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[DPEPhosbcpCu]PF6: A General and Broadly Applicable Copper-Based Photoredox Catalyst
Published on: May 21, 2019
Light-Induced Divergent Cyanation of Alkynes Enabled by Phosphorus Radicals
Yanyan Zhang1, Yunhong Han2, Shengqing Zhu1
1State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, Center for Advanced Low-Dimension Materials, Donghua University, College of Chemistry, Chemical Engineering and Biotechnology, Shanghai, 201620, China.
Abstract:
A photochemically induced selective and divergent cyanation reaction of alkynes, enabled by phosphorus radicals, is described. With the use of simple triarylphosphine as a co-catalyst, three cyanation reactions, including di-hydrocyanation, anti-Markovnikov hydrocyanation, and domino hydrocyanation/reduction, can be divergently achieved, furnishing a wide array of alkyl dinitriles, alkenyl nitriles, and alkyl nitriles under mild conditions. Terminal and internal alkynes are applicable with high efficiency and excellent selectivity. Synthetic applications for biologically active agents and preliminary experimental and computational mechanistic studies are reported.
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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.
02:35Electrophilic Addition to Alkynes: Hydrohalogenation
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.
02:47Alkynes 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.
01:16Radical Reactivity: Nucleophilic Radicals