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eaction failed to go to completion, which is attributed to the electron withdrawing effect of the
trfluoromethyl group. Increased heating drives the reaction further but results in impurities
(Scheme 4.46).
Scheme 4.46 Unsuccessful examples of pyrrole formation.
H
BzN O
MeO2C Bn
H O
O
307
N
BzN
MeO2C Bn
H
H 2N H 2N CF 3
no reaction
R-NH 2, AcOH, EtOH
50 °C, 3h
slow and incomplete reaction
To determine whether the newly formed acyl pyrroles 308a-p are more stable than the alkyl-
pyrroles as initially hypothesized, we performed an NMR experiment where an alkyl and acyl-
pyrrole of benzyl amine were placed in an NMR tube with a standard (p-phthalic acid ethyl ester)
in d6-DMSO. w The sample was kept at rt in a sealed NMR tube. Monitoring of the 1 H NMR of
the sample over a period of 60 days, revealed that the alkyl-pyrrole 298a had been reduced to
half of its initial amount, whereas the acyl-pyrrole 308a remained virtually unchanged (Scheme
4.47).
w NMR study was performed by Dr. Stefan Fischer (Prof. Curran group).
119
H
309
N R
O
N