교과서 질문
What substituted alkene would you use in the Heck reaction to make the following products?
(a)
(b)
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35. Transition Metals
Heck Reaction
객관식
Which of the following is the major product when (bromobenzene) reacts with (ethyl acrylate) in the presence of a palladium catalyst under Heck reaction conditions?
A
(ester formation by direct substitution)
B
is recovered unchanged
C
(trans-stilbene derivative)
D
(alkylated product)
검증된 단계별 안내1
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.
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.
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).
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.
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.
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