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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) 335<br />

O<br />

Ti<br />

O<br />

OPr i<br />

O<br />

O<br />

Ti<br />

Pr i O O<br />

(S,S)-543<br />

Fig. 2.37<br />

Table 2.22 Asymmetric 1,3-dipolar cycloadditions of nitrones with acrole<strong>in</strong>a Bn<br />

Bn<br />

R<br />

N<br />

1<br />

2<br />

3<br />

4<br />

5<br />

6<br />

7<br />

8<br />

+<br />

O<br />

−<br />

+<br />

OHC<br />

Ph<br />

4-MePh<br />

4-MeOPh<br />

4-ClPh<br />

2-naphthyl<br />

But cyclohexyl<br />

S<br />

S<br />

24<br />

24<br />

40<br />

39<br />

24<br />

14<br />

24<br />

24<br />

(S,S)- 543 (10 mol%) NaBH 4<br />

CH 2Cl 2, −40°C, EtOH<br />

Entry R Time (h) Yield (%) b,c ee (%) d<br />

a The reaction of nitrones <strong>and</strong> acrole<strong>in</strong> (1.5 equiv) was carried out <strong>in</strong> the<br />

presence of chiral bis-Ti(IV) oxide (S,S)-543 <strong>in</strong> CH2Cl2 at −40oC. b Isolated yield.<br />

c Only the endo isomer was detected by 1H NMR spectroscopy.<br />

d Determ<strong>in</strong>ed by HPLC analysis us<strong>in</strong>g chiral column (Chiral-pak OD-H,<br />

Daicel Chemical Industries, Ltd.).<br />

94<br />

81<br />

76<br />

85<br />

92<br />

90<br />

62<br />

86<br />

It has been reported that diiron acyl complexes (564) undergo stereo- <strong>and</strong><br />

regioselective 1,3- cycloadditions with a variety of nitrones (Scheme 2.260).<br />

These complexes are then oxidatively converted to synthetically useful thio esters<br />

(769).<br />

Dipolarophile D6 . A complete theoretical study of the 1,3-dipolar cycloaddition<br />

reaction of D-glyceraldehyde nitrone (N) to methyl acrylate (MA) has been<br />

93<br />

94<br />

88<br />

88<br />

93<br />

97<br />

70<br />

97<br />

HO<br />

R<br />

N<br />

O

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