Novel one-pot synthesis of acetoxy-2,4-cyclohexadienones

Article abstract of DOI:10.1081/SCC-200061717

A new, simple, one-pot method for the oxidative acetylation of some substituted phenols leading to acetoxycyclohexa-2,4-dienones is described. A novel diacetoxycyclohexadienone 12 has also been prepared using the present method from 2-hydroxymethyl phenol (salicyl alcohol). Copyright Taylor & Francis, Inc.

Full text of DOI:10.1081/SCC-200061717

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Novel One‐Pot Synthesis of
Acetoxy‐2,4‐Cyclohexadienones
Pradeep T. Deota a , Piyush R. Upadhyay b & Hemant
S. Parmar a
a Applied Chemistry Department, Faculty of
Technology and Engineering , The Maharaja
Sayajirao University of Baroda , Vadodara, India
b Department of Chemistry, Faculty of Science , The
Maharaja Sayajirao University of Baroda , Vadodara,
India
Published online: 16 Aug 2006.
To cite this article: Pradeep T. Deota , Piyush R. Upadhyay & Hemant S. Parmar
(2005) Novel One‐Pot Synthesis of Acetoxy‐2,4‐Cyclohexadienones, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 35:12, 1715-1723, DOI: 10.1081/SCC-200061717
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Synthetic Communicationsw, 35: 1715–1723, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200061717
Novel One-Pot Synthesis of
Acetoxy-2,4-Cyclohexadienones
Pradeep T. Deota
Applied Chemistry Department, Faculty of Technology and Engineering,
The Maharaja Sayajirao University of Baroda, Vadodara, India
Piyush R. Upadhyay
Department of Chemistry, Faculty of Science, The Maharaja Sayajirao
University of Baroda, Vadodara, India
Hemant S. Parmar
Applied Chemistry Department, Faculty of Technology and Engineering,
The Maharaja Sayajirao University of Baroda, Vadodara, India
Abstract: A new, simple, one-pot method for the oxidative acetylation of some substi-
tuted phenols leading to acetoxycyclohexa-2,4-dienones is described. A novel diace-
toxycyclohexadienone 12 has also been prepared using the present method from
2-hydroxymethyl phenol (salicyl alcohol).
Keywords: Acetoxy-2,4-cyclohexadienones, ortho-quinols, oxidative acetylation
Cyclohexa-2,4-dienones of the type 1 are emerging as valuable intermediates
in organic synthesis[1] because of their diverse chemical behavior. There are
several elegant examples of efficient syntheses using them in a variety of
reactions.[2] In general, these are prepared by oxidation of phenols with
several reagents such as lead tetraacetate (LTA),[3] benzeneseleninic
anhydride (BSA),[4] hypervalent iodide reagents,[5] and sodium metaperio-
date.[6] Occasionally, diacyl peroxide[7] and trifluoro-peroxyacetic acid[8]
Received in India February 16, 2005
Address correspondence to Pradeep T. Deota, Applied Chemistry Department,
Faculty of Technology and Engineering, The Maharaja Sayajirao University of
Baroda, Vadodara 390 001, India. E-mail: deotapt@yahoo.com
1715

1716
P. T. Deota, P. R. Upadhyay, and H. S. Parmar
have also been used for their preparation. The oxidation of phenols with LTA,
known as “Wessely oxidation,” is a generally used method for their prep-
aration.[3] However, it often proceeds in low yields and furnishes a mixture
of products depending upon the nature of the substituents on the aromatic
ring.[3] Alternatively, ortho-quinols 1a can also be prepared in the dimeric
form by the periodate oxidation of phenols as investigated by Adler et al.[6]
Wessely oxidation gives acetoxycyclohexadienones 1b in one step, albeit
in low yields. On the other hand, Adler’s method gives relatively better yields
but results in the formation of corresponding ortho-quinol dimer, which needs
to be acetylated to the corresponding diacetate dimer. The dimeric diacetate
needs to be pyrolyzed to furnish the corresponding acetate 1b, which results
in lower overall yield. The chemistry of ortho-quinols 1a is dominated by
their propensity toward [4 þ 2] dimerization, which can be suppressed
partially by converting them into acetates 1b to exploit their synthetic
potential (Figure 1).
With an appreciation of their utility as synthons, we set out to devise a
general method for the preparation of 1b with the hope that such a method
might be useful in the synthesis. Toward the realization of this objective,
we explored the reaction of phenols with periodate in acetic anhydride
medium. We postulated that the oxidative acetylation of phenol would give
corresponding acetoxy-2,4-cyclohexadienone 1b directly in one step (Figure 1).
Thus, 2,6-dimethyl phenol 2 (Scheme 1) in acetic anhydride was treated
with sodium metaperiodate (1.2 equiv.) added in portions, with stirring for 5 h
at room temperature, which gave 3 and its dimer 4 in 32 and 36% yields,
respectively, after usual workup and chromatography. All the physical and
spectral characteristics of the compounds 3 and 4 were in full accordance
with those reported in the literature.[6]
Encouraged by this observation, we attempted this procedure on other
phenols. Accordingly, 2,4,6-trimethylphenol 5 was treated with 1.2 equivalent
of sodium metaperiodate in acetic anhydride in similar way to obtain the cor-
responding acetoxycyclohexadienone 6 (30%) along with its dimer 7 (33%).
All the physical and spectral characteristics of these compounds were also
found to be in good agreement with those reported in literature.[6]
Figure 1. Cyclohexa-2,4-dienones.

Acetoxy-2,4-Cyclohexadienones
1717
Figure 2. Substituted phenols and corresponding cyclohexadienones obtained by
oxidative acetylation.
When 2,4-dimethyl phenol 8 was oxidized in similar manner, we obtained
9 (32%) along with the 10 (34%). The melting point, UV, IR, and elemental
analysis of the compound 9 were in good agreement with those reported in
the literature.[6] The compound 10 also gave matching spectral and analytical
characteristics with those reported in the literature.[6] It should be mentioned
1
here that the H NMR spectrum of compound 10 was not reported earlier.[6]
1
The H NMR spectrum of 10 displayed signals at dH (200 MHz, CDCl3):
6.21 (d, 1H at C3) 6.0 (d, 1H at C4), 5.5 (d, 1H at C12, olefinic), 3.8 (s, OH),
3.2 (s, 1H), 2.85 (d, 1H, bridgehead at C1), 2.2 (s, OH), 1.8 (s, 3H, olefinic
CH3), 1.6 (s, 3H, CH3), 1.4 (s, 3H, CH3), 1.39 (s, 3H, CH3).
It was interesting to observe that when salicyl alcohol 11 was subjected to
similar oxidation, a novel 1-(acetoxymethyl)-6-oxocyclohexa-2,4-dienyl
acetate 12 was obtained in 53% yield (Scheme 2). The structure of 12 was
1
fully discernible from its UV, IR, H NMR, 13C MR, mass spectra, and
elemental analysis. It showed a strong band at 1740 cm21 in addition to the
characteristic carbonyl absorptions at 1625 and 1570 cm21 in its IR
spectrum. Its UV spectrum showed a band at 300 nm, indicating the
Scheme 1.

1718
P. T. Deota, P. R. Upadhyay, and H. S. Parmar
Scheme 2.
1
presence of a 2,4-cyclohexadienone ring system.[9] Its H NMR spectrum
showed signals at dH (200 MHz, CDCl3): 7.51 (dd, J1 ¼ 6 Hz, J2 ¼ 2 Hz, 1H
at C2), 7.41 (dd, J1 ¼ 8 Hz, J2 ¼ 6 Hz, 1H at C3), 7.35 (dd, 1H at C4), 7.12
(d, 1H at C5), 5.12 (s, 2H, methylene proton), 2.3 (s, 3H, COCH3), 2.1
(s, 3H, COCH3). The 13C MR of 12 exhibited carbonyl resonances at dc
150.16 and two acetate carbonyls at dc 170.69 and 169.38. The olefinic
carbons appeared at dc 130.62, 129.82, 128.45, and 126.36, the highly
deshielded tetra-substituted carbon at dc 122.98, a methylene carbon at dc
61.90, and methyl carbons at dc 20.95. The mass spectrum of 12 gave
following fragmentation patterns: M-43 (CH3COþ) and M-60
(CH3COOH),[9] and was correctly analyzed for C11H12O5.
Vanillin, upon similar oxidation, also gave the expected acetate dienone
14 whose 1H NMR spectrum exhibited singlets at dH 9.91 and 3.88, indicating
the presence of aldehyde and methoxy groups respectively among other
signals. 4-Methyl-7-hydroxy coumarin 15, however, gave rise to only one
regioisomer 16 exhibiting a doublet at dH 7.59 and a singlet at 7.10 for
one proton each in its 1H NMR spectrum, ruling out the possibility of
presence of other isomers. 4-Hydroxy-40-chlorobenzophenone 17 furnished
3-(4-chlorobenzoyl)-6-oxocyclohexa-2,4-dienyl acetate 18 under similar con-
ditions, which was evident because the mass spectrum of 18 displayed a base
peak at M-140, which suggests loss of the C6H4ClCOþ ion, among other
characteristic signals. Oxidation of 4-hydroxy butyranilide 19 also led to
similar observation producing 20, whose 1H NMR spectrum revealed a
doublet at dH 1.60 for a single proton in addition to other supporting
evidence. 4-Methoxy phenol, thymol, and o-, m-, and p-cresols gave rise
to complex mixtures under reaction conditions.[10] Various acetoxy-2,
4-cyclohexadienones prepared by the present method are listed in Table 1,
which summarizes the reaction temperature, yields, and mp of various products
obtained from the oxidative acetylation of various substituted phenols.
EXPERIMENTAL
Melting points were recorded in open capillary tubes and are uncorrected.
Ultraviolet spectra were recorded on a Perkin-Elmer Lambda-19 spec-
trometer. Infrared spectra were recorded on a Perkin-Elmer PC-16 FTIR

Table 1. Yields of products of oxidative acetylation of substituted phenols
Phenol
(mols)
Reaction
temp. (8C)
Cyclohexadienone
(% yield)
Reported
mp[6] (8C)
Dimer
(% yield)
Reported Mp[6]
Mp (8C)
Mp (8C)
(8C)
2 (0.032)
5 (0.029)
8 (0.032)
Ambient
Ambient
Ambient
Ambient
60
3 (32)
6 (30)
32–35
80–82
53–55
235
34–35
82–84
53–54
—
4 (36)
7 (33)
10a (34)
—
158–159
164–166
225–228
—
159–160
162–163
225–228
—
9a (32)
12 (53)
14 (59)
16 (52)
18 (60)
20 (52)
11 (0.032)
13 (0.013)
15 (0.011)
17 (0.002)
19 (0.004)
85
171
—
—
—
—
—
—
—
—
85
70
134
102
—
—
—
—
—
—
—
—
Ambient
aCorresponding hydroxy compounds isolated.

1720
P. T. Deota, P. R. Upadhyay, and H. S. Parmar
1
spectrophotometer. H NMR (200/300 MHz) spectra and 13CMR (50 MHz)
were recorded either on a Bruker-200 FT-NMR or on a Bruker-300 FT-
NMR using CDCl3 as solvent containing tetramethylsilane as an internal
standard. Mass spectra were recorded on a Shimadzu QP-5050-A mass spec-
trometer. Microanalyses were performed on a Perkin-Elmer 2400 series II
laser instrument.
Column chromatography was performed using Acme’s silica gel (60–120
mesh size), and the elution was done using light petroleum and ethyl acetate
mixtures. The percent yields are reported based on the isolated material after
column chromatography. Thin-layer chromatography was performed using
Acme’s silica gel for TLC, and spots were visualized in iodine vapor.
General Procedure for the Oxidative Acetylation
of Substituted Phenols
To a stirred solution of phenol in acetic anhydride (15–20 mL) was added
sodium metaperiodate (1.2 mol, excess) in portions over a period of 1 h.
Stirring was further continued for 4–5 h either at room or at elevated tempera-
tures in cases of phenols 13, 15, and 17. The reaction mixture was then poured
into a saturated solution of sodium bicarbonate and stirred vigorously to neu-
tralize excess acetic acid. The aqueous layer was extracted with ethyl acetate
(4 ꢀ 25 mL) and combined organic extracts were washed successively with
saturated sodium bicarbonate (25 mL), water (25 mL), and brine solution
(20 mL), followed by drying over anhydrous sodium sulphate. Removal of
solvent under reduced pressure furnished a residue, which was chromato-
graphed using mixtures of light petroleum and ethyl acetate to give corre-
sponding acetoxycyclohexadienones. The corresponding dimeric diacetates
were also obtained additionally in cases of phenols 2, 5, and 8.
Thus, oxidation of 2,6-dimethyl phenol 2 gave 1,5-dimethyl-6-oxocyclo-
hexa-2,4-dienyl acetate 3, as a pale yellow thick liquid (32%), mp 32–358C.
n
max: 3020, 1739, 1674, 1346, and 1226 cm21. UV (lmax): 295 nm.
Elemental analysis: Found C, 65.96%; H, 6.43%; requires C, 66.66%; H,
6.66% for C10H12O3 along with 6,9-diacetoxy-1,4,6,9-tetramethyltricyclo
[6.2.2.02,7]dodeca-3,11-dien-5,10-dione 4, as a white crystalline solid (36%),
mp 158–1598C. nmax: 3007, 2982, 1744, 1698, 1654, 1456, 1368, 1232 and
700 cm21. UV (lmax): 241 nm. dH (200 MHz, CDCl3): 6.26 (d, 1H at C12),
6.15 (dd, 1H at C11), 5.61 (d, 1H at C3), 3.78 (d, 1H at C8, bridgehead), 3.44
(d, 1H at C2), 3.0 (dd, 1H at C7), 2.2 (s, 3H, CH3, at COCH3), 2.1 (s, 3H,
CH3 at COCH3), 1.82 (s, 3H, CH3, olefinic), 1.72 (s, 3H, CH3), 1.49 (s, 3H,
CH3), and 1.39 (s, 3H, CH3). MS m/z: 361(M þ 1), 300 (M–CH3COOH),
241[M-(2CH3COOH)], and 181[(M þ 1)-monomer]. Elemental analysis:
Found C, 67.12%; H, 6.67%; requires C, 66.66%; H, 6.66% for C20H24O16.
Similarly, oxidation of 2,4,6-trimethylphenol 5 gave 1,3,5-trimethyl-6-
oxocyclohexa-2,4-dienyl acetate 6 as a white solid (30%), mp 80–828C.

Acetoxy-2,4-Cyclohexadienones
1721
n
max: 3078, 2855, 1745, 1719, 1693, and 1621 cm21 along with 6,9-diacetoxy-
1,2,4,6,9,11-hexamethyltricyclo[6.2.2.02,7]dodeca-3,11-diene-5,10-dione 7,
as a white crystalline solid (33%), mp 164–1668C. nmax: 3033, 2982, 2876,
1735, 1695, 1651, 1540, 1258, 1180, 1080, 834, and 725 cm21. UV (lmax):
241 nm. dH (200MHz, CDCl3): 5.91 (s, 1H, olefinic), 5.12 (d, 1H at C7), 3.53
(d, 1H, bridgehead), 3.0 (s, 1H, olefinic), 2.2 (s, 3H, CH3, at COCH3), 2.1
(s, 3H, CH3 at COCH3), 1.79 (d, 3H, CH3, olefinic), 1.73 (d, 3H, CH3), 1.70
(s, 3H, CH3), 1.54 (s, 3H, CH3), 1.26 (s, 3H, CH3) and 1.09 (s, 3H, CH3).
MS m/z: 389 (M þ 1), 329 (M–CH3COOH), 269 [M-(2CH3COOH)], and
194 [(M þ 1)-monomer)]. Elemental analysis: Found C, 67.89%, H, 7.54%,
requires C, 68.04%; H, 7.21% for C22H28O16.
Oxidation of 2,4-dimethyl phenol 8 furnished 4-hydroxy-2,4-dimethylcy-
clohexa-2,5-dienone 9, as a white crystalline solid (33%), mp 53–558C. nmax
:
3456, 1662, 1631, 1292, 1130, and 1095 cm21. UV (lmax): 239 nm. dH
(200 MHz, CDCl3): 6.87 (d, 1H at C6), 6.81 (d, 1H at C5), 6.67 (m, 1H at
C3, olefinic), 2.45 (s, OH), 1.89 (d, 3H, CH3), and 1.5 (s, 3H, CH3). dc
(50 MHz, CDCl3): 16.20 (methyl carbon), 27.52 (olefinic methyl carbon),
68.11 (carbon at OH), 152.67, 148.32, 134.28, 127.61 (four olefinic carbon),
and 186.83 (keto carbon). Elemental analysis: Found C, 69.65%; H, 7.96%;
requires C, 69.56%; H, 7.24%, for C8H10O2 along with 6,9-dihydroxy-
2,6,9,11-tetramethyltricyclo[6.2.2.02,7]dodeca-3,11-diene-5,10-dione 10 as a
white solid (32%), mp 225–2288C. nmax: 3425, 1720, 1681, and 1643 cm21
.
UV (lmax): 230 nm. dH (200 MHz, CDCl3): 6.21 (d, 1H at C3), 6.0 (d, 1H at
C4), 5.5 (d, 1H at C12, olefinic), 3.8 (s, OH), 3.2 (s, 1H), 2.85 (d, 1H, bridge-
head at C1), 2.2 (s, OH), 1.8 (s, 3H, olefinic CH3), 1.6 (s, 3H, CH3), 1.4 (s, 3H,
CH3), 1.39 (s, 3H, CH3). Elemental analysis: Found C, 69.53%; H, 8.87%;
requires C, 69.56%; H, 7.30% for C16H20O4.
Oxidation of salicyl alcohol 11 furnished 1-(acetoxymethyl)-6-oxocyclo-
hexa-2,4-dienyl acetate 12, as a pale yellow liquid (53%), bp 2378C (dec.), UV
(lmax): 300 nm, nmax: 1740, 1625, 1570, 1491, 1369, 1226 and 753 cm21, dH
(200 MHz, CDCl3): 7.51 (dd, J1 ¼ 6 Hz J2 ¼ 2 Hz, 1H at C2), 7.41 (dd,
J1 ¼ 8 Hz, J2 ¼ 6 Hz, 1H at C3), 7.35 (dd, 1H at C4), 7.12 (d, 1H at C5),
5.12 (s, 2H, methylene proton), 2.3 (s, 3H, COCH3), 2.1 (s, 3H, COCH3). dc
(50 MHz, CDCl3): 20.95 (sp3 carbon), 61.90 (–CH2– carbon), 122.98 (tetra-
substituted carbon), 126.36, 128.45, 129.82, and 130.62 (four olefinic carbon),
170.69, 169.38 (two acetate carbonyls), 150.16 (keto carbon). MS m/z: M-43
(M–CH3COþ) and M-60 (M–CH3COOH). Elemental analysis: Found C,
57.99%; H, 5.51%; requires C, 58.92%; H, 5.35% for C11H12O5.
Oxidative acetylation of vanillin 13 gave 3-formyl-1-methoxy-6-oxocy-
clohexa-2,4-dienyl acetate 14 as a white crystalline solid (59%), mp 858C,
n
max: 3018, 1757, 1690, 1678, 1647, 1155 cm21, UV (lmax): 320 nm. dH
(300 MHz, CDCl3): 9.91 (s, 1H CHO), 7.48 (s, 1H at C2), 7.44 (d, J ¼ 6 Hz,
1H at C4), 7.21 (d, J ¼ 6 Hz, 1H at C5), 3.88 (s, 3H, –OCH3), 2.32 (sharp
s, 3H, –COCH3). dc (50 MHz, CDCl3): 20.36 (OCOCH3), 55.87 (OCH3),
110.57 (tetra subst., –O-C–O– type), 135, 144, 151, 168 (four olefinic C),

1722
P. T. Deota, P. R. Upadhyay, and H. S. Parmar
190.8, 191.2, 206.5 (three carbonyl C), MS m/z: 210 (Mþ), 196, 168, 154, 104,
97, 89, 80. Elemental analysis: Found C, 57.21%; H, 4.68%, requires C;
57.14%; H, 4.76% for C10H10O5.
Oxidation of 4-methyl-7-hydroxy coumarin 15 gave 4-methyl-2,7-dioxo-
chroman-6-yl acetate 16 as a white crystalline solid (52%), mp 1718C, nmax
:
3053, 2968, 1765, 1726, 1713 cm21, UV (lmax): 280 nm, dH (300 MHz,
CDCl3): 7.59 (d, 1H at C5), 7.10 (s, 1H at C8), 6.25 (s, 1H, olefinic H at
C3), 2.42 (sharp s, 3H, –COCH3), 2.33 (sharp s, 3H, olefinic –CH3), 1.72
(broad s, 1H at C6), dc (50 MHz, CDCl3): 20.9 (–OCOCH3), 63.6 (olefinic -
CH3), 96.4 (C6), 110.4, 114.4, 118.0, 125.4, 132.2, 140.3 [six olefinic C
(sp2 type)], 154.1, 160.5, 168.8 (three carbonyl C), MS m/z: 234 (Mþ),
217, 207, 192, 175, 165, 100, 77. Elemental analysis: Found C, 60.98%; H,
4.19%; requires C, 61.53%; H, 4.27% for C12H10O5.
Similarly, oxidation of 4-hydroxy-40-chlorobenzophenone 17 furnished
3-(4-chlorobenzoyl)-6-oxocyclohexa-2,4-dienyl acetate 18 as a white crystal-
line solid (60%), mp 1348C, nmax: 3051, 1757, 1694, 1683, 759 cm21, UV
(lmax): 300 nm, dH (300 MHz, CDCl3): 7.79 (d, J ¼ 8 Hz, 2H, aromatic ring
p-substituted), 7.82 (d, J ¼ 8 Hz, 2H, aromatic ring p-substituted), 7.45
(d, J ¼ 11 Hz, 2H at C4 and C2), 7.49 (merged with signal of C2-olefinic
proton), 7.24 (d, J ¼ 12 Hz, 1H at C5), 2.35 (sharp s, 3H, –COCH3), 1.63
(sharp s, 1H at C6). dc (50 MHz, CDCl3): 21.1 (OCOCH3), 65.1(C6), 101.9,
121.4, 121.6, 121.9 (four olefinic C), 128.9, 131.3, 131.8, 134.7, 135.8,
138.9 (six aromatic C), 154.1, 168.9, 194.3 (three carbonyl C), MS m/z:
Mþ ¼ 292.6, M þ 2 ¼ 294.6 (of 1/3 intensity of Mþ), M-140 (loss of
C6H4ClCOþ), and M-60 (M–CH3COOH). Elemental analysis: Found C,
61.88%; H, 3.83%; requires C, 61.96%; H, 3.78% for C15H11O4Cl.
Oxidation of 4-hydroxy butyranilide 19 gave 3-butyramido-6-oxocyclo-
hexa-2,4-dienyl acetate 20 as a white crystalline solid (52%), mp 1028C,
n
max: 3310, 2945, 1763, 1661, 1532, 1366, 1221, 904, 835 cm21, UV
(lmax): 300 nm, dH (300 MHz, CDCl3): 7.55 (d, 1H at C2), 7.30 (s, 1H,
NHCO), 7.15 (d, 1H at C4), 7.00 (d, 1H at C5), 2.35 (t, merged with
–OCOCH3 signal, 2H, NHCOCH2–), 2.30 (s, 3H, –OCOCH3), 1.75
(m, 2H, –CH2–CH3), 1.60 (d, 1H at tetra-substituted carbon), 1.00 (t, 3H,
–CH3). dc (50 MHz, CDCl3): 13.3, 18.4, 21.2, 39.3 (methyl and methylene
C), 97.4 (tetra-substituted C), 121.1, 122.0, 135.8, 146.6 (four olefinic C),
MS m/z: 237 (Mþ), 220, 178. Elemental analysis: Found C, 50.69%; H,
6.28%; N, 6.10%; requires C, 50.53%; H, 6.33%; N, 5.90% for C12H15NO4.
CONCLUSION
We have demonstrated a new, simple, one-pot method for the preparation of
acetoxy-2,4-cyclohexadienones. A novel 1-(acetoxymethyl)-6-oxocyclohexa-
2,4-dienyl acetate 12 was also obtained. Application of this method for the
synthesis of various carbocyclic systems is underway.

Acetoxy-2,4-Cyclohexadienones
1723
ACKNOWLEDGMENTS
The authors thank V. B. Valodkar and S. P. Sahoo for their help.
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