title: Synthesis of Chiral Pyrazoles: A 1,3-Dipolar Cycloaddition/[1,5] Sigmatropic Rearrangement with Stereoretentive Migration of a Stereogenic Group.
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.
authors.affiliation: Departamento de Química Orgánica e Inorgánica and Instituto Universitario de Química Organometálica "Enrique Moles", Universidad de Oviedo, c/Julián Clavería 8, Oviedo 33006 (Spain).
authors.forename: M Carmen
authors.initials: MC
authors.lastname: Pérez-Aguilar
authors.affiliation: Departamento de Química Orgánica e Inorgánica and Instituto Universitario de Química Organometálica "Enrique Moles", Universidad de Oviedo, c/Julián Clavería 8, Oviedo 33006 (Spain). acvg@uniovi.es.
authors.forename: Carlos
authors.initials: C
authors.lastname: Valdés
mesh_terms: D000480:Alkynes / Q000737:chemistry*; D061565:Cycloaddition Reaction; D006835:Hydrazones / Q000737:chemistry*; D015394:Molecular Structure; D011720:Pyrazoles / Q000138:chemical synthesis* / Q000737:chemistry; D011789:Quantum Theory; D013237:Stereoisomerism
chemical_list: D000480:Alkynes; D006835:Hydrazones; D011720:Pyrazoles
keywords: cycloaddition; diazo compounds; heterocycles; rearrangements; tosylhydrazone