Cycloaddition of bis-cyclohexa-2,4-dienones: Synthesis of novel carbocycles

Article abstract of DOI:10.1080/00397911.2011.598440

Syntheses of novel carbocycles (4) and (5) based on cycloaddition of bis-cyclohexa-2,4-dienone (3) and cyclopentadiene is reported. An improved method for the preparation of tetramethyl bisphenol-F (2), a precursor of bis-cyclohexa-2,4-dienone (3), is also presented.

Full text of DOI:10.1080/00397911.2011.598440

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Cycloaddition of Bis-cyclohexa-2,4-
dienones: Synthesis of Novel Carbocycles
Deepak Singh a & Pradeep T. Deota a
a Applied Chemistry Department, Faculty of Technology and
Engineering , Maharaja Sayajirao University of Baroda , Vadodara ,
India
Accepted author version posted online: 09 Feb 2012.Published
online: 18 Oct 2012.
To cite this article: Deepak Singh & Pradeep T. Deota (2013) Cycloaddition of Bis-cyclohexa-2,4-
dienones: Synthesis of Novel Carbocycles, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 43:2, 292-300, DOI:
10.1080/00397911.2011.598440
To link to this article: http://dx.doi.org/10.1080/00397911.2011.598440
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Synthetic Communications1, 43: 292–300, 2013
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2011.598440
CYCLOADDITION OF BIS-CYCLOHEXA-2,4-DIENONES:
SYNTHESIS OF NOVEL CARBOCYCLES
Deepak Singh and Pradeep T. Deota
Applied Chemistry Department, Faculty of Technology and Engineering,
Maharaja Sayajirao University of Baroda, Vadodara, India
GRAPHICAL ABSTRACT
Abstract Syntheses of novel carbocycles (4) and (5) based on cycloaddition of bis-cyclohexa-
2,4-dienone (3) and cyclopentadiene is reported. An improved method for the preparation of
tetramethyl bisphenol-F (2), a precursor of bis-cyclohexa-2,4-dienone (3), is also presented.
Keywords Bis(3,5-dimethyl-3-acetoxy-4-oxocyclohexa-1,5-dienyl)methane;
dimethyl-4-hydroxyphenyl)methane; cycloaddition
bis(3,5-
INTRODUCTION
Phenolic compounds, both from natural and synthetic origins, constitute an
important family of antioxidants.[1] Bisphenols can be broadly classified as two phe-
nolic units connected to each other by a methylene or similar group. Bisphenols find
numerous applications in industries such as food packaging, molding, casting, coat-
ing, encapsulating, and adhesives.[2,3] Interestingly, they have also been employed in
the design of supramolecular hosts.[4] Literature records a number of methods for
their synthesis from phenols, using a variety of catalysts such as mineral acids,[5]
mesoporous silica,[6] solid acid catalysts,[7] zeolites,[3,8] nonzeolite molecular sieves,[9]
acid pretreated montmorillonite clays,[10] cation-exchange resins,[11,12] and bases.[13]
Received April 6, 2011.
Address correspondence to Pradeep T. Deota, Applied Chemistry Department, Faculty of
Technology and Engineering, Maharaja Sayajirao University of Baroda, Vadodara 390 001, India.
E-mail: deotapt@yahoo.com
292

CYCLOADDITION OF BIS-CYCLOHEXA-2,4-DIONES
293
There are several reports of oxidation of phenols to corresponding cyclohexa-2,
4-dienones and subsequent cycloaddition reactions.[14–16] The adducts from such
cycloadditions have been exploited for the development of new routes toward
synthesis of natural products possessing interesting biological profiles.[17,18]
Our interest in this area prompted us to explore cycloaddition of bis-
cyclohexadienone of type (3) with cyclopentadiene to access novel molecular architec-
tures such as that in adduct 4, which is hitherto unknown in the literature. Our efforts
to prepare carbocycle 4, from 3 are described here.
We reported previously a preparation of tetramethyl bisphenol-F (2) from
2,6-dimethyl phenol (1) by heating it under reflux in the presence NaOH.[13] We
now report an improvised procedure for an expedient preparation of 2 using aqueous
HCl (36%). The oxidation of bisphenol 2 to corresponding bis-cyclohexadienone 3
was not known in the literature prior to our own report[13] and to the best of our
knowledge there has been no report on the cycloaddition of biscyclohexadienones.
We also found during this study that the oxidative acetylation of tetramethyl
bisphenol 2 to biscyclohexadienone 3 using lead tetra-acetate may be accomplished
in toluene instead of benzene.[13]
Cyclohexadienones are reactive intermediates that easily undergo dimerization.[15]
In a similar manner, bis-cyclohexadienone 3, containing two cyclohexadienone
moieties, could also be expected to undergo intramolecular cycloaddition with either
a,b- or c,d-double bonds to give two different products 6 and 7 (Fig. 1).
In principle the reaction of cyclopentadiene and bis-cyclohexadienone 3 could
give rise to 11 major isomers (6–14) (Fig. 1) (4 and 5 in Scheme 2), in addition to
their corresponding stereoisomers.
Structures 8 and 9 may result from cycloaddition of cyclopentadiene as 4p and 3
as 2p partner. Similarly 8 and 9 could undergo subsequent intramolecular cycloaddi-
tion to generate 10 and 11 respectively. On the other hand, the two cyclohexadienone
units in 3 could also participate independently in cycloaddition with cyclopentadiene
to form 12 and 13 involving participation of a,b- or c,d-double bonds. While 4 and 5
could be formed from cycloaddition of 3 behaving as a 4p component and cyclopen-
tadiene as 2p component with addition of respectively one and two molecules
of cyclopentadiene, the structure 5 could also give rise to 14 via intramolecular
cycloaddition of the remaining cyclohexadienone unit with the double bond in the
cyclopentene ring.
Thus the reaction of bis-cyclohexadienone 3 and cyclopentadiene could in
principle give rise to a number of products. However, we obtained only adducts 4
and 5 from the reaction. The adduct 4 was also obtained alternatively by heating
5 with cyclopentadiene in toluene at 90 ꢀC for 28 h.
The structures of 4 and 5 were readily discernible through their spectral and
1
analytical data. The H NMR spectrum of adduct 5 exhibited singlets at d 1.30,
1.53, 1.73, and 1.98 for protons on methyl groups and singlet at d 2.07 for protons
on acetate methyl groups. It also showed a doublet at d 2.00, a multiplet at d 2.51,
and a doublet of doublet at d 3.66 for protons on the methine group, along with
two multiplets at d 2.76 and 2.91 and a singlet at d 3.02 for protons on methylene
groups in addition to singlets at d 5.26, 5.49, and 6.52, a multiplet at d 5.72, and a
doublet of doublet at d 5.89 for olefinic protons. Its 13C NMR spectrum displayed
signals at d 15.38, 15.80, 20.04, 20.06, 22.74, and 24.26 for six methyl carbons and

294
D. SINGH AND P. T. DEOTA
Figure 1. Structures of possible products resulting from cycloaddition of cyclopentadiene and bis-cyclo-
hexadienone 3.
signals at d 35.27, 38.39, and 43.32 for three methine carbons with d 48.92 and 51.90
for two methylene carbons, d 53.96 for a quaternary carbon, and d 78.19 and 80.75 for
two carbons attached with the acetate group. Similarly, signals at d 127.71, 128.55,
129.96, 133.68, 134.18, 136.56, 139.7, and 142.75 for eight olefinic carbons in addition
to characteristic signals at d 169.34, 170.28, 198.61, and 206.85 for acetate and ketonic
carbonyl carbons were also observed. The structure of 5 was further proved by its
single-crystal x-ray analysis (Fig. 2), which clearly displayed the endo stereochemistry
of the adduct with a free cyclohexadienone unit.
Because the structure of adduct 4 is highly symmetrical, its 1H, 13C, 2D 1H 1H
1
correlation spectroscopic (COSY), H 13C heteronuclear single-quantum coherence
(HSQC) NMR spectra showed only half the number of signals of total protons
Scheme 1.

CYCLOADDITION OF BIS-CYCLOHEXA-2,4-DIONES
295
Scheme 2.
and carbons. Thus the 1H NMR spectrum of 4 exhibited singlets at d 1.29, 1.51, and
2.05 for protons on methyl groups and a doublet at d 1.98, a multiplet at d 2.52, and a
doublet of doublet at d 3.64 for protons on methine groups, along with multiplets at d
2.72 and 2.88 and a singlet at d 3.16 for protons of methylene groups. It also showed a
singlet at d 5.35, a doublet of doublet at d 5.51, and a multiplet d 5.69 for olefinic pro-
tons. The 13C NMR spectrum was also consistent with proposed structure, which
exhibited resonances at d 15.96, 20.56, and 22.76 for methyl carbons and signals at d
Figure 2. ORTEP representation of carbocycle (5). (Figure is provided in color online.)

296
D. SINGH AND P. T. DEOTA
Figure 3. 1H 1H COSY NMR spectrum of bis-adduct (4).
35.34, 38.36, and 52.29 for three methine carbons with d 43.61 and 53.76 for two meth-
ylene carbons. It also displayed resonances at d 51.39 and 88.68 for a quaternary car-
bon and a carbon attached with acetate group respectively. Similarly it should signals
Figure 4. 1H 13C HSQC NMR of bis-adduct (4).

CYCLOADDITION OF BIS-CYCLOHEXA-2,4-DIONES
297
at 126.68, 128.69, 134.59, and 141.27 for olefinic carbons and characteristic signals at d
170.27 and 206.70 for acetate and ketonic carbonyl carbons. The structure deduced
1
1
1
1
from H and 13C NMR was further proved by 2D H H COSY and H 13C HSQC
NMR.
1
1
In H H COSY NMR spectrum of adduct 4 exhibited signals at d 1.29, 1.51,
and 2.05, having no corresponding off-diagonal peaks to represent the three methyl
groups. Other diagonal peaks at d 1.98, 2.52, and 3.64 having one, four, and two
corresponding off-diagonal peaks represent three protons of methine groups. It also
exhibited diagonal peaks at d 2.72 and 2.88 with three corresponding off-diagonal
peaks for each for the two protons of methylene group of the cyclopentadiene moiety.
The diagonal peak at d 3.16 having no off-diagonal peak represents the central meth-
ylene group. The diagonal peak at d 5.35 has no corresponding off-diagonal peak and
diagonal peaks at d 5.51 and 5.69 have two and three corresponding off-diagonal
peaks and display three olefinic protons.
The 1H 13C HSQC NMR spectrum displayed cross peaks for proton and carbon
at d (1.29, 15.96), (1.51, 20.56), and (2.05, 22.76) for three methyl groups and d (1.98,
35.34), (2.52, 38.36), and (3.64, 52.29) for three methine groups with d (2.72, 53.76)
and (2.88, 53.76) for methylene group of cyclopentene ring. It also showed resonance
at d (3.16, 43.61) for the central methylene group along with characteristic resonance
at d (5.35, 126.68), (5.51, 128.69), and (5.69, 134.59) for olefinics. The quaternary
carbon, carbon attached to acetate group, acetate carbonyl, and keto carbon did
not display any signals because they have no protons on corresponding carbon atoms.
EXPERIMENTAL
Infrared (IR) spectra were recorded on a Perkin-Elmer PC-16 Fourier trans-
1
form (FT) IR spectrometer. H NMR and 13C NMR spectra were recorded on
Bruker-400 FT NMR spectrometer using CDCl3 as solvent containing tetramethylsi-
lane (TMS) as an internal standard. Mass spectra were obtained on a Shimadzu
QP-5050 mass spectrometer. 2,6-Dimethyl phenol and dicyclopentadiene were pur-
chased from Sigma Aldrich. Freshly cracked cyclopentadiene was used. Hydrochloric
acid (36% w=v) was purchased from Merck. All other solvents were purchased from
Merck and distilled prior to use.
Column chromatography was performed using Acme’s silica gel (60–120 mesh)
and the elution was done using light petroleum and ethyl acetate mixtures.
Thin-layer chromatography (TLC) was performed using Acme’s silica gel, and spots
were visualized in iodine vapor. The yields (%) are reported based the recovery of the
starting material after column chromatography.
Tetramethyl Bisphenol-F (2)
Hydrochloric acid (10 ml, 36% w=v) was added dropwise over a period of 15 min
to a stirred solution of 2,6-dimethyl phenol (1) (10 g, 0.082 mol) and formaldehyde
(15 ml, 37% w=v, 0.185 mol) in light petroleum (60:80) (40 ml) at room temperature
(ꢁ27 ꢀC) and was further stirred for 5 h. The reaction mixture was diluted 10 times
its volume with water and was further stirred for 15 min. The solid thus obtained
was filtered on a Buchner funnel, washed thoroughly with water, and dried at

298
D. SINGH AND P. T. DEOTA
85–90 ꢀC under vacuum to give a solid, which was chromatographed on a column of
silica gel. Elution of the column with light petroleum=ethyl acetate (90:10) afforded
bisphenol 2 as a white crystalline solid (10.5 g, 93%). Its identity was confirmed by
1
comparison of its mp, IR, and H and 13C NMR with the reported data.[13]
Biscyclohexadienone (3) in Toluene (Vide Supra)
Lead tetra-acetate (2.66 g, 0.006 mol) was added to a solution of tetramethyl
bisphenol-F (2) (0.5 g, 0.002 mol) in dry toluene (30 ml) in portions with continuous
stirring over a period of 15 min. The reaction mixture was stirred at room temperature
(ꢁ27 ꢀC) for 1 h, after which it was diluted with ethyl acetate (150 ml) and stirred
further for 15 min. Removal of the residue by filtration and concentration of the
filtrate under reduced pressure furnished a pale yellow liquid, which was chromato-
graphed over a column of silica gel. Elution of the column with light petroleum
and ethyl acetate (95:5) gave 3 as a light yellow crystalline solid (45%). Comparison
1
of its mp, IR, and H and 13C NMR with the reported data proved its identity.[13]
Adducts 4 and 5
A solution of bis-cyclohexadienone (3) (4.0 g, 0.010 mol) in dry toluene (40 ml)
was heated to 90 ꢀC in an oil bath while circulating cooled water (10–15 ꢀC) and
freshly cracked cyclopentadiene (23 ml) was added to it in portions (1 ml every 2 h).
The reaction was continued for 46 h, after which it was allowed to cool to room tem-
perature (ꢁ27 ꢀC). The solvent was removed under reduced pressure to furnish a thick
yellow liquid, which was chromatographed over a column of silica gel. Elution of the
column with light petroleum=ethyl acetate (90:10) afforded the bis-adduct (4) as a
white solid (0.5 g, 21%), mp 240 ꢀC. IR (KBr) 3040, 1739, 1732, 1637, 1440, 1367,
and 1234 cmꢂ1 1H NMR (400 MHz, CDCl3) 1.29 (s, 6H, 2CH3), 1.51 (s, 6H,
.
2CH3), 1.98 (d, 2H, J ¼ 4.8 Hz methine), 2.05 (s, 6H, COOCH3), 2.52 (m, 2H, meth-
ine), 2.72 (m, 2H, methylene), 2.88 (m, 2H, methylene), 3.16 (s, 2H, methylene), 3.64
(dd, 2H, J ¼ 6.0 Hz, 2.0 Hz, methine), 5.35 (s, 2H), 5.51 (dd, 2H, J ¼ 5.6 Hz, 2.4 Hz),
5.69 (m, 2H). 13C NMR (100 MHz; CDCl3): 15.96, 20.56, 22.76 (3C methyl), 35.34,
38.36, 52.29 (3C methine), 43.61, 53.76 (2C, methylene), 51.86 (1C quaternary car-
bon), 80.86 (1C attached with acetate), 126.68, 128.89, 134.59, 141.27 (4C, olefinic)
=
=
170.27 (C O, OCOCH3) 206.65 (C O, ketone). HRMS (EI): m=z calculated for
C31H36O6: 504.61; found 504.250 (Mþ). Analysis calculated for C31H36O6 (504): C,
73.80; H, 7.14%. Found: C, 73.86; H, 7.34%.
Further elution of the column with light petroleum=ethyl acetate (85:15)
afforded the monoadduct 5 as a white crystalline solid (1.5 g, 51%), mp 178 ꢀC, IR
1
(KBr): 3040, 1739, 1732, 1685, 1447, 1377, and 1260 cmꢂ1. H NMR (400 MHz,
CDCl3) 1.30 (s, 3H, CH3), 1.53 (s, 3H, CH3), 1.73 (s, 3H, CH3), 1.98 (s, 3H, CH3),
2.00 (d, 1H, J ¼ 3.6 Hz, methine), 2.07 (s, 6H, acetate methyl), 2.51 (m, 1H, methine),
2.76 (m, 1H, methylene), 2.91 (m, 1H, methylene), 3.02 (s, 2H, methylene), 3.66 (dd,
1H, J ¼ 4.4 Hz, 2.0 Hz, methine), 5.26 (s, 1H, olefinic), 5.49 (s, 1H, olefinic), 5.72
(m, 1H), 5.89 (dd, 1H, J ¼ 6.0 Hz, 2.4 Hz, olefinic proton of cyclopentene ring), 6.52
(s, 1H, olefinic). 13C NMR (100 MHz, CDCl3): 15.38, 15.80, 20.04, 20.06 (4C methyl),
22.74, 24.26 (2C acetate methyl), 35.27, 38.39, 43.32 (3C, methine), 48.92 (1C

CYCLOADDITION OF BIS-CYCLOHEXA-2,4-DIONES
299
quaternary carbon), 51.90, 53.96 (2C, methylene) 78.28, 80.75 (2C, attached with
acetate), 127.71, 128.55, 129.96, 133.68, 134.18, 136.56, 139.7, 142.75 (8C, olefinic),
=
=
169.34, 170.28 (2C, C O OCOCH3), 198.61, 206.85 (2C, C O ketone). HRMS
(EI): m=z calculated for C26H30O6 438.51; found 438.20 (Mþ). Analysis calculated
for C26H30O6(438): C, 71.23; H, 6.84%. Found: C, 71.61; H, 7.02%. ORTEP diagram
of single crystal analysis is shown in Fig. 2.
Conversion of 5 into 4
A solution of the adduct 5 (2 g, 0.004 mol) in dry toluene (20 ml) was heated to
90 ꢀC in an oil bath while circulating cooled water (10–15 ꢀC), and freshly cracked
cyclopentadiene (14 ml) was added to it in portions (1 ml every 2 h). The reaction
was continued for 28 h, after which it was allowed to cool to room temperature.
The solvent was removed under reduced pressure to give a thick yellow liquid, which
was chromatographed over silica elution with light petroleum=ethyl acetate (90:10) to
afford adduct 4 (0.5 g, 37%), mp 240 ꢀC. Its identity was confirmed by completely
matched mp, IR, and 1H and 13C NMR data with compound 4 mentioned previously.
ACKNOWLEDGMENTS
This article is dedicated to Prof. Vishwakarma Singh on his 61st birthday.
The authors are grateful to Pradeep Mathur, Incharge, National Single Crystal
X-ray Diffraction Facility, Indian Institute of Technology, Bombay, for providing
1
single-crystal x-ray analysis and SAIF CDRI, Lucknow, for providing H, 13C, 2D
1
1
1H H COSY, and H 13C HSQC high-field NMR data.
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