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Updated: Sep 10, 2026
Synthesis of Hypervalent Iodonium Alkynyl Triflates for the Application of Generating Cyanocarbenes
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Sulfur-Boron Lewis Pair-Catalyzed Hydrohalogenation of Alkynes via Formal Hydrogen Atom Transfer
Yun Soo Shim1, Jin Qian2, Sourav Dey2
1Department of Chemistry, Division of Advanced Materials Science, Pohang University of Science and Technology (POSTECH), Pohang, South Korea.
Abstract:
The catalytic synthesis of both (E)- and (Z)-haloalkenes from internal aryl alkyl alkynes via a sulfur-boron Lewis pair has been developed. The catalytically active Lewis pair complex is generated in situ from 2-naphthalenethiol and B(C6F5)3, enabling the selective synthesis of chloro-, bromo-, and iodoalkenes with exclusive Markovnikov regioselectivity. Both (E)- and (Z)-haloalkenes were obtained in good yields with high selectivities by simply controlling the reaction temperature. Experimental mechanistic studies support the intermediacy of vinyl radicals generated through an overall formal hydrogen atom transfer (HAT) process. Computational investigations further support a stepwise proton transfer-electron transfer (PT-ET) mechanism rather than a concerted HAT event. The origin of the stereodivergence is also elucidated by combining experimental observations with theoretical calculations. This work demonstrates a new strategy for vinyl radical generation through sulfur-boron Lewis pair catalysis and suggests that formal HAT reactivity can emerge from a stepwise PT-ET mechanism in main-group catalysis.
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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.
02:35Electrophilic Addition to Alkynes: Hydrohalogenation
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.
02:38Electrophilic 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.
03:08Hydroboration-Oxidation of Alkenes
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Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.