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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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REACTIONS OF DIPOLAR 1,3-CYCLOADDITION ([3 + 2] CYCLOADDITION) 345<br />

Cycloaddition of the nitrone (595a) with ethyl cyclopropylideneacetate (596)<br />

gave diastereomeric adducts (597) <strong>and</strong> (598) <strong>in</strong> good yield. They were obta<strong>in</strong>ed<br />

<strong>in</strong> a 5:1 ratio via anti-endo <strong>and</strong> anti-exo approaches (Scheme 2.266) (777).<br />

2-Chloro-2-cyclopropylideneacetate (599) <strong>and</strong> its spiropentane analog (600)<br />

undergo cycloaddition to enantiopure, Þve-membered cyclic nitrones (595a) <strong>and</strong><br />

(595b) to give, quantitatively, the correspond<strong>in</strong>g 4’-chlorospirocyclopropane-<br />

1,5’-isoxazolid<strong>in</strong>es (601) <strong>and</strong> (602). These compounds undergo cascade r<strong>in</strong>g<br />

enlargements to yield <strong>in</strong>dolizid<strong>in</strong>one derivatives (603) <strong>and</strong> (604) <strong>in</strong> 53% to 70%<br />

yield (Scheme 2.267) (778).<br />

Bu t O CO2Et<br />

+N<br />

_<br />

O<br />

595 a<br />

N<br />

O<br />

+<br />

−<br />

69%<br />

O N<br />

+ +<br />

5:1<br />

596<br />

OR<br />

595 a R = Bu t<br />

595 b R = Si ( i Pr)3<br />

( )n<br />

Cl<br />

HO<br />

EtO2C<br />

H<br />

Scheme 2.266<br />

CO 2Me<br />

599 n = 0<br />

600 n = 1<br />

R = ( i Pr)3Si<br />

N<br />

OBu t<br />

EtO2C<br />

H<br />

O N<br />

597 598<br />

CO2Me<br />

O<br />

604<br />

EtOH, CsF<br />

reflux<br />

( )n<br />

Scheme 2.267<br />

N<br />

O<br />

OR<br />

H<br />

( ) n<br />

n = 0, 1<br />

Cl CO2Me<br />

601 (R = Bu t )<br />

602 (R = i Pr)<br />

Bu t O<br />

R = Bu t<br />

N<br />

CO2Me<br />

O<br />

603<br />

DMF, NEt 3<br />

80 ° C<br />

( )n<br />

OBu t

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