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Table 4.5 Preparation of a 14-member library of acyl-pyrroles from 307.
H
BzN O
MeO2C Bn
H O
H 2N
H 2N
H 2N
H 2N
H 2N
O
307
O
OMe
OMe
OMe
OH
OH
H2N N
O
O
H 2N N
N
H 2N R, AcOH, EtOH
50 °C, 2-3 hours
H 2N
H 2N
H 2N
H 2N
H
BzN
MeO2C Bn
H
OH
O
H 2N CO 2Me
H 2N
NH 3
308a-n
R
N
N
amine product yield (%) amine product yield (%)
308a 80%
308b 88%
308c 72%
308d 85%
308e 63%
308f 39%
308g 81%
O
308h 70%
308i 93%
308j 89%
308k 69%
308l 79%
308m 95%
308n 64%
Two pyrroles were also prepared from diketone 306 using the same conditions (Scheme 4.45).
Scheme 4.45 Preparation of pyrroles from diketone 306.
BzN O
MeO2C Bn
H O
H H
306
O
N
H 2N
H 2N
R-NH 2, AcOH, EtOH
O
50 °C, 3h
amine product yield
OMe
OH
308o 36%
308p 70%
BzN
MeO2C Bn
H
308o-p
The most suitable aliphatic amines for the Paal-Knorr reaction do not have branching at the
position alpha to the amine since cyclohexylamine failed to give any product (Scheme 4.46).
When 2,2,2-trifluoroethylamine was used the reaction rate was significantly retarded, and the
118
N R
O
N