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Updated: May 26, 2026

Synthesis of Hypervalent Iodonium Alkynyl Triflates for the Application of Generating Cyanocarbenes
Published on: September 8, 2013
Terminal alkyne addition to diazodicarboxylates: synthesis of hydrazide linked alkynes (ynehydrazides)
Ramsay E Beveridge1, Robert A Batey
1Davenport Research Laboratories, Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, ON, Canada.
Abstract:
A new route to form C(sp)-N bonds has been developed via addition of in situ generated lithium acetylides to sterically hindered diazodicarboxylates. The reaction provides straightforward access to a previously unexplored ynehydrazide class of stable N-linked alkynes directly from commercially available precursors. Preliminary results show that alkynyl hydrazides are useful reagents for the selective installation of nitrogen functional groups and as precursors to pharmaceutically relevant heterocycles using metal catalyzed cycloadditions and condensations.
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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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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.
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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.
Electrophilic Addition to Alkynes: Hydrohalogenation
Electrophilic Addition to Alkynes: Halogenation
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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Analogous to alkenes, alkynes also undergo acid-catalyzed hydration. While the addition of water to an alkene gives an alcohol, hydration of alkynes produces different products such as aldehydes and ketones.