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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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R<br />

CO2Me<br />

TiCl 4<br />

reflux,<br />

overnight<br />

N<br />

OH<br />

H Cl<br />

REACTIVITY OF NITRONATES 541<br />

R Cl<br />

O N MeO2C O O<br />

O CO2Me MeO2C H CO 150 a,b<br />

a – R = Cl;<br />

b – R = Br<br />

a = 33%<br />

151a,b<br />

b = 38%<br />

152a<br />

2Me<br />

14%<br />

Mechanistic consideration:<br />

150<br />

151<br />

LA<br />

MeO 2C<br />

+<br />

N<br />

O A<br />

HO<br />

MeO 2C<br />

N<br />

HO<br />

R<br />

H<br />

OLA CO 2Me<br />

H<br />

H<br />

Cl<br />

CO2Me O<br />

N<br />

MeO 2C<br />

R<br />

+<br />

A<br />

O<br />

R<br />

OLA<br />

CO2Me H<br />

N<br />

MeO2C<br />

Cl<br />

H OTiCl3 Scheme 3.122<br />

(LA= TiCl 4)<br />

+<br />

MeO 2C<br />

R<br />

N<br />

OH<br />

O<br />

N<br />

MeO 2C<br />

A′<br />

O<br />

152<br />

+<br />

−<br />

O<br />

Cl<br />

+ LA<br />

(R = Cl)<br />

bond to give the correspond<strong>in</strong>g functionalized oximes (332). The mechanistic<br />

<strong>in</strong>terpretation of this transformation is shown at the bottom of the Scheme 3.124.<br />

F<strong>in</strong>ally, the rearrangement of seven-membered cyclic nitronate (159) (170)<br />

accompanied by the r<strong>in</strong>g contraction to form oxime (160) was documented<br />

(Scheme 3.125). Details of this transformation were not reported.<br />

3.4.3. <strong>Nitronates</strong> <strong>in</strong> [3 + 2]-Cycloaddition Reactions<br />

Examples of [3 + 2]- (or 1,3-dipolar) cycloaddition reactions have been known<br />

for many years. However, only after the ma<strong>in</strong> pr<strong>in</strong>ciples of this type of transformations<br />

have been formulated by Huisgen (333), [3 + 2]-cycloaddition became<br />

one of the most important tools <strong>in</strong> organic synthesis (334, 335). Actually, the<br />

simultaneous formation of two new bonds makes it possible to efÞciently assemble<br />

a complex molecule from simple <strong>and</strong> readily available precursors. Due to

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