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

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REACTIONS OF DIPOLAR 1,3-CYCLOADDITION ([3 + 2] CYCLOADDITION) 347<br />

HO<br />

Me<br />

N +<br />

O<br />

COOMe<br />

OH<br />

HO<br />

COOMe<br />

610<br />

Me<br />

N<br />

O<br />

COOMe<br />

O N<br />

Me<br />

RO<br />

608 R = H<br />

609 R = TBDPS<br />

Me<br />

N<br />

O<br />

COOMe<br />

RO<br />

RO<br />

O<br />

OR<br />

Me<br />

N<br />

COOMe<br />

COOMe<br />

Me<br />

N<br />

O<br />

COOMe<br />

613 a 613 b<br />

a b<br />

611 a-d: R = H<br />

612 a-d: R = TBDPS<br />

+ +<br />

HO<br />

613 c<br />

Me<br />

N<br />

O<br />

COOMe<br />

585<br />

−<br />

+<br />

Scheme 2.269<br />

L-glycero D7 d proceed with high stereoselectivity <strong>in</strong> the cases of D7a, D7c<br />

<strong>and</strong> D7 d. They yield the correspond<strong>in</strong>g adducts (616), (617) <strong>and</strong> (618) (Scheme<br />

2.270). In the case of the racemate D7c/D7 d, the cycloaddition proceeds with a<br />

signiÞcant k<strong>in</strong>etic resolution (783).<br />

In all these reactions only the exo approach of the dipole (614) hasbeen<br />

observed. The high steric requirements of the tert-butoxy groups precluded the<br />

endo geometry of the transition state (Fig. 2.41).<br />

+<br />

c, d

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