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

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238 NITRONES: NOVEL STRATEGIES IN SYNTHESIS<br />

MOMO<br />

+<br />

N<br />

− O<br />

312<br />

OMOM<br />

BnO<br />

ArCH 2MgCl<br />

CH 2Cl 2<br />

MOMO<br />

O<br />

+ Bn<br />

O H N −<br />

H O<br />

A<br />

Re attack<br />

Mg<br />

R X<br />

N<br />

OH<br />

HO<br />

314<br />

315<br />

Scheme 2.133<br />

OMOM<br />

MOMO<br />

N<br />

OMOM<br />

Ar OH Ar<br />

ArCH2 − = MeOC6H4CH2 −<br />

N<br />

H<br />

syn anti<br />

Fig. 2.21<br />

+<br />

OR OMe<br />

R = COMe anisomyc<strong>in</strong><br />

R = H deacetylanisomyc<strong>in</strong><br />

O H<br />

H N<br />

O<br />

BnO<br />

B<br />

+<br />

Si attack<br />

R<br />

O<br />

Mg X<br />

−<br />

Bn<br />

Al<br />

Et Cl<br />

Et<br />

The change <strong>in</strong> selectivity <strong>in</strong> the complexation of nitrone (316) with diethylalum<strong>in</strong>um<br />

chloride makes it possible to carry out a shortened synthesis of epimers<br />

at C2 of both deacetylanisomic<strong>in</strong>e (315) <strong>and</strong> anisomic<strong>in</strong>e (314) (Scheme 2.134,<br />

Fig. 2.21) (200).<br />

A seven step synthesis of (−)-codonops<strong>in</strong><strong>in</strong>e (312) <strong>and</strong> a ten step synthesis of<br />

(−)-radicam<strong>in</strong>e B (310b) also <strong>in</strong>clude nucleophilic addition of (4-methoxybenzyl)<br />

magnesium chloride <strong>and</strong> p-benzyloxyphenylmagnezium bromide derivatives to<br />

pyrrol<strong>in</strong>e-N -oxides as one of the key steps.

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