Among all functional groups, alkynes
occupy a privileged position
in synthetic and medicinal chemistry, chemical biology, and materials
science. Thioalkynes, in particular, are highly useful, as they combine
the enhanced reactivity of the triple bond with a sulfur atom frequently
encountered in bioactive compounds and materials. Nevertheless, general
methods to access these compounds are lacking. In this article, we
describe the mechanism and full scope of the alkynylation of thiols
using ethynyl benziodoxolone (EBX) hypervalent iodine reagents. Computations
led to the discovery of a new, three-atom concerted transition state
with a very low energy barrier, which rationalizes the high reaction
rate. On the basis of this result, the scope of the reaction was extended
to the synthesis of aryl- and alkyl-substituted alkynes containing
a broad range of functional groups. New sulfur nucleophiles such as
thioglycosides, thioacids, and sodium hydrogen sulfide were also alkynylated
successfully to lead to the most general and practical method yet
reported for the synthesis of thioalkynes.
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