480
Bull. Chem. Soc. Jpn. Vol. 82, No. 4 (2009)
Photolysis of Indandiones in Ar-O2 Matrix
O
O
O
O
Me3Si
O
Me3Si
O
Me3Si
O
Me3Si
O
Me3Si
O
O2
10
O
O
O
O
Me3Si
SiMe3
SiMe3
SiMe3
10
SiMe3
O
O
11
Scheme 6.
1H), 7.05 (dd, J = 8.0 Hz, J = 2.0 Hz, 1H), 6.99 (dd, J = 8.0 Hz,
J = 2.0 Hz, 1H); IR (KBr) ¯max (cm¹1): 1741 (s), 1618 (s). IR (Ar,
10 K) ¯ (cm¹1): 1832 (s), 1753 (s), 1616 (s), 1466 (m), 1325 (m),
accelerated by oxygen. Oxygen is known to enhance the overall
S1 ¼ T1 process.20 Thus, in the presence of oxygen, the
intersystem crossing efficiency of initially generated singlet
state to the triplet is accelerated, which results in the increase in
population of the triplet n,³* state from which ¡-cleavage of
the ketones takes place.
1300 (m), 1070 (m), 1062 (m), 856 (m). UV -
(CH2Cl2) nm
max
(¾/M¹1 cm¹1): 360 (2140), 287.0 (10200). MS m/z 148 [M]+.
1-Methylisatin (1c). Sodium hydride (0.48 g, 12 mmol) free
from mineral oil was added to isatin (1.47 g, 10 mmol) in DMF
(20 mL) under an inert atmosphere. After stirring for 30 min, a
solution of methyl iodide (0.68 g, 11 mmol) in DMF (2 mL) was
added and the solution was stirred at room temperature for 1 h to
give a dark red solution. The reaction was quenched by careful
addition of water (30 mL) and was extracted with dichloromethane.
The dichloromethane layer was washed with distilled water. After
drying the dichloromethane layer and removal of solvent, the
residue was purified by column chromatography. 1-Methylisatin
(1c) was recrystallized from ethanol as yellowish solid, yield 95%,
mp 132-133 °C. Lit.132-134 °C;30 1H NMR (CDCl3): ¤ 7.65 (dd,
J = 7.8 Hz, J = 1.6 Hz, 1H), 7.60 (td, J = 7.8 Hz, J = 1.6 Hz, 1H),
7.14 (td, J = 7.8 Hz, J = 1.6 Hz, 1H), 6.92 (dd, J = 7.8 Hz,
J = 1.6 Hz, 1H); IR (KBr) ¯max (cm¹1): 1747, 1725; IR (Ar,
10 K) ¯ (cm¹1): 1751 (s), 1641 (s), 1475 (m), 1371 (m), 1331
(m), 1159 (w), 1117 (m), 1009 (w), 754 (m) cm¹1. UV -max
(CH2Cl2) nm (¾/M¹1 cm¹1): 426.5 (820), 299.0 (3620), 242.5
(29760). MS m/z 161 [M]+.
Conclusion
The present observation reveals that photolysis of ketones in
oxygen-doped matrix at low temperature provides useful
information concerning the reactivities of ketones toward
type I cleavage. It has been suggested that even a ketone which
appears completely inert toward the cleavage may be analyzed
by employing this method.
Experimental
General Methods.
1H NMR and 13C NMR spectra were
recorded on a Varian GEMINI 200 FT/NMR spectrometer in
CDCl3 with Me4Si as an internal reference. IR spectra were
measured on a Shimadzu FTIR-4800S spectrometer, and UV-vis
spectra were recorded on a Shimadzu UV-2450 spectrophotometer.
The mass spectra were recorded on a Hitachi MS-80B mass
spectrometer. Gel permeation chromatography (GPC) was carried
out on a JASCO model HLC-01 instrument. The GPC column was
a Shodex H-2001. Thin-layer chromatography was carried out on a
Merck Kieselgel 60 PF254. Column chromatography was per-
formed on silica gel (Nacalai tesque) for column chromatography.
Indan-1,2,3-trion (1a). 1a was prepared by heating ninhydrin
at 120 °C for a few hours under reduced pressure and was purified
by sublimation as dark reddish-violet needles, yield 93%, mp
254-255 °C, Lit. mp 255 °C;28 1H NMR (CDCl3): ¤ 8.24-8.18
(m, 2H), 8.12-8.06 (m, 2H); IR (KBr) ¯max (cm¹1): 1771, 1740,
1711; IR (Ar, 10 K) ¯ (cm¹1): 1774 (m), 1751 (s), 1729 (s), 1600
(m), 1239 (m), 1228 (m), 979 (m), 750 (m); UV - max (CH2Cl2) nm
(¾/M¹1 cm¹1): 335.5 (2419), 327.5 (2350), 258.0 (19619). MS
m/z 160 [M]+.
Benzo[b]furan-2,3-dione (1b). To a solution of isatin (1.47 g,
0.01 mol) in 1 M aqueous sodium hydroxide (150 mL) was added
sodium nitrite (0.7 g) and the mixture was stirred under cooling
with an ice bath. To the cold solution, 15 mL of 2.5 M sulfuric acid
was added slowly. The solution was stirred for 10 min and then
warmed to 60 °C and allowed to stand for 1 h with occasional
shaking. The solution was filtered from activated charcoal (0.1 g)
and extracted with ethyl acetate (30 mL). Drying and removal of
the solvent left crude 2-hydroxyphenylglyoxylic acid. The entire
preparation of acid was dissolved in 30 mL of benzene and 20 mL
of heptane. Phosphorus pentoxide (1.5 g) was added and the
mixture was refluxed for 30 min. The solution was filtered and
evaporated to 5 mL. Addition of heptane produced a yellow
solid. Recrystallization from benzene-heptane gave 1b, yield
46%, mp 128-130 °C, lit. 132 °C.29 1H NMR (CDCl3): ¤ 8.12
(dd, J = 8.0 Hz, J = 2.0 Hz, 1H), 7.61 (dd, J = 8.0 Hz, J = 2.0 Hz,
Matrix-Isolation Spectroscopy.
Matrix experiments were
performed by means of standard techniques31,32 using a closed-
cycle helium cryostat. For IR experiments, a CsI window was
attached to the copper holder at the bottom of the cold head. Two
opposing ports of a vacuum shroud surrounding the cold head were
fitted with KBr with a quartz plate for UV irradiation and a
deposition plate for admitting the sample and matrix gas. For UV
experiments, a sapphire cold window and a quartz outer window
were used. The temperature of the matrix was maintained by a
controller (gold vs. chromel thermocouple).
All the samples used in this study were not easily vaporized and
hence were directly deposited on the window from a glass tube
equipped with a ceramic heater under the stream of argon.
Therefore, the concentration of the sample on the window was
different at each run.
Irradiations were carried out with a 500-W xenon high-pressure
arc lamp. For broad-band irradiation, cutoff filters were used (50%
transmittance at the specified wavelength). For monochromatic
light irradiation, a monochrometer was used.
Computational Procedures. DFT calculations were carried
out using the Gaussian 94,33 programs. Optimized geometries were
obtained at the B3LYP/6-31G(d)34 levels of theory. Vibrational
frequencies obtained at the B3LYP level of theory were scaled by
0.961 and zero-point energies (ZPE) by 0.981.35 Transition states
were located using Gaussian program (Rational Function Opti-
mization-pseudo-Newton-Raphsonthe method).36 The nature of
each stationary point was confirmed with harmonic frequency
calculations, i.e., minima have exactly one imaginary frequency
related to the expected movement.