Chemistry Reference
In-Depth Information
(10:1
0:1) to give bis-Boc-lactam 942 (255 mg, 71%) as colorless crystals;
mp 108-110
C (ethyl acetate/hexane); R
f
!
¼
0.68 (ethyl acetate/methanol, 10:1);
[a]
18
D
1740, 1698 cm
1
.
An iodolactonization reaction of the iodocarbonate cyclization type [670], as described
in the last example of Section 4.3.3.5, has been performed with homopropargylic
alcohols 944 and Boc
2
O, to afford non-racemic b-hydroxy ketones 947 [671]. The
tert-butyloxycarbonylation reaction with Boc
2
O furnishes 945 in 98% yield.
¼
66 (c
¼
0.44, CHCl
3
); IR (CHCl
3
): n
max
¼
OtBu
O
946
98 %
O
O
H
OH
O
O
IBr
H
Boc
2
O
DMAP
CH
2
Cl
2
I
Et
3
N, THF
945
944
O
OH
947
Acyl carbonate 949 is formed as an intermediate in the reaction of anhydride 948
with carbonate 885. It decomposes to afford the corresponding ester 950. This
exchange reaction between anhydrides and carbonate offers a new, solvent-free
method for the synthesis of esters in the presence of Ti- or Sn-based catalysts [672].
Various esters have been synthesized by this method, typically in yields of 80-90%,
although the reaction requires high temperatures of about 300
C, and is thus in-
compatible with sensitive compounds.
O
O
O
O
cat.
950
+
+
O
O
300°C
30 min
O
O
O
O
O
948
O
885
949
cat = Ti(OBu)
4
Sn(OMe)
2
Bu
2
O
+
CO
2
O
950
