Efficient and Mild Oxidative Decarboxylation of Aryl-substituted Carboxylic Acids by Iron and Manganese Porphyrin Periodate Systems

Article abstract of DOI:10.1039/a805700a

The oxidative decarboxylation of α-aryl carboxylic acids to the corresponding carbonyl derivatives was observed in catalytic systems containing tetrabutylammonium periodate and metallotetraphenylporphyrins (metal = Fe^III or Mn^III) at room temperature.

Full text of DOI:10.1039/a805700a

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820 J. CHEM. RESEARCH (S), 1998
J. Chem. Research (S),
1998, 820±821$
Efficient and Mild Oxidative Decarboxylation of
Aryl-substituted Carboxylic Acids by Iron and
Manganese Porphyrin Periodate Systems$
Shahram Tangestaninejad* and Valiollah Mirkhani
Department of Chemistry, Esfahan University, Esfahan, 81744, Iran
The oxidative decarboxylation of ꢀ-aryl carboxylic acids to the corresponding carbonyl derivatives was observed in
catalytic systems containing tetrabutylammonium periodate and metallotetraphenylporphyrins (metal ˆ FeIII or MnIII) at
room temperature.
There has been considerable growth in understanding the
catalytic action of metalloporphyrins in the last twenty
years.1,2 Numerous studies have been carried out employing
metalloporphyrins in association with various single oxygen
donors for the catalytic oxidation of alkenes,3 alkanes,4
amines,5 phenols,6 thiols7 and sul®des.8 Such investigations
In this report we wish to describe an ecient decarboxyla-
tion reaction using iron(III) and manganese(III) tetra-
phenylporphyrins as catalysts, M(tpp)Cl (0.012 mmol), for
decarboxylation of a-substituted acetic acids, R1R2-
CHCOOH (1 mmol), which a€ord the corresponding
carbonyl derivatives in the presence of tetrabutylammonium
periodate, Bu4NIO4 (2 mmol), in dichloromethane solution
[reaction (1)].
have resulted in
a better understanding of oxidative
metabolism of foreign organic compounds in biological
systems by cytochrome P-450 and peroxidase. However,
so far very few chemical model systems based on metallo-
porphyrin derivatives that catalyze the oxidative decarboxy-
lation of carboxylic acids have been reported.9,10
a
Table 1 Oxidative decarboxylation of a-aryl carboxylic acids by MIII(tpp)Cl/Bu4NIO4
Yieldb (%) (t/h)
Run
1
Substrate
Product
FeIII(tpp)Cl/IO4
MnIII(tpp)Cl/IO4
84 (3)
88 (3)
94 (3)
2
90 (3)
3
92 (3)
87 (3)
4
5
6
93 (3)
95 (1)
94 (1)
90 (3)
92 (1)
92 (1)
7
8
9
93 (8)
74 (4)
60 (8)
89 (8)
70 (4)
57 (8)
10
71 (8)
94 (4)
61 (8)
90 (4)
11
aReaction conditions: substrate (1mmol), Bu4NIO4 (2 mmol), MIII(tpp)Cl (0.012 mmol), CH2Cl2
(10 ml), room temperature. bIsolated yields.
The results which are summarized in Table 1 show that
*To receive any correspondence.
this catalytic system led to decarboxylation of aryl-
substituted acetic acids to carbonyl derivatives in good
isolated yields (57±95%) at room temperature. It was found
$This is a Short Paper as de®ned in the Instructions for Authors,
Section 5.0 [see J. Chem. Research (S), 1998, Issue 1]; there is there-
fore no corresponding material in J. Chem. Research (M).

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J. CHEM. RESEARCH (S), 1998 821
Bu4NIO4 (2 mmol) were added and the solution stirred magnetically
at room temperature for 1±8 h. Reaction progress was followed by
TLC. Puri®cation of crude products on a silica gel plate or silica gel
column (eluent: CCl4±Et2O) a€orded pure products in 57±95%
yields (Table 1).
that the principal product in all of the reactions was the
carbonyl derivative and only a small amount of the alcohol
derivative was observed. Here, we show that MIII(tpp)Cl
can catalyze the selective oxidation by Bu4NIO4 of alco-
hols to carbonyl compounds. Iron(III) tetraphenylporphyrin
exhibits a greater catalytic power than the corresponding
manganese(III) compound, whereas the reverse situation was
observed for epoxidation of alkenes.11
We are thankful to the Esfahan University Research
Council.
Decarboxylation of a-hydroxy carboxylic acids (Runs
5 and 6) were fast and completed in 1 h. By analogy
with earlier studies,9,10,12 the faster reaction rates can be
assigned to the formation of relatively stable a-hydroxy
alkyl radicals from interaction of the carboxylic acids with
a highly electrophilic intermediate generated by IO4 ±MIII
porphyrin.
The oxidation of anti-in¯ammatory drugs such as
Indomethacin and Ibuprofen (Runs 10 and 11) a€orded
corresponding carbonyl derivatives as the major products
in 61 and 94% yields, respectively. Such an oxidative
decarboxylation pathway has been also observed during
metabolism of non-steroidal anti-in¯ammatory drugs.10 In
this report we have shown that these reactions can be
eciently mimicked using simple iron and manganese
porphyrin.
Received, 21st July 1998; Accepted, 7th September 1998
Paper E/8/05700A
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Experimental
All chemicals used were reagent grade. The porphyrin ligand,
tpp, was prepared and metalated according to the literature pro-
cedures.14,15
General Procedure for Oxidative Decarboxylation of ꢀ-Aryl Sub-
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acids (1 mmol) in CH2Cl2 (10 ml), MIII(tpp)Cl (0.012 mmol) and
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