- High nucleophilicity of cyclic amidocarbene toward aryl isocyanates, new approach to spiro[azetidinone-4,3′-indolinone] derivatives
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The nucleophilic addition of β-lactam-4-ylidenes 2, a type of ambiphilic cyclic amidocarbene, to aryl isocyanates has been studied and their application in organic synthesis has been demonstrated. Thermolysis of spiro[β-lactam-4,2′-oxadiazolines] 1 in the
- Cheng, Ying,Wang, Bo,Cheng, Lan-Qing
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p. 4418 - 4427
(2007/10/03)
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- Spiro-fused β-lactam oxadiazolines by formal cycloaddition of 2-imino-Δ3-1,3,4-oxadiazolines to ketenes
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Sixteen spiro-fused β-lactam oxadiazolines were prepared by treatment of 2-imino-Δ3-1,3,4-oxadiazolines with carboxylic acid chlorides in the presence of triethylamine.Two others were prepared by methylation of β-lactam oxadiazoline anion equivalents with methyl iodide.Isomer ratios, spectra, stereochemistry, and relative thermodynamic stabilities of a pair of diastereomeric β-lactam oxadiazolines are reported.Three cases of failure of the approach are noted, to define some of the limitations.The oxadiazolines are known to undergo thermolysis, in solution, to afford N2, a ketone, and a β-lactam-4-ylidene.Phenyl substitution at C5 of the oxadiazoline ring serves to decrease the thermolysis temperature by about 50 deg C but it also leads to the onset of a side reaction that lowers the yield of ylidene.This observation indicates a limitation of the oxadiazoline approach to the generation of β-lactam-4-ylidene.
- Zoghbi, Michel,Warkentin, John
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p. 912 - 918
(2007/10/02)
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- β-Lactam-4-ylidenes
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β-Lactam-4-ylidenes, generated by thermolysis of easily accessible spiro-fused β-lactam oxadiazolines, are trapped in typical intramolecular and intermolecular carbene reactions.
- Zoghbi, Michel,Warkentin, John
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p. 3214 - 3215
(2007/10/02)
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