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Ar
1
[O]
Ar
1
H
O
N
..
Path
A
N
O
O
Ar
2
Ar
2
H
+
Ar
2
NH
2
1
Ar
2
Ar
1
H
Ar
1
H
OH
H
Path
B
[O]
2
Ar
2
Ar
1
3
Scheme 1.9 Possible pathway for the direct oxidative amidation of aldehydes with
anilines.
NCX
NCY
N
N
NH
2
X
X
Y
NH
2
R
2
H
R
1
R
2
H
R
1
NH
R
1
NH
ball-milling
ball-milling
H
2
N
ortho
78-99%
or
para
X, Y = S or O
R
1
, R
2
= H, Cl, NO
2
, OCH
3
Some selected examples:
S
S
S
S
NH
HN
NH
HN
O
2
N
NH
HN
Cl
H
3
CO
NH
HN
Cl
97%
99%
S
O
S
O
NH
HN
HN
NH
O
2
N
NH
HN
H
3
CO
NH
HN
99%
99%
Scheme 1.10
Synthesis of symmetrical and non-symmetrical phenylenediami-
ne(thio)urea derivatives by ball milling.
A new methodology has been developed for the desymmetrization of
aromatic diamines to non-symmetrical thiourea derivatives by click-
mechanochemistry in a ball mill.
11
Phenylenediamines (o-, p-) were desym-
metrized through a one-pot mechanochemical click reaction sequence to
furnish mono- and bis(thio)ureas or mixed thiourea-ureas (Scheme 1.10).
o-Phenylenediamine reacted selectively with either one or two equivalents
of phenyl isothiocyanate to yield the non-symmetrical amino-thiourea or the
symmetrical bis-thiourea in 95% and 499% yields respectively. The excellent
control of the stoichiometric composition of the product in mechan-
ochemical click-thiourea coupling demonstrates that it provides a facile and
clean one-pot route to desymmetrization of aromatic diamines, and to the
synthesis of symmetrical and non-symmetrical bis-(thio)ureas that are ob-
tained in poor yields in solution.
12
A chemoselective C-N bond formation has been achieved by the acylation
of primary aliphatic amines using a vibrational ball mill in 10 min (120 min
for aromatic amines). Azobenzene functionalized esters were employed to
react with various amines (primary and secondary) in presence of a base,
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