Chemistry Reference
In-Depth Information
OH
PCl
5
Ph
Ph
N
C
R
Ph
R
R
Ph
O
H
N
N
72
H
2
O
N
C
C
Ph
Ph
R
Ph
Ph
Ph
Ph
Ph
Cl
Ph
Δ
Ph
Ph
N
74
75
76
77
C
R
Ph
73
SCHEME 10.10.
alkyl group from carbon to divalent nitrogen would indicate that the nitrogen was
significantly electron deficient” (Scheme 10.11).
2g
Treatment of a methanolic
solution of
heated at reflux with silver nitrate provided azabicyclo[3.2.1]octane
82
, as a mixture of
exo
and
endo
isomers in moderate yield.
41
Gassman rationalized
this rearrangement by proposing two possible mechanistic routes, both proceeding
through iminium ion
78
. In pathway a, Ag
þ
-assisted heterolysis of
81
78
generates
discrete nitrenium ion
79
, which then undergoes Wagner-Meerwein rearrangement
to form
.
Pathway b, on the other hand, involves the concerted loss of chlorine and accompa-
nying alkyl migration to provide
81
. Subsequent trapping by methanol then yields both isomers of
82
directly. Although an electron-deficient nitrogen
species must be involved regardless of which pathway is operating, a definitive
conclusion regarding the participation of a discrete nitrenium ion intermediate could
not be made.
Observing that the solvolysis of bicyclic
N
-chloramines often produced small
amounts of the parent secondary amine
81
, Gassman concluded that this occurred
when the initially generated singlet-state nitrenium ion underwent intersystem
83
a
N
79
AgNO
3
MeOH
+
N
OMe
N
N
H
MeOH
Δ
Cl
82
(60%)
83
(trace)
78
81
b
N
80
SCHEME 10.11.
