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Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation

Reduction of Alkynes to cis-Alkenes: Catalytic Hydrogenation

Introduction
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.

Reduction of Alkenes: Asymmetric Catalytic Hydrogenation

Reduction of Alkenes: Asymmetric Catalytic Hydrogenation

Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...

Reduction of Alkenes: Catalytic Hydrogenation

Reduction of Alkenes: Catalytic Hydrogenation

Alkenes undergo reduction by the addition of molecular hydrogen to give alkanes. Because the process generally occurs in the presence of a transition-metal catalyst, the reaction is called catalytic hydrogenation.
Metals like palladium, platinum, and nickel are commonly used in their solid forms — fine powder on an inert surface. As these catalysts remain insoluble in the reaction mixture, they are referred to as heterogeneous catalysts.
The hydrogenation process takes place on the...

Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation

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Introduction
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.

Alkynes to Aldehydes and Ketones: Acid-Catalyzed Hydration

Alkynes to Aldehydes and Ketones: Acid-Catalyzed Hydration

Introduction
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.

Electrophilic Addition to Alkynes: Hydrohalogenation

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Electrophilic addition of hydrogen halides, HX (X = Cl, Br or I) to alkenes forms alkyl halides as per Markovnikov's rule, where the hydrogen gets added to the less substituted carbon of the double bond. Hydrohalogenation of alkynes takes place in a similar manner, with the first addition of HX forming a vinyl halide and the second giving a geminal dihalide.

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Semihidrogenación electrocatalítica de alquinas terminales mediante transferencia de protones y electrones basada en

Maia E Czaikowski¹, Sophie W Anferov¹, Alex P Tascher¹

¹Department of Chemistry, University of Chicago, Chicago, Illinois 60637, United States.

Journal of the American Chemical Society

|January 1, 2024

Resumen

Este estudio presenta un nuevo método electroquímico para la semihidrogenación selectiva de alquinos utilizando un complejo de níquel. El proceso convierte eficientemente las alquinas terminales en alquenos con alta selectividad Z, evitando la sobre-reducción.

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Área de la Ciencia:

Química orgánica
La electroquímica
Catálisis

Sus antecedentes:

La semihidrogenación de alquinos es crucial para la síntesis de compuestos orgánicos valiosos.
El desarrollo de sistemas catalíticos selectivos y eficientes sigue siendo un desafío clave en la síntesis química.
Los métodos existentes a menudo luchan con la quimio-selectividad y la sobre-reducción.

Objetivo del estudio:

Introducir un nuevo método electroquímico para la semihidrogenación selectiva de las alquinas terminales.
Para utilizar un complejo dihidrazonopirrol de níquel (Ni) para esta transformación.
Para aclarar el mecanismo y optimizar las condiciones de reacción.

Principales métodos:

Reducción electroquímica de alquinas terminales mediante el uso de un complejo de Ni.
Estudios mecanicistas detallados que impliquen la síntesis in situ de los productos intermedios propuestos.
Cálculos computacionales para apoyar la vía de reacción propuesta.

Principales resultados:

Se ha logrado una semi-hidrogenación altamente quimioselectiva de las alquinas terminales sobre las alquinas y alquenos internos.
Se ha demostrado la formación Z-selectiva de alquenos terminales con altos rendimientos.
Se identificó una vía de transferencia de átomos de hidrógeno basada en ligandos que involucra una especie de Ni (I), distinta de los mecanismos hidruro tradicionales.

Conclusiones:

El método electroquímico desarrollado ofrece un rendimiento superior en comparación con los catalizadores homogéneos existentes para la semihidrogenación alquina terminal.
La cooperación metal-ligando en la transferencia de hidrógeno permite una reducción eficiente del alquino y minimiza la evolución del hidrógeno.
Esta estrategia proporciona un plan versátil para otras transformaciones electrorreductivas.