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Updated: May 31, 2025
Synthesis of Hypervalent Iodonium Alkynyl Triflates for the Application of Generating Cyanocarbenes
Published on: September 8, 2013
Reactions of Tertiary Aliphatic Cations with Silylated Alkynes: Substitution, Cyclization and Unexpected C-H
Paul Charki1, Marie Cordier1, Kai E O Ylijoki2
1Univ Rennes, CNRS, ISCR (Institut des Sciences Chimiques de Rennes)-UMR6226, F-35000, Rennes, France.
Abstract:
Capozzi's groundbreaking work in 1982 introduced a fascinating reaction involving highly reactive tertiary aliphatic cations and silylated alkynes. This reaction provided an innovative solution to the challenge of coupling a fully substituted tertiary aliphatic fragment with an alkyne moiety. Building upon Capozzi's pioneering efforts, we started an extensive exploration of reaction conditions to expand the initial scope of this reaction. Through meticulous control of the reaction parameters, we uncovered conditions capable of accommodating various functional groups, thereby enhancing the reaction's applicability. Intriguingly, our study revealed remarkably high diastereoselectivities for substrates with substitution in the α-position. Additionally, we made an unexpected discovery: an intriguing C-H activation of a cyclooctane ring furnishing a cyclooctane-fused cyclobutene. These findings not only extend the utility of Capozzi's original concept but also underscore the potential of highly reactive cations in modern organic C-H activation reactions.
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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.
02:38Electrophilic 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.
02:40Alkynes to Aldehydes and Ketones: Acid-Catalyzed Hydration
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.
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.
01:10α-Alkylation of Ketones via Enolate Ions