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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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O<br />

BnO<br />

Ph<br />

Et 2N<br />

O<br />

BnO<br />

H<br />

317<br />

O<br />

O<br />

HO N<br />

anti<br />

315<br />

O<br />

314<br />

−<br />

316<br />

Ph<br />

O −<br />

N<br />

+ O MeMgBr<br />

N<br />

Bn<br />

+ +<br />

Ph<br />

OMe<br />

O<br />

+<br />

MeO<br />

BnO<br />

Scheme 2.134<br />

Ph<br />

Et 2N<br />

O<br />

Me<br />

H<br />

N<br />

Bn OH<br />

Scheme 2.135<br />

NITRONE REACTIONS 239<br />

O<br />

HO N<br />

syn<br />

Ph<br />

MgX<br />

O<br />

Ph<br />

Et 2N<br />

H<br />

318<br />

OMe<br />

High selective addition of Grignard reagents to C -cyclopropyl nitrone (317)<br />

is the basis of the synthesis of PEDC (318), an efÞcient antagonist of NMDA<br />

(N -methyl-D-aspartic acid), a receptor with potential therapeutic properties for<br />

epilepsy <strong>and</strong> ischemia. X-ray <strong>and</strong> NOE analyses of (318) show that the bisected<br />

s-trans conformation appears to be more stable both <strong>in</strong> the solid state <strong>and</strong> <strong>in</strong><br />

solution. Addition of the Grignard reagent to nitrone (317) proceeds stereoselectively,<br />

giv<strong>in</strong>g the anti-product with <strong>in</strong>creas<strong>in</strong>g selectivity <strong>in</strong> the presence of<br />

MgBr2 used as an additive (Scheme 2.135) (222, 223, 556, 557).<br />

To carry out enantioselective alkylation of 2-thiazolyl nitrone (319) (Scheme<br />

2.136), chiral additives presented <strong>in</strong> Fig. 2.22 <strong>and</strong> Lewis acids (MgBr2, Et2AlCl,<br />

Me<br />

NH 2

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