Co(salen)-catalyzed tert-butyl hydroperoxide oxidation of tert-butylphenols bearing an unsaturated side chain

Article abstract of DOI:10.1021/jo950944k

Co(salen)-catalyzed oxidation of 2,4- and 2,6-di-tert-butylphenols bearing an unsaturated side chain, with tert-butyl hydroperoxide (TBHP) in CH₂Cl₂ at rt, results predominantly in the formation of tert-butylperoxylated products. The position of tert-butylperoxylation depends on the nature of the unsaturated side chain: predominantly the ortho position for 4-alkynyl-2,6-di-tert-butylphenols, the side chain for 4-alkenyl-2,6-di-tert-butylphenols, and the para position for 4-cyano- or 4-(1-methoxyimino)alkyl-2,6-di-tert-butylphenols as well as 2-alkynyl-, 2-alkenyl-, and 2-cyano-4,6-di-tert-butylphenols. The ortho tert-butylperoxylated products arise mainly from initially formed para tert-butylperoxylated products, by migration of the tert-butylperoxy group.

Full text of DOI:10.1021/jo950944k

3342
J . Org. Chem. 1996, 61, 3342-3349
Co(sa len )-Ca ta lyzed ter t-Bu tyl Hyd r op er oxid e Oxid a tion of
ter t-Bu tylp h en ols Bea r in g a n Un sa tu r a ted Sid e Ch a in
Kazushige Maruyama,* Takahiro Kusukawa, Takahiro Mashino, and Akira Nishinaga*
Department of Applied Chemistry, Osaka Institute of Technology, Ohmiya 5, Asahi-ku, Osaka 535, J apan
Received May 23, 1995X
Co(salen)-catalyzed oxidation of 2,4- and 2,6-di-tert-butylphenols bearing an unsaturated side chain,
with tert-butyl hydroperoxide (TBHP) in CH2Cl2 at rt, results predominantly in the formation of
tert-butylperoxylated products. The position of tert-butylperoxylation depends on the nature of
the unsaturated side chain: predominantly the ortho position for 4-alkynyl-2,6-di-tert-butylphenols,
the side chain for 4-alkenyl-2,6-di-tert-butylphenols, and the para position for 4-cyano- or 4-(1-
methoxyimino)alkyl-2,6-di-tert-butylphenols as well as 2-alkynyl-, 2-alkenyl-, and 2-cyano-4,6-di-
tert-butylphenols. The ortho tert-butylperoxylated products arise mainly from initially formed para
tert-butylperoxylated products, by migration of the tert-butylperoxy group.
In tr od u ction
urated substituent. The tert-butylperoxylation takes
place predominantly at the para position for 6-alkenyl-,
6-alkynyl-, and 6-cyano-2,4-di-tert-butylphenols, and also
for 2,6-di-tert-butylphenols bearing a sterically less hin-
dered alkenyl or R-(methoxyimino)alkyl group at the
4-position. Interestingly, however, ortho tert-butylper-
oxylated products are obtained exclusively with 4-alky-
nyl-2,6-di-tert-butylphenols, 2,6-di-tert-butyl-4-(1-isopropyl-
2-methyl-1-propenyl)phenol, and 2,6-di-tert-butyl-4-[2,2-
dimethyl-1-(methoxyimino)propyl]phenol. The formation
of the ortho tert-butylperoxylated products are shown to
result from migration of the tert-butylperoxy group of the
first formed 4-tert-butylperoxylated products.
Mechanistic studies of metal-catalyzed oxidations are
of value not only from the standpoint of understanding
enzymatic oxidations, but also for the development of new
synthetic methods.1 Cobalt Schiff base complexes cata-
lyze highly selective oxidation reactions using molecular
oxygen which lead to dioxygenations,2 monooxygen-
ations,3 and dehydrogenations4 that mimic biological
oxidations. Among the cobalt Schiff base complexes, CoII-
(salen) [H2 salen ) 1,6-bis(2-hydroxyphenyl)-2,5-diaza-
1,5-hexadiene] has been found to also catalyze the tert-
butyl hydroperoxide (TBHP) oxidation of 4-alkyl- and
4-aryl-2,6-di-tert-butylphenols,5 aromatic ketoximes,6 2,6-
di-tert-butylanilines,7 benzyl alcohols,8 and benzylamines.9
The TBHP oxidations of phenolic substrates normally
give tert-butylperoxylated products in which the tert-
butylperoxy group is incorporated exclusively at the para
position.5 However, little is known about such TBHP
oxidations of phenols that bear an unsaturated group.
Resu lts
Oxid a tion of 4-Alk yn yl-2,6-d i-ter t-bu tylp h en ols
(1) w ith TBHP . A mixture of 4-alkynylphenol (1) (1
mmol) and TBHP (10 mmol) in CH2Cl2 in the presence
of Co(salen) (0.1 mmol) was stirred at rt under N2. The
oxidation of 1 was completed in 20 min. Separation of
products from the mixture gave 4-alkynyl-6-tert-butyl-
peroxy-2,6-di-tert-butyl-2,4-cyclohexadienone (2), 2,6-di-
tert-butyl-p-benzoquinone (3), and 4-(acylcarbonyl)-2,6-
di-tert-butylphenol (4) (Table 1).
The present paper deals with the Co(salen)-catalyzed
TBHP oxidation of 2,6- or 2,4-di-tert-butylphenols bearing
an unsaturated side chain at the 4- or 6-position. We
find that mainly tert-butylperoxylated products are ob-
tained, but the position for incorporation of the tert-
butylperoxy group depends on the nature of the unsat-
X Abstract published in Advance ACS Abstracts, May 1, 1996.
(1) Sheldon, R. A.; Kochi, J . K. Metal Catalyzed Oxidations of
Organic Compounds; Academic Press: New York, 1981. Hayaishi, O.,
Ed.; Molecular Mechanisms of Oxygen Activation; Academic Press:
New York, 1974.
(2) Nishinaga, A.; Tomita, H. J . Mol. Catal. 1980, 7, 1. Nishinaga,
A.; Yano, M.; Kuwashige, T.; Maruyama, K.; Mashino, T. Chem. Lett.
1994, 817. Nishinaga, A.; Kuwashige, T.; Tsutsui, T.; Mashino, T.;
Maruyama, K. J . Chem. Soc., Dalton Trans. 1994, 805. Nishinaga, A.;
Tsutsui, T.; Moriyama, H.; Wazaki, T.; Mashino, T.; Fujii, Y. J . Mol.
Catal. 1993, 83, 117.
(3) Nishinaga, A.; Yamada, T.; Fujisawa, H.; Ishizaki, K.; Ihara, H.;
Matsuura, T. J . Mol. Catal. 1988, 48, 249. Nishinaga, A.; Maruyama,
K.; Yoda, K.; Okamoto, H. J . Chem. Soc., Chem. Commun. 1990, 876.
Nishinaga, A.; Yamato, H.; Matsuura, T.; Abe, T.; Maruyama, K.
Tetrahedron Lett. 1988, 29, 6309.
(4) Nishinaga, A.; Yamazaki, S.; Matsuura, T.; Chem. Lett. 1986,
505. Tetrahedron Lett. 1987, 28, 6309; 1988, 29, 4115.
(5) Nishinaga, A.; Yamazaki, S.; Nogusa, H.; Yamashita, T.; Mat-
suura, T. Nippon Kagaku Kaishi 1985, 378.
(6) Nishinaga, A.; Yamazaki, S.; Miwa, T.; Matsuura, T. React. Kinet.
Catal. Lett. 1991, 43, 273.
(7) Nishinaga, A.; Fo¨rster, S.; Eichhorn, E.; Speiser, B.; Rieker, A.
Tetrahedron Lett. 1992, 33, 4425-4428.
(8) Nishinaga, A.; Sugimoto, I.; Matsuura, T. Nippon Kagaku Kaishi
1988, 495.
(9) Maruyama, K.; Kusukawa, T.; Higuchi, Y.; Nishinaga, A. Chem.
Lett. 1991, 1093.
Analytical and NMR data of the compounds 2 are in
good agreement with their structures. 1H NMR signals
S0022-3263(95)00944-3 CCC: $12.00 © 1996 American Chemical Society

Co(salen)-Catalyzed Oxidation of tert-Butylphenols
J . Org. Chem., Vol. 61, No. 10, 1996 3343
Ta ble 1. Co(sa len )-Ca ta lyzed Oxid a tion of P h en ols 1
w ith TBHP
the reaction of 3,5-di-tert-butyl-o-benzoquinone with an
appropriate alkynylmagnesium bromide13 to give the
corresponding 6-alkynyl-2,4-di-tert-butyl-6-hydroxy-2,4-
cyclohexadienones (7), followed by the reduction with Zn/
HCl in EtOH.
yield (%)a
reaction
time (min)
conversion
(%)
1
2
3
4
b
1a
1b
1c
20
20
20
100
100
100
91.7
47.6
58.7
-
3.3
17.3
14.5
23.8
18.9
a
b
Isolated yield. Not determined.
Ta ble 2. 1H NMR (CDCl3) Da ta (δ, p p m ) for An a logs of 2
2
2-But
6-But
-OOBut
3-CH
5-CH
R
2a
2b
2c
1.21
1.24
1.24
0.96
0.93
1.02
1.21
1.24
1.27
6.48
6.54
6.75b
6.48
6.54
6.64b
1.29
a
-
c
-
0.18-1.8 (m, 7H), 2.1-2.5 (m, 2H). d, 1H, J ) 2.0 Hz. c 7.2-
a
b
7.7 (m, 5H).
for the 3- and 5-positions of the 2,4-cyclohexadienone
system normally appear as a set of doublets around δ
6-7 ppm.10 However, the corresponding signals of 2a
and 2b appear as singles (Table 2), although the signals
for the 2-t-Bu and 6-t-Bu groups appear at the expected
chenical shifts.10 Therefore, there is no way to determine
1
the structure of 2 by means of the H NMR data alone.
The characteristic 13C NMR data for 2 are consistent with
the cyclohexa-2,4-dienone system (Table 3).
The similar chemical shifts observed for the protons
at the 3- and 5-positions in 2a and 2b are probably due
to the electronic effect of the alkynyl group at the 4-
position. The spectral data of the analogs of 4 were iden-
The oxidation of 8 with TBHP under the same condi-
tions described for 1 gave 2-alkynyl-4,6-di-tert-butyl-4-
(tert-butylperoxy)-2,5-cyclohexadienones (9) in approxi-
mately quantitative isolated yields: 9a , 95%; 9b, 95%;
9c, 95%. These structures are clearly supported by their
13C NMR (Table 4) and analytical data.
Oxid a tion of 4-Alk en yl-2,6-d i-ter t-bu tylp h en ols
(10) w ith TBHP . The oxidation of 10 has been briefly
reported,5 but not in detail. Thus, we reinvestigated
more thoroughly the oxidation of 4-alkenylphenols 10.
The reaction was usually completed in 20 min. Silica gel
TLC separation of the reaction mixture gave quinone
methide 11 in which the tert-butylperoxy group is incor-
porated into the side chain, peroxy-o-quinol ether 12, and
peroxy-p-quinol ether 13. Analytical and spectral data
tical to those of known products.11 The characteristic 13
C
NMR data of 2 may be utilized conveniently for the spec-
ification of the cyclohexa-2,4-dienone system (Table 3).
Ch em ica l Sh ifts in 13C NMR sp ectr a a s Str u ctu r a l
P r obes for Cycloh exadien on e System s. Carbon NMR
spectroscopy is useful for distinguishing structures of the
2,5- and 2,4-cyclohexadienone systems.12 Thus, we ex-
amined 13C NMR spectra of 6-(tert-butylperoxy)-2,6-di-
tert-butyl-2,4-cyclohexadienones (5), 4-(tert-butylperoxy)-
2,6-di-tert-butyl-2,5-cyclohexadienones (6),5 the analogs
of 2, and related systems. Characteristic data for 2,4-
cyclohexadienones and 2,5-cyclohexadienones are given
in Tables 3 and 4, respectively.
As seen from Tables 3 and 4, the chemical shifts for
C-1, C-4, and C-6 (a tert-butylperoxy group is attached),
and C-7 (2-t-Bu group) (Table 5) conveniently distinguish
between 5 and 6. These data can also be applied to the
structural determination of other cyclohexadienone sys-
tems described in this work. Thus, the 2,4-cyclodienone
structures of compounds 2 are readily apparent from
their 13C NMR data.
Oxid a tion of 2-Alk yn yl-4,6-d i-ter t-bu tylp h en ols
(8) w ith TBHP . Analogs of phenol 8 were prepared by
were in good agreement with the structures of these
(10) Nishinaga, A.; Nishizawa, K.; Tomita, H.; Matsuura, T. J . Am.
Chem. Soc. 1977, 99, 1287.
(11) Nishinaga, A.; Iwasaki, H.; Shimizu, T.; Toyoda, Y.; Matsuura,
T. J . Org. Chem. 1986, 51, 2257.
(12) Rieker, A.; Berger, S. Org. Magn. Reson. 1972, 4, 857.
(13) Rieker, A.; Bracht, J .; Dreher, E.-L.; Schneider, H.-P. Houben-
Weyl-Mu¨ller; Georg Thieme Verlag: Stuttgart, 1979; Vol. 7, Part 3b,
p 775.

3344 J . Org. Chem., Vol. 61, No. 10, 1996
Ta ble 3. Ch a r a cter istic 13C NMR (CDCl3, δ) Da ta for o-Qu in oid Com p ou n d s
Maruyama et al.
compd
C-1
C-2
C-3
C-4
C-5
C-6
C-7
C-8
C-9
C-10
C-11
C-12
2a
2c
199.7
199.5
199.3
201.2
200.5
201.3
201.3
201.5
199.8
200.0
200.7
145.6
146.1
145.5
145.1
146.1
146.0
145.0
144.5
146.7
145.5
144.9
143.5
145.3
143.4
134.1
137.3
139.3
138.9
139.1
143.2
139.0
137.7
119.9
119.6
119.8
143.0
140.0
137.8
140.8
139.7
130.0
132.0
130.4
136.2
135.2
135.7
132.1
135.2
137.1
137.1
135.5
129.7
131.9
135.5
88.6
88.8
88.4
88.1
88.6
88.0
88.2
88.0
88.6
88.5
88.6
42.0
42.1
41.7
41.1
41.8
41.4
41.4
34.6
34.8
34.4
34.7
34.8
34.7
34.5
80.0
80.2
79.7
79.4
79.8
79.7
79.7
29.3
29.3
29.2
29.4
29.4
29.5
29.3
25.2
25.1
24.9
25.0
25.1
25.1
25.2
26.8
26.5
26.5
26.6
26.6
26.6
26.6
2b
5a
5b
5c
12d
12e
25a
25b
25e
a
a
a
a
a
a
-
-
-
-
-
-
41.8
41.8
41.2
34.9
34.9
34.5
80.1
80.0
79.7
29.3
29.3
29.4
25.0
25.2
24.9
26.6
26.6
26.6
a
Not determined.
Ta ble 4. Ch a r a cter istic 13C NMR (CDCl3, δ) Da ta for p-Qu in oid Com p ou n d s
compd
C-1
C-2
C-3
C-4
C-5
C-6
C-7
C-8
C-9
C-10
C-11
C-12
6a a
6b
6c
186.8
186.6
187.1
187.0
186.4
186.7
186.6
186.5
186.5
182.0
182.6
182.0
185.9
185.2
184.8
185.3
148.0
146.7
146.7
146.4
148.5
147.8
147.4
147.4
147.4
146.7
146.8
147.0
138.2
142.1
143.0
143.7
141.5
141.7
140.9
141.1
134.9
136.1
136.8
136.8
137.2
143.0
143.5
143.6
144.4
143.6
142.9
142.7
82.5
76.1
79.9
79.6
76.4
79.0
79.9
79.9
80.2
82.2
82.4
82.5
82.5
82.5
82.6
82.6
141.5
141.7
140.9
141.1
134.9
136.1
136.8
136.8
137.1
149.5
150.2
151.4
143.4
142.7
146.4
145.8
148.0
146.7
146.7
146.4
148.5
147.8
147.4
147.4
147.4
127.1
127.2
147.0
147.1
147.5
147.6
147.5
35.0
34.7
34.9
34.8
35.1
35.1
35.0
35.1
35.1
34.8
34.9
35.0
34.9
34.9
34.9
34.9
35.0
34.7
34.9
34.8
35.1
35.1
35.0
35.1
35.1
-
79.2
79.3
79.7
79.3
80.3
80.0
79.3
79.7
78.9
79.6
79.8
79.9
79.4
79.6
79.6
79.5
29.6
29.5
29.5
29.5
29.3
29.4
29.3
29.4
29.3
29.2
29.3
29.3
-
29.6
29.5
29.5
29.5
29.3
29.4
29.3
29.4
29.3
-
26.5
26.5
26.6
26.6
26.5
26.5
26.5
26.5
26.5
26.4
26.4
26.4
26.1
26.1
26.5
26.5
6d
26a
26b
26c
26d
26f
9a b
9bc
9cd
-
-
-
-
15a e
15bf
15cg
15d g
-
29.4
29.5
29.3
29.3
-
-
-
-
-
-
a
b
d
4-t-Bu: 40.5, 26.1 (Me). 4-t-Bu: 40.5, 25.9 (Me). c 4-t-Bu: 40.7, 26.1 (Me). 4-t-Bu: 40.8, 26.1 (Me). e 4-t-Bu: 40.4, 26.1 (Me). f 4-t-
g
Bu: 40.6, 26.1 (Me). 4-t-Bu: 40.2, 26.1 (Me).
Ta ble 5. Ch em ica l Sh ifts in 13C NMR a s Str u ctu r a l P r obe
for 5 a n d 6a
different types of products (15-19), depending on the
compd
C-1
C-4
C-6
2-t-Bu
5
6
200.7
186.7
-
79.1
88.4
-
41.5
35.0
a
Average values are given.
Ta ble 6. P r od u ct Distr ibu tion in Oxid a tion of 10 w ith
TBHP
product yielda
10
11
12
13
b
10a
10b
10c
10d
10e
89.8%
94.5
81.5
-
6.1
-
9.5
b
b
b
-
-
41.0
13.7
73.0
39.9
b
b
-
-
a
b
Isolated yield. Not detected.
products. The 13C NMR data of 12d and 12e are given
in Table 3. Although the 13C NMR data of 13a , 13c, and
1
13d were not available, H NMR data support their the
structures. Product distribution seems to be affected by
the substituent in the side chain (Table 6). That is, in
the case of 10a -10c which have a relatively unhindered
side chain (R1 ) H), the reaction takes place at the side
chain leading to the predominant formation of 11. As
the steric hindrance presented by the alkene side chain
increases, the reaction center shifts to the aromatic ring.
Interestingly, 10e gives only (tert-butylperoxy)-o-quinol
ether 12e, probably resulting from direct tert-butylper-
oxylation at the ortho position. These results are ratio-
nalized in terms of the phenoxy radical intermediates of
these phenols.5
nature of the alkenyl side chain, although the main
product was 2-alkenyl-4,6-di-tert-butyl-4-(tert-butylper-
oxy)-2,5-cyclohexadienones (15), for which 13C NMR data
are listed in Table 4. The product distribution is given
in Table 7. Analytical and spectral data of the products
were in good agreement with structures 15-19 (see the
Experimental Section).
The 13C NMR spectrum of 16a shows methyl signals
at 25.0 (4-t-Bu), 26.7 (t-BuOO), and 29.0 (6-t-Bu) ppm.
On the other hand, the tert-butyl carbon signals of 17b
Oxid a tion of 2-Alk en yl-4,6-d i-ter t-bu tylp h en ols
(14) w ith TBHP . The Co(salen)-catalyzed oxidation of
2-alkenyl-4,6-di-tert-butylphenols (14) with TBHP gave

Co(salen)-Catalyzed Oxidation of tert-Butylphenols
J . Org. Chem., Vol. 61, No. 10, 1996 3345
Ta ble 7. P r od u ct Distr ibu tion in Oxid a tion of 14 w ith
TBHP
Ta ble 8. P r od u ct Distr ibu tion in Oxid a tion of 24 w ith
TBHP
product yield (%)a
product yield(%)a
14
15
16
17
18
19
24
25
26
b
b
b
14a
14b
14c
14d
58.6
41.9
51.2
41.0
7.8
-
-
-
24a
24b
24c
24d
24e
24f
51.8
8.1
6.9
16.1
91.1
29.6
47.8
87.8
92.2
79.9
6.8
b
b
b
b
-
-
43.2
22.1
-
-
-
b
b
-
b
b
-
-
42.6
2.5
a
b
Isolated yield. Not determined.
69.9
Sch em e 1
a
Isolated yield.
Oxid a tion of 2,6-Di-ter t-bu tyl-4-a cylp h en ol Oxim e
O-Meth yl Eth er s (24) w ith TBHP . The Co(salen)-
catalyzed oxidation of 2,6-di-tert-butyl-4-acylphenol oxime
O-methyl ethers (24) with TBHP gave o-(tert-butylper-
oxy)quinol ether 25 and p-(tert-butylperoxy)quinol ether
26 as main products. No oxidation at the nitrogen atom
in the side chain was observed. The structures of 25 and
26 are supported by their 13C NMR data (Table 3 and
Table 4). The distribution of the products depended on
the substituent R on 24 (Table 8).
appear at 26.6 (t-BuOO), 28.8 (4-t-Bu), and 29.2 (6-t-Bu),
and for 17c at 26.6 (t-BuOO), 28.5 (4-t-Bu), and 29.3 (6-
1
t-Bu) ppm, respectively. These data as well as H NMR
data are in good agreement with these structures.
Interestingly, 14d gave compound 18 as one of the main
products, which strongly suggests an intramolecular
addition of a phenoxy radical intermediate5 to the alkene
side chain followed by the tert-butylperoxylation. The
comparable formation of 18 and 15d from 14d suggests
that the tert-butylperoxylation on the aromatic ring
competes with the intramolecular addition of phenoxy
radical 14d • to the double bond in the side chain leading
to 14d •′ (Scheme 1).
Oxid a t ion of Di-ter t-b u t ylcya n op h en ols w it h
TBHP . In the oxidation of 2,6-di-tert-butyl-4-cyanophe-
nol (20) and 2,4-di-tert-butyl-6-cyanophenol (22) with
TBHP, the tert-butylperoxylation took place predomi-
nantly at the 4-position to give 2,6-di-tert-butyl-4-tert-
butylperoxy-4-cyano-2,5-cyclohexadienone (21) (53%) and
2,4-di-tert-butyl-4-tert-butylperoxy-6-cyano-2,5-cyclohexa-
dienone (23) (99%), respectively, although the reaction
of 20 did not go to completion and gave two other
unknown products. The products 21 and 23 gave satis-
factory analytical and spectral data.
As seen in Table 8, the tert-butylperoxy group was
incorporated predominantly into the 4-position, except
in the case of 24e. Compounds 25d , 26c, and 26d are
composed of syn and anti stereoisomers, which were not
separated, but the ratio of the isomers could be deter-
1
mined by H NMR spectroscopy: (syn/anti) 25d (67/33),
26c (90/10), and 26d (86/14). The predominant formation
of 25e should be attributed to the steric nature of the
side chain.
Discu ssion
Rea ction P a th for th e F or m a tion of 2 fr om 1. The
1
course of the oxidation of 1a was tracked by H NMR
spectroscopy by looking at the change in chemical shift
of the CH proton of the cyclohexa-2,4-dienone system
(Figure 1). As seen from Figure 1, the signal that
appeared at δ 6.6 ppm in the initial stage, assignable to
a cyclohexa-2,5-dienone system,13 shifted gradually to δ
6.5 ppm. This time-dependent change is rationalized by
assuming that tert-butylperoxylation takes place first at
the para position leading to 2,5-cyclohexadienone 27,
followed by the migration of the tert-butylperoxy group
to the ortho position to give 2a (Scheme 2). A similar
migration reaction has been reported in the conversion
of 4-bromo-2,4,6-tri-tert-butyl-2,5-cyclohexadienone to

3346 J . Org. Chem., Vol. 61, No. 10, 1996
Maruyama et al.
F igu r e 2. Time course of thermal rearrangement of 26b to
25b at 38.8 °C determined by 1H NMR following change in
strength of signals for ring CH protons: 26b (O), 25b (0), and
29 (4).
F igu r e 1. Time-dependent chemical shift of ring CH signal
of the product in the oxidation of 1a .
Sch em e 2
F igu r e 3. Plot of the initial rate in the rearrangement of 26b
to 25b.
6-bromo-2,4,6-tri-tert-butyl-2,4-cyclohexadienone.14 The
migration of a tert-butylperoxy group was actually dem-
onstrated by the thermal reaction of 26b. Heating a
solution of 26b in CHCl3 at 50 °C for 7 h gave 24b (12%),
25b (18%), and o-benzoquinone 29 (45%), whereas at 40
°C for 5 h, 25b (26%) and 29 (5%) were obtained with
37% conversion. The formation of 24b at 50 °C suggests
that the reaction proceeds via a π-complex intermediate
28. Since compound 29 apparently arises from the
thermal decomposition of the resulting 25b, the migra-
tion reaction takes place almost quantitatively at lower
temperature. In fact, the time course of the thermal
Sch em e 3
1
reaction of 26b as monitored by H NMR spectroscopy
(38.8 °C) (Figure 2) showed that the conversion of 26b
to 25b proceeds quantitatively within 12 h, following
first-order kinetics with respect to the substrate. A plot
of log y vs time gives a straight line up to 55% conversion
(Figure 3; kobs ) 1.7 × 10-5 s-1), followed by the formation
of 26b. The results also support the mechanism involv-
ing intermediate 28 (Scheme 3). On the other hand, a
similar experiment with 25b in an NMR tube at 38.8 °C
showed only the formation of 29 but not 26b. Therefore,
the conversion of 26b to 25b must be irreversible. The
involvement of an intermediate of type 28 was also
supported by the thermal decomposition of 6d , from
which products 30-32 were obtained. In the presence
of a radical scavenger such as ascorbic acid, the formation
of 32 predominates (Table 9), suggesting radical nature
of the intermediates of type 28.
Mech a n ism for Oxid a tion of 1. The involvement
of phenoxy radical intermediates has been well docu-
mented for the Co(salen)-catalyzed TBHP oxidation of
4-alkyl- and 4-aryl-2,6-di-tert-butylphenols.5 Thus, the
mechanism for the oxidation of 1 may be similarly
rationalized as depicted in Scheme 4. The reaction is
initiated by the hydrogen abstraction of 1 with t-BuOO•,
resulting from the decomposition of CoIII(salen)(OOBut)
formed in situ.5,15 The coupling between t-BuOO• and a
mesomeric species 33′ must be kinetically preferable to
give 27, which undergoes migration via a radical pair
transition state 28′ to thermodynamically preferable
(14) Rieker, A.; Zeller, N.; Kessler, H. J . Am. Chem. Soc. 1968, 90,
6566.
(15) Nishinaga, A.; Tomita, H.; Ohara, H. Chem. Lett. 1983, 1751.

Co(salen)-Catalyzed Oxidation of tert-Butylphenols
J . Org. Chem., Vol. 61, No. 10, 1996 3347
Ta ble 9. Th er m a l Rea r r a n gem en t of 6d a
literature.12 Co(salen),16 Co(salpr),17 alkynylphenols,11 alk-
enylphenols,11 cyanophenols,18 and 2,6-di-tert-butyl-4-acylphe-
nol oxime O-methyl ether18 were prepared following the
reported methods.
2-Alk yn yl-4,6-d i-ter t-bu tyl-2-h yd r oxy-3,5-cycloh exa d i-
en on es (7). The procedure for para isomers reported in the
literature19 was modified. To a solution of an appropriate
alkynylmagnesium bromide (22.7 mmol) in THF (20 mL),
prepared from the reaction of ethylmagnesium bromide with
the corresponding alkyne, was added dropwise a solution of
3,5-di-tert-butyl-o-benzoquinone (5.0 g, 22.7 mmol) in THF (15
mL) with stirring at -78 °C. The resulting mixture was
product yield(%)b
30 31 32
warmed to room temperature over a period of 0.5 h.
A
saturated NH4Cl aqueous solution was then added. Extraction
with ether followed by silica gel column chromatographic
separation gave 2-alkynyl-4,6-di-tert-butyl-2-hydroxy-3,5-cy-
clohexadienones. Analytical and spectral data for 7 thus
obtained are given below.
solvent
T (°C)
t (h)
conv (%)
MeOH
60
60
60
40
60
2
2
2.5
12
1
100
100
86
54
100
26.4
41.5
51.8
42.3
1.3
11.7
5.9
10.9
5.1
25.3
30.3
-
i-PrOH
(CH2)2Cl2
MeOH
1.9
7a : Yield 57%; pale yellow prisms; mp 40.0-41.0 °C; IR
MeOHc
1.1
91.0
1
(KBr) 3496, 2234, 1653, 1688 cm-1; H NMR (CDCl3) δ 1.11
a
b
6d (1 mmol), solvent (40 mL) under nitrogen. Isolated yield.
(s, 18 H), 1.26 (s, 9 H), 3.66 (br s, 1 H), 6.01 (d, 1 H, J ) 2.4
Hz), 6.75 (d, 1H, J ) 2.4 Hz); 13C NMR (CDCl3) δ 199.9 (1),
143.3 (2), 140.9 (4), 134.9 (3), 128.6 (5), 91.4 (12), 76.1 (11),
72.1(6), 34.3 (8 or 10), 34.2 (8 or 10), 30.6 (R), 29.2 (7), 28.3
(9), 27.3 (R). Anal. Calcd for C20H30O2: C, 79.35; H, 9.92.
Found: C, 79.13; H, 9.96.
c Ascorbic acid (10 mmol) was added.
Sch em e 4
7b: Yield 52%; pale yellow oil; IR (neat) 3497, 2218, 1688,
1653 cm-1; 1H NMR (CDCl3) δ 0.7-1.7 (m, 5 H), 1.15 (s, 9 H),
1.29 (s, 9 H), 2.0-2.4 (m, 2 H), 3.77 (br s, 1 H), 6.04 (d, 1 H, J
) 2.4 Hz), 6.79 (d, 1 H, J ) 2.4 Hz); 13C NMR (CDCl3) δ 199.6
(1), 143.2 (2), 140.9 (4), 135.2 (3), 128.3 (5), 83.6 (12), 77.5 (11),
71.9 (6), 34.2 (8 or 10), 34.1 (8 or 10), 30.2 (R), 29.0 (7), 28.3
(9), 21.6 (R), 18.2 (R), 13.4 (R). Anal. Calcd for C20H30O2: C,
79.35; H, 9.92. Found: C, 79.30; H, 9.91.
7c: Yield 53%; pale yellow prisms; mp 103.3-104.3 °C; IR
1
(KBr) 3468, 2218, 1684, 1651 cm-1; H NMR (CDCl3) δ 1.17
(s, 9 H), 1.31 (s, 9 H), 3.99 (br s, 1 H), 6.12 (d, 1H, J ) 2.2 Hz),
6.82 (d, 1H, J ) 2.2 Hz), 7.1-7.5 (m, 5 H); 13C NMR (CDCl3)
δ 199.2 (1), 143.5 (2), 141.7 (4), 135.5 (3), 131.9 (R), 128.7 (5),
128.2 (R), 127.7 (R), 122.1 (R), 86.3 (12), 82.5 (11), 72.4 (6),
34.5 (8 or 10), 34.3 (8 or 10), 29.2 (7), 28.4 (9). Anal. Calcd
for C22H26O2: C, 81.87; H, 8.06. Found: C, 81.90; H, 7.98.
2-Alk yn yl-4,6-d i-ter t-bu tylp h en ols (8). The phenols were
obtained by reduction of 7 with Zn powder and concentrated
HCl in EtOH according to the known procedure,20 and the
products were recrystallized from EtOH. Analytical and
spectral data for these phenols are given below.
8a : Yield 59%; colorless plate; mp 130.8-131.2 °C; IR (KBr)
3492 cm-1; 1H NMR (CDCl3) δ 1.26 (s, 9 H), 1.36 (s, 9 H), 1.41
(s, 9 H), 6.01 (s, 1 H), 7.18 (d, 1 H, J ) 2.2 Hz), 7.24 (d, 1 H,
J ) 2.2 Hz); 13C NMR (CDCl3) δ 152.6 (1), 141.8 (4), 134.4 (2),
125.5 (5), 124.3 (3), 109.8 (6), 105.5 (12), 74.1 (11), 34.9 (8 or
10), 34.3 (8 or 10), 31.5 (9), 31.2 (R), 29.5 (7), 28.4 (R). Anal.
Calcd for C20H30O: C, 83.78; H, 10.47. Found: C, 83.81; H,
10.47.
1
8b: Yield 77%; colorless oil; IR (KBr) 3496 cm-1; H NMR
(CDCl3) δ 0.7-1.1 (m, 3 H), 1.2-1.8 (m, 4 H), 1.26 (s, 9 H),
1.41 (s, 9 H), 2.3-2.6 (m, 2 H), 6.03 (s, 1 H), 7.14 (d, 1 H, J )
2.2 Hz), 7.23 (d, 1 H, J ) 2.2 Hz); 13C NMR (CDCl3) δ 152.9
(1), 134.5 (2), 141.9 (4), 124.3 (3), 125.5 (5), 110.0 (6), 97.1 (12),
75.6 (11), 34.9 (8 or 10), 34.2 (8 or 10), 31.5 (9), 30.9 (R), 29.5
(7), 22.1 (R), 19.3 (R), 13.5 (R). Anal. Calcd for C20H30O: C,
83.78; H, 10.47. Found: C, 83.85; H, 10.42.
8c: Yield 53%; colorless needles; mp 81.8-82.6 °C; IR (KBr)
3506 cm-1; 1H NMR (CDCl3) δ 1.29 (s, 9 H), 1.42 (s, 9 H), 6.05
(s, 1 H), 7.2-7.7 (m, 7 H); 13C NMR (CDCl3) δ 152.9 (1), 142.3
(4), 134.9 (2), 131.6 (R), 128.6 (R), 128.5 (R), 125.8 (5), 125.3
compound 2. The coupling of t-BuOO• with another
resonance species 33′′ should give diketone 4. The
involvement of 33′′ in the formation of 4 from 1 has also
been demonstrated in the Co(salen)-catalyzed oxygen-
ation of 1.11 A detailed mechanism for the formation of
p-benzoquinone 3 is not yet known, but a succeeding
reaction of diketone 4 with TBHP may be responsible.5
(16) Calvin, M.; Barklew, C. H. J . Am. Chem. Soc. 1946, 68, 2267.
(17) Sacconi, L.; Bertini, I. J . Am. Chem. Soc. 1966, 88, 5180.
Nishinaga, A.; Tomita, H.; Nishizawa, K.; Matsuura, T. J . Chem. Soc.,
Dalton Trans. 1981, 1504.
(18) Nishinaga, A.; Shimizu, T.; Toyoda, Y.; Matsuura, T. J . Org.
Chem. 1982, 47, 2278.
(19) Hauff, V.; Krauss, P.; Rieker, A. Chem. Ber. 1972, 105, 1446.
(20) Rieker, A.; Scheffler, K. J ustus Liebigs Ann. Chem. 1965, 78,
689.
Exp er im en ta l Section
All melting points are uncorrected. Elemental analyses
were performed by the Analytical Center of our department.
The assignments for the 13C NMR data are based on the

3348 J . Org. Chem., Vol. 61, No. 10, 1996
Maruyama et al.
(3), 122.7 (R), 109.4 (6), 95.9 (12), 84.2 (11), 35.1 (8 or 10), 34.3
(8 or 10), 31.5 (9), 29.5 (7). Anal. Calcd for C22H26O: C, 86.15;
H, 8.48. Found: C, 85.97; H, 8.44.
13C NMR (CDCl3) δ 186.7, 148.9, 148.0, 144.6, 134.6, 132.5,
126.3, 80.5, 75.1, 35.3, 34.9, 29.5, 26.4, 18.9.
11b: Yellow needles; mp 73.8-84.3 °C; IR (KBr) 1632, 1620
1
Co(sa len )-Ca ta lyzed Oxid a tion of 4-Alk yn ylp h en ols
(1) w ith TBHP . To a solution of 1 (1 mmol) and TBHP (70%,
d ) 0.91, 1400 µL, 10 mmol) in CH2Cl2 (15 mL) was added
dropwise a solution of Co(salen) (32.5 mg, 0.1 mmol) in CH2-
Cl2 (10 mL) under N2 with stirring at rt. After completion of
the reaction (20 min), monitored by TLC, the complex was
removed by filtration of the mixture through a short silica gel
column eluted with CH2Cl2, and the filtrate was evaporated.
The resulting residue was dissolved in pentane and the
solution was washed with water to remove unreacted TBHP.
The pentane layer was dried (Na2SO4) and evaporated to give
a mixture of 2, 3, and 4, which were separated by silica gel
TLC. The results are listed in Table 1. 1H NMR and
characteristic 13C NMR data of 2 are listed in Tables 2 and 3,
respectively. Analytical and other spectral data for 2 are given
below. Spectral data of 3 and 4 were identical with those of
authentic samples.12
cm-1; H NMR (CDCl3) δ 1.27 (s, 18 H), 1.32 (s, 9 H), 5.96 (d,
1 H, J ) 8.4 Hz), 6.39 (d, 1 H, J ) 8.4 Hz), 6.84 (d, 1 H, J )
2.4 Hz), 7.34 (br s, 6 H); 13C NMR (CDCl3) δ 186.5, 149.2, 148.1,
142.0, 138.5, 134.6, 132.7, 128.8, 128.6, 127.5, 126.4, 81.6, 80.9,
31.6, 30.2, 29.6, 29.5, 26.5. Anal. Calcd for C26H36O3: C, 78.75;
H, 9.15. Found: C, 78.79; H, 9.12.
11c: Yellow prisms; mp 68.9-69.5 °C; IR (KBr) 1618 cm-1
;
1H NMR (CDCl3) δ 1.21 (s, 9 H), 1.24 (s, 9 H), 1.27 (s, 9 H),
1.51 (s, 6 H), 6.26 (br, 1 H), 6.76 (d, 1 H, J ) 2.4 Hz), 7.96 (d,
1 H, J ) 2.4 Hz); 13C NMR (CDCl3) δ 186.4, 149.3, 148.0, 147.1,
135.8, 131.7, 127.8, 80.8, 79.1, 35.4, 34.8, 29.6, 29.5, 29.3 26.7.
Anal. Calcd for C22H36O3: C, 75.82; H, 10.41. Found: C,
75.09; H, 10.65.
11d : Yellow needles; mp 101.5-102.1 °C; IR (KBr) 1613
cm-1; 1H NMR (CDCl3) δ 1.06 (s, 9 H), 1.26 (s, 9 H), 1.35 (s, 9
H), 1.41 (s, 6 H), 6.46 (d,1 H, J ) 2.4 Hz), 6.9-7.5 (m, 5 H),
8.34 (d, 1 H, J ) 2.4 Hz); 13C NMR (CDCl3) δ 186.8, 158.4,
146.6, 146.2, 140.6, 132.9, 130.7, 130.0, 128.4, 127.7, 127.2,
83.2, 79.2, 31.1, 30.6, 29.8, 29.3, 28.6, 26.8. Anal. Calcd for
C28H40O3: C, 79.20; H, 9.49. Found: C, 79.10; H, 9.46.
12d : Yellow prisms; mp 74.2-75.4 °C; IR (KBr) 1684, 1655
cm-1; 1H NMR (CDCl3) δ 0.97 (s, 9 H), 1.12 (s, 9 H), 1.18 (s, 9
H), 1.76 (s, 3H), 1.94 (s, 3H), 6.19 (d, 1 H, J ) 2.0 Hz), 6.29(d,
1 H, J ) 2.0 Hz) 7.23 (br s, 5H); 13C NMR (CDCl3) δ 137.0,
136.3, 131.6, 129.8, 128.0, 126.5, 22.7, 22.1. Anal. Calcd for
C28H40O3: C, 79.20; H, 9.49. Found: C, 79.22; H, 9.45.
2a : Yellow prisms; mp 89.7-90.3 °C; IR (KBr) 2220, 1686,
1642 cm-1 13C NMR (CDCl3) δ 97.3, 78.6, 31.1, 27.9. Anal.
;
Calcd for C24H38O3: C, 76.89; H, 10.15. Found: C, 76.88; H,
10.13.
2b: Yellow oil; IR (neat) 2226, 1684, 1640 cm-1 13C NMR
;
(CDCl3) δ 89.1, 79.9, 30.7, 21.9, 18.9, 13.5. Anal. Calcd for
C24H38O3: C, 76.89; H, 10.15. Found: C, 76.41; H, 10.13.
2c: Yellow needles; mp 82.8-73.5 °C; IR (KBr) 2212, 1684,
1636 cm-1 13C NMR (CDCl3) δ 131.7, 128.5, 128.4, 122.9, 88.7,
;
88.4. Anal. Calcd for C26H34O3: C, 79.08; H, 8.62. Found:
C, 79.14; H, 8.87.
12e: Yellow prisms; mp 95.0-96.5 °C; IR (KBr) 1670 cm-1
;
1H NMR (CDCl3) δ 1.02 (s, 9 H), 1.04 (d, 6 H, J ) 7.5), 1.22 (s,
9 H), 1.26 (s, 9H), 1.65 (s, 3H), 1.78 (s, 3 H), 2.95 (m, 1 H),
5.90 (d, 1 H, J ) 2.0 Hz), 6.34 (d, 1 H, J ) 2.0 Hz); 13C NMR
(CDCl3) δ 138.3, 126.5, 30.0, 22.4, 21.6, 21.4, 19.3. Anal. Calcd
for C28H40O3: C, 79.20; H, 9.49. Found: C, 79.22; H, 9.45.
1
4a : H NMR (CDCl3) δ 1.31 (s, 9 H), 1.45 (s, 18 H), 5.87 (s,
1 H), 7.69 (s, 2 H); 13C NMR (CDCl3) δ 212.1, 204.7, 159.8,
136.4, 127.5, 124.9, 42.6, 34.4, 30.0, 26.6.
4b: 1H NMR (CDCl3) δ 0.9-1.4 (m, 7 H), 1.46 (s, 18 H), 2.6-
3.0 (t, 2 H, J ) 7 Hz), 5.89 (s, 1 H), 7.85 (s, 2 H); 13C NMR
(CDCl3) δ 204.7, 192.4, 160.0, 136.4, 128.0, 123.84 38.7, 34.3,
30.0, 25.0, 23.0, 13.7.
13a : Colorless oil; IR (neat) 1667, 1649 cm-1 1H NMR
;
(CDCl3) δ 1.19 (s, 9 H), 1.23 (s, 18 H), 1.64 (br d, J ) 4.8 Hz,
3 H), 5.3-5.6 (m, 2 H), 6.54 (s, 2 H).
4c: 1H NMR (CDCl3) δ 1.31 (s, 9 H), 1.45 (18 H), 5.87 (s, 1
H), 7.69 (s, 2 H); 13C NMR (CDCl3) δ 195.3, 193.9, 160.2, 136.6,
134.5, 133.6, 129.9, 128.8, 128.0, 125.0, 30.0, 34.4.
Co(sa len )-Ca ta lyzed Oxid a tion of 2-Alk yn ylp h en ols
(8) w ith TBHP . The oxidation of 8 was carried out similar
to that of 1. Cyclohexa-2,5-dienones 9 were obtained in
approximately quantitative yield as described in the text.
Characteristic 13C NMR data are listed in Table 4. Analytical
and other spectral data of 9 are given below.
13c: Colorless oil; IR (neat) 1669, 1647 cm-1 1H NMR
;
(CDCl3) δ 1.17 (s, 9 H), 1.24 (s, 18 H), 1.64 (br, 3 H), 1.73 (br,
3 H), 5.14 (br, 1 H), 6.50 (s, 2 H).
13d : Colorless oil; IR (neat) 1667, 1644 cm-1 1H NMR
;
(CDCl3) δ 1.07 (s, 18 H), 1.19 (s, 9 H), 1.46 (s, 3 H), 2.12 (s,
3H), 6.56 (s, 2 H), 6.7-7.3 (m, 5 H).
Co(sa len )-Ca ta lyzed Oxid a tion of 2-Alk en ylp h en ols
(14) w ith TBHP . The procedure was the same as that for 1.
Compounds 15-19 were obtained. The results are listed in
Table 7. Analytical and spectral data for these products are
given below. Characteristic 13C NMR data for 15 are listed
in Table 4.
9a : Colorless needles; mp 93.8-94.8 °C; IR (KBr) 2224, 1669,
1
1651, 1618 cm-1; H NMR (CDCl3) δ 1.02 (s, 9 H), 1.24 (s, 9
H), 1.29 (s, 9 H), 1.35 (s, 9 H), 6.77 (d, 1 H, J ) 2.8 Hz), 7.05
(d, 1 H, J ) 2.8 Hz); 13C NMR (CDCl3) δ 101.4 (R), 73.6 (R),
30.8 (R), 26.9(R). Anal. Calcd for C24H38O3: C, 76.89; H, 10.15.
Found: C, 76.81; H, 10.16.
15a : Colorless oil; IR (neat) 1665, 1644 cm-1 1H NMR
;
(CDCl3) δ 1.01 (s, 9 H), 1.22 (s, 9 H), 1.26 (s, 9 H), 1.80 (br s,
3 H), 1.87 (br s, 3 H), 6.06 (br s, 1 H), 6.77 (d, 1 H, J ) 2.8
Hz), 6.79 (d, 1 H, J ) 2.8 Hz); 13C NMR (CDCl3) δ 137.1, 119.8,
40.4, 26.6, 26.5, 19.6. Anal. Calcd for C22H36O3: C, 75.75; H,
10.33. Found: C, 75.52; H, 10.12.
9b: Colorless oil; IR (neat) 2234, 1669, 1647, 1613 cm-1
;
1H NMR (CDCl3) δ 0.7-1.8 (m, 7 H), 0.98 (s, 9 H), 1.19 (s, 9
H), 1.24 (s, 9 H), 2.2-2.6 (m, 2 H), 6.77 (d, 1 H, J ) 2.8 Hz),
7.09 (d, 1 H, J ) 2.8 Hz); 13C NMR (CDCl3) δ 94.0 (R), 75.2
(R), 30.7 (R), 22.1 (R), 19.3(R), 13.5 (R). Anal. Calcd for
C24H38O3: C, 76.89; H, 10.15. Found: C, 76.88; H, 10.21.
9c: Colorless needles; mp 107.3-108.8 °C; IR (KBr) 2254,
15b: Colorless prisms, mp 31.5-31.8 °C; IR (KBr) 1667,
1647 cm-1; 1H NMR (CDCl3) δ 1.00 (s, 9 H), 1.21 (s, 9 H), 1.26
(s, 9 H), 1.97 (br s, 3H), 5-5.2 (m, 2 H), 6.79 (s, 2 H); 13C NMR
(CDCl3) δ 143.4, 115.6, 40.6, 26.5, 22.5. Anal. Calcd for
C21H34O3: C, 75.34; H, 10.16. Found: C, 75.27; H, 10.37.
15c: Colorless prisms; mp 103.5-104.3 °C; IR (KBr) 1669,
1
1669, 1647, 1613 cm-1; H NMR (CDCl3) δ 1.03 (s, 9 H), 1.21
(s, 9 H), 1.27 (s, 9 H), 6.78 (d, 1 H, J ) 2.8 Hz), 7.1-7.6 (m, 6
H); 13C NMR (CDCl3) δ 131.8 (R), 128.4 (R),128.1 (R), 122.9-
(R), 92.7 (R), 84.2 (R). Anal. Calcd for C26H34O3: C, 79.08;
H, 8.62. Found: C, 78.87; H, 8.50.
1
1649, 1615 cm-1; H NMR (CDCl3) δ 1.06 (s, 9 H), 1.22 (s, 9
H), 1.25 (s, 9 H), 5.27 (d, 1 H, J ) 2.0 Hz), 5 58 (d, 1 H, J )
2.0 Hz), 6.79 (d, 1 H, J ) 2.6 Hz), 6.93 (d, 1 H, J ) 2.6 Hz)
7.1-7.5 (m, 5 H); 13C NMR (CDCl3) δ 146.2, 139.9, 128.2, 127.5,
126.1, 115.1, 40.2, 26.1. Anal. Calcd for C26H36O3: C, 78.67;
H, 9.08. Found: C, 78.66; H, 8.97.
Co(sa len )-Ca ta lyzed Oxid a tion of 4-Alk en ylp h en ols
(10) w ith TBHP . The oxidation of 10 was carried out similar
to that of 1 described above. Compounds 11-13 were isolated
by silica gel TLC. The results are given in Table 6. Charac-
teristic 13C NMR data for 12d and 12e are listed in Table 3.
Analytical and other spectral data for 11, 12, and 13 are given
below.
15d : Colorless prisms; mp 81.0-82.0 °C; IR (KBr) 1649
1
cm-1; H NMR (CDCl3) δ 0.99 (s, 9 H), 1.20 (s, 18 H), 1.74 (s,
H), 1.79 (s, 3 H), 6.75 (s, 2 H), 7.22 (br s, 5 H); 13C NMR (CDCl3)
δ 141.9, 132.5, 129.2, 127.5, 125.9, 40.2, 26.2, 21.6, 22.6. Anal.
Calcd for C28H40O3: C, 79.13; H, 9.42. Found: C, 79.11; H,
9.52.
11a : Yellow prisms; mp 57.2-58.1 °C [lit.5 mp 57.2-58.1
°C]; IR (KBr) 1618 cm-1; 1H NMR (CDCl3) δ 1.24 (s, 9 H), 1.30
(s, 18 H), 1.37 (d, 3 H, J ) 7.5 Hz), 5.09 (m, 1 H), 6.12 (d, 1 H,
J ) 9.0 Hz), 6.80 (d, 1 H, J ) 2.0 Hz), 7.23 (d, 1 H, J ) 2.0);
16a : Yellow oil; IR (neat) 1686, 1649 cm-1; 1H NMR (CDCl3)
δ 0.92 (s, 9 H), 1.13 (s, 9 H), 1.17 (s, 9 H), 1.74 (s, H), 1.78 (br

Co(salen)-Catalyzed Oxidation of tert-Butylphenols
J . Org. Chem., Vol. 61, No. 10, 1996 3349
24
s, 3 H), 1.84 (br s, 3 H), 6.06 (d, 1 H, J ) 2.4 Hz), 6.16 (d, 1 H,
J ) 2.4 Hz), 6.75 (br s, 1 H); 13C NMR (CDCl3) for t-Bu groups
δ 24.98, 26.70, 28.97.
for C H41NO4: C, 70.77; H, 10.06; N, 3.43. Found: C, 70.69;
H, 10.08; N, 3.36.
26a : IR (KBr) 1671, 1653 cm-1; H NMR (CDCl3) δ 1.24 (s,
9 H), 1.29 (s, 18 H), 3.82 (s, 3 H), 6.63 (s, 2 H), 7.40 (s, 1 H);
13C NMR (CDCl3) δ 130.0, 61.9.
1
17b: Yellow prisms; mp 37.8-39.0 °C; IR (KBr) 1684 cm-1
;
1H NMR (CDCl3) δ 1.18 (s, 9 H), 1.24 (s, 18 H), 1.64 (br s, 3
H), 4.88 (br s, 3 H), 5.06 (br s, 1 H), 5.98 (d, 1 H, J ) 2.4 Hz),
6.81 (d, 1 H, J ) 2.4 Hz); 13C NMR (CDCl3) for t-Bu groups δ
26.6, 28.8, 29.2. Anal. Calcd for C21H34O3: C, 75.34; H, 10.16.
Found: C, 74.92; H, 10.69.
26b: Pale yellow needles; mp 43.6-44.2 °C; IR (KBr) 1667,
1649 cm-1 1H NMR (CDCl3) δ 1.21 (s, 9 H), 1.26 (s, 18 H),
;
1.91 (s, 3 H), 3.79 (s, 3 H), 6.64 (s, 2 H); 13C NMR (CDCl3) δ
146.8, 61.8, 10.8. Anal. Calcd for C21H35NO4: C, 68.94; H,
9.58; N, 3.83. Found: C, 68.93; H, 9.66; N, 3.77.
17c: Yellow oil; IR (neat) 1684, 1657 cm-1; 1H NMR (CDCl3)
δ 1.04 (s, 9 H), 1.17 (s, 9 H), 1.20 (s, 9 H), 5.21 (d, 1 H, J ) 1.2
Hz), 5.46 (d, 1 H, J ) 1.2 Hz), 5.95 (d, 1 H, J ) 2.4 Hz), 6.93
(d, 1 H, J ) 2.4 Hz), 7.0-7.4 (m, 5 H); 13C NMR (CDCl3) for
t-Bu groups δ 26.6, 28.5, 29.3. Anal. Calcd for C26H36O3: C,
78.72; H, 9.15. Found: C, 78.66; H, 9.23.
18: Colorless prisms; mp 122.3-123.0 °C; 1H NMR (CDCl3)
δ 0.78 (s, 3 H), 0.83 (s, 9 H), 1.28 (s, 9 H), 1.36 (s, 9 H), 1.54
(s, 3 H), 7.1-7.7 (m, 7 H); 13C NMR (CDCl3) δ 156.6, 141.3,
138.6, 132.4, 128.3, 127.8, 127.5, 124.2, 123.4, 93.5, 91.5 79.7,
34.6, 34.3, 32.0, 29.5, 26.4, 26.0, 19.4. Anal. Calcd for
C28H40O3: C, 79.13; H, 9.42. Found: C, 78.88; H, 9.32.
19: 1H NMR data [(CDCl3) δ 1.24 (s, 9 H), 1.47 (s, 9 H), 7.3-
7.8 (m, 7 H), 12.72 (s, 1 H)] were identical with that of an
authentic sample.11
Com p ou n d 26c was obtained as a mixture of syn and anti
stereo isomers which could not be separated, but recognized
readily by H NMR. The same is the case for 26d .
26c (syn ): Colorless oil; IR (KBr) 1669, 1651 cm-1; 1H NMR
(CDCl3) δ 1.09 (t, 3 H, J ) 7.6 Hz), 1.22 (s, 9 H), 1.26 (s, 18
H), 2.37 (q, 2 H, J ) 7.6 Hz), 3.77 (s, 3 H), 6.65 (s, 2 H);
13C NMR (CDCl3) δ 160.9, 61.8, 19.4, 11.0. Anal. Calcd for
22H37NO4: C, 69.62; H, 9.83; N, 3.65. Found: C, 69.46; H,
9.85; N, 3.66.
1
C
26c (a n ti): Colorless oil; IR (KBr) 1669, 1649 cm-1; 1H NMR
(CDCl3) δ 1.19 (s, 9 H), 1.20 (d, 3 H, J ) 7.5 Hz), 1.23 (s, 18
H), 2.45 (q, 2 H, J ) 7.5 Hz), 3.61 (s, 3 H), 6.48 (s, 2 H).
26d (syn ): Pale yellow prisms; mp 51.2-52.1 °C; IR (KBr)
Co(sa len )-Ca ta lyzed Oxid a tion of Cya n op h en ols (20
a n d 22) w ith TBHP . The procedure was the same as that
for 1. Only cyclohexa-2,5-dienones 21 and 23 were isolated.
21: Colorless needles; mp 86.5-87.2 °C; IR (KBr) 1673, 1653,
1669, 1651 cm-1; H NMR (CDCl3) δ 1.22 (s, 9 H), 1.26 (s, 18
1
H), 1.26 (d, 6 H, J ) 7.2 Hz), 2.81 (sep, 1 H, J ) 7.2 Hz), 3.73
(s, 3 H), 6.66 (s, 2 H); 13C NMR (CDCl3) δ 163.1, 61.8, 30.1,
18.5. Anal. Calcd for C23H39NO4: C, 70.13; H, 9.91; N, 3.56.
Found: C, 70.13; H, 9.92; N, 3.61.
26d (a n ti): Colorless oil; IR (neat) 1669, 1647 cm-1; 1H NMR
(CDCl3) δ 1.19 (d, 6 H, J ) 6.8 Hz), 1.19 (s, 9 H), 1.23 (s, 18
H), 2.93 (sep, 1 H, J ) 6.8 Hz), 3.60 (s, 3 H), 6.47 (s, 2 H).
;
26e: Colorless oil; IR (neat) 1669, 1647 cm-1 1H NMR
(CDCl3) δ 1.17 (s, 9 H), 1.23 (s, 18 H), 1.34 (s, 9 H), 3.54 (s, 3
H), 6.29 (s, 2 H); 13C NMR (CDCl3) for t-Bu group δ 29.4, 26.7,
29.3.
1624 cm-1 1H NMR (CDCl3) δ 1.26 (s, 18 H), 1.34 (s, 9 H),
;
6.61 (s, 2 H). Anal. Calcd for C19H29NO3: C, 71.39; H, 9.08;
N, 4.38. Found: C, 71.46; H, 9.06; N, 4.43.
23: Colorless prisms; mp 90.2-91.8 °C; IR (KBr) 2240, 1671,
1
1647, 1615 cm-1; H NMR (CDCl3) δ 1.06 (s, 9 H), 1.21 (s, 9
H), 1.28 (s, 9 H), 6.86 (d, 1 H, J ) 2.8 Hz), 7.66 (d, 1 H, J )
2.8 Hz); 13C NMR (CDCl3) δ 178.6, 160.3, 146.9, 144.5, 119.4,
114.0, 92.6, 80.6, 41.1, 35.1, 29.0, 26.3, 25.9. Anal. Calcd for
C19H29NO3: C, 71.39; H, 9.08; N, 4.38. Found: C, 71.40; H,
9.10; N, 4.35.
26f (syn ): Colorless prisms; mp 82.5-83.8 °C; IR (KBr) 1667,
1647 cm-1 1H NMR (CDCl3) δ 1.22 (s, 27 H), 3.74 (s, 3 H),
;
Co(sa len )-Ca ta lyzed Oxid a tion of 4-Acylp h en ol Oxim e
O-Meth yl Eth er s (24) w ith TBHP . The procedure was the
same as that for 1. Cyclohexadienones 25 and 26 were
obtained. Analytical and spectral data for these products are
given below. Characteristic 13C NMR data for 25a , 25b, and
25e are listed in Table 3, and for 26a -26d , and 26f in Table
4, respectively.
25a : Yellow prisms; mp 72.8-73.6 °C; IR (KBr) 1686, 1653
cm-1; 1H NMR (CDCl3) δ 0.96 (s, 9 H), 1.20 (s, 9 H), 1.26 (s, 9
H), 3.93 (s, 3 H), 6.43 (d, 1 H, J ) 2.0), 7.20 (d, 1 H, J ) 2.0),
7.74 (s, 1 H); 13C NMR (CDCl3) δ 147.4, 62.0. Anal. Calcd for
C20H33NO4: C, 68.34; H, 9.46; N, 3.98. Found: C, 68.32; H,
9.25; N, 3.95.
25b: Yellow oil; IR (neat) 1684 cm-1; 1H NMR (CDCl3) δ 0.95
(s, 9 H), 1.18 (s, 9 H), 1.25 (s, 9 H), 2.06 (s, 3 H), 6.54 (d, 1 H,
J ) 2.0), 7.39 (d, 1 H, J ) 2.0); 13C NMR (CDCl3) δ 152.4, 62.0,
10.5. Anal. Calcd for C21H35NO4: C, 68.94; H, 9.58; N, 3.83.
Found: C, 68.82; H, 9.42; N, 3.63.
25c: Yellow oil; IR (neat) 1684 cm-1; 1H NMR (CDCl3) δ 0.97
(s, 9 H), 1.11 (t, 3 H, J ) 7.5 Hz), 1.20 (s, 9 H), 1.25 (s, 9 H),
2.60 (q, 2 H, J ) 7.5 Hz), 3.97 (s, 3 H), 6.59 (d, 1 H, J ) 2.2
Hz), 7.42 (d, 1 H, J ) 2.2 Hz).
6.57 (s, 2 H), 7.0-7.5 (m, 5 H); 13C NMR (CDCl3) δ 157.5, 132.2,
128.6, 128.3, 127.4, 62.3. Anal. Calcd for C26H37NO4: C, 73.04;
H, 8.72; N, 3.28. Found: C, 73.08; H, 8.76; N, 3.18.
Th er m a l Decom p osition of 26b. A solution of 26b (366
mg, 1 mmol) in CHCl3 (30 mL) was heated at 50 °C under N2.
The original material disappeared in 7 h. The reaction
mixture was concentrated and separated by silica gel TLC
(CH2Cl2/hexane ) 2/1) to give 24b (40 mg, 12%), 25b (61 mg,
18%), and 29 (106 mg, 45%). When 26b (366 mg, 1 mmol)
was heated at 40 °C for 5 h, 25b (97 mg, 27%) and 29 (13 mg,
5%) were obtained with recovery of 26b (232 mg, 63%).
29: Green needles; mp 111.5-111.9 °C; IR (KBr) 1659 cm-1
;
1H NMR (CDCl3) δ 1.29 (s, 9 H), 2.09 (s, 3 H), 4.06 (s, 3 H),
6.44 (d, 1 H, J ) 2.2 Hz), 7.64 (d, 1 H, J ) 2.2 Hz); 13C NMR
(CDCl3) δ 181.5, 179.7, 152.3, 149.8, 146.3, 131.9, 123.9, 63.3,
35.6, 29.2, 10.4. Anal. Calcd for C13H17NO3: C, 66.36; H, 7.28;
N, 5.95. Found: C, 66.31; H, 7.12; N, 5.94.
Tim e Cou r se of Th er m a l Rea r r a n gem en t of 26b.
solution (0.25 mol/L) of 26b (37 mg, 0.1 mmol) in CDCl3 was
kept in an NMR tube set up in an NMR machine at 38.8 °C,
and the reaction was followed by H NMR spectroscopy. The
A
1
Com p ou n d 25d was obtained as a mixture of syn and anti
stereoisomers which could not be separated, but was recog-
results are given in Figure 2.
1
nized readily by H NMR.
Th er m a l Rea r r a n gem en t of 6d in Va r iou s Solven ts.
A solution of 6d (401 mg, 1 mmol) in an appropriate solvent
(40 mL) was heated at 60 °C under N2. The reaction mixture
was separated by silica gel TLC to give compounds 30 [1H
NMR (CDCl3) δ 0.97 (s, 9 H), 1.19 (s, 9 H), 1.23 (s, 9 H), 3.79
(s, 3 H), 6.49 (d, 1 H, J ) 2.3 Hz), 6.98 (d, 1 H, J ) 2.3 Hz),
6.7-7.5 (m, 4 H)], 31, and 32. Addition of ascorbic acid as a
radical scavenger (1.75 g, 10 mmol) in MeOH (40 mL) afforded
32 (284 mg, 91%) along with a minute amount of 30 (5 mg,
1%) and 31 (3 mg, 1%). The results are given in Table 9.
1
25d (syn ): H NMR (CDCl3) δ 0.99 (s, 9 H), 1.24 (d, 6 H, J
) 6.2 Hz), 1.57 (s, 9 H), 1.59 (s, 9 H), 3.39 (sep, 1 H, J ) 6.2
Hz), 3.93 (s, 3 H), 6.52 (d, 1 H, J ) 2.2 Hz), 7.03 (d, 1 H, J )
2.2 Hz).
25d (a n ti): 1H NMR (CDCl3) δ 0.99 (s, 9 H), 1.09 (d, 6 H, J
) 6.2 Hz), 1.57 (s, 9 H), 1.59 (s, 9 H), 2.69 (sep, 1 H, J ) 6.2
Hz), 3.84 (s, 3 H), 6.19 (d, 1 H, J ) 2.0 Hz), 6.44 (d, 1 H, J )
2.0 Hz).
25e: Yellow prisms; mp 52.2-53.3 °C; IR (KBr) 1684 cm-1
;
1H NMR (CDCl3) δ 1.00 (s, 9 H), 1.19 (s, 9 H), 1.23 (s, 18 H),
3.82 (s, 3 H), 6.03 (d, 1 H, J ) 2.0 Hz), 6.27 (d, 1 H, J ) 2.0
Hz); 13C NMR (CDCl3) δ 164.8, 61.3, 37.2, 28.1. Anal. Calcd
J O950944K