Chemistry Reference
In-Depth Information
OH
O
CHCl
3
R
1
= Ph, R
2
= H (98%)
R
1
= Pr, R
2
= H (80%)
R
1
= R
2
= Me (75%)
R
1
CCl
3
R
2
R
1
DBU (
1
) (1 equiv)
R
2
Scheme 3.28
Amidine mediated trichloromethylcarbinol synthesis
OMe
O
OBn
O
OBn
BnOCH
2
DBU (
1
) (cat)
O
CF
3
CO
2
H
RO
OMe
RO
CHO
RO
OH
toluene-DCM
MeCN-H
2
O
HO
OBn
HO
OBn
HO
OBn
R = H (67%); R = Bn (58%)
from glycosides
Scheme 3.29
DBU (1) promoted intramolecular aldol reaction
DBU (
1
)
(0.1 equiv)
O
O
XH
X
-
H
-
R
1
+
R
1
R
2
R
2
H
+
MeCN
+
N
2
N
2
X = O, NR
3
R
1
= OEt, Ph, Me
Scheme 3.30
DBU (1) catalysed addition of acyldiazomethane to aldehyde or imine
Nucleophilic addition of acyldiazomethane to aldehydes or imines is one of the methods
for preparing
-aminoacyldiazomethanes. Stoichiometric amounts of rather
strong bases such as BuLi, lithium diisopropylamide, sodium hydride (NaH), potassium
hydroxide and so on are frequently required. DBU (1) was found to be an effective catalyst
in this reaction under milder conditions without using anhydrous conditions [48]
(Scheme 3.30). Moderate to high yields (58-97%) are achieved on the reaction of
a
-hydroxy- or
a
a
-
diazoacetate (R
1
OEt) with aromatic and aliphatic aldehydes. The reaction with electron-
rich aromatic aldehydes such as p-anisaldehyde was sluggish.
¼
-Diazoacetate (R
1
a
¼
Ph,
Me) reacts only with electron-poor aromatic aldehydes (R
2
¼
m-CF
3
-C
6
H
4
, m-NC-C
6
H
4
).
N-Tosylimides (R
3
¼
Ts) are also promising electrophiles and the corresponding
b
-(N-
-diazoesters or ketones (R
3
tosylamino)-
a
¼
Ts) are obtained. This reaction system can be
carried out under aqueous conditions [49].
3.3.3 Azidation
Evans et al. [50] examined the DBU (1)-mediated azidation of
-hydroxy ester with
phosphoryl azides and found that the amount of DBU (1) is critical for asymmetric
induction (Table 3.3). In the reaction with bis( p-nitrophenyl)phosphoryl azide in DMF, the
use of 1.2 equiv. of 1 resulted in the production of azide with 80% ee (run 5), while product
was obtained with less than 2% racemization and in good yield when 0.95 equiv. of 1
was used.
a
