Video Experimental Relacionado
Updated: May 26, 2025
Chemoselective Preparation of 1-Iodoalkynes, 1,2-Diiodoalkenes, and 1,1,2-Triiodoalkenes Based on the Oxidative Iodination of Terminal Alkynes
Published on: September 12, 2018
Difuncionalización electroquímica multicomponente enantioselectiva de las alquinas terminales
Qiannan Wang1, Xinyu Wang1, Yong Liu1
1Institutes of Physical Science and Information Technology, Anhui University, Hefei 230601, China.
Este estudio introduce un método electroquímico para crear moléculas complejas a partir de alquinas simples. La reacción catalizada por níquel construye eficientemente estereocentros cuaternarios desafiantes con alta selectividad.
Área de la Ciencia:
- Química orgánica
- Catálisis
- La electroquímica
Sus antecedentes:
- La funcionalización radical de las alquinas es clave para la síntesis de alceno.
- La creación de estereocentros cuaternarios de carbono enantioselectivamente a través de reacciones radicales es un desafío.
Objetivo del estudio:
- Desarrollar una reacción radical enantioselectiva multicomponente para sintetizar alquenos sustituidos.
- Abordar las limitaciones de compatibilidad, selectividad y eficiencia de los métodos actuales.
Principales métodos:
- Acoplamiento cruzado de tres componentes electroquímico catalizado por níquel.
- Se utilizaron alquinas terminales, precursores de radicales alquilo racémicos y reactivos de transferencia de grupos.
- Generación anódica de radicales terciarios intermedios unidos al níquel.
Principales resultados:
- Se obtuvieron excelentes selectividades regionales, estéreo y enantiológicas (hasta el 95% ee) para más de 70 ejemplos.
- Se ha demostrado una amplia compatibilidad de grupo funcional con las alquinas alifáticas y aromáticas.
- Habilitado la difuncionalización anti-estereoselectiva de las alquinas.
Conclusiones:
- El enfoque electroquímico desarrollado transforma eficientemente las alquinas terminales en diversas estructuras con centros estereogénicos alfa-cuaternarios.
- Este método expande el alcance de la difuncionalización de alquinas y la síntesis estereoselectiva.
Videos de Conceptos Relacionados
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.
02:42Acidity of 1-Alkynes
The acidic strength of hydrocarbons follows the order: Alkynes > Alkenes > Alkanes. The strength of an acid is commonly expressed in units of pKa — the lower the pKa, the stronger the acid. Among the hydrocarbons, terminal alkynes have lower pKa values and are, therefore, more acidic. For example, the pKa values for ethane, ethene, and acetylene are 51, 44, and 25, respectively, as shown here.
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.
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.