Chemistry Reference
In-Depth Information
or a boron-containing benzaldehyde in the presence of BF
3
·OEt
2
, gave the target
porphyrins as regioisomeric mixtures after oxidation with
para
-chloranil. Pure
ʲ
-substituted carboranylporphyrins
18
and
19
were also synthesized in good yields
(18-78%) by direct functionalization or pre-formed tetra- and octa-bromoporphyrins,
using a Pd(0)-catalyzed coupling reaction in anhydrous toluene, excess carboranyl-
methylphenyl boronic acid, and anhydrous K
2
CO
3
[
52
].
Using a MacDonald [2+2] condensation [
53
] between bis[3,5-(methyl-
ortho
-carboranyl)methyl]benzaldehyde and various dipyrromethanes, a series of
carboranylporphyrins, including
20
-
22
, were prepared in 4-40% yields [
54
-
56
]. The
lower yields obtained were due to acid-catalyzed scrambling during the conden-
sation reaction. The water-soluble carboranylporphyrins were obtained by cleavage
and hydrolysis of phosphonic esters using bromotrimethylsilane (to give
20
), by
quaternization of the peripheral amine groups with methyl iodide (to give
21
), or by
deboronation of the
ortho
-carboranes with pyridine/piperidine 3:1 (to give
22
).
Symmetric porphyrins
23
and
24
were synthesized in very high yields (
90%)
from the reaction of the corresponding pre-formed
meso
-hydroxyphenylporphyrins
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