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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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372 NITRONES: NOVEL STRATEGIES IN SYNTHESIS<br />

Me<br />

MeO<br />

Me<br />

Ph<br />

Ph<br />

223 a<br />

N<br />

N<br />

203<br />

N<br />

+<br />

O −<br />

O −<br />

N<br />

+<br />

Me<br />

Me<br />

DMAD<br />

DMAD<br />

Ph<br />

Me<br />

Me<br />

N<br />

N<br />

Me<br />

Ph<br />

OMe<br />

Me<br />

N O<br />

719<br />

Scheme 2.299<br />

N O<br />

COOMe<br />

COOMe<br />

COOMe<br />

Scheme 2.300<br />

COOMe<br />

Ph<br />

Me<br />

Me<br />

Ph<br />

Me<br />

N<br />

Me<br />

Me<br />

N<br />

O −<br />

N<br />

223 g<br />

OMe<br />

+<br />

N O<br />

720<br />

Me<br />

N<br />

H<br />

O<br />

Me<br />

Ph<br />

Me<br />

N<br />

H<br />

O<br />

DMAD<br />

Ph<br />

−H 2O<br />

OMe<br />

COOMe<br />

N<br />

721<br />

COOMe<br />

COOMe<br />

COOMe<br />

H 2O<br />

OH<br />

H<br />

N<br />

721 a<br />

COOMe<br />

COOMe<br />

The latter reacts with a second DMAD molecule to give cycloadduct (726). The<br />

reaction proceeds via open<strong>in</strong>g of the azirid<strong>in</strong>e r<strong>in</strong>g to give compound (725). The<br />

cyclo-adduct (726) undergoes a 1,3-sigmatropic shift <strong>and</strong> aromatization to give<br />

compound (723) (Scheme 2.302) (816).

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