1. Asymmetric Aza-Wacker-Type Cyclization of N.Ts Hydrazine-Tethered Tetrasubstituted Olefins: Synthesis of Pyrazolines Bearing One Quaternary or Two Vicinal Stereocenters.
- Author
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Xuezhen Kou, Qihang Shao, Chenghao Ye, Guoqiang Yang, and Wanbin Zhang
- Subjects
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RING formation (Chemistry) , *DIASTEREOISOMERS , *ALKENES , *METHYL groups , *ENANTIOSELECTIVE catalysis - Abstract
We have developed an asymmetric aza-Wackertype cyclization of N-Ts hydrazine-tethered tetrasubstituted olefins, affording optically active pyrazolines bearing chiral tetrasubstituted carbon stereocenters. This reaction is tolerant to a broad range of substrates under mild reaction conditions, giving the desired chiral products with high enantioselectivities. Generation of two vicinal stereocenters on the C=C double bonds was also achieved with high selectivities, a process which has been rarely studied for Wacker-type reactions. A mechanistic study revealed that this aza-Wackertype cyclization undergoes a syn-aminopalladation process. It was also found that for substrates bearing two linear alkyl substituents on the outer carbon atom of the olefin, both of which are larger than a methyl group, the alkyl substituent that is cis to the intranucleophilic group participates more readily in β-hydride elimination. When one of the two alkyl substituents on the outer carbon atom of the olefin is a methyl group, β-hydride elimination proceeds selectively at the methylene side, thus both diastereomers can be prepared via switching the configuration of the olefin. Furthermore, the product can be converted to a pharmaceutical compound in high yields over three steps. [ABSTRACT FROM AUTHOR]
- Published
- 2018
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