362
Published on the web March 6, 2010
Cyclic O-Acyloximes as Novel Photolatent Bases
Kanji Suyama,* Tomohiro Inoue, and Masamitsu Shirai
Department of Applied Chemistry, Osaka Prefecture University, 1-1 Gakuen-cho, Naka-ku, Sakai, Osaka 599-8531
(Received January 8, 2010; CL-100028; E-mail: suyama@chem.osakafu-u.ac.jp)
Cyclic O-acyloximes were prepared as novel photolatent
Table 1. Physical properties and ¯254 of O-acyloximes
a
b
bases with good photoreactivity and thermal stability. They were
transformed into cyclic imines on irradiation at 254 nm and
showed higher crosslinking ability for poly(glycidyl methacry-
late) compared with an O-acyloxime with noncyclic structure.
Mp
/°C
Td
-
max
¾ at 254 nmb
b,c
¯
254
O-Acyloxime
/°C /nm /L mol¹1 cm
¹1
1
2a
2b
42-43.5 201 245
136-137 208 246
215-216.5 233 252
14200
13800
13300
0.35
0.36
d
®
¹1
aTd from thermogravimetric analysis. Heating at 10 °C min
under N2. bIn acetonitrile. cBased on normal phase HPLC
analysis of irradiated acetonitrile solution (2 © 10¹4 M) under
N2. dNot measured because the solubility of 2b was too low to
prepare 2 © 10¹4 M.
Photolatent catalysts have been widely used as key materials
for imaging and coating technologies.1,2 Photochemical gener-
ation of free-radicals and acids has already been investigated
extensively, and compounds that generate basic materials have
been increasing recently.2-5 O-Acyloximes are photoreactive
compounds with good thermal stability and are known to
generate primary amines on UV irradiation.6,7 For example,
acetophenone O-phenylacetyloxime (1) generates benzylamine
on irradiation followed by hydrolysis of resulting imine 1a as
shown in Scheme 1. However, acetophenone is also produced as
a by-product. In some applications, the elution or migration of
by-products is undesirable. Herein we designed O-acyloximes
with a cyclic structure, 4,5,6,7-tetrahydro-3-phenyl-8H-1,2-
oxazocin-8-one (2a) and 4,5-dihydro-3-phenyl-7H-1,2-oxaze-
pin-7-one (2b), which will not release ketones. The cyclic
structure is advantageous for the formation of imines after
decarboxylation. In this communication, photochemical and
physical properties of 2a and 2b are clarified, and photo-
crosslinking behaviors of poly(glycidyl methacrylate) (PGMA)
containing these O-acyloximes are compared.
2a and 2b were higher than 200 °C, showing high thermal
stability as well as 1. UV absorption characteristics of 2a and 2b
in acetonitrile were similar to 1. Quantum yield of photolysis at
254 nm (Φ254) for 2a was found to be essentially the same as 1.
The acetonitrile solution of 2a after irradiation with
60 mJ cm was analyzed by GC-MS.9 The GC chromatogram
¹2
showed peaks at 26 (broad), 24.3, and 9.4 min, which were
assigned to 2-phenyl-3,4,5,6-tetrahydropyridine (3a) (m/z 159),
2-phenylpyridine (4a) (m/z 155), and benzonitrile (m/z 103),
respectively. Similarly, 2b showed GC-MS9 peaks assignable to
3b (m/z 145), 2-phenylpyrrole (4b) (m/z = 143), and benzoni-
trile. From these results, photoreaction mechanisms are proposed
as Scheme 2, where both cyclic imines and benzonitrile were
produced from biradical intermediates. It is unclear whether 4a
and 4b were formed during irradiation or pretreatment for GC-
MS.
2a and 2b were prepared from 6-hydroxyimino-6-phenyl-
hexanoic acid and 5-hydroxyimino-5-phenylpentanoic acid,
respectively. The acids were treated with thionyl chloride in
pyridine-diethyl ether mixture at below ¹5 °C. After purifica-
In general, ketimines are easily hydrolyzed10 to form
ketones and amines in air. Thus, 3a was prepared authentically11
from 5-chlorovaleronitrile and phenyllithium as described in the
literature,12 and its stability was investigated. When 3a having a
1
tion, cyclic products were isolated and identified by IR, H and
13C NMR spectra, and elemental analysis.8 The yields of 2a and
2b were 41 and 10%, respectively.
¹1
C=N stretching band at 1635 cm in IR spectrum was treated
¹1
Thermal and optical properties of O-acyloximes are summa-
rized in Table 1. Thermal decomposition temperatures (Tds) of
with concd. HCl, yellowish solid having a peak at 1685 cm
assignable to C=O stretching band was obtained, indicating the
formation of hydrochloride salt of 5a. After treating with NaOH
aqueous solution and extraction with chloroform, the solid was
1
turned into brownish oil whose H NMR and IR spectra were
identical to those of 3a. These results suggest that 3a was stable
in 6-membered cyclic form and not hydrolyzed immediately to
5a in contrast to 1a.
CH3
CH3
O
C
N
C
N
ν
h
C
The photocrosslinking of PGMA containing O-acyloximes
was performed. Mn and glass transition temperature of PGMA
were 17000 and 70 °C, respectively. On irradiation followed by
heating, the films became insoluble in tetrahydrofuran (THF).
Figure 1 shows the changes of insoluble fraction of PGMA films
containing 3 mol % of O-acyloximes13 based on the ratio of film
thickness before and after soaking in THF. Irradiation energy
required for the insolubilization of films containing 2a and 2b
was less than that containing 1, showing the high crosslinking
ability of 2a and 2b.
CH2
O
CH2
H2O
- CO2
1
1a
CH3
NH2
+
C
CH2
O
Scheme 1. Photoreaction of 1.
Chem. Lett. 2010, 39, 362-363
© 2010 The Chemical Society of Japan
Suyama, Kanji
