634
X. Ma, Z. Li
Letter
Synlett
A plausible mechanism for the synthesis of 2a is shown
in Scheme 5. Phenyldiazonium tetrafluoroborate (1a) first
reacts with palladium(0) [Pd(PPh3)4] to form the (phenyldi-
azenyl)palladium salt A,8d which releases dinitrogen to give
the phenylpalladium salt B. B combines with an iodide an-
ion to yield the phenylpalladium iodide C. Meanwhile calci-
um carbide is hydrolyzed by water to afford acetylene in si-
tu, with loss of calcium hydroxide, which acts as a base in
the subsequent processes. Acetylene is then transformed
into ethynylcopper in the presence of cuprous iodide.
Ethynylcopper further reacts with complex C to produce
ethynyl(phenyl)palladium (D). D undergoes reductive elim-
ination to generate phenylethyne, which combines with cu-
prous iodide to yield (phenylethynyl)copper. This reacts
with another mole of C to give the palladium complex E
with elimination of cuprous iodide. E undergoes reductive
elimination once again to give the final product diphenyl-
ethyne (2a), with release of the palladium(0) catalyst.
Funding Information
The authors thank the National Natural Science Foundation of China
(21462038) for financial support of this work.
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Supporting Information
Supporting information for this article is available online at
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References and Notes
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Scheme 5 Proposed mechanism for the synthesis of 2a
In summary, an efficient method for the synthesis of di-
arylethynes from aryldiazonium salts as the starting mate-
rials and calcium carbide as an alkyne source in a DES has
been developed. A series of diarylethynes with various sub-
stituents were synthesized at room temperature in satisfac-
tory yields. This protocol has the advantages using an inex-
pensive and easy-to-handle alkyne source; a nontoxic, non-
volatile, and recyclable solvent; mild and open-air
conditions; and a simple workup procedure. This method
provides a good alternative for the synthesis of diaryl-
ethynes, and will further enrich the range of applications of
calcium carbide in organic synthesis.
© 2020. Thieme. All rights reserved. Synlett 2021, 32, 631–635