Chemistry Reference
In-Depth Information
NH
+
H
+
N
N
N
N
3
5
7
4
6
N
N
N
H
H
10
11
9
8
H
+
NH
+
SCHEME 8.2.
in solution to afford 2-aminoazepines.
7
Not surprisingly, singlet
p
-biphenylyl nitrene
10
affords a higher yield of the azacycloheptatetraene
11
, observed at about 1900 cm
1
in the Ar matrix photolysis at
515 nm.
9
Both nitrenes,
are protonated to
form the corresponding nitrenium ions on photolysis of the azides in Ar matrices
containing 30% HCl (Scheme 8.2). Similarly, 1-naphthyl nitrene was protonated to
afford the 1-naphthyl nitrenium ion.
9
The nucleophilic N atom of a pyrazole substituent in
l
>
5
and
10,
12
also serves as a nitrene
trap, leading to formation of pyrazolotriazole
13
in competition with the trappable
.
11
Moreover,
azacycloheptatetraene
14
13
is in photochemical equilibrium with the
triazasemibullvalene
15
, as demonstrated by matrix-isolation IR and UV spectros-
copy (Scheme 8.3).
12
The photolysis of 4-hydroxyphenyl azides allows an intramolecular trapping of
the azacycloheptatetraene
.
13
When the
16
to generate unstable 4
H
-azepin-4-ones
17
OH group is in the
ortho
position (
), such ring expansion does not take place at all,
because a rapid 1,4-H shift generates the
o
-quinone imine
18
, which on further
photolysis ring opens to a mixture of geometrical isomers of cumulene
19
.
14
An
20
o
-amino group also traps the nitrene
21
to generate
o
-quinone diimine
22
, but ring
opening was not observed in this case (Scheme 8.4).
14
