The Heck reaction is a palladium-catalyzed cross-coupling that forms what product from aryl or vinyl halides and alkenes?

The Heck reaction is a palladium-catalyzed cross-coupling that forms what product from aryl or vinyl halides and alkenes?

• A. Substituted alkenes
• B. Alcohols
• C. Aldehydes
• D. Alkanes

Answer: (A)

The main idea here is that this palladium-catalyzed cross-coupling creates a new carbon–carbon bond between an aryl (or vinyl) fragment and an alkene, yielding a substituted alkene as the product. In the mechanism, palladium(0) first performs oxidative addition with the aryl or vinyl halide to form a Pd(II)–aryl (or Pd(II)–vinyl) species. The alkene then coordinates to this Pd complex and undergoes migratory insertion, giving a Pd–alkyl intermediate. A subsequent beta-hydride elimination releases the substituted alkene product and a Pd–hydride species, which is regenerated to Pd(0) by the base. The key outcome is that the aryl or vinyl group ends up attached to the double bond, producing an alkene with new substituents—typically the preferred geometry is the trans (E) form under common conditions. Because of this pathway, the reaction cleanly delivers substituted alkenes rather than alcohols, aldehydes, or alkanes, which would require different reagents or reaction steps.

The main idea here is that this palladium-catalyzed cross-coupling creates a new carbon–carbon bond between an aryl (or vinyl) fragment and an alkene, yielding a substituted alkene as the product. In the mechanism, palladium(0) first performs oxidative addition with the aryl or vinyl halide to form a Pd(II)–aryl (or Pd(II)–vinyl) species. The alkene then coordinates to this Pd complex and undergoes migratory insertion, giving a Pd–alkyl intermediate. A subsequent beta-hydride elimination releases the substituted alkene product and a Pd–hydride species, which is regenerated to Pd(0) by the base. The key outcome is that the aryl or vinyl group ends up attached to the double bond, producing an alkene with new substituents—typically the preferred geometry is the trans (E) form under common conditions.

Because of this pathway, the reaction cleanly delivers substituted alkenes rather than alcohols, aldehydes, or alkanes, which would require different reagents or reaction steps.