Which of the following is the major product when $C_6{H}_5\mathrm{Br}$ (bromobenzene) reacts with ${\mathrm{CH}}_2=\mathrm{CHCOOEt}$ (ethyl acrylate) in the presence of a palladium catalyst under Heck reaction conditions?

• A. $C_6{H}_5\mathrm{COOEt}$ (ester formation by direct substitution)
• B. $C_6{H}_5\mathrm{Br}$ is recovered unchanged
• C. $C_6{H}_5-\mathrm{CH}=\mathrm{CHCOOEt}$ (trans-stilbene derivative)
• D. $C_6{H}_5\mathrm{CH}-\mathrm{CH}{\_}_2\mathrm{COOEt}$ (alkylated product)

Answer: (C)

Verified step by step guidance

1. Identify the type of reaction: The problem describes a Heck reaction, which is a palladium-catalyzed coupling between an aryl halide (bromobenzene) and an alkene (ethyl acrylate). This reaction forms a substituted alkene by coupling the aryl group to the alkene.
2. Understand the reactants: Bromobenzene (C\_6H\_5Br) is the aryl halide, and ethyl acrylate (CH\_2=CHCOOEt) is the alkene with an electron-withdrawing ester group. The palladium catalyst facilitates the coupling between these two.
3. Outline the mechanism steps: (1) Oxidative addition of Pd(0) into the C-Br bond of bromobenzene to form an aryl-Pd(II) complex. (2) Coordination and insertion of the alkene (ethyl acrylate) into the Pd-aryl bond. (3) Beta-hydride elimination to form the substituted alkene product. (4) Reductive elimination regenerates Pd(0).
4. Predict the product stereochemistry: The Heck reaction typically gives the trans (E) alkene as the major product due to the syn insertion and anti beta-hydride elimination steps. Therefore, the product will be a trans-stilbene derivative where the phenyl group is coupled to the alkene of ethyl acrylate.
5. Exclude other options: Direct substitution to form an ester on the benzene ring is not typical under Heck conditions. Recovery of bromobenzene unchanged would mean no reaction occurred, which is unlikely with a palladium catalyst present. Alkylated products without the double bond are not formed in Heck reactions, which preserve the alkene moiety.