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

320 NITRONES: NOVEL STRATEGIES IN SYNTHESIS
O
MeN
Bu t
O
Ph
N
O
R 2
O
O
Ph
16 489 a-c
O
N
+
+
O
−
−
R 1
R 1 = R 2 = H (a);
R 1 + R 2 = (CH2)3 (b);
R 1 = H, R 2 = C6H13(c);
R
MeN
Bu t
H
N
O H
490 491 a-c
R = Ph (a); p-Bu t C6H4 (b); C6H11 (c);
Scheme 2.239
Table 2.18 Isoxazolidine derivatives 491 a–c obtained from the 1,3-dipolar
cycloaddition of 490 to alkenes
Alkene Cycloadduct a Yield b ; exo/endo c
D1
D1
D2
Bu t
MeN
NO
Ph
But O H
491 a
MeN
NO
p-But Bu
Ph
t
O H
MeN
NO
Cy
But 491 b
O H
491 c
N
89%; d 10:1
R 1
O
95% (91%); >20:1
86% (76%); 10:1
a Reactions were performed with 2–10 equiv alkene in ClCH2CH2Cl at
reflux for 5–52 h. The structure of the major isomer is shown.
b Total yield of exo and endo isomers (purified major isomer).
c Exo refers to 5-alkyl or aryl substituent; determined by integration of 1 H
NMR spectra of unpurified reaction mixture.
d Major isomer not isolated in pure form.
R 2
R