Photolysis of 3-(2-Formylphenyl)-3-chlorodiazirine in an Ar Matrix at Low Temperature

Article abstract of DOI:10.1021/jo049802t

Photolysis of 3-(2-formylphenyl)-3-chlorodiazirine in an Ar matrix at 13 K was monitored by IR and UV-vis spectroscopies. Characterization of the products was carried out by comparing the spectra with the theoretical IR spectra obtained by using DFT, which suggested that anti,anti-2-formylphenyl(chloro)carbenes (a,a-2), ketenes (syn- and anti-3), chlorobenzocyclobutenone (4), and chloroisobenzofurane (5) were formed. This indicates that carbene 2 interacts with both hydrogen and oxygen in the formyl group. When the matrix containing a,a-2 was allowed to stand in the dark at 13 K, a gradual increase of the band due to anti-ketene 3 at the expense of 2 was observed. In contrast to its protio analogue, the deuterated carbene 2-d showed almost no changes either for the decay of 2-d or the growth of 3-d within the time range where the protio analogue appreciably decayed. These observations are interpreted in term of a quantum mechanical tunneling mechanism.

Full text of DOI:10.1021/jo049802t

P h otolysis of 3-(2-F or m ylp h en yl)-3-ch lor od ia zir in e in a n Ar Ma tr ix
a t Low Tem p er a tu r e
Norio Nakane, Tomonori Enyo, and Hideo Tomioka*
Chemistry Department for Materials, Faculty of Engineering, Mie University, Tsu, Mie 514-8507, J apan
tomioka@chem.mie-u.ac.jp
Received February 4, 2004
Photolysis of 3-(2-formylphenyl)-3-chlorodiazirine in an Ar matrix at 13 K was monitored by IR
and UV-vis spectroscopies. Characterization of the products was carried out by comparing the
spectra with the theoretical IR spectra obtained by using DFT, which suggested that anti,anti-2-
formylphenyl(chloro)carbenes (a,a-2), ketenes (syn- and anti-3), chlorobenzocyclobutenone (4), and
chloroisobenzofurane (5) were formed. This indicates that carbene 2 interacts with both hydrogen
and oxygen in the formyl group. When the matrix containing a,a-2 was allowed to stand in the
dark at 13 K, a gradual increase of the band due to anti-ketene 3 at the expense of 2 was observed.
In contrast to its protio analogue, the deuterated carbene 2-d showed almost no changes either for
the decay of 2-d or the growth of 3-d within the time range where the protio analogue appreciably
decayed. These observations are interpreted in term of a quantum mechanical tunneling mechanism.
The chemistry of carbenes constitutes a central topic
in the study of reactive intermediates under matrix
conditions, since they can be easily and cleanly gener-
This paper is a report of our attempt to generate
2-formylphenylchlorocarbene, which is expected to react
1
4
either with formyl oxygen, leading to a furan, or with
ated by photolysis of the corresponding nitrogenous
precursors even at very low temperature in a rigid
matrix. They are neutral and divalent and, hence, are
forced to find some routes to normal tetravalent com-
pounds with only their own resources, without taking
external bonding or electrons, under these highly uni-
molecular conditions. For instance, the photolysis of
phenyldiazomethane in Ar at 10 K results in the genera-
tion of phenylcarbene in its triplet ground state. The
triplet carbene exists infinitely as long as the matrix
conditions are retained and is further excited upon
continued irradiation to produce 1,2,4,6-cycloheptatet-
raene. The tetraene regenerates the carbene upon ir-
radiation under these conditions.2
It is possible to divert the rearrangement from a
slippery energy surface to some other energy surfaces if
a functional group is introduced around the divalent
center. Since carbenes are highly energetic molecules,
such reactions often lead to highly reactive species with
exotic bond modes. Actually, a series of new reactive
formyl hydrogen, producing a ketene.5
Resu lts a n d Discu ssion
3-(2-Formylphenyl)-3-chlorodiazirine 1 was deposited
in an Ar matrix at 20 K and irradiated (λ ) 341 nm) at
13 K. The progress of the reaction was monitored by IR
spectroscopy, which indicated that the peaks due to the
-
1
carbonyl and diazirine groups (1709 and 1602 cm
,
respectively) appeared to diminish simultaneously in
intensity as new absorption bands were observed. A
careful analysis of those product absorption bands by
plotting their intensities as a function of the irradiation
time and wavelength of light revealed that there were
at least six major products, designated A to F (Figures 1
and 2). Among those products, B and C were featured
-
1
by strong, sharp bands at 2105 and 2093 m , respec-
tively, probably ascribable to cumulated double bonds,
whereas A, D, and E showed bands at 1705, 1815, and
-
1
1
788 cm , respectively, due to a carbonyl group. That
two ketene bands are ascribable to two different species,
not due to site effect or Ferimi resonance, is also
confirmed on the basis of the dependence of the intensi-
ties on the irradiation time and wavelength of the light.
To characterize those products, DFT calculations were
carried out at the B3LYP/6-31G(d) level of theory. First,
species has been generated and characterized using the
reaction routes.3
(1) See for reviews: (a) Dunkin, I. R. Chem. Soc. Rev. 1980, 9, 1. (b)
Sheridan, R. S. Organic Photochemistry; Padwa, A., Ed.; Dekker: New
York, 1987; Vol. 8, pp 159-248. (c) Sander, W.; Bettinger, H. F. In
Advances in Carbene Chemistry; Brinker, U., Ed.; J AI Press: Green-
wich, CT, 2001; Vol. 3, pp 160-203. (d) Sander, W.; Kirschfeld, A. In
Advances in Strain and Organic Chemistry; Halton, B., Ed.; J AI
Press: Greenwich, CT, 1995; Vol. 4, pp 1-80. (e) Sander, W. In Carbene
Chemistry; Bertrand, Ed.; Fontis Media S.A.: Lausanne, 2002, pp
(3) (a) See for review: Tomioka, H. Bull. Chem. Soc. J pn. 1998, 71,
1501. (b) Nicolaides, A.; Tomioka, H. In Photochemistry of Organic
Molecules in Isotropic and Anisotropic Media; Ramamurthy, V.,
Schanze, K. S. Eds.; Marcel Dekker: New York, 2003; pp 133-184.
(4) (Methoxycarbonyl)phenylcarbene gave the corresponding furan
as a result of the interaction of the carbenic center with carbonyl
oxygen. Murata, S.; Ohtawa, Y.; Tomioka, H. Chem. Lett. 1989, 853.
(5) Methylphenylcarbene generated o-quinodimethane as a result
of 1,4-H migration from methyl hydrogen to the carbenic center.
McMahon, R. J .; Chapman, O. L. J . Am. Chem. Soc. 1987, 109, 683.
1
-25. (f) Maier, G.; Reisenauer, H. P. In Advances in Carbene
Chemistry; Brinder, U., Ed.; J AI Press: Greenwich, CT, 2001; Vol. 3,
pp 116-157.
(2) West, P. R.; Chapman, O. L.; LeRoux, J . P. J . Am. Chem. Soc.
1
982, 104, 1778.
1
0.1021/jo049802t CCC: $27.50 © 2004 American Chemical Society
Published on Web 04/23/2004
3
538
J . Org. Chem. 2004, 69, 3538-3545

Photolysis of 3-(2-Formylphenyl)-3-chlorodiazirine
F IGURE 1. (a) Total IR spectra of 1 before irradiation. (b) Difference IR spectrum between the photoproduct formed after 95 s
of irradiation (λ ) 341 nm) of 1 (negative peaks) and 1 before irradiation (positive peaks). (c, d) Calculated (B3LYP/6-312G(d))
spectra for anti,anti-2-formylphenyl(chloro)carbene (a,a-2) (c) and anti-ketene (a-3) (d).
the geometries of plausible products expected to be
formed in the photolysis of 1 were optimized, and the
vibrational frequencies were calculated. They are singlet
The optimized structures indicate that whereas the a,a-
isomer has almost completely planar structure, in its
s,a-2 isomer, the C-Cl bond at the carbene and C-H
bond of the formyl groups are rotated by 29.6 and 16.9
degree, respectively, from the phenyl plane as a result
of through space interaction between anti-Cl and formyl
hydrogen. This can explain the stability difference be-
tween the two isomers. Ketenes 3 are calculated to be
less stable than their cyclic isomer, butanone 4, by ca.
2
-formylphenyl(chloro)carbenes (2), ketenes (syn- and
anti-3), chlorobenzocyclobutenone (4), and chloroisoben-
zofurane (5) (Figure 3 and Table 1). Among four possible
1
7-20 kcal/mol. On the other hand, furan 5 is found to
be very close in energy to butanone 4. In this respect, it
is interesting to note that, in 4, ring strain is evident from
elongated bond lengths in the four-membered ring, while
partial loss of aromaticity is apparent from bond alterna-
tion in the benzene ring of 5.
A comparison of the experimental spectrum with that
calculated for possible products suggested that A is most
likely the anti,anti-isomer of carbene (a,a-2), B and C are
assignable to anti- and syn-ketene (a-3 and s-3, respec-
tively), and D and F are probably due to cyclobutenone
4
and furan 5, respectively (Figures 1 and 2). The band
-
1
at 1717 cm
predicted in A was not obvious in the
experimental spectrum in the figures owing to the strong
-1
starting material band at 1709 cm . However, this band
became apparent in the difference spectra before and
after standing in dark (vide infra; Figure S1, Supporting
-
1
Information). Also, a predicted band at 1360 cm in F
was not apparent in the experimental spectrum again
owing to the strong starting material band, but this band
showed up more clearly after prolonged irradiation
(Figure S2, Supporting Information). The formation of
the furan was further supported by the UV-vis spectral
observation that a peak shape and fine structure very
rotamers of carbenes 2, anti(C-Cl),syn(CdO)- and
syn,syn-isomers (a,s- and s,s-2, respectively) were not
optimized (see below). The most stable conformer was
calculated to be anti,anti-isomer (a,a-2), while syn,anti-
isomer (s,a-2) was located 4.08 kcal/mol higher in energy.
6
similar to those of the parent molecule were observed
upon irradiation of 1 (Figure 4). The assignments were
J . Org. Chem, Vol. 69, No. 10, 2004 3539

Nakane et al.
F IGURE 2. Photolyis of 1 in Ar at 13 K. (a) Difference IR spectrum between the photoproduct formed after 500 s of irradiation
(
λ ) 341 nm) of 1 (negative peaks) and 1 before irradiation (positive peaks). (b-d) Calculated (B3LYP/6-312G(d)) spectra for
syn-ketene (s-3) (b), cyclobutenone(4) (c), and isobenzofuran(5) (d).
F IGURE 3. Selected geometrical parameters (distances in Å and angles in deg) for a,a-2, s,a-2, a-3, s-3, 4, and 5 at the B3LYP
level of theory. Only important angles are indicated here for sake of clarity.
further supported by isotopic shift by deuterated deriva-
tives (vide infra). All attempts to characterize E were
unsuccessful.
ketene (a-3) were detected. After 65 s of irradiation, the
bands due to syn-ketene (s-3), cyclobutenone 4, and furan
5
became apparent along with continued increase in the
Monitoring of the spectral changes as a function of the
irradiation time provided information on the reaction
pathway. Thus, at the very initial stage (after 20 s of
irradiation), the bands due to carbene (a,a-2) and anti-
bands due to a,a-2 and a-3. Upon further irradiation, all
the bands continued to grow but the band due to carbene
stopped increasing at around 300 s irradiation while
other bands still kept growing. The following experiments
indicated that ketenes and cyclobutanone were in pho-
toequilibrium. Thus, irradiation with a longer wavelength
(6) (a) Wege, D. Tetrahedron Lett. 1971, 2337. (b) Warrener, R. N.
J . Am. Chem. Soc. 1971, 93, 2346.
3
540 J . Org. Chem., Vol. 69, No. 10, 2004

Photolysis of 3-(2-Formylphenyl)-3-chlorodiazirine
TABLE 1. Tota l (h a r tr ee) a n d Rela tive (k ca l/m ol)
En er gies of a ,a -2, s,a -2, a -3, s-3, 4, a n d 5 a t th e B3LYP
a
Level of Th eor y
total energies
(hartree)
relative energies
(kcal/mol)
compound
a,a-2 (singlet)
s,a-2 (singlet)
a-3
s-3
4
-843.05554
-843.049034
-843.10347
-843.10740
-843.13435
-843.13379
0
4.08
-30.49
-33.01
-51.63
-50.87
5
a
With the 6-31G(d) basis set and including ZPE corrections
based on the frequencies scaled by 0.981.
F IGURE 5. Plot of decay of the band due to a,a-2 and a,a-
-d and the growth of the band due to a-3 and a-3-d as a
2
1
/2
function of time (h ) in dark at 13 K.
9
yet, in contrast with that of frequencies. The reliability
of the examination was thus checked by estimating the
total amount of generated 3, 4, and 5 versus the amount
of reacted 2 by using calculated IR intensities. The total
amount of the product formation is estimated to be 78 (
F IGURE 4. UV-vis spectrum obtained by irradiation (λ )
4
% for seven measured points.
3
41 nm) of 1 in Ar at 13 K.
Additional calculations gave some more details. The
rotation of the formyl group in anti,anti-carbene 2 along
the C-C bond so as to generate an anti,syn-isomer
always led to the formation of furan 5. This, along with
the fact that optimization of a,s- and s,s-2 always resulted
in the formation of 5, suggests that carbene center
efficiently interacts with carbonyl oxygen when the
oxygen is located at the syn conformation. Presumably,
the isomerization of the anti,anti-isomer of 2 upon
excitation led spontaneously to the formation of 5.
The transition state (TS) for the formation of the
ketene 3 was computed. The transition structure (Figure
6) for the migration shows that the geometry is es-
sentially planar with the breaking and forming CH bond
distances of 1.278 and 1.482 Å, respectively. An only
slight increase on going from the starting ant,anti-
carbene 2 to the breaking bond length in the TS (i.e., from
light resulted in the increase in the band due to 4 at the
expense of the band due to 3, whereas irradiation with a
shorter wavelength light favored the formation of 3.
From these observations, the formation of furan 5 and
anti-ketene 3 is most probably explained in terms of the
4
5
interaction of carbene with carbonyl oxygen and H in
the ortho formyl group, respectively, upon excitation,
while cyclobutenone 4 is derived as a result of the
photocyclization7 of ketenes 3. The formation of anti-
ketene 3 at the very initial stage of the irradiation
suggests, on the other hand, that some of this ketene is
also formed from the excited state of diazirine.8
Those observations indicate that carbene 2 can interact
with both reactive site in the formyl group. Then it is
interesting to examine the difference in reactivity of 2
toward hydrogen versus carbonyl oxygen. This can be
estimated by calibrating the ratio of the absorbance of
1
.100 to 1.278 Å) indicates an early product like TS. The
calculated activation energy is 8.5 kcal/mol. These cal-
culations support the estimated ratio of H abstraction
to oxygen attack.
The calculated barrier for H abstraction also means
that thermal migration will not be possible, at least at
-
1
-1
ketenes 3 (2105 cm ), cyclobutanone 4 (1814 cm ), and
-
1
furan 5 (1003 cm ) to that of theoretically predicted
intensity (1048, 412, and 61 km/mol for 3, 4 and 5,
respectively). Such treatments gave the ratio of the H
abstraction (3 + 4) to oxygen attack (5) to be 1:6.8.
Significant preference for oxygen attack over H abstrac-
tion is thus noted. It should be noted here that the
reliability of calculated IR intensities are not established
1
3 K. However, when the matrix containing a,a-2 (1217
-1
cm ) was allowed to stand in the dark at 13 K, a gradual
increase of the band due to anti-ketene 3 (2105 cm ) at
the expense of the band due to 2 was observed. The decay
-
1
(
9) See for instance: (a) Radziszewski, J . G.; Nimlos, M. R.; Winter,
(
7) (a) Chapman, O. L.; McIntosh, C. L.; Pacansky, J .; Calder, G.;
P. R.; Ellison, G. B. J . Am. Chem. Soc. 1996, 118, 7400. (b) Friderich-
sen, A. V.; Radziszewski, J . G.; Nimlos, M. R.; Winter, P. R.; Dayton,
D. C.; David, D. E.; Ellison, G. B. J . Am. Chem. Soc. 2001, 123, 1977.
(c) Komornicki, A.; J affe, R. L. J . Chem. Phys. 1979, 71, 2150. (d)
Yamaguchi, Y.; Frisch, M.; Gaw, J .; Schaefer, H. F.; Binkley, J . S. J .
Chem. Phys. 1986, 84, 2262.
Orr, G. J . Am. Chem. Soc. 1973, 95, 4061. (b) Chapman, O. L.; Mattes,
K.; McIntosh, C. L.; Pacansky, J .; Calder, G.; Orr, G. J . Am. Chem.
Soc. 1973, 95, 6134.
(8) Modarelli, D. A.; Morgan, S.; Platz, M. S. J . Am. Chem. Soc. 1992,
1
14, 7034.
J . Org. Chem, Vol. 69, No. 10, 2004 3541

Nakane et al.
the formyl proton was deuterated, was prepared and
irradiated under identical conditions. The photolysis of
1
-d gave essentially the same products as in the pho-
tolysis of 1, although the product ratios were somewhat
different (Figures 7 and 8). Thus, the formation of
ketenes (3-d), cyclobutenone (4-d) and benzofuran (5-d)
along with carbene (a,a-2-d) were again confirmed by
comparing the spectra with those calculated by DFT.
Predicted isotopic shift by deuteration was also noted in
-
1
this case. For instance, for a,a-2, the band at 1717 cm
-
1
was predicted to shift to 1695 cm (Tables S2 and S7,
Supporting Information). The band at 1705 cm was
actually shifted to 1680 cm . Similarly, for 5, the
band at 1417 cm (predicted at 1402 cm ) was shifted
to 1403 cm (predicted at 1388 cm ) (Tables S6 and
S11, Supporting Information). The ratio of the H abstrac-
tion (3-d + 4-d) to oxygen attack (5-d) was estimated
to be 1:4.3 in this case. This value, when compared
with the value observed in the photolysis of its protio
analogue, indicates that kinetic deuterium isotope effect
in the reaction involving photochemical process is rather
small.
-
1
-
1
F IGURE 6. Selected geometrical parameters (distance in Å
and angles in deg) for transition state for hydrogen migration
at the RB3LYP level of theory. Only important angels are
indicated for the sake of clarity.
-
1
-1
-
1
-1
of the IR bands due to carbene 2 and the growth of those
ascribable to ketene 3 were monitored as a function of
time (Figure 5). The kinetics of the processes were
1
/2
analyzed in terms of the usual (time) dependence for
solid-state reactions.1
0,11
Neither first-order nor second-
order kinetics fit the data well. The rate constants for
Upon leaving the matrix in the dark for 11 h, little
change in the spectrum was observed. In contrast to its
protio analogue, the deuterated carbene 2-d, when plot-
ted, clearly showed almost no changes either for the decay
of 2-d (1195 cm ) or the growth of 3-d (2102 cm ) within
the time range where the protio analogue appreciably
decayed (Figure 5). It was stable up to 19 K; at higher
the decay of 2 and the growth of 3 were estimated to be
-4
-1/2
-5 -1/2
1
.5 × 10
s
and 7.7 × 10
s
, respectively. The rate
of the ketene growth is, however, slower compared with
that of the carbene decay. This may suggest that the
thermal decay of carbene leads to other product as well.
However, no appreciable changes in the absorption bands
of other products were noted to the limit of our IR
detection. Moreover thermal decay of the carbene was
practically stopped when the fromyl hydrogen was re-
placed with deuterium (vide infra). Although we do not
understand the discrepancy in the rate, we think that 2
abstracts H from o-formyl group to produce 3 in dark at
this low temperature, at least in part.
-1
-1
temperatures, the matrix softened. Thus, we were unable
16
D
to accurately measure k .
The present observations, the appreciable thermal H
migration at very low temperature and apparently large
KDIE, suggest that a quantum mechanical tunneling
mechanism is likely to be involved in the present reac-
tion. It will be necessary, however, to examine the
temperature dependence of the rate constant for the
hydrogen migration in order to confirm this mechanism
more definitely. Because argon matrix softens above 19
K, one needs to use other less volatile matrix, e.g., xenon,
to obtain kinetic data in wider temperature ranges. H
atom tunneling in carbene reactions is relatively well
documented.1 The most relevant example of the present
reaction is 1,4-H migration in triplet 2-methylphenyl-
carbene, leading to o-quinodimethane at low tempera-
ture. A critical difference between the two is the multi-
plicity of the carbene involved. Although the triplet state
One can estimate the rate constant for a classical H
transfer at low temperature by using kinetic parameters
obtained in solution. The absolute kinetics of the 1,2 H
shift of a series of alkylhalocarbenes have been measured
by laser flash photolysis.12 These studies gave the activa-
tion energies of 2-6 kcal/mol and the preexponential
8
-1
factors of ca. 10 s . From these values, the rate constant
3,14
-
26
-92
at 13 K is predicted to be about 2.6 × 10
to 5.3 × 10
-1
s
. The energy barrier for 1,4 H shift in 2 was calculated
to be higher than those values. This suggests that the
reaction should not occur at 13 K. Thus, the observed
appreciable decay of 2 and growth of 3 even at 13 K in
the dark suggest that the tunneling pathway is involved
in this migration.13,14
(13) Intermolecular H atom abstractions of triplet carbenes have
been shown to proceed by a QMT mechanism at very low temperature.
See for reviews: (a) Platz, M. S. Acc. Chem. Res. 1988, 21, 236. (b)
Tomioka, H. Res. Chem. Intermed. 1994, 20, 605. (c) Platz, M. S. In
Kinetics and Spectroscopy of Carbenes and Biradicals; Platz, M. S.,
Ed.; Plenum: New York, 1990; pp 143-212. (d) Tomioka, H. In Reactive
Intermediate Chemistry; Moss, A. M., Platz, M. S., J ones, M., J r., Eds.;
Wiley: New York, 2004; pp 375-461.
Tunneling is featured by four kinetic phenomena, i.e.,
a large kinetic isotope effect, a nonlinear Arrhenius plot,
a large difference in the activation energies, and the
1
5
preexponential factors for H and D transfers.
To obtain the kinetic deuterium isotope effect (KDIE)
on this process, formylphenylchlorodiazirine 1-d, in which
(
14) Intramolecular H atom abstractions of carbenes are also known.
a) Wierlacher, S.; Sander, W.; Liu, M. T. H. J . Am. Chem. Soc. 1993,
15, 8943. (b) Zuev, P. S.; Sheridan, R. S. J . Am. Chem. Soc. 1994,
(
1
(
10) Intermolecular solid-state reactions of carbene generally exhibit
116, 4123. (c) Dix, E. J .; Herman, M. S.; Goodman, J . L. J . Am. Chem.
Soc. 1993, 115, 10424. See also ref 5.
1
/2
a t dependence due to multiple reaction sites in the solid host. (a)
Senthilnathan, V. P.; Platz, M. S. J . Am. Chem. Soc. 1980, 102, 7637.
(15) (a) Brunton, G.; Griller, D.; Barclay, L. R. C.; Ingold, K. U. J .
Am. Chem. Soc. 1976, 98, 6803. (b) Brunton, G.; Gray, J . A.; Griller,
D.; Barclay, L. R. C.; Ingold, K. U. J . Am. Chem. Soc. 1978, 100, 4197.
(16) We can roughly estimate a kinetic isotope effect of at least 100.
This value is not large enough to implicate tunneling, as a kinetic
(
b) Platz, M. S.; Senthilnathan, P. V.; Wright, B. B.; McCurdy, C. E.
J . Am. Chem. Soc. 1982, 104, 6494.
11) Intramolecular solid-state reactions of carbene also exhibit a
t1/2 dependence. See refs 5 and 8a.
12) Moss, R. A. In Advances in Carbene Chemistry; Brinker, U.,
Ed.; J AI Press: Greenwich, CT, 1994; Vol. 1, pp 59-88.
(
1
2
(
isotope effect can be as large as 10 at 20 K even for a classical H
5
transfer reaction.
3
542 J . Org. Chem., Vol. 69, No. 10, 2004

Photolysis of 3-(2-Formylphenyl)-3-chlorodiazirine
F IGURE 7. Photolysis of 1-d in Ar at 13 K. (a) Total IR spectra of 1-d before irradiation. (b) Difference IR spectrum between the
photoproduct formed after 95 s of irradiation (λ ) 341 nm) of 1 (negative peaks) and 1 before irradiation (positive peaks). (c, d)
Calculated (B3LYP/6-312G(d)) spectra for anti,anti-2-deuterated carbene (a,a-2-d) (c) and anti-ketene (a-3-d) (d).
F IGURE 8. Photolysis of 1-d in Ar at 13 K. (a) Difference IR spectrum between the photoproduct formed after 500 s of irradiation
(
λ ) 341 nm) of 1-d (negative peaks) and 1-d before irradiation (positive peaks). (b-d) Calculated (B3LYP/6-312G(d)) spectra for
syn-ketene (s-3-d) (b), cyclobutenone(4-d) (c), and isobenzofuran(5-d) (d).
is involved in the H migration in 2-methylphenylcarbene,
the singlet state is the most likely one for the present
system.17 This suggests that multiplicities are not a
crucial factor to determine the tunneling process.
J . Org. Chem, Vol. 69, No. 10, 2004 3543

Nakane et al.
1H); 13C NMR(75.5 MHz, CDCl
, ppm) δ 46.1, 52.7, 127, 130,
SCHEME 1
3
-
1
1
31, 133, 135, 166; IR (NaCl, neat, cm ) ν 1730 (s), 1571 (m).
(
d ) P r ep a r a tion of 2-(3-Ch lor o-3H-d ia zir in e-3-yl)ben z-
a ld eh yd e (1). To a stirred and cooled solution of methyl 2-(3-
chloro-3H-diazirine-3-yl) benzoate (9, 133.6 mg, 0.63 mmol) in
absolute n-hexane (8.0 mL) was added diisobutylaluminum
hydride (Dibal-H) (0.93 M n-hexane solution, 0.92 mL, 0.67
mmol) dropwise at -78 °C. After stirring at -78 °C for 1 h,
saturated ammonium chloride aq (6.0 mL) was added. After
stirring for 1 h at 0 °C, the resulting mixture was extracted
with n-hexane. The combined hexane portions were dried (Na
SO ), filtered, and evaporated. The residue was purified by
gel permeation chromatography to give 2-(3-chloro-3H-diaz-
2
-
4
1
irine-3-yl)benzaldehyde (1) in 57% yield as a yellow liquid:
NMR (300 MHz, CDCl , ppm) δ 7.70-7.56 (m, 3H), 7.98 (d, J
7.35 Hz, 1H), 10.79 (s, 1H); 13C NMR(75.5 MHz, CDCl
, ppm)
δ 44.0, 127.2, 130.5, 131.0, 134.7, 136.0, 190.0; IR (NaCl, neat,
H
3
)
3
-
1
-1
cm ) ν 1700 (s), 1570(m); IR (Ar, 10 K, cm ) ν 1711 (w), 1692
(
s), 1603 (m), 1587 (w), 1575 (w), 1251 (m), 1215 (w), 909 (m),
8
83 (m), 792 (w), 765 (m);UV (Ar, 10 K, nm) 248, 295.
P r ep a r a tion of 2-(3-Ch lor o-3H-d ia zir in e-3-yl)ben za l-
2
d eh yd e (C HO) (1-d). Diisobutylaluminum deuteride (Dibal-
2
0
D) was prepared following the literature procedure. Lithium
deuteride (d 99%, 82.8 mg, 9.2 mmol) was placed in a dried,
sidearm flask equipped with a reflux condenser. The system
was flushed thoroughly with dry nitrogen, and the open necks
were capped with No-Air stoppers. Absolute ether (2.1 mL)
was weighed into a 3-mL syringe and diluted with ether to a
total volume of ∼3 mL. After stirring at 0 °C for 30 min,
n-hexane (5.2 mL) solution of diisobutylaluminum chloride
Exp er im en ta l Section
P r ep a r a tion of 2-(3-Ch lor o-3H-d ia zir in e-3-yl)ben za l-
d eh yd e (1). (a ) P r ep a r a tion of Meth yl o-P h en ylen ebis-
im id ica ceta te Hyd r och lor id e (7). Dry hydrogen chloride
was passed into a solution of o-phthalonitrile (6, 5.0 g, 39
mmol) in absolute methanol (3.2 mL, 78 mmol) and absolute
1
8
(1.26 g, 7.13 mmol) was added to this reaction mixture at 0
CHCl
stopperred, the reaction mixture was allowed to stand in a
freezer. After standing for 2 weeks, absolute Et O (ca 20 mL)
was added to the mixture and the mixture was stirred. The
precipitate formed was filtered, washed (Et O), and dried in
3
(60 mL) for 30 min at -20 °C. After the flask was tightly
°
C. After heating at 40 °C for 2 days, the resulting mixture
was used in next reaction. To a stirred and cooled solution of
methyl 2-(3-chloro-3H-diazirine-3-yl) benzoate (9, 76.0 mg, 0.33
mmol) in absolute n-hexane (4.0 mL) was added diisobutyl-
aluminum deuteride (Dibal-D) (vide ante, 1.26 M n-hexane
solution, 0.35 mL, 0.37 mmol) dropwise at -78 °C. After
stirring at -78 °C for 1 h, saturated ammonium chloride aq
2
2
vacuo to give methyl o-phenylenebisimidicacetate hydrochlo-
ride (7, 6.9 g, 66%) as a white solid: mp 209-214 °C; H NMR
1
(
6
300 MHz, DMSO-d , ppm) δ 7.93 (s, 6H), 8.70 (d, J ) 5.33
(
3.5 mL) was added. After stirring at 0 °C for 1 h, the resulting
mixture was extracted with n-hexane. The combined hexane
portions were dried (Na SO ), filtered, and evaporated. The
residue was purified by gel permeation chromatography to give
2-(3-chloro-3H-diazirine-3-yl)benzaldehyde (C HO) (1-d) in
57% yield as a yellow liquid. Deuterium content in 1-d based
on H NMR spectrum was 99%: H NMR (300 MHz, CDCl3,
Hz, 2H), 9.35 (d, J ) 5.70 Hz, 2H), 12.3 (br, 4H); IR (KBr disk,
cm ) ν 3500-2500 (br. s), 1720 (s).
-
1
2
4
(
b) P r ep a r a tion of 3-Im in oisoin d olin -1-on e (8).18 To a
solution of ethanol (30 mL) saturated with ammonia was added
the methyl ester hydrochloride (7, 3.0 g, 11.3 mmol), and the
mixture was stirred overnight of -20 °C. The resulting solution
was filtered to remove ammonium chloride, and the chloride
2
1
1
ppm) δ 7.59-7.57 (m, 3H), 7.97 (dd, J ) 7.35, 1.10 Hz, 1H);
was washed with Et
2
O. The combined Et
2
O portions were
13C NMR(75.5 MHz, CDCl , ppm) δ 44.0, 127.2, 130.4, 131.0,
3
evaporated and dried in vacuo to give 3-iminoisoindolin-1-one
134.7, 136.0; IR (NaCl, neat, cm-1) ν 1700 (s), 1570(m); IR (Ar,
1
-1
(
8, 2.1 g, quantitatively) as white solid: mp 135-140 °C; H
NMR (300 MHz, DMSO-d , ppm) δ 7.6-7.2 (br, 2H), 7.60-
.77 (m, 3H), 8.03 (d, J ) 6.98 Hz, 1H), 9.3-10.5 (br, 1H); IR
10 K, cm ) ν 1692 (s), 1602 (m), 1588 (w), 1574 (w), 1250 (m),
6
1215 (w), 908 (m), 883 (m), 792 (w), 765 (m).
7
Ma tr ix-Isola tion Sp ectr oscop y. Matrix experiments were
-
1
21,22
(
1
KBr disk) ν 3250 (br), 1720 (s), 1450 (m) cm ; EI MS (m/z)
performed by means of standard techniques
using a closed-
+
+1
45.6 (M ,100%), 146.6 (M ,17.2).
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 fit 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
controlled by a controller (gold vs chromel thermocouple).
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 monochromator was
used.
(
c) P r ep a r a tion of Meth yl 2-(3-Ch lor o-3H-d ia zir in e-3-
1
9
yl)ben zoa te (9). A mixture of 3-iminoisoindolin-1-one (8, 400
mg, 2.7 mmol), lithium chloride (770 mg, 18.2 mmol) in
methanol (28 mL) and n-hexane (8 mL) was cooled at -20 °C.
To this mixture was added a sodium hypochlorite solution
(
8.5∼13.5%, 26.8 mL) containing sodium chloride (4.6 g)
rapidly under vigorous stirring. After the reaction mixture was
stirred for 1 h, the resulting mixture was extracted with
n-hexane (3 × 10 mL). The combined hexane portion were
2 4
dried (Na SO ), filtered, and evaporated. The residue was
purified by column chromatography on silica gel. Methyl 2-(3-
chloro-3H-diazirine-3-yl)benzoate (9) was obtained as yellow
1
liquid in 14% yield; H NMR (300 MHz, CDCl
3
, ppm) δ 4.07
(
3
s, 3H), 7.48 (dd, J ) 5.33, 3.50 Hz, 1H), 7.53 (dd, J ) 7.72,
(18) Kranz, J . Chem. Ber. 1967, 100, 2261.
(
(
19) Graham, W. H. J . Am. Chem. Soc. 1965, 87, 4396.
20) Kalvin, D. M.; Woodard, R. W. Tetrahedron 1984, 18, 3387.
.67 Hz, 1H), 7.97 (d, J ) 7.53 Hz, 1H), 8.40 (d, J ) 9.03 Hz,
Whitesides, G. M.; Filippo, J . S., J r. J . Am. Chem. Soc. 1970, 92, 6611.
(21) H. Tomioka, H.; N. Ichikawa, N.; K. Komatsu, K. J . Am. Chem.
Soc. 1992, 114, 6045.
(22) McMahon, R. J .; Chapman, O. L.; Hayes, R. A.; Hess, T. C.;
Krimmer, H. P. J . Am. Chem. Soc. 1985, 107, 7597.
(
17) It is well-known that halocarbenes have a singlet ground state.
See, for instance: J ones, M. J r.; Moss, R. A. In Reactive Intermediate
Chemistry; Moss, A. M., Platz, M. S., J ones, M., J r., Eds.; Wiley: New
York, 2004; pp 273-328.
3
544 J . Org. Chem., Vol. 69, No. 10, 2004

Photolysis of 3-(2-Formylphenyl)-3-chlorodiazirine
Com p u ta tion a l P r oced u r es. DFT calculations were car-
have exactly one imaginary frequency related to the expected
movement.
2
3
ried out using the GAUSSIAN 94, programs. Optimized
2
3,24
geometries were obtained at the B3LYP/6-31G(d)
levels of
Su p p or tin g In for m a tion Ava ila ble: Difference IR spec-
trum between the photoproduct formed after 500 s of irradia-
tion (λ ) 341 nm) of 1 and the same spectrum after standing
theory. Vibrational frequencies obtained at the B3LYP level
of theory were scaled by 0.961 and zero-point energies (ZPE)
2
5
by 0.981. Transition states were located using Gaussain
program (Rational Function Optimization-pseudo-Newton-
Raphsonthe method).26 The nature of each stationary point was
confirmed with harmonic frequency calculations, i.e., minima
1
1 h in dark (Figure S1); difference spectrum between the
photoproduct formed after 3 h of irradiation (λ > 350 nm) of 1
and 1 before irradiation (Figure S2); plots of the absorbance
of products as a function of irradiation time in the photolysis
of 1 and 1-d (Figures S3 and S4); IR bands of a,a-2(-d), s,a-
(23) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Gill, P. M.;
2
(-d), a-3(-d), s-3(-d), 4(-d), and 5(-d) observed in Ar at 13 K
J ohnson, B. G.; Robb, M. A.; Cheeseman, J . R.; Keith, T.; Petersson,
G. A.; Montgomery, J . A.; Raghavachari, K.; Al-Laham, M. A.;
Zakrzewski, V. G.; Ortiz, J . V.; Foresman, J . B.; Cioslowski, J .;
Stefanov, B. B.; Nanayakkara, A.; Challacombe, M.; Peng, C. Y.; Ayala,
P. Y.; Chen, W.; Wong, M. W.; Andres, J . L.; Replogle, E. S.; Gomperts,
R.; Martin, R. L.; Fox, D. J .; Binkley, J . S.; DeFrees, D. J .; Baker, J .;
Stewart, J . J . P.; Head-Gordon, M.; Gonzalez, C.; Pople, J . A. GAUSS-
IAN 94; Gaussian Inc.: Pittsburgh, PA, 1995.
and calculated by B3LYP/6-31G(d) (Tables S1-S11); Gaussian
archive entries (Table S12); and Cartesian coordinates (Tables
S13-S20). This material is available free of charge via the
Internet at http://pubs.acs.org.
J O049802T
(
24) (a) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785.
b) Miehlich, B.; Savin, A.; Stoll, H.; Preuss, H. Chem. Phys. Lett. 1989,
57, 200. (c) Becke, A. D. J . Chem. Phys. 1993, 98, 5648.
(25) Scott, A. P.; Radom, L. J . Phys. Chem. 1996, 100, 16502.
(26) Simons, J .; J orgensen, P.; Taylor, H.; Ozment, J . J . Phys. Chem.
1983, 87, 2745.
(
1
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