Chemistry Reference
In-Depth Information
SCHEME 4.6.
Photolysis of phenyl azide in acetic acid.
even at high ethanol concentration, it was assumed that
20
and
21
are derived from
.
67
The products generated in the
stronger acids TFA and TFSA in the presence of
efficient internal return of the tight ion pair
24
-nucleophiles such as benzene
were attributed to nitrenium ions generated directly from the protonated azide.
68,69
Under these more strongly acidic conditions, nitrene-derived products were not
detected.
Photogeneration of nitrenium ions from 3-substituted-2,1-benzisoxazoles (3-
substituted anthranils),
p
, or 3-substituted-
N
-alkyl-2,1-benzisoxazolium salts
(3-substituted
N
-alkylanthranilium salts),
27
, was investigated.
70-75
Photolysis of
anthranils in concentrated acids generates products apparently derived from nitre-
nium ions. For example, photolysis of
25
,
26
in concentrated HCl or H
2
SO
4
generates the products shown in Scheme 4.7.
70-72
Thermolysis of
25a
and
25b
28
in concentrated
H
2
SO
4
leads to the same products as
, in lower yield with a different product
ratio.
72
If the 5-position of the anthranil is blocked by an alkyl or halogen substituent,
as in
25a
26
, products analogous to those previously observed by Bamberger
for
rearrangement
of
4-substituted-
N
-arylhydroxylamines
are
generated
(Scheme 4.7).
71,72
For
26a
, another pathway was revealed by the hydroxymethyl
.
72
In the presence of aromatics such
as anisole both N- and C-substitution products similar to those reported by Bamberger
are observed.
73
Under neutral or weakly acidic conditions, photolysis of
product
30a
that is apparently generated from
29a
26a
leads to
azepines characteristic of aryl nitrenes.
72,74
Photolysis products generated in acid were attributed to nitrenium ions formed by
photolysis of the N-protonated anthranil.
70-73
It is likely that the nitrenium dication
is present under these conditions and responsible for some products. Support for the
mechanism for
25
or
26
at the bottom of Scheme 4.7 came from the observation that
