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  • Title: Synthesis of Chiral Pyrazoles: A 1,3-Dipolar Cycloaddition/[1,5] Sigmatropic Rearrangement with Stereoretentive Migration of a Stereogenic Group.
    Author: Pérez-Aguilar MC, Valdés C.
    Journal: Angew Chem Int Ed Engl; 2015 Nov 09; 54(46):13729-33. PubMed ID: 26390991.
    Abstract:
    The reactions between terminal alkynes and α-chiral tosylhydrazones lead to the obtention of chiral pyrazoles with a stereogenic group directly attached at a nitrogen atom. The cascade reaction includes decomposition of the hydrazone into a diazocompound, 1,3-dipolar cycloaddition of the diazo compound with the alkyne, and [1,5] sigmatropic rearrangement with migration of the stereogenic group. This strategy has been successfully applied to the synthesis of structurally diverse chiral pyrazoles through α-chiral tosylhydrazones, obtained from α-phenylpropionic acid, α-amino acids, and 2-methoxycyclohexanone. Notably, the stereoretention of the [1,5] sigmatropic rearrangements represent very rare examples of this stereospecific transformation.
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