Generation and study of benzylchlorocarbene from a phenanthrene precursor

Article abstract of DOI:10.1021/ja980251w

The curved plots of (carbene adduct)/(carbene-rearrangement product) versus carbene trapping agent, tetramethylene [TME], reported with benzylchlorodiazirine 1 have been reproduced. However, with the use of a non- nitrogenous precursor, plots of this type are approximately linear over the range of [TME] employed. Thus, any complex formed between benzylchlorocarbene and TME must collapse to form cyclopropane faster then it can fragment with rearrangement to β-chlorostyrene and TME. Diazirine 1 does photoisomerize to diazo compound 7, but this process is inefficient (φ = 0.075) and is not likely to be responsible for the curvature in plots of adduct/styrene versus [TME] observed with the diazirine precursor. Thus, the second, noncarbene, pathway to β-chlorostyrene is neither a carbene-olefin complex nor a diazo intermediate. It is proposed that the second pathway involves a rearrangement in the excited state of the diazirine, although other explanations cannot be discarded.

Full text of DOI:10.1021/ja980251w

J. Am. Chem. Soc. 1998, 120, 8055-8059
8055
Generation and Study of Benzylchlorocarbene from a Phenanthrene
Precursor
†
,†
‡
,‡
Manisha Nigam, Matthew S. Platz,* Brett M. Showalter, John P. Toscano,*
,§
§
§
Richard Johnson,* Sarah C. Abbot, and Mary M. Kirchhoff
Contribution from the Department of Chemistry, Newman and Wolfrom Laboratory of Chemistry,
The Ohio State UniVersity, 100 West 18th AVenue, Columbus, Ohio 43210, Department of Chemistry,
Johns Hopkins UniVersity, 3400 North Charles Street, Baltimore, Maryland 21218, and Department of
Chemistry, UniVersity of New Hampshire, Durham, New Hampshire 03824
ReceiVed January 22, 1998. ReVised Manuscript ReceiVed May 28, 1998
Abstract: The curved plots of (carbene adduct)/(carbene-rearrangement product) versus carbene trapping agent,
tetramethylene [TME], reported with benzylchlorodiazirine 1 have been reproduced. However, with the use
of a non-nitrogenous precursor, plots of this type are approximately linear over the range of [TME] employed.
Thus, any complex formed between benzylchlorocarbene and TME must collapse to form cyclopropane faster
then it can fragment with rearrangement to â-chlorostyrene and TME. Diazirine 1 does photoisomerize to
diazo compound 7, but this process is inefficient (φ ) 0.075) and is not likely to be responsible for the curvature
in plots of adduct/styrene versus [TME] observed with the diazirine precursor. Thus, the second, noncarbene,
pathway to â-chlorostyrene is neither a carbene-olefin complex nor a diazo intermediate. It is proposed that
the second pathway involves a rearrangement in the excited state of the diazirine, although other explanations
cannot be discarded.
I. Introduction
Scheme 1
In 1984 Tomioka, Liu, and co-workers reported that pho-
tolysis of benzylchlorodiazirine 1 produced benzylchlorocarbene
2
3
which rearranged to a mixture of E and Z â-chlorostyrenes
1
.
When the photolysis was repeated in the presence of
tetramethylethylene (TME) cycloadduct 4 was isolated. A
simple interpretation of the data (Scheme 1) predicts that a plot
of 4/3 versus [TME] will be linear with a slope of kA/kR. The
expected linear dependence was not observed, however. The
data indicate that there are two pathways which form â-chlo-
rostyrene product. It was proposed that carbene 2 reacts with
TME to form a π complex (5) which partitions between collapse
c
c
to form cyclopropane 4 (k a) and rearrangement (k R) to
â-chlorostyrene 3. Thus, not all of the carbene can be diverted
to cyclopropane, even at infinite concentration of TME (Scheme
Scheme 2
2
). Furthermore, some dependence of the intercept of plots of
[3/adduct (e.g., 4)] versus 1/[alkene] on the nature of the alkene
was found, as predicted by the carbene-alkene complex
mechanism.2 Subsequently, it was found that the E/Z ratio of
â-chlorostyrenes varies with [TME], which is also consistent
with Scheme 2. The kinetics and spectroscopy of benzylchlo-
†
The Ohio State University.
Johns Hopkins University.
University of New Hampshire.
‡
§
(
1) Tomioka, H.; Hayashi, N.; Izawa, Y.; Liu, M. T. H. J. Am. Chem.
Soc. 1984, 106, 454.
2) (a) Liu, M. T. H.; Bonneau, R. J. Am. Chem. Soc. 1990, 112, 3915.
b) Liu, M. T. H.; Soundararajan, N.; Paike, N.; Subramaniam, R. J. Org.
(
(
Chem. 1987, 52, 4223. (c) Liu, M. T. H.; Bonneau, R.; Wierlacher, S.;
Sander, W. J. Photochem. Photobiol. A: Chem. 1994, 84, 133. (d) New
rocarbene have also been studied by laser flash photolysis
2
,3
10.0
techniques.
Arrhenius parameters for rearrangement (Ea ) 3.2 kcal/mol, A ) 100
-
s
1
Many groups have postulated that carbene-olefin complexes4
) have recently been reported and are used in our analysis. See: Merrer,
D. C.; Moss, R. A.; Liu, M. T. H.; Banks, J. T.; Ingold, K. U. J. Org.
Chem. 1988, 63, 3010. This study was performed in tetrachloroethane. Our
deduced Arrhenius parameters obtained in methylene chloride must be
considered suspect as the Arrhenius parameters to rearrangment are solvent
dependent.
(COC) are formed prior to the formation of cyclopropane.
(3) (a) Liu, M. T. H. Acc. Chem. Res. 1994, 27, 287. (b) Liu, M. T. H.;
Stevens, I. D. R. The Chemistry of the Diazirines; Liu, M. T. H., Ed.; CRC
Press: Boca Raton, FL, 1987; Vol. I, p 111.
S0002-7863(98)00251-0 CCC: $15.00 © 1998 American Chemical Society
Published on Web 07/30/1998

8056 J. Am. Chem. Soc., Vol. 120, No. 32, 1998
Nigam et al.
Scheme 3
3 with TME, and the dependence of 3/4 versus [alkene] type
plots on the nature of the alkene trap, is consistent with the
intermediacy of a diazo compound (Scheme 4) that can react
8
with alkenes. It has been suggested that all three pathways
2
,11,12
may be operating simultaneously in this system.
To distinguish between these views, an independent precursor
to benzylchlorocarbene is needed. If a carbene-alkene complex
5
is the second route to â-chlorostyrenes then the originally
reported observations will be independent of precursor, if not
the anomalies should disappear. Phenanthrene 8 appeared to
us to be a precursor that would allow the differentiation of the
various mechanistic proposals.
LFP of 8 produces carbene 2 that can be trapped with pyridine
1
3
to form ylide 9.
Scheme 4
Obviously 8 cannot form a diazo intermediate. Furthermore,
if 8 opens to form biradical 10 upon photolysis, we expect that
this biradical (unlike 6, Scheme 3) will isomerize to 11 rather
than somehow form â-chlorostyrene 3, as the thermal fragmen-
tation of alkylcyclopropanes into a pair of alkenes (via cleavage
1
4
with rearrangement) is unknown. Thus, we expect that a
second pathway to alkene 3 is unlikely when this precursor is
employed.
Calculations find that carbene-olefin complexes are not minima
5
but collapse immediately to form cyclopropanes. However,
recent experimental and theoretical work indicates that carbenes
do form bound complexes with benzene.6
Other interpretations of the data are possible. Following Frey
7
and other early workers in this field, we have attributed the
second â-chlorostyrene pathway to either a diazirine excited
8
state (Scheme 3) and/or the decomposition of an unstable diazo
9
compound 7 formed by photoisomerization of diazirine 1
(
7
Scheme 4). Again, following Frey the second pathway to
â-chlorostyrene has been associated with an excited state of
the carbene by Warner.10 These schemes also predict curvature
of plots of 4/3 versus [TME]. The change of the E/Z ratio of
(
4) (a) Skell, P. S.; Cholod, M. S. J. Am. Chem. Soc. 1969, 91, 7131.
(
b) Gould, I. R.; Turro, N. J.; Butcher, J., Jr.; Doubleday, C., Jr.; Hacker,
N. P.; Lehr, G. F.; Moss, R. A.; Cox, D. P.; Guo, W.; Munjal, R. C.; Perez,
L. A.; Fedorynski, M. Tetrahedron 1985, 41, 1587.
(
5) (a) Houk, K. N.; Rondan, N. G.; Mareda, J. Tetrahedron 1985, 41,
1
1
555. (b) Houk, K. N.; Rondan, N. G.; Mareda, J. J. Am. Chem. Soc. 1984,
06, 4291. (c) Blake, J. F.; Wierschke, S. G.; Jorgensen, W. C. J. Am.
Chem. Soc. 1989, 111, 1919.
6) (a) Khan, M. I.; Goodman, J. L. J. Am. Chem. Soc. 1995, 117, 6635.
b) Moss, R. A.; Yan, S.; Krogh-Jespersen, K. J. Am. Chem. Soc. 1998,
20, 1088. (c) Jones, M., Jr.; Thamattoor, D. M.; Ruck, R. T. Kyushu
International Symposium on Physical Organic Chemistry, December 2-5,
997, Kyushu University.
Herein we are pleased to report our studies of the photo-
chemistry of 8, in the presence and absence of TME. The results
are consistent with Scheme 3 and rule out π complex 5 as a
(
(
1
1
(11) Bonneau, R.; Liu, M. T. H.; Kim, K. C.; Goodman, J. C. J. Am.
Chem. Soc. 1996, 118, 3829.
(12) Bonneau, R.; Shustov, G. V.; Liu, M. T. H. Kyushu International
Symposium on Physical Organic Chemistry, December 2-5, 1997, Kyushu
University.
(13) Robert, M.; Likhotvorik, I.; Platz, M. S.; Abbot, S. C.; Kirchoff,
M. M.; Johnson, R. J. Phys. Chem. 1988, 102, 1507.
(14) Gajewski, J. Thermal Hydrocarbon Isomerizations; Academic
Press: New York, NY 1981.
(
(
7) Frey, H. M. AdV. Photochem. 1964, 4, 225.7.
8) (a) Platz, M. S.; White, W. R., III.; Modarelli, D. A.; Celebi, S. A.
Res. Chem. Intermed. 1994, 175. (b) Modarelli, D. A.; Morgan, S.; Platz,
M. S. J. Am. Chem. Soc. 1992, 114, 7034. (c) Platz, M. S. AdVances in
Carbene Chemistry; Brinker, U., Ed.; JAI Press: Greenwich, CT, 1998;
Vol. 2, p 133.
(
(
9) White, W. R., III; Platz, M. S. J. Org. Chem. 1992, 57, 2841.
10) Warner, P. M. Tetrahedron Lett. 1984, 25, 4211.

Benzylchlorocarbene from a Phenanthrene Precursor
J. Am. Chem. Soc., Vol. 120, No. 32, 1998 8057
Figure 1. A plot of 4/3 vs [TME] obtained at 350 nm from ([)
A R
Figure 3. The Arrhenius treatment of the k /k data obtained by
photolysis of 8 in the presence of TME in dichloromethane at 300 nm.
phenanthrene 8 at 15 °C in CH
Cl
, (b) diazirine 1 at 15 °C in isooctane, and (9) data of Liu2 et al.
at 10 °C in isooctane.
2 2 2
Cl , (2) diazirine 1 at 15 °C in CH -
,3
2
Figure 4. The E/Z ratio of the â-chlorostyrenes formed at 15 °C under
various conditions: ([) precursor 8, 300 nm, CH Cl ; (9) precursor
8, 350 nm, CH Cl ; (2) precursor 1, 350 nm, isoocctane; (0) precursor
2 2
Figure 2. A plot of 4/3 vs [TME] obtained from phenanthrene 8 in
CH Cl at (b) 9, (0) 13, ([) 23, (2) 33, and (O) 42 °C at 300 nm.
Error bars are not shown but are comparable to those of Figure 1.
2
2
2
2
2 2
1, 350 nm, CH Cl ; (b) precursor 1, 350 nm, isoocctane (10 °C),
references 2, 11, and 15.
species capable of forming â-chlorostyrene at a rate comparable
to its collapse to cyclopropane. The results do not exclude the
possibility of the formation of π complex 5, but such a species,
A
5.7 -1
kcal/mol and A ) 10 s as the corresponding values of the
2
d
rearrangement have been reported.
c
c
if formed, can only form cyclopropane 4 (k A . k R, Scheme
).
The E/Z Ratio as a Function of [TME]. The E/Z ratios of
the â-chlorostyrenes produced on photolysis were studied as a
function of precursor, photolysis wavelength, solvent, and the
presence of TME. The data are summarized in Figure 4. The
results seem to be sensitive to each experimental parameter.
It was possible to synthesize a 90/10 mixture of 3 E/Z. The
E/Z ratio varies upon photolysis (280-320 nm) in CH2Cl2 at
2
II. Results
We first set out to reproduce the original findings. In our
hands, photolysis (320-380 nm, Rayonet Reactor) of diazirine
1
3
in the presence of TME, in isooctane, produces both styrenes
and cyclopropane 4. A plot of 4/3 versus [TME] is curved
1
1
5 °C (Figure 5) and photolysis (320-380 nm) in CH2Cl2 at
5 °C (Figure 5) in the presence of TME. The E/Z ratio of 3
(Figure 1). The slight difference between our findings and those
also changes from 90/10 E/Z to 50/50 in CH2Cl2 and to 33/66
in isooctane upon photolysis in the absence of TME.
Upon photolysis of 3 and TME a photoproduct was formed
in small yield. The product was characterized by GC-MS and
its cracking pattern was consistent with that of a [2+2]
cycloadduct.
Time-Resolved IR Spectroscopy. Laser flash photolysis of
diazirine 1 produces a transient with a strong IR absorption at
044 cm . The transient is long-lived (τ. 200 µs) and, we
believe, associated with diazo compound 7. LFP of chloro-
propyldiazirine 12 and 13 produces diazo compounds 14 (2030
of the earlier workers is likely due to the small (5°) difference
in temperature of the two studies or to small variation in GC
response factors.
Photolysis of 8 in the presence of TME again produces
â-chlorostyrenes 3 and cyclopropane 4. A plot of 4/3 versus
[TME] in CH2Cl2 can be fit to a straight line over the range of
[TME] where such plots obtained with diazirine 1 are curved
(Figure 1). Precursor 8 is insoluble in isooctane, hence the
-1
2
change of solvent. The slope of this plot was measured as a
function of temperature (Figure 2). A plot of log(kA/kR) versus
1
/T(K) is linear (Figure 3), which provides the differential
-1
-1
15
cm ) and 15 (2028 cm ), respectively.
A
R
-4.3
activation energies ∆∆Ea ) +1.6 kcal/mol and A /A ) 10
M . These can be converted into absolute values ∆E ) 1.6
-1
A
(15) Bonneau, R.; Liu, M. T. H. J. Am. Chem. Soc. 1996, 118, 7229.

8058 J. Am. Chem. Soc., Vol. 120, No. 32, 1998
Nigam et al.
with cycloaddition as per the Reactivity Selectivity Principle.
Figure 5. The E/Z ratio as a function of [TME] obtained by the
photolysis of a 90% E isomer of 3 in dichloromethane at 15 °C at (2)
A
R
From the data of Figures 2 and 3, values of ∆Ea - ∆Ea ) +
A
R
-4.3
-1
1
.6 kcal/mol and A /A ) 10
M
can be deduced. As
mentioned previously, it has been reported that ∆Ea ) 3.2 kcal/
mol and A ) 10 s . This indicates that ∆Ea ) 1.6 kcal/
3
00 and (9) 350 nm.
R
R
10.0 -1 2e
A
1
6
A
5.7 -1
mol, which seems plausible, and that A ) 10 s , which
seems rather low. It is important to note that the 1,2 migration
of the hydrogen reaction is sensitive to solvent and different
solvents were used in this study and the absolute kinetic study.
Considering that 3 both photoisomerizes and reacts with TME
under our photolysis conditions, we feel it is unwise to attach
much significance to the variation of the E/Z ratio in the presence
of TME. 3Z and 3E may react with TME at different rates.
Furthermore, 3Z and 3E may react with TME to form a biradical
that can fragment with net isomerization of the alkene. Thus,
we feel the variation of the 3 E/Z ratio with TME is of little
mechanistic significance.
Bonneau and co-workers have shown that the quantum yields
of the formation of 14 from 12 and diazo compound 15 from
1
1
3 are approximately the same (0.10-0.13).15 Diazirines 1 and
3 were studied under identical conditions. On the basis of
the analysis of the IR intensities of diazirine depletion bands
and formation of diazo absorption bands we conclude that the
quantum yield of diazo formation with benzylchlorodiazirine
is 0.075, or about half that of diazirines 12 and 13.
III. Discussion
The curved plots of 4/3 first discovered by Tomioka et al.1
are precursor dependent. Curvature is observed with diazirine
1
but not with phenanthrene 8 over the range of TME
concentration employed in the original study. The curvature
observed with precursor 1 cannot be due to a complex between
carbene 2 and TME that was postulated to form styrene 3 in
competition with collapse to cyclopropane 4.
Our experiments do not reveal the precise mechanism for
the noncarbene pathway operating in diazirines. The second
pathway may involve excited states of the carbene10 or of the
diazirine. The latter pathway has been dubbed a “Rearrange-
ment in Diazirine Excited State” (RIES) mechanism.8 Ac-
cording to theory, irradiation of the nπ* band of a diazirine
leads to opening of the three membered ring to form a
Many scientists have speculated that carbenes form complexes
,9
4
with alkenes on the way to forming cyclopropanes. The
putative complex is formed by the interaction of the empty
p-orbital of the singlet carbene with the π electrons of the alkene
17
diradical, which we postulate can migrate hydrogen in concert
with nitrogen extrusion (Scheme 3). Of all the decay routes
possible for diradical 6 this is surely the most exothermic
(Scheme 2).
Theory predicts that these types of complexes are not minima
5
on the potential surface in the gas phase. Our results do not
rule out the possibility that a complex such as 5 is formed and
has a finite lifetime in solution. However, the data require that
if 5 is indeed formed, it must form cyclopropane 3 much faster
than it forms 2 plus TME (k′A . k′R).
7
,8
route.
In principle, biradical 6 can also be formed upon
pyrolysis of diazirine 1.
It is also conceivable that hydrogen migrates in concert with
ring opening of the diazirine excited state to form biradical 16,
although this process has not been considered explicitly by
theory.
Bonneau et al. have made the reasonable suggestion that the
importance of the RIES mechanism varies with the structure of
the diazirine. In fact, it is claimed that the RIES mechanism
accounts for only 6% of the products formed from benzylchlo-
Is this reasonable? We believe it is. Any complex of a
carbene and an alkene must be enthalpically stable relative to
its free components or it will not be formed. The rearrangement
of R hydrogen in a carbene is traditionally viewed as a hydride-
like shift where the hydride moves to the empty p-orbital of
the carbene carbon. The experimentally determined barrier to
2d
this rearrangement is 3.2 kcal/mol. Complexation must surely
(16) Moss, R. A.; Turro, N. J. Kinetics and Spectroscopy of Carbenes
raise the barrier to 1,2 hydrogen migration. In contrast,
and Biradicals; Platz, M. S., Ed.; Plenum: New York, 1990; 213.
(17) (a) Bigot, B.; Ponec, R.; Sevin, A.; Devaquet, A. J. Am. Chem.
Soc. 1978, 100, 6573. (b) M u¨ ller-Remmers, P. L.; Jug, K. J. Am. Chem.
Soc. 1985, 107, 7275. (c) Yamamoto, N.; Bernardi, F.; Bottoni, A.; Olivucci,
M.; Robb, M. A.; Wilsey, S. J. Am. Chem. Soc. 1978, 116, 2064.
5
(according to theory) the barrier to collapse of the complex to
form cyclopropane is close to zero, if it exists at all. Thus,
complexation should make rearrangement even less competitive

Benzylchlorocarbene from a Phenanthrene Precursor
J. Am. Chem. Soc., Vol. 120, No. 32, 1998 8059
(1, 20 mM) in dichloromethane was photolyzed at 320-380 nm with
use of a rayonet reactor equipped with RPR-350 bulbs at 15 °C in the
presence of varying amounts of tetramethylethylene (TME) ranging
from 0.1 to 2.2 M. The solutions were degassed before the photolysis.
The photolytic reaction gave the carbene trapped product 1-benzyl-1-
chloro-2,2,3,3-tetramethylcyclopropane (4) and the 1,2 H-migration
produced (E)- and (Z)-chlorostyrenes (3).
Photolysis of 8 in Dichloromethane. 1-Benzyl-1-chloro-1a,9b-
dihydrocyclopropa[1]phenanthrene (8, 20 mM) in dichloromethane was
photolyzed at 320-380 and 280-320 nm with use of a rayonet reactor
equipped with RPR-350 and RPR-300 bulbs, respectively, at 9, 13,
rodiazirine.12 It was further stated in this study12 that the RIES
mechanism cannot explain various relative rate measurements.
Photolysis (320-380 nm) of diazirine 1 and phenanthrene 8
in a 1/1 (v/v) mixture of TME and CH2Cl2 at ambient
temperature leads to ratios of adduct [4/(styrenes 3)] of 2/1 and
1
6/1, respectively. Under these conditions, nearly all photo-
2
3, 33, and 42 °C in the presence of varying amounts of teramethyl-
generated carbene should be trapped with TME before it can
ethylene (TME) ranging from 0.1 to 1.4 M. The solutions were
degassed before the photolysis. The photolytic reaction gave the
carbene-trapped product 1-benzyl-1-chloro-2,2,3,3-tetramethylcyclo-
propane (4) and the 1,2 H-migration produced (E)- and (Z)-chlorosty-
renes (3).
Photolysis of 3 in Dichloromethane. 20 mM solutions of 90% 3E
in dichloromethane were photolyzed at 320-380 and 280-320 nm
using a rayonet reactor equipped with RPR-3000 and RPR-3500 bulbs,
respectively, at 15 °C in the presence of varying amounts of tetram-
ethylethylene (TME) ranging from 0.1 to 2.2 M. The solutions were
degassed before the photolysis.
GC-MS Protocols. Products 3 and 4 were identified by NMR and
GC-MS analysis. The relative yields of products were analyzed on a
HP 6889 GC with use of a 30m × 0.25 mm × 0.25 µm column packed
with 5% PH ME Siloxane and HP 5973 MS detector. The peak area
ratio 3/4 was multiplied by a response factor of 2.92 to convert into a
molar ratio.
rearrange,2
,11,15
but this is observed only with precursor 8. As
the quantum yield of diazo formation is 7.5% and the quantum
3
yield of disappearance of diazirines is typically unity, a 26%
yield of â-chlorostyrene remains to be explained with diazirine
precursor 1. Although we cannot quantify the importance of
RIES to the 26% yield of the noncarbene pathway from our
1
0
data, we posit that RIES (or an excited state of the carbene )
makes a substantial contribution to the second pathway to
1
1
olefinic product with benzylchlorodiazirine, the PAC data
notwithstanding.
IV. Conclusions
The curved plots of (carbene adduct)/(carbene-rearrangement
product) versus carbene trapping agent, tetramethylene [TME],
1
reported by Tomioka et al. with benzylchlorodiazirine 1 have
Time-Resolved Infrared Protocols. TRIR experiments were
been reproduced. However, using a non-nitrogenous precursor,
plots of this type are linear over the range of [TME] used in
the original study. Thus, any complex formed between ben-
zylchlorocarbene and TME must collapse to form cyclopropane
faster then it can fragment with rearrangement to â-chlorostyrene
and TME. The anomalous behavior observed when benzyl-
chlorodiazirine is used as precursor can be interpreted without
recourse to the existence of carbene-alkene complexes. We
posit that rearrangements proceed in the diazirine excited state,
although other explanations are possible. Diazirine 1 does
photoisomerize to diazo compound 7, but this process is
inefficient (φ ) 0.075) and is not likely to be responsible for
the curvature in plots of adduct/styrene versus [TME] observed
with the diazirine precursor.
20
performed following the method of Hamaguchi and co-workers. This
-1
method allows access to the entire mid-IR spectrum (4000-800 cm
)
with high sensitivity and sufficient time (ca. 50 ns) and frequency
-1
(
4-16 cm ) resolution to probe a wide range of transient intermediates
in solution. The broadband output of a newly developed MoSi infrared
2
source (JASCO) is crossed with excitation pulses (355 nm, 10 ns, 0.6
mJ) from a Continuum HPO-300 diode-pumped Nd:YAG laser.
Changes in infrared intensity are monitored by a MCT photovoltaic
IR detector (Kolmar Technologies, KMPV11-1-J1), amplified by an
NF Electronic Instruments 5305 low noise amplifier, and digitized with
a Tektronix TDS520A oscilloscope. Data are collected at a repetition
rate of 200 Hz, the maximum data handling speed of our digitizing
oscilloscope, and acquisition is synchronized with the stepwise scan
of a JASCO TRIR-1000 dispersive spectrometer. To obtain spectra
with sufficient sensitivity, several thousand laser shots are typically
signal averaged at each IR frequency of interest. Since data are
collected at relatively high repetition rates, a flowing cell is necessary
to prevent excessive sample decomposition. A reservoir of ca. 15 mL
of solution is continually circulated between two calcium fluoride salt
plates.
V. Experimental Section
The synthesis of phenanthrene 8, diazirine 1,2,15 â-chlorostyrene
1
3
,18,19
2,15
3
and cyclopropane adduct 4 have all been reported.
Photolysis of 1 in Isooctane. 3-Chloro-3-benzyldiazirine (1, 20
mM) in isooctane was photolyzed at 320-380 nm with use of a rayonet
reactor equipped with RPR 350 bulbs at 15 °C in the presence of
varying amounts of tetramethylethylene (TME) ranging from 0.1 to
Acknowledgment. Support of this work by the NSF in Ohio
(CHE-9613861), in Maryland (CHE-9733052), and in New
Hampshire (CHE-9616388) is gratefully acknowledged. The
authors are indebted to Professors Liu, Bonneau, Moss, and
Jones for valuable discussions.
2
.2 M. The solutions were degassed before the photolysis. The
photolytic reaction gave the carbene trapped product 1-benzyl-1-chloro-
,2,3,3-tetramethylcyclopropane (4) and the 1,2 H-migration produced
2
(E)- and (Z)-chlorostyrenes (3).
JA980251W
Photolysis of 1 in Dichloromethane. 3-Chloro-3-benzyldiazirine
(
18) Miyano, S.; Izuni, Y.; Fujii, K.; Ohno, Y.; Hashimoto, H. Bull.
Chem. Soc. Jpn. 1979, 52, 1197.
19) Liu, M. T. H. J. Chem. Soc., Chem. Commun. 1985, 982.
(20) (a) Iwata, K.; Hamaguchi, H. Appl. Spectrosc. 1990, 44, 1431. (b)
Yuzawa, T.; Kato, C.; George, M. W.; Hamaguchi, H. Appl. Spectrosc.
1994, 48, 684.
(