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Updated: Dec 21, 2025
Metal-free Synthesis of Ynones from Acyl Chlorides and Potassium Alkynyltrifluoroborate Salts
Published on: February 24, 2015
Synthesis of alkynes from non-alkyne sources
Ranjay Shaw1, Amr Elagamy1, Ismail Althagafi2
1Department of Chemistry, University of Delhi, North Campus, Delhi 110007, India. ramendrapratap@gmail.com.
Abstract:
Alkynes are a very important class of compounds and used as precursors for the assembly of a variety of carbocycles and heterocycles. Alkynes are classified into two classes: terminal alkynes and internal alkynes. Terminal alkynes were used as one of the precursors for the synthesis of internal alkynes. Besides, various elimination reactions were conducted to obtain alkynes. Various applications of alkynes are known but no compiled review is reported so far regarding their synthesis. Therefore, we have compiled the literature available for the synthesis of various functionalized alkynes from non-alkyne sources in this review. We have not discussed the synthesis of internal alkynes from terminal alkynes. Based on the available literature, the synthesis of alkynes can be classified into three major types of reactions: (a) synthesis of alkynes through α,β-elimination, (b) synthesis of alkynes through carbene rearrangement and (c) synthesis of alkynes via miscellaneous approaches. In this review, we have focused on the different methods available for these transformations including their scope, limitations and recent developments. We have also discussed the mechanism involved during the reaction.
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02:27Preparation of Alkynes: Alkylation Reaction
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.
02:34Preparation 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.
02:24Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation
Like alkenes, alkynes can be reduced to alkanes in the presence of transition metal catalysts such as Pt, Pd, or Ni. The reaction involves two sequential syn additions of hydrogen via a cis-alkene intermediate.
02:39Nomenclature of Alkynes
02:38Electrophilic 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.
02:47Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
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.