Chemistry Reference
In-Depth Information
cyanopyrroles
, or whether these are formed in concerted reactions of the
pyridyl nitrenes.
22,55-57
DFT calculations indicate that both pathways are possible,
but the ring-opening-ring-closure reactions
210
and
211
have, in fact,
the lowest activation barrier.
57
The cyanopyrroles are known to interconvert under
FVT conditions.
18,53
The photochemical and medium temperature FVT (600
C) reactions of
pyridazinyl carbene
188
were described in Scheme 8.30. Very remarkably, FVT
at 700-800
C gives, in addition to the products described in Scheme 8.30, low yields
of the products expected from 2-pyridyl nitrene, namely,
203/205!207!210
209
,
210
, and
211
, but the
relative yield of glutacononitrile
209
is higher when starting from triazole
186
than
(Scheme 8.34).
57
The formation of these products suggests that
from tetrazole
202
188
, albeit in low yield
(Scheme 8.34). Energy calculations at the B3LYP/6-31G
level support the feasi-
bility of this rearrangement. The relative energies indicated in Scheme 8.34 suggest
that the cyclization of
can rearrange to
203
and/or the cyclic ketene hydrazone
215
requires a very
modest energy barrier, and its rearrangement to the seven-membered ring
188
to the unobserved cyclopropene
214
215
is
N
N
N
N
N
N
N
N
3
N
186
202A
N
202T
H
C
FVT
41
36
52
N
N
N
N
[50]
[45]
700ºC
N
N
N
N
N
N
TS 69[77]
188
214
216
215
203
T
0
0, S
1
[16.2]
34
E
: 59
Z
: 55.0
28[26]
51 [51]
40[29]
14 [12]
24[23]
NH
N
N
N
CN
CN
207
204
2,6 [0.5]
20[23]
208
-13 [-10]
CN
CN
CN
H
H
CN
211
209
210
Energies in kcal/mol in plain font at the B3LYP/6-31G* [CASPT2] levels.
SCHEME 8.34.
