A comparative study in oxidative free radical reactions between 9-benzylidene-9-h fluorene derivatives and β-dicarbony1 compounds in the presence of mn(oac) 3 and can

Article abstract of DOI:10.2174/157017811796504990

The reactions of some 1,3-dicarbonyl compounds with 9-benzylidene-9-H- fluorene derivatives in the presence of manganese(III)acetate and ceric ammonium nitrate (CAN) were searched. 9-benzylidene-9-H-fluorene compounds form mainly [2+3] dipolar cycloadditi

Full text of DOI:10.2174/157017811796504990

488
Letters in Organic Chemistry, 2011, 8, 488-494
A Comparative Study in Oxidative Free Radical Reactions between 9-
Benzylidene-9-H Fluorene Derivatives and ꢀ-Dicarbonyl Compounds in
the Presence of Mn(OAc)3 and CAN
Hulya Demirhan, Mustafa Arslan*, Mustafa Zengin and Mustafa Kucukislamoglu
Sakarya University, Faculty of Arts and Sciences, Department of Chemistry, 54187, Sakarya, Turkey
Received January 03, 2011: Revised April 15, 2011: Accepted April 15, 2011
Abstract: The reactions of some 1,3-dicarbonyl compounds with 9-benzylidene-9-H-fluorene derivatives in the presence
of manganese(III)acetate and ceric ammonium nitrate (CAN) were searched. 9-benzylidene-9-H-fluorene compounds
form mainly [2+3] dipolar cycloaddition products such as dihydrofuran and lactone which are spirally attached to the C-9
position of flourene ring with manganese(III)acetate and oxidative addition products with CAN. The best yield of
cyclization products was obtained from the reaction between 2c and 1a-c in both oxidants. The stereochemistry of the
products 3d, 4d and 5d was only transformed which has coupling constant 13 Hz.
Keywords: 9-benzylidene-9H-fluorene, cerium(IV) ammonium nitrate (CAN), manganese(III) acetate, radicalic oxidation, ꢀ-
dicarbonyl compounds.
INTRODUCTION
2a-c in the presence of Mn(OAc)3 in acetic acid and CAN in
methanol with 1a-c [15] and the reaction is shown in Scheme
1. Acetic acid and methanol were used as a solvent because
they have good solubility for Mn(OAc)3 and CAN respec-
tively.
Free radical and oxidative cyclization reactions have be-
come increasingly important in the synthesis of useful and
complex molecules in organic synthesis for a long time [1].
The oxidative addition of carbon centered radicals to double
bond mediated by transition metal salts such as Mn+3, Ce+4,
Co+3, Cu+2 has received considerable attention for the forma-
tion of carbon-carbon bond in organic synthesis. Among
these, manganese(III)acetate [2] and cerium(IV) ammonium
nitrate (CAN) [3], one electron oxidant, have been used most
efficiently. Enolizable ꢀ-diketones or ꢀ-ketoester or ꢀ-
ketoamide can be oxidized by the salts to generate ꢁ-carbon
radicals which can attack double or triple bonds [4]. These
reactions can be performed intramolecularly or intermolecu-
larly and prepared functionalized products such as furans [5],
ꢂ-lactones [1b, 6], ꢀ-lactams [7], biologically active com-
pounds and natural products [8].
RESULTS AND DISCUSSION
Dihydrofuran and lactone derivatives of fluorene were
prepared by the [2+3] oxidative cycloaddition of 1,3-
dicarbonyl compounds to 9-benzylidene-9H-fluorene deriva-
tives by Mn(OAc)3/Cu(OAc)2 and CAN in which a substi-
tuted dihydrofuran unit or lactone is attached to the C-9 posi-
tion of the fluorene ring. Methoxyl, hydroxyl, nitrate substi-
tuted acyclc addition products were obtained when CAN was
used as an oxidant. Recommended radicalic cyclization
mechanism of 4e and 5e with 9-benzylidene-9H-fluorene
derivatives (1a-c) is given in Scheme 2 and the results of the
experiment are given in Table 1 and 2.
Fluorene and its derivatives are important compounds
and have different types of biological activities, such as anti-
inflammatory [9] and antitumor activities [10]. The com-
pounds are important intermediate materials, which are
widely used for the synthesis of advanced pigments, dyes,
polymers and drugs [8a, 11]. Fluorene-based derivatives
have been applied in electronic, photonic and these applica-
tions are light emitting diodes, sensors, field effect transis-
tors, two-photon absorbing materials and charge transfer
agents [12].
According to the mechanism shown in Scheme 2,
Mn(OAc)3 and acetylacetone give Manganase(III)-enolate
complex [5b]. Then Mn+3 is reduced to Mn+2. A radical in-
termediate product is obtained by the addition of the ꢁ-
carbon radical which is stable and this radical is added to 9-
benzylidene-9H-fluorene derivatives. The intermediate prod-
uct is oxidized to the carbocation with the equivalent of
Mn(OAc)3. And the intramolecular cyclization can lead to
the products 4e and 5e.
In this paper, we synthesized firstly 9-benzylidene-9H-
fluorene derivatives (1a-c) by reacting substituted benzalde-
hydes and fluorene with tert-BuOK in EtOH [13, 14] and
described the reaction of some 1,3-dicarbonyl compounds
A plausible mechanism for additional products is pro-
posed in Scheme 3. A radical cation forms firstly with CAN
and then it turns to stable radical intermediate by nucleo-
philic addition. The radical intermediate is oxidized to the
carbocation with the equivalent of CAN [16] and finally
nücleophilic addition occurs. Additionally, these products
are depending on alcohol used as a solvent [17]. When
methanol or ethanol was used as a solvent, methoxy or
ethoxy substituted addition products were obtained.
*Address correspondence to this author at the Sakarya University, Faculty
of Arts and Sciences, Department of Chemistry, 54187, Sakarya, Turkey;
Tel: +90 264 2956045; Fax: +90 264 2955950;
E-mail: marslan@sakarya.edu.tr
1570-1786/11 $58.00+.00
© 2011 Bentham Science Publishers

A Comparative Study in Oxidative Free Radical Reactions
Letters in Organic Chemistry, 2011, Vol. 8, No. 7
489
O
H
t-BuOK
2a-c
Cyclization and
Addition Products
+
EtOH
CAN, MeOH or
Mn(OAc)3, AcOH
R
R
R: H, CH3, Cl
1a-c
Scheme 1.
Mn+3
O
O
Mn(OAc)3 , AcOH
-AcOH
O
O
Mn+2
O
O
Mn+2
O
R
R
.
O
Mn(OAc)3
Mn+2
O
O
O
R
R
O
+
Scheme 2.
CAN
Nü
Nü
CAN
Nü
Nü
Nü
Nü
Nü : -ONO2 , -OCH3 , -OH
Scheme 3.

490 Letters in Organic Chemistry, 2011, Vol. 8, No. 7
Demirhan et al.
Table 1. Oxidative Addition of Dimethylmalonate, Acetylacetone and Dimedone to 9-Benzylidene 9H-Fluorene Derivatives in the
Presence of CAN
9-benzylidene-9H-fluorene
derivative
1,3-Dicarbonyl
compound
Products/ Isolated yields (%)
O
O
O
O
O
H3CO
H3CO
3a (32%)
HO
H3CO
O2NO
O
OCH3
2a
H3CO
O
3c (13%)
3b (7%)
1a
3d (28%)
O
O
O
HO
O
-
H3CO
O2NO
H3CO
O
HO
2b
3c (5%)
1a
3e (34%)
3f (36%)
O
O
-
-
HO
H3CO
O
O
3b (4%)
2c
2a
1a
3g (61%)
O
O
O
H3CO
HO
H3CO
H3CO
O
O
O
O2NO
OCH3
H3CO
O
4c (4%)
4a (49%)
4b (4%)
4d (28%)
1b
O
O
O
H3CO
-
-
H3CO
O
2b
4a (5%)
1b
4e (65%)
O
O
H3CO
-
-
O
H3CO
O
4a (5%)
2c
2a
1b
4f (65%)
O
O
O
Cl
H3CO
HO
H3CO
H3CO
Cl
Cl
Cl
O
Cl
O
O
O2NO
OCH3
H3CO
O
5c (4%)
5a (20%)
5b (5%)
5d (46%)
1c

A Comparative Study in Oxidative Free Radical Reactions
Letters in Organic Chemistry, 2011, Vol. 8, No. 7
491
(Table 1). Contd…..
9-benzylidene-9H-fluorene
derivative
1,3-Dicarbonyl
compound
Products/ Isolated yields (%)
O
O
O
Cl
-
-
-
Cl
O
2b
1c
5e (40%)
O
O
H3CO
H3CO
-
-
O
Cl
Cl
Cl
O
5a (15%)
2c
1c
5f (45%)
Table 2. Oxidative Addition of Dimethylmalonate, Acetylacetone and Dimedone to 9-Benzylidene-9H-Fluorene Derivatives in the
Presence of Mn(OAc)3 /Cu(OAc)2
9-benzylidene-9H-fluorene derivative
1,3-Dicarbonyl compound
Products/Isolated yields (%)
O
O
O
O
O
O
2a
OCH3
O
1a
3d (40%)
O
O
HO
2b
O
HO
1a
1a
1b
3f (85%)
O
O
O
O
2c
3g (95%)
O
O
O
O
O
O
2a
OCH3
O
4d (65%)

492 Letters in Organic Chemistry, 2011, Vol. 8, No. 7
Demirhan et al.
(Table 2). Contd…..
9-benzylidene-9H-fluorene derivative
1,3-Dicarbonyl compound
Products/Isolated yields (%)
O
O
O
2b
O
1b
4e (81%)
O
O
O
2c
O
1b
4f (97%)
O
O
O
Cl
O
O
Cl
O
2a
OCH3
1c
O
5d (75%)
O
O
O
Cl
Cl
2b
O
1c
5e (90%)
O
O
Cl
O
Cl
O
2c
1c
5f (95%)
In the radical cyclization, dimethyl malonate, acetylace-
tone and dimedone were used as 1,3-dicarbonyl compounds.
When dimethyl malonate was used, cyclization products
were lactones. On the other hand when acetylacetone or di-
medone were used, cyclization products were dihydrofuran
units. Besides lactone units which are formed with dimethyl
malonate and 9-benzylidene-9H-fluorene derivatives were
obtained in lower yield than dihydrofuran units. 3d (28 %),
4d (28%) and 5d (46%) were obtained with 1a-c and 2a in
the presence of CAN, but these products were obtained with
40%, 65% and 75% yield in the presence of
Mn(OAc)3/Cu(OAc)2 respectively. Similarly, 4e (65%) and
5e (40%) were obtained by mediated CAN, although these
products were formed with 81% and 90% yield mediated

A Comparative Study in Oxidative Free Radical Reactions
Letters in Organic Chemistry, 2011, Vol. 8, No. 7
493
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CONCLUSIONS
Consequently, simple, novel and efficient method for the
oxidative cyclizations and additions of ꢁ-dicarbonyl com-
pounds mediated Mn(OAc)3/ Cu(OAc)2 and CAN with 9-
benzylidene-9H-fluorene derivatives have comparatively
been studied. As a result, we determined spiro-configurated
cyclization products (dihydrofuran and lactone derivatives)
in the presence of Mn(OAc)3/ Cu(OAc)2 and either cycliza-
tion or addition products in the presence of CAN. Addition
products were obtained by using 2a. The stereochemistry of
the products 3d, 4d and 5d was only transconfiguration
which had a coupling constant 13 Hz.
[6]
[7]
[8]
ACKNOWLEDGEMENT
Authors thank Sakarya University Scientific Research
Foundation for financial support (Project No: 02.04.07/
2007).
SUPPLEMENTARY MATERIAL
Supplementary material is available on the publishers
Web site along with the published article.
[9]
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Typical procedure for coupling reactions of 9-benzylidene-9-H
fluorene derivatives with 1,3-dicarbonyl compounds in the pres-
ence of CAN: 9-benzylidene-9-H fluorene derivatives (6 mmol)
were stirred in methanol (20 ml) until dissolved at room tempera-
ture. 1,3- dicarbonyl compounds (6 mmol) which were dissolved in
methanol (10 ml) were added under argon atmosphere and stirred
for 0.5 h. CAN (18 mmol) was added with dropping funnel under
argon atmosphere too. The mixture was stirred in ice bath or at
room temperature until color of reaction had disappeared Alcohol
was removed by rotary evaporator. Then, the mixture was worked-
up with chloroform. Further purification of the products was car-
ried out by column chromtography on silica gel using hex-
ane:ethylacetate.
tic acid. Then, Cu(OAc)2(1.8 mmol) was added to the flask. 1,3-
dicarbonyl compounds (6 mmol) which were dissolved in acetic
acid were added under argon atmosphere and stirred for 0.5 h at
room temperature. 9-benzylidene-9-H fluorene derivatives (6
mmol) were added slowly by dropping funnel. Temperature was
o
[13]
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methane. Solvent was evaporated. Further purification of the prod-
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Typical procedure for coupling reactions of 9-benzylidene-9-H
fluorene derivatives with 1,3- dicarbonyl compounds in the pres-
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(50 ml) by azeotropic destillation system and was dissolved in ace-
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