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Nitrile Oxides, Nitrones, and Nitronates in Organic Synthesis : Novel ...

Nitrile Oxides, Nitrones, and Nitronates in Organic Synthesis : Novel ...

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R<br />

Me<br />

Me<br />

Me<br />

Me<br />

H<br />

N<br />

H<br />

259<br />

O<br />

O<br />

255a–c<br />

+<br />

N<br />

O<br />

258<br />

_<br />

Ph<br />

O<br />

Ph<br />

N Ph +<br />

O<br />

−<br />

dry benzene, reflux<br />

8 h<br />

R = H (a), Cl (b), Me (c)<br />

Me<br />

Me<br />

Me<br />

Scheme 2.94<br />

Me<br />

H<br />

N<br />

_<br />

+<br />

N<br />

O<br />

Ph<br />

Ph<br />

O<br />

Scheme 2.95<br />

R<br />

R<br />

NITRONE REACTIONS 211<br />

O<br />

O<br />

(70%)<br />

256a–c<br />

+<br />

O<br />

O<br />

(25%)<br />

H<br />

O<br />

N H<br />

Ph<br />

257a–c<br />

Me<br />

Me<br />

Me<br />

N<br />

_ _<br />

260<br />

O<br />

CHNHPh<br />

O<br />

Ph<br />

Me N<br />

O<br />

(261) (Scheme 2.95). Usually these reactions afford dimerization products. Their<br />

absence is likely a consequence of the steric effect of the phenyl group.<br />

Beckman rearrangement of nitrone (262) <strong>in</strong>to amide (263) occurs <strong>in</strong> the reaction<br />

with lithium cyanide. However, this reaction gives lactam (264) <strong>in</strong>stead of<br />

the expected 2-cyanopyrrolid<strong>in</strong>e 1-oxide (265) (Scheme 2.96) (473).<br />

_<br />

261<br />

Ph<br />

H

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