9280 J. Phys. Chem. A, Vol. 104, No. 40, 2000
Snoonian and Platz
SCHEME 3
effect on kp. If 15 were the trappable intermediate, then the lone-
pair of electrons on the nitrogen of pyridine would have to attack
a carbon with a formal negative charge to give adduct 10, thus,
the actual kp value may be considerably smaller than the value
9
-1 -1
of 1-5 × 10 M
s
that is typically used in our laboratory
to deduce the lifetime of singlet carbenes.
Acknowledgment. Support of this work by the NSF (Grant
CHE-9613861) is gratefully acknowledged. One of us (J.R.S.)
gratefully acknowledges support by an Ohio State University
Postdoctoral Fellowship administered by the Graduate School
of The Ohio State University.
References and Notes
(1) (a) Regitz, M.; Maas, G. Diazo Compunds; Academic Press:
Orlando, FL, 1986. (b) 1. (b) Meier, H.; Zeller, P.-K. Angew. Chem., Int.
Ed. Engl. 1975, 14, 32. (c) Kirmse, W. Carbene Chemistry, 2d ed.;
Academic Press: New York, 1971; pp 475-493. (d) Padwa, A.; Chinn, R.
L.; Hornbuckle, S. F.; Zhang, Z. J. J. Org. Chem. 1991, 56, 3271. (e) Ando,
W. In The Chemistry of Diazonium and Diazo Compounds, Part 2; Patai,
S., Ed.; Wiley: New York, 1978; pp 458-475. (f) For a review on the
Wolff rearrangement, see: Gill, G. B. ComprehensiVe Organic Synthesis;
Pergamon Press: Oxford, 1991; Vol. 3, pp 887-912 and references therein.
(
2) (a) Jones, M., Jr.; Ando, W.; Hendrick, M. E.; Kulczycki, A., Jr.;
Howley, P. M.; Hummel, K. F.; Malament, D. S. J. Am. Chem. Soc. 1972,
4, 7469. (b) Kammula, S. C.; Tracer, H. L.; Shevlin, P. B.; Jones, M., Jr.
J. Org. Chem. 1977, 42, 293.
3) Wang, J. L.; Toscano, J. P.; Platz, M. S.; Nikolaev, V.; Popic, V.
V. Conclusions
9
The photochemistry of 1 and 2 was studied. The steady-state
photolysis of 1 in EtOH demonstrates that the primary photo-
products 5 and 3 are produced in a 3:1 ratio, respectively.
Furthermore, none of the product 7 that would result from the
Wolff rearrangement of 1 in EtOH is produced. Thus, the Wolff
rearrangement of 1 gives exclusive migration of SEt over OEt.
LFP studies are consistent with the trapping of an intermediate
with λmax ) 425 nm, attributed to that of ylide 10, likely formed
from the reaction of singlet 9 with pyridine. The deduced
lifetime of both 9 and 13 are essentially the same in Freon-
(
J. Am. Chem. Soc. 1995, 117, 5477.
(4) (a) Platz, M. S.; White, W. R., III.; Modarelli, D. A.; Celebi, S. A.
Res. Chem. Intermed. 1994, 175-193.; (b) Celebi, S. A.; Levya, S.;
Modarelli, D. A.; Platz, M. S. J. Am. Chem. Soc. 1993, 115, 8613. (c)
Modarelli, D. A.; Morgan, S.; Platz, M. S. J. Am. Chem. Soc. 1992, 114,
7034. (d) Wulfman, D. S.; Poling, B.; McDaniel, R. S., Jr. Tetrahedron
Lett 1975, 4519.
(5) (a) Toscano, J. P.; Platz, M. S.; Nikolaev, V.; Popic, V. J. Am.
Chem. Soc. 1994, 116, 8146. (b) Snoonian, J. R.; Zhu, Z.; Platz, M. S.;
Wiberg, K. B. J. Phys. Chem. 2000. Submitted for publication.
(
6) Preliminary results presented at the Physical Organic Chemistry
Gordon Conference, Holderness, NH, June 29-July 4, 1997.
7) The lowest triplet state of diazo ketones has been reported as the
1
13, yet compared to dicarbomethoxycarbene 14, at ambient
3
temperature the lifetime of 9 and 13 was found to be about six
times shorter. Calculations at the B3LYP/6-31 G* level of
theory indicate that the two lowest energy conformers 1A and
(
source of H-abstraction products in other syatems. (a) Weygand, F.;
Schwenke, W.; Bestmann, H. J. Angew. Chem. 1958, 70, 106. (b) Baumann,
N. HelV. Chim. Acta 1972, 55, 2716.
1
B, are those in which the carbonyl moiety bonded to the S-Et
(
8) Platz, M. S.; Modarelli, D. A.; Morgan, S.; White, W. R., III.;
group is cis to the diazo group. This forces the S-Et group
bonded to the cis carbonyl to occupy a trans position relative
to the diazo group. Therefore, in both of these conformations
the migrating SEt group is ideally located to migrate with
displacement of nitrogen. These findings are in agreement with
Mullins, M.; Celebi, S. A.; Toscano, J. P. Prog. React. Kinet. 1994, 19, 93.
(9) Jackson, J. E.; Platz, M. S. In AdVances in Carbene Chemistry;
Brinker, U. H., Ed.; JAI Press: Greenwich, CT, 1994; Vol. 1, pp 89-160.
(10) (a) Kaplan, F.; Meloy, G. K. J. Am. Chem. Soc. 1966, 88, 950. (b)
Kaplan, F.; Mitchell, M. L. Tetrahedron Lett. 1979, 20, 759.
11) Parr, R. G.; Yang, W. Density Functional Theory in Atoms and
Molecules; Oxford University Press: New York, 1989.
12) March, J. AdVanced Organic Chemistry, 3rd. ed.; Wiley and Sons:
New York, 1985; pp 208.
13) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.;
(
10
Kaplan, Meloy, and Mitchell who proposed that the photo-
chemistry of R-diazo ketones could be influenced by confor-
mational factors, and that the photochemical Wolff rearrange-
ment takes place preferentially from the s-cis conformer, in
which displacement of nitrogen concurrent with migration of
R is possible. Possibly contributing to the exclusive migration
of SEt is the involvement of ylide 15 on the reaction coordinate
leading to 5. Although our data are consistent with the trapping
of singlet 9 with pyridine, our results do not rule out the
possibility that we are trapping 15. Thus, the shorter lifetime
for 9 and 13 as compared to 14 may also be a result of a large
(
(
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Gordon, M.; Gonzalez, C.; Pople, J. A., Gaussian 94, Revision D.3;
Gaussian, Inc.: Pittsburgh, PA, 1995
(14) Gritsan, N. P.; Zhai, H. B.; Yuzawa, T.; Karweik, D.; Brooke, J.;
Platz, M. S. J. Phys. Chem. 1997, 101, 2833.