Chemistry Reference
In-Depth Information
Diamine ligands are effective promoters of copper-catalyzed C-N bond
formation in organic solvents and water. CuI in combination with trans-N,N
0
-
dimethyl-1,2-diaminocyclohexane (DMCDA) catalyzes the arylation of azoles,
amides and amines in water under air at 80 1C. The catalyst can be recovered
with the aqueous-phase and reused four times with minimal decrease in
reaction yield, although the system is limited to aryl iodides.
59
Intra-
molecular cyclization of bromobenzofuran 24 in water catalyzed by CuI
in the presence of N,N
0
-1,2-dimethyl-1,2-diaminoethane (DMEDA), which
was used as base and ligand, affords benzo[4,5]furo[3,2-b]indole 25
(Scheme 14.21).
60
The aqueous, copper-catalyzed system gave superior re-
sults to copper-catalyzed coupling in toluene or palladium-catalyzed ring
closure. Copper(I) iodide catalyzes the cyclization of 2-bromobenzyl ketone
derivatives to give benzofurans in the presence of TMEDA as the base and
ligand.
61
Thiolation of aryl iodides in water at 120 1C is catalyzed by CuCl in
combination with trans-1,2-diaminocyclohexane (CDA).
62
The aqueous
catalyst solution could be used for three reaction cycles before a decrease in
catalyst activity was observed.
A series of substituted phenanthroline derivatives were explored as lig-
ands for the copper-catalyzed coupling of azoles, amines and amides with
aryl iodides in water with PEG-400 as an additive.
63
4,7-Dipyrrolylphenan-
throline (26) was identified as the optimal ligand (Scheme 14.22). Copper(II)
chloride/phenanthroline (phen) catalyzes the diarylation of thiocyanate
to give diaryl sulfides in water from aryl iodides and bromides at 130 1C
(Scheme 14.23).
64
Cu
2
O in combination with pyridine-2-aldoxime catalyzed
the hydroxylation of aryl halides in water with TBAB as promoter.
65
Glyoxal
Br
T
N
CuI (8.5 mol %)
DMEDA (3.5 eq)
H
2
O, 120 °C
85%
O
O
TsHN
24
25
Scheme 14.21
AcHN
AcHN
CuBr (5 mol %)
26
(10 mol %)
PEG-400 (20 mol %)
KOH, H
2
O
120 °C, 48 h
N
N
Br
+
N
H
N
N
26
Ph
91%
Scheme 14.22
CuCl
2
2H
2
O (10 mol %)
phen (10 mol %)
Cs
2
CO
3
, TBAF, H
2
O
130 °C, 48 h
Br
+ KSCN
S
73%
Scheme 14.23
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