title: Phosphonylpyrazoles from Bestmann-Ohira reagent and nitroalkenes: synthesis and dynamic NMR studies.
abstract: Application of diethyl 1-diazo-2-oxopropylphosphonate (Bestmann-Ohira reagent) as a cycloaddition partner with nitroalkenes has been extensively investigated. Base-mediated reaction of the Bestmann-Ohira reagent with various nitroalkenes such as beta-substituted, alpha,beta-disubstituted, and nitroethylene that are part of a carbocyclic or heterocyclic ring provided functionalized phosphonylpyrazoles through a one-pot regioselective reaction at room temperature in high yield. The substituted nitroalkenes employed in these reactions also included Morita-Baylis-Hillman adducts of conjugated nitroalkenes with various electrophiles. Detailed dynamic NMR studies were performed on the prototropic tautomerism exhibited by the phosphonylpyrazoles using CDCl(3) and DMSO-d(6) as solvents and (1)H and (31)P as the probe nuclei. These studies unraveled the existence of two tautomers in solution with a small energy difference but considerable barrier to interconversion.
authors.affiliation: Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400 076, India.
authors.forename: Rajendran
authors.initials: R
authors.lastname: Muruganantham
authors.forename: Irishi
authors.initials: I
authors.lastname: Namboothiri
mesh_terms: D000475:Alkenes / Q000737:chemistry*; D001391:Azo Compounds / Q000737:chemistry*; D002384:Catalysis; D003500:Cyclization; D007202:Indicators and Reagents / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009574:Nitro Compounds / Q000737:chemistry*; D009943:Organophosphorus Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D011407:Propane / Q000031:analogs & derivatives* / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D000475:Alkenes; D001391:Azo Compounds; D007202:Indicators and Reagents; D009574:Nitro Compounds; D009943:Organophosphorus Compounds; C550064:diethyl 1-diazo-2-oxopropylphosphonate; D011407:Propane