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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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458 NITRONATES<br />

NO2<br />

R 1<br />

Halogenation<br />

step 1<br />

NO2<br />

R 1<br />

29<br />

Hal<br />

R 1 = H, Me, Et, Ph, Bn, n-C 6H 13<br />

Hal - Br(step 1 - KOH/Br 2);<br />

F (step 1 - selectfluor)<br />

Silylation<br />

step 2<br />

R 3<br />

O<br />

R 4<br />

R 1<br />

R 2 R 3 C CHR 4<br />

31<br />

(3+2)-cyclo-addition<br />

N<br />

R<br />

O<br />

2<br />

OSi<br />

Hal<br />

30<br />

step 3<br />

N<br />

R 1<br />

32<br />

Hal<br />

OSi<br />

SiHal<br />

elim<strong>in</strong>ation<br />

R 3<br />

R<br />

O<br />

2<br />

N<br />

O<br />

step 4<br />

R4 R1 24i<br />

yield 50%–90% (on 29)<br />

31 - CO2Me<br />

Ph , CO2Me,<br />

, CO2Me , COMe ,<br />

Me(CH2)4CH CH2 , OEt , SiEt3 N , , ,<br />

Scheme 3.31<br />

requir<strong>in</strong>g 1 month for completion (86). Accord<strong>in</strong>g to quantum chemical calculations,<br />

the nature of Hal-atom <strong>in</strong> nitronates (30) has the follow<strong>in</strong>g effect on the<br />

rate of step 3: I < Cl∼Br

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