- Flash Vacuum Pyrolysis of Stabilized Phosphorous Ylides. Part 5. Selective Extrusion of Ph3PO from β,γ,β'-Trioxo Ylides to give Doacylalkynes
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Sixteen examples of the previously unknown trioxo ylides 7 have been prepared by acylation of stabilized phosphorus ylides 8 with α-oxo acid chlorides 9.Extrusion of Ph3PO from these is readily achieved using FVP at 500 deg C in most cases, to afford the diacylalkynes 10 in moderate yield.Three examples failed to give the expected alkynes and the nature of the processes involved in these cases is certain.Fully assigned 13C NMR spectra are presented for the ylides and an unexpected pattern is observed in the value of JP-C for the three carbonyl carbons depending on the nature of the substituents present.There is some correlation between the value of 2JP-C for the central carbonyl carbon and the success of the pyrolysis although this is not complete.The method has been used to prepare a specifically 13C labelled acetylenic diester 14.
- Aitken, R. Alan,Herion, Hugues,Janosi, Amaya,Karodia, Nazira,Raut, Swati V.,et al.
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p. 2467 - 2472
(2007/10/02)
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- Isothiazoles. Part 3. Cycloadditions of Diazoalkanes to 3-Dialkylaminoisothiazole 1,1-Dioxides. Competitive Ring Cleavage in 3a,4-Dihydro-6aH-pyrazoloisothiazole 1,1-Dioxides: Formation of 2-Thia-3-azabicyclohex-3-ene 2,2-Dioxides and/or Pyrazoles
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3-Dialkylaminoisothiazole 1,1-dioxides 1 readily undergo cycloadditions with diazoalkanes 2.The reaction is characterized by high site- and regio-selectivity.Cycloadducts 3 and 4 were found to undergo straightforward thermolysis reactions at elevated temperature through two different paths characterized respectively by loss of nitrogen or sulfur dioxide and diethylcyanamide.The different transformations affording pyrazoles 6 and derivatives of the new heterocycle 2-thia-3-azabicyclohex-3-ene 2,2-dioxide 5 are discussed.
- Clerici, Francesca,Ferrario, Tiziano,Gelmi, Maria Luisa,Marelli, Roberto
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p. 2533 - 2536
(2007/10/02)
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- Pyrolysis of β,γ,β'-trioxo phosphorus ylides: Convenient synthesis of symmetrical and unsymmetrical diacylalkynes
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Flash vacuum pyrolysis of a series of 1,2,4-trioxo-3-triphenylphosphoranylidene-butane derivatives, formed by acylation of β-oxo-phosphorus ylides with α-oxo-acid chlorides, results in extrusion of Ph3PO exclusively across the 2,3-position to give diacylalkynes.
- Aitken,Herion,Janosi,Raut,Seth,Shannon,Smith
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p. 5621 - 5622
(2007/10/02)
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