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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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(a)<br />

SiO<br />

O N<br />

6<br />

Nu<br />

(b) N<br />

N<br />

(c)<br />

SiO<br />

Si<br />

O<br />

5<br />

SILYLATION OF NITRO COMPOUNDS AS A PROCESS 639<br />

R<br />

Dom<strong>in</strong>ant<br />

O N<br />

357 SiO 357′<br />

N<br />

Bond<strong>in</strong>g<br />

orbital<br />

N<br />

N C<br />

Nu′<br />

Nu<br />

R<br />

Nu<br />

Si N<br />

N C<br />

+<br />

Anomeric<br />

effect<br />

Antibond<strong>in</strong>g<br />

orbital<br />

−Si +<br />

6<br />

N<br />

N C<br />

Nu<br />

5<br />

R<br />

M<strong>in</strong>or<br />

Chart 3.23 Mechanistic <strong>in</strong>terpretation of C,C-coupl<strong>in</strong>g of six-membered cyclic nitronates<br />

with nucleophiles.<br />

is performed through coord<strong>in</strong>ation of the nitrogen lone pair <strong>and</strong> the silicon atom<br />

of the nucleophile <strong>in</strong> the transition state (see Chart 3.23, c).<br />

The <strong>in</strong>ßuence of catalytic C,C-coupl<strong>in</strong>g of six-membered cyclic nitronates can<br />

be used, under more drastic conditions, for the construction of nitrogen-conta<strong>in</strong><strong>in</strong>g<br />

heterocycles via cascade chemical transformations (see, e.g., the coupl<strong>in</strong>g reaction<br />

of nitronate (368) with silyl enolates (369a–d) <strong>in</strong> the presence of trimethylsilyl<br />

trißate (154) (Scheme 3.211)).

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