Synthesis of a novel bis-triquinane: A photochemical rearrangement in cyclohexadienone moiety resulting in aromatisation

Article abstract of DOI:10.1016/j.tetlet.2012.09.077

The first synthesis of the bird-shaped bis-triquinane 7, possessing a fascinating molecular architecture from readily available materials 2,6-dimethyl phenol and cyclopentadiene has been reported. Pentasubstituted phenols 9 and 10 were isolated during attempted photochemical oxa di-π methane rearrangement of acetic acid 3-(9-acetoxy-7,9-dimethyl-8-oxo-3a,4,7,7a-tetrahydro-1H-4,7- ethano-inden-5-ylmethyl)-1,5-dimethyl-6-oxo-cyclohexa-2,4-dienylester 4, a fused bicyclic system connected with a 2,4-cyclohexadienone unit. A probable mechanism is proposed for aromatisation.

Full text of DOI:10.1016/j.tetlet.2012.09.077

Tetrahedron Letters 53 (2012) 6527–6530
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Synthesis of a novel bis-triquinane: a photochemical rearrangement in
cyclohexadienone moiety resulting in aromatisation
⇑
Deepak Singh, Pradeep T. Deota
Department of Applied Chemistry, Faculty of Technology & Engineering, The Maharaja Sayajirao University of Baroda, Vadodara 390 001, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The first synthesis of the bird-shaped bis-triquinane 7, possessing a fascinating molecular architecture
Received 20 August 2012
Revised 17 September 2012
Accepted 19 September 2012
Available online 2 October 2012
from readily available materials 2,6-dimethyl phenol and cyclopentadiene has been reported. Pentasubsti-
tuted phenols 9 and 10 were isolated during attempted photochemical oxa di-p methane rearrangement of
acetic acid 3-(9-acetoxy-7,9-dimethyl-8-oxo-3a,4,7,7a-tetrahydro-1H-4,7-ethano-inden-5-ylmethyl)-1,
5-dimethyl-6-oxo-cyclohexa-2,4-dienylester 4, a fused bicyclic system connected with a 2,4-cyclohexadi-
enone unit. A probable mechanism is proposed for aromatisation.
Keywords:
Bis-triquinane
Ó 2012 Elsevier Ltd. All rights reserved.
2,4-Cyclohexadienones
Photoisomerisation
Ring fission
ODPM rearrangement
Triquinane natural products are a subset of polyquinanes which
constitute an important class of sesquiterpenoids.1 Linear triqu-
inane natural products are isolated from plants, microbes and mar-
ine organisms and they have been attracting continuous attention
from synthetic chemists due to their promising biological activity
and their role as building blocks for exotic molecular architec-
ture.1,2 As a result, numerous strategies have been developed for
the construction of the triquinane framework since its discovery
in 1966.3
inner carbon of peripheral cyclopropane ring to generate an array
of a bird. Towards this we explored the photochemical rearrange-
ment of bis-cycloadduct of type 5 to assemble hitherto unknown
bis-triquinane 7.
The precursors 4 and 5 were readily available in three steps
from 2,6-dimethylphenol 1 as follows. Tetramethyl bisphenol-F 2
was obtained by the condensation of 1 with formaldehyde. The
oxidative acetylation of 2 furnished bis-cyclohexadienone 3 which
on cycloaddition with cyclopentadiene gave 4 as major and 5 as a
minor product4 (Scheme 1).
In this context we conceived a bird-shaped bis-triquinane
molecule C31H36O6 (Fig. 1), which is assembled through the union
of two triquinane skeletons connected by a methylene group with
The photochemical reactions have attracted great attention for
their ability to act as a key step in the creation of complex molec-
ular architecture and in various natural products syntheses.5
Photochemical reaction of rigid b,
c
-unsaturated carbonyl systems
has great synthetic potential.5 Compounds containing b,
c
-enones
undergo two unique reactions that are characteristic of their
excited states. The triplet sensitised irradiation leads to a 1,2-acyl
shift while direct excitation induces a 1,3-acyl shift.5,6
Thus, when a solution of 5 in acetone both as a solvent and as a
triplet sensitiser was irradiated with mercury vapour lamp
(125 W) in a quartz immersion well for 2 h, the products 6 and 7
were isolated after the removal of solvent under reduced pressure
followed by column chromatography (Scheme 2). The structures of
the compounds were readily discernible through their FTIR, 1H, 13C,
DEPT-90, DEPT-135 NMR and mass analysis data.10 It was interest-
ing to observe half number of signals in the NMR spectrum of 7 due
to its symmetric structure.
Figure 1. Energy minimised ‘bird shape’ skeleton of bis-triquinane 7.
⇑
Corresponding author. Tel.: +91 0265 2434188x415/212; fax: +91 0265
2423898.
Alternatively, it was envisioned that the bis-triquinane
7
could also be accessed through tandem photochemical-
E-mail address: deotapt@yahoo.com (P.T. Deota).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.09.077

6528
D. Singh, P. T. Deota / Tetrahedron Letters 53 (2012) 6527–6530
OAc
OAc
O
O
OH
OAc
OH
HO
O
O
+
OAc
O
O
OAc
AcO
1
2
3
5
4
Scheme 1.
O
O
O
O
AcO
OAc
hν, 2h
OAc
5
+
Acetone
AcO
7
6
Scheme 2.
OH
O
OH
AcO
O
AcO
O
OAc
h
ν
,
+
1
.5
AcO
A
h
c
et
O
o
O
ne
OAc
OAc
OAc
(29 %)
hν
7
(32 %)
9
10
8
6
Δ
,
O
e
n
o
t
e
OAc
c
A
h
ν,
1
h
5
10
4
9
Accetone
(64 %)
(57 %)
Scheme 3.
thermal-photochemical protocol from precursor 4 as shown in
Scheme 3. However attempted photochemical reaction of precur-
sor 4 resulted in the formation of 9 as well as 10 and did not
furnish the expected product 8. The photochemical reaction of 4
in acetone for 0.5 h furnished product 9.11 It is interesting to note
that when the same reaction was continued for 1.5 h, additionally
aryl substituted tetracycle 10 was also isolated however com-
pound 8 was not obtained at all.12 The photochemical aromatisa-
tion of cyclohexadienone moiety under these reaction conditions
is hitherto unknown in the literature to the best of our knowledge.
Figure 2. ORTEP diagram of 9.

D. Singh, P. T. Deota / Tetrahedron Letters 53 (2012) 6527–6530
6529
O
O
C
hν
11
13
12
OH
R2
O
R4
R3
R1
OAc
R4
R3
OMe
R1
OAc
hν
R2
14 (a-c)
15 (a-c)
(a) R1, R2 = CH3, R3, R4 = H, b) R1, R2, R4 = CH3, R3=H, c) R1, R3 = CH3, R2,R4 = H
Scheme 4. Products reported from photochemical reactions of cyclohexadienones.
AcO
R
AcO
R
AcO
R
AcO
R
AcO
R
O
O
O
O
O
O
hν
i.c.
i.c.
17
16
19
4
18
O
AcO
R
AcO
hν
ODPM
R
=
9
10
R
O
OAc
21
20
Scheme 5. Suggested mechanism of formation of 9 and 10.
C. K.; Kiessling, A. J.; Link, J. S. Org. Lett. 2002, 5, 3811; (d) Singh, V.; Thomas, B. J.
Org. Chem. 1997, 62, 5310.
2. (a) Mehta, G.; Nair, M. S. J. Am. Chem. Soc. 1985, 107, 7519; (b) Mehta, G.; Vidya,
R. Tetrahedron Lett. 1998, 39, 6403.
Structure of 9 was established through its spectral data and by
its single crystal X-ray analysis.7 The ORTEP diagram is shown in
Fig. 2.
3. Comer, F. W.; Trotter, J. J. Chem. Soc., Phys. Org. 1966, 1, 11.
Hart et al. reported the photochemical transformation of
2,4-cyclohexadienone 11 by ring fission to give ketene 12 which
thermally rearranges to a bicyclo[3.1.0]hexenone 13.8a,b Baldwin
and Mcdaniel also investigated the photochemical reaction of
6-acetoxycIohexa-2,4-dienones 14(a–c) and have proposed the
formation of the open chain products 15(a–c)8c (Scheme 4).
The probable mechanism for the formation of 9 and 10 from 4 is
outlined in Scheme 5. Photolytic ring cleavage converts cyclohexa-
dienone 4 into 16 which perhaps rearranges to 17.8a,b The bicyclic
ketone 17 may further give 9 via a series of steps.9
4. (a) Singh, D.; Deota, P. T. Synth. Commun. 2012, 43; (b) Deota, P. T.; Parmar, H.
S.; Valodkar, V. B.; Upadhaya, P. R.; Sahoo, S. P. Synth. Commun. 2006, 36, 673;
(c) Deota, P. T.; Upadhyay, P. R.; Parmar, H. S. Synth. Commun. 2005, 35, 1715.
5. (a) Zimmerman, H. W.; Armesto, D. Chem. Rev. 1996, 96, 3065; (b) Armesto, D.;
Ortiz, M. J.; Agarrabeitia, A. R.; Noureddin, E. Angew. Chem., Int. Ed. 2005, 44,
7739; (c) Armesto, D.; Ortiz, M. J.; Agarrabeitia, A. R.; Fontecha, M. Org. Lett.
2005, 5. 2687.0LETVol.
6. (a) Hoffmann, N. Chem. Rev. 2008, 108, 1052; (b) Bruce, J. Annu. Rep. Prog. Chem.
Sect. B 2007, 103, 370; (c) Singh, V. K.; Vedantham, P.; Sahu, P. K. Tetrahedron
2004, 60, 8161; (d) Cheng, C. P.; Chen, C. H.; Chuang, G. J.; Liao, C. C. Tetrahedron
Lett. 2009, 50, 3414; (e) Lee, T. H.; Rao, P. D.; Liao, C. C. Chem. Commun. 1999,
801; (f) Hsu, D. S.; Chou, Y. Y.; Tung, Y. S.; Liao, C. C. Chem. Eur. J. 2010, 16, 3121.
7. The single crystal data are deposited at Cambridge Crystallographic Data
Centre and it has been allocated the deposition number CCDC 892381.
8. (a) Hart, H.; Murray, R. K. J. Am. Chem. Soc. 1970, 35, 1970; (b) Hart, H.; Lankin,
D. C. J. Org. Chem. 1968, 33, 4398; (c) Baldwin, J. E.; Mcdaniel, M. C. J. Am. Chem.
Soc. 1968, 90, 6118.
In this Letter, we have reported
a novel synthesis of
bis-triquinane and an unusual photochemical rearrangement of 4
in acetone to either 9 or a mixture of 9 and 10 with different time
intervals.
9. Zimmerman, H. E. Angew. Chem., Int. Ed. 1969, 8, 4.
10. Synthesis of 6 and 7: A solution of precursor 5 (0.5 g 0.0009 mol) in acetone
(600 ml) was irradiated for 2 h with a mercury vapour lamp of 125 W in a
quartz photochemical reactor. The solvent was removed under reduced
Acknowledgments
pressure to furnish
a yellow solid which was chromatographed over a
We are thankful to Dr. S.M. Mobin, (IIT, Indore) for providing
single crystal X-ray analysis. We also thank SAIF CDRI, Lucknow,
for providing NMR spectra and Professor B.V. Kamath for providing
GC–MS facility.
column of silica gel. Elution of column with petroleum ether/ethyl acetate
(90:10) afforded compound 7 (0.146 g, 20%). It was interesting to observe half
number of signals in the NMR spectrum due to its highly symmetrical
structure.
Mp = 252 °C.
IR (KBr): 2931, 3039, 1728 and 1234 cmÀ1
.
1H NMR (400 MHz, CDCl3): d 5.69 (1H, m), 5.68 (1H, dd, J1 = 5.5 Hz, J2 = 2 Hz),
3.36 (1H, t, J = 2.4 Hz), 3.04 (1H, s, H- to carbonyl), 2.91 (1H, superimposed dd,
Supplementary data
a
J = 7.6), 2.77 (1H, m), 2.54 (2H, m, CH2 allylic), 2.07 (3H, s, acetatemethyl), 1.90
(1H, s, CH2), 1.53 (3H, s, CH3), 1.25 (3H, s, CH3).
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.tetlet.2012.
09.077.
13C NMR (100 MHz CDCl3): d 206.78 (2 Â C, CO), 170.22 (2 Â C, OCOCH3),
128.77, 127.55 (4 Â C, olefinic), 80.47 (2 Â C, attach to OCOCH3), 64.26 (2 Â C,
Cq), 58.58, 53.46 (4 Â C, CH), 51.73 (2 Â Cq), 51.20 (2 Â C, CH), 43.61, 38.40
(2 Â C, CH2), 35.30 (2 Â C, CH), 21.98, 20.43, 15.72 (6 Â C, CH3).
Mass (EI+): m/z 504.14 M+, 443 (60.73%), 401 (100%), 228.14 (59.15%), 202
(88.30%).
References and notes
Further elution of column with petroleum ether/ethyl acetate (85:15)
furnished compound 6 (0.164 g, 32 %).
1. (a) Mehta, G.; Srikrishna, A. Chem. Rev. 1997, 97, 671–719; (b) Singh, V. K.;
Praveena, G. D.; Karki, K.; Mobin, M. S. J. Org. Chem. 2007, 72, 2058; (c) Mcclure,

6530
D. Singh, P. T. Deota / Tetrahedron Letters 53 (2012) 6527–6530
Mp = 236 °C.
IR: (KBr): 3126, 2950, 1730, 1754, 1586 cmÀ1
13C NMR (75 MHz CDCl3): d 207.12, 170.21, 168.98 (3 Â C, CO), 151.61, 146.40,
.
144.97, 133.82, 129.78, 128.27 (6 Â C, aromatic), 125.45, 121.24, 120.49,
116.65 (4 Â C, olefinic), 80.78 (1C, attach to OCOCH3), 53.61 (1C, Cq), 51.34,
48.67, 38.27 (3 Â C, CH), 37.84, 35.71 (2 Â C, CH2), 21.88, 20.47, 19.88, 15.74,
15.55, 9.76 (6 Â C, CH3).
1H NMR (300 MHz, CDCl3): d 5.71 (2H, m), 5.70 (1H, s, b-H of enone group),
5.48 (2H, m), 3.52 (1H, s, CH bridgehead), 3.26 (1H, d, J = 8 Hz, CH), 2.99 (1H, m,
CH superimposed with signal of CH2), 2.93 (2H, m, CH2), 2.76–2.39 (cluster of
multiplets, 3H, CH), 2.12–2.35 (2H, m, CH2), 2.07 (s, 6H, CH3), 1.71–1.83 (2H, m,
Mass (EI+): m/z (%) 438.16 M+, 279.12 (10.65%), 149 (100%).
CH2), 1.58 (3H, s, CH3), 1.51 (3H, s, CH3), 1.43 (1H, s,
1.08 (3H, s, CH3).
a
-CH), 1.24 (3H, s, CH3),
12. Synthesis of 9 and 10: Precursor 4 (0.5 g, 0.0011 mol) was dissolved in acetone
(600 ml) in a quartz photochemical reactor and irradiated for 1.5 h. The solvent
was removed under reduced pressure to furnish a yellow solid which was
13C NMR (75 MHz CDCl3): d 207.86, 206.57 (2 Â C, CO) 170.20, 169.42 (2 Â C,
OCOCH3), 141.92, 133.76, 132.93, 131.06, 128.49, 124.76 (6 Â C, olefinic),
88.87, 80.50 (2 Â C, attach to OCOCH3), 58.06, 57.58, 53.59 (3 Â CH), 51.42 (Cq),
50.26 (CH), 48.62, 45.08 (2 Â Cq), 42.16, 41.97 (2 Â CH), 40.48, 38.23, 37.95
(3 Â CH2), 35.31 (CH), 22.17, 21.97, 21.57, 20.39, 17.11, 15.04 (6 Â CH3).
Mass (EI+): m/z (%) 503.66 M+, 401.13 (22%), 269.78 (33.74%), 201 (90.73%),
186.18 (100%).
chromatographed over
a column of silica gel. Elution of column with
petroleum ether/ethyl acetate (90:10) afforded compound 5-(4-hydroxy-
2,3,5-trimethyl-benzyl)-7,9,9-trimethyl-3a,4,7,7a-tetrahydro-3H-4,7-ethano-
inden-8-one
9 (0.146 g, 29%). Its identity was confirmed by completely
matching mp, IR, 1H and 13C NMR data with the compound 9 mentioned above.
Further elution of column with petroleum ether/ acetate (85:15) afforded
compound 10 (0.164 g, 32%).
11. Synthesis of 9:
A solution of precursor 4 (0.5 g, 0.0011 mol) in acetone
(600 mL) was irradiated for 0.5 h with a mercury vapour lamp in a quartz
photochemical reactor. The solvent was removed under reduced pressure to
give a crude yellow solid which was purified over a column of silica gel
(petroleum ether/ethyl acetate 90:10) to furnish pure compound 9 (0.32 g,
64%).
Mp = 186 °C.
IR: (KBr): 3282, 2976, 1757, 1716, 1481, 1444 cmÀ1
.
1H NMR (400 MHz, CDCl3): d 6.81 (1H, s, aromatic), 5.68 (2H, m, olefinic), 4.84
(1H, s, phenolic exchangeable OH), 3.14 (1H, s, methine), 3.04 (2H, m,
methine), 2.36 (3H, s, CH3), 2.31 (2H, m, CH2), 2.19 (3H, s, CH3), 2.06 (6H, s,
2CH3), 1.72 (2H, s, CH2), 1.63 (1H, d, J = 4.8 Hz, CH), 1.28(6H, s, 2CH3).
13C NMR (100 MHz CDCl3): d 209.48, 169.90, 169.10 (3 Â C, carbonyl), 151.67,
146.26 132.59, 130.83, 129.36, 122.48, (6 Â C, aromatic), 121.35, 116.70 (2 Â C,
olefinic), 88.06 (1C, attach to OCOCH3), 55.15, 54.82 (2 Â C, Cq), 49.90, 47.82,
45.91, 42.54 (4 Â C, CH), 38.02, 28.67 (2 Â C, CH2), 21.67, 20.69,18.41, 17.53,
15.74, 9.88 (6 Â C, CH3).
Mp = 194 °C.
IR: (KBr): 3572, 2944, 1757 and 1486 cmÀ1
.
1H NMR (300 MHz, CDCl3): d 6.70 (1H, s, CH), 5.70 (1H, m, cyclopentane), 5.46
(1H, m, cyclopentane), 5.19 (1H, bs, phenolic OH), 4.93 (1H, s, olefinic), 3.71
(1H, s, CH bridgehead), 3.20 (2H, s, CH2), 2.86 (1H, m, CH2), 2.73 (1H, m, CH2),
2.47 (1H, m, CH), 2.27 (3H, s, CH3), 2.16 (3H, s, CH3), 2.05 (3H, s, CH3), 2.00 (3H,
s, CH3), 1.78 (2H, superimposed dd, J = 3.9 Hz, CH), 1.50 (3H, s, CH3), 1.18 (3H, s,
CH3).
Mass (EI+): m/z 437.20 (M+).