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R
O
O
+
50-100 °C
O
OH
2
MBM
20-25 s
-1
,
1 h
O
R
OH
O
R = OH, H, Cl, NO
2
Scheme 2.20 Cascade reaction of dimedone with aromatic aldehydes.
OH
OH
O
CN
+
97 °C
O
O
CN
CN
CN
MBM
20-25
s
-1
,
1 h
HO
O
OH
CN
NH
2
O
Scheme 2.21 Michael addition of dimedone and 2-[(4-hydroxyphenyl)methylene]-
propanedinitrile as part of a cascade reaction.
O
1.65 equiv I
2
2.5 equiv. DMAP
O
R
O
O
+
R
O
MBM
30 s
-1
,
1 h
O
O
R = 3-NO
2
C
6
H
4
,
4-NO
2
C
6
H
4
,
4-CNC
6
H
4
, 3,4-Cl
2
C
6
H
3
,
4-CHOC
6
H
4
,
4-
CH
3
OC
6
H
4
,
3,4-(CH
3
)
2
C
6
H
3
,
3,4-(OCH
3
)
2
C
6
H
3
,
H, Et,
n-CH
2
CH
2
CH
3
,
2-pyridyl, 2-furyl, 2-thiophenyl
1.65 equiv I
2
2.5 equiv. DMAP
O
O
O
O
+
R
MBM
30 s
-1
, 1 h
O
O
R
O
R = 3-NO
2
C
6
H
4
,
4-NO
2
C
6
H
4
,
4-CNC
6
H
4
,
3,4-Cl
2
C
6
H
3
,
4-CHOC
6
H
4
,
4-BrC
6
H
4
,
4-ClC
6
H
4
,
4-CH
3
C
6
H
4
,
C
6
H
5
Scheme 2.22 Reaction sequence of Knoevenagel condensation and Michael add-
ition forming dihydrofuran and cyclopropane derivatives.
Furthermore, dimedone underwent Michael addition with 2-[(4-hydroxy-
phenyl)-methylene]propanedinitrile followed by a rearrangement and
cyclization step (Scheme 2.21).
39
2-Amino-3-cyano-7,7-dimethyl-4-(4-hydroxy-
phenyl)-5-oxo-5,6,7,8-tetra-4H-chromene could be obtained in quantitative
yields after milling at 97 1C in the melt for 1 h.
Dihydrofuran and cyclopropane structure motifs can be found in bioactive
compounds and are interesting for the synthesis of pharmaceuticals. Wang
and Gao developed a solvent-free reaction protocol to synthesize these
structures by ball milling (Scheme 2.22).
43
This cascade reaction started with
a Knoevenagel condensation of dimedone with aldehyde followed by an at-
tack of the 1,3-dicarbonyl compound leading to the Michael addition
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