Chemistry Reference
In-Depth Information
O
C.C.E.
(2.5 F/mol
)
Anodic
oxidation
"Preoxidized
iodobenzene"
PIFA
MeO
O
N
OMe
HN
TFE-LiClO
4
349
(%)
44
52
82
OMe
O
348
349
SCHEME 10.54.
successful formation of a spirocyclic
-lactam(entry 3) is particular notable and reflects
the weakly acidic conditions under which this process takes place.
In what represents an affirmation of Glover's early assertion,
17
that the carbonyl
substituent in
N-
acyl-
N-
alkoxy nitrenium ions plays little role in the energy of these
species, Togo has demonstrated that
N-
sulfonyl-
N
-methoxy nitrenium ions
b
354
, gener-
ated through the iodine(III) oxidation of the sulfonamides
, undergomany of the same
reactions as their acyl nitrenium analogs.
133
For example, treatment of
353
353
(R
¼
H) with
Koser's reagent (HTIB) in acetonitrile generated benzothiazine-2,2-dioxide
355
,while
353
356
(Scheme 10.55). Recent work from this group has demonstrated that these useful
transformations can also be accomplished under catalytic conditions, employing ion-
supported aryl iodides and
m
CPBA as the bulk oxidant.
134
Although considerable interest exists in asymmetric dearomatization,
135
the issue
of
p
-facial selectivity as it relates to the spirocyclization of acyl nitrenium ions
has until recently, received surprisingly little, if any, attention.
136
A review of the
(R
¼
OMe), which bears a
p
-methoxy group underwent spirocyclization to yield
TABLE 10.7. Iodine(III)-Mediated Spirocyclization of O-Alkyl
Arylhydroxamates and Related Compounds under Catalytic Conditions
m-
CBA
m-
CPBA
354
353
I
III
*
I
OMe
O
OMe
Me
Me
X
X
X
353
(10 mol %)
m-
HN
N
N
CPBA (1.5 eq)
TFEA, rt
n
n
n
O
O
O
350
351
352
Entry
n
X
Yield (%)
1
1
OMe
86
2
1
NPhth
83
3
0
OMe
84
4
2
OMe
64
