Biomedical Engineering Reference
In-Depth Information
Me
CO
2
Et
OMe
CO
2
Et
1. Tf
2
O,
OMe
t-
Bu
N
t-
Bu
OTf
O
O
O
2.
i
-Pr
2
NEt
N
N
O
O
315
316
OMe
CO
2
Et
OMe
EtO
2
C
H
H
O
N
68%
N
O
H
O
O
318
317
Me
OR
O
O
OR
OR
Ph
Ph
1. Tf
2
O,
H
H
H
H
N
N
O
t-
Bu
N
t-
Bu
+
N
CHO
O
O
N
N
2.
i-
Pr
2
NEt,
Ph
H
EtO
H
EtO
EtO
N
O
O
O
O
319a
(R = TBS)
319b
(R = Me)
320a
(R = TBS; 62%)
320b
(R = Me; 69%)
321a
(R = TBS; 16%)
321b
(R = Me; 23%)
Me
O
O
OMe
OMe
OMe
H
R
Ph
Ph
H
R
1. Tf
2
O,
R
N
N
O
t-
Bu
N
t-
Bu
O
+
O
O
N
N
N
Ph
2.
i-
Pr
2
NEt,
H
EtO
H
EtO
EtO
N
O
O
O
O
322a
(R = Me)
322b
(R = Ph)
323
(31%)
324
(31%)
SCHEME 13.60
Accordingly,
311
reacted with
312
to produce
313
. Without isolation,
313
was heated
at 80
C for 32 h with H
unig's base to give
314
in 81%yield. Cleavage of the isopropyl
groups using AlCl
3
furnished lamellarin K in 96% yield.
B
€
evesque described a cascade sequence initiated by a
Vilsmeier-Haack cyclization that terminates with a dipolar cycloaddition [106].
The polyfunctional formyl amide
315
was treated with triflic anhydride to effect a
Vilsmeier-Haack reaction so as to produce
316
(Scheme 13.60). Deprotonation
and loss of triflate generated azomethine ylide
317
that when added to the
pendant alkene furnished a mixture containing predominantly
318
together with
an undetermined diastereomer in an 8:1 ratio and 77% yield. In order to explore
the versatility of the cascade, substrate
319a
was constructed and exposed to
triflic anhydride followed by treatment with H
elanger and L
unig's base and
N
-phenylmaleimide
to produce a 4:1 mixture of
320a
and
321a
in 78% yield. When subjected to the
same conditions,
319b
produce a 3:1 mixture of
320b
and
321b
, predominating in
the former, in 92% yield. Interestingly,
322a
failed to react in the cascade
sequence due to enamine formation from the initial Vilsmeier intermediate. Aryl
amide
322b
, however, produced a nearly equimolar mixture of
323
and
324
in
63% yield.
€
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