Chemistry Reference
In-Depth Information
O
O
Cl
Cl
O
l
OO
Cl
OH
2 equiv CCl
3
OCOCl,
CH
2
Cl
2
reflux
81
82
1:1
83
0.05 equiv Py
CH
2
Cl
2
O
O
l
78 %
82
The diazoester of hydroxyacetic acid methyl ester 87 was prepared via the chloro-
formate 86 using diphosgene as chloroformylating agent [47].
O
CCl
3
OCOCl
O
O
HO
CH
3
Cl
O
CH
3
Pyridine, CH
2
Cl
2
0 °C to r.t.
O
O
85
86
O
CH
2
N
2
N
2
O
O
CH
3
Et
2
O
O
53 %
87
Phosgene, diphosgene, and triphosgene react readily with a variety of aldehyde
substrates under mild conditions thereby affording the corresponding a-chloro
chloroformates in good yields [48-51].
On a laboratory scale, the best catalyst for the addition of phosgene to aldehydes
is benzyl tri-n-butylammonium chloride (BTBAC). The most important reagent, a-
chloroethyl chloroformate (''ACE-Cl'') is typically isolated in 96% yield after stirring
acetaldehyde with neat phosgene (1.1 equiv.) for 1 h in the presence of 3 mol%
BTBAC. Even chloromethyl chloroformate can be prepared using this process, but
it is essential that the monomeric gaseous formaldehyde is introduced into the
reactor already containing the catalyst and phosgene, so that it reacts immediately
and is not repolymerized [50, 52].
A method for the preparation of a-chloro chloroformates using triphosgene was
developed by Coghlan (Table 4.4) [51].
