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Updated: Jan 18, 2026

Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions
Published on: July 30, 2017
Palladium-Catalyzed Arylthiolation of Alkynes Enabled by Surmounting Competitive Dimerization of Alkynes
Daisuke Uno1, Keisuke Nogi1, Hideki Yorimitsu1
1Department of Chemistry, Graduate School of Science , Kyoto University , Sakyo-ku, Kyoto 606-8502 , Japan.
Abstract:
By overcoming the unwanted catalytic dimerization of terminal alkynes, palladium-catalyzed carbothiolation of alkynes with heteroaryl sulfides has been accomplished to provide the corresponding β-heteroaryl alkenyl sulfides with high regio- and stereoselectivity. The key for the preferential arylthiolation is the use of arylsulfanyl segments, instead of alkylsulfanyl, for smooth C(heteroaryl)-SR1 bond cleavage and/or of alkylacetylenes that are reluctant to undergo the dimerization. The reaction proceeds under mild and neutral conditions, with various functionalities being thus tolerated.
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Alkylation of terminal alkynes with primary alkyl halides in the presence of a strong base like sodium amide is one of the common methods for the synthesis of longer carbon-chain alkynes. For example, treatment of 1-propyne with sodium amide followed by reaction with ethyl bromide yields 2-pentyne.
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One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
Preparation of Alkynes: Dehydrohalogenation
Alkynes can be prepared by dehydrohalogenation of vicinal or geminal dihalides in the presence of a strong base like sodium amide in liquid ammonia. The reaction proceeds with the loss of two equivalents of hydrogen halide (HX) via two successive E2 elimination reactions.
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Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
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