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

REACTIONS OF DIPOLAR 1,3-CYCLOADDITION ([3 + 2] CYCLOADDITION) 297
[~P n A] CH 3
−
O
+
N
H3C
+
H H3C OH
HDN
CH2
O
O
C
COOCH 3
Scheme 2.209
O
O
O
+
N
H
OH
HMPN
Fig. 2.30
−
[~P n + 1
−
O
+
N
H 3C
H H3C OH
HMDN
successively, due to the introduction of monomer at the labile bond [∼Pn·—·A].
As a result, polymers with narrow molecular weight distribution (MWD) are
formed (Scheme 2.209).
Therefore, nitrones, being potential sources of stable radicals are able to participate
directly in the growth stage of the polymer chain. In the case of nitrones
the “pseudoliving” mechanism is realized at lower temperatures (50–60 ◦ C) then
in the case of nitroxides ( > 100 ◦ C).
Radical copolymerization of diaryl nitrones, such as α-(2-hydroxyphenyl)-N -
(2,6-dimethylphenyl) nitrone (HDN), α-(2-hydroxy-4-methacryloyloxyphenyl)-
N -(2,6-dimethylphenyl) nitrone (HMDN), and α-(2-hydroxy-4-methacryloyloxyphenyl)-N
-phenylnitrone (HMPN) (Fig. 2.30), with methyl methacrylate leads
to copolymers in good yields with considerable quantities of hydroxy substituted
diaryl nitrone pendants. The presence of photoactive nitrone pendants in
these copolymers allows one to control photochemically the refractive index of
polymethyl methacrylate Þlms (468, 700, 701).
2.8. REACTIONS OF DIPOLAR 1,3-CYCLOADDITION
([3 + 2] CYCLOADDITION)
2.8.1. Cycloaddition of Alkenes
2.8.1.1. Intramolecular Reactions Intramolecular 1,3-cycloaddition with high
regio- and stereo-control seems to be an important instrument for an effective
A]