Chemistry Reference
In-Depth Information
Me
OSiMe
3
R
1
ν
(350 n
m
)
h
R
3
BF
4
-
R
2
Me
N
Me
N
N
30 min
Ph
Ph
522
523
R
1
R
2
O
N
N
Ph
O
R
3
N
H
526a
R
1
R
2
R
1
R
3
R
2
or
524
525
O
R
1
R
2
R
3
524
(%)
525
(%)
526a
(%)
526b
(%)
R
3
N
Ph
526b
-
Me
H
OMe
OMe
29
12
6
Me
Me
28
11
19
-
H
H
Me
Ph
22
0
-
2
H
H
24
0
-
3
SCHEME 10.86.
N
NC
OMe
NC
NH
NC
N
CH
3
CN
H
+
OMe
+
MeO
HN
CN
NC
H
OMe
or Δ
NC
N
527
528
529
530
SCHEME 10.87.
(pathway b).
205,206
Dihydropyrazine products
a[2
þ
1] cycloaddition to form
535
536
then arise through the rearrangement of this aziridinium ion. Evidence for this
mechanism is outlined in Table 10.9. When styrene and
p
-halostyrenes
537a
-
c
react
with DISN (
527
), the only products formed are aziridines
538c
. However, with the
more electron-rich substrates
p
-methoxystyrene (
537d
) and 2-vinylfuran (
537e
),
only [4
are
isolated. It is instructive to note that the cycloaddition of DISN with 1,2-disubstituted
olefins occurs with complete retention of stereochemistry, for example, (
E
)-anethole
(
þ
2] cycloadducts, dicyanotetrahydropyrazines
539
and pyrazines
540
541
) reacts to provide
trans
adduct
542
, while (
E
)
-
phenylpropene (
543
) yields
trans
-aziridine
(Scheme 10.89).
Fukunaga concluded from these observations that the reaction of DISN with
olefins proceeds through mutual
544
interaction between the lowest unoccupied
