Chemistry Reference
In-Depth Information
*
*
NH
2
N
N
N
N
Δ
C
8
H
17
SH
*
N
N
N
14
N
15
N
N
Ph
N
Ph
N
Ph
167
168
169
Δ
or
hν
N
N
Ph
*
*
N
N
N
N
CN
N
Δ
Solution
N
N
N
CPh
Ph
N
Ph
170
172
171
Δ
N
N
CN
N
N
N
N
FVT
*
N
Ph
380
º
C
N
Ph
N
Ph
N
174
173
175
C
8
H
17
SH
N
N
NH
2
N
N
Ph
N
176
177
* =
15
N or
14
N
SCHEME 8.27.
spectroscopy (2008 cm
1
) in the matrix photolyses of
167
(unlabeled) and
173
at
300 nm.
45
Continued photolysis led to the cyanobenzimidazole
l
>
175
in both
cases. The result of
15
N labeling of
is also shown in Scheme 8.27: on FVT, the
nitrene label ends up exclusively in the N1 position in the benzimidazole
167
.
46
175
The likely route to ring contraction is via ring opening of the cyclic carbodiimide
170
to the open chain nitrile ylide
172
, which then cyclizes to
175
.
The nitrile ylide
172
was finally detected by IR and UV spectroscopy by bleaching
.
45
Thus, a mixture of the (unlabeled) nitrene
the nitrene
168
168
(
l
max
¼
548 and
735 nm) and ylide 1
536 nm) is generated by matrix photolysis at 308 nm.
Further irradiation of the matrix at
72
(
l
max
¼
610 nm caused disappearance of the nitrene
and formation of the cyclic carbodiimide
l
>
, absorbing strongly at 2008 cm
1
in the
IR. Further irradiation of the same matrix at
170
395 nm caused disappearance of
the ylide and again formation of the cyclic carbodiimide
l
>
170
. Therefore, IR bands
at 2281, 2141, and 2119 cm
1
could be assigned to ylide
172
(
s-E
and
s-Z
conformations).
