Materials
Specially Promoted Research (No. 12002007). Support from
the Mitsubishi Foundation and the Nagase Science and
Technology Foundation is also appreciated.
The preparation of all the diazo compounds and ketones
was reported elsewhere.12,13 TEMPO (Tokyo Kasei, >98.0%),
4-hydroxy-TEMPO (Hakuto Chemicals, >99.0%), 4-methoxy-
TEMPO (Tokyo Kasei, >98.0%) and 4-oxo-TEMPO (Tokyo
Kasei, >95.0%) were purchased from commercial sources and
used without further purification.
References
1 See for instance J. E. Leffler, An Introduction to Free Radicals, Wiley,
New York, 1993.
2 J. Chateauneuf and K. U. Ingold, J. Org. Chem., 1988, 53, 1629.
3 A. L. J. Beckwith and V. W. Bowry, J. Org. Chem., 1988, 53, 1632.
4 A. L. J. Beckwith, V. W. Bowry and K. U. Ingold, J. Am. Chem. Soc.,
1992, 114, 4983.
5 V. W. Bowry and K. U. Ingold, J. Am. Chem. Soc., 1992, 114, 492.
6 T. J. Connolly, M. V. Baldovi, N. Mohtat and J. C. Scaiano,
Tetrahedron Lett., 1996, 37, 4919.
7 H. L. Casal, N. H. Werstiuk and J. C. Scaiano, J. Org. Chem., 1984,
49, 5214.
8 E. A Lissi, J. C. Scaiano and A. E. Villa, Chem. Commun., 1971, 475.
9 G. B. Watts, D. Griller and K. U. Ingold, J. Am. Chem. Soc., 1972,
94, 8784.
10 H. Tomioka in Reactive Intermediates Chemistry, ed. R. A. Moss,
M. S. Platz and M. Jones, Jr., Wiley, New York, 2003, ch. 9.
11 See for reviews (a) H. Tomioka, Acc. Chem. Res., 1997, 30, 315;
(b) H. Tomioka, in Advances in Carbene Chemistry, ed. U. Brinker,
JAI Press, Greenwich, CT, 1998, vol. 2. pp. 175–214; (c) H. Tomioka,
in Advances in Strained and Interesting Organic Molecules, ed.
B. Halton, JAI Press, Greenwich, CT, 2000, vol. 8, pp. 83–112;
(d ) H. Tomioka, in Carbene Chemistry, ed. G. Bertrand, Fontis
Media S. A., Lausanne, 2002, pp. 103–152.
12 (a) H. Tomioka, K. Hirai and C. Fujii, Acta Chem. Scand., 1993, 46,
680; (b) H. Tomioka, K. Hirai and T. Nakayama, J. Am. Chem. Soc.,
1993, 115, 1285; (c) M. Kawano, K. Hirai, H. Tomioka and
Y. Ohashi, J. Am. Chem. Soc., 2001, 123, 6904.
Irradiation for product analysis
In a typical run, a solution of the diazo compound (1, ca. 10
mg) and TEMPO (10 equiv.) in solvent was placed in a Pyrex
tube and irradiated with a high-pressure, 300 W mercury lamp
until all the diazo compound was destroyed. The irradiation
mixture was then concentrated on a rotary evaporator below
20 ЊC. Individual components were isolated by preparative TLC
and identified by NMR and MS.
Flash photolysis
All flash measurements were made on a Unisoku TSP-601 flash
spectrometer. A Lamda Physik LEXTRA XeCl excimer laser
(308 nm pulses of up to 200 mJ per pulse and 17 ns duration)
was used as an excitation lamp. The beam shape and size were
controlled by a focal length cylindrical lens.
A Hamamatsu 150 W xenon short-arc lamp (L 2195) was
used as the probe source, and the monitoring beam, guided with
an optical fiber scope, was arranged perpendicular to the
excitation source. The probe beam was monitored with
a
Hamamatsu R2949 photomultiplier tube through a
13 (a) H. Tomioka, T. Watanabe, K. Hirai, K. Furukawa, T. Takui and
K. Itoh, J. Am. Chem. Soc., 1995, 117, 6376; (b) H. Tomioka,
M. Hattori and K. Hirai, J. Am. Chem. Soc., 1996, 118, 8723;
(c) H. Tomioka, T. Watanabe, M. Hattori, N. Nomura and K. Hirai,
J. Am. Chem. Soc., 2002, 124, 474.
14 See for review (a) W. Sander, Angew. Chem., Int. Ed. Engl., 1990, 29,
344; (b) W. Bunnelle, Chem. Rev., 1991, 91, 336.
Hamamatsu S3701-512Q MOS linear image sensor (512
photodiodes used). Timing of the excitation pulse, the probe
beam, and the detection system was achieved through an
Iwatsu Model DS-8631 digital synchro scope, which was
interfaced to an NEC 9801 RX2 computer. This allowed for
rapid processing and storage of the data and provided
printed graphic capabilities. Each trace was also displayed on
an NEC CRT N5913U monitor.
A sample was placed in a long-necked Pyrex tube with a side
arm connected to a quartz fluorescence cuvette and degassed
using a minimum of four freeze–degas–thaw cycles at a pressure
near 10Ϫ5 Torr immediately prior to being flashed. The sample
system was flame-sealed under reduced pressure, and the
solution was transferred to the quartz cuvette, which was placed
in the sample chamber of the flash spectrometer. A cell holder
block of the sample chamber was equipped with a thermostat
and allowed to come to thermal equilibrium. The concentration
of the sample was adjusted so that it absorbed a significant
portion of the excitation light.
15 J. C. Scaiano, W. G. McGimpsey and H. L. Casal, J. Org. Chem.,
1989, 54, 1612.
16 For reviews, see (a) M. S. Platz, Kinetics and Spectroscopy of
Carbenes and Biradicals, Plenum, New York, 1990; (b) J. E. Jackson
and M. S. Platz, in Advances in Carbene Chemistry; ed. U. Brinker,
JAI Press, Greenwich, CT, 1994, vol. 1, pp. 87–160; (c) See also,
G. L. Closs and B. E. Rabinow, J. Am. Chem. Soc., 1976, 98, 8190.
17 L. M. Hadel, V. M. Maloney, M. S. Platz, W. G. McGimpsey and
J. C. Scaiano, J. Phys. Chem., 1986, 90, 2488.
18 (a) H. Tomioka, E. Iwamoto, H. Itakura and K. Hirai, Nature, 2001,
412, 626; (b) E. Iwamoto, K. Hirai and H. Tomioka, J. Am. Chem.
Soc., 2003, 125, 14664.
19 (a) T. Iwamoto, H. Masuda, S. Ishida, C. Kabuto and M. Kira,
J. Am. Chem. Soc., 2003, 125, 9300; (b) T. Iwamoto, H. Masuda,
S. Ishida, C. Kabuto and M. Kira, J. Organomet. Chem., 2004, 689,
1337.
20 It is possible that amino radicals may react with triplet carbenes, but
in the present case, the reaction of sterically congested triplet
diarylcarbene with sterically crowded amino radical, i.e.,
tetramethylpiperidinyl radical, is not considered to be efficient. Also
the concentration of the amino radical must be low in the light of its
lifetime.
21 M. J. Frisch, G. W. Trucks, B. Schlegel, P. M. Gill, B. G. Johnson,
M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson,
J. A. Montgomery, K. Raghavachari, M. A. Al-Laham,
V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, J. Cioslowski,
B. B. Stefanov, A. Nanayakkara, M. Challacombe, C. Y. Peng,
P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle,
R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. DeFrees,
J. Baker, J. J. P. Stewar, M. Head-Gordon, C. Gonzalez and
J. A. Pople, GAUSSIAN 94, Gaussian Inc.: Pittsburgh, PA, 1995.
22 (a) C. Lee, W. Yang and R. G. Parr, Phys. Rev. B, 1988, 37, 785; (b)
B. Miehlich, A. Savin, H. Stoll and H. Preuss, Chem. Phys. Lett.,
1989, 157, 200; (c) A. D. Becke, J. Chem. Phys., 1993, 98, 5648.
23 A. P. Scott and L. Radom, J. Phys. Chem., 1996, 100, 16502.
24 J. Simons, P. Jorgensen, H. Taylor and J. Ozment, J. Phys. Chem.,
1983, 87, 2745.
Computational procedures
DFT calculations were carried out using the GAUSSIAN 94,21
programs. Optimized geometries were obtained at the B3LYP/
6-31G(d)22,23 levels of theory. Vibrational frequencies obtained
at the B3LYP level of theory were scaled by 0.961 and
zero-point energies (ZPE) by 0.981.23 Transition states were
located using Gaussian program (Rational Function Optim-
ization-pseudo-Newton-Raphsonthe method).24 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.
Acknowledgements
The authors are grateful to the Ministry of Education, Culture,
Sports, Science, and Technology of Japan for support of this
work through a Grant-in-Aid for Scientific Research for
O r g . B i o m o l . C h e m . , 2 0 0 4 , 2, 1 5 0 0 – 1 5 0 3
1503