Biomedical Engineering Reference
In-Depth Information
Cu(OAc)
2
CH
2
Cl
2
, rt
Y
Ar-B(OH)
2
HY-R
Ar
R
Y = O, N, S, NR', NCOR', NSO
2
R'
OMe
Cu(OAc)
2
, pyridine
4
Å
MS, CH
2
Cl
2
, rt
MeN
H
OMe
O
I
OH
O
(81%)
O
I
NMe
NH
2
MeO
2
C
O
MeO
HO
2
C
I
OH
I
Cu(OAc)
2
, pyridine
Thyroxine
(
−
)-Tejedine
4
Å
MS, CH
2
Cl
2
, rt
(57%)
Cu(OAc)
2
, Et
3
N
OH
4
Å
MS, CH
2
Cl
2
, rt
Cu(OAc)
2
, Et
3
N
O
Me
(55-70%)
4
Å
MS, CH
2
Cl
2
, rt
HO
(67%)
O
O
Me
OH
O
Combrestatin D2
Rodgersinol
SCHEME 3.38
Chan-Lam-Evans cross-coupling reactions.
3.4. MISCELLANEOUS
3.4.1. Chan-Lam-Evans
The Chan-Lam-Evans reaction [99] is a very useful method, based on boronic acids as
arylating agents combined with copper(II) acetate (between 1 and 2 equiv), that gives an
interesting alternative to the more classical copper-catalyzed Ullmann cross-coupling
reactions. These transformations are compatible with a broad range of heteroatom
nucleophiles (e.g., amines, amides, nitrogen heterocycles, alcohols, and phenols) and
tolerate high functional groups to form C-heteroatom bonds from arylboronic acids
under mild conditions. Therefore, it is widely used in the context of natural product
synthesis and selected examples are summarized in Scheme 3.38 [99c,100].
3.4.2. Iron/Copper-Mediated Methodologies
Iron salts that are cheaper, nontoxic, stable, and environmentally benign have arisen as
a promising alternative for some cross-coupling reactions in total synthesis [101].
Recent reports show that C-N, C-O, and C-S bond formation were possible by using
iron salts/ligand combinations (Scheme 3.39). For example, Taillefer and coworkers
devised a cooperative bimetallic Fe-Cu catalyst system that allowed
N
-arylation of
nucleophiles from aryl bromides, while each metal alone was incapable of achieving
the transformation [102]. One year later, they proposed a novel alternative in which
the use of ligand
in combination with Fe or Cu salts permits related arylation of
phenols from aryl halides [103]. Similar observation was reported by Bolm and
coworkers, who showed that the use of the ligand
L12
L10
in combination with FeCl
3
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