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Cooperative B(C6F5)3/Chiral Secondary Amine-Catalyzed Asymmetric [4 + 2] Cycloaddition Reaction
Dan-Dan Ma1, Li-Xue Xiong1, Wen-Jing Wang1
1Ministry of Education Key Laboratory for the Synthesis and Application of Organic Functional Molecules, Hubei Key Laboratory for Precision Synthesis of Small Molecule Pharmaceuticals, College of Chemistry and Chemical Engineering, Hubei University, Wuhan 430062, P. R. China.
Abstract:
A highly stereoselective [4 + 2] cycloaddition reaction of pyrazolone derivatives with enals via dienamine/Lewis acidic borane synergistic activation has been developed. The reaction proceeded under mild reaction conditions with a wide functional group tolerance. A series of spirooxindole-pyran-pyrazole derivatives with three contiguous stereocenters were obtained in moderate to good yields with excellent enantioselectivities and diastereoselectivities. This protocol provides the compatibility of chiral secondary amines and B(C6F5)3 catalysts and enriches the synergistic catalytic system of Lewis acidic boranes and chiral organocatalysts.
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Preparation of Alcohols via Substitution Reactions
Alcohols can be synthesized from alkyl halides via nucleophilic substitution reactions. The highly polar carbon-halogen bond in the substrate makes halide a good leaving group. The hydroxide ion or water can act as a nucleophile to take the place of halide and form an alcohol. The substitution reactions occur via two different reaction pathways, SN1 or SN2, depending on the nature of carbon attached to the halide.
Primary alcohols are synthesized from primary alkyl halides, and the...

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