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Published on: February 16, 2020
Copper-Assisted (Pseudo-)Halochalcogenation of Arynes
Jasper Mindner1, Sina Rombach1, Daniel B Werz1
1Institute of Organic Chemistry, Albert-Ludwigs-Universität Freiburg, Albertstrasse 21, 79104 Freiburg im Breisgau, Germany.
This study introduces a novel multicomponent reaction for synthesizing ortho-(pseudo)halogenated chalcogenides using arynes and chalcogen sources. Copper catalysis facilitates the efficient formation of these versatile building blocks for complex molecule synthesis.
Area of Science:
- Organic Chemistry
- Synthetic Chemistry
Background:
- Multicomponent reactions offer efficient synthetic routes.
- Arynes are versatile synthetic intermediates.
- Chalcogenides are important in various chemical applications.
Purpose of the Study:
- To develop a novel multicomponent coupling reaction.
- To synthesize ortho-(pseudo)halogenated chalcogenides.
- To demonstrate the utility of these compounds as building blocks.
Main Methods:
- Reaction of arynes with (pseudo)halides and electrophilic chalcogen species.
- Copper salt catalysis to improve reaction efficiency.
- Use of various aryne precursors and seleno-/thiosulfonates.
Main Results:
- Successful synthesis of a broad spectrum of ortho-(pseudo)halogenated chalcogenides.
- Copper salt addition suppressed side reactions and enabled smooth conversion.
- Demonstrated applicability in subsequent cross-coupling reactions.
Conclusions:
- The developed multicomponent reaction is effective for synthesizing valuable ortho-(pseudo)halogenated chalcogenides.
- These chalcogenides serve as versatile building blocks for constructing complex molecular architectures.
- The methodology offers a new pathway in synthetic organic chemistry.
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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.
02:34Preparation 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.
02:35Electrophilic Addition to Alkynes: Hydrohalogenation
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.
02:47Alkynes 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.