beneficial for easy
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FULL PAPER
Table 1. Azidation of Alkyl Halides and Halide End-functional PMMA.
R─X
Azide
[
a]
3
-1 -1
Entry
Solvent
T (°C)
t (min)
Conv (%)
k (×10 ) (M s )
(
40 mM)
(60 mM)
1
2
3
4
5
6
7
8
9
EMA─I
EMA─I
EMA─I
EMA─Br
EMA─Br
EA─I
BNN
3
Toluene-d
Toluene-d
Toluene-d
Toluene-d
Toluene-d
Toluene-d
Toluene-d
Toluene-d
Toluene-d
Toluene-d
8
8
8
rt
180
20
96
99
96
90
96
99
93
98
100
85
58
96
100
62
100
3
11
190
–
BNN
3
50
50
rt
[
b]
BNN
3
45
360
60
1
BNN
BNN
BNN
BNN
BNN
BNN
BNN
3
3
3
3
3
3
3
8
8
3.2
28
–
50
50
50
50
50
50
8
8
8
8
8
EA─Br
EA─Cl
MB─Br
MB─Cl
20
30
10
–
–
–
10
480
–
1
0
–
11
PMMA─I
BNN
3
3
Toluene-d
8
50
20
–
3
0
0
–
3
–
12
PMMA─Br
BNN
Toluene-d
8
8
50
60
–
[
c]
C1
C2
C3
EMA─I
EMA─Br
EMA─Br
NaN
NaN
NaN
3
Toluene-d
50
rt
120
120
30
0.081
6.7
110
3
3
DMSO-d
6
89
99
DMSO-d
6
50
1
[
a] Calculated by H NMR spectra. For Entries 11 and 12, the conversions were calculated by using the corresponding PMMA-b-PEG copolymers. [b] 48 mM. [c]
Addition of 18-crown-6-ether (60 mM).
-
1
-1
values (Figure 3 and Table 1). The k values (M s ) for EMA‒I
–
3
–3
(
190×10 (50 °C) and 11×10 (rt)) were 3–7 times larger than
–3
–3
those for EMA–Br (28×10 (50 °C) and 3.2×10 (rt)) (Table 1,
Entries 1, 2, 4 and 5). The temperature dependence of this
azidation was large, as the k value increased by a factor of 10–
2
0 from rt to 50 °C for EMA–I and EMA–Br. The comparison
system with NaN /18-crown-6-ether has small value
0.081×10 (50 °C)) (Table 1, Entry C1).
Using EMA–Br, we also studied the conventional NaN
3
a
k
–3
(
3
-
–3
azidation in DMSO. The obtained k values (110×10 (50 °C)
–3
and 6.7×10 (rt)) (Table 1, Entries C2 and C3) are similar in
magnitude to those in the present BNN -azidation in toluene
28×10 (50 °C) and 3.2×10 (rt)), quantitatively confirming that
the BNN -azidation in the nonpolar solvent is as effective as the
conventional NaN -azidation in the polar solvent.
3
–3
–3
(
3
3
The BNN3-azidation was amenable not only to tertiary
alkyl halides but also to secondary alkyl halides, i.e., ethyl 2-
iodopropionate (EA–I), ethyl 2-bromopropionate (EA–Br), ethyl
2
-chloropropionate (EA–Cl), (1-bromoethyl)benzene (MB−Br),
Figure 3. Second-order kinetic plots in the azidation reactions. The alkyl
halides, azidation agents, solvents, temperature, symbols are indicated in the
figure. The experimental conditions are given in Table 1 (Entries 1, 2, 4, 5, C2,
and C3).
and (1-chloroethyl)benzene (MB−Cl) (Figure 1) at 50 °C using
1.5 eq of NaN3 (Table 1, entries 6–10). EA–X and MB−X are
unimer models of polyacrylate−X and poly-styrene−X,
respectively. The reaction of EA−I was extremely fast and
completed within 1 min (Table 1, entry 6). Among the alkyl
bromides, the reaction was faster in the order of EMA–Br (60
min) < EA–Br (20 min) < MB–Br (10 min for reaching >90%
The reaction was virtually an irreversible (Finkelstein-type)
azidation. We may use the general integrated rate law for the
A+B type second-order reaction given by
3
conversion at 50 °C) (Table 1, entries 5, 7, and 9). The BNN -
azidation was effective even for alkyl chlorides. The reaction of
EA–Cl completed in a short time (30 min) (Table 1, entry 8), and
that of MB–Cl was relatively slow but still attained a high
conversion (85%) after 8 h (Table 1, entry 10).
ꢀ
ꢂꢃꢄꢄ ꢆꢉꢊ–ꢋꢌꢇ
ꢅ
ln ꢎ ꢆꢇꢏ ꢐ ꢑꢒ
ꢉꢊ–ꢋꢌꢂꢃꢄꢄ
ꢅ
(1)
ꢁ
ꢂꢃꢄꢄ
ꢅ
ꢆ
ꢇ
ꢈꢉꢊ–ꢋꢌ ꢍ
ꢇ
where k is the rate constant, R–X is the alkyl halide, and t is the
reaction time. Using eq (1), we experimentally deter-mined the k
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Figure 4. (a) Synthesis of PMMA−N
3
and PMMA-b-PEG block copolymer. (b) IR spectra of PMMA−I, PMMA−N
3
, and PMMA-b-PEG. (c) 1H NMR spectrum
3
(CDCl ) of PMMA-b-PEG. The reaction condition is given in Table 1 (Entry 11 for 30 min).
1
On the basis of the successful azidation of the tertiary alkyl
halides (EMA–I and EMA–Br) in the low-mass systems, we
studied the chain-end azidation of poly(methyl methacrylate)
CuAAC, from the H NMR peak areas for the PMMA (a, 3.60
ppm) and PEG (g and h, 3.64 ppm) segments in PMMA-b-PEG
(Figure 4c), we estimated the amount of the azide in PMMA–N
3
,
(
PMMA). PMMA–I (M
n
= 2600 and Ð = 1.14 after purification)
hence the conversion of PMMA–X to PMMA–N . The conversion
3
was prepared via RCMP of methyl methacrylate (MMA) with 2-
iodo-2-methylpropionitrile (CP–I) as an alkyl iodide initiator and
tributylmethylphosphonium iodide (BMPI) as an organic catalyst,
was virtually 100% in 30 min for PMMA–I and in 60 min for
PMMA–Br at 50 °C (Table 1, Entries 11 and 12). This result
demonstrates that the BNN -azidation is highly effective in
3
where Ð = M
w
/M
n
and M
n
and M
w
are the number-average and
polymer systems, enabling rapid and quantitative synthesis of
azido-end PMMA from both iodo- and bromo-end PMMAs.
weight-average molecular weights, respectively. PMMA–Br was
synthesized via atom transfer radical polymerization (ATRP) of
MMA using ethyl α-bromophenylacetate (EPh–Br) and
copper(I) catalyst. PMMA–Br was purified by reprecipitation and
subsequently by preparative GPC to remove a trace of copper.
Recent metal-free photo ATRP may be used to seek a
The BNN
azido-end polymethacrylates, including diazido-end PMMA (N
PMMA–N ), triazido-end PMMA (3-arm star PMMA–N ), azido-
end poly(lauryl methacrylate) (PLMA–N ), azido-end poly(2-
methoxyethyl methacrylate) (PMEMA–N
poly(2,2,2-trifluoroethyl methacrylate) (PTFEMA–N
3
-azidation also enabled the synthesis of various
a
3
–
3
3
3
3
),
azido-end
[25–27]
completely metal-free synthesis of PMMA–Br.
PMMA–I and PMMA–Br (M = 2800 and Ð = 1.11 after
purification) were reacted with BNN (1.5 eq) in toluene at 50 °C
Table 1, Entries 11 and 12). The obtained azido-end PMMA
PMMA–N ) was purified in a robust manner via reprecipitation
3
), and azido-
n
end poly(methyl methacrylate)-b-poly(benzyl methacrylate)
(PMMA-b-PBzMA–N (Table S1 and Figures S24–S29,
Supporting information). Particularly, hydrophobic PLMA–N is
insoluble in polar solvents and hence is unable to synthesize in
the conventional NaN -azidation using polar solvents. Therefore,
the synthesis of PLMA–N is unique to the present BNN
3
3
)
(
(
3
3
from a hexane/ethanol (v/v = 4/1) mixture, where the unreacted
BNN and the generated BNI were dis-solved in the
3
3
3
3
-
hexane/ethanol mixture and hence easily re-moved. BNI may
also be removed via filtration because of its insolubility in the
reaction solvent (toluene). The presence of the azide in PMMA–
azidation using the nonpolar solvent. The fast reaction and
broad polymer scope are highly beneficial for practical
applications.
-
1
N
3
was confirmed from a peak at 2120 cm in the IR spectrum
Figure 4b). For a quantitative analysis of the azide, the obtained
PMMA–N3 was reacted with an alkyne-bearing polyethylene
glycol (PEG-alkyne, M = 1000, Ð = 1.06) via CuAAC to give a
PMMA-b-PEG block copolymer (Figure 4a). After CuAAC, the IR
peak of the azide completely disappeared, suggesting
quantitative CuAAC (Figure 4b). Assuming the quantitative
(
Conclusions
n
In conclusion, a novel and effective azidation method using
a
BNN
3
in a nonpolar solvent was successfully developed. This
method enabled the synthesis of functional azido-end
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Chemistry - A European Journal
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FULL PAPER
polymethacrylates without using a large excess of BNN
3
in a
This work was supported by National Research Foundation
short reaction time (≤ 60 min). The rapid and quantitative
reaction, no use of any metals or polar solvents, and broad
scope in alkyl halides and polymethacrylates are attractive and
(
NRF) Investigatorship in Singapore (NRF-NRFI05-2019-0001)
and Academic Research Fund (AcRF) Tier 2 from Ministry of
Education in Singapore (MOE2017-T2-1-018).
[
28]
unique features of this azidation.
Conflict of interest
Experimental Section
The authors declare no competing financial interest.
Synthesis of PMMA−I.
A mixture of MMA (10.0 g, 100 mmol), CP−I (0.66 g, 3.37 mmol), BMPI
0.60 g, 1.75 mmol), and toluene (3.33 g) was heated in a 50 mL flask at
0 °C under argon atmosphere with magnetic stirring. After 4 h, the
Keywords: azidation • tetrabutylammonium azide •
(
6
polymethacrylate • click reaction • metal-free
mixture was quenched to room temperature and diluted with THF (15
mL). The polymer was reprecipitated in hexane (300 mL), collected by
filtration, and dried in vacuo to give PMMA−I (6.62 g); monomer
[
1]
2]
S. Bräse, C. Gil, K. Knepper, V. Zimmermann, Angew. Chem. 2005,
17, 5320-5374; Angew. Chem. Int. Ed. 2005, 44, 5188-5240.
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1440-11453.
1
[
n
conversion = 72%; M = 2600 and Đ = 1.14 after purification.
1
[
3]
4]
M. Minozzi, D. Nanni, P. Spagnolo, Chem. Eur. J. 2009, 15, 7830-7840.
H. C. Kolb, M. G. Finn, K. B. Sharpless, Angew. Chem. 2001, 113,
Synthesis of PMMA−Br.
[
2
056-2075; Angew. Chem., Int. Ed. 2001, 40, 2004-2021.
A solution of MMA (5.0 g, 50 mmol), EPh−Br (0.82 g, 3.37 mmol), and
CuBr (71.6 mg, 0.50 mmol) in a Schlenk flask was purged with argon for
[5]
[6]
M. Meldal, Macromol. Rapid Commun. 2008, 29, 1016-1051.
J. A. Johnson, M. G. Finn, J. T. Koberstein, N. J. Turro, Macromol.
Rapid Commun. 2008, 29, 1052-1072.
5
min. In the second Schlenk flask, a solution of MMA (5.0 g, 50 mmol)
and N,N,N’,N”,N”-pentamethyldiethylenetriamine (PMDETA, 0.17 g, 1.00
mmol) was purged with argon for 5 min. The solution in the second flask
was transferred to the first flask under argon atmosphere through a
degassed syringe. The reaction mixture was heated at 80 °C under argon
atmosphere with magnetic stirring. After stirring for 3 h, the reaction
mixture was diluted with THF (10 mL), filtrated, and reprecipitated in
hexane (300 mL). The obtained solid was further purified by preparative
gel permeation chromatography to give PMMA−Br (6.40 g); monomer
[7]
[8]
P. L. Golas, K. Matyjaszewski, Chem. Soc. Rev. 2010, 39, 1338-1354.
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48, 1296-1307.
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J. Dhineshkumar, K. R. Prabhu, Eur. J. Org. Chem. 2016, 447-452.
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Chem. 1999, A36, 667-679.
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E. Hennink, T. Vermonden, Chem. Commun. 2011, 47, 6972-6974.
n
conversion = 69%; M = 2800 and Đ = 1.11 after purification.
[
13] H. Han, N. V. Tsarevsky, Chem. Sci. 2014, 5, 4599-4609.
[14] A. Goto, A. Ohtsuki, H. Ohfuji, M. Tanishima, H. Kaji, J. Am. Chem. Soc.
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15] A. Ohtsuki, L. Lei, M. Tanishima, A. Goto, H. Kaji, J. Am. Chem. Soc.
015, 137, 5610-5617.
3
Synthesis of PMMA−N .
2
[
In a typical run, PMMA−I (M
n
= 2600, Đ = 1.14, 40 mM) or PMMA−Br (Mn
(60 mM) were dissolved in toluene.
2
=
2500, Đ = 1.12, 40 mM) and BNN
3
[
[
16] C.-G. Wang, F. Hanindita, A. Goto, ACS Macro Lett. 2018, 7, 263-268.
17] C.-G. Wang, C. Chen, K. Sakakibara, Y. Tsujii and A. Goto, Angew.
Chem. 2018, 130, 13692-13696; Angew. Chem. Int. Ed. 2018, 57,
The reaction mixture was heated at 50 °C with stirring. After a prescribed
time t, the reaction solution was reprecipitated in hexane/ethanol (v/v =
4
/1, 100 mL) mixture. The polymer was collected and dried in vacuo to
give PMMA−N . The other functional azido-end polymethacrylates were
prepared similarly with BNN in toluene.
1
3504-13508.
18] C.-G. Wang, X. Y. Oh, X. Liu, A. Goto, Macromolecules 2019, 52,
712-2718.
3
[
3
2
[
19] C. Chen, L. Xiao, A. Goto, Macromolecules 2016, 49, 9425-9440.
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Copper-catalyzed azide-alkyne cycloaddition of PMMA−N
alkynes.
3
with
[
13738-13741.
[
[
21] C.-G. Wang, A. Goto, J. Am. Chem. Soc. 2017, 139, 10551-10560.
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Polym. Chem. 2017, 8, 3858-3861.
In a typical run, a solution of PMMA−N
3 n
(M = 2800, Đ = 1.13, 150 mg,
0
.058 mmol) and CuBr (12.4 mg, 0.087 mmol) in THF (1.0 mL) in a
Schlenk flask was purged with argon. In the second Schlenk flask, a
solution of PMDETA (30.1 mg, 173 mmol) and PEG-alkyne (90.0 mg,
[
[
[
23] M. Gervais, A. Labbé, S. Carlotti, A. Deffieux, Macromolecules 2009,
42, 2395-2400.
0
.087 mmol) in THF (1.0 mL) was purged with argon for 2 min. (The
24] L. Kürti, B. Czakó, Strategic Applications of Named Reactions in
Organic Synthesis, Elsevier, Dorecht, 2005, pp. 170-171.
[19]
syntheses of PEG-alkyne are described in a previous publication. ) The
solution in the second flask was transferred to the first flask under argon
atmosphere through a degassed syringe. After stirring for 24 h at room
temperature under argon atmosphere, the solution was filtered to remove
the precipitated salts. The remaining polymer solution was purified by
reprecipitation in methanol/water (v/v = 2/1) or using preparative GPC to
remove unreacted PEG-alkyne. The PMMA-b-PEG block copolymer was
dried in vacuo.
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[
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Chemistry - A European Journal
10.1002/chem.201903188
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An effective method to synthesize
azido-end polymethacrylates using
tetrabutylammonium azide (BNN )
3
Chen-Gang Wang, Amerlyn Ming Liing
Chong, Yunpeng Lu, Xu Liu and Atsushi
Goto*
was developed. Alkyl halides and
polymethacrylate-halides were
Page No. – Page No.
3
reacted with BNN in toluene to
generate the corresponding azides.
The azidation was rapid and
Metal-Free Fast Azidation Using
Tetrabutylammonium Azide: Effective
Synthesis of Alkyl Azides and Well-
defined Azido-end Polymethacrylates
quantitative without using a large
excess of BNN
solvents.
3
, any metals, or polar
This article is protected by copyright. All rights reserved.