Homenorks - CHEM 333 Ac SP18 333 HW3.pdf X+ ?? 0 ? ? https:/ uic blackboard on b
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Homenorks - CHEM 333 Ac SP18 333 HW3.pdf X+ ?? 0 ? ? https:/ uic blackboard on bbcs ebda pid-5861363 t content d-606 9368 2/course 2018. pnngchem.333.26430/5P18 20333%20H 3pdf 1. Opoints) All cioss coupling ieactions have theit advantages and disadvantages, and therefoue some are better used under certain conditions. Considering the reactions below, identify which is the better cross coupling reaction to use and explain why a) Stile or Kumada? HO NMe ?? NMc M SnBls orMgBr b) Negishi or Stille? PO(PPh.4 c) Kumada oi Suzuki? NI(acac) O Type here to search 0:20 AM 4/13/2018Explanation / Answer
Stille Coupling- It is a cross coupling reaction between organotin based reagents and organohalides catalyzed by palladium.
The limitations are very few on the side groups of halides and organotin based reagents .However, the main drawback is due to the toxic nature of tin compounds and their poor solubility in water (because they are less polar).This limits their application in pharmaceuticals.
The reaction can be easily carried out in the presence of air.A variety of functional groups are tolerated. The tolerance of NO 2 , CN, OMe, COOR, and even CHO is observed with the halide substrate.
Kumada Coupling-It is a cross coupling reaction between an aryl ,alkyl, vinyl halide or tryflate and aryl, alkenyl or alkyl Grignard reagents catalysed by nickel or palladium.
This coupling has limited use because the Grignard reagents are incompatible with certain functional groups i.e having low tolerance for functional groups. Recently , the scope of this reaction has been extended to aryl-aryl coupling with improved tolerance for functional group at low temperatures.
The Stille coupling method is better than Kumada Coupling.
Negishi coupling -It is a cross coupling reaction between an organozinc compound and an organic halide catalysed by nickel or palladium to form a new carbon -carbon covalent bond.
Preparation of unsymmetrical biaryls in good yields was first reported by this reaction.This reaction should be carried out in a water and air free atmosphere due it's high sensitivity towards them.
Negishi coupling is often preferred over Stille coupling for alkenylation.
Suzuki coupling-It is cross coupling reaction between organoboron compounds (which is usually boronic acid) and organic halides catalysed by palladium.
This reaction has good tolerance for the presence of functional groups in the coupling partners. The boronic acids are non toxic. They are stable in presence of air and water both.Due to non- toxicity of boron side products, this reaction has applications in pharmaceutical industry. Reaction can be used to couple highly hindered substrates and to carry out asymmetric synthesis. Reaction can be carried out at room temperature and using low amount of catalyst .
Therefore, Suzuki coupling is preferred over Kumada coupling .
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