Biomedical Engineering Reference
In-Depth Information
R
N
N
N
N
R
R
O
Y
(34-98%)
[102,104a]
R = H, Cl, Me, OMe, CO
2
Et,
F, CF
3
, CN, NH
2
, NO
2
(60-84%)
[102,104a]
R = H or CO
2
Et
Y = C or N
(48-81%)
[102,104a]
R = H, Me, OMe
O
NR
1
N
S
S
R
R
2
R
H
R
R
2
(78-97%)
[104a]
R = H, Me, Cl
(81-98%)
[104d]
R = H, Me, NO
2
, CO
2
Me, Cl
(32-71%)
[104d]
R = H, Me, OMe
R
1
= H or Me R
2
= H or Ph
S
N
O
R
R
1
R
2
S
(80-91%)
[104d]
R = H, Cl, OMe
(50-99%)
[103,105a]
R
1
= H, Ph, Me, OMe,
t
Bu, COMe, Cl, F
R
2
= H, Cl, OMe, Me, F, NO
2
, CO
2
Et
SCHEME 3.39
Selected examples of C-Heteroatom bond formations.
allowed
S-
and
N
-arylations in the absence of Cu salts from aryl iodides [104].
Intriguingly, for the synthesis of diaryl ethers from phenols and aryl halides, ligand
L12
appeared to be more effective [105]. It is worth noting that many researchers who
carried out the above-mentioned studies observed that the purity and the commercial
source of the metal could affect the catalytic activity [106]. While studies were
conducted to investigate whether trace amounts of other metals (e.g., copper impu-
rities) could influence these Fe-catalyzed transformations, the authors could only
assume that such impurities could, in certain cases, significantly impact these cross-
coupling reactions. Another elegant method allowing C-N cross-coupling under
ligand-free conditions via recyclable heterogeneous Fe catalysis (e.g., reusable
graphite-supported
iron(III)
acetyl
acetonate) was
devised
by Rao
and
coworkers [107].
3.4.3. Other Metals
The main idea for preparing this chapter was to give readers an overview of the most
important methods allowing C-heteroatom bond formation and their application to
the total syntheses of selected complex bioactive compounds. Two selectedways have
been treated: Pd-mediated transformations (Buchwald-Hartwig-type reactions) and
Cu-mediated cross-coupling (Ullmann-type reactions). Although these two metals
are very efficient, exhibit both powerful catalytic properties and a broad substrate
compatibility, and allow the use of many attractive protocols, it should be pointed out
that other metals (e.g., iron, nickel, gold, iridium, and platinum) are also very effective
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