Cycloaddition of cyclohexa-2,4-dienones, ring-closing metathesis, and photochemical reactions: A common stereoselective approach to duprezianane, polyquinane and sterpurane frameworks

Article abstract of DOI:10.1021/jo062416m

A novel approach to three different types of carbocyclic frameworks belonging to dupreziananes, sterpuranes, and polyquinanes from simple aromatic precursors has been presented. Cycloaddition of appropriately appended cyclohexa-2,4-dienones with acyclic d

Full text of DOI:10.1021/jo062416m

Cycloaddition of Cyclohexa-2,4-dienones, Ring-Closing Metathesis,
and Photochemical Reactions: A Common Stereoselective Approach
to Duprezianane, Polyquinane and Sterpurane Frameworks
Vishwakarma Singh,*,† G. D. Praveena,† Kapil Karki,† and Shaikh M. Mobin‡
Department of Chemistry and National Single X-ray Diffraction Facility, Indian Institute of Technology,
Bombay, Mumbai 400 076, India
Vks@chem.iitb.ac.in
ReceiVed NoVember 23, 2006
A novel approach to three different types of carbocyclic frameworks belonging to dupreziananes,
sterpuranes, and polyquinanes from simple aromatic precursors has been presented. Cycloaddition of
appropriately appended cyclohexa-2,4-dienones with acyclic dienes gave bridged bicyclic octanes suitably
disposed with olefinic chains, which upon ring-closing metathesis led to functionalized tricyclo[5.2.2.01,5]-
undecanes related to dupreziananes. Photochemical sigmatropic 1,2- and 1,3-acyl shifts in tricyclo[5.2.2.01,5]
undecanes upon triplet and singlet excitation provided stereoselective routes to sterpurane and polyquinane
frameworks.
Introduction
the last two are formed via a common biogenetic pathway
involving a humulene cyclization cascade.6a Among these,
polyquinane natural products have stimulated intense interest
for the past 2 decades6b-d that is continuing unabated.7,8 This
Creation of structural, functional, and stereochemical com-
plexity in efficient fashion from simple precursors is one of
the most desired aspects of development of new synthetic
methodology.1 Tandem reactions,2,3 multicomponent reactions4
and reactive species from aromatics5 have been employed to
achieve these objectives. â-Dupreziananes, sterpuranes, and
polyquinanes are important classes of sesquiterpenoids, of which
(5) (a) Magdziak, D.; Meek, S. J.; Pettus, T. R. R. Chem. ReV. 2004,
104, 1383-1430 and references therein. (b) Liao, C. C.; and Peddinti, R.
K. Acc. Chem. Res. 2002, 35, 856-866. (c) Drutu, I.; Njardarson, J. T.;
Wood, J. L. Org. Lett. 2002, 4, 493-496. (d) Quideau, S.; Lebon, M.;
Lamidey, A.-M. Org. Lett. 2002, 4, 3975-3978. (e) Bonnarme, V.; Mondon,
M.; Gesson, J.-P.; Cousson, A. J. Chem. Soc., Chem. Commun. 1999, 1143-
1144.; (f) Carlini, R.; Higgs, K.; Rodrigo, R.; Taylor, N. J. Chem. Soc.,
Chem. Commun. 1998, 65-66.
† Department of Chemistry.
‡ National Single X-ray Diffraction Facility.
(1) (a) Chanon, M.; Barone, R.; Baralotto, C.; Julliard, M.; Hendrickson,
J. B. Synthesis 1998, 1559-1583. (b) Corey, E. J.; Cheng, X.-M. The Logic
of Chemical Synthesis; John Wiley & Sons: New York 1989.
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Chem. ReV. 1996, 96, 3-30. (c) Winkler, J. D. Chem. ReV. 1996, 96, 167-
176. (d) Malacria, M. Chem. ReV. 1996, 96, 289-306. (e) Sheehan, S. M.;
Lalic, G.; Chen, J. S.; Shair, M. D. Angew. Chem., Int. Ed. 2000, 39, 2714-
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10.1021/jo062416m CCC: $37.00 © 2007 American Chemical Society
Published on Web 02/21/2007
2058
J. Org. Chem. 2007, 72, 2058-2067

Duprezianane, Polyquinane, and Sterpurane Frameworks
SCHEME 1
FIGURE 1. Structures of polyqinane natural products, sterpuranes,
and dupreziananes.
reaction12a and iron-carbene complexes12c have been reported.
However, except for a few, most of the methods generate the
tricyclic ring system in iterative fashion and employ a π2s +
π2s cycloaddition for the creation of the four-membered ring.
â-Duprezianane 4a, its epimer 4b, and its functionalized
analogue 4c are a rare class of sesquiterpenes, isolated from
the essential oil of Juniperus thurefera L. that contain an unusual
tricyclo[5.2.2.01,5]undecane framework in their molecular
architecture.14a Tricyclic systems having annulated bicyclo[2.2.2]-
octane framework are also present in other natural products such
as lacinanes,14b khusiol,14c and ermolactones.14d
is presumably due to continuing isolation of new polyquinane
natural products from various sources and their interesting
biological properties.9 For example, dichotimol 19a and conna-
tusin A 2 and congeners,9c recently isolated from the mycelial
cultures of Dichomitus squalens and the fungus Lentinus
connatus, respectively, exhibited nematicidal and cytotoxic
activities.
Sterpuranes, though not as abundant as polyquinanes, are a
unique class of sesquiterpenoids. The earlier members such as
3b,c (Figure 1) were isolated from Stereum perpureum10 and
are known to be responsible for silver leaf disease in plants.
Subsequently, many other sterpuranes were also isolated from
various sources.11 Recently, the hydroxysterpurene 3a was
isolated from Gloeophyllum, a fungus causing brown rot of
colonized wood.11a Despite their structural and stereochemical
complexity, sterpuranes have elicited only modest interest, and
there are only a few methods for their synthesis.12,13 Recently,
highly elegant routes to sterpurene employing quasi-Favorskii
In continuation of our interest15 we considered the develop-
ment of a common route to sterpurane, polyquinane, and
duprezianane frameworks and wish to report herein a stereo-
selective approach to all the three types of carbocyclic frame-
works from o-hydroxymethyl phenols.
Our strategy for the synthesis of functionalized duprezianane,
sterpurane, and triquinane frameworks is outlined in Scheme
1. The cornerstone of our plan is the recognition of a structural
and stereochemical relationship between the tricyclic network
7 belonging to dupreziananes and those of sterpuranes and
triquinanes. It was considered that the tricyclic system of type
7 may be obtained from the bridged bicyclic system 9 via ring-
closing metathesis to 8 followed by functional group manipula-
tion. The precursor 9 was thought to be accessible via oxidation
of the phenol 10 into the corresponding cyclohexa-2,4-dienone
and interception with acyclic-1,3-dienes. Further, it was envi-
sioned that a sigmatropic 1,3-acyl shift in tricyclic compounds
such as 7 upon singlet (1S) excitation would generate the
sterpurane framework 5 in a fashion so as to create all three
rings of sterpuranes in correct relative orientation and place the
double bond in the desired position, in a single stereoselective
step. On the other hand, it was also considered that a triplet
sensitized 1,2-acyl shift or oxa-di-π-methane rearrangement16
in 7 would give the tricyclic compound 6 containing a triquinane
framework.
(8) (a) Harrowven, D. C.; Lucas, M. C.; Howes, P. D. Tetrahedron 2001,
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Chem. 1998, 63, 5302-5303.
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1990, 46, 2389-2400. (d) Cimino, G.; Giulio, A. D.; Rosa, S. D.; Stefano,
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Tetrahedron Lett. 1988, 29, 4337-4340.
There are several noteworthy features in the aforementioned
strategy. For example, one of the olefinic tethers required in
the precursor 9 is derived from the aromatic compound 10, while
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Pava, O. V. D. J. Chem. Soc., Perkin Trans. 1 1997, 1523-1526. (c) Zhao,
S. K.; Helquist, P. J. Org. Chem. 1990, 55, 5820-5821. (d) Gibbs, R. A.;
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Am. Chem. Soc. 1988, 110, 5818-5826. (f) Moens, L.; Baizer, M. M.; Little,
R. D. J. Org. Chem. 1986, 51, 4497-4498.
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3717- 3723. (b) Fukushi, Y.; Yajima, C.; Mizutani, J.; Tahara, S.
Phytochemistry 1998, 49, 593-600. (c) Ganguly, R. N.; Trivedi, G. K.;
Bhattacharya, S. Indian J. Chem. 1978, 16B, 23-26. (d) Golsmith, D. In
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Prathap, S. Tetrahedron 1996, 52, 14287-14296.
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24, 973-975. (b) Demuth, M.; Schaffner, K. Angew. Chem., Int. Ed. Engl.
1982, 21, 820-836.
J. Org. Chem, Vol. 72, No. 6, 2007 2059

Singh et al.
SCHEME 2a
FIGURE 2. Precursors and potential intermediates.
a Reagents and conditions: (i) 95-100 °C, o-dichlorobenzene; (ii) 105
°C, o-dichlorobenzene.
the other would be introduced in the endo position by virtue of
the cycloaddition, thus keeping both the tethers in appropriate
stereochemical disposition required for ring-closing metathesis.
Further, both carbocyclic systems 5 and 6 are generated in a
single step from the tricyclic precursor 7 via modulation of
chemical reactivity in the excited states. Moreover, the key
precursors 8 and 9 are generated from simple aromatics, thus
generating molecular complexity in the very beginning of the
synthetic route, which is one of the important aspects of
development of methodology.1
SCHEME 3a
Results and Discussion
a Reagents and conditions: (i) aq KOH, CHCl3, CTAB, 9a (87%), 18
(90%); (ii) 19, CH2Cl2, rt, (55% from 9a, 35% from 18).
Synthesis of Tricyclo[5.2.2.01,5]undecanes. Toward the
realization of the above strategy, it was necessary to devise a
new method for the synthesis of tricyclic systems of type 7 and
8 since they are not readily accessible.17 In the beginning, we
considered to develop a synthesis of the keto-epoxide 9a from
the aromatic precursor 10a via its oxidation to the spiroepoxy-
dienone 11a and subsequent interception with 1,3-pentadiene.
Therefore, the compound 10a, readily prepared from p-cresol,
was oxidized with aqueous sodium m-periodate in presence of
excess 1,3-pentadiene at 0-5 °C following a procedure earlier
developed in our laboratory.15b However, it did not give the
desired adduct 9a, and instead the dimer 12a was obtained
(Figure 2). Moreover, an attempt to generate the dienone 11a
by retro Diels-Alder reaction of 12a and interception with
1,3-pentadiene was also futile and gave a mixture of pro-
ducts containing small amounts of 2-hydroxy-3-allyl-5-methyl
benzaldehyde.
In order to circumvent the aforementioned problems, the
epoxy-dimer 12a was prepared by periodate oxidation of 10a
and converted into chloro-hydroxy derivative 13a with a view
to generate 14a and intercept with 1,3-pentadiene. Indeed,
pyrolysis of the chloro-hydroxy dimer 13a in the presence of
1,3-pentadiene led to the desired adduct 15 in excellent yield
(80%) as a mixture of endo and exo isomers, having endo as a
major isomer (Scheme 2). Similarly, the pyrolysis of the 13a
in the presence of the butadiene sulfone, a source of butadiene,
gave the adduct 16 in addition to a small amount of cis-decalin
derivative 17, the latter formed as a result of Cope rearrangement
of the adduct.
Grubbs catalyst 19 in dichloromethane ensued a smooth ring-
closing metathesis18,19 and gave the desired product 8a in good
yield (55%), along with some unreacted starting material (mostly
the exo isomer). Similarly, the adduct 16 was also converted
into the keto-epoxide 18, which upon ring-closing metathesis
furnished the same tricyclic keto-epoxide 8a in good yield
(Scheme 3).
The structure of the cyclized product 8a was deduced from
its spectroscopic features and comparison with its precursor.
The 1H NMR (300 MHz, CDCl3) spectrum showed signals for
three olefinic protons at δ 5.80-5.75 (m, 1H), 5.65-5.61
(m, 1H), and 5.40 (br m, 1H) (as compared to six in its
precursor), clearly indicating that ring-closing metathesis (RCM)
1
had occurred. Moreover, the H NMR spectrum exhibited a
signal for only one methyl group at δ 1.90 (d, J ) 1.5 Hz),
which further suggested that RCM had taken place. The
methylene protons of the oxirane ring appeared as an AB quartet
at δ 3.20 (part of an AB pattern merged with a multiplet,
JAB ) 6 Hz, 1H) and 2.83 (part of an AB pattern, JAB ) 6 Hz,
1H). In addition, other signals appeared at 3.22-3.16 (m merged
with AB system, 1H), 2.41-2.22 (merged m, 3H), and
1.40-0.98 (m, 1H). The 13C NMR spectrum displayed signals
at δ 203.4 (CO), 145.9, 132.0, 130.4, and 125.0 for the carbonyl
and four olefinic carbons, respectively. Other carbons gave
signals at 62.09, 57.36, 51.55, 48.13, 44.79, 33.83, 26.14, and
20.09, thus accounting for all 13 carbon atoms. These spectral
features suggested the gross structure of the cyclized product.
However, it was difficult to ascertain the stereochemistry of
the oxirane ring. Hence, the structure 8a was confirmed through
The adduct 15 was efficiently converted to the keto-epoxide
9a (endo/exo mixture). Treatment of 9a with first generation
(17) (a) Buchi, G.; Hauser, A.; Limacher, J. J. Org. Chem. 1977, 42,
3323-3324. (b) Yamada, Y.; Nagaoka, H.; Kimura, M. Synthesis 1977,
581-582. (c) Demuth, M. Hinsken, W. HelV. Chim. Acta, 1988, 71, 569-
576. (d) Hariprakash, H. K.; Subbarao, G. S. R. Tetrahedron Lett. 1997,
38, 5343-5346. (e) Singh, V.; Alam, S. Q. J. Chem. Soc., Chem. Commun.
1999, 2518-2519.
(18) (a) Hand Book of Metathesis; Grubbs, R. H., Ed.; Wiely-VCH:
Weinheim, Germany, 2003. (b) Alkene Metathesis in Organic Synthesis;
Furstner, A., Ed.; Springer-Verlag: Germany, 1998.
(19) (a) Katz, T. Angew. Chem. Int. Ed. 2005, 44, 3010-3019. (b)
Schrock, R. R.; Hoveyda, A. H. Angew. Chem. Int. Ed. 2003, 42, 4592-
4633. (c) Schmidt, B. Angew. Chem. Int. Ed. 2003, 42, 4996-4999.
2060 J. Org. Chem., Vol. 72, No. 6, 2007

Duprezianane, Polyquinane, and Sterpurane Frameworks
SCHEME 4
SCHEME 6a
SCHEME 5
a Reagents and conditions: (i) Zn, NH4Cl, MeOH/H2O; (ii) Jones
oxidation; (iii) aq THF, ∆; (iv) Zn, NH4Cl, dry dioxane, ∆; (v) NaH/THF,
Mel, ∆.
a single-crystal X-ray structure determination (see Supporting
Information).
manipulation. Thus, reduction of the keto-epoxide 8a with
activated zinc and ammonium chloride in aqueous methanol15,22
at ambient temperature (∼30 °C) gave the â-keto alcohol 20a
as the major product (73%) (syn/anti mixture, 1H NMR), along
with very minor amount of the ketone 22a (Scheme 6). The
keto-alcohol 20a was oxidized with Jones’ reagent23a and the
resulting â-keto-acid was decarboxylated23b in refluxing aqueous
THF to give the desired compound 21a in moderate yields (45%
for two steps). Alternatively, the reduction of the epoxy-ketone
8a with activated zinc in refluxing dry dioxane containing
ammonium chloride furnished the ketone 22a as a major product
(62%, syn/anti mixture) as a result of deoxygenation of the
oxirane ring, along with the minor compound 20a (Scheme 6).
Alkylation of the ketone 22a with methyl iodide in the pre-
sence of NaH-THF gave the tricyclic system 23a (52%)
(Scheme 6). Similarly, reduction of the keto-epoxide 8b with
Zn in aqueous methanol gave the â-keto-alcohol 20b as a major
product and minor amounts of 22b (5%) and the trienol 24
(19%). The keto-alcohol 20b was converted into the tricyclic
compound 21b. Further, compound 8b was also reduced with
Zn-NH4Cl in dry dioxane to give 22b along with minor
amounts of the trienol 24 (25%) and the keto-alcohol 20b (15%).
The compound 22b was then alkylated to give the tricyclic
compound 23b. The trienol 24 was oxidized with PDC to give
the trienone 25.
Having checked the approach, we adopted it to the synthesis
of the tricyclic compound 8b containing dimethyl groups. Thus,
2-allyl-3,5-dimethylphenol, easily prepared from 3,5-dimeth-
ylphenol, was subjected to hydroxymethylation with aqueous
formaldehyde and sodium hydroxide. However, it gave a
complex mixture of polymeric products. After considerable
experimentation, treatment of 2-allyl-3,5-dimethylphenol with
p-formaldehyde in the presence of sodium ethoxide20 furnished
the desired product 10b in moderate yield (Scheme 4). In order
to prepare the dimer 12b, the phenol 10b was oxidized with
sodium m-periodate. However, it did not furnish the desired
dimer, and instead the monomer 11b was isolated in excellent
yield, whose structure was readily revealed from its spectro-
scopic features.
It was indeed surprising to isolate the cyclohexadienone 11b,
especially since spiroepoxycyclohexadienones are known to
have only fleeting existence during the oxidation and instanta-
neously dimerize.21 It was interesting to note that the spiroep-
oxycyclohexa-2,4-dienone 11b was quite stable, unlike many
others, and did not show propensity to undergo Diels-Alder
dimerization, although heating at high temperatures (∼140 °C)
led to decomposition. It appears that the steric hindrance due
to the presence of the allyl and methyl groups prevents the
dimerization of 11b.
Further, we considered functionalization of the five-membered
Fortunately, heating a solution of the cyclohexadienone 11b
and 1,3-pentadiene (cis + trans) in o-dichlorobenzene in a sealed
tube at 100 °C followed by chromatography afforded the adduct
9b in good yield (80%) as a mixture of endo and exo isomers
containing endo as a major isomer. The mixture of adducts was
then treated with first generation Grubbs’ catalyst 19, which
gave the cyclized product 8b in 49% yield (Scheme 5).
The contiguous presence of oxirane ring and carbonyl group
in tricyclic compounds 8a,b provided opportunity for further
ring in 21a,b via allylic oxidation.24 Thus, the ketone 21a was
t
treated with PDC in the presence of BuOOH in dry benzene
(Scheme 7). However, it did not give the expected enones 27
and/or its regioisomer, and instead the enone 26a was ob-
tained (62%). Attempts for allylic oxidation with PCC and
CrO3-dimethyl pyrazole also gave the same enone as a major
(22) (a) Singh, V.; Deota, P. T.; Bedekar, A. V. J. Chem. Soc., Perkin
Trans. 1, 1992, 903-912. (b) Singh, V.; Deota, P. T. J. Chem. Res. 1989,
390-391.
(23) (a) Harrison, I. T.; Harrison, S. Compendium of Organic Synthetic
Methods; Wiley-Interscience: New York, 1971. (b) House, H. O. Modern
Synthetic Reactions; W. A. Benzamin: Menlo Park, CA, 1972.
(24) Bullman Page, P. C.; McCarthy, T. J. In ComprehensiVe Organic
Synthesis; Ley, S.V., Ed.; Pergamon Press: New York, 1991; Vol. 7, pp
83-117.
(20) Finn, S. R.; Lewis J. J.; Negson, N. J. L. J. Soc. Chem. Ind. 1950,
129-132.
(21) (a) Adler, E.; Bransen, S.; Miyake, H. Acta Chem. Scand. 1971,
25, 2055-2069. (b) Adler, E.; Holmberg, K. Acta Chem. Scand. 1974, 28B,
465-472.
J. Org. Chem, Vol. 72, No. 6, 2007 2061

Singh et al.
SCHEME 7
SCHEME 8
product, and oxidation with SeO2 gave a complex mixture.
Similarly, the oxidation of 21b also gave the dienone 26b. It
was indeed intriguing to note the formation of 26a,b during
the oxidation especially, since the double bond migrated to
afford the more highly substituted alkenes. The structure of the
enones 26a,b was clearly revealed from their spectral data and
comparison with the spectral features of the precursors.
It may be mentioned that tricyclic compounds of type 8 and
20-26 having a â,γ-unsaturated carbonyl chromophore are not
readily available, and the present methodology provides a novel
and efficient route to such systems.
SCHEME 9
Studies on Photochemical Reactions of Tricyclic System
21a,b and Congeners upon Singlet and Triplet Excitation.
Photochemical reactions of â,γ-enones have generated interest
for a long time,25 an interest that is further enhanced recently
as a result of their synthetic potential.16,26,27 In general, â,
γ-enones undergo two unique reactions, namely, the 1,2-acyl
shift (or the oxa-di-π-methane rearrangement) and the 1,3-acyl
shift.25-27 Demuth and co-workers have examined oxa-di-π-
methane reaction of several types of â,γ-enones and demon-
strated its synthetic potential.16,25b,d Though the photoreactions
of â,γ-enones are quite characteristic of their excited states, i.e.,
1,2-shift from lowest triplet (T1) and 1,3-shift from singlet (S1)
or higher triplet (T2), small changes in the structure of the
chromophore and substituents are known to control the outcome
in a subtle fashion. Moreover, selective population of excited
states is also required for specific photochemical reaction.25a,27a,b
Keeping the above in mind, photoreaction of tricyclic chro-
mophoric systems 21a,b-26 was explored under direct and
sensitized irradiation.
of the photolysate gave the desired tricyclic compound 28 in
moderate yield (40%) along with a very minor amount of
decarbonylated product and some unreacted starting material.
The photoproduct, however, appeared to be relatively unstable.
The structure of compound 28 was deduced from its spectral
data and comparison with the spectral features of its precursor
21a. Thus, the IR spectrum of the compound showed an
absorption band at 1770 cm-1, which is characteristic of a
1
carbonyl group present in a four-membered ring. Its H NMR
spectrum (300 MHz) showed characteristic signals at δ 5.91-
5.60 (m, 2H) and 5.30 (br s, 1H) for the three olefinic protons.
The appearance of an upfield signal at δ 1.30 (s, 3H) for methyl
protons also suggested that the desired structural reorganization
had occurred. Other signals were observed at δ 3.20-2.96
(merged m, 4H), 2.86-2.76 (dd, J1 ) 18 Hz, J2 ) 5 Hz, 1H),
2.40-2.30 (m, 1H), 2.15-2.07 (d of dd, J1 ) 13.5 Hz, J2 )
4.0 Hz, J3 ) 1.5 Hz, 1H), and 1.12-1.00 (d of superimposed
dd, J1 ) 13.5 Hz, J2 ≈ 4.0 Hz, 1H). The 13C NMR spectrum
(75 MHz) showed resonances at δ 211.7 for carbonyl carbon
and 146.1, 133.2, 129.8, and 118.1 for the four olefinic carbons.
It further showed signals at δ 62.8, 45.9, 40.1, 38.7, 31.0, 26.01,
and 21.1, thus accounting for all 12 carbon atoms.
Toward the synthesis of the sterpurane framework, photo-
chemical reaction of the tricyclic ketone 21a was explored
upon direct irradiation. Thus, a solution of the ketone 21a in
benzene was irradiated with a mercury vapor lamp (125 W,
Applied Photophysics) for 30 min in a Pyrex immersion well
(Scheme 8). Removal of solvent and careful chromatography
The irradiation of 21b under similar conditions also led to
1
the formation of 1,3-acyl shift product 29 (IR and H NMR).
However, the photoproduct could not be separated from its
starting material. The photochemical reaction of the dienone
26a upon singlet excitation was indeed surprising, as its direct
irradiation in benzene did not give the 1,3-acyl shift product
30, but instead the triquinane 31 was obtained as a result of
oxa-di-π-methane rearrangement (Scheme 9). The absence of
1,3-acyl migration in the direct irradiation of 26a is presumably
due the absorption of light by the R,â-enone chrompore present
in 26a; apparently the compound 31 is formed by self-
sensitization via oxa-di-π-methane reaction. The sensitized
irradiation of 26a in acetone also gave the triquinane 31.
Toward synthesis of triquinane framework, we first examined
the photochemical reaction of 21a upon triplet-sensitized
irradiation. Thus, a solution of the compound 21a in degassed
dry acetone (as both solvent and sensitizer) was irradiated in a
Pyrex immersion well under nitrogen for 1 h. Removal of
solvent and chromatography furnished the tetracyclic compound
32 in moderate yield (52%) as a result of 1,2-acyl shift
(25) (a) Schuster, D. I. In Rearrangement in Ground and Excited States;
de Mayo, P., Ed; Academic Press, New York, 1980; Vol. 3, pp 167 and
references cited therein. (b) Houk, K. N. Chem. ReV. 1976, 76, 1-74. (c)
Coffin, R. L.; Givens, R. S.; Carlson, R. G. J. Am. Chem. Soc. 1974, 96,
7554-7556. (d) Hixon, S. S.; Mariano, P. S.; Zimmerman, H. E. Chem.
ReV. 1973, 73, 531-551. (e) Givens, R. S.; Oettle, W. F. J. Chem. Soc.,
Chem. Commun. 1969, 1164-1165.
(26) (a) Zimmerman, H. E.; Armesto, D. Chem. ReV. 1996, 96, 3065
and references therein. (b) Demuth, M. In Organic Photochemistry; Padwa,
A., Ed.; Marcell Dekker, Inc.: New York, 1991; Vol. 11, pp 37-97. (c)
Padwa, A.; Zhi, L.; Fryxel, Z. E. J. Org. Chem. 1991, 56, 1077-1083. (d)
Schaffner, K.; Demuth, M. In Modern Synthetic Methods; Scheffold, R.,
Ed.; Springer-Verlag: Berlin, 1986; Vol. 4, pp 61.
(27) (a) Armesto, D.; Ortiz, M. J. Angew. Chem., Int. Ed. 2005, 44,
7739-7741. (b) Armesto, D.; Ortiz, M. J.; Agarrabeitia, A. R.; Martin-
Fontecha, M. Org. Lett. 2005, 7, 2687-2690. (c) Armesto, D.; Ortiz, M.
J.; Agarrabeitia, A. R. In Organic Photochemistry and Photobiology;
Horspool, W. M., Lenci, F., Eds.; CRC Press: Boca Raton, FL, 2004;
Chapter 77. (d) Singh, V. In Organic Photochemistry and Photobiology;
Horspool, W. M., Lenci, F., Eds.; CRC Press: Boca Raton, FL, 2004;
Chapters 78 and 79.
2062 J. Org. Chem., Vol. 72, No. 6, 2007

Duprezianane, Polyquinane, and Sterpurane Frameworks
SCHEME 10
(50 mL) was added an aqueous solution of sodium m-periodate
(48 g, 0.224 mol, 400 mL water) dropwise at ∼10 °C, and the
reaction mixture was stirred for 1 h. After further stirring for 3 h
at room temperature, the product was filtered, washed with water
(3 × 100 mL), and dried to give the epoxy dimer 12a as a pale
yellow solid (13.8 g, 70%), which was recrystallized from petroleum
ether/ethyl acetate (10:2). Mp: 115-116 °C. IR (neat) νmax: 1732,
1
1692 cm-1. H NMR (300 MHz, CDCl3): δ 6.29 (s, 1H), 5.84-
5.66 (m, 2H), 5.51-5.49 (t, J ) 1.5 Hz, 1H), 5.16-5.04 (m, 4H),
3.15 (part of an AB system, J ) 6.5 Hz, 1H), 3.08-2.88 (complex
m, 3H), 2.95 (part of AB system partly merged with m, J ) 6.5
Hz, IH), 2.81 (s, 2H), 2.6 (t, J ) 1.6 Hz, 1H), 2.24-2.14 (merged
m, 2H), 1.88 (d, J ) 1.5 Hz, 3H), 1.34 (s, 3H). 13C NMR
(100 MHz, CDCl3): δ 204.7, 192.3, 146.4, 143.5, 139.4, 134.5,
125.9, 118.6, 117.5, 62.0, 58.9, 58.2, 57.9, 53.2, 48.4, 46.5, 45.9,
33.8, 30.7, 23.9, 21.0. Mass (m/z): 352 (M+). Analysis: found C,
74.95; H, 6.81; requires C, 74.97; H, 6.86 for C22H24O4.
(Scheme 10). A small amount of starting material was also
recovered. Similarly, sensitized irradiation of compounds 22a
and 23a in acetone using a mercury vapor lamp gave the
corresponding ODPM products 33 and 34 in 43% and 32%
yields, respectively (Scheme 10). Sensitized irradiation of 21b
also gave the tetracyclic product 35 as a result of 1,2-acyl shift.
6,9-Bis-chloromethyl-1,4-diallyl-6,9-dihydroxy-2,12-dimethyl-
tricyclo[6.2.2.02,7]dodec-3,11-dien-5,10-dione (13a). To a solution
of epoxy dimer 12a (10 g, 28.41 mmol) in dioxane (100 mL) was
slowly added concd HCl (25 mL) at ∼10 °C with stirring. After
stirring for 1 h, a yellow precipitate was obtained. The reaction
mixture was filtered, and the precipitate was washed with water
and dried to give the compound 13a (10.7 g, 89%), which was
recrystallized from chloroform to give a colorless solid. Mp:
Conclusion
1
122-123 °C. IR (neat) νmax: 3466, 1736, 1703 cm-1. H NMR
In summary, an efficient synthesis of various tricyclo-
[5.2.2.01,5]undecanes 8a,b and 20-26 belonging to duprezi-
ananes and a stereoselective entry to the triquinane and
sterpurane frameworks has been described. The methodology
involved ring-closing metathesis on appropriately designed
bicyclo[2.2.2]octenones and photochemical transformations of
the resulting tricyclic systems. The bridged bicyclic precursors
having suitable olefinic appendages were assembled from simple
starting materials via the in situ generation of cyclohexa-2,4-
dienones followed by their interception with acyclic dienes.
Photochemical reactions of tricyclo[5.2.2.01,5]undecanes 21a,b
upon direct irradiation led to the formation of 1,3-acylshift
products 28 and 29, whereas direct irradiation of 26a gave the
triquinane 31 as a result of oxa-di-π-methane reaction. Triplet
sensitized irradiation of 21a,b, 22a, 23a, and 26a gave triquinane
frameworks, 32, 35, 33, 34, and 31, respectively, in a single
stereoselective step. The present methodology also demonstrates
creation of structural diversity from simple aromatic precursors.
Further application of the methodology toward synthesis of
natural products is underway.
(300 MHz, CDCl3): δ 6.07 (s, 1H), 5.81-5.55 (m, 2H), 5.32
(t, J ) 1.6 Hz, 1H), 5.15-5.03 (merged m, 4H), 4.23 (br s, 1H,
OH), 3.74-3.44 (merged m, 6H), 3.11-2.72 (br m, 4H), 2.06 (dd,
J1 ) 13.5 Hz, J2 ) 9.0 Hz, 1H), 1.77 (d, J ) 1.8 Hz, 3H), 1.30 (s,
3H). 13C NMR (75 MHz, CDCl3): δ 208.9, 197.1, 144.7, 144.4,
136.7, 134.1, 134.0, 125.5, 118.7, 117.9, 74.0, 67.1, 61.7, 53.9,
49.9, 46.6, 46.5, 45.1, 34.1, 30.7, 23.7 and 21.0. Mass (m/z): 447.10
(M+ + Na+). Analysis: found C, 61.33; H, 6.89; requires C, 61.11;
H, 6.55 for C22H26O4Cl2.
1-Allyl-3-chloromethyl-3-hydroxy-5-methyl-7-propenyl-bicyclo-
[2.2.2]oct-5-en-2-one (15). A solution of the dimer 13a (1 g, 2.35
mmol) and 1,3-pentadiene (mixture of cis and trans) (1.5 mL,
excess) in o-dichlorobenzene (2 mL) was heated at 105-110 °C
in a sealed tube for 7 h. The reaction mixture was then charged as
such on silica gel. Elution with petroleum ether first gave
o-dichlorobenzene. Further elution with petroleum ether/ethyl
acetate (96:4) gave an inseparable endo/exo mixture of adducts 15
(1.03 g, 78%) as a colorless liquid. Repeated chromatography of
the mixture of adducts on silica gel (100-200 mesh) furnished the
1
major isomer in pure form. IR (neat) νmax: 3476, 1720 cm-1. H
NMR (300 MHz, CDCl3): signals for the major isomer, δ 5.8-
5.64 (m, 2H), 5.48-5.36 (m, 1H), 5.16-5.04 (merged m, 3H), 3.58
(part of an AB system, JAB ) 12.0 Hz, 2H), 2.95 (br m, 1H), 2.45-
2.31 (m, 3H), 2.19-2.10 (m, 1H), 1.93-1.75 (d, merged with m,
J ) 1.2 Hz, total 5H), 1.6 (two sets of d dd, J ) 1.8 Hz, total 3H).
ESI HRMS: calcd for C16H21O2ClNa [M+ + Na] 303.1128, found
303.1128.
Experimental Section
6-Allyl-4-methyl-2-hydroxymethylphenol (10a). To a solution
of 2-allyl-4-methylphenol (50 g, 0.338 mol) in aqueous sodium
hydroxide (1 M, 500 mL) was added formaldehyde (35% w/v; 138
mL, 1.69 mol), and the mixture was stirred for 24 h at room
temperature. The reaction mixture was cooled in a crushed ice bath,
acidified with dilute hydrochloric acid, and then extracted with ethyl
acetate (4 × 100 mL). The organic layer was separated and dried
over anhydrous sodium sulfate. Removal of solvent and column
chromatography (petroleum ether/ethyl acetate 90:10) gave the
compound 10a (45 g, 75%) as a colorless solid. Mp: 62-63 °C.
11-Methyl-8-spiroepoxy-tricyclo[5.2.2.01,5]undec-3,10-dien-9-
one (8a). To a solution of the adduct 15 (5 g, 17.82 mmol) in
chloroform (500 mL) containing cetyltrimethylammonium bromide
(CTAB) (0.35 g) as a phase transfer catalyst was added an aqueous
solution of potassium hydroxide (1.25 g, 22.3 mmol in 100 mL
water). The reaction mixture was stirred at ambient temperature
for 5 h, after which the organic phase was separated and the aqueous
layer was extracted with chloroform (3 × 40 mL). The combined
organic extract was washed with brine (1 × 30 mL) and dried over
anhydrous sodium sulfate. Removal of solvent in vacuo followed
by chromatography (petroleum ether/ethyl acetate (97:3) of the
residue gave an inseparable mixture of keto-epoxide 9a (3.78 g,
87%) as a colorless liquid [IR (neat) νmax: 1733 cm-1, HRMS:
calcd for C16H20O2Na [M+ + Na] 267.1361, found 267.1363] which
was directly subjected to the ring-closing metathesis as described
below.
1
IR (neat) νmax: 3407, 3347 cm-1. H NMR (400 MHz, CDCl3):
δ 6.88 (s, 1H), 6.72 (s, 1H), 6.04-5.96 (m, 1H), 5.12-5.07
(m, 2H), 4.76 (s, 2H), 3.7 (d, J ) 6 Hz, 2H), 2.23 (s, 3H). 13C
NMR (100 MHz, CDCl3): δ 151.7, 137.0, 130.6, 129.2, 126.9,
126.7, 124.6, 115.9, 64.6, 34.4 and 20.5. Mass (m/z): 178 (M+).
Analysis: found C, 74.04; H, 8.17; calcd for C11H14O2 C, 74.13;
H, 7.92.
6,9-Bis-spiroepoxy-1,4-diallyl-2,12-dimethyl-tricyclo[6.2.2.02,7]-
dodec-3,11-dien-5,10-dione (12a). To a solution of the 6-allyl-4-
methyl-2-hydroxymethylphenol 10a (20 g, 0.112 mol) in acetonitrile
J. Org. Chem, Vol. 72, No. 6, 2007 2063

Singh et al.
To a degassed solution of compound 9a (0.5 g, 2.05 mmol) in
dichloromethane (205 mL, 0.01 M) was added Grubbs catalyst 19
(68 mg, 4 mmol %), and the reaction mixture was stirred at ambient
temperature under nitrogen. Removal of solvent under reduced
pressure followed by column chromatography of the residue with
petroleum ether/ethyl acetate (97:3) first gave the unreacted starting
material (0.18 g, 36%, mostly the exo isomer). Continued elution
with petroleum ether/ethyl acetate (96:4) gave the cyclized com-
pound 8a as a colorless solid (0.227 g, 55%). Mp: 70-72 °C. IR
(neat) νmax: 1736 cm-1. 1H NMR (300 MHz, CDCl3): δ 5.8-5.75
(m, 1H), 5.65-5.61, (m, 1H), 5.4 (br m, 1H), 3.22-3.16 (m partly
merged with an AB system, 1H), 3.20 (part of an AB system merged
with m, JAB ) 6.0 Hz, 1H), 2.98-2.88 (m of d, J ) 16 Hz, 1H),
2.83 (part of an AB system, JAB ) 6.0 Hz, 1H), 2.41-2.22 (merged
m, 3H), 1.90 (d, J ) 1.5 Hz, 3H), 1.40-0.98 (m, 1H). 13C NMR
(75 MHz, CDCl3): δ 203.4, 145.9, 132.0, 130.4, 125.0, 62.0, 57.3,
51.5, 48.1, 44.7, 33.8, 26.1, and 20.0. ESI HRMS: calcd for
C13H14O2Na [M+ + Na] 225.0891, found 225.0896.
mol) to dry ethanol (90 mL) dropwise at ∼5 °C. To this solution
were added slowly 2-allyl-3,5-dimethylphenol (20 g, 0.123 mol)
and p-formaldehyde (13.28 g, 0.148 mol) and stirring was contin-
ued. After completion of reaction (TLC), the reaction mixture was
neutralized with NH4Cl and extracted with ethyl acetate (4 × 40
mL). The combined extract was washed with brine (2 × 10 mL)
and dried. The solvent was removed under vacuum, and the residue
was chromatographed on silica gel. Elution with petroleum ether/
ethyl acetate (92:8) gave the compound 10b (10.7 g, 45%) as a
1
solid. Mp: 80-82 °C. IR (neat) νmax: 3286 cm-1. H NMR (400
MHz, CDCl3): δ 7.66 (br s, 1H), 6.54 (s, 1H), 5.99-5.90 (m, 1H),
5.01-4.96 (m, 2H), 4.86 (s, 2H), 3.4 (s with str, J ) 4.0 Hz, 2H),
2.5-2.3 (br s, 1H), 2.2 (s, 3H), 2.19 (s, 3H). 13C NMR (75 MHz,
CDCl3): δ 154.6, 137.4, 136.1, 133.2, 123.8, 123.1, 120.3, 114.7,
60.7, 30.3, 19.3 and 19.0. ESI HRMS: calcd for C12H16O2Na [M+
+ Na] 215.1048, found 215.1054.
2-Allyl-3,5-dimethyl-6-spiroepoxycyclohexa-2,4-dienone (11b).
To a solution of phenol 10b (10 g, 52.08 mmol) in acetonitrile (25
mL) was added a solution of sodium m-periodate (22.3 g, 0.104
mol in ∼220 mL water) at ∼10 °C. The reaction mixture was stirred
for 2 h at room temperature, filtered, and extracted with ethyl acetate
(4 × 50 mL). The combined organic layer was then washed with
brine (2 × 30 mL) and dried. The solvent was evaporated, and the
residue was purified by column chromatography. Elution with
petroleum ether/ethyl acetate (94:6) gave the compound 11b (8.11
1-Allyl-3-chloromethyl-3-hydroxy-5-methyl-7-vinylbicyclo-
[2.2.2]oct-5-en-2-one (16) and 4-Allyl-2-chloromethyl-2-hydroxy-
6-methylbicyclo[4.4.0]dodeca-4,8-dien-3-one (17). A mixture of
the dimer 13a (1 g, 2.35mmol) and butadiene sulfone (8 g, excess,
added at regular intervals over a period of 7 h) in o-dichlorobenzene
was heated at 105 °C for 7 h. The solvent was distilled off, and the
residue was chromatographed on silica gel. Elution with petroleum
ether gave some o-dichlorobenzene. Continued elution with petro-
leum ether/ethyl acetate (97:3) furnished the adduct 16 as a mixture
of endo and exo isomers(0.8 g, 64%) and 17 as a minor product
(0.05 g, 4%).
1
g, 82%) as a low-melting solid. IR (neat) νmax: 1654 cm-1. H
NMR (400 MHz, CDCl3): δ 6.2 (s, 1H), 5.8-5.7 (m, 1H), 5.02-
4.9 (m, 2H), 3.22-3.16 (AB pattern overlapped with m, 4H), 2.1
(s, 3H), 1.8 (s, 3H). 13C NMR (75 MHz, CDCl3): δ 194.1, 150.1,
143.7, 134.8, 129.7, 129.4, 115.0, 58.3, 57.8, 29.3, 20.58 and 16.0.
HRMS: calcd for C12H15O2 [M+ + H] 191.1072, found 191.1080.
7,10-Dimethyl-8-spiroepoxy-tricyclo[5.2.2.01,5]undec-3,10-dien-
9-one (8b). A solution of cyclohexadienone 11b (1 g, 5.263 mmol)
and 1,3-pentadiene (mixture of cis and trans) (2 mL, excess) in
o-dichlorobenzene (1.5 mL) was heated in a sealed tube at 100 °C
for 5 h. The reaction mixture was then was charged as such on
silica gel and chromatographed. Elution with petroleum ether/ethyl
acetate (97:3) gave the adduct 9b (1.09 g, 80%) as a mixture of
isomers [IR (neat) νmax: 1730 cm-1. 1H NMR (300 MHz, CDCl3):
δ 6.04-5.88 (m, 2H), 5.48-5.36 (m, 1H), 5.28-5.04 (complex
m, 3H), 3.1-3.06 (part of an AB system, JAB ) 6.0 Hz, 1H), 2.92-
2.88 (part of an AB system, JAB ) 6.0 Hz, 1H), 2.76-2.5 (m, 1H),
2.4-2.28 (m, 1H), 2.24-2.14 (m, 2H), 1.9-1.74 (m, 2H), 1.68-
1.52 (m, 4H), 1.22-1.04 (two sets of dd, 1H), 0.9 (s, 3H). HRMS:
calcd for C17H22O2Na [M+ + Na] 281.1517, found 281.1517] which
was subjected to ring-closing metathesis as described below.
To a degassed solution of the adduct 9b (0.5 g, 1.938 mmol) in
dichloromethane (195 mL, 0.01 M) was added Grubbs catalyst 19
(63 mg, 4 mmol %), and the mixture was stirred at ambient
temperature under nitrogen. Removal of solvent under reduced
pressure followed by column chromatography of the residue with
petroleum ether/ethyl acetate (97:3) first gave the unreacted starting
material (0.18 g, 36%). Continued elution with petroleum ether/
ethyl acetate (96:4) gave the desired compound 8b as a colorless
liquid (0.205 g, 49%), which solidifies upon keeping in the
refrigerator. Mp: 86-88 °C. IR (neat) νmax: 1734 cm-1. 1H NMR
(300 MHz, CDCl3): δ 6.03 (br m, 1H), 5.83-5.78 (m, 1H), 5.65-
5.62 (m, 1H), 3.24-3.16 (m, 1H), 3.12 (part of an AB system, JAB
) 6 Hz, 1H), 2.9 (part of an AB system, JAB ) 6 Hz, 1H), 2.76 (m
of d, J ) 14.6 Hz, 1H), 2.55 (dd, J1 ) 14.6 Hz, J2 ) 3.0 Hz, 1H),
2.13 (dd, J1 ) 11.7 Hz, J2 ) 10.2 Hz, 1H), 1.74 (d, J ) 1.5 Hz,
3H), 1.37 (dd, J1 ) 11.7 Hz, J2 ) 8.8 Hz, 1H), 1.03 (s, 3H). 13C
NMR (100 MHz, CDCl3): δ 203.4, 136.0, 135.9, 132.2, 130.2,
65.0, 59.8, 48.8, 48.3, 39.1, 35.8, 29.8, 20.0 and 17.9. HRMS: calcd
for C14H17O2 [M+ + H] 217.1229, found 217.1221.
Data for 16 (mixture of endo, exo). IR νmax: 1720, 3476 cm-1
.
1H NMR(CDCl3, 400 MHz): δ, 5.84-5.40 (m merged with s, total
3H), 5.09-4.94(m, total 4H), 3.62-3.42 (two sets of AB system,
JAB ) 7.5 Hz, total 2H), 2.98 (br m, 1H), 2.80, 2.72 (two s, total
1H), 2.53-2.40(merged m, total 3H), 2.25-2.20 (m, 1H), 1.97
(two sets of d, J ) 1.5 Hz, total 3H), 1.26-1.19 (m, 1H). 13C NMR
(100 MHz, CDCl3): δ 210.8, 145.1, 137.9, 133.8, 124.1, 118.4,
117.2, 75.0, 54.8, 503, 47.9, 44.5, 33.3, 26.7, 21.1. HRMS: calcd
for C15H19O2ClNa [M+ + Na] 289.0766, found 289.0729 [M+
+
Na].
Data for 17. Mp: 59-61 °C. IR νmax: 3457, 1669 cm-1. H
NMR(CDCl3, 400 MHz): δ, 6.64 (s 1H), 5.85-5.71(m, 3H), 5.11-
5.06 (m, 2H), 3.93 (part of an AB system, JAB ) 11 Hz, 1H), 3.54
(part of an AB system, JAB ) 11 Hz, 1H), 3.06-2.97 (m, 2H),
2.70 (s, 1H), 2.44-2.37 (m, 2H), 2.03-1.97 (d with structure, J )
∼13.5 Hz, 1H), 1.24 (s, 3H). 13C NMR (CDCl3, 75 MHz): δ 196.9,
156.9, 135.1,134.3, 125.7, 124.6, 116.9, 46.4, 38.7, 36.8, 33.9, 33.4,
27.5, 22.5. Analysis: found C, 67.30; H, 7.40; calcd C, 67.53; H,
7.17 for C15H20ClO2.
1
Transformation of 1-Allyl-3-chloromethyl-3-hydroxy-5-meth-
yl-7-vinylbicyclo[2.2.2]oct-5-en-2-one (16) into 8a. A solution of
the adduct 16 (0.478 g, 1.79mmol) was treated with aqueous KOH
(2.34 mmol, 10 mL) in the presence of cetyltrimethylammonium
bromide (0.035 g) as described earlier. Usual workup and chro-
matography gave the keto-epoxide 18 [(0.352 g, 85%), IR νmax
:
1732, cm-1. 1H NMR (300 MHz, CDCl3): δ 5.93-5.40 (two sets
of m and s, total 3H); 5.16-4.97(m, 4H), 3.10 (two set of part of
AB system, JAB ) 6.2 Hz, total, 1H), 2.87 (two set of part of AB
system, JAB ) 6.2 Hz, total, 1H), 2.60-2.23 (cluster of m, total
5H), 2.10-1.8 (multiplet overlapped with two sets of d, J ) 1.5
Hz, total 4H), 1.45-1.38 (m, 1H). MS calcd for C15H18O2Na
(M+ + Na) 253.266, found 253.116 (M+ + Na)]. The keto-epoxide
(0.487 g, 2.10 mmol) was then treated with Grubbs first generation
catalyst 19 (0.066 g, 4 mol %) in degassed dichloromethane (215
mL) for 24 h. Removal of solvent followed by chromatography
[petroleum ether/ethyl acetate (97:3)] gave the tricyclic compound
8a (0.234 g, 55%) as a solid which was found to be identical with
the sample prepared earlier.
11-Methyl-tricyclo[5.2.2.01,5]undec-3,10-dien-9-one (21a). To
a solution of the adduct 8a (3 g, 14.85 mmol) in MeOH/H2O (6:1,
105 mL) were added zinc (activated, 18 g, excess) and NH4Cl (3.5
g, 65.4 mmol). The reaction mixture was stirred at ambient
6-Allyl-3,5-dimethyl-2-hydroxymethyl Phenol (10b). Sodium
ethoxide was prepared by adding freshly cut sodium (2.84 g, 0.124
2064 J. Org. Chem., Vol. 72, No. 6, 2007

Duprezianane, Polyquinane, and Sterpurane Frameworks
temperature (∼30 °C). After completion of reaction (TLC, 8 h),
the reaction mixture was filtered through a celite bed and washed
with ethyl acetate (5 × 50 mL). The filtrate was concentrated under
vacuum; the residue was diluted with water (15 mL) and extracted
with ethyl acetate (4 × 25 mL). The combined extract was washed
with brine and dried. The solvent was evaporated under reduced
pressure and the residue was chromatographed. Elution with
petroleum ether/ethyl acetate (96:4) first gave the compound 22a
as a liquid (syn/anti mixture, 0.28 g, 10%). Further elution with
petroleum ether/ethyl acetate (80:20) gave the â-keto alcohol 20a
as a liquid (syn/anti mixture, 2.21 g, 73%) [IR (neat) νmax: 3418,
diluted with water (20 mL) and extracted with ether (4 × 30 mL).
The extract was combined and dried, and the solvent was removed
under vacuum to give the crude acid, which was subjected to
decarboxylation without further purification. The carboxylic acid
was dissolved in a THF/H2O mixture (1:1, 60 mL) and refluxed
for 12 h. The reaction mixture was saturated with sodium chloride,
extracted with ether (4 × 30 mL), and dried. The solvent was
evaporated under reduced pressure, and the crude product was
purified by column chromatography. Elution with petroleum ether/
ethyl acetate (97:3) gave the compound 21b as a thick liquid (0.776
1
g, 45% after 2 steps). IR (neat) νmax: 1726 cm-1. H NMR (300
1
1714 cm-1. H NMR (300 MHz, CDCl3): δ 5.77-5.72 (m, 1H),
MHz, CDCl3): δ 6.0-5.96 (br m, 1H), 5.81-5.75 (m, 1H), 5.63-
5.57 (m, 1H), 3.06-3.01 (m, 1H), 2.63 (m of part of an AB system,
JAB ) 16.8 Hz, 1H), 2.52 (d of part of an AB system, JAB ) 16.8
Hz, J2 ) 3.6 Hz, 1H), 2.04 (part of an AB system, JAB ) 18 Hz,
1H), 1.9-1.82 (merged m, 2H), 1.68 (d, J ) 2 Hz, 3H), 1.38-1.3
(m, 1H), 1.24 (s, 3H). 13C NMR (100 MHz, CDCl3): δ 209.8, 137.6,
133.9, 132.4, 130.1, 65.7, 47.7, 45.9, 38.1, 37.9, 29.4, 24.0 and
19.4. HRMS: calcd for C13H17O [M+ + H] 189.1279, found
189.1283.
5.63-5.55 (m, 1H), 5.29-5.23 (m, 1H), 3.84-3.68 (two sets of
m, total 1H), 3.63-3.52 (two sets of m, total 1H), 3.29 (br s, 1H),
3.06-2.66 (m, 3H), 2.34-2.09 (m, 3H), 1.85 (d, J ) 1.4 Hz, 3H),
1.40-1.25 (m, 1H). HRMS: calcd for C13H16O2Na [M+ + Na]
227.1048, found 227.1051]. The keto-alcohol thus obtained was
then subjected to oxidation and decarboxylation as described below.
To a solution of the â-keto-alcohol 20a (1 g, 4.90 mmol) in
acetone (30 mL) at ∼5 °C was added freshly prepared Jones’
reagent dropwise. After completion of reaction (TLC), acetone was
removed under vacuum without heating. The residue was diluted
with water (20 mL) and extracted with ether (5 × 25 mL). The
extract was combined and dried, and the solvent was removed under
vacuum to give a â-keto-acid, which was subjected to decarboxy-
lation without further purification. The carboxylic acid thus
obtained, was dissolved in THF/H2O mixture (1:1, 40 mL) and
refluxed for 12 h. The reaction mixture was saturated with sodium
chloride, extracted with ether (4 × 30 mL), and dried. The solvent
was evaporated under reduced pressure, and the crude product was
purified by column chromatography. Elution with petroleum ether/
ethyl acetate (97:3) gave the compound 21a as a colorless liquid
(0.384 g, 45% after 2 steps). IR (neat) νmax: 1724 cm-1. 1H NMR
(300 MHz, CDCl3): δ 5.78-5.74 (m, 1H), 5.63-5.59 (m, 1H),
5.27 (br s, 1H), 3.06-2.96 (br m, 1H), 2.87-2.78 (m of d, J )
15.0 Hz, 1H), 2.71-2.67 (m, 1H), 2.21 (m of d, J ) 15.0 Hz, 1H),
2.16-2.00 (m, 3H), 1.83 (d, J ) 1.5 Hz, 3H), 1.39-1.31 (m, 1H).
13C NMR (75 MHz, CDCl3): δ 210.5, 148.4, 132.6, 130.5, 123.1,
62.3, 46.7, 38.7, 38.3, 33.9, 28.8 and 19.5. HRMS: calcd for
C12H15O 175.1123 [M+ + H], found 175.1124.
8,11-Dimethyl-tricyclo[5.2.2.01,5]undec-3,10-dien-9-one (22a).
To a suspension of activated zinc (12 g, excess) and ammonium
chloride (3.5 g excess) in dry dioxane (50 mL) was added the keto-
epoxide 8a (2 g, 9.90 mmol) in dry dioxane (50 mL), and the
reaction mixture was refluxed till completion of reaction (TLC, 8
h). The reaction mixture was filtered through a celite bed, and the
bed was washed with EtOAc (3 × 20 mL). The filtrate was
evaporated under reduced pressure; the residue was diluted with
water (20 mL) and extracted with EtOAc (4 × 30 mL). The
combined organic layer was washed with brine (20 mL) and dried,
and solvent was evaporated under reduced pressure. Column
chromatography of the crude residue on silica gel with petroleum
ether/EtOAc (96:4) gave the title compound 22a (syn/anti mixture,
1
1.15 g, 62%) as a volatile liquid. IR (neat) νmax: 1724 cm-1. H
NMR (400 MHz, CDCl3): δ 5.78-5.73 (m, 1H), 5.60-5.56 (m,
1H), 5.26 (d, J ) 1.6 Hz, 1H), 2.94-2.86 (br t, 1H), 2.86-2.78
(m of d, J ) 15.0 Hz, 1H), 2.48 (br m, 1H), 2.24-2.16 (m, 2H),
2.1-2.04 (m, 1H), 1.83 (d, J ) 1.6 Hz, 3H), 1.25 (m, 1H), 1.1 (d,
J ) 7.5 Hz). 13C NMR (100 MHz, CDCl3): δ 213.3, 149.1, 132.5,
130.7, 123.7, 62.6, 46.8, 44.5, 42.0, 34.2, 24.5, 19.7 and 15.7.
HRMS: calcd for C13H16ONa [M+ + Na] 211.1099, found
211.1090. Elution with petroleum ether/EtOAc (80:20) gave the
alcohol 20a (syn/anti mixture, 0.36 g, 18%).
7,10-Dimethyl-tricyclo[5.2.2.01,5]undec-3,10-dien-9-one (21b).
To a solution of the adduct 8b (3 g, 13.89 mmol) in MeOH/H2O
(6:1, 105 mL) were added zinc (activated, 18 g, excess) and NH4-
Cl (3.5 g, 65.4 mmol). The reaction mixture was stirred at ambient
temperature (∼30 °C). After completion of reaction (TLC, 10 h)
the reaction medium was filtered on a celite bed and washed with
ethyl acetate (5 × 35 mL). The filtrate was concentrated under
vacuum, and the residue was diluted with water (15 mL) and
extracted with ethyl acetate (4 × 25 mL). The combined extract
was washed with brine and dried. The solvent was removed under
reduced pressure, and the residue was purified by column chro-
matography. Elution with petroleum ether/ethyl acetate (97:3) gave
minor compounds 22b as a liquid (syn/anti mixture, 0.14 g, 5%)
and the enol 24 (0.53, 19%). Further elution with petroleum ether/
ethyl acetate (80:20) gave the â-keto alcohol 20b as a liquid as a
major product (syn/anti mixture, 2.09 g, 69%. IR (neat) νmax: 3492,
1717 cm-1. 1H NMR (300 MHz, CDCl3): δ 6.03,5.90 (two sets of
br s, total 1H), 5.81-5.76 (m, 1H), 5.63-5.55 (m, 1H), 3.91-3.8
(m, 1H), 3.64-3.56 and 3.56-3.46 (two sets of dd, total 1H), 3.1-
2.9 (m merged with s, total 2H), 2.74-2.46 (m, 2H), 2.12-1.82
(m, total 2H), 1.68 (two sets of d, J ) 1.5 Hz, total 3H), 1.38-
1.20 (m merged with two singlets, total 4H). 13C NMR (75 MHz,
CDCl3) (syn/anti mixture): δ 214.2, 212.9, 139.3, 136.9, 134.0,
132.8, 132.5, 132.0, 130.3, 65.9, 65.2, 62.7, 61.6, 54.3, 52.8, 48.4,
46.4, 39.7, 39.6, 39.5, 34.5, 29.6, 29.4, 22.1, 21.6, 19.6, 19.3.
The â-keto-alcohol 20b thus obtained (2 g, 9.194 mmol) was
dissolved in acetone (40 mL), and freshly prepared Jones’ reagent
was added to it dropwise at ∼5 °C. After completion of reaction
(TLC), acetone was removed under vacuum. The residue was
8,8,11-Trimethyl-tricyclo[5.2.2.01,5]undec-3,10-dien-9-one (23a).
Sodium hydride (0.75 g, 60% w/w suspension, excess) was placed
in a dry two-necked flask and washed with dry petroleum ether,
and dry THF (10 mL) was added. A solution of the compound 22a
(0.5 g, 2.66 mmol) in THF (10 mL) was added to the reaction
mixture, which was refluxed for 1 h. The reaction mixture was
brought to ambient temperature; methyl iodide (1.5 mL, excess)
was added and refluxed for 6 h after which it was cooled (0 °C)
and quenched by addition of cold water. The reaction mixture was
saturated with NaCl, the organic layer was separated, and the
aqueous layer was extracted with ether (3 × 20 mL). The combined
organic layer was washed with sodium thiosulfate (1 × 20 mL)
and dried. The solvent was evaporated under reduced pressure, and
the residue was chromatographed on silica gel. Elution with light
petroleum ether/EtOAc (98:2) gave the title compound 23a as a
volatile liquid (0.28 g, 52%). IR (neat) νmax: 1726 cm-1. 1H NMR
(400 MHz, CDCl3): δ 5.78 (m, 1H), 5.60 (m, 1H), 5.20 (br s, 1H),
3.05 (m, 1H), 2.8 (d, J ) 16.0 Hz, 1H), 2.3-2.2 (merged m, 3H),
1.85 (s, 3H), 1.25 (m, 1H), 1.09 (s, 3H), 1.04 (s, 3H). 13C NMR
(75 MHz, CDCl3): δ 215.0, 149.1, 132.8, 130.5, 122.0, 62.3, 50.5,
46.5, 44.4, 34.3, 25.8, 25.5, 24.5 and 21.2. HRMS: calcd for
C14H19O [M+ + H] 203.1436, found 203.1431.
7,8,10-Trimethyl-tricyclo[5.2.2.01,5]undec-3,10-dien-9-one (22b).
To a suspension of activated zinc (12 g, excess) and ammonium
chloride (3.5 g excess) in dry dioxane (50 mL) was added the keto-
epoxide 8b (2 g, 9.26 mmol) in dry dioxane (50 mL), and the
J. Org. Chem, Vol. 72, No. 6, 2007 2065

Singh et al.
reaction mixture was refluxed till completion of reaction (TLC,
7 h). The reaction mixture was filtered through a celite bed and
washed with EtOAc (3 × 30 mL). The filtrate was evaporated under
reduced pressure; the residue was diluted with water (20 mL) and
extracted with EtOAc (4 × 30 mL). The combined organic layer
was washed with brine (20 mL) and dried, and the solvent was
removed under reduced pressure. Column chromatography of the
residue on silica gel [petroleum ether/EtOAc (97:3)] gave the title
compound 22b (syn/anti mixture, 0.935 g, 50%) as a liquid. IR
5.88 (d, J ) 1.5 Hz, 1H), 5.83-5.77 (m, 1H), 5.63-5.59 (m, 1H),
5.2 (d, J ) 1.2 Hz, 1H), 3.04-2.95 (m, 1H), 2.76 (m of part of an
AB system, JAB ) 15.0 Hz, J2 ) 3.2 Hz, 1H), 2.56 (d of part of an
AB system, JAB ) 15.0 Hz, 1H), 1.9 (superimposed dd, J ) 10.5
Hz, 1H), 1.70 (d, J ) 1.5 Hz, 3H), 1.43-1.39 (dd, J1 ) 10.5 Hz,
J2 ) 8.0 Hz, 1H), 1.37 (s, 3H). 13C NMR (75 MHz, CDCl3): δ
197.6, 146.8, 136.2, 135.6, 132.4, 130.5, 113.5, 65.0, 48.2, 41.7,
39.2, 29.9, 20.8 and 19.7. HRMS: calcd for C14H16ONa
[M+ + Na] 223.1099, found 223.1088
1
(neat) νmax: 1725 cm-1. H NMR (300 MHz, CDCl3): δ 6.10
11-Methyl-tricyclo[5.2.2.01,5]undec-4,10-dien-3,9-dione (26a).
To a solution of the ketone 21a (0.5 g, 2.87 mmol) in 50 mL
benzene at ∼15 °C were added PDC (5.37 g, 14.36 mmol) and
tBuOOH (2 mL, excess). After the reaction mixture stirred for 15
min, it was brought to ambient temperature and further stirred for
24 h. The reaction mixture was diluted with ether (10 mL), filtered
through a celite bed, and washed with ethyl acetate (2 × 10 mL).
The filtrate was concentrated under reduced pressure, and the
residue was chromatographed on silica gel. Elution with petroleum
ether/ethyl acetate (80:20) furnished the enone 26a (0.335 g, 62%)
as a solid, which was recrystallized from petroleum ether/ethyl
(br m, 1H), 5.75-5.74 (m, 1H), 5.59-5.54 (m, 1H), 2.96-2.87
(m, 1H), 2.64 (m of part of an AB system, JAB ) 16.0 Hz, 1H),
2.50 (dd of part of an AB system, JAB ) 16.0 Hz, J2 ) 3.0 Hz,
1H), 1.96 (dd, J1 ) 11.2 Hz, J2 ) 8.7 Hz, 1H), 1.82-1.72 (merged
m, 1H), 1.67 (d, J ) 2.0 Hz, 3H), 1.26-1.20 (merged m, 1H),
1.18 (s, 3H), 1.06 (d, J ) 7.5 Hz, 3H). 13C NMR (75 MHz,
CDCl3): δ 213.3, 139.3, 133.9, 132.3, 130.3, 65.4, 48.0, 47.5, 40.4,
33.2, 29.7, 22.1, 19.6 and 13.1. HRMS: calcd for C14H18ONa
[M+ + Na] 225.1255, found 225.1254.
Further elution with petroleum ether/ethyl acetate (93:7) gave
1
1
the enol 24 (0.467 g, 25%). IR (neat) νmax: 3405 cm-1. H NMR
acetate. Mp: 126-128 °C. IR (neat) νmax: 1712, 1652 cm-1. H
(300 MHz, CDCl3): δ 5.74-5.68 (merged m, 2H), 5.60-5.56
(m, 1H), 5.12 (d, J ) 2.4 Hz, 1 H), 4.80 (d, J ) 2.4 Hz, 1H), 3.9
(s, 1H), 3.08-3.0 (m, 1H), 2.56 (m of part of an AB system,
JAB ) 16.0 Hz, 1H), 2.42 (d of part of an AB system, JAB ) 16.0
Hz, J2 ) 3.5 Hz, 1H), 1.9 (br s, 1H), 1.76-1.64 (m merged
with d, 4H), 1.36-1.28 (dd, J1 ) 11.5 Hz, J2 ) 8.0 Hz, 1H), 1.2
(s, 3H, CH3). 13C NMR (75 MHz, CDCl3): δ 158.2, 140.1, 134.6,
133.6, 129.8, 106.2, 72.9, 58.7, 42.5, 41.8, 40.9, 31.3, 21.7 and
19.7. HRMS: calcd for C14H19O [M+ + H] 203.1436, found
203.1438
NMR (300 MHz, CDCl3): δ 5.87 (br m, 1H), 5.67 (br m, 1H),
3.34 (d, J ) 20 Hz, 1H), 3.08-3.02 (m, 1H), 2.72 (m of AB system,
JAB ) 18.0 Hz, 2H), 2.36 (m of d, J ) 18.0 Hz, 1H), 2.24
(d, J ) 20.0 Hz, 1H), 2.18-2.11 (m of d, J ) 18.0 Hz, 1H), 1.94
(d, J ) 1.5 Hz, 3H). 13C NMR (75 MHz, CDCl3): δ 207.7, 204.8
(CO), 177.0, 147.3, 125.8, 122.5, 64.1, 38.8, 37.6, 37.5, 31.2 and
20.3. HRMS: calcd for C12H12O2Na [M+ + Na] 211.0735, found
211.0745.
7,10-Dimethyl-tricyclo[5.2.2.01,5]undec-4,10-dien-3,9-dione (26b).
Oxidation of the ketone 21b (0.5 g, 2.66 mmol) in 50 mL benzene
t
Elution with petroleum ether/ethyl acetate (80:20) furnished the
alcohol 20b (syn/anti mixture, 0.303 g, 15%).
at ∼15 °C with PDC (5.37 g, 14.36 mmol) and BuOOH (2 mL,
excess) as described above followed by chromatography [petroleum
ether/ethyl acetate (80:20)] furnished the enone 26b (0.295 g, 55%)
as a solid, which were recrystallized from petroleum ether/ethyl
7,8,8,10-Tetramethyl-tricyclo[5.2.2.01,5]undec-3,10-dien-9-
one (23b). Sodium hydride (0.70 g, 60% w/w suspension, excess)
was placed in a dry two-necked flask and washed with dry
petroleum ether, and dry THF (10 mL) was added. A solution of
the compound 22b (0.4 g, 1.98 mmol) in tetrahydrofuran (10 mL)
was added to the reaction mixture, which was refluxed for 1 h.
The reaction mixture was then brought to ambient temperature;
methyl iodide (1.5 mL, excess) was added and refluxed for 6 h.
The reaction mixture was cooled (0 °C) and quenched by addition
of cold water. The reaction mixture was saturated with sodium
chloride, the organic layer was separated, and the aqueous layer
was extracted with ether (3 × 20 mL). The combined organic layer
was washed with sodium thiosulfate (1 × 20 mL) and dried. The
solvent was evaporated under reduced pressure, and the residue
was chromatographed on silica gel. Elution with light petroleum
ether/EtOAc (98:2) gave the title compound 23b as a volatile liquid
1
acetate. Mp: 120-121 °C. IR (neat) νmax: 1710, 1655 cm-1. H
NMR (300 MHz, CDCl3): δ 6.02 (br m, 1H), 5.82 (t, 1H, J ) 1.8
Hz), 3.25-3.19 (part of an AB system, JAB ) 18.0 Hz, 1H),
2.62-2.45 (m, total 3H), 2.2 (d of part of an AB system, JAB
)
18.0 Hz, J2 ) 3.0 Hz, 1H), 2.06 (part of an AB system, JAB ) 18.0
Hz, 1H), 1.76 (d, J ) 1.5 Hz, 3H), 1.42 (s, 3H). 13C NMR
(75 MHz, CDCl3): δ 207.5, 204.7, 177.6, 136.3, 135.6, 125.4, 67.5,
46.4, 39.5, 36.5, 33.8, 23.3 and 18.2. HRMS: calcd for C13H14O2-
Na [M+ + Na] 225.0891, found 225.0902.
1-Methyl-tricyclo[7.2.0.03,7]undec-2,5-dien-11-one (28). A so-
lution of 21a (0.1 g, 0.575 mmol) in benzene (110 mL) was
irradiated with a mercury vapor lamp (125 W, Applied Photophys-
ics) in a Pyrex immersion well for 30 min. Benzene was evaporated
under reduced pressure and the photolysate was chromatographed.
Elution with petroleum ether/ethyl acetate (98:2) afforded the
1,3-acyl shift product 28 (0.04 g, 40%) as a colorless liquid, which
was very sensitive. IR (neat) νmax: 1770 cm-1. 1H NMR (300 MHz,
CDCl3): δ 5.91-5.60 (m, 2H), 5.30 (br s, 1H), 3.20-2.96 (merged
m, 4H), 2.86-2.76 (dd, J1 ) 18.0 Hz, J2 ) 5.0 Hz, 1H), 2.4-2.3
(m, 1H), 2.15-2.07 (d of dd, J1 ) 13.5 Hz, J2 ) 4.0 Hz, J3 ) 1.5
Hz, 1H), 1.30 (s, 3H), 1.12-1.00 (d of superimposed dd, J1 ) 13.5
Hz, J2 ) 4.0 Hz, 1H). 13C NMR (75 MHz, CDCl3): δ 211.7, 146.1,
133.2, 129.8, 118.1, 62.8, 45.9, 40.1, 38.7, 31.0, 26.0 and 21.1.
HRMS: calcd for C12H15O [M+ + H] 175.1123, found 175.1126.
2-Methyl-tetracyclo[6.3.0.0.1,302,6]undec-8-en-4,10-dione (31).
A solution of 26a (0.1 g, 0.532 mmol) in benzene (110 mL) was
irradiated with a mercury vapor lamp (125 W, Applied Photophys-
ics) in a Pyrex immersion well for 30 min. Benzene was evaporated
under reduced pressure, and the photolysate was chromatographed.
Elution with petroleum ether/ethyl acetate (65:35) afforded the
oxa-di-π-methane product 31 (0.053 g, 53%) as a solid. Mp: 127-
128 °C. IR (neat) νmax: 1704, 1682 cm-1 (five-membered ring
1
(0.214 g, 50%). IR (neat) νmax: 1726 cm-1. H NMR (400 MHz,
CDCl3): δ 5.94 (br m, 1H), 5.79-5.75 (m, 1H), 5.60-5.56
(m, 1H), 3.02-2.95 (m, 1H), 2.61 (m of part of AB system, JAB
)
16.6 Hz, 1H), 2.51 (d of part of an AB system, JAB ) 16.6 Hz,
J2 ) 2.7 Hz, 1H), 2.03 (dd, J1 ) 12.4 Hz, J2 ) 9.7 Hz 1H), 1.65
(d merged with signal due to H2O, 3H), 1.26 (dd, J1 ) 12.4 Hz,
J2 )8.5 Hz, 1H), 1.13 (s, 3H), 1.01 (s, 3H), 0.98 (s, 3H). 13C NMR
(100 MHz, CDCl3): δ 215.0, 138.9, 132.6, 132.3, 130.3, 65.1, 47.4,
46.6, 43.6, 35.7, 30.3, 24.6, 21.8, 19.4 and 19.2. HRMS: calcd for
C15H21O [M+ + H] 217.1592, found 217.1598.
7,10-Dimethyl-tricyclo[5.2.2.01,5]dodec-3,8(12),10-trien-9-
one (25). To a suspension of PDC (2 g, 5.35 mmol) in 25 mL dry
dichloromethane was added the compound 24 (0.5 g, 2.48 mmol),
and the reaction mixture was stirred at ambient temperature
(∼25 °C). After completion of reaction (TLC), the reaction mixture
was filtered through a celite pad and washed with ethyl acetate
(3 × 15 mL). The solvent was evaporated, and the residue was
purified by chromatography. Elution with petroleum ether/ethyl
1
acetate (97:3) gave compound 25 (0.445 g, 90%). IR (neat) νmax
:
CO, R,â-unsaturated enone). H NMR (300 MHz, CDCl3): δ 6.0
1715 cm-1 1H NMR (300 MHz, CDCl3): 5.94 (br m, 1H),
.
(s, 1H), 3.2-3.02 (merged m, 2H), 2.86-2.74 (m, 1H), 2.62 (part
2066 J. Org. Chem., Vol. 72, No. 6, 2007

Duprezianane, Polyquinane, and Sterpurane Frameworks
of an AB system, JAB ) 19.0 Hz, 1H), 2.40 (part of an AB system,
JAB ) 19.0 Hz, 1H), 2.31 (d, J ) 17.0 Hz, 1H), 2.21 (br s, 1H),
2.08 (d, J ) 17.0 Hz, 1H), 1.57 (s, 3H). 13C NMR (75 MHz,
CDCl3): δ 211.4, 206.9, 188.1, 126.3, 57.8, 50.6, 49.5, 48.5, 45.3,
41.4, 37.2 and 14.0. HRMS: calcd for C12H12O2Na [M+ + Na]
211.0735, found 211.0735.
(110 mL) was irradiated for 50 min as described earlier. Acetone
was removed under vacuum and the reaction mixture was chro-
matographed. Elution with petroleum ether/ethyl acetate (98:2)
gave some unreacted starting material (0.011 g, 15%). Further
elution with petroleum ether/EtOAc (96:4) afforded product 34
(0.024 g, 32%) as a colorless liquid. IR (neat) νmax: 1726 cm-1
.
Similarly, irradiation of 26a (0.075 g, 0.398 mmol) in degassed
acetone (110 mL) with a mercury vapor lamp (125 W, Applied
Photophysics) in a Pyrex immersion well for 1 h under nitrogen,
followed by removal of solvent and chromatography with petroleum
ether/ethyl acetate (65:35), afforded product 31 (0.041 g, 54%).
2-Methyl-tetracyclo[6.3.0.0.1,302,6]undec-9-en-4-one (32). A
solution of 21a (0.1 g, 0.575 mmol) in degassed acetone (110 mL)
was irradiated with a mercury vapor lamp (125 W, Applied
Photophysics) in a Pyrex immersion well for 1 h, under nitrogen.
Acetone was removed under vacuum, and the reaction mixture was
chromatographed. Elution with petroleum ether/ethyl acetate
(97:3) gave some unreacted starting material (0.01 g, 10%). Further
elution with petroleum ether/EtOAc (94:6) afforded product 32
1H NMR (400 MHz, CDCl3): δ 5.79-5.74 (m, 1H), 5.72-5.68
(m, 1H), 2.8-2.7 (m, 1H), 2.38 (m of AB system, JAB ) 17.0 Hz,
2H), 2.16 (d, J ) 6.4 Hz, 1H), 2.02 (dd, J1 ) 13.0 Hz, J2 ) 6.4
Hz, 1H), 1.93 (s, 1H), 1.56-1.48 (m, 1H), 1.4 (s, 3H), 1.12
(s, 3H), 0.88 (s, 3H). 13C NMR (100 MHz, CDCl3): δ 206.8, 134.6,
128.7, 57.3, 51.3, 49.2, 45.2, 44.6, 40.5, 34.3, 29.1, 18.0, 14.5.
HRMS: calcd for C14H19O [M+ + H] 203.1436, found 203.1444.
3,6-Dimethyl-tetracyclo[6.3.0.0.1,302,6]undec-9-en-4-one (35).
A solution of 21b (0.1 g, 0.532 mmol) in degassed acetone
(110 mL) was irradiated for 1 h as described earlier. Acetone was
removed under vacuum, and the residue was chromatographed.
Elution with petroleum ether/ethyl acetate (97:3) first gave some
unreacted starting material (0.012 g, 12%). Further elution with
petroleum ether/ethyl acetate (95:5) afforded the product 35 (0.046
g, 46%) as a colorless liquid. IR (neat) νmax: 1720 cm-1. 1H NMR
(400 MHz, CDCl3): δ 5.80-5.76 (m, 1H), 5.74-5.70 (m, 1H),
2.94-2.88 (m, 1H), 2.54 (m of d, J ) 12.3 Hz, 1H), 2.30-2.20
(merged m, 2H), 2.05 (part of an AB system, JAB ) 18.4 Hz, 1H),
(0.052 g, 52%) as a colorless liquid. IR (neat) νmax: 1726 cm-1
.
1H NMR (300 MHz, CDCl3): δ 5.81-5.76 (m, 1H), 5.73-5.68
(m, 1H), 3.06 (m, 1H), 2.66-2.56 (merged m, 2H), 2.44-2.32
(m of an AB system, JAB ) 18.0 Hz, 2H), 1.9-1.76 (m, 3H), 1.74-
1.62 (m, 1H), 1.38 (s, 3H). 13C NMR (75 MHz, CDCl3): δ 215.7,
134.3, 128.7, 50.7, 49.5, 48.4, 47.3, 46.3, 45.3, 44.5, 34.2 and 13.6.
HRMS: calcd for C12H15O [M+ + H] 175.1123, found 175.1118.
2,5-Dimethyl-tetracyclo[6.3.0.0.1,302,6]undec-9-en-4-one (33).
Irradiation of a solution of 22a (0.075 g, 0.399 mmol) in degassed
acetone (110 mL) in a Pyrex immersion well for 50 min as described
above followed by removal of solvent and chromatography
[petroleum ether/ethyl acetate (95:5)] afforded product 33 (0.032
g, 43%) as a colorless liquid. IR (neat) νmax: 1725 cm-1. 1H NMR
(300 MHz, CDCl3): δ 5.76-5.73 (m, 1H), 5.71-5.67 (m, 1H),
2.78-2.70 (m, 1H), 2.63 (dd, J1 ) 10.0 Hz, J2 ) 3.5 Hz, 1H),
2.5-2.24 (merged m, 4H), 2.02 (dd, J1 ) 12.5 Hz, J2 ) 3.5 Hz,
1H), 1.56-1.44 (m merged with signal due to H2O present in
CDCl3, 1H), 1.4 (s, 3H), 0.85 (d, J ) 7.5 Hz, 3H). 13C NMR
(75 MHz, CDCl3): δ 212.2, 134.5, 128.6, 51.2, 49.2, 48.8, 46.1,
45.0, 39.0, 34.2, 29.7, 13.4, 9.7. HRMS: calcd for C13H17O [M+
+ H] 189.1279, found 189.1282.
1.90-1.85 (m, 2H), 1.55 (m of superimposed dd, J1 ) J2
)
7.2 Hz, J3 ) 1.2 Hz, 1H), 1.35 (s, 3H), 1.20 (s, 3H). 13C NMR
(100 MHz, CDCl3): δ 216.5, 134.3, 128.0, 54.5, 53.3, 51.2, 50.1,
49.4, 46.4, 44.9, 36.0, 24.9, 12.4. HRMS: calcd for C13H17O [M+
+ H] 189.1279, found 189.1283.
Acknowledgment. We thank CSIR New Delhi for continu-
ing financial support. G.D.P. is thankful to CSIR New Delhi
for a fellowship. Thanks are due to DST for creating the National
Single-Crystal X-ray Facility.
Supporting Information Available: 13C NMR spectra of
compounds 8a,b, 10a,b, 11b, 12a, 13a, 16, 17, 21a,b-23a,b, 24,
1
25, 26a,b, 28, and 31-35; H NMR spectrum of compound 15;
CIF data of compound 8a; and ORTEP diagram of 8a. This material
is available free of charge via the Internet at http://pubs.acs.org.
2,5,5-Trimethyl-tetracyclo[6.3.0.0.1,302,6]undec-9-en-4-one (34).
A solution of 23a (0.075 g, 0.371 mmol) in degassed acetone
JO062416M
J. Org. Chem, Vol. 72, No. 6, 2007 2067