Easy preparation of 1,4,5-trisubstituted 5-(2-alkoxy-1,2-dioxoethyl)-1,2,3- triazoles by chemoselective trapping of copper(I)-carbon bond with alkoxalyl chloride

Article abstract of DOI:10.1016/j.tetlet.2013.08.121

We found that alkoxalyl chloride (ClCOCO₂R) did not carry out an acylation on 1-copper(I) alkyne in solvent without additives, but chemoselectively on 5-copper(I) 1,2,3-triazole (an intermediate in cycloaddition of 1-copper(I) alkyne and azide). Thus, a one-pot preparation of 1,4,5-trisubstituted 5-(2-alkoxy-1,2-dioxoethyl)-1,2,3-triazole was achieved by simply stirring the mixture of 1-copper(I) alkyne, azide, and alkoxalyl chloride at room temperature for 4 h.

Full text of DOI:10.1016/j.tetlet.2013.08.121

Accepted Manuscript
Easy preparation of 1,4,5-trisubstituted 5-(2-alkoxy-1,2-dioxoethyl)-1,2,3-tria‐
zoles by chemoselective trapping of copper(I)-carbon bond with alkoxalyl
chloride
Bo Wang, Muhammad Naeem Ahmed, Jianlan Zhang, Wenwen Chen, Xinyan
Wang, Yuefei Hu
PII:
S0040-4039(13)01519-0
DOI:
http://dx.doi.org/10.1016/j.tetlet.2013.08.121
TETL 43484
Reference:
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
27 June 2013
19 August 2013
29 August 2013
Please cite this article as: Wang, B., Ahmed, M.N., Zhang, J., Chen, W., Wang, X., Hu, Y., Easy preparation of
1,4,5-trisubstituted 5-(2-alkoxy-1,2-dioxoethyl)-1,2,3-triazoles by chemoselective trapping of copper(I)-carbon
bond with alkoxalyl chloride, Tetrahedron Letters (2013), doi: http://dx.doi.org/10.1016/j.tetlet.2013.08.121
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Easy preparation of 1,4,5-trisubstituted 5-(2-alkoxy-
1,2-dioxoethyl)-1,2,3-triazoles by chemoselective
trapping of copper(I)-carbon bond with alkoxalyl
chloride
Leave this area blank for abstract info.
Bo Wang, Muhammad Naeem Ahmed, Jianlan Zhang, Wenwen Chen, Xinyan Wang, Yuefei Hu
no reaction
BnN3, PhCl
[(PhC CCu)2]n, BnN3
[B] or [L], PhCl, rt, 4 h
[(PhC CCu)2]n, BnN3
PhCl, rt, 4 h
N
rt, 4 h
Bn
N
N
mixture
ClCOCO2Et
88%
Ph
COCO2Et
[(PhC CCu)2]n
PhCl, rt, 4 h
20 Examples
in 70-92% yields
no reaction

1
Tetrahedron Letters
journal homepage: www.elsevier.com
Easy preparation of 1,4,5-trisubstituted 5-(2-alkoxy-1,2-dioxoethyl)-1,2,3-
triazoles by chemoselective trapping of copper(I)-carbon bond with alkoxalyl
chloride
Bo Wang, Muhammad Naeem Ahmed, Jianlan Zhang, Wenwen Chen, Xinyan Wang, Yuefei Hu
Department of Chemistry, Tsinghua University, Beijing 100084, P. R. China
ARTICLE INFO
ABSTRACT
Article history:
Received
Received in revised form
Accepted
We found that alkoxalyl chloride (ClCOCO2R) did not carry out an acylation on 1-copper(I) alkyne in
solvent without additives, but chemoselectively on 5-copper(I) 1,2,3-triazole (an intermediate in
cycloaddition of 1-copper(I) alkyne and azide). Thus, a one-pot preparation of 1,4,5-trisubstituted 5-
(2-alkoxy-1,2-dioxoethyl)-1,2,3-triazole was achieved by simply stirring the mixture of 1-copper(I)
alkyne, azide and alkoxalyl chloride at room temperature for 4 h.
Available online
2009 Elsevier Ltd. All rights reserved.
Keywords:
1-Cuprous-Alkynes
C-Cu bond
Click chemistry
Triazoles
Acylation
Since CuAAC reaction was discovered in 2002,1 the
applications of 1,2,3-triazole have been increased continuously in
organic synthesis, biology and material science.2 As shown in
Figure 1, all types of substituted 1,2,3-triazoles (1-4) have been
prepared by metal-catalyzed cycloaddition of alkynes and
organoazides to data. Recently, many 1,4,5-trisubstituted 1,2,3-
triazoles (4) have shown novel properties3 and more of them are
expected because they possess the most substituents and
structural diversity. But, their preparation remains a challenging
task comparing with other types of 1,2,3-triazoles (1-3).
attempts have been made to trap 8 by an exogenous electrophile
(E+) to prepare 1,4,5-trisubstituted 1,2,3-triazoles (4) in the early
studies.6 But, the desired product 4 usually was obtained as a
mixture accompanied by 2 as a byproduct. This drawback is
inevitably caused by the fact that two electrophilic substitutions
on the Cu-C bond of 8 occurred competitively between the
exogenous electrophile E+ and the endogenous electrophile H+
(from the terminal alkyne 5).
[Cu]+
N
N
R
R
2
N
N
N
N
N
R1C CH
N
N
N
R
R
R
R
3 N
N1
H
N
N
N
N
N
N
+
R1
E
R1
H
H
5
4
2
H 4
5
R1
H
H
R1
R1
R2
1
2
3
4
+
N
RN3 (7)
E
R
R1C C-[Cu]
N
N
Figure 1. 1,2,3-Triazoles from metal-catalyzed cycloaddition of
alkynes and organoazides.
6
R1 [Cu]
8
Figure 2. Competitive electrophilic substitution between E+ and H+.
Among all types of 1,2,3-triazoles, 1,4-disubstituted 1,2,3-
triazole (2) could be prepared most easily by CuAAC
reaction.2a,2h,2i,4 As shown in Figure 2, realizing 5-Cu(I)-1,2,3-
triazole (8) was the intermediate of CuAAC reaction,1a,5 many
Thus, the cycloadditions of some structurally novel 1-
substituted alkynes have been developed to overcome the
———
Corresponding author. Tel.: +86-10-62795380; fax: +86-10-62771149; e-mail: yfh@mail.tsinghua.edu.cn

2
Tetrahedron
drawbacks caused by the terminal alkynes. For example, 5-
the cycyloaddition of 6a and 7a when DOAc was used as an
electrophile (entry d).13 This result indicated that the
cycyloaddition of 6a and 7a proceeded indeed and 5-Cu(I)-1,2,3-
triazole (8a) must be an intermediate (entry e).
bromo,7 5-iodide8 and 5-Au-1,4,5-trisubstituted 1,2,3-triazoles9
were prepared smoothly from the corresponding 1-bromo, 1-
iodide and 1-Au-alkynes. Both 1-Mg10 and 1-Al-alkynes11 have
become considerably important because they could be used to
prepare a range of 1,4,5-trisubstituted 1,2,3-triazoles. As shown
in Scheme 1, each of them initially carried out a cycloaddition to
give 4-Mg or 5-Al-1,2,3-triazole as an intermediate, respectively.
Scheme 3
nBuCOCl, LiI, Et2O, rt, 20 h
a
PhC C-COBun
R = Ph (6a), 95%
Then, the intermediates were trapped by
a variety of
electrophiles, such as D2O, I2, CO2, ClCO2Me, PhCHO, PhCNO,
(CCl3)CO3 or ClCONR2, to give the corresponding products 4’ or
4.
MeCOCl, neat, rt, 24 h
R = nPr, 75%
b
c
nPrC C-COMe
Scheme 1
N
Bn
BnN3 (7a), H2O/tBuOH, rt, 5 h
N
N
N
N
R
R
RC C-[Cu]
X
R1C C-MgBr
N
N
N
N
E+
R = Ph (6a)
Ph
H
6
2a
thermal condition
[Mg]
R1
E
R1
4¡¯
BnN3 (7a), DOAc (1 equiv)
C6H12, rt, 5 min
N
Bn
d
e
RN3
N
N
R = Ph (6a), 98%
7
N
N
R
R
R1C C-AlMe2
Cu(I)-catalyzed
N
N
N
N
Ph
D
2a-d1
E+
R1
[Al]
R1
E
N
D+
Bn
N
BnN3 (7a)
N
4
cycloaddition
electrophile
[Cu] substitution
Ph
8a
Recently, our research projects need a number of 1,4,5-
trisubstituted 1,2,3-triazoles. Among three substitutents, at least
one is electron-withdrawing-group and 2-alkoxy-1,2-dioxoethyl
group (-COCO2R) is one of them. Unfortunately, the complicated
mixtures were obtained by using ethoxalyl chloride (ClCOCO2Et,
9a) as an electrophile under the standard conditions of 1-Mg-
alkyne or 1-Al-alkyne. As shown in Scheme 2, the problems may
be caused by the incontrollable reactivity of the M-C bonds in the
intermediates. In fact, no acylation product was reported to be
prepared from 1-Mg-alkyne or 1-Al-alkyne in their original
articles.10,11
Thus, a group of conditional experiments were tested. As
shown in Scheme 4, the experiments proved that 9a reacted
neither with 6a nor with 7a in CH2Cl2 without additives. In the
presence of a base or a ligand, such as NEt3, DIPEA, 1,10-
phenanthroline or pyridine, the suspension of 6a, 7a and 9a in
CH2Cl2 gave a complicated mixture as a result. To our delight,
the same suspension gave the desired product 4a in 79% yield as
a single product under the base-free or ligand-free conditions.
Furthermore, the structure of 1-(3-methylbutyl)-4-phenyl-5-(2-
ethoxy-1,2-dioxoethyl)-1,2,3-triazole (4h) was confirmed by
single crystal X-ray diffraction analysis (Figure 3).
Scheme 2
ClCOCO2Et
N
Scheme 4
N
Bn
Bn
N
N
(9a)
BnN3
N
N
PhC C-MgBr
X
no reaction
[Mg]
Ph
EtO2CCO
Ph
7a, CH2Cl2
4a'
rt, 4 h
N
6a, 7a, [B] or [L]
CH2Cl2, rt, 4 h
6a, 7a
CH2Cl2, rt, 4 h
Bn
N
N
mixture
ClCOCO2Et
N
ClCOCO2Et
BnN3
CuI, L
Bn
79%
N
N
N
Ph
COCO2Et
Bn
9a
(9a)
X
N
N
PhC C-AlMe2
4a
6a, CH2Cl2
rt, 4 h
as a single product
Ph
[Al]
Ph
COCO2Et
4a
no reaction
Thus, there is a necessary to find other 1-metal alkynes for our
synthetic purpose. We were surprised to find that 1-Cu(I)-alkyne
(6) has been recognized as an intermediates in CuAAC reaction,
but it never used for the preparation of 1,4,5-trisubsituted
triazoles. However, the investigation of literature gave us two
opposite suggestions. As shown in Scheme 3, one indicated that 6
could not be used for our purpose because it directly reacted with
acyl chlorides to give -ynones in moderate to high yields in the
presence of an additive (base or ligand) (entry a)12a-c or under
solvent-free conditions (entry b).12d Furthermore, 1-Cu(I)-
phenyethyne (6a) has proven to be ineffective in its cycloaddition
with benzyl azide (7a) under Sharpless conditions (entry c).5,13
On the contrary, the other one implied that 6 may work well for
our purpose because it reacted with acyl chlorides extremely
slow in solvents without additives.12 Additionally, 5-D-1-benzyl-
4-phenyl-1,2,3-trazole (2a-d1) was produced in 98% yield from
Figure 3. The structure of 4h.
The regioselective formation of 4a (but not 4a’) confirmed
that the cycloaddition of 6a and 7a have occurred to give 8a as

3
an intermediate. It also revealed a rare chemoselectivity that 9a
preferred to carry out an acylation on the intermediate 8a (with
an in situ formed Cu-C bond) rather than on the substrate 6a
(with a pre-made Cu-C bond). This may result in the fact that 6a
structurally is a metal cluster (also a polymeric dinuclear
complex)14 with extremely chemical stability. Since copper-
catalyzed cycloaddition between 6a and 7a is a “click reaction”
having a high thermodynamic driving force, therefore the
cycloaddition occurred preferentially. As shown in Table 1, this
method is so easy that it could be operated in most common
solvents (entries 1-7). As shown in entries 8 and 9, the aromatic
solvents gave the best yields. Finally, the entry 9 was assigned as
our standard conditions because chlorobenzene also was a good
solvent for other substrates.
further works for preparation of a series of 1,4,5-trisubstituted
1,2,3-triazoles will be reported in due course.
Scheme 5
ClCOCO2R2 (9)
PhCl, rt, 4 h
N
R
N
N
[(R1C CCu)2]n
+
RN3
70-92%
R1
COCO2R2
7
4
6
N
N
N
N
N
N
N
N
N
N
N
N
Ph
Ph-4-Me
COCO2Et
Ph-4-NO2
Phth-2
Ph
COCO2Et
Ph
COCO2Et
Ph
Ph
COCO2Et
4a, 89%
4b, 92%
4c, 85%a
4d, 88%a
Table 1. The effect of solvent on the reactiona
N
N
N
N
OMe
OMe
N
N
N
N
N
N
N
N
Ph
COCO2Et
ClCOCO2Et (9a)
solvent, rt, 4 h
N
Ph
COCO2Et
Ph
Ph
COCO2Et
Ph
COCO2Et
Bn
N
N
4e, 70%
4f, 75%
4g, 86%
4h, 77%
+
BnN3
[(PhC CCu)2]n
51-89%
Ph
COCO2Et
4a
6a
7a
N
N
N
N
N
N
N
N
N
N
N
N
Ph
Ph-4-Me
Ph
Ph
Ph
COCO2Et
6
3-F-Ph
COCO2Et
2-F-Ph
COCO2Et
4-MeOPh
COCO2Et
Ph
Yield of 4a (%)b
4l, 82%
4k, 84%
4j, 78%
4i, 82%
Entry
Solvent
1,4-dioxane
MeCN
1
2
3
4
5
6
7
8
9
51
53
62
65
78
79
84
87
89
N
N
N
N
N
N
N
N
N
N
N
N
Ph
COCO2Et
4m, 77%
Ph
6
nBu
THF
COCO2Et 4-MePh
COCO2Et 4-Me-Ph
COCO2Et
4n, 81%
4o, 90%
4p, 86%
CHCl3
BrCH2CH2Br
CH2Cl2
N
N
N
N
N N
N
N
N
N
N
N
Ph-4-Me
Ph-4-Me
COCO2Me 4-MeOPh
4r, 88% 4s, 79%
Ph
COCO2Me Ph
4t, 91%
4-Cl-Ph
COCO2Et Ph
COCO2Me
ClCH2CH2Cl
C6H5Me
4q, 83%
a.
C6H5Cl
Products 4c and 4d were obtained by using CH Cl as reaction solvent.
2 2
a
To the suspension of 6a (82 mg, 0.5 mmol) and 7a (80 mg, 0.6 mmol) in
solvent (1 mL) was added 9a (68 mg, 0.5 mmol) dropwise. The resultant
mixture was then stirred at room temperature for 4 h in air.
b The isolated yields were obtained.
Acknowledgments
As shown in Scheme 5, this method was quite general for
wide range of substrates. By fixing 1-Cu(I)-phenyethyne (6a),
different azides were tested to give the desirable products 4a-4i.
The product 4e was obtained in the lowest yield possibly because
the cyclohexyl azide has bulky size. By fixing benzyl azide (7a),
the tested 1-Cu(I)-alkynes (prepared from alkyl or aryl
substituted alkynes) all gave the desirable products 4j-4n in
comparable yields. It is worthy to note that no matter the
products were obtained in good or excellent yields, they were the
only products in the reaction with very easy work-up procedures.
Under the standard conditions, products 4a and 4h have been
synthesized in five grams scales to give the similar yields.
This work was supported by National Natural Scientific
Foundation of China (No. 21072112 and 21221062).
Supplementary Material
1
Supplementary data (Experiments, characterization, H NMR
and 13C NMR spectra for products 4a-4t, as well as and CIF file
for the single crystal X-ray diffraction analysis of 4h.) associated
with this article can be found, in the online version, at
http://dx.doi.org/
References and notes
In conclusion, we found that 1-Cu(I)-alkyne does not react
with alkoxalyl chloride in solvent under base-free and ligand-free
conditions since it is a metal cluster and has extremely chemical
stability. But it can be converted into 5-Cu(I)-1,4,5-trisubstituted
1,2,3-triazole intermediate by cycloaddition with azides. Thus, a
rare chemoselectivity was discovered, by which the Cu-C bond in
5-Cu(I)-1,2,3-triazole intermediate (in situ formed) was trapped
selectively by alkoxalyl chloride in the presence of 1-Cu-alkyne
(pre-made). Finally, a novel one-pot three-component method for
efficient preparation of 1,4,5-trisubstituted 5-(2-alkoxy-1,2-
dioxoethyl)-1,2,3-triazoles was established. This novel
chemoselectivity also be observed by using other electrophiles,
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