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Vinilcinación catalizada por el hierro de los alcinos terminales
Qiang Huang1, Yu-Xuan Su1, Wei Sun1
1Frontiers Science Center for New Organic Matter, the State Key Laboratory and Institute of Elemento-Organic Chemistry, College of Chemistry, Nankai University, Tianjin 300071, China.
Este estudio introduce un nuevo método catalizado por el hierro para la vinilzincación de alquinas terminales. Este enfoque sintetiza eficientemente diversos reactivos organozinc, superando las limitaciones de los métodos anteriores.
Área de la Ciencia:
- Química organometálica
- Química orgánica sintética
Sus antecedentes:
- Los reactivos orgánicos son cruciales en la síntesis.
- La carbocinación alquina está limitada por una baja tolerancia alquina terminal y por las difíciles transformaciones del producto.
Objetivo del estudio:
- Desarrollar un nuevo método para la vinilzincación de alquinas terminales.
- Para sintetizar diversos reactivos organozinc con mayor eficiencia y tolerancia del grupo funcional.
Principales métodos:
- Se utilizaron catalizadores de hierro recientemente desarrollados con ligandos de 1,10-fenantrolina-imina.
- Se utilizan reactivos de vinilzinco y alquinas terminales como sustratos.
Principales resultados:
- Se ha logrado una vinilcinación eficiente de las alquinas terminales.
- Se ha demostrado una excelente tolerancia al grupo funcional (amino, éster, hidroxilo, etc.) y un amplio ámbito de aplicación de sustratos (arilo, alquenilo, acetileno alquilo).
- Muestra alta quimioselectividad, regioselectividad y estereoselectividad.
Conclusiones:
- El nuevo método catalizado por el hierro permite el acceso a nuevos reactivos organozinc.
- Los catalizadores de hierro con ligandos específicos ofrecen ventajas sobre otros metales en actividad y selectividad.
- Este método puede mejorar la síntesis de moléculas bioactivas como la vitamina A.
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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.
02:24Reduction 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
02:47Alkynes 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.
02:42Acidity 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.