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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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460 NITRONATES<br />

R<br />

NO 2<br />

R<br />

R'<br />

OH<br />

O N<br />

R' O HO<br />

NO2 O N<br />

34a<br />

EtO2CN NCO2Et<br />

Ph3P<br />

35a<br />

;<br />

34b<br />

Ph3P<br />

O<br />

35b 94%<br />

R' = H, R = Ph (93%); SO2Ph (91%); cyclohexen-l-yl (81%); R' = Me, R = CO2Et (94%)<br />

AlkO 2C<br />

AlkO2C<br />

37<br />

Scheme 3.34<br />

+ HC(NO 2)RX AlkO2C<br />

36<br />

C(NO2)RX<br />

HO C(NO2)RX<br />

38<br />

Hal C(NO 2)RX<br />

[H]<br />

base<br />

O<br />

EtO2CN NCO2Et<br />

37<br />

C(NO 2)RX<br />

O<br />

(1)<br />

HO C(NO2)RX (2)<br />

38<br />

39 O N<br />

O<br />

35c<br />

Hal C(NO2)RX<br />

39<br />

X (or R)<br />

R – H, alkyl; X – H, EWG, NO2 (R or X = H); Hal Cl, Br, I<br />

NH 3OH HCl/KOH<br />

Br C(NO2) 3 Br C(NO2) 2 K<br />

40<br />

41<br />

Scheme 3.35<br />

O N<br />

Precursors of six-membered cyclic nitronates (35c), viz., compounds (39), can<br />

be synthesized <strong>in</strong> three steps from the simplest nitro compounds (36) bythe<br />

Michael reaction (Scheme 3.35).<br />

The Þrst step (1) gives rise to nitrocarboxylic acid esters (37) (If R=X=H,<br />

special conditions are required to prevent the double addition of the Michael<br />

substrate to reagents (36)).<br />

Selective reduction of the ester function <strong>in</strong> products (37), step (2), affords<br />

nitro alcohols (38), which are either transformed <strong>in</strong>to halo-conta<strong>in</strong><strong>in</strong>g compounds<br />

35d<br />

NO 2<br />

O<br />

(3)<br />

(4)<br />

(5)

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