Catalytic oxidative domino degradation of alkyl phenols towards 2- and 3-substituted muconolactones

Article abstract of DOI:10.1080/00397910802369687

The catalytic oxidative domino degradation of phenols was investigated. Hydrogen peroxide (30% aq.) was used as an oxidant and 2,2′-dinitro-4, 4′-ditrifluoromethyldiphenyl diselenide 4e as a catalyst. The products were muconic acid 5, and muconolactones muconolactones - 5-carboxymethylfuran- 2(5H)-ones 7 and 9. Phenols with alkyl groups at 2 or 4 positions of the benzene ring were converted regioselectively to corresponding muconolactones substituted at alkenylene ring carbon atoms. The reaction mechanism is proposed. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910802369687

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Catalytic Oxidative Domino
Degradation of Alkyl Phenols
Towards 2- and 3-Substituted
Muconolactones
Mirosław Giurg a , Ewa Kowal a , Hubert Muchalski a
, Ludwik Syper a & Jacek Młochowski a
a Department of Organic Chemistry, Faculty of
Chemistry , Wrocław University of Technology ,
Wrocław, Poland
Published online: 22 Dec 2008.
To cite this article: Mirosław Giurg , Ewa Kowal , Hubert Muchalski , Ludwik Syper
& Jacek Młochowski (2008) Catalytic Oxidative Domino Degradation of Alkyl Phenols
Towards 2- and 3-Substituted Muconolactones, Synthetic Communications: An
International Journal for Rapid Communication of Synthetic Organic Chemistry, 39:2,
251-266, DOI: 10.1080/00397910802369687
To link to this article: http://dx.doi.org/10.1080/00397910802369687
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Synthetic Communications1, 39: 251–266, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910802369687
Catalytic Oxidative Domino Degradation of
Alkyl Phenols Towards 2- and 3-Substituted
Muconolactones
Mirosław Giurg, Ewa Kowal, Hubert Muchalski, Ludwik Syper, and
Jacek Młochowski
Department of Organic Chemistry, Faculty of Chemistry,
Wrocław University of Technology, Wrocław, Poland
Abstract: The catalytic oxidative domino degradation of phenols was investi-
gated. Hydrogen peroxide (30% aq.) was used as an oxidant and 2,20-dinitro-
4,40-ditrifluoromethyldiphenyl diselenide 4e as a catalyst. The products were
muconic acid 5, and muconolactones muconolactones—5-carboxymethylfuran-
2(5H)-ones 7 and 9. Phenols with alkyl groups at 2 or 4 positions of the benzene
ring were converted regioselectively to corresponding muconolactones substituted
at alkenylene ring carbon atoms. The reaction mechanism is proposed.
Keywords: Diselenides, domino reaction, hydrogen peroxide, muconolactones,
oxidation
Compounds containing heterocyclic skeleton of muconolactones, 2(5H)-
furanones, belong to the group of 2-butenolides, important synthetic tar-
gets and biologically active natural products, and they may play a signif-
icant role in the discovery of new therapeutic agents.[1,2] Although the
butenolides can be obtained several different ways,[2–5] there is a lack
of general method for synthesis of muconolactones. A simple, naturally
occurred 2-methylmuconolactone has been obtained in a multistep
way involving 1,3-dipolar cycloaddition, followed by CrO3=H2SO4
Received June 7, 2008.
Address correspondence to Mirosław Giurg, Department of Organic Chemis-
´
try, Faculty of Chemistry, Wrocław University, Wybreze, Wyspianskiego 27,
˙
Wrocław 50-370, Poland. E-mail: miroslaw.giurg@pwr.wroc.pl
251

252
M. Giurg et al.
oxidation of formed hydroxymethyl group, whereas 3-methylmucono-
lactone has been prepared by treating 4-methyl-2-nitrophenol with hot
sulfuric acid.[3]
The muconolactones substituted on alkenyl carbon atoms have been
obtained in particular ways such as enzymatic and chemical oxidative
degradation of benzenes, intra-diol cleavage of catechols, and intra-
dion cleavage of ortho-benzoquinones followed by lactonizations
of 2,4-hexadienedioic acids. Unfortunately, direct lactonization of
2,4-hexadienedioic acids is limited to a few examples, and this method
has little synthetic value.[4–6]
The more versatile method for synthesis of the muconolactones
presented in this work is based on domino oxidation of phenols.[7,8] It
should be noted that the domino reactions have attracted considerable
attention in synthetic chemistry because they result in reduction of the
number of separation processes, amount of solvents, time, and energy,
and a single synthetic step could convert an inexpensive material into a
highly complex heterocyclic product.[9]
The 2- and 3-substituted muconolactones were obtained by oxidation
of mono-substituted phenols with hydrogen peroxide (H2O2) in the presence
of a catalytic amount of 2,20-dinitro-4,40-di(trifluoromethyl)diphenyl disele-
nide. This approach is based on the known fact that diaryl diselenides
are oxidized in situ with H2O2 to intermediate areneperoxyseleninic acids,
which are highly active oxygen donors.[10] Recently, we reported hydrogen
peroxide=organoselenium reagents for functional group transformations,
ring contraction of cycloalkanones, cyclocondensation of 2-aminophenols
and degradation of aromatic ring in naphthalene.[7,11,12]
Aqueous hydrogen peroxide (30%) was chosen as an oxidant because
it is safe, is convenient to use, and contains a high proportion of active
oxygen. Moreover, it is a cheap and environmentally friendly reagent,
and because its only reduction product is water, it can be used both in
laboratory and industry.[12,13]
We have found that oxidation of 2,4-di-tert-butylphenol (1a) with
30% aq. hydrogen peroxide in tert-butanol, at 80 ꢀC for 20 h in the
presence of different selenium catalysts, gave the 2,4-di-tert-butyl-
muconolactone (2) accompanied by minute amounts of 3,5-di-tert-
butyl-ortho-benzoquinone (3), in three cases (Scheme 1). The optimized
molar ratio of H2O2 to the substrate was 5:1. Selenium(IV) oxide and
11 diphenyl diselenides were tested as the catalysts 4a–k (Scheme 1). They
were used in 5% molar ratio to phenol 1a. No reaction progress was
observed without catalyst. In the presence of selenium(IV) oxide, muco-
nolactone 2 was formed in only low 24% yield. The higher preparative
yield of muconolactone 2 could be obtained by the use of organoselenium
catalysts, listed in Table 1. The most active catalysts were diphenyl

Oxidation of Phenols to Muconolactones
253
Scheme 1. Oxidation of 2,4-di-tert-butylphenol (1a).
diselenides 4c–f and 4i, having two nitro groups at the 2 and 20 positions,
because they are easy to prepare, they were catalysts of choice. Among
them, the most efficient was diphenyl diselenide 4e, having two differ-
ent electron-withdrawing substituents at benzene ring, the nitro and
trifluoromethyl groups (Table 1).
It should be noted that 2,20-dinitro-4,40-di(trifluoromethyl)diphenyl
diselenide (4e) is conveniently prepared by selenenylation of cheap,
commercially available 1-chloro-2-nitro-4-trifluoromethylbenzene with
dilithium diselenide. Using this catalyst, the pure product 2 was prepared
in the satisfactory 70% yield (Table 2).
The reagent H2O2=4e was successfully applied for preparative domino
oxidation of 15 different phenols and catechols (1b–e, 6a–e, 8a–e,11) to
the corresponding 2- and 3-substituted alkyl muconolactones 7 and 9 or,
in some cases, to muconic acids (5a, 5b, 21a, 22a). The oxidized phenols
belong to two different groups. The one group consists of phenol and its
ortho-substituted derivatives 1b–e, 6a–e; the second group consists of mono-
substituted phenols 8a–e having both equivalent ortho-positions free. The
reaction was carried out in tert-butanol under gentle reflux for 20 h.

254
M. Giurg et al.
Table 1. Results of oxidative conversion of phenol 1a
into muconolactone 2 with H2O2=catalyst system
Catalyst
Product 2 yield (%)a
b
none
SeO2
4a
—
24
45
48c
63
60
70c
67c
50
30
52
49
45
4b
4c
4d
4e
4f
4g
4h
4i
4j
4k
aPreparative yield.
bUnreacted substrate 1a was isolated almost
quantitatively.
c3,5-Di-tert-butyl-1,2-benzoquinone (3) was formed in
up to 5.0% yield.
Phenol, catechol, guaiacol, and salicylaldehyde 1b–e were oxidized to
the mixture of EE- and EZ-hexa-2,4-dienedioic acids 5. The alkyl mono-
substituted phenols 6a–e, and 8a–e underwent regioselective ring rearran-
gements to muconolactones 7a–e, and 9a–e. In the case of 2-alkylphenols
6a–e, oxidative domino sequence was ended by ring clousure, and
although both isomeric muconolactones, substituted at 2 and 5 positions,
could be produced, the reaction proceeded regiospecifically to 2-substi-
tuted derivatives of 7a–e. Similarly, from 4-substituted alkyl phenols
8a–e, both isomeric muconolactones with substituent at 3 and 4 positions
could be produced, but the regiospecific ring closure gave 3-derivatives
9a–e. When 3-tert-butylphenol (10), having both nonequivalent ortho
positions free, was oxidized to 2- and 3-substituted muconolactones 7d
and 9d, 3-tert-butylmuconolactone (9d) was a major product. The
additional experiments showed that oxidation of the 1,2-dihydroxy-4-
tert-butylbenzene (11) gave lactone 9d, the same as obtained from
corresponding phenols 8d and 10 (Scheme 2, Table 2).
Taking into consideration the mechanism for oxidation of
phenols with benzeneseleninic acid or its anhydride, proposed by D. R.
H. Barton,[14,15] and the results of our experiments, the plausible reaction
sequence can be proposed (Scheme 3). Initially, the phenol (1b) is

Oxidation of Phenols to Muconolactones
255
Table 2. Results of oxidative degradation of phenols into muconic
acids and muconolactones
Substrate
Product
Yielda (%)
No.
R
–
No.
1a
1b
1c
1d
1e
6a
2
5
70
R4 ¼ H
R4 ¼ OH
R4 ¼ OMe
R4 ¼ CHO
R5 ¼ Me
50b,c
49b
47b
45b
40
5
5
5
7a
21a
7b
7c
7d
7e
9a
22a
9b
9c
9d
9e
7d
9d
9d
20b,d
80
70
65
6b
6c
6d
6e
8a
R5 ¼ i-Pr
R5 ¼ s-Bu
R5 ¼ t-Bu
R5 ¼ Bz
75
R6 ¼ Me
40
35e
72
8b
8c
8d
8e
10
R6 ¼ i-Pr
R6 ¼ s-Bu
75
72
80f
(17)
(52)
77
R6 ¼ t-Bu
R6 ¼ t-BuCH2CMe2
—
11
—
aPreparative yield. Data in parantheses were determined on 1H
NMR analysis.
bMixture of EZ and EE muconic acids were formed.
1
c5a and 5b were determined on H NMR analysis in 1:3 ratio.
d2-Methylmuconic acids 21a were determined on 1H NMR analysis
in 1:1 ratio.
eEE-3-methylmuconic acid was formed.
fThe reaction was prolonged to 72 h.
O-selenenylated by seleninic acid 13, produced in situ from diselenide 4e
and hydrogen peroxide. The formed ester 15 immediately rearranges, in
2,3-sigmatropic way, to seleneate 16 or to its tautomer 17. The ester 16
is oxidized to 1,2-benzoquinone 18, while selenenic acid 12 is eliminated.
Then, quinone 18 undergoes Baeyer–Villiger oxidation to the muconic
anhydride 19, which hydrolyses to 2Z,4Z-hexa-2,4-dienedioic acid, cis,-
cis-muconic acid (20), and subsequent isomerization finally gives stable,
in the reaction conditions, trans-muconic acids 5. The alternative reaction
path involves elimination of seleninic acid from the tautomer 17 and

256
M. Giurg et al.
Scheme 2. Oxidative conversion of phenols to muconic acid 5 and mucono-
lactones 7 and 9.
subsequent oxidation of formed catechol (1c) to the quinone (18). This
route seems to be less probable since our attempts to trap catechol
intermediates failed.
The (2Z)-hexa-2,4-dienedioic acids 21b–e and 22b–e, formed in situ
from benzyl, secondary, and tertiary alkyl-substituted phenols 6b–e and
8b–e, underwent instantly regiospecific intramolecular Michael lactoniza-
tion, and substituted alkenyl carbon atom muconolactones 7b–e and 9b–e
were obtained. The reaction proceeds via route A because lack of lactones
23 and 24 among the products excludes the alternative route B (Scheme 4).
In conclusion, we indicated that 2- and 4-substituted phenols can
be efficiently converted by oxidation with 30% aqueous hydrogen per-
oxide in the presence of 2,20-dinitro-4,40-di(trifluoromethyl)diphenyl
diselenide as a catalyst to 2- and 3-substituted muconolactones, 3- and
4-substituted-5-carboxymethylfuran-2(5H)-ones. It is the first case of
the preparative regiospecific oxidative domino conversion of cheap and
easily available phenolic precursors to muconolactones alkyl substituted
on alkenyl carbon atom.

Oxidation of Phenols to Muconolactones
257
Scheme 3. The plausible reaction sequence from phenol (1b) to trans-muconic
acids 5.
Scheme 4. Regiospecific muconic acids 21 and 22 intermediate lactonization.

258
M. Giurg et al.
EXPERIMENTAL
Melting points were determined on a digital melting-point apparatus,
Electrothermal IA 91100. 1H NMR (300 MHz) and 13C NMR
(75 MHz) were measured with a Bruker DRX 300 spectrometer. IR
was measured on a Perkin-Elmer 2000 FT spectrometer.
Aqueous hydrogen peroxide (30%), phenols, selenium(IV) oxide, tert-
butanol, silica gel (70–230 mesh.), and other commercially available
reagents and solvents were purchased from Aldrich, Fluka, or Merck.
2,20-Dicarboxydiphenyl diselenide (4a) was obtained from anthranilic acid
according to the procedure reported earlier.[16] The 2,20-di(trifluoro-
methyl)diphenyl diselenide 4b was synthesized from the corresponding
arylmagnesium iodides and elemental selenium following the procedure
of Reich et al.[17] The catalysts 4c–f and 4i–k were obtained by selenenyla-
tion of corresponding haloarenes as reported in our previous works.[18]
Reduction of the nitro group in the compounds 4d and 4e with hydrazine
hydrate in the presence of Raney nickel gave anilines 4g and 4h, respec-
tively.[19] The purity of the products was confirmed by comparison of their
1
melting point with data given in literature and by measuring their H
NMR, 13C NMR, and IR spectra. Because some physicochemical data
reported in the some previous papers have been incorrect, we revised them
carefully.
2,20-Dinitro-4,40-di(trifluoromethyl)diphenyl Diselenide (4e)[19]
The solution of dilithium diselenide, prepared according to Ref. 7 from
lithium (0.750 g, 0.108 mol) and selenium powder (8.00 g, 0.101 mol) in
anhydrous tetrahydrofuran (THF) (50ml) and hexamethylphosphoramide
(HMPT) (25.6 g, 25.0 ml, 0.143 mol), was added to a stirred solution of
1-chloro-2-nitro-4-trifluoromethylbenzene (22.56 g, 0.100 mol) in anhydrous
THF (40 ml) in an ice-water bath, and the reaction was continued for 20 h at
room temperature. THF was distilled off, hot water (100 ml) was added, and
then the cold reaction mixture was allowed to stand in a refrigerator for 2 h.
The residue was filtered off, washed with water and ethanol (3 ꢁ 15 ml), and
recrystallized from acetonitrile–water 5:1 (250 ml) to give yellow-greenish
needles of 4e (20.00g, 37.2 mmol, 74.3%), which melt at 178–181ꢀC. Recrys-
tallization from acetonitrile (120 ml) with charcoal give yellow needles
(17.49 g, 32.5 mmol, 65.0%). Mp 180–182 ꢀC, Ref. [19]: 180–182 ꢀC. nmax
1
(KBr) cmꢂ1 3100–3020 (CH), 1521 and 1331 (NO2), 708 (C-Se). H NMR
(DMSO-d6): 8.62 (d, J ¼ 2.0 Hz, 2H, H-3, H-30), 8.11 (d, J ¼ 8.5Hz, 2H,
H-6, H-60), 8.00 (dd, J¼ 8.5, 2.0 Hz, 2H, H-5, H-50). 13C NMR (DMSO-
d6): 146.3, 133.3, 128.7 (q, J¼ 33.8 Hz) (C), 133.0, 131.2 (q, J ¼ 3.1 Hz),

Oxidation of Phenols to Muconolactones
259
123.1 (q, J ¼ 3.8 Hz) (CH), 122.8 (q, J¼ 272.6Hz, CF3). Found: C, 31.04; H,
1.35; C14H6F6N2O4Se2 538.12 requires C, 31.25; H, 1.12.
Catalyst Evaluation
To a solution of 2,4-di-tert-butylphenol (1a) (1.032 g, 5.00 mmol) and a
catalyst, SeO2 or 4a–k (0.25 mmol, 5.00 mol %) in tert-butanol (20 ml),
H2O2 (2.5 ml, 25 mmol) was added. The reaction mixture was stirred
under gentle reflux for 20 h. Then the mixture was treated with a pinch
of Pt=C. Cold brine (25 ml) and NaHCO3 were added during vigorous stir-
ring until the evolution of dioxygen and carbon dioxide ceased. The mix-
ture was washed with diethyl ether, and the aqueous layer was acidified
with aq. hydrochloric acid to pH ca. 2. The lactone was extracted with
diethyl ether (50 and 4 ꢁ 15 ml). The combined extracts were dried with
anhydrous Na2SO4, the solvent was distilled off, and residue was dried
1
in dessicator (20 mmHg, P2O5) to give pure (by H NMR) 5-carboxy-
methyl-3,5-di-tert-butylfuran-2(5H)-one (2), See Table 1 for the results.
Preparative Oxidation of Phenols
To a solution of phenol (1a–e, 6a–e, 8a–e, 10, 11) (10.0 mmol) and hydrogen
peroxide (5.0 ml, 50mmol) in tert-butanol (40 ml), 2,20-dinitro-4,40-di-
(trifluoromethyl)diphenyl diselenide (4e) (0.270g, 0.500 mmol, 5.00mol%)
was added. The mixture was stirred under gentle reflux for 20 h. Then it
was treated with a pinch of Pt=C, and solvent was distilled off. The cooled
residue was treated with brine (25 ml), and NaHCO3 was added portion-
wise during vigorous stirring until the evolution of carbon dioxide ceased.
The mixture was shaken with diethyl ether. The aqueous layer was acidified
with aq. hydrochloric acid to pH ca. 2 and extracted with diethyl ether (50
and 4 ꢁ 25ml). The combined extracts were dried with anhydrous Na2SO4,
the solvent was distilled off, and the residue was dried in dessicator
(20 mmHg, P2O5). The residue were pure lactone 2, 7b–e, and 9b–e. Lac-
tones 7a and 9a were extracted with CHCl3 (3 ꢁ 2 ml) and purified by col-
umn chromatography on silica gel using n-hexane–ethyl acetate–acetic acid
(5:1:1) or CHCl3–ethyl acetate (1:1) as an eluent. The mixture of lactones 7d
and 9d obtained from 10 were analyzed by means of 1H NMR. Unsoluble
in CHCl3, the methyl derivatives of muconic acids 21a and 22a were recrys-
talized from hot acetic acid and characterized (Table 2 and Data). The ana-
lytical samples of 7b–e and 9b–e were obtained by column chromatography
on silica gel (70–230 mesh) using CHCl3 and CHCl3–ethyl acetate gradient
for 1:0 to 1:1 and characterized (see Data).

260
M. Giurg et al.
The red diethyl ether extract of NaHCO3 aqueous phase from 1a was
poured on a silica-gel column and eluted with methylene chloride to
obtain 3,5-di-tert-butyl-1,2-quinone (3) (80.1 mg, 0.364 mmol) in 3.6%.
Recrystalization from methanol give dark red prisms. Mp 118–120 ꢀC,
1
Ref., [15]: 109–112 ꢀC, Ref., [20]: 115–117 ꢀC. H NMR (CDCl3): 6.91
(d, J ¼ 2.3 Hz, 1H, H-4), 6.19 (d, J ¼ 2.3 Hz, 1H, H-6), 1.24 (s, 9H,
CH3), 1.20 (s, 9H, CH3). IR (KBr): c ¼ 3066, 2963, 2908, 2872 cmꢂ1
(CH), 1661, 1652 cmꢂ1 (C¼O), 1623 cmꢂ1 (C¼C).
From a concentrated reaction mixture obtained from phenol (1b),
colorless flakes of (2E,4E)-hexa-2,4-dienedioic acid (5b) (m ¼ 0.2420 g,
1.703 mmol) crystallized in 17% as colorless plates. Mp 300–302 ꢀC, Ref.,
1
[21]: 296–298 ꢀC. H NMR (DMSO-d6): 12.68 (s, 2H, COOH), 7.22–7.36
(m, 2H, CH ¼ CH-COOH), 6.24–6.38 (m, 2H, CH-COOH). 13C NMR
(DMSO-d6): 2 ꢁ 167.0 (C), 2 ꢁ 141.0, 2 ꢁ 129.2 (CH). IR (KBr):
c ¼ 2000–3500 cmꢂ1 (COOH), 1684 cmꢂ1 (C¼O), 1634, 1610 cmꢂ1 (C¼C).
Data
5-Carboxymethyl-3,5-di-tert-butylfuran-2(5H)-one (2)
White prisms. Mp 133–135 ꢀC (dichloromethane) (Ref. [10b]: 132–
133 ꢀC). 1H NMR (CDCl3): 12.5 (s, 1H, COOH), 6.90 (s, 1H, H-4),
2.89 (d, J ¼ 14.3 Hz, 1H, CHCOOH), 2.75 (d, J ¼ 14.3 Hz, 1H,
CHCOOH), 1.16 (s, 9H, t-Bu), 0.92 (s, 9H, t-Bu). 13C NMR (CDCl3):
175.3, 171.2, 143.7, 88.1, 37.6, 31.4 (C), 145.6 (CH), 37.3 (CH2),
3 ꢁ 27.8, 3 ꢁ 25.1 (CH3). IR (KBr): c ¼ 2600–3100 cmꢂ1 (br.) (COOH),
1763, 1748, 1713 cmꢂ1 (C¼O), 1194 or 1176 cmꢂ1 (C–O).
5-Carboxymethyl-3-methylfuran-2(5H)-one (7a)
Colorless prisms. Mp 106.5–108.5 ꢀC (chloroform) (Ref. [6,22] not
reported). 1H NMR (CDCl3): 10.32 (s, 1H, COOH), 7.17 (dk, J ¼ 1.5 Hz,
Hz, 1H, H-4), 5.26 (m, 1H, H-5), 2.81 (dd, J ¼ 16.7, 7.4 Hz, 1H,
CHCOOH), 2.68 (dd, J ¼ 16.7, 6.7 Hz, 1H, CHCOOH), 1.92 (dd,
J ¼ 1.8, 1.5 Hz, 3H, CH3). 13C NMR (CDCl3): 174.6, 173.7, 130.9 (C),
147.6, 76.5 (CH), 37.8 (CH2), 10.6 (CH3). IR (KBr): c ¼ 2200–
3300 cmꢂ1 (br.) (COOH), 1772, 1756 cmꢂ1 (C¼O), 1706 cmꢂ1 (C¼C).
5-Carboxymethyl-3-isopropylfuran-2(5H)-one (7b)
Colorless prisms. Mp 71–75 ꢀC (diethyl ether–methylcyclohexane)
1
(Ref. [22]:76 ꢀC). H NMR (CDCl3): 10.17 (s, 1H, COOH), 7.09 (dd,

Oxidation of Phenols to Muconolactones
261
J ¼ 1.4 Hz, 1H, H-4), 5.25 (ddd, J ¼ 7.2, 6.9, 1.4 Hz, 1H, H-5), 2.83 (dd,
J ¼ 16.6, 7.2 Hz, 1H, CHCOOH), 2.67 (dd, J ¼ 16.6, 6.9 Hz, 1H,
CHCOOH), 2.66 (m, J ¼ 6.9, 1.4 Hz, 1H, CHCH3), 1.17 (d, J ¼ 6.9 Hz,
6H, CH3). 13C NMR (CDCl3): 174.4, 172.8, 140.9 (C), 145.2, 76.5, 25.3
(CH), 37.7 (CH2), 20.7, 20.6 (CH3). IR (KBr) c ¼ 2500–3300 cmꢂ1 (br.)
(COOH), 3091, 2969, 2927, 2876 cmꢂ1 (C–H), 1760, 1757, 1713 cmꢂ1
(C¼O), 1640 cmꢂ1 (C¼C), 1160 cmꢂ1 (C–O).
3-sec-Butyl-5-carboxymethylfuran-2(5H)-one (7c)
Transparent oil with odor of lovage (Levisticum officinalis). The product
1
is a two diastereoisomers in 1:1 ratio. H NMR (CDCl3): 8.15 (s, 1H,
COOH), 7.11 (s, 1H, H-4), 5.27 (dd, J ¼ 7.2, 6.8 Hz, 1H, H-5), 2.82
(dd, J ¼ 16.6, 7.2 Hz, 1H, CHCOOH), 2.63–2.73 (m, 1H, CHCOOH),
2.42–2.54 (m, 1H, CH), 1.57–1.73 (m, 1H, CH2CH3), 1.37–1.53 (m, 1H,
CH2CH3), 1.14 (d, J ¼ 6.9 Hz, 3H, CH3CH), 0.87 (t, J ¼ 7.4 Hz, 3H,
CH3CH2). 13C NMR (CDCl3): 174.3 (C), 172.9 (C), 140.0 (C), 145.9
(CH), 76.5 (CH), 37.96 and 37.91 (CH2), 31.93 and 31.86 (C), 27.63
and 27.53 (CH2), 18.18 and 18.11 (CH3), 11.32 and 11.25 (CH3). IR (film)
c ¼ 2500–3600 cmꢂ1 (COOH), 3092, 2967, 2935, 2879 cmꢂ1 (C-H),
1748 cmꢂ1 (br.) (C¼O), 1175, 1161 cmꢂ1 (C–O). Found: C, 60.39; H,
7.16. (C10H14O4) 198.22 requires C, 60.59; H, 7.12.
3-tert-Butyl-5-carboxymethylfuran-2(5H)-one (7d)
Colorless prisms. Mp 78–80 ꢀC (chloroform–ethyl acetate). 1H NMR
(DMSO-d6): 12.48 (s, 1H, COOH), 7.28 (d, J ¼ 1.3 Hz, 1H, H-4), 5.20
(ddd, J ¼ 8.1, 5.1, 1.3 Hz, 1H, H-5), 2.78 (dd, J ¼ 16.3, 5.1 Hz, 1H,
CHCOOH), 2.45 (dd, J ¼ 16.3, 8.1 Hz, 1H, CHCOOH), 1.18 (s, 9H, t-
Bu). 13C NMR (CDCl3): 174.8, 171.3, 143.3, 31.5 (C), 145.0, 75.4
(CH), 37.9 (CH2), 27.9 ꢁ 3 (CH3). IR (KBr): c ¼ 2700–3500 cmꢂ1 (br.)
(COOH), 3060, 2962, 2873 cmꢂ1 (C–H), 1741, 1717 cmꢂ1 (C¼O),
1636 cmꢂ1 (C¼C), 1184 cmꢂ1 (C–O). Found: C, 60.64; H, 7.06.
(C10H14O4) 198.22 requires C, 60.59; H, 7.12.
3-Benzyl-5-carboxymethylfuran-2(5H)-one (7e)
Solidifies upon standing at room temperature. Mp 68–72 ꢀC.1H NMR
(CDCl3): 10.40 (s, 1H, COOH), 7.36 (dd, J ¼ 7.9, 6.1 Hz, 2H, ArH3,5),
7.28 (t, J ¼ 6.1 Hz, 1H, ArH4), 7.25 (d, J ¼ 7.9 Hz, 2H, ArH2,6), 6.98
(d, J ¼ 1.6 Hz, 1H, H-4), 5.28 (ddd, J ¼ 7.3, 6.7, 1.6 Hz, 1H, H-5), 3.62
(s, 2H, CH2Ph), 2.81 (dd, J ¼ 16.8, 7.3 Hz, 1H, CHCOOH), 2.67 (dd,

262
M. Giurg et al.
J ¼ 16.8, 6.7 Hz, 1H, CHCOOH). 13C NMR (CDCl3): 174.3, 172.8, 136.8,
135,1 (C), 148.0, 2ꢁ 128.8, 2 ꢁ 128.7, 126.8, 76.8 (CH), 37.6, 31.6 (CH2). IR
(film): c ¼ 2300–3400 cmꢂ1 (COOH), 3087, 3063, 3030, 2926 cmꢂ1 (C–H),
1757, 1720 cmꢂ1 (C¼O), 1654 cmꢂ1 (C¼C), 1185, 1173cmꢂ1 (C–O). Found:
C, 66.94; H, 5.16. (C13H12O4) 232.24 requires C, 67.23; H, 5.21.
5-Carboxymethyl-4-methylfuran-2(5H)-one (9a)
Colorless prisms. Mp 133.5–135.5 ꢀC (ethyl acetate) (Ref. [6]:119–121 ꢀC).
1H NMR (DMSO-d6): 12.59 (s, 1H, COOH), 5.93 (s, 1H, H-3), 5.24 (dd,
J ¼ 8.6, 3.7 Hz, 1H, H-5), 2.96 (dd, J ¼ 16.4, 3.7 Hz, 1H, CHCOOH), 2.39
(dd, J ¼ 16.4, 8.6 Hz, 1H, CHCOOH), 2.05 (s, 3H, CH3).13C NMR
(DMSO-d6): 172.4, 170.8, 169.6 (C), 116.0, 80.8 (CH), 36.7 (CH2), 13.5
(CH3). IR (KBr): c ¼ 2300–3300 cmꢂ1 (br.) (COOH), 1736, 1694 cmꢂ1
(C¼O), 1645 cmꢂ1 (C¼C), 1179 cmꢂ1 (C–O).
5-Carboxymethyl-4-isopropylfuran-2(5H)-one (9b)
Colorless flakes. Mp 84–86 ꢀC (diethyl ether–methylcyclohexane).
1H NMR (CDCl3): 9.13 (s, 1H, COOH), 5.84 (dd, J ¼ 1.6, 1.4 Hz, 1H,
H-3), 5.37 (ddd, J ¼ 8.7, 3.8, 1.6 Hz, 1H, H-3), 2.91 (dd, J ¼ 16.4,
3.8 Hz, 1H, CHCOOH), 2.58 (dd,J ¼ 16.4, 8.7 Hz, 1H, CHCOOH),
2.55 (kkd, J ¼ 7.0, 6.6, 1.4 Hz, 1H, CHCH3), 1.25 (d, J ¼ 6.6 Hz, 3H,
CH3), 1.18 (d, J ¼ 7.0 Hz, 3H, CH3). 13C NMR (CDCl3): 178.0, 173.7,
173.1 (C), 114.4, 79.1, 27.4 (CH), 36.9 (CH2), 21.4, 20.1 (CH3). IR (film):
c ¼ 2500–3500 cmꢂ1 (br.) (COOH), 2972, 2938, 2880 cmꢂ1 (C–H),
1739 cmꢂ1 (br.) (C¼O), 1632 cmꢂ1 (C¼C), 1176 cmꢂ1 (C–O). Found:
C, 58.53; H, 6.67. (C9H12O4) 184.19 requires C, 58.69; H, 6.57.
4-sec-Butyl-5-carboxymethylfuran-2(5H)-one (9c)
1
Transparent oil, which is two diastereoisomers in a 1:1 ratio. H NMR
(CDCl3): 9.11 (s, 1H, COOH), 5.82–5.86 (m, 1H, H-3), 5.30–5.40 (m,
1H, H-5), 2.91 (dd, J ¼ 16.4, 2.9 Hz, 1H, CHCOOH), 2.52–2.60 (m,
1H, CHCOOH), 2.22–2.47 (m, 1H, CHCH3), 1.38–1.78 (m, 2H,
CH2CH3), 1.12–1.22 (m, 3H, CH3CH), 0.86–1.00 (m, 3H, CH3CH2).
13C NMR (CDCl3): 177.22 and 177.09 (C), 173.82 (C), 173.07 and
172.98 (C), 115.38 and 114.69 (CH), 79.43 and 79.19 (CH), 37.02
and 36.96 (CH2), 34.32 and 33.66 (CH), 28.33 and 27.34 (CH2), 19.52
and 17.25 (CH3), 11.39 and 10.53 (CH3). IR (film): c ¼ 2300–3500 cmꢂ1
(COOH), 2970, 2936, 2880 cmꢂ1 (C–H), 1747 cmꢂ1 (br.) (C¼O),

Oxidation of Phenols to Muconolactones
263
1631 cmꢂ1 (C¼C), 1169 cmꢂ1 (C–O). Found: C, 60.80; H, 7.31.
(C10H14O4) 198.22 requires C, 60.59; H, 7.12.
4-tert-Butyl-5-carboxymethylfuran-2(5H)-one (9d)
Colorless prisms. Mp 146–149 ꢀC (benzene–light petrolum ether 2=1)
1
(Ref. [23]: 143–146). H NMR (DMSO-d6): 12.59 (s, 1H, COOH), 5.90
(d, J ¼ 1.5 Hz, 1H, H-3), 5.38 (ddd, J ¼ 8.9, 3.0, 1.5 Hz, 1H, H-5), 3.16
(dd, J ¼ 16.3, 3.0 Hz, 1H, CHCOOH), 2.41 (dd, J ¼ 16.3, 8.9 Hz, 1H,
CHCOOH), 1.20 (s, 9H, t-Bu). 13C NMR (CDCl3): 180.3, 172.0, 170.6,
33.2 (C), 115.2, 79.4 (CH), 38.0 (CH2), 28.9 (CH3). IR (KBr) c ¼ 2400–
3400 cmꢂ1 (COOH), 2927, 2942, 2877 cmꢂ1 (C–H), 1756, 1714 cmꢂ1
(C¼O), 1620 cmꢂ1 (C¼C), 1194 or 1176 cmꢂ1 (C–O).
4-(1,1,3,3-Tetramethyl)butyl-5-carboxymethylfuran-2(5H)-one (9e)
Colorless prisms. Mp 98.5–100.0 ꢀC. 1H NMR (CDCl3): 9.55 (s, 1H,
COOH), 5.93 (d, J ¼ 1.4 Hz, 1H, H-3), 5.51 (ddd, J ¼ 9.6, 3.0, 1.4 Hz,
1H, H-5), 3.14 (dd, J ¼ 16.3, 3.0 Hz, 1H, CHCOOH), 2.56 (dd,
J ¼ 16.3, 9.6 Hz, 1H, CHCOOH), 1.59 (s, 2H, CH2), 1.33 (s, 3H, CH3),
1.28 (s, 3H, CH3), 0.96 (s, 9H, t-Bu). 13C NMR (CDCl3): 180.1, 174.1,
172.5, 38.0, 32.4 (C), 117.0, 79.6 (CH), 54.0, 38.7 (CH2), 31.6 ꢁ 3, 29.6,
29.4 (CH3). IR (KBr) c ¼ 2300–3300 cmꢂ1 (br.) (COOH), 3097,
2968 cmꢂ1 (C–H), 1776, 1718 cmꢂ1 (C¼O), 1624 cmꢂ1 (C¼C), 1192 or
1184 cmꢂ1 (C–O). Found: C, 66.32; H, 8.46. (C14H22O4) 254.32 requires
C, 66.12; H, 8.72.
(2E,4E)-2-Methyl-2,4-hexadienedioic Acid (21a)
Colorless needles. Mp 271 ꢀC (dec.) (acetic acid) (Ref. [21]: 282–283 ꢀC).
1H NMR (DMSO-d6): 12.6 (s, 1H, COOH), 7.43 (dd, J ¼ 15.0, 11.9 Hz,
1H, H-4), 7.20 (d, J ¼ 11.9 Hz, 1H, H-3), 6.26 (d, J ¼ 15.0 Hz, 1H, H-
5), 1.95 (s, 3H, CH3). 13C NMR (DMSO-d6): 168.5, 167.1, 135.2 (C),
138.1, 134.0, 128.0 (CH), 13.0 (CH3). IR (KBr), 2100–3300 cmꢂ1 (br.)
(COOH), 1683 cmꢂ1 (C¼O), 1626, 1599 cmꢂ1 (C¼C).
(2E,4E)-3-Methyl-2,4-hexadienedioic Acid (22a)
Colorless crystaline powder. Mp 238.5–239.5 ꢀC (dec.) (acetic acid) (Ref.
[21]: 226–228 ꢀC). 1H NMR (DMSO-d6): 12.53 (s, 2H, COOH), 7.24

264
M. Giurg et al.
(d, J ¼ 15.8 Hz, 1H, H-4), 6.18 (d, J ¼ 15.8 Hz, 1H, H-5), 6.14 (s, 1H,
H-2), 2.19 (s, 3H, CH3). 13C NMR (DMSO-d6): 168.5, 167.1, 135.1
(C), 138.1, 134.0, 128.0 (CH), 13.0 (CH3). IR (KBr): c ¼ 2200–3300
cmꢂ1 (br.) (COOH), 1686 cmꢂ1 (C¼O), 1630, 1601 cmꢂ1 (C¼C).
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