Synthesis of benzofuran derivatives using manganese (III) acetate mediated addition of β-dicarbonyl compounds to alkyne and alkenes - A comparative study

Article abstract of DOI:10.1081/SCC-100108239

β-Dicarbonyl compounds were easily oxidized with manganese (III) acetate in acetic acid to form the corresponding α-carboradicals, which attacked alkyne and alkenes to give furan derivatives in good yield.

Full text of DOI:10.1081/SCC-100108239

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SYNTHESIS OF BENZOFURAN DERIVATIVES USING
MANGANESE (III) ACETATE MEDIATED ADDITION OF β-
DICARBONYL COMPOUNDS TO ALKYNE AND ALKENES –
A COMPARATIVE STUDY
Mehmet Yilmaz a & A. Tarik Pekel a
a Science Faculty, Department of Chemistry , Ankara University , 06100, Tandoğan,
Ankara, Turkey
Published online: 09 Nov 2006.
To cite this article: Mehmet Yilmaz & A. Tarik Pekel (2001) SYNTHESIS OF BENZOFURAN DERIVATIVES USING MANGANESE
(III) ACETATE MEDIATED ADDITION OF β-DICARBONYL COMPOUNDS TO ALKYNE AND ALKENES – A COMPARATIVE STUDY,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 31:24,
3871-3876, DOI: 10.1081/SCC-100108239
To link to this article: http://dx.doi.org/10.1081/SCC-100108239
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SYNTHETIC COMMUNICATIONS, 31(24), 3871–3876 (2001)
SYNTHESIS OF BENZOFURAN
DERIVATIVES USING MANGANESE
(III) ACETATE MEDIATED ADDITION
OF b-DICARBONYL COMPOUNDS
TO ALKYNE AND ALKENES – A
COMPARATIVE STUDY
Mehmet Yilmaz* and A. Tar|k Pekel
Ankara University, Science Faculty, Department of
Chemistry, 06100 Tandogan, Ankara, Turkey
ABSTRACT
b-Dicarbonyl compounds were easily oxidized with manga-
nese (III) acetate in acetic acid to form the corresponding
a-carboradicals, which attacked alkyne and alkenes to give
furan derivatives in good yield.
In the last two decades, the free radical chemistry has been improved
by formation of radicals with the aid of transition metals and their oxides
and by investigation of redox methods in detail. Reactions formed with
Mnþ3, Coþ3, Feþ3, Agþ2, and Ceþ4 are amongthe most widely investigated
ones.1 These metal oxidants exhibit regioselectivity, particularly in the syn-
thesis of polyfunctional organic compounds.
*Correspondingauthor.
3871
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

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In addition; they form new radicals, which cannot be obtained with
traditional techniques. Amongthose oxidants Manganese (III) acetate that
has attracted most attention, has been used to form various compounds
2–4
includingcomplex natural products.
Heiba and Dessau realised the first experiments about the free radical
cyclization with MAH. The addition of ketones and carboxylic acids to
alkenes,5 and aromatic nitromethylation of Kurz6 are the other investiga-
tions about this subject. The cyclization of 1,3-diones7,8 in the presence of
MAH with alkenes are the other results reported about this subject. But,
there are no comparative researches performed about the reactions of the
b-dicarbonyl compounds with alkenes and alkynes havingdifferent func-
tional groups.
We have investigated comparative reactions of dimedon and 5-phenyl-
1,3-cyclohexandione with phenylacetylene and some alkenes (styrene,
allylbenzene, vinylacetate, metacrylamide and cyclohexene). We have syn-
thesised benzofuran and dihydrobenzufuran derivatives with high yield.
Manganese (III) acetate mediated reactions of active methylene compounds
with a,b-unsaturated amide hasnot been reported yet. We have realised the
synthesis of 2-carbamoyl dihydrobenzofurans usingmetacrylamide as
alkene.
While the reaction of dimedone with conjugated alkene (styrene) exhi-
bited high yield (93%), it was only 20% with allylbenzene. However, the
reaction with conjugated alkyne (phenylacetylene) resulted in 50% yield. On
the other hand, it was found that electron-rich alkenes (vinylacetate) formed
benzofurans with higher yield than electron-poor alkenes (cyclohexene).
However, a,b-unsaturated carbonyl compound (metacrylamide) was found
to be more reactive in both alkene types. As shown in table, the product
yield was found to be lowered by 30–50%, when 5-phenyl-1,3-cyclohexane-
dione was used instead of dimedone.
This reaction formed only desired heterocyclic compounds in one
step and no other by-products were isolated. Accordingly, we suggest
that the present reaction is a convenient synthetic method of preparing
the benzofurans.
EXPERIMENTAL
Instruments: Meltingpoints were obtained on Gallencamp capillary
meltingpoint apparatus. IR spectrums (KBr disc, CH Cl2) were obtained
2
with a Matson 1000 FT-IR in the 400–4000 cmꢀ1 range with 4 cmꢀ1 reso-
1
lution. H NMR and 13C-NMR were obtained in CDCl3 and DMSO-d6 on
a Bruker DPX-400 MHz high performance digital FT-NMR spectrometer

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Table. Synthesis of Benzofuran Derivatives by MAH Promoted Oxidative
Addition of Dimedon and 5-Phenyl-1,3-Cyclohexanedione to Alkenes and an Alkyne
(internal standard TMS). Mass spectra (MS) were obtained by EI method in
micromass UK Platform-II LC/MS spectrometer. Element analysis was
performed by Leco 932 CHNS-O analyser. Quantitative gas chromato-
graphic analysis for determination of conversions were performed by the
internal standard (dipenthylether) method on a UNICAM 610. Series gas

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YILMAZ AND PEKEL
chromatograph equipped with a capillary column (15 m ꢁ 0.24 nm). The
column is coated with dimethylpolysiloxane (film thickness 25 mm), FID
dedector, hydrogen as carrier gas, and temperature programmed from 50
to 250–280ꢂC at 10ꢂ/min.
Reagent: Manganese (III) acetate, which is used for the oxidation was
11
prepared accordingto the procedure in literature. Acetic acid, dimedone,
5-phenyl-1,3-cyclohexanedione, phenyl acetylene, metacrylamide styrene
and other alkenes were commercial products with highest reagent grade.
Generalprocedure: A solution of manganese (III) acetate (10 mmol,
2.7 g) in 40 mL of glacial acetic acid was heated under nitrogen atmosphere
at 80ꢂC until it dissolves. After MAH is dissolved completely the solution is
cooled down to 40ꢂC. A solution of b-dicarbonyl compound (5 mmol) and
alkene (6 mmol) in 10 mL acetic acid is added to this mixture. The reaction is
finished when dark brown colour of the solution disappears. Acetic acid is
evaporated out under reduced pressure. The remainingmixture is neutra-
lised by saturated NaHCO3 solution and extracted with ethyl acetate
(2 ꢁ 20 mL). The combined organic extracts were dried over anhydrous
Na2SO4 and evaporated. Quantitative analysis of the resultingmixture
was carried out usingGC after dilution with EtOAc and addition of
dipenthylether as internal standard. The residue obtained was subjected
to chromatography on silica column (2 ꢁ 15 cm). Elusion with 20% ethyl
acetate in light petroleum afforded the dihydrofuran derivative.
2-Benzyl-6,6-dimethyl-2,3,4,5,6-hexahydro-4-oxo-benzo [b] furan (2):
Rt: 13.97; IR (KBr disc, CH2Cl2) cmꢀ1: 3044, 1709, 1635, 758, 701; 1H-NMR
(CDCl3) d: 1 (3H, s), 1.1 (3H, s), 2.15 (2H, d, J 5), 2.25 (2H, s), 2.6 (1H, dd, J
7 and 7), 2.9 (1H, dd, J 10 and 2), 3 (1H, dd, J 15 and 18), 3.1 (1H, dd, J 15
and 18), 5.1 (1H, dtd, J 4, 3 and 3), 7.2 (3H, d, J 6), 7.3 (2H, t, J 7);
13C-NMR (CDCl3) d: 28.9, 29.1, 30.9, 34.4, 38.2, 42.3, 51.1, 86.4, 111.8,
127.2, 128.8, 129.8, 136.7, 176.7, 195.3; MS m/z: 259, 258, 257, 256 (Mþ),
255, 165, 129, 128, 123, 119 (100), 115, 109, 108, 105, 104, 103; Anal. Calcd.
For C17H20O2 C 79.69, H 7.8 found C 79.39, H 7.52.
2,6-Diphenyl-4,5,6,7-tetrahydro-4-oxo-benzo [b] furan (4): mp (colour-
less, from EtOAc): 107–109ꢂC; IR (KBr disc) cmꢀ1: 3050, 1677, 1619, 1621,
1
765, 708. H-NMR (CDCl3) d: 2.9 (2H, d, J 8), 3.2 (1H, dd, J 18 and 11),
3.35 (1H, dd, J 17 and 5), 3.7 (1H, m), 7.0 (1H, s), 7.5 (8H, m), 7.75 (2H, d, J
8); 13C-NMR (CDCl3) d: 31.6, 41.2, 45.8, 101.4, 123.1, 124.8, 127.2, 127.5,
128.6, 129.2, 129.3, 130.0, 142.2, 155.3, 166.1, 193.5; MS m/z: 290, 289, 288
(Mþ), 183, 155, 104 (100); Anal. Calcd. For C20H16O2 C 83.3, H 5.55 found
C 82.75, H 5.97.
2-Acetyl-6,6-dimethyl-2,3,4,5,6,7-hexahydro-4-oxo-benzo [b] furan (5):
Rt; 10.63; IR (KBr disc, CH2Cl2) cmꢀ1: 1766, 1740, 1650. 1H-NMR
(CDCl3) d: 1.05 (3H, s), 1.1 (3H, s), 2.25 (1H, d, J 15), 2.25 (1H, d, J 12),

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2.30 (1H, d, J 13), 2.35 (1H, dd, J 18), 2.8 (1H, d, J 16), 3.05 (1H, dd, J 8 and
7), 5.25 (1H, s), 6.7 (1H, dd, J 5 and 2); 13C-NMR (CDCl3) d: 21.1, 28.5,
29.1, 32.1, 34.5, 37.6, 51.1, 53.8, 99.3, 111.2, 169.6, 174.8; MS m/z: 255, 224
(Mþ), 115, 87, 85, 83, 82, 70, 69, 57, 55 (100); Anal. Calcd. For C12H16O4; C
64.29, H 7.14, found: C 64.04, H 7.28.
2-Carbamoyl-6,6-dimethyl-2,3,4,5,6,7-hexahydro-2-methyl-4-oxo-benzo
[b] furan (6): Rt: 12.31; mp (colourless, from EtOAc): 196–198ꢂC; IR (KBr
1
disc) cmꢀ1: 3380, 3210, 1702, 1660, 1625; H-NMR (CDCl3 and DMSO-d6)
d: 0.5 (3H, s), 0.6 (3H, s), 1.0 (3H, s), 1.6 (2H, s), 1.75 (1H, d, J 18), 1.9 (1H,
d, J 18), 2.1 (1H, d, J 15), 2.55 (1H, d, J 15), 6.4 (1H, s), 6.6 (1H, s);
13C-NMR (CDCl3 and DMSO-d6) d: 30.5, 33.7, 33.8, 39.2, 42.1, 42.7,
56.1, 96.0, 116.1, 179.3, 180.5, 199.2; MS m/z: 226, 225, 224 (100), 223
(Mþ), 206, 179, 178, 150, 137, 123, 122, 95, 55, 53. Anal. Calcd. For
C12H17NO3: C 64.57, H 7.62, N 6.27, found: C 65.01, H 8.24, N 6.32.
2-Carbamoyl-2,3,4,5,6,7-hexahydro-2-methyl-6-phenyl-4-oxo-benzo [b]
furan (7): mp (colourless, from MeOH): 216–218ꢂC; IR (KBr disc) cmꢀ1
:
3387, 3157, 1727, 1651, 1625, 782, 706; 1H-NMR (DMSO-d6) d: 1.5 (3H, s),
2.3 (1H, dd, J 16 and 4), 2.55 (1H, d, J 2), 2.65 (1H, d, J 4), 2.8 (2H, dt, J 14
and 3), 2.95 (1H, d, J 16), 3.4 (1H, m), 7.25 (1H, t, J 7), 7.35 (4H, m), 7.4
(1H, s), 7.5 (1H, s); 13C-NMR (DMSO-d6) d: 25.6, 31.4, 37.7, 44.5, 91.2,
112.1, 127.6, 127.8, 129.4, 144.1, 175.3, 175.8, 176.0, 193.7; MS m/z: 273, 271
(Mþ), 255, 254 (100), 227, 184, 149 (100), 121, 123, 43; Anal. Calcd. For
C16H17NO3: 70.84, H 6.27, N 5.16, found: C 70.67, H 6.25, N 5.24.
ACKNOWLEDGMENTS
The spectral analyses of this work were supported by TUBITAK,
Instrumental Analyses Laboratory.
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Received in the Netherlands February 9, 2001

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