Chemistry Reference
In-Depth Information
O
O
N
3
N
3
Ar
Ar
69
70
SCHEME 12.33.
The lifetime of the transient assigned to
3
61a
m
was measured to be about 9
sin
deoxygenated ethanol and
8 ms in methanol and methanol-d
4
. Saturation of the
solvents with oxygen caused an anomalis decrease in the lifetime of intermediate
assigned to
3
61a
. The bimolecular rate constant of reaction with oxygen was
measured to be 1.4
10
9
M
1
s
1
in cyclohexane and 1.6
10
9
M
1
s
1
in etha-
nol,
146
which are not typical of reaction of triplet nitrenes with oxygen. For instance,
the rate constants of reaction of triplet aryl nitrenes with molecular oxygen are
substantially lower and are in the range (0.8-8)
10
6
M
1
s
1
.
150-152
The rate
constant of the reaction of triplet nitrenes
69
and
70
with oxygen was estimated
10
4
M
1
s
1
(Scheme 12.33).
153,154
The nitro and nitroso compounds
were isolated after photolysis of corresponding aryl and alkyl azides in solutions
saturated with oxygen.
150-154
Thus, assignment of the intermediate observed by Maloney and coworkers
146
to
triplet tosyl nitrene is questionable. In general, the direct spectroscopic detection of
the intermediates (including singlet and triplet sulfonyl nitrenes) as well as compu-
tational studies is required to better understand the mechanism of the sulfonyl azide
photolysis.
Recently,
26,149
N-substituted dibenzothiophene sulfilimines were proposed as a
source of acyl nitrenes, including sulfonyl nitrenes. To evaluate the ability of
dibenzothiophene N-substituted sulfilimines as photochemical nitrene sources, their
photolyzes in the presence of several trapping reagents, such as sulfides, olefins, and
phosphorus compounds, were performed.
149
Photolysis of
N
-tosyliminodibenzo-
thiothene (
to be 3-5
) in different solvents in the presence of diphenylsulfide gave
dibenzothiophene
71a
72
(90-99%),
N
-tosyl sulfilimine
73
(25-73%), and tosylamide
74
in 0-17% yield (Scheme 12.34).
Photolysis of
was also performed in the presence of several cyclic olefins and
trivalent phosphorus compounds (Schemes 12.35 and 12.36). The corresponding
71a
-NSO
2
C
6
H
4
-Me
-NSO
2
C
6
H
4
-Me
+
S
S
h
v >300 nm
Solvent
+ Ph-S-Ph
+ Ph-S-Ph
+
+ Me-C
6
H
4
SO
2
NH
2
71a
72
73
74
SCHEME 12.34.
Photolysis of
N
-tosyliminodibenzothiothene (
71a
) in the presence diphenyl
sulfide.
149
