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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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N O<br />

NO<br />

S<br />

O2<br />

16 17<br />

R<br />

REACTIONS OF NITRILE OXIDES 13<br />

S<br />

N O<br />

NO<br />

The stability of o-sulfonylbenzonitrile oxides <strong>and</strong> their thiophene analogs<br />

probably depends on electronic factors. The same factors do not prevent dimerization,<br />

as can be seen from data concern<strong>in</strong>g several differently substituted nitrile<br />

oxides of the thiophene series (103). Sterically stabilized 3-thiophenecarbonitrile<br />

oxides 18 (R = R 1 = R 2 = Me; R = R 2 = Me, R 1 = i-Pr), when boiled <strong>in</strong> benzene<br />

or toluene, isomerized to isocyanates (isolated as ureas on reaction with anil<strong>in</strong>e)<br />

while nitrile oxides 18 with electron-withdraw<strong>in</strong>g substituents (R 1 <strong>and</strong>/or<br />

R 2 = SO2Me, Br) dimerized to form furoxans 19.<br />

R<br />

R 1 CNO<br />

R 1<br />

S<br />

R2 R<br />

S<br />

R2 O NO N<br />

18 19<br />

S<br />

O2<br />

R 1<br />

R<br />

S<br />

2 R<br />

3,3-Diphenylacrylonitrile oxide, exhibit<strong>in</strong>g unexpected stability, presumably<br />

due to delocalization, dimerized to furoxan 20 or 1,4,2,5-dioxadiaz<strong>in</strong>e 21 (22).<br />

Ph<br />

Ph<br />

N<br />

O<br />

20<br />

NO<br />

Ph<br />

Ph<br />

Ph<br />

Ph<br />

N<br />

O N<br />

Diaryl- (85), diaroyl- (71), bis(4-substituted-1,2,5-oxadiazol-3-yl)furoxans<br />

(104) as well as “exotic” 1,2,2,5,5-pentamethyl-4-(nitromethyl)-3-imidazol<strong>in</strong>e<br />

3-oxide-derived furoxan 22 (105) were obta<strong>in</strong>ed via correspond<strong>in</strong>g nitrile oxides.<br />

Me<br />

Me<br />

O<br />

N NO<br />

21<br />

O<br />

N<br />

O<br />

N<br />

Me<br />

N<br />

Me Me<br />

Me<br />

Me<br />

N<br />

Me<br />

Me<br />

Me<br />

22<br />

O<br />

Ph<br />

Ph

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