Chemistry Reference
In-Depth Information
the reaction proceeds primarily by S
N
2, with some contribution from S
N
1 and/or
S
N
i mechanisms.
Chloroformates and chlorides are also formed when secondary benzylic alcohols
are treated with diphosgene in the presence of triethylamine [16]. The distribution
of products can be controlled.
O
l
OH
Cl
N
N
N
CCl
3
OCOCl
Et
3
N, THF, 6 hrs
75 %
15 %
5
6
7
Diphosgene has also been used to selectively prepare chloroformates 9 of primary
or secondary 2-nitrobenzyl alcohols 8 [17]. A similar conversion has been per-
formed with triphosgene and triethylamine in diethyl ether [18].
R
R
O
CCl
3
OCOCl
OH
O
Cl
R = CH
3
, H
THF, 4 hrs
NO
2
NO
2
8
9
Protection of the 7-hydroxyl group in Paclitaxel (taxol
2
) 10 as the carbonate 13 of
the maleimido-peptide-benzyl alcohol 12 was carried out through the correspond-
ing chloroformate using diphosgene in the presence of pyridine/DIE [19].
O
O
OH
O
O
l
CCl
3
OCOCl
Py, DIE, 1.5 h,
0°C-rt
O
O
O
O
O
O
10
11
O
O
OH
O
O
l
O
OO
DIEA,CH
2
Cl
2
MC
Phe
Lys(MMT )
0°C-rt, 16 h, 50-60%
O
O
O
O
O
O
11
12
13
