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Synthesis of Chiral Pyrazoles: A 1,3‐Dipolar Cycloaddition/[1,5] Sigmatropic Rearrangement with Stereoretentive Migration of a Stereogenic Group
Author(s) -
PérezAguilar M. Carmen,
Valdés Carlos
Publication year - 2015
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201506881
Subject(s) - stereocenter , sigmatropic reaction , chemistry , cycloaddition , stereochemistry , chiral auxiliary , enantioselective synthesis , organic chemistry , catalysis
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.