Chemistry Reference
In-Depth Information
ion. The
meta
-products
appear to come from rearrangement of an initial
para
-adduct.
160
The reactions are efficient since 0.1M amine completely suppresses
the solvolysis products except the rearrangement product generated from a tight ion
pair.
160
The reduction product
120
and
121
122
is generated only in the presence of PhNMe
2
, and
it appears to be produced by a single electron transfer from the amine to the nitrenium
ion.
160
The reduction by-product, generated in equimolar quantities with
,
a known product of decomposition of PhNMe
2
radical cation in the presence of
excess PhNMe
2
.
161
The change in mechanism from
122
,is
123
appears to be caused
by steric hindrance to the approach of the aromatic amine in an S
N
2 attack at N by the
N
-acetyl group.
Takeuchi and coworkers showed that the N- to C-substitution ratio on the apparent
64a
68o
to
68n
by a series of aromatics in arene-TFA mixtures is sensitive to the structure of the
precursor (phenyl azide,
N
-phenylhydroxylamine, or
O
-trifluoroacetyl-
N
-phenyl-
hydroxylamine) even though the decomposition rates of the precursor is unaffected
by the identity of the arene.
162
This is consistent with characterization of
from
trapping studies in water as a short-lived species that reacts through leaving group-
dependent ion pair or preassociation processes.
107,109,110,115
Falvey and coworkers performed LFP studies on the reactions of
N
-methyl-4-
biphenylyl nitrenium ion
64a
with electron rich
aromatics.
163,164
Their conclusions are summarized in Scheme 4.34. The
64y
and diphenyl nitrenium ion
86
p
-complex
124
64y
with a series of aromatics correlates well with the equilibrium constant for formation
was not directly detected during LFP experiments, but the rate of reaction of
SCHEME 4.34.
Mechanistic scheme for the reaction of nitrenium ions with arenes.
