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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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REACTIVITY OF NITRONATES 549<br />

Ref.52, 57, 258 Ref.52, 258 Si Ref.365<br />

Me3Si<br />

Ref.366<br />

CO2Me Ref.52, 54, 57,<br />

258, 304, 368<br />

OAc Ref.52 OH Ref.51 Br Ref.367<br />

O<br />

O<br />

N<br />

Ph Ref.52, 258, Ref.52, 258 CO2Et Ref.49<br />

342,364 CN<br />

SiMe2Cl Ref.48, Ph<br />

66, 368<br />

Ref.363<br />

Ref.367 CO<br />

Ref.363<br />

2Me<br />

Ref.363 Ref.363 Ph Ref.363<br />

O<br />

CO2Me Ref.364<br />

Me<br />

Ref.363<br />

Ref.363<br />

Chart 3.13 [3 + 2]Reactivity of Þve-membered cyclic nitronates.<br />

behavior <strong>in</strong> [3 + 2]-cycloaddition reactions is the least known (48, 49, 51, 52, 54,<br />

57, 66, 258, 363–369) (Chart 3.13).<br />

Most of the [3 + 2]-cycloaddition reactions considered here were performed at<br />

high temperature. The rules of regioselectivity, which were formulated <strong>in</strong> two<br />

previous sections, are also true for these reactions.<br />

It should be noted that tetramethylethylene was <strong>in</strong>volved <strong>in</strong> the [3 + 2]-cycloaddition<br />

with Þve-membered cyclic nitronates (363).<br />

3.4.3.1.4. Six-membered Cyclic <strong>Nitronates</strong> As can be seen from Chart 3.14,<br />

the range of oleÞns <strong>in</strong>volved <strong>in</strong> <strong>in</strong>termolecular [3 + 2]-cycloadditions with sixmembered<br />

nitronates, is substantially wider (49, 91, 92, 97, 138, 143, 146, 151,<br />

156, 160–162, 370–373) compared to Þve-membered nitronates.<br />

The behavior of six-membered cyclic nitronates <strong>in</strong> this process was studied<br />

more systematically.<br />

Let us remember the rule of orientation of substituents <strong>in</strong> viz. disubstituted<br />

oleÞns directed to the C-4 atom of the cycloadduct: H > Si > C > O (162) (the<br />

atom of the substituent <strong>in</strong> oleÞn bound to C-4 <strong>in</strong> the result<strong>in</strong>g adduct). As <strong>in</strong> the<br />

previous case, many reactions proceed at high temperature. It should be emphasized<br />

that unsubstituted 5,6-dihydro-[4H ]-oxaz<strong>in</strong>e N -oxides were successfully<br />

<strong>in</strong>volved <strong>in</strong> [3 + 2]-cycloaddition. Professor Chlenov was the Þrst to perform this<br />

reaction with the use of styrene (the yield was 21%) (337). More recently, the

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