copper(I) catalytic species for CuAAC reactions. Our results
support the involvement of intermediates calculated to have
short Cu–Cu internuclear distances. In our continuing work
we are exploring other heterogeneous reactions involving the
use of the polymeric alkynecopper(I) catalysts.
B. R. B. thanks Research Councils UK for a RCUK
fellowship and the Nuffield Foundation for a Summer Bursary
Studentship (to D. P. H.). The authors thank Loughborough
University for funding (to E. C. S.).
Scheme 4 Reagents and conditions: (a) [(PhCCCu)2]n (10 mol%),
BnN3, microwave, MeCN.
We next carried out a microwave reaction with a solution of
benzylazide and an excess of phenylacetylene in acetonitrile in
the presence of 10 mol% of copper(II) hydroxyacetate. As
anticipated, GC/MS analysis showed that 1,4-diphenylbuta-
1,3-diyne (1) and 1-benzyl-4-phenyltriazole (5) were both
formed and that the ratio of (1) : (5) was 1 : 10, isolated in
77% and 92% yields, respectively, together with the conversion of
the copper(II) hydroxyacetate into the phenylethynylcopper(I)
(2) in 82% yield; shown in Scheme 3.
Notes and references
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A similar reaction, but using 1 mol% of copper(II)
hydroxyacetate, gave the compound (2), and a 72% yield of
1-benzyl-4-phenyltriazole (5): 1,4-diphenylbuta-1,3-diyne (1)
was not detected in this reaction, presumably because it was
formed in a yield below the level of detection using GC/MS. A
series of experiments was conducted using different alkynes,
the results of some of which are given in Table 1 (entries 1–6)
(additional results are given in the ESIw).
We investigated next the function of the phenylethynyl-
copper(I) ladder polymer.18 A reaction in carefully degassed
acetonitrile, using a mixture of benzylazide, phenylacetylene
and phenylethynylcopper(I) (2), using our established microwave
reaction conditions, gave the triazole (5) in 86% yield. Use of
the recovered phenylethynylcopper(I) gave a similar yield. A
reaction in which 10 mol% of phenylethynylcopper(I) (2)
together with a solution of p-tolylacetylene and benzylazide
in acetonitrile gave 1-benzyl-4-phenyltriazole (5) (10%) and
1-benzyl-4-p-tolyltriazole (6) (85%) (Scheme 4); thus showing
that the alkyne attached to copper is replaced during the
reaction. The recovered yellow material was then used in a
reaction with p-tolylacetylene and benzylazide and gave the
triazole (6) in 85% yield. The recovered yellow insoluble
material was shown by XRD to be compound (4), shown in
Scheme 4, by comparison with the material prepared earlier.
As anticipated, a reaction of 1-[2H]-2-phenylethyne with
benzylazide in the presence of the phenylethynylcopper(I) (2)
gave 1-benzyl-4-phenyl-5-[2H]-triazole in 65% yield with a
quantitative incorporation of deuterium; the above result
confirms that under our reaction conditions the proton source
in the triazole product is derived from the added alkyne e.g.
phenylacetylene. A reaction of the compound (2) with benzylazide
gave the triazole (5) in 85% yield together with a brown
insoluble residue that regenerated the yellow phenylethynyl-
copper(I) (2), after the addition of a solution of phenylacetylene in
acetonitrile. Some of the reactions of phenylacetylene with a
series of different azides, using the compound (2), and of
p-tolylacetylene with the compound (4) and the different azides
are also shown in Table 1 (entries 7–12) (additional results are
given in the ESIw).
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18 Phenylethynylcopper(I) prepared by a number of other methods
gave identical results.
In summary, we have shown that copper(II) hydroxyacetate
acts as a pre-catalyst that generates efficient polymeric bi-nuclear
ꢀc
This journal is The Royal Society of Chemistry 2010
2276 | Chem. Commun., 2010, 46, 2274–2276