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

REACTIONS OF DIPOLAR 1,3-CYCLOADDITION ([3 + 2] CYCLOADDITION) 327
OH
1. 1.5 Et2Zn
2. 1.0 (R,R)- DIPT
3. 1.0 EtZnX
−
O
4.
R 2
R 1
R1 N
R
H
2
+
in CHCl3
515 a–c
N O
517 a–c
OH
R 1
X O
+ O Zn
H N
O
−
+
R 2
O
R 2
R 1
Zn
T°C
N O
O
516 a–c
O i Pr
O i Pr
R 1 = CN, R 2 = Ph (a); R 1 - CO2Bu t , R 2 = Me (b); R 1 = CONBn2, R 2 = PH (c);
R 2
H
R
N
O 1 +
−
+
OH
Scheme 2.246
R 1
R 2
N O
OH
R 1
R 2
OH
N O
499 a–f 518 a–f 519 a–f
Scheme 2.247
Table 2.21 Reaction of nitrones 499 with allyl alcohol
Microwave conditions Classical
time isolated heating c 518/519
Entry Nitrone R 1 R 2 (min) a yield b (%) (% yield) ratio
1 499 a Me 9-anthryl 80 53 1 1.1:1.0
2 499 b Me 9-phenanthryl 20 83 30 1.3:1.0
3 499 c Me 1-pyrenyl 20 75 20 1.5:1.0
4 499 d Bn 1-pyrenyl 20 85 30 1.6:1.0
5 499 e Bn 9-phenanthryl 20 39 NR d 1.5:1.0
6 499 f Bn 9-anthryl 80 NR e NR
a Irradiation at 90 W; the temperatures reached by the reaction mixture are in the range from 150 to
160 ◦ C.
bReaction performed in a pressure tube equipped with stir bar, in the absence of solvent, using a
1:200 relative ratio of dipole/dipolarophile.
cReaction performed in sealed tube in absence of solvent, using a 1:200 relative ratio of
dipole/dipolarophile at 130 ◦ C for 48 h.
dNo reaction.
e ◦
When irradiated at 120 W (200–210 C), only decomposition products are observed.
+
OH