Direct observation for the cyclization of a diarylcarbonyl oxide

Article abstract of DOI:10.1016/j.tetlet.2004.06.022

Trapping and laser flash spectroscopic experiments showed that the cyclization of diphenylcarbonyl oxide is turned into a very facile process by introducing p-methoxyl substituent, the lifetime of which is as short as 10 ^-8 s. The trapping with

Full text of DOI:10.1016/j.tetlet.2004.06.022

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 5791–5793
Direct observation for the cyclization of a diarylcarbonyl oxide
Hiroshi Hanaki, Yuta Fukatsu, Masaki Harada and Yasuhiko Sawaki*
Department of Applied Chemistry, Graduate School of Engineering, Nagoya University, Chikusa-ku, Nagoya 464-8603, Japan
Received 28 April 2004; accepted 4 June 2004
Abstract—Trapping and laser flash spectroscopic experiments showed that the cyclization of diphenylcarbonyl oxide is turned into a
very facile process by introducing p-methoxyl substituent, the lifetime of which is as short as 10ꢀ8 s. The trapping with diphenyl-
sulfide and -sulfoxide suggested the intervention of a dioxirane intermediate.
ꢀ 2004 Elsevier Ltd. All rights reserved.
Carbonyl oxides (1) are the key intermediate in the
ozonolysis of olefins1 and have attracted interest in the
various fields of synthetic, mechanistic, biological and
atmospheric chemistry.2 On the other hand, the cyclic
isomers, dioxiranes (2), can be prepared by the peroxy-
sulfate oxidation of ketones3 and are employed as a
versatile oxygen transfer agent.4
responding ketones.10;11 As a special case, dimesityl CO
is reported to be stable in solutions because of the
presence of bulky mesityl group.7a In the course of the
study on the reaction of carbenes and oxygen9;12 we have
surveyed various types of CO’s by trapping and laser-
flash spectroscopic experiments. The oxides were pro-
duced by the laser-flash at 308 nm for the corresponding
diazomethanes in the presence of oxygen in acetonitrile
(Eq. 1, Ar ¼ Ph and X–C6H4).13
_
_
O
O
O
O
R
R
R
R
R
R
+
+
C
C
O
C = O
1b
1a
2
hν
O2
Ar2CN2
Ar2C :
Ar2COO
Ar2C=O
ð1Þ
The structural and chemical property of these peroxidic
species are significantly dependent on their substitu-
ents.5 Carbonyl oxides (CO) are characterized as a
nucleophilic O-transfer agent,2b;6 and usually do not
isomerize to the more stable dioxiranes (DO) because of
the C–O double bond nature as shown in 1a. While the
cyclization of CO’s to DO’s is known to proceed photo-
chemically,7 the thermal reaction has been suggested
only for the exceptional case of oxides with a-methoxyl8
or a-amino substituent.9 Herein, we report on the first
direct observation of the facile cyclization of a diaryl
CO.
3
5
4
Aryl CO’s are reported to possess the strong absorption
at 410 20 nm.2a A typical case of diaryl CO is shown in
Figure 1. When diphenyldiazomethane (3a, Ar ¼ Ph)
was irradiated in the presence of oxygen, diphenyl CO
(5a) could be detected as its absorption spectra with
kmax ¼ 410 nm as shown in Figure 1A. The reaction
course of Eq. 1 could be followed by monitoring the
decay of carbene 4a at 340 nm or by the formation of
CO 5a at 410 nm. The resulting rate constant for the
reaction of 4a with O2 was 3.2 · 109 Mꢀ1 sꢀ1, which is
close to the reported value of 5.0 · 109 Mꢀ1 sꢀ1 11c
.
Time
Diaryl CO’s (1, R ¼ Ar) are known to decay slowly
course of the absorbance of 5a is shown in Figure 1B; its
formation, which was faster under oxygen (a) than that
under air (b),14 was almost completed within 1 ls and its
decay was slow and below 5% after 10 ls. The same was
true for the cases of p-chlorophenyl or p-methylphenyl
CO. The weak absorption for the flash under argon (c) is
probably due to the formation of azine derivative by the
reaction of 4a with starting 3a.
according to the second-order kinetics yielding the cor-
Keywords: Carbonyl oxides; Cyclizations; Dioxiranes; Peroxides; Oxi-
dation; Mechanism.
* Corresponding author at present address: Department of Applied
Chemistry, Aichi Institute of Technology, Toyota 470-0392, Japan.
Tel./fax: +81-561-740266; e-mail: ysawaki@apchem.nagoya-u.ac.jp
0040-4039/$ - see front matter ꢀ 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.06.022

5792
H. Hanaki et al. / Tetrahedron Letters 45 (2004) 5791–5793
Table 1. Trapping of active oxygen species during the photooxidation
of Ar2CN2 in acetonitrilea
Ar
Additive
Productsb (%)
Rel. reactivity
SO/Sc
Ph
Ph2S, 50 mM
Ph2SO, 50 mM
MeOH, 1.3 M
Ph2S, 50 mM
Ph2SO, 50 mM
Ph2S, 8 mM
Ph2SO, 2.2
Ph2SO2, 19
ROOHd, 51e
Ph2SO, 37
Ph2SO2, 42
Ph2SO, 29
Ph2SO2, 18
ROOH,d 35
8.6
Anisf
1.1
Ph2SO, 8 mM
MeOH, 2.5 M
0.62
a Solutions of Ar2CN2 (4–20 mM), Rose Bengal (0.3 mM) and the
additive were irradiated at >400 nm with a 300 W Hg lamp (1.5 h, ca.
20 ꢁC).
b Products from additives were determined by GLC and % yields are
based on the starting Ar2CN2.
c Relative reactivity of Ph2SO/Ph2S.
Figure 1. Formation and decay of diphenyl CO (5a) by the laser flash
(308 nm) for 3a in acetonitrile. A: Spectra of 5a at 0.1 and 1.0 ls after
the flash under air. B: Time-course of the 410 nm absorbance under
oxygen (a), air (b) and argon (c).
d ROOH: Ar2C(OMe)OOH. Yields were determined by 1H NMR.
e Ref. 12b.
f Anis ¼ p-MeOC6H4.
When di(p-methoxyphenyl)diazomethane (3b, Ar ¼ p-
MeOC6H4)15 was photolyzed under the same conditions,
a quite different time course was obtained. As shown in
Figure 2, the growth of the absorption at 410 nm is
comparable to the other diaryl CO’s, but its decay is
very fast. It is interesting to note that the decay curve is
well reproduced, as shown in the line of Figure 2, by the
first-order rate constant of k1 ¼ 4:5 ꢁ 107 sꢀ1. Similar
results were obtained as 3.8, 3.6. 3.8 and 3.5 · 107 sꢀ1
with 0.04–0.20 mM 3b, affording k1 ¼ ð3:9ꢂ0:4Þꢁ
107 sꢀ1 for the decay in acetonitrile at 25 ꢁC. The decay
in benzene was similarly fast, the resulting k1 value being
(2.1 0.4) · 107 sꢀ1. The lifetime of transient species (i.e.,
2.6 · 10ꢀ8 s) was too short for monitoring with the
conventional CCD system, but its spectra could be ob-
tained, as shown in Figure 2 (inset), by the time-resolved
observation at 17.5 ns after the laser-flash. The transient
species with kmax ¼ 395 nm is soundly assigned as CO 5b
since it appeared only in the presence of oxygen and aryl
CO’s are known to possess strong absorption at
410 20 nm.2a;11c
In order to characterize the transient species, O-transfers
to diphenylsulfide (S) and sulfoxide (SO) were examined.
Here, CO’s were produced by the singlet oxygen oxi-
dation of diazomethane11c;13a to avoid the possible
reaction of carbenes and additives. As shown in Table 1,
the reaction of diphenyl CO (5a) with the sulfide was
inefficient compared to that with the sulfoxide. Thus, the
resulting relative reactivity of SO/S was 8.6, reflecting
the nucleophilic nature of typical CO’s.2b;6 In contrast,
the resulting SO/S ratio for intermediate(s) from p-anisyl
diazomethane 3b was as low as ca. 1. Now it is appar-
ent that the transient species observed by the laser
flash spectroscopy is dianisyl CO (5b, Ar ¼ p-anisyl) but
the intermediate trapped by additives is another one,
that is, DO 6b. This may be rationalized since the life-
time of 10ꢀ8 s is too short to be trapped intermole-
cularly. DO’s are known to be a potent electrophilic
oxidant4;16 and hence the sulfide and sulfoxide were
oxidized equally efficiently, resulting in the SO/S ratio
of ca. 1.
When methanol was added in the photooxidation of 3b,
the resulting product was a-methylhydroperoxide (7b,
Ar2C(OMe)OOH).17 The formation of 7b seems to be
evidence for the trapping of CO intermediates as re-
ported repeatedly.2 In the present case, however, it is
not the case. This is because the reaction of diphenyl
CO’s with alcohols is a much slower reaction (e.g., the
second-order rate constant of ca. 104 Mꢀ1 sꢀ1
12b
)
and
because the lifetime of CO 5b is too short to be trapped
intermolecularly. An assumption of the very fast (i.e.,
close to the diffusion control rate) reaction between 5b
and MeOH is not reasonable since the p-anisyl
substituent is well known to reduce significantly the
reactivity of cationic species with nucleophiles.18
Thus, the acceptable conclusion here is such that
)
and that the resulting 6b reacts with the additives,
that is, the O-transfer (Eq. 2a) and the addition of
Figure 2. Formation and decay of dianisyl CO (5b, Ar ¼ p-MeOC6H4),
as monitored at 410 nm, by the laser flash (308 m) for 3b in acetonitrile
under oxygen at 25 ꢁC. The decay line is obtained according to
k1 ¼ 4:5 ꢁ 107 sꢀ1. Inset: the transient spectra obtained 17.5 ns after the
flash.
the cyclization of 5b to 6b is facile (k1 ¼ 3:9 ꢁ 107 sꢀ1

H. Hanaki et al. / Tetrahedron Letters 45 (2004) 5791–5793
5793
3. Murray, R. W.; Jeyaraman, R. J. Org. Chem. 1985, 50,
2847.
O - Transfer
(2a)
(2b)
_
O
O
O
+
Ar2C
6b
Ar2C = O
4. (a) Murray, R. W. Chem. Rev. 1989, 89, 1187; (b) Adam,
W.; Curci, R.; Edwords, J. O. Acc. Chem. Res. 1989, 22,
205; (c) Adam, W.; Hajiiarapoglou, L. P.; Curci, R.;
Mello, R. In Organic Peroxides; Ando, W., Ed.; Wiley:
New York, 1992; p 195.
5. (a) Yamaguti, K.; Takada, K.; Otsuji, Y.; Mizuno, K. In
Organic Peroxides; Ando, W., Ed.; Wiley: New York,
1992; p 1; (b) Ishiguro, K.; Nojima, T.; Sawaki, Y. J. Phys.
Org. Chem. 1997, 10, 787; (c) Ishiguro, K.; Sawaki, Y.
Bull. Chem. Soc. Jpn. 2000, 73, 535.
OOH
OMe
Ar2 C
MeOH
5b
7b
methanol (Eq. 2b). The latter reaction is speculated to
be facile since the ring-opening reaction of 6b is facili-
tated by the release of three-membered ring strain, by
the hydrogen bonding between the ring oxygen and
MeOH, and by the stabilization of carbocation by
p-anisyl group. An attempted detection of 6b by 13C
NMR method was unsuccessful, which means that the
lifetime of 6b is not enough to be detected.
6. Sawaki, Y.; Kato, H.; Ogata, Y. J. Am. Chem. Soc. 1981,
103, 3832.
7. (a) Sander, W.; Schroeder, K.; Muthusamy, S.; Kirschfeld,
A.; Kappert, W.; Boese, R.; Kraka, E.; Sosa, C.; Cremer,
D. J. Am. Chem. Soc. 1997, 119, 7265; (b) Sander, W.;
Block, K.; Kappert, W.; Kirschfeld, A.; Muthusamy, S.;
Schroeder, K.; Sosa, C. P.; Kraka, E.; Cremer, D. J. Am.
Chem. Soc. 2001, 123, 2618.
8. Kopecky, K. R.; Xie, Y.; Molina, J. Can. J. Chem. 1993,
71, 272.
9. Ishiguro, K.; Hirabayashi, K.; Nojima, T.; Sawaki, Y.
Chem. Lett. 2002, 796.
10. Platz, M. S.; Maloney, V. M. In Kinetics and Spectroscopy
of Carbenes and Biradicals; Platz, M. S., Ed.; Plenum: New
York, 1990; p 250.
11. (a) Casal, H. L.; Sugamori, S. E.; Scaiano, J. C. J. Am.
Chem. Soc. 1984, 106, 7623; (b) Casal, H. L.; Tanner, M.;
Werstiuk, N. H.; Scaiano, J. C. J. Am. Chem. Soc. 1985,
107, 4616; (c) Scaiano, J. C.; McGimpsey, W. G.; Casal,
H. L. J. Org. Chem. 1989, 54, 1612.
The thermal isomerization of CO’s to more stable DO’s
is known not to occur because of the high cyclization
energy of >80 kJ molꢀ1 and hence the two active oxygen
species are regarded as the separate intermediates.2;4;5
A
few exceptional cases are CO’s with a-methoxyl8 and
a-amino substituents,9 where the products analysis
indicated the cyclization to DO’s. The present study on
the trapping and laser-flash experiments reveals clearly
that the cyclization of diaryl CO’s becomes facile by
substituting the resonance-stabilizing group. The acti-
vation enthalpy for the isomerization of CO (8) to DO
(10) was analyzed by a DFT/PM3 method.19 Since the
anisyl group is too big for the calculation, CO’s with a-
MeO group were analyzed (Eq. 3, R1 and/or R2 ¼ MeO).
12. (a) Makihara, T.; Nojima, T.; Ishiguro, K.; Sawaki, Y.
Tetrahedron Lett. 2003, 44, 865; (b) Hanaki, H.; Fukatsu,
Y.; Harada, M.; Sawaki, Y. Tetrahedron Lett. 2004, 45,
2559.
13. Acetonitrile solutions of Ar2CN2 (0.1–0.2 mM) were
irradiated at 308 nm with an Eximer laser. Nano second
laser-flash spectroscopy was carried out as described
previously: (a) Nojima, T.; Ishiguro, K.; Sawaki, Y. J.
Org. Chem. 1997, 62, 6911; (b) Yokoi, H.; Nakano, T.;
Fujita, W.; Ishiguro, K.; Sawaki, Y. J. Am. Chem. Soc.
1998, 120, 12453.
14. Oxygen concentrations in acetonitrile are 9.1 and 1.9 mM
under oxygen and air, respectively: Murov, S. L.; Carmi-
chael, I.; Hug, G. L. Handbook of Photochemistry; Marcel
Dekker: New York, 1993; p 289.
15. Diazomethane 3b was prepared from the corresponding
hydrazone: Smith, L. I.; Howard, K. L. Organic Syntheses;
Wiley: New York, 1955; Collect. Vol. III, p 351.
16. (a) Murray, R. W.; Jeyaraman, R.; Pillay, M. K. J. Org.
Chem. 1987, 52, 746; (b) Adam, W.; Chan, Y.-Y.; Cremer,
D.; Gauss, J.; Scheutzow, D.; Schindler, M. J. Org. Chem.
1987, 52, 2800.
O
_
O
O
O
R
R
1
1
+
R
R
1
C
C
O
C = O
ð3Þ
R
2
R
2
2
8
9
10
The activation enthalpy (DH#) of 64.8 kJ molꢀ1 for the
parent CO (8a, R1 ¼ R2 ¼ H) was decreased down to
48.5 for anti-MeO (8b, R1 ¼ H, R2 ¼ MeO) and to only
8.0 kJ molꢀ1 for dimethoxyl CO (8c, R1 ¼ R2 ¼ MeO). A
small decrease in DH# (i.e., 31.8 kJ molꢀ1) was obtained
for the CO with R1 ¼ MeO and R2 ¼ F, but not for other
cases of dichloro- or difluoro CO (55.6 kJ molꢀ1). These
results indicate that the corporative interaction of two
resonance-stabilizing groups is important to reduce the
relative enthalpy of transition state 9, that is, the acti-
vation energy for the cyclization. In other words, the
introduction of two MeO groups is to increase
the importance of 1b with C–O single bond leading to
the facile cyclization to DO’s.
17. Acetonitrile solution of 3.8 mM 3b and 0.3 mM Rose
Bengal was irradiated at >400 nm (Hg lamp) in the
presence of 2.5 M MeOH under oxygen. Products were
extracted from the mixture with water, affording 7b
(Ar ¼ p-MeOC6H4) in 35% yield as analyzed by 1H
NMR (200 MHz, CDCl3) d 3.34 (3H, s), 3.78 (6H, s),
6.9–7.3 (8H, m).
In conclusion, it is shown that the reactivity of CO
intermediates is controlled and turned by the resonance-
stabilizing donor substituent.
References and notes
18. (a) McClelland, R. A. In Organic Reactivity: Physical and
Biological Aspects; Golding, B. T., Griffin, R. J., Maskill,
H., Eds.; Royal Soc. Chem.: Cambridge, 1995; p 301; (b)
Minegishi, S.; Mayer, H. J. Am. Chem. Soc. 2003, 125,
286.
19. A DFT calculation: pBP/DNꢃꢃ/PM3 (Spartan). Spartan
package: MacSpartan Plus 2.0, Wavefunction, Irvine, CA
92612.
1. Bailey, P. S. In Ozonation in Organic Chemistry; Aca-
demic: New York, Vol. 1, 1978; Vol. 2, 1982.
2. (a) Sander, W. Angew. Chem., Int. Ed. Engl. 1990, 29, 344;
(b) Bunnelle, W. H. Chem. Rev. 1991, 91, 335; (c)
McCullough, K. J.; Nojima, M. In Organic Peroxides;
Ando, W., Ed.; Wiley: New York, 1992; p 661.