Chemistry and Kinetics of Dipropylcarbene
J. Phys. Chem. A, Vol. 103, No. 27, 1999 5337
TABLE 1: Values of kPYRτ Obtained by LFP of Precursor
UV (pentane): 235, 321 nm. HRMS (EI): calcd for C10H21N2O2
1
3
a, 1b, or 1b-d in the Presence of Pyridine at Ambient
(
M + 1) 201.1604, found 201.1617.
Temperature
3
2,2-Dimethoxy-5,5-dipropyl-∆ -1,3,4-oxadiazoline (1b). Com-
precursor
solvent
k
PYR
τ
8
pound 1b was prepared using the procedure of El-Saidi et al.
1
1
1
1
1
1
a
b
b-d
b
b
CH
CH
CH
CF ClCFCl
2 2
c-C
c-C
2
2
2
Cl
Cl
Cl
2
2
2
0.9 ( 0.1
0.9 ( 0.2
2.2 ( 0.2
0.5 ( 0.1
0.5 ( 0.1
0.5 ( 0.1
4-Heptanone (2.7 g, 11.8 mmol) and methyl hydrazinecarboxy-
late (1.07 g, 11.8 mmol) were refluxed in benzene. Water was
removed with a Dean-Stark trap. Rotary evaporation removed
solvent and generated the methoxycarbonyl hydrazone of
3
6
H
D
12
4
-heptanone (99%), which was used without purification in the
b
6
12
next step. It could be recrystallized after drying under vacuum.
1
H NMR (200 MHz, CDCl3, ppm): δ 3.78 (s, 3H), 3.69 (s,
H), 2.15 (m, 4H), 1.49 (m, 4H), 0.89 (m, 6H). C NMR (50
Herein we are pleased to report the results of this study, which
include studies of the photochemistry of 1a and 1b by laser
flash photolysis, classical chemical analysis, and argon matrix
isolation techniques.
1
3
1
MHz, CDCl3, ppm): δ 157.5, 128.0, 52.5, 38.5, 30.5, 20.0, 18.5,
14.0, 13.7. Mp: 73-74 °C. A solution of 1-methoxycarbonyl-
2-(4-heptylidene)hydrazine in methanol was added dropwise to
II. Experimental Section
a solution of lead tetraacetate (5.7 g, 12.9 mmol) in methanol
cooled with an ice bath. After 4 h at room temperature,
potassium hydroxide (0.66 g, 11.8 mmol) in methanol (10 mL)
was added and the solution was stirred overnight under argon.
The mixture was extracted with dichloromethane (3 × 50 mL),
the combined dichloromethane extracts were dried (MgSO4),
the solvent was evaporated, and the residue was chromato-
graphed (silica, 10% EtOAc in hexane). The yield was 89%.
Materials. Solvents (Aldrich) were used as received. 1-Pen-
tene was passed through an alumina column immediately before
use. Methanol, pyridine, and piperidine were purified by
distillation. E- and Z-3-heptene were used as received from
Aldrich.
Typical Procedure for Photolysis Experiments. Various
amounts of carbene quenchers were added to each cuvette with
maintenance of a constant concentration (typically 0.01 M) of
carbene precursor. Solvent was then added to each cuvette in
order to achieve a constant volume of sample (0.3 mL) for each
experiment. Samples were degassed by purging with oxygen-
free argon for 3 min before they were irradiated individually
with sixteen 300 nm bulbs in a Ray-o-Net reactor for 2 h. The
yields of products were then determined by integration of peaks
in gas chromatograms using analytical GC, with decane as
internal standard. Analytical gas chromatography was performed
on a Perkin-Elmer 8500 gas chromatograph equipped with a
flame ionization detector, using a Supelco fused silica capillary
column cross-linked with methylsilicone (i.d. 0.32 mm, length
1
H NMR (200 MHz, CDCl3, ppm): δ 3.52 (s, 6H), 1.78 (m
13
4
H), 1.35 (m, 4H), 0.91 (t, 6H). C NMR (50 MHz, CDCl3,
ppm): δ 136.5, 124.7, 52.0, 38.2, 17.5, 14.4. HRMS: calcd
for C10H20N2O3 216.1474, found 216.1510.
3
2
,2-Dimethoxy-5,5-dipropyl-∆ -1,3,4-oxadiazoline (1b-d3).
4-Heptanone (5.4 g, 23.8 mmol) was stirred with a trace amount
of sodium methoxide in CD3OD overnight under argon. After
CD3OD was evaporated, water was added to quench the sodium
methoxide and the resulting mixture was extracted with dichlo-
romethane (3 × 50 mL). The combined dichloromethane
extracts were evaporated, generating 4-heptanone-d3. The
1
product was used without purification in the next step. H NMR
(
1
7
200 MHz, CDCl3, ppm): δ 2.31 (m, 1H), 1.55 (q, 4H, J )
3
0 m, film thickness 3 µm). GC/MS analyses were performed
0.5 Hz), 0.88 (t, 6 H). MS (EI), m/z (rel intensity): 117 (28),
on a HP-6890 Series GC System with an HP-1 methylsiloxane
capillary column (40.0 m × 100 µm × 0.20 µm). Compounds
giving rise to those peaks were identified from their mass
spectral fragmentation patterns and by comparison with authentic
3 (100), 61 (10), 45 (93). This deuterated ketone was used to
1
prepare 1b-d3 by the method already described for 1b. H NMR
(
200 MHz, CDCl3, ppm): δ 3.50 (s, 6H), 1.74 (m, 1H), 1.35
1
3
(m, 4H), 0.88 (t, 6H). C NMR (50 MHz, CDCl3, ppm): δ
samples.
3
136.4, 124.5, 51.7, 37.4 (m), 16.4, 16.3, 14.0. HRMS: calcd
for C10D3H17N2O3 219.1662, found 219.1641. Using a Kratos
MS-25 with direct cold probe injection, 1b and 1b-d3 were
analyzed for their isotopic composition. For 1b-d3, the relative
ratios of d0, d1, d2, d3, and d4 were determined to be 3:14:53:
2-Methoxy-2-methyl-5,5-dipropyl-∆ -1,3,4-oxadiazoline (1a).
4
1
-Heptanone (2.7 g, 11.8 mmol) and acetylhydrazine (0.87 g,
1.8 mmol) were refluxed in benzene; water was removed with
a Dean-Stark trap. The solvent was removed from the resultant
mixture to yield crude 1-acetyl-2-(4-heptylidene)hydrazine,
which was purified by column chromatography (silica, 50%
1
00:77. This analysis was performed on the intense peaks with
1
m/z ) 185-189, which correspond to loss of CH3O from the
molecular ion.
EtOAc in hexane, 85% yield). H NMR (200 MHz, CDCl3,
ppm): δ 9.58 (s, 1H), 2.11 (m, 7H), 1.42 (m, 4H), 0.86 (m,
1
3
Azine of 4-Heptanone (6). 4-Heptanone (5.4 g, 0.6 mmol)
and hydrazine (0.38 g, 11.8 mmol) in benzene (120 mL) were
refluxed overnight. Water was removed with a Dean-Stark trap.
The crude product was purified on a column of silica gel by
6
H). C NMR (50 MHz, CDCl3, ppm): δ 173.8, 155.1, 38.5,
1.7, 21.5, 19.5, 18.9, 14.0, 13.5. Mp: 38-39 °C. A solution
3
of the 1-acetyl-2-(4-heptylidene)hydrazine in methanol was
added dropwise to a solution of lead tetraacetate (5.7 g, 12.9
mmol) in methanol cooled with an ice bath. After 4 h at room
temperature, the yellow color of the mixture disappeared.
Potassium hydroxide (0.66 g, 11.8 mmol) in methanol (10 mL)
was added, and the resultant mixture was stirred overnight under
argon. The mixture was extracted with dichloromethane (3 ×
1
elution with 50% EtOAc in hexane (yield 87%). H NMR (500
MHz, CDCl3, ppm): δ 2.26 (m, 8H), 1.61 (m, 4H), 1.45 (m,
1
3
4
H), 0.97 (m, 6H), 0.91 (m, 6H). C NMR (126 MHz, CDCl3,
ppm): δ 165.3, 39.0, 33.1, 20.2, 19.8, 14.8, 14.5. MS (EI), m/z
(
(
rel intensity): 224 (M, 4), 181 (100), 140 (92), 112 (55), 70
86).
7
0 mL), the combined organic layers were dried (MgSO4), the
solvent was evaporated, and the residue was chromatographed
1,1,2-Tripropylcyclopropane (8). Oxadiazoline 1a (0.14 g,
1
(silica, 5% EtOAc in hexane). The yield was 79%. H NMR
0.70 mmol) and neat 1-pentene (5.5 mL) were irradiated (300
nm) for 16 h after bubbling with dry Ar for several minutes.
The remaining 1-pentene was removed by rotary evaporation,
and the mixture was chromatographed (silica, 7.5% EtOAc in
(
1
200 MHz, CDCl3, ppm): δ 3.16 (s, 3H), 1.60 (s, 3H), 1.70-
.58 (m, 8H), 0.85 (m, 6H). 13C NMR (50 MHz, CDCl3, ppm):
δ 132.2, 125.2, 50.7, 38.1, 37.7, 21.9, 17.2, 16.8, 14.3, 14.2.