Publication: Density Functional Theory Computational Study on the Thermal Cycloreversion of 2-Acetoxy-2-methoxy-5,5-dimethyl- 3-1,3,4-oxadiazoline: Evidence for a Carbonyl Ylide Intermediate.

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Title	Density Functional Theory Computational Study on the Thermal Cycloreversion of 2-Acetoxy-2-methoxy-5,5-dimethyl- 3-1,3,4-oxadiazoline: Evidence for a Carbonyl Ylide Intermediate.
Authors/Editors*	Wojciech Czardybon, John Warkentin, Nick Henry Werstiuk
Where published*	J. Org. Chem.
How published*	Journal
Year*	2005
Volume	70
Number	21
Pages	8431 -8436
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Abstract	Three [3 + 2] cycloreversions of 2-acetoxy-2-methoxy-5,5-dimethyl-3-1,3,4-oxadiazolines were examined by computation at the density functional level of theory. The lowest activation energies are those for cycloreversion to 2-diazopropane and acetic methylcarbonic anhydride and for cycloreversion to N2 and a carbonyl ylide. Those are the reactions that are observed experimentally. A third cycloreversion, to acetoxy(methoxy)diazomethane and acetone, has a much larger barrier. The carbonyl ylide is a real intermediate, but it fragments easily to acetone and acetoxy(methoxy)carbene. The lifetime of the ylide may be so short, in some cases, as to blur the distinction between a two-step cycloreversion of the oxadiazoline and a concerted process that generates three fragments in one step.