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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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+<br />

R 1 N R2<br />

O<br />

O<br />

R 1 N R 2<br />

−<br />

R 1<br />

R 2<br />

+<br />

N OH<br />

392H<br />

+<br />

+<br />

−<br />

Li SO2Ph 390<br />

SO 2Ph<br />

H 3O<br />

392 / 393<br />

N<br />

O<br />

+<br />

−<br />

R 1<br />

R 2<br />

OBu t<br />

Ph<br />

−<br />

+<br />

Li<br />

390<br />

R 1<br />

R 2<br />

R 1<br />

X<br />

SO2Ph<br />

R 1<br />

N<br />

OH<br />

a-addition<br />

R 2<br />

X<br />

R 1<br />

NITRONE REACTIONS 271<br />

SO 2Ph<br />

R 1<br />

N<br />

R OH 2<br />

g-addition<br />

N<br />

O<br />

R<br />

N<br />

O 2<br />

N<br />

R OH 2<br />

−<br />

392a−h<br />

392a−h<br />

−<br />

392a−h<br />

A B C<br />

R 2<br />

SO 2Ph<br />

N O<br />

Me<br />

393a−h<br />

H 3O<br />

391<br />

R 1<br />

N O<br />

R 2<br />

SO 2Ph<br />

Me<br />

R 1<br />

X<br />

SO 2Ph<br />

Michael<br />

addition<br />

a b c d e f g h<br />

Ph Ph Ph Ph<br />

Ph Bu Bn Bn Bn Bn Bn<br />

t Pr<br />

Me<br />

i<br />

2-Py 2-Furyl O<br />

O<br />

M - CN<br />

Scheme 2.170<br />

N<br />

OH<br />

OBu t<br />

Scheme 2.171<br />

Ph<br />

CN<br />

+<br />

+<br />

−<br />

N<br />

−<br />

OH<br />

OBu t<br />

are used as cyanat<strong>in</strong>g reagents. Addition of trimethylsilyl cyanide <strong>and</strong> diethylalum<strong>in</strong>ium<br />

cyanide to chiral nitrones proceeds <strong>in</strong> good to excellent diastereoselectivity,<br />

<strong>and</strong> <strong>in</strong> high yield (<strong>in</strong> some cases quantitatively) (Scheme 2.171)<br />

(628–630).<br />

The stereocontrolled addition of TMSCN to chiral 3,4-dihydro-2H - pyrrol<strong>in</strong>e<br />

N - oxides (394) is be<strong>in</strong>g used to prepare enantiopure 2-am<strong>in</strong>omethylpyrrolid<strong>in</strong>es<br />

(395) <strong>and</strong> (396) (Scheme 2.172) (631).<br />

On the basis of theoretical data <strong>and</strong> experimental observations it was concluded<br />

that TMSCN reacts via a concerted transition state. Et2AlCN <strong>in</strong>itially forms a<br />

CN<br />

Ph

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