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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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166 NITRONES: NOVEL STRATEGIES IN SYNTHESIS<br />

N<br />

H<br />

96a−d<br />

N-O-H<br />

R<br />

C 6H 6; Δ<br />

12/14 hr<br />

80/85 %<br />

R = COOCH3 (a), COCH3 (b), CN (c), CONH2 (d)<br />

Scheme 2.39<br />

N<br />

H<br />

97a−d<br />

+<br />

N<br />

O<br />

−<br />

CH 2CH 2R<br />

Bromocyclization of γ,δ-unsaturated oximes (98) <strong>and</strong> (99) affords the correspond<strong>in</strong>g<br />

bromomethylpyrrol<strong>in</strong>e-N -oxides (100) <strong>and</strong> (101). Depend<strong>in</strong>g on the structural<br />

characteristics, the yields vary from 23% to 87% (Scheme 2.40).<br />

Reversal of steps, that is addition of Br/OH to the C=C bond of the unsaturated<br />

aldehyde (102) Þrst, followed by oximation, opens access to six-membered<br />

nitrones (103) (Scheme 2.41) (290).<br />

O<br />

Ph<br />

OH<br />

N<br />

98<br />

OH<br />

N<br />

99<br />

NBS, H2O, DMSO<br />

62 %<br />

Br<br />

Br 2, NaHCO 3<br />

[60:40]<br />

23 %<br />

Br2, NaHCO3<br />

87 %<br />

Scheme 2.40<br />

O<br />

HO<br />

102 103<br />

OH<br />

Scheme 2.41<br />

Br<br />

Br<br />

Ph<br />

100<br />

101<br />

1. NH 2OH.HCl, NaOAc<br />

CH 3CN/H 2O<br />

O<br />

N<br />

−<br />

O<br />

N<br />

−<br />

+<br />

+<br />

2. NaHCO3, CH2Cl2, Δ , 73 %<br />

−<br />

+<br />

O<br />

N

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