Chemistry Reference
In-Depth Information
afforded pyrroles 6 or indole 9 quantitatively within 3 h despite the multistep
course of the reaction.
A plausible reaction pathway is depicted in Scheme 1.32. In the first step,
Michael addition followed by the hydrogen transfer produces 11, which
undergoes an imine/enamine rearrangement to give 12. The generated
amino group then interacts with the carbonyl function leading to the
formation of a five-membered ring 13, which provides pyrrole 14 by the
elimination of water. An analogous mechanism was postulated for indole
starting from 7. Furthermore, the quantitative formation of thioorotic acid
amide 17 from a cascade reaction between the thiohydantoin 15 and methyl
amine shows the versatility of this method (Scheme 1.33).
Kaupp and co-workers have reported the quantitative formation of (R)-
thiazolidine by ball-milling a stoichiometric mixture of
L
-cysteine and
(HCHO)
n
for 1 h (Scheme 1.34).
32
It has been observed that a 1 : 1 mixture of
phthalic anhydride and 4-toluidine when subjected to ball milling affords the
corresponding imide in high yields. Interestingly, cyclic thiourea was obtained
quantitatively when bifunctional isothiocyanates and amine were ball milled.
A series of heterocycles can be obtained by condensation of
o-phenylenediamines with various 1,2-dicarbonyl compounds under ball
O
Ph
H
O
O
O
R
Ph
Ph
H
Ph
+
X
X
N
R'
O
O
5
R
N
R'
10
11
O
Ph
Ph
Ph
O
H
O
O
H
O
O
X
Ph
X
X
Ph
Ph
N
O
OH
N
R
R
R
NH
R'
R'
R'
14
13
12
Scheme 1.32 Plausible mechanistic pathway of the cascade reactions to give pyrrole
and indole derivatives.
O
O
O
NH
O
O
Ar
N
H
-MeOH
H
O
N
Ar
+
MeNH
2
O
N
N
N
S
N
H
H
H
S
N
Ar
S
H
O
15
16
17
Ar = 4-BrC
6
H
4
Scheme 1.33 Mechanochemical
formation of
thioorotic acid amide from a
thiohydantoin.
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