Chemistry Reference
In-Depth Information
by 49.5% of the corresponding amide 22, which did not react further [27]. In con-
trast, phosphoryl chloride, another low-priced reagent, reacted with the carbox-
aldoxime 20 to form the nitrile 21 in 83% yield [27] (see Section 4.5.1.1).
Br
N
P
2
O
5
toluene
reflux, 6 h
28 %
+
49.5 %
H
2
NOC
N
Br
Br
N
22
N
Ph
or
N
N
NC
N
POCl
3
reflux, 30 min
83 %
H
20
Ph
21
Ph
It is remarkable that phosphorus pentoxide did not react further with the carbox-
amide by-product, especially in view of the fact that this reaction is otherwise a
standard method for preparing nitriles. This illustrates the point that even proven
standard methods cannot be applied in all cases.
3-Cyanopyridine 23
3-Cyanopyridine 23 has been prepared from nicotinic amide by several methods, in
good to excellent yield in each case. As dehydration reagents, phenyl chloroformate
[28], phenyl chlorothionoformate [29], oxalyl chloride/DMSO [30], triflic anhydride
[31], and the Burgess reagent [32] have been used, giving yields of 23 of 92%, 92%,
75%, 93%, and 92%, respectively.
PhOCOCl
CH
2
Cl
2
, pyridine
rt, 8-10 h
92 %
or
PhOCSCl
CH
2
Cl
2
, pyridine
rt, 6 h
92 %
or
O
(COCl)
2
/ DMSO
CH
2
Cl
2
, Et
3
N
-78°C to rt, 1 h
CN
75 %
NH
2
N
N
or
23
Tf
2
O
CH
2
Cl
2
, Et
3
N
rt, 19 min
or
93 %
Burgess reagent
CH
2
Cl
2
, rt, 2 h
92 %
The reactions with the two chloroformates require rather long reaction times (6-
10 h), whereas those with triflic anhydride, under Swern conditions, and with the
