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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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622 NITRONATES<br />

SiO<br />

SiO<br />

N OSi<br />

R<br />

N OSi<br />

NO2<br />

SiOTf/Et3N<br />

Si – Me2Bu t Si<br />

NO2<br />

H<br />

R<br />

341<br />

NEt 3<br />

R<br />

R = Me, Ph, CH2CO2Me<br />

O<br />

N<br />

N(OSi) 2<br />

77%<br />

OSi<br />

Scheme 3.200<br />

MeO2C<br />

–Et3NHOTf<br />

–Et 3NHOTf<br />

SiO<br />

N<br />

Si – trialkylsilyl<br />

Scheme 3.201<br />

Et3N<br />

OSi<br />

R = CO2Me<br />

H<br />

O<br />

N<br />

OSi<br />

SiOTf/Et3N<br />

R<br />

OSi<br />

N<br />

OSi<br />

R<br />

NO2<br />

N(OSi) 2<br />

Double silylation of primary AN occurs stereoselectively to give only the<br />

trans isomer of the correspond<strong>in</strong>g BENA. Only one stereoisomer is detected <strong>in</strong><br />

tris-substituted BENAs.<br />

3.5.1.3. Silylation of Cyclic <strong>Nitronates</strong> As can be seen from Chart 3.20 <strong>and</strong><br />

Scheme 3.197, double silylation of AN necessarily <strong>in</strong>volves silylation of <strong>in</strong>termediate<br />

SENAs. In this connection, silylation of alkyl nitronates as nearest<br />

analogous of SENAs is of obvious <strong>in</strong>terest. This reaction would be expected<br />

to give “mixed” nitroso acetals conta<strong>in</strong><strong>in</strong>g the > C=C–N(OAlk)OSi fragment.<br />

Until recently, such derivatives were unknown. However, cyclic nitronates are of<br />

particular <strong>in</strong>terest, because cleavage of the endocyclic N–O bond does not lead<br />

to simpliÞcation of the <strong>in</strong>itial molecule. This provides additional possibilities for<br />

the use of these nitroso acetals <strong>in</strong> organic synthesis.

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