5998 J. Am. Chem. Soc., Vol. 120, No. 24, 1998
Huang and Platz
dropwise to a suspension of LiAlH4 in anhydrous ether (25 mL).
Themixture was stirred at room temperature for 24 h. Methanol (2
mL) was added to the mixture to quench the excess of LiAlH4. The
reaction mixture was poured into ice cold 5% H2SO4 solution. The
organic layer was separated, dried over anhydrous Na2SO4, and
concentrated in vacuo. Fractional distillation through a short Vigreux
column gave 1-bromo-2-tert-butylcyclopropane (2.5 g, 60%). MS: m/e
176, 178, M+, M+ + 2 176, 178.
on the two cyclopropyl rings. MS stereoisomer 8a: m/e (rel intensity)
M+ 178 (1.0), 163 (1.2), 135 (6.0), 108 (32), 93 (100), 79 (67), 67
(61), 41 (63). MS stereoisomer 8b: m/e (rel intensity) M+ 178 (0.5),
163 (1.0), 135 (5.0), 108 (31), 93 (100), 79 (70), 67 (61), 41 (66).
When diazirine 4 was photolyzed in the presence of n-propylamine,
in addition to cyclobutene 7 and alkene 8, an adduct of carbene 5 with
the amine was also formed. MS: m/e (rel intensity) M+ 169 (4.2),
140 (61), 111 (15), 98 (15), 69 (100), 55 (58), 41 (75). Its structure
was confirmed by comparison with an authentic sample prepared by
reductive amination of the trans-tert-butylcyclopropanecarboxyaldehyde
according to a procedure reported in the literature.34
11-tert-Butylcyclopropyl-11H-tricyclo[4.4.1.01,6]undeca-2,4,8-
triene (16). 1-Bromo-2-tert-butylcyclopropane (2.2 g, 12.4 mmol) in
5 mL diethyl ether was added to a stirred suspension of chopped lithium
(0.18 g, 26 mmol) in anhydrous ether (15 mL) at 0 °C. The mixture
was stirred at 0 °C for 45 min. The gray reaction mixture containing
alkyllithium was then added to a stirred suspension of CuI (1.2 g, 6.2
mmol) in anhydrous ether (25 mL) over 30 min under argon. The
internal temperature was kept below -60 °C during addition by cooling
the flask in a dry ice/acetone bath. The mixture was allowed to stir
for 45 min at -70 °C, and a solution of 11,11-dibromotricyclo[4.4.1.01,6]-
undeca-2,4,8-triene31b (0.45 g,1.4 mmol) in THF (10 mL) was added
dropwise over 30 min. The temperature of reaction mixture was kept
below -65 °C during the addition. The resulting mixture was allowed
to stir for another hour at -70 °C and then allowed to warm to room
temperature. Methanol (2 mL) was added, and the reaction mixture
was poured into ice water (30 mL). The residue was washed with
ether (20 mL), and the combined ether layers were washed with water
and brine, dried over anhydrous Na2SO4, and concentrated in vacuo.
The product mixture was separated by column chromatography to give
16 (0.17 g, 50%). It was further purified by preparative TLC. MS:
m/e 240, M+ 240. 1H NMR (CDCl3): δ ppm 6.10, 5.90 (m, 4H, diene-
H), 5.45 (m, 2H, alkenyl H), 2.80, 2.70, 2.25, 2.15 (m, 4H, allyl H),
0.65 (s, 9H, tert-butyl H), 0.40, 0.15, -0.10 (m, 4H, cyclopropyl H).
13C NMR (CDCl3): δ ppm 128.55, 123.00, 121.37, 32.12, 30.08, 29.47,
28.55, 24.10, 21.01, 20.05, 7.74. HRMS: calcd for C18H24 (M+),
240.1879; found, 240.1879.
Product Studies. Stock solutions of 4 (10 mM) were purified by
column chromatography before usage. To the Pyrex tubes were added
250 µL stock solution and the requisite quantity of carbene trapping
reagents. All tubes were then degassed using the freeze-pump-thaw
method and sealed under vacuum with a torch. The tubes were then
submerged in the water bath at desired temperature and subjected to
photolysis or pyrolysis. Photolysis was performed in a Rayonet
photoreactor fitted with 350 nm UV bulbs. Pyrolysis was accomplished
by heating the sealed tubes in a boiling water bath for 30 min. The
tubes were then opened, and the resulting solutions were analyzed by
analytical GC.
When diazirine 4 was photolyzed in the presence of trifluoroethanol,
in addition to cyclobutene 7 and alkene 8, an adduct of carbene 5 with
the alcohol was also formed. The adduct was separated by preparatory
1
GC and characterized by H and 13C NMR and GC-MS. 1H NMR
(CDCl3): δ ppm 3.72 (q, 2H), 3.38 (d, m, 2H), 0.95 (m, 1H), 0.79 (s,
9H), 0.52 (m, 2H), 0.36 (m, 1H). 13C NMR (CDCl3): δ ppm 68.424,
67.882, 67.340, 29.550, 29.208, 28.923, 28.309, 26.482, 13.582, 6.446.
MS: m/e (rel intensity) M+ 210 (1.5), 153 (3.6), 139 (6.1), 113 (8.3),
95 (17), 70 (100), 55 (64).
Laser Flash Photolysis.16 In the laser flash photolysis (LFP)
experiments, two types of laser sources were used. In those experiments
where optical yields were measured, a Lumonics TE-861-4 excimer
laser (351 nm, 60 mJ, 17 ns) or a Lambda Physik LPX-100 excimer
laser (308 nm, 120 mJ, 17 ns) was used. The laser intensity of the
two XeF excimer lasers remained stable for a period of several hours
and met the experimental requirement of constant laser output. Direct
time-resolved LFP experiments were performed with a 150 ps pulse
laser generated from a Continuum PY62C-10 Nd:YAG laser (355 nm,
30 mJ, 0.15 ns).
Two kinds of sample cells were used. For the experiments using
XeF excimer laser, the cells were made from square quartz tubing
purchased from Vitro Dynamics. The length of the cuvettes was 1
cm, and the middle part of the cuvettes where the light passed was
close to square-shaped. For the experiments using Nd:YAG laser, a
Suprasil quartz flurorescence-free static cell was purchased from
Scientific Products. An almost perfectly flat surface of this type of
quartz cell results in the minimum scattering of incident laser beam.
Stock solutions of photolabile carbene precursors were prepared
immediately before LFP experiment. Absorbances of all diazirine
samples used in kinetic studies were close to 1.0 at the wavelength of
laser radiation. Laser samples were placed in the appropriate cuvettes
fitted with rubber septum or Teflon stopcock, deaerated by bubbling
argon for 2-3 min or the freeze-pump-thaw method (3 cycles). Each
of the sample cells with varying amounts of pyridine was then irra-
diated with a laser pulse. The shutter was opened a few milliseconds
before the laser pulse to allow the monitoring light beam to pass the
sample at a right angle of laser light. The monitoring light was
generated from a 150 W Xe arc lamp fitted with an aspherab beam
columinator, and it could be pulsed to temporarily increase bright-
ness. After passing through the sample, the monitoring beam was
focused on the slit of an Oriel 77200 monochromator, selected for
the wavelength of interest, with both front and rear slits set be-
tween 0.2 and 0.5 mm depending on the intensity of signal. Signals
were obtained with an IP 28 photomultiplier tube detector and were
digitized by a Tektronix 7912 A/D transient digitizer. The entire
apparatus is controlled by an Macintosh Iix computer which was also
used for data storage. The analyses of the data were performed using
a program based on the Marquad Algorithm or Igor (designed by
Wavemetrics).
Characterization of Products Derived from Decomposition of
Diazirine 4 in the Presence of Various Carbene Quenchers. When
diazirine 4 was photolyzed in the presence of TME, the major products
are cyclobutene 7, TME addition product 9, and tert-butylethylene (8).
Compounds 7 and 9 were separated by preparatory GC and character-
ized by NMR and GC-MS. Data for 9: 1H NMR (CDCl3) δ ppm 0.98
(s, 12 H, 4 methyl Hs), 0.7I (s, 9H, tert-butyl Hs), 0.48 (m, 1H), 0.35
1
(m, 1H), 0.22 (m, 1H), 0.09 (m, 1H), -0.42 (d, 1H); H decoupling
NMR revealed that δ 0.48, 0.35, 0.22, 0.09 are the protons on tert-
butyl-substituted cyclopropyl ring and δ 0.42 is the proton on
tetramethyl-substituted cyclopropyl ring; 13C NMR (CDCl3) δ ppm
38.88, 30.39, 29.66, 28.59, 23.66, 20.87, 17.76, 17.46, 9.81, 7.77; MS
m/e (rel intensity) M+ 194 (8.0), 137 (16), 109 (100), 95 (46), 81 (40),
57 (50). Data for 7: 1H NMR (CDCl3) δ ppm 6.05 (m, 1H), 5.98 (m,
1H), 2.63 (m, 1H), 2.36 (d, m, 1H), 2.18 (d, m, 1H), 0.85 (s, 9H); 13
C
NMR (CDCl3) δ ppm 138.91, 135.65, 55.03, 31.98, 31.17, 26.48; MS
m/e (rel intensity) M+ 110 (35), 95 (100), 67 (68), 55 (38). Compound
8 was identified by comparison with an authentic sample (purchased
from Aldrich Chemical Co.).
Acknowledgment. Support of this work by the NSF
CHE9613861 is gratefully acknowledged. The authors are
indebted to Professors Jones, Moss, and Shechter for useful
conversations.
When diazirine 4 was photolyzed in the presence of cyclopentene,
in addition to cyclobutene 7 and alkene 8, addition products to cyclo-
pentene were also formed as a pair of stereoisomers. 1H NMR of the
adduct revealed that there are no olefinic protons at δ 5.7 ppm. Thus,
the carbene does not insert into the allylic C-H bond. Two sharp
singlets at δ 0.75 and 0.70 ppm correspond to tert-butyl protons. Sev-
eral multiplets δ ranging from 0.5 to -0.1 ppm correspond to hydrogens
(34) Mattson, R. J.; Pham, K. M.; Leuck, D. J.; Cowen K. A. J. Org.
Chem. 1990, 55, 2552.