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

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710 NITRONATES<br />

[529] + [530]<br />

MeO2C CH<br />

H<br />

MeO 2C<br />

MeO 2C<br />

MeO 2C<br />

D<br />

O<br />

CH N<br />

CH<br />

C<br />

C<br />

529a<br />

CH N<br />

H<br />

CH N<br />

CH N<br />

OSiMe 3<br />

O<br />

OH<br />

MeO2C C CH N OH<br />

R 1<br />

R 1<br />

X<br />

X<br />

R 1<br />

X<br />

X<br />

R 1<br />

Et 3N<br />

R 2<br />

A<br />

R 2<br />

B<br />

O<br />

Me 3SiOH<br />

OH Me3SiCl/Et3N<br />

N O<br />

N O<br />

R 2<br />

NO 2<br />

SiMe3<br />

SiMe3<br />

N O<br />

R 2<br />

+<br />

MeO2C −<br />

CH<br />

MeO2C<br />

HNO 2<br />

X<br />

R 1<br />

O<br />

CH N<br />

CH<br />

529′a<br />

MeO 2C<br />

OSiMe 3<br />

CH<br />

2<br />

CH N<br />

530a<br />

R 2<br />

N OSiMe3<br />

O<br />

CH N(O)OSiMe3<br />

MeO2C CH CH<br />

C<br />

N OH<br />

MeO2C<br />

534 533<br />

Scheme 3.271<br />

C<br />

CH N<br />

OSiMe3<br />

MeO2C C CH N OSiMe3<br />

as heterodiene or as heteroalkene (491, 541, 542) (Scheme 3.272). For example,<br />

ethyl v<strong>in</strong>yl ether, which cannot be <strong>in</strong>volved <strong>in</strong> the ene reaction, undergoes “normal”<br />

[4 + 2]-cycloaddition to give product (539).<br />

Under these reaction conditions, the latter undergoes silylation to form dihydrooxaz<strong>in</strong>e<br />

(538), which can be aga<strong>in</strong> easily desilylated with methanol to form<br />

531

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