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Nitrile Oxides, Nitrones, and Nitronates in Organic Synthesis : Novel ...

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234 NITRONES: NOVEL STRATEGIES IN SYNTHESIS<br />

Ph<br />

N<br />

H LDA, −70°C<br />

N +<br />

+ N<br />

H<br />

O −<br />

Allylacetone<br />

OH<br />

Ph<br />

225 309 310<br />

N<br />

229<br />

−<br />

O<br />

+<br />

N<br />

s-BuLi<br />

− O<br />

N<br />

Scheme 2.126<br />

Li O −<br />

a: E = (CH 3) 3SiCl; R = Si(CH 3) 3<br />

b: E = (C 2H 5) 3GeCl; R = Ge(C 2H 5) 3<br />

c: E = (n-C4H9)3SnBr; R = Sn(n-C4H9)3<br />

d: E = HgCl 2; R = HgCl<br />

e: E = Ph 2P(O)Cl; R = P(O)Ph 2<br />

f: E = Ph 2PCl; R = PPh 2<br />

−<br />

N<br />

N<br />

+<br />

+ N<br />

O<br />

N<br />

Scheme 2.127<br />

E<br />

Hg O<br />

+<br />

N<br />

N<br />

212k<br />

−<br />

R<br />

N<br />

O<br />

−<br />

N<br />

OH<br />

+<br />

N<br />

211a-j<br />

OH<br />

N<br />

Ph<br />

g: E = PhSSPh; R = SPh<br />

h: E = PhSeSePh; R = SePh<br />

i: E = TsF; R = SO 2CH 6H 4-(p-<br />

CH 3)<br />

j: E =TsCl; R = Cl<br />

k: E = HgCl 2; 0.5 equiv<br />

group (135). This spatial requirement is connected with the fact that deprotonation<br />

is carried out <strong>in</strong> the complex formed by the organolithium compound or<br />

alcoholate <strong>and</strong> the oxygen of the nitrone group at a stage immediately preced<strong>in</strong>g<br />

the proton removal. The formation of this complex, k<strong>in</strong>etically facilitates proton<br />

removal from the syn-position to the N -oxide group. The participation of such<br />

a complex <strong>in</strong> deprotonation proves that metalation of aldonitrones is a Complex<br />

Induced Proximity Effect (CIPE)-controlled process(Scheme 2.128) (553).

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