Linear Ketenimines
J . Org. Chem., Vol. 67, No. 4, 2002 1091
After being stirred at 0 °C for 0.5 h, the mixture was extracted
with water and the extracts were washed with toluene. The
aqueous extracts were stirred with methyl iodide (426 mg, 0.19
mL, 3.00 mmol) for 14 h at 4 °C. The precipitate was collected
and recrystallized from ethanol to give colorless prisms of 9a
(146 mg, 39%): mp 117-118 °C; IR (KBr) ν 3322 s, 2209 s,
2187 vs, 1555 vs, 1496 w, 1402 s, 1287 m, 1157 vw, 972 vw,
method being B3LYP/6-311+G(3df,2p)//B3LYP/6-31G*.
The chosen method can be presumed to have an accuracy
between B3LYP/6-311+G(2d,p)//B3LYP/6-31G* and
B3LYP/6-311+G(3df,2df,2p)//B3LYP/6-31G*. When com-
pared with the experimental data from the Gaussian G2
molecule set, these two methods had mean absolute
deviations (standard deviations) of less than 13(12.5) and
less than 11(11) kJ mol-1 and largest errors of 57/-84 and
53/-39 kJ mol-1, respectively.29 While the overall mean
absolute deviation of the energies calculated with the
chosen method is estimated at <13 kJ mol-1, the mean
absolute deviation for closely related compounds would
be expected to be smaller. Enthalpies were calculated
using energy values from the higher level and an un-
scaled correction from the vibration calculation at the
lower level. Entropies were taken directly from the
vibration calculation at the lower level. The free energies
were then calculated from these two values. The tem-
perature used in the vibration calculations and hence the
free energy values was 298.15 K. All transition state
structures were characterized by having one imaginary
vibration. These vibrations are listed in the Supporting
Information. Self-consistent reaction field (SCRF) calcu-
lations29 were performed in two steps. The volume of the
structure was calculated and then used with the ap-
propriate value in a Gaussian 98 SCRF dipole calculation
to optimize geometry and obtain frequency data. If the
geometry changed markedly, these two steps were re-
peated. A single point energy calculation using the
expanded basis set was then performed within the SCRF.
1
923 w cm-1; H NMR (200 MHz, CDCl3, 25 °C) δ 6.53 (bs, 1
H), 3.20 (d, J ) 5.1 Hz, 3 H), 2.67 (s, 3 H); 13C NMR (50 MHz,
CDCl3, 25 °C) δ 175.3, 115.60, 115.42, 51.8, 33.1, 17.2. Anal.
Calcd for C6H7N3S: C, 47.04; H, 4.61; N, 27.43; S, 20.93.
Found: C, 47.06; H, 4.62; N, 27.52; S, 20.78.
Dicya n o-N-m eth ylk eten im in e 10a . FVT of 9a at 500 °C
followed by deposition of the thermolysate as a neat film, or
by co-deposition with argon onto a KBr window, gave rise to
the following spectra: IR (film, 135 K) ν 2282 m, 2256 m, 2213
s, 2175 sh/m, 2100 m, 2086 m, 1441 w, 1396 w, 1370 w, 1321
w, 1241 w, 1030 vw, 907 vw cm-1; IR (Ar matrix, 13 K) ν 2948
w, 2259 m, 2235 m, 2138 vs, 2133 vs, 2122 vs, 2117 vs, 1570
m, 1528 m, 1457 m, 1411 m, 1218 m, 1111 m, 617 m, 486 m
cm-1; additional peaks at ν ) 2939 w, 1446 m, 1436 w, 1070
w cm-1 belong to MeSH.19
2-Cyan o-3-m eth ylth io-3-eth ylam in oacr ylon itr ile 9b was
prepared as described for 9a from malononitrile (203 mg, 3.07
mmol), butyllithium solution (2.5 M, 1.10 mL, 2.75 mmol),
ethyl isothiocyanate (260 mg, 0.25 mL, 2.98 mmol), and
iodomethane (426 mg, 0.19 mL, 3.00 mmol) to give crystals
after standing for 14 h at 4 °C. The precipitate was collected
and recrystallized from ethanol/water yielding colorless crys-
tals of 9b (300 mg, 60%): mp 82-83.5 °C; IR (KBr) ν 3292 m,
2987 w, 2942 w, 2208 s, 2195 s, 1547 s, 1516 m, 1464 m, 1280
1
m cm-1; H NMR (400 MHz, CDCl3, 25 °C) δ 6.40 (bs, 1 H),
3.62 (dq, J ) 7.2 and 5.9 Hz, 2 H), 2.67 (s, 3 H), 1.30 (t, J )
7.2 Hz, 3 H); 13C NMR (50 MHz, CDCl3, 25 °C) δ 174.3, 115.53,
115.26, 52.3, 41.7, 17.5, 15.2. Anal. Calcd for C7H9N3S: C,
50.28; H, 5.42; N, 25.13; S, 19.17. Found: C, 50.25; H, 5.44;
N, 25.14; S, 19.20.
Exp er im en ta l Section
Dicya n o-N-eth ylk eten im in e 10b. FVT of 9a above 500
°C followed by co-deposition of the thermolysates with argon
onto KBr or FVT at 700 °C with isolation of the product as a
neat film on KBr gave rise to the following spectra: IR (film,
134 K) ν 2255 m, 2172 vs, 2055 sh,w, 1415 m, 1375 m, 1330
m, 1280 m, 1240 m, 1173 w, 1086 m cm-1; IR (Ar matrix, 17
K) ν 3008 w, 2985 w, 2948 w, 2265 m, 2235 m, 2142 s, 2103
m, 2089 m, 1540 m, 1440 s, 1389 m, 1327 w, 1177 w, 1147 w,
Ma ter ia ls. Compound 3 was prepared according to the
literature procedure.30 Cyano-N-phenylketenimine 13 and its
precursor, 3-methylthio-3-(phenylamino)acrylonitrile, were pre-
pared according to ref 2.
Matr ix Isolation . Argon matrixes were prepared by vacuum
deposition of samples with argon (99.999%) onto a KBr window
at ca. 25 K using a closed-cycle liquid helium cryostat (Air
Products DE202 with a Lakeshore 330 temperature controller).
In FVT experiments,31 a mixture of argon and sample was led
through a quartz tube (10 cm length, 0.8 cm inner diameter,
equipped with heating wire and a thermocouple), and the
product was isolated on the cold window at ca. 25 K. Photolyses
were carried out using a 1000 W Hanovia Xe/Hg lamp
equipped with a water filter. IR spectra were recorded at 7-17
K.
Nea t Isola tion of F la sh Va cu u m Th er m olysis P r od -
u cts. The sample was sublimed in a high vaccum (1.0 × 10-5
mbar) into the same quartz thermolysis tube as described
above, and the thermolysates were isolated on a KBr window
at ca. 130 K. IR spectra were recorded at 130-143 K.
2-Cyan o-3-m eth ylth io-3-m eth ylam in oacr ylon itr ile 9a.32
To a stirred solution of malononitrile (198 mg, 3.00 mmol) in
dry THF (3 mL) at -78 °C was added butyllithium (2.5 M in
hexane, 1.10 mL, 2.75 mmol) over 10 min. After the mixture
was stirred for a further 0.5 h at -78 °C, methyl isothiocyanate
(219 mg, 3.00 mmol in 2 mL of THF) was added over 15 min.
1023 m, 949 s, 852 w, 798 w, 666 w, 578 w, 460 w cm-1
.
2-Cya n o-3-m eth ylth io-3-p h en yla m in oa cr ylon itr ile 9c
was prepared as described for 9a from malononitrile (1.54 g,
23.3 mmol), butyllithium solution (2.5 M, 8.70 mL, 21.8 mmol),
phenyl isothiocyanate (3.10 g, 2.74 mL, 22.9 mmol), and
iodomethane (3.20 g, 1.41 mL, 22.5 mmol). The precipitate was
collected and recrystallized from ethanol yielding colorless
crystals of 9c (2.40 g, 48%): mp 174-178 °C; IR (KBr) ν 3292
vs, 2207 vs, 2197 vs, 2182 vs, 1595 m, 1520 s, 1493 s, 1451 m,
1
1264 m, 967 m cm-1; H NMR (200 MHz, (CD3)2CO, 25 °C) δ
7.25-7.50 (m, 5 H), 3.10 (bs, 1 H), 2.51 (s, 3 H); 13C NMR (50
MHz, (CD3)2CO, 25 °C) δ 172.5, 139.3, 130.1, 127.5, 124.8,
115.0 (two CN groups with identical shift), 56.1, 16.2. Anal.
Calcd for C11H9N3S: C, 61.37; H, 4.21; N 19.52; S, 14.89.
Found: C, 61.50; H, 4.26; N, 19.47; S, 14.70.
Dicya n o-N-p h en ylk eten im in e 10c. FVT at 650 °C fol-
lowed by co-deposition of the thermolysate with argon onto
KBr or FVT above 700 °C with isolation of a neat film of the
thermolysate on KBr gave rise to the following spectra: IR
(film, 134 K) ν 2229 vs, 2173 s, 1491 m, 1442 m, 762 s cm-1
;
(29) Foresman, J . B.; Frisch, M. J . Exploring Chemistry with
Electronic Structure Methods, 2nd. ed.; Gaussian Inc., Pittsburgh, PA,
1999.
(30) (a) Dijkstra, R.; Bacher, H. Recl. Trav. Chim. Pays-Bas 1953,
73, 569-574. (b) Dijkstra, R.; Bacher, H. Recl. Trav. Chim. Pays-Bas
1953, 73, 575-580.
(31) Kuhn, A.; Plu¨g; C.; Wentrup, C. J . Am. Chem. Soc. 2000, 122,
1945. Kappe, C. O.; Wong, M. W.; Wentrup, C. J . Org. Chem. 1995,
60, 1686.
additional signals prevalent at lower pyrolysis temperatures
at ν 2284 w, 2213 s, 2134 br/m, 2097 sh/m, 2084 sh/m, 2066
sh/m, 1464 m, 1424 m cm-1 are possibly due to the imine
tautomer of 9c; IR (Ar matrix, 17 K) ν 3008 w, 2948 w, 2234
m, 2090 vs, 2077 sh/m, 1492 m, 1295 m, 1073 m, 760 s, 685 s,
580 m, 524 m cm-1
.
2-Cya n o-3-a zid ocin n a m on itr ile 11. Since azide 11 de-
composes slowly at ambient temperature (20 °C), all steps
should be carried out in ice-cooled vessels. At -20 °C, sodium
azide (414 mg, 6.36 mmol) in water (1 mL) was added to
(32) (a) Metzger, C.; Wegler, R. Chem. Ber. 1968, 101, 1131. (b)
Saalfrank, R. W.; Schobert, K.; Trummer, S.; Wolski, A. Z. Naturforsch.
B 1995, 50, 642.