Chemistry Reference
In-Depth Information
OMe
O
MeO
H
PIFA
MeOH
OMe
MeO
OMe
MeO
β
NH
N
OTIPS
N
OMe
CH
2
Cl
2
-78 to -20°C
O
MeO
O
O
OTIPS
OTIPS
428
430
(99%, d.r. = 9:1)
429
3 step
s
5 step
s
Kishi
et
al
.
OH
MeO
O
H
C
4
H
9
-
n
O
N
N
NH
n
-C
5
H
11
O
O
OTIPS
(-)-12H-HTX (
433
)
431
(90%)
432
(25%)
SCHEME 10.69.
hemiacetal
441
, which upon
in situ
reduction with sodium triacetoxyborohyride
provided
-hydroxymethyl glutamic acid, in
good overall yield. This one-pot transformation is generally applicable and was
employed to access a number of important target systems (
b
-hydroxy ester
442
, a masked form of
a
443
-
446
), including 4,4-
)
168
and quaternary tetrahydroisoquinoline-3-carboxylic
acid (Tic) derivatives such as
disubstituted
b
-lactams (
443
.
169
In addition to simple reduction, latent
446
b
-formyl
441
ester
can also be intercepted with a variety of weakly basic nucleophiles, to
provide 2-substituted pyroglutamate derivatives
447
-
450
.
Birch
reduction
OO
Ozonolys
i
s
R
1
R
2
R
2
R
2
R
1
R
1
436
(R
1-2
= H, alkyl, OR)
434
435
OR
4
O
OO
Dearomatizat
i
on
Ozonolys
i
s
R
1
R
3
R
3
R
1
R
3
R
1
R
2
E
R
2
R
2
E
O
439
(R
1-3
= H, alkyl, OR)
437
438
OHC
CHO
SCHEME 10.70.
