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Updated: Aug 8, 2025
Metal-free Synthesis of Ynones from Acyl Chlorides and Potassium Alkynyltrifluoroborate Salts
Published on: February 24, 2015
1-Phospha-Butadienes and 1H-Phospholes via Alkynylation of Acetylenic Phosphaalkenes
Muhammad Anwar Shameem1, Arvind Kumar Gupta1, Mate Erdelyi2
1Department of Chemistry - Ångström Laboratories. Synthetic Molecular Chemistry., Uppsala University., BOX 523, 75120, Uppsala, Sweden.
Abstract:
Carbon-rich motifs are important building blocks for the fabrication of functional and opto-electronic materials. Electronic tuning can be achieved by alteration of bonding topologies but also via incorporation of heteroelements, for example phosphorus. Herein we present the palladium/copper mediated formation of branched 1-phospha-butadiene derivatives through an unusual alkynylation of a phospha-enyne fragment. Structural and NMR studies provide mechanistic insights into this alkynylation. Furthermore, we disclose a complex cyclisation of the thus obtained 3-yne-1-phosphabutadiene motifs to give highly substituted phosphole derivatives identified by 2D NMR and SC-XRD analysis.
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Related Concept Videos
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.
02:38Electrophilic 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.
02:24Reduction 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.
02:47Alkynes 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.
02:42Acidity of 1-Alkynes
The acidic strength of hydrocarbons follows the order: Alkynes > Alkenes > Alkanes. The strength of an acid is commonly expressed in units of pKa — the lower the pKa, the stronger the acid. Among the hydrocarbons, terminal alkynes have lower pKa values and are, therefore, more acidic. For example, the pKa values for ethane, ethene, and acetylene are 51, 44, and 25, respectively, as shown here.