Chemistry Reference
In-Depth Information
Torr at 37
C, compared with 0.15 Torr at 20
C for triphosgene; see Tables 3.2 and
3.3, Chapter 3). DMC is of low toxicity (a TLV of 200 ppm, as compared with 0.1
ppm for phosgene possibly arising from the triphosgene; see Table 3.4, Chapter 3).
The reaction temperature of about 90
C (bp of DMC) is also acceptable. Both re-
actions are useful, although handling and work-up are easier with DMC.
(Cl
3
CO)
2
CO
pyridine
5°C, 2 h
O
89 %
H
O
O
6
O
5
O
O
O
or
O
H
O
BnO
80 %
(3 steps from
diacetoneglucose)
BnO
DMC
NaOMe
reflux, 3 h
O
O
15
(2S,3S)-4-Benzyloxy-1,2,3-butanetriol 1,2-cyclic carbonate 16 and (2S,3S)-4-benzyloxy-
1,2,3-butanetriol 2,3-cyclic carbonate 17
In some cases, different phosgenation reagents can show different selectivities to-
wards certain substrates. Thus, (2S,3S)-4-benzyloxy-1,2,3-butanetriol reacts with
triphosgene in the presence of pyridine to form solely the five-membered external
(2S,3S)-4-benzyloxy-1,2,3-butanetriol 1,2-cyclic carbonate 16 in 77% yield, whereas
reaction of the 1,2,3-triol with DMC affords the five-membered internal (2S,3S)-4-
benzyloxy-1,2,3-butanetriol 2,3-cyclic carbonate 17 in 65% yield [24] (see also Sec-
tion 4.3.5.3).
(Cl
3
CO)
2
CO
OH
BnO
O
77 % external
cyclocarbonate
CH
2
Cl
2
, py
-70°C, 15 min
16
O
OH
O
BnO
OH
OH
BnO
OH
DMC
17
65 % internal
cyclocarbonate
O
O
NaH
rt, 30 min
O
6.2.2.3
Chlorination
(See Section 4.4)
Oleoyl chloride 18 and lauroyl chloride 19
The conversion of long-chain carboxylic acids into their carboxylic chlorides using
excess thionyl chloride is a standard method. Thus, oleoyl chloride 18 has been
prepared in yields of 97-99% (crude material) from oleic acid by refluxing with
thionyl chloride [25]. An equivalent alternative method is the reaction of a fatty
acid with phosgene (for a safe source, see Chapter 7). In this way, lauroyl chloride
