Photochemistry of arylidene-β-ionones: A highly efficient route to novel tricyclic ketones through intramolecular, exoselective photochemical (4 + 2) cycloadditions, occurring only in an aqueous-organic solvent

Article abstract of DOI:10.1021/jo010963w

(E,E)-Arylidene-β-ionones (1a-f) are converted to 1,7,7-trimethyl-3-(E-2′-arylethenyl)-2-oxabicyclo-[4.4.0]deca-3, 5-dienes (3a-f, ～90%) by irradiating in anhydrous solvents. Irradiation of (3a-f) in aqueous methanol results in Z,E-arylidene-β-ionones (2)

Full text of DOI:10.1021/jo010963w

2234
J . Org. Chem. 2002, 67, 2234-2240
P h otoch em istr y of Ar ylid en e-â-ion on es: A High ly Efficien t Rou te
to Novel Tr icyclic Keton es th r ou gh In tr a m olecu la r , Exoselective
P h otoch em ica l (4 + 2) Cycloa d d ition s, Occu r r in g On ly in a n
Aqu eou s-Or ga n ic Solven t
Mohan Paul S. Ishar,*,† Rajinder Singh,† Kamal Kumar,† Gurmit Singh,† D. Velmurugan,‡
A. Subbiah Pandi,‡ S. S. Sundra Raj,§ and H. K. Fun§
Department of Pharmaceutical Sciences, Guru Nanak Dev University, Amritsar 143005, Punjab, India,
Department of Crystallography and Biophysics, University of Madras, Guindy campus, Chennai 600 025,
Tamilnadu, India, and X -ray Division, Department of Physics, Universiti Sains Malaysia,
Pinang, Malaysia
mpsishar@angelfire.com
Received October 1, 2001
(E,E)-Arylidene-â-ionones (1a -f) are converted to 1,7,7-trimethyl-3-(E-2′-arylethenyl)-2-oxabicyclo-
[4.4.0]deca-3,5-dienes (3a -f, ∼90%) by irradiating in anhydrous solvents. Irradiation of (3a -f) in
aqueous methanol results in Z,E-arylidene-â-ionones (2), through retro-electrocyclization, which
undergoes an intramolecular, exo-selective [4 + 2] photocycloaddition leading to 11-(exo)-aryl-1,7,7-
trimethyl-tricyclo[4.4.0.12,4]undec-5-ene-3-ones (8a -f, 60-80%). The latter rearrange over silica
gel to afford, quantitatively, 5-aryl-7,11,11-trimethyl-tricyclo[5.4.0.03,6]undec-1-ene-4-ones (5a -f).
Irradiation of 1a -f in aqueous methanol leads to 8a -f, except in case of 1c,f wherein formation,
respectively, of tricyclic ketones 9c (55%) and 9f (80%), derived from photodeconjugation in 2,
followed by intramolecular [4 + 2] cycloaddition, is observed.
In tr od u ction
phototransformation available to conjugated ketones3 and
â-ionone derivatives,4 and also the known lability of
bicyclic systems such as 4 (both under UV irradiations5
and under acidic conditions6), we have recently reinves-
tigated the above phototransformation.7
It has been reported that (E,E)-arylidene-â-ionones
(1a -f) when irradiated under anhydrous conditions
undergo regioselective E-Z isomerization, which is fol-
lowed by 6π-electrocyclization, yielding 1,7,7-trimethyl-
3-(E-2′-arylethenyl)-2-oxabicyclo[4.4.0]-deca-3,5-dienes
(3a -f) in high yields.1 Further it has been reported by
Gandhi et al.2 that 3a -c, on irradiation in aqueous
solvents such as methanol, acetonitrile, and acetone,
undergo an intramolecular phototransformation to yield
11-(endo)-aryl-1,7,7-trimethyl-tricyclo[4.4.0.12,4]undec-5-
en-3-ones (4a -c) in high yield; the latter phototransfor-
mation is postulated to involve an intramolecular pho-
tochemical (πa4 + πs2) cycloaddition in Z,E-arylidene-â-
ionone (2, Scheme 1). In view of the diverse modes of
Initially, compounds 1a -c were irradiated in anhy-
drous benzene, under nitrogen atmosphere, to obtain the
corresponding pyrans 3a -c, which were isolated and
identified spectroscopically.1 Further irradiation of py-
rans 3a -c was carried out in aqueous methanol under
conditions as employed by Gandhi et al.,2 whereupon
column chromatographic resolution of the photolyzates
led to isolation of substances that gave the same melting
points, as well as NMR and other spectroscopic data as
reported for 4a -c.2 However, X-ray crystallographic
structure determination of the compound derived from
3b (earlier assigned as 4b) led to its actual structure as
7,11,11-trimethyl-5-p-tolyl-tricyclo-[5.4.0.03,6]undec-1-
ene-4-one (5b).8 Since the spectroscopic data earlier
attributed to 4a ,c can be successfully explained by
structure 5a ,c, hence it is logical that structures of 4a ,c
shall also revised to 5a ,c, respectively.
* To whom correspondence should be addressed. Fax: +91-183-
258819/20.
† Guru Nanak Dev University.
‡ University of Madras.
§ Universiti Sains Malaysia.
(1) Gandhi, R. P.; Kumar, S.; Aryan, R. C.; Ishar, M. P. S. Synth.
Commun. 1989, 19, 1759.
(2) (a) Gandhi, R. P.; Aryan, R. C. J . Chem. Soc., Chem. Commun.
1988, 1024. (b) Aryan, R. C. Ph.D. Thesis, Submitted to Indian Institute
of Technology, Delhi, New Delhi, 1985 (IIT-Delhi Library Acc. No.
1292).
(3) (a) Baldwin, S. W.; Gross, P. M. In Organic Photochemistry;
Padwa, A., Ed.; Marcell Dekker: New York, 1981; Vol. 5, Chapter 2,
p 162. (b) Elad, O. In Organic Photochemistry; Marcell Dekker: New
York, 1983; Vol. 2, Chapter 2, p 109. (c) Trecker, D. J . In Organic
Photochemistry; Padwa, A., Ed.; Marcell Dekker: New York, 1983; Vol.
2, Chapter 5.
(4) (a) Frei, B.; Eichenberger, H.; Wartburg, B.; Wolf, H. R.; J eger,
O. Helv. Chim. Acta 1977, 60, 2968. (b) Ishii, K.; Lyle, T. A.; Schweizer,
B.; Frei, B. Helv. Chim. Acta 1982, 65, 595 and references therein. (c)
Ishii, K.; Mathies, P.; Nishio, T.; Wolf, H. R.; Frei, B.; J eger, O. Helv.
Chim. Acta 1984, 67, 1175. (d) van Wageningen, A.; Cerfontain, H.;
Greenevasen, A. J . J . Chem. Soc., Perkin Trans. 2 1975, 1283. (e) van
Wageningen, A.; Cerfontain, H. Tetrahedron Lett. 1972, 3679. (f)
Cerfontain, H.; Geenevasen, J . A. J . Tetrahedron 1981, 37, 1571.
(5) (a) Erman, W. F. J . Am. Chem. Soc. 1967, 89, 3828. (b) Erman,
W. F.; Kretschmar, H. C. J . Am. Chem. Soc. 1967, 89, 3842 and
references therein.
(6) (a) Erman, W. F.; Treptow, R. S.; Bakuzis, P.; Wenkert, E. J .
Am. Chem. Soc. 1971, 93, 657.
(7) Doubts regarding the assigned structure were also raised by the
recorded observation2b that the compounds assigned as 4a -c did not
rearrange under acidic conditions, which was in sharp contrast to
reported6 facile rearrangement of related systems under acidic condi-
tions.
(8) The X-ray structure plot of 5b (Figure 1) refers to data of crystal
system monoclinic; space group P21/c; unit cell dimensions
a )
11.0125(4) Å, b ) 14.2946(4) Å, c ) 11.8980(4) Å, R ) γ ) 90°, â )
110.8180(10)°; V ) 1750.70(10) Å3; Z ) 4; calculated density ) 1.117
Mg/m3; final R indices [I >2σ(I)] R1 ) 0.0568, wR2 ) 0.1414; R indices
(all data) R1 ) 0.1224, wR2 ) 0.1753; goodness-of-fit on F2 ) 0.825.
10.1021/jo010963w CCC: $22.00 © 2002 American Chemical Society
Published on Web 03/08/2002

Photochemistry of Arylidene-â-ionones
J . Org. Chem., Vol. 67, No. 7, 2002 2235
Sch em e 1
Sch em e 2
It has been reported6 in the literature that cyclobu-
tanones related to 5a -c, e.g., 2,4,4-trimethylbicyclo[3.2.0]-
hept-2-en-7-one (7), are easily derived from highly labile
2,4,4-trimethylbicyclo[3.1.1]hept-2-en-6-one (6) under both
acidic and basic conditions (Scheme 2).
The next step, therefore, was to establish whether
compounds 5a -c are generated directly during irradia-
tion of 3a -c, respectively, or are derived from rearrange-
ment of an initially formed photoproduct. Toward this
end compound 3b was irradiated in aqueous methanol
under the same conditions as employed earlier, and the
1H NMR spectrum of the crude residue, obtained on
concentration of photolyzate under vacuum, was re-
corded. To our great surprise the 1H NMR spectrum
clearly indicated that not even a trace of 5b was present.
Similar absence of 5a ,c in the crude photolyzates ob-
tained, respectively, from 3a ,c was, subsequently, estab-
lished by the 1H NMR spectral monitoring. These 1H
NMR spectra also indicated that identical types of
photoproducts are initially produced in all the cases.
However, when these photolyzates were passed through
a silica gel column or their chloroform solutions were
stirred with silica gel for 3 h, the photoproducts were
quantitatively converted to corresponding 5.9 These
experiments clearly established that 5a -c are not pro-
duced directly on irradiation but rather are derived from
rearrangement of an initially formed photoproduct on
silica gel. However, it was not possible to isolate the
initially formed photoproduct in requisite pure form for
its characterization as it resisted attempts at crystal-
Sch em e 3
lization from the photolyzate and during attempted
chromatographic purification it was quantitatively con-
verted to corresponding 5.
Taking cognizance of the similarity between the NMR
spectral features of the elusive initially formed photo-
product and the NMR spectral data reported for 11-(exo)-
p-bromophenyl-1,7,7-trimethyl-tricyclo[4.4.0.12,4]undec-
5-en-3-ones (8d )10 (Scheme 3), the investigations were
subsequently extended to (1d ,e). The arylidene-â-ionones
(1d ,e) were converted to the corresponding pyrans (3d ,e)
by irradiating their anhydrous benzene solutions under
nitrogen atmosphere; the latter were isolated by column
chromatography and identified spectroscopically. When
3d ,e were irradiated in aqueous methanol, and after
completion of reaction (TLC, 3.5 h) the photolyzates were
1
concentrated under vacuum and H NMR spectra of the
crude products were recorded, they revealed the forma-
(9) The crude photolysates were >80% pure as indicated by TLC
and 1H NMR; however, the major product was indistinguishable from
5a -c on TLC.
(10) It has been reported2b that irradiation of pyrans 3a -c under
aqueous conditions leads to the endo products (4a -c), whereas
irradiation of 3d affords (after chromatographic resolution) the cor-
responding exo product (8d ). This differing behavior has been at-
tributed to a change in the nature of involved frontier interaction in
the photocycloaddition step!
F igu r e 1.

2236 J . Org. Chem., Vol. 67, No. 7, 2002
Ishar et al.
Sch em e 4
Sch em e 5
tion of photoproducts having critical NMR spectral
features similar to those displayed by photoproducts
derived from 3a -c. However, in the case of 3d ,e the
photoproducts (8d ,e) crystallized out of the crude pho-
tolyzates. These were recrystallized from hexane, and
complete spectroscopic data were recorded. A comparison
of the spectral data with the related systems5,6,11 led to
characterization of these compounds as 11-(exo)-aryl-
1,7,7-trimethyl-tricyclo[4.4.0.12,4]undec-5-en-3-ones (8d,e),
thus confirming the earlier assignment of 8d .2a,10 Here
1
however, in the case of 1c,f the H NMR of photolyzates
indicated the formation of another product in each case,
besides 8c and 8f, respectively. Consequently, the pho-
tolyzates derived from 1c,f were resolved column chro-
matographically to obtain 5c,f and the other products,
which have been characterized as 9c and 9f, respectively
(Scheme 5).
1
the presence of a singlet in the H NMR spectrum at δ
3.09 assigned to C11-H(endo) was critical, i.e., lack of its
observable coupling with C2-H and C4-H led to the
assigned stereochemistry at C11. However, 8d ,e on stir-
ring with silica gel or passing through a silica gel column
underwent facile rearrangement to corresponding 5-aryl-
7,11,11-trimethyl-tricyclo[5.4.0.03,6]undec-1-ene-4-ones
(5d ,e), which contradicts the reported2b isolation of 8d
after column chromatography over silica gel. The inves-
tigations were also extended to 3f, and the results so far
have established that irradiation of 3a -f in aqueous
solvent produces only the 11-(exo)-aryl-1,7,7-trimethyl-
tricyclo[4.4.0.12,4]undec-5-en-3-ones (8a -f) and that the
latter undergo facile rearrangement in the presence of
silica gel to the corresponding 7,11,11-trimethyl-5-
aryltricyclo[5.4.0.03,6]undec-1-ene-4-ones (5a -f, Scheme
3).
Verification of the formation of tricyclic ketones 8a -e
as a photochemical transformation has been established
by refluxing the (E,E)-arylidene-â-ionones (1a -c) in
aqueous pyridine,12 wherein their isomerization to (Z,E)-
arylidene-â-ionones is accompanied with electrocycliza-
tion to pyrans 3a -c (Scheme 4). Although the yield of
3a -c under thermal conditions is low (<30%) and a
complex mixture is obtained, cycloaddition leading to
formation of 8a -c (hence 5a -c) is not observed.
Direct irradiation of (E,E)-arylidene-â-ionones 1a -f in
MeOH-H2O, under nitrogen atmosphere, was taken up
next because it has been reported2b that it gives similar
products as are obtained on irradiation of corresponding
pyrans,13 though with slightly reduced yields. A 1H NMR
examination of the crude photolyzates obtained on ir-
radiation of 1a -f in aqueous methanol revealed the
formation of only the corresponding [4 + 2] adducts
(8a ,b,d ,e) in the case of photolyzates of (1a ,b,d ,e);
The structures of 9c,f have been established by rigor-
ous spectroscopic analysis including 2D NMR (1H COSY
and Het COSY) and DEPT 13C NMR spectral measure-
ments. The initial inference regarding involvement of a
methyl group in phototransformation (1c,f f 9c,f) was
based on NMR spectra that indicated the presence of only
two methyl groups. Complete 1H NMR assignments were
aided by known, rigorously worked out 1H NMR cou-
plings in the case of closely related bicyclo[3.2.1]oct-2-
ene systems.14 Here again the lack of 1H coupling between
C12-H and C3-H/C6-H, the presence of long-range coupling
between C12-H and C5-Hb (due to W relationship, ob-
1
served by H COSY), coupling involving C3-H and C6-H
(due to W relationship, observed by 1H COSY), and a
coupling pattern involving C6-H with C5-H’s as also C3-H
with C2-H’s were quite instructive.13 The structural
conclusions are also corroborated by 13C NMR spectral
assignments.
Mechanistically, the conversion of 3a -f to 8a -f in-
2
volves a photochemical, exo-selective (πs4 + πa , Scheme
6) addition in (Z,E)-arylidene-â-ionone (2); the latter is
derived from photochemical retro-electrocyclization of
3a -f.12,15 Since this intramolecular cycloaddition occurs
only in aqueous solvent and is not realized in solvents
such as dry CH3CN,2 the role of water may have to be
identical with the generally observed role of aqueous
medium in facilitating [4 + 2] cycloadditions,16 though a
possible involvement of intramolecular electron transfer
and intermediates such as A and B may be the other
plausible alternative (Scheme 6). Involvement of inter-
mediates such as B has been postulated in photoreorga-
nization of verbenone to bicyclic ketones related to 8.5
The mechanism of rearrangement of bicyclic-ketones
related to 8 to cyclbutanones of type 5, including stereo-
(11) (a) Kaplan, F.; Schulz, C. O.; Weisleder, D.; Klopfenstein, C. J .
Org. Chem. 1968, 33, 1728. (b) Bates, R. B.; Thalacker, V. P. J . Org.
Chem. 1968, 33, 1730.
(12) Marvell, E, N.; Chadwick, T.; Caple, G.; Gosink, T.; Zimmer,
G. J . Org. Chem. 1972, 37, 2992.
(14) (a) J efford, C. W.; Mahajan, S.; Waslyn, J .; Waegell, B. J . Am.
Chem. Soc. 1965, 87, 2183. (b) Waegell, B.; J efford, C. W. Bull. Soc.
Chim. France 1964, 844. (c) J efford, C. W.; Waegell, B.; Ramey, K. J .
Am. Chem. Soc. 1965, 87, 2191.
(15) Marvell, E, N.; Caple, G.; Gosink, T. A.; Zimmer, G. J . Am.
Chem. Soc. 1966, 88, 619.
(13) Direct irradiation of only 1a -d in aqueous methanol has been
described. 2b
(16) Kumar, A. Chem. Rev. 2001, 101, 1 and references therein.

Photochemistry of Arylidene-â-ionones
J . Org. Chem., Vol. 67, No. 7, 2002 2237
Sch em e 6
Sch em e 7
chemical disposition around cyclobutanone ring, has been
well investigated and has been reported to proceed under
a variety of conditions including acid catalysis.6 The
important aspect that requires mentioning here is that
conversion of 8 to 5 on silica gel is quantitative and
stirring of 8b,e with pTSA (catalytic amount) in chloro-
form led to 5b,e along with a mixture of other products
(Tlc, 1H NMR); no attempt was made to isolate the
products, though formation of a number of them is
anticipated.6
of 3f in aqueous methanol.17 This influence of relatively
electron-rich aryl groups (p-methoxyphenyl and furan-
2-yl) is not in keeping with the known involvement of
n-π* photoexcited state of carbonyl group in H-abstrac-
tion and suppression of H-abstraction when the carbonyl
group is extensively conjugated, particularly with electron-
rich π-systems; in the latter case the π-π* triplet is
reported to be lower than the n-π* triplet.18
Con clu sion s
Formation of 9c,f from 1c,f, quite apparently, involves
a photochemical H-abstraction in 2, by the carbonyl
oxygen leading to deconjugated intermediate (C), which
is followed by an intramolecular exo-selective [4 + 2]
cycloaddition; such intramolecular H-abstraction and
deconjugation are precedented in â-ionone photochem-
istry.4
Though the mechanistic aspects including the role of
aqueous solvents19 as well as possible involvement of
intramolecular electron transfer/exciplexes in the ob-
served phototransformations require further probing, the
present investigations have led to correction of structural
However, two interesting observations of the present
investigations are the role of aqueous solvent in promot-
ing the H-abstraction and cycloaddition, and the role of
the nature of the aryl group. In the case of irradiation of
3c in aqueous methanol, no detectable amount of 9c is
produced and only 8c (and hence 5c) is produced in 70%
yield, whereas direct irradiation of 1c generates 9c to
the extent of 55%. On the other hand, direct irradiation
of 1f in aqueous methanol produces 9f to the extent of
80% and 8f is also produced (∼40%) during irradiation
(17) Compound 9f was missed during initial irradiation of 3f in
aqueous methanol as a result of close Rf of 9f and 8f and probably the
relative instability of 5f, 8f, and 9f. However after isolation and
characterization of 9f from direct irradiation of 1f in aqueous methanol,
a reinspection of the 1H NMR spectrum of crude obtained from the
irradiation of 3f in aqueous methanol revealed that 8f and 9f were
formed approximately in the ratio of 60:40.
(18) (a) Wagner, P. J .; Siebert, E. J . J . Am. Chem. Soc. 1981, 103,
7329. (b) Wagner, P. J .; Kemppainen, A. E.; Scott, H. N. J . Am. Chem.
Soc. 1973, 95, 5604. (c) Wagner, P. J . Acc. Chem. Res. 1989, 22, 83.
(19) During present investigations it has been observed that ∼2%
of H2O is the optimum amount; increasing the amount of water beyond
2% leads to formation of multiple products.

2238 J . Org. Chem., Vol. 67, No. 7, 2002
Ishar et al.
chloroform as eluant, yielded 5-aryl-7,11,11-trimethyl-tricyclo-
[5.4.0.03,6]undec-1-ene-4-ones (5a -f), whose physical and spec-
troscopic data are as follows.
assignments, establishment of exo-selectivity of these
photocycloadditions, and discovery of an alternative mode
of phototransformation of arylidene-â-ionones, i.e., for-
mation of 9c,f. These high throughput phototransforma-
tions, which involve rather uncommon intramolecular,
stereoselective [4 + 2] cycloadditions,20 have provided
easy access to tricyclic cyclobutanones and complex
molecular frameworks. Many such cyclobutanones have
proven to be extremely versatile synthons involved in the
total synthesis of a number of important biologically
active molecules.21
5-P h en yl-7,11,11-tr im eth yl-tr icyclo[5.4.0.03,6]u n d ec-1-
en e-4-on e (5a ). Colorless solid, yield 80%, mp 75-76 °C
(hexane). IR (KBr)/cm-1: 1770(CdO), 1600(m), 1500(m),
1460(m), 1380(w-m). 1H NMR (CDCl3, 200 MHz): δ 7.28-7.23-
(m, 5H, arom.-Hs), 5.43(br d, 1H, J ) 3.0 Hz, C2-H), 4.4(dd,
1H, J 5,6 ) 6.8, J 5,3 ) 3.3 Hz, C5-H), 4.03-3.98(m, 1H, C3-H),
2.65(t, 1H, J ∼ 6.8 Hz, C6-H), 1.84-1.46(m, 6H, 3 × -CH2),
1.31(s, 3H, -CH3), 1.18(s, 3H, -CH3), 1.17(s, 3H, -CH3). 13C
NMR (CDCl3, 50 MHz): δ 201.3(CdO), 158.8(C1), 136.5(q.
arom.), 128.1(q. arom.), 126.9(CH), 126.22(CH), 117.8(C2),
66.4(C5), 62.1(C3), 49.2(C11), 48.4(C6), 40.3(C10), 34.5(C7), 32.9-
(C8), 31.4(-CH3), 29.7(-CH3), 28.5(-CH3), 18.8(C9). MS: m/z
281(M+ + 1, 7), 280(M+, 22), 238(98), 182(42), 168(50), 163(97),
162(28), 154(75), 148(96), 132(30), 130(20), 129(20), 120(20).
Anal. Calcd for C20H24O: C, 85.67; H, 8.63. Found: C, 85.61;
H, 8.68.
Exp er im en ta l Section
Gen er a l. Starting materials and reagents were purchased
from commercial suppliers and used after further purification
(crystallization/distillation). Arylidene-â-ionones were pre-
pared by condensing the corresponding aldehydes with â-ion-
one (Fluka) in the presence of sodium hydroxide in a mixture
of water and ethyl alcohol.1,2 NMR chemical shifts are reported
in ppm as downfield displacements from tetramethylsilane
used as the internal standard, and J values are in Hertz. All
melting points, measured in open glass capillary, are uncor-
rected.
Gen er a l P r oced u r e for Ir r a d ia tion of Ar ylid en e-â-
ion on es (1a -f) in Ben zen e. Arylidene-â-ionones 1a -f (500
mg) were dissolved in anhydrous benzene and taken in an
immersion well type Pyrex glass, water-cooled photoreactor,
and the solutions were purged with dry oxygen-free N2 for at
least 15 min prior to irradiation. The irradiation was carried
out for 0.5 h with a 125-W medium pressure Hg arc placed
coaxially inside the reactor, and N2 was continuously bubbled
during irradiation. At the end of reaction (TLC), solvent was
removed from photolyzates under reduced pressure using an
Eyela rotary evaporator, and products were separated by
column chromatography over silica gel (Acme Synthetic Chemi-
cals, Mumbai, India, 60-120 mesh, 20 g, packed in hexane),
using hexane as eluant, to obtain 3a -f. Identity of the
products was established by spectroscopic analysis.2
Gen er a l P r oced u r e for Ir r a d ia tion of 1,7,7-Tr im eth yl-
3-(E-2′-a r ylet h en yl)-2-oxa b icyclo[4.4.0]d eca -3,5-d ien es
(3a -f) in Aq u eou s Met h a n ol. 1,7,7-Trimethyl-3-(E-2′-
arylethenyl)-2-oxabicyclo[4.4.0]deca-3,5-dienes (3a -f, 400 mg)-
were dissolved in a mixture of methanol (250 mL) and water
(5 mL) and taken in an immersion well type Pyrex glass,
water-cooled photoreactor, and the solutions were purged with
dry oxygen-free N2 for at least 15 min prior to irradiation. The
irradiation was carried out for 3.5 h with a 125-W medium
pressure Hg arc placed coaxially inside the reactor, and N2
was continuously bubbled during irradiation. Progress of the
reaction was monitored by TLC. At the end of reaction solvent
was distilled off from photolyzates under reduced pressure
using an Eyela rotary evaporator. Products were extracted
with hexane, and separation by column chromatography over
silica gel (Acme Synthetic Chemicals, Mumbai, India, 60-120
mesh, 15 g, columns packed in hexane) using hexane-
5-p-Tolyl-7,11,11-tr im eth yl-tr icyclo[5.4.0.03,6]u n d ec-1-
en e-4-on e (5b). Colorless solid, yield 78%, mp 60-61 °C
(hexane). IR (KBr)/cm-1: 1766.7(CdO), 1595(m), 1517.9(m),
1458(m), 1440(w), 1371(m), 1357.8(m), 1170(w), 1084(m),
1
1005(w), 980(w), 831(m). H NMR (CDCl3, 200 MHz): δ 7.11-
(s, 4H, arom.-Hs), 5.44(br d, 1H, J ) 2.1 Hz, C2-H), 4.45(dd,
1H, J 5,6 ) 6.8, J 3,5 ) 3.0 Hz, C5-H), 4.08-4.00(m, 1H, C3-H),
2.68(dis t, 1H, J ≈ 6.8 Hz, C6-H), 2.32(s, methyl on aromatic
ring), 1.88-1.48(m, 6H, 3 × -CH2), 1.30(s, 3H, -CH3), 1.18(s,
3H, -CH3), 1.17(s, 3H, -CH3). 13C NMR (CDCl3, 50 MHz): δ
205.78(CdO), 159.59(C1), 136.10(q. arom.), 133.63(q. arom.),
129.14(CH), 127.16(CH), 117.65(C2), 66.82(C5), 62.47(C3), 49.68-
(C11), 48.59(C6), 40.48(C10), 34.64(C7), 32.84(C8), 31.41(-CH3),
28.73(-CH3), 28.46(-CH3), 21.02(methyl on aromatic ring),
18.82(C9). MS: m/z 295(M+ + 1, 6), 294(M+, 26), 279(60),
266(40), 251(25), 162(49), 147(100), 132(87), 119(15), 91(18),
77(11). Anal. Calcd for C21H26O: C, 85.67; H, 8.90. Found: C,
85.62; H, 8.96.
5-p-An isyl-7,11,11-tr im eth yl-tr icyclo[5.4.0.03,6]u n d ec-1-
en e-4-on e (5c). Colorless solid, yield 70%, mp 96-97 °C
(hexane). IR (KBr)/cm-1: 1775(CdO), 1622(m), 1591(m), 1521-
(w-m), 1478(m), 1451(m), 1308(m), 1260(m-s), 1186(m),
1
853(m), 830(m). H NMR (CDCl3, 200 MHz): δ 7.10(d, 2H, J
) 8.6 Hz, arom.-Hs), 6.81(d, 2H, J ) 8.6 Hz, arom.-Hs), 5.43-
(br d, 1H, J ) 2.1 Hz, C2-H), 4.40(dd, 1H, J 5,6 ) 6.8, J 3,5 ) 3.0
Hz, C5-H), 4.06-4.00(m, 1H, C3-H), 3.77(s, 3H, -OCH3), 2.62-
(t, 1H, J ≈ 6.3 Hz, C6-H), 1.87-1.47(m, 6H, 3 × -CH2), 1.29(s,
3H, -CH3), 1.17(s, 3H, -CH3), 1.16(s, 3H, -CH3). 13C NMR
(CDCl3, 50 MHz): δ 202.06(CdO), 158.09(C1), 158.01(q. arom.),
128.41(CH), 117.86(C2), 114.12(CH), 67.76(C5), 62.23(C3), 55.20-
(-OCH3), 49.84(C11), 49.00(C6), 40.64(C10), 34.79(C7), 33.02(C8),
31.58(-CH3), 28.90(-CH3), 28.64(-CH3), 19.00(C9). MS: m/z 311-
(M+ + 1), 310(M+), 296(10), 295(45), 282(52), 268(19), 267(93),
211(17),148(100), 147(15), 121(90), 91(18), 71(8). Anal. Calcd
for C21H26O2: C, 81.25; H, 8.44. Found: C, 81.19; H, 8.50.
5-p-Br om op h en yl-7,11,11-tr im eth yl-tr icyclo[5.4.0.03,6]-
u n d ec-1-en e-4-on e (5d ). Colorless solid, yield 80%, mp 84-
85 °C (hexane). IR (KBr)/cm-1: 1764(CdO), 1593.4(s), 1541(m),
1508(m), 1474(w), 1458(m), 1385(m), 1354(m), 1090(m), 853(m),
1
(20) Some of the common examples of photochemical [4 + 2]
cycloadditions are (a) Zimmerman, H. E.; Iwamura, H. J . Am. Chem.
Soc. 1970, 92, 2015. (b) Hart, H.; Miyashi, T.; Buchanan, D. N.; Sasson,
S. J . Am. Chem. Soc. 1974, 96, 4857. (c) Yoon, H.; Chae, W. Tetrahedron
Lett. 1997, 38, 5169. (d) Lambert, J . J . M.; Laarhover, W. H. Recl. Trav.
Chim. Pays-Bas. 1984, 103, 131. (e) Seeley, D. A. J . Am. Chem. Soc.
1972, 94, 4378.
(21) (a) Paquette, L. A.; Heidelbaugh, T. M. Synthesis 1998, 495.
(b) Corey, E. J .; Carpino, P. Tetrahedron Lett. 1990, 31, 7555. (c)
Collins, P. W.; Djuric, S. W. Chem. Rev. 1993, 93, 1533. (d) Kertesz,
D. J .; Kluge, A. F. J . Org. Chem. 1988, 53, 4962. (e) Kluge, A. F.;
Kertesz, D. J .; O-Yang, C.; Wu, H. Y. J . Org. Chem. 1987, 52, 2860.
(f) Collington, E. W.; Finch, H.; Wallis, C. J . Tetrahedron Lett. 1983,
24, 3121. (g) Collington, E. W.; Wallis, C. J .; Waterhouse, I. Tetrahe-
dron Lett. 1983, 24, 3125. (h) Audran, G.; Mori, K. Eur. J . Org. Chem.
1992, 57, 7. (i) Cotterill, I. A.; Roberts, S. M. J . Chem. Soc., Perkin
Trans. 1 1992, 2585. (j) Greene, A. E.; Luche, M. J .; Depres, J . P. J .
Am. Chem. Soc. 1983, 105, 2435. (h) Adam, J . M.; Ghosez, L.; Houk,
K. N. Angew. Chem. 1999, 38, 2728.
831(m). H NMR (CDCl3, 300 MHz): δ 7.43(d, 2H, J ) 8.4 Hz,
arom.-Hs), 7.10(d, 2H, J ) 8.4 Hz, aroma.-Hs,), 5.4(d, 1H, J )
2.1 Hz, C2-H), 4.44(dd, 1H, J 5,6 ) 6.9, J 3,5 ) 3.0 Hz, C5-H),
4.08-4.02(m, 1H, C3-H), 2.65(t, 1H, J ) 6.3 Hz, C6-H), 1.76-
(m, 2H, -CH2), 1.67-1.49(overlapping multiplets, 4H, 2 ×
-CH2), 1.30(s, 3H, -CH3), 1.18(s, 3H, -CH3), 1.16(s, 3H, -CH3).
13C NMR (CDCl3, 75 MHz): δ 205.22(CdO), 159.86(C1), 135.66-
(q. arom.), 131.55(CH), 128.97(CH), 120.59(q. arom.), 117.43-
(C2), 67.03(C5), 61.99(C3), 49.75(C11), 48.41(C6), 40.41(C10),
34.65(C7), 32.91(C8), 31.37(-CH3), 28.65(-CH3), 28.44(-CH3),
18.80(C9). MS: m/z 361(M+ + 2, 4), 360(M+ + 1, 15), 359(M+,
12), 358(16), 345(21), 343(17), 333(20), 332(78), 331(22), 330(82),
318(42), 317(85), 316(45), 315(85), 284(30), 283(37), 277(32),
275(20), 263(32), 262(29), 261(54), 260(23), 259(30), 248(33),
247(49), 246(23), 245(50), 147(100). Anal. Calcd for C20H23
BrO: C, 66.86; H, 6.45. Found: C, 66.79; H, 6.50.
-

Photochemistry of Arylidene-â-ionones
J . Org. Chem., Vol. 67, No. 7, 2002 2239
5-p-Ch lor op h en yl-7,11,11-tr im eth yl-tr icyclo[5.4.0.03,6]-
u n d ec-1-en e-4-on e (5e). Colorless solid, yield 80%, mp 99-
100 °C (hexane). IR (KBr)/cm-1: 1767(CdO), 1593.4(s), 1509(m),
1491(w), 1458(m), 1385(m), 1354(m-s), 1088(w), 1071(w),
1.65-1.52(m, 2H, -CH2), 1.42-1.29(m, 2H, -CH2), 1.40(s, 3H,
-CH3), 1.14(s, 3H, -CH3), 1.10(s, 3H, -CH3). 13C NMR (CDCl3,
75 MHz): δ 203.27(CdO), 150.78(C6), 140.06(q. arom.), 131.77-
(CH), 128.59(CH), 124.74 (C5), 120.64(q. arom.), 76.78(C4),
61.59(C11), 52.12(C7), 43.46(C2), 41.89(C8), 38.86(C10), 35.97-
(C1), 31.77(-CH3), 27.56(-CH3), 26.15(-CH3), 18.86(C9). MS: m/z
361(M+ + 2, 3), 360(M+ + 1, 14), 359(M+, 10), 358(16), 345(74),
344(16), 343(71), 332(16), 330(16), 318(24), 317(85), 316(25),
315(85), 283(18), 261(40), 259(24), 248(23), 247(47), 245(45),
237(29). Anal. Calcd for C20H23BrO: C, 66.86; H, 6.45. Found:
C, 66.78; H, 6.37.
1
1015(w), 853(m), 831(m). H NMR (CDCl3, 300 MHz): δ 7.28
(d, 2H, J ) 8.4 Hz, arom.-Hs), 7.16 (d, 2H, J ) 8.4 Hz, arom.-
Hs), 5.43 (d, 1H, J ) 2.1 Hz, C2-H), 4.46 (dd, 1H, J 5,6 ) 6.8,
J 3,5 ) 3.0 Hz, C5-H), 4.09-4.05(m, 1H, C3-H), 2.65 (t, 1H, J ∼
6.3 Hz, C6-H), 1.86-1.79 (m, 2H, -CH2), 1.67-1.49(m, 4H, 2 ×
-CH2), 1.30 (s, 3H, -CH3), 1.17 (s, 3H, -CH3), 1.15 (s, 3H, -CH3).
13C NMR (CDCl3, 75 MHz): δ 205.61(CdO), 159.96(C1), 135.18-
(q. arom.), 132.62(q. arom.), 128.68(CH), 117.52(C2), 67.09(C5),
62.02(C3), 49.84(C11), 48.54(C6), 40.48(C10), 34.72(C7), 32.98-
(C8), 31.42(-CH3), 28.72(-CH3), 28.49(-CH3), 18.84(C9). MS: m/z
316(M+ + 2, 6), 315(M+ + 1, 5), 314(M+, 25), 301(38), 300(20),
299(96), 289(15), 288(18), 287(9), 286(35), 271(23), 251(9),
165(13), 163(9), 162(58), 148(13), 147(100). Anal. Calcd for
11-(exo)-p -C h lo r o p h e n y l-1,7,7-t r im e t h y l-t r ic y c lo -
[4.4.0.12,4]u n d ec-5-en -3-on e (8e). Colorless solid, yield 80%,
mp 140-141 °C (hexane). IR (KBr)/cm-1: 1770.5(CdO), 1595(br),
1495(s), 1458(m), 1420(w), 1375(m), 1363(s), 1352(w), 1242(w),
1221(w), 1190(w), 1150(w), 1107(m), 1090(m), 1045(m-s),
1015(m-s), 978(w), 895(m), 864(w), 839(w), 812(s), 773(m),
1
C
20H23ClO: C, 76.30; H, 7.36. Found: C, 76.21; H, 7.41.
704(w), 663(m). H NMR (CDCl3, 200 MHz): δ 7.29 (d, 2H, J
7,11,11-Tr im eth yl-5(fu r an -2-yl)-tr icyclo[5.4.0.03,6]u n dec-
) 8.4 Hz, arom.-Hs), 7.16 (d, 2H, J ) 8.4 Hz, arom.-Hs), 5.99
(d, J ) 7.7 Hz, C5-H), 3.27 (t, J ≈ 8.1 Hz), 3.14 (s, 1H, C11-H),
2.78 (d, J 2,4 ) 8.4 Hz, C2-H), 1.90-1.84(m, 2H, -CH2), 1.67-
1.26 (m, 4H, 2 × -CH2 with a sharp singlet, 3H at δ 1.42, -CH3),
1.16 (s, 3H, -CH3), 1.12 (s, 3H, -CH3). 13C NMR (CDCl3, 75
MHz): δ 203.39(CdO), 150.78(C6), 139.53(q. arom.), 132.59-
(q. arom), 128.83(CH), 128.23(CH), 124.75(C5), 76.81(C4),
61.66(C11), 52.17(C7), 43.39(C2), 41.89(C8), 38.86(C10), 35.97-
(C1), 31.78(-CH3),), 27.56(-CH3),), 26.18(-CH3), 18.86(C9). MS:
m/z 316(M+ + 2, 7), 315(M+ + 1, 6), 314(M+, 28), 301(34),
300(22), 299(97), 289(12), 288(15), 286(37), 271(21), 162(61),
148(19), 147(100). Anal. Calcd for C20H23ClO: C, 76.30; H, 7.36.
Found: C, 76.21; H, 7.41.
1-en e-4-on e (5f). Colorless viscous material, yield 60%. IR
(CHCl3)/cm-1: 1777(s), 1565(m), 1500(m), 1462(m), 1453(m),
1435(w), 1367(m), 1214(m), 826(w). 1H NMR (CDCl3, 200
MHz): δ 7.41(d, 1H, J ) 1.8 Hz, C4′-H), 6.35(dd, 1H, J ) 3.1,
1.8 Hz, C3′-H), 6.05(d, 1H, J ) 3.1 Hz, C2′-H), 5.38(br d, 1H, J
) 2.2 Hz, C2-H), 4.51(dd, 1H, J 5,6 ) 6.8, J 3,5 ) 3.1 Hz, C5-H),
4.15-4.03(m, 1H, C3-H), 2.65 (t, 1H, J ∼ 6.3 Hz, C6-H), 1.86-
1.49(m, 6H, 3 × -CH2), 1.27 (s, 3H, -CH3), 1.17 (s, 3H, -CH3),
1.15 (s, 3H, -CH3). MS: m/z 271(M+ + 1, 8), 270(M+, 25),
269(17), 256(24), 255(37), 254(14), 242(8), 241(31), 240(22),
239(7), 227(10), 226(15), 170(8), 169(89). Anal. Calcd for
C
18H22O2: C, 79.96; H, 8.20. Found: C, 79.88; H, 8.27.
Gen er a l P r oced u r e for Ir r a d ia tion of 1,7,7-Tr im eth yl-
Con ver sion of 11-(exo)-Ar yl-1,7,7-tr im eth yl-tr icyclo-
[4.4.0.12,4]u n d ec-5-en -3-on es (8d ,e) to 5-Ar yl-7,11,11-tr i-
m eth yl-tr icyclo[5.4.0.03,6]-u n d ec-1-en e-4-on es (5a ,e) on
Silica Gel. exo-11-Aryl-1,7,7-trimethyl-tricyclo[4.4.0.12,4]undec-
5-en-3-ones (8d ,e, 200 mg) were stirred with silica gel (5 g) in
chloroform (30 mL) for 3 h, when TLC monitoring indicated
their complete consumption. Solvent was distilled off from the
reaction mixture under reduced pressure. Column chroma-
tography over silica gel (Acme Synthetic Chemicals, Mumbai,
India, 60-120 mesh, 5 g, columns packed in hexane) using
hexane-chloroform as eluant yielded 5d ,e quantitatively.
Gen er a l P r oced u r e for Ir r a d ia tion of Ar ylid en e-â-
ion on es (1a -f) in Aq u eou s Met h a n ol a n d Isola t ion of
9c,f. Solutions of 1a -f (400 mg) in a mixture of methanol (250
mL) and water (5 mL) were irradiated for 3.5 h. The photo-
lyzates were concentrated under vacuum, and products were
extracted with hexane. 1H NMR spectrum of the crude oily
residues derived from 1a ,b,d ,e showed the presence of only
8a -f, respectively. However, in case of the photolyzates
derived from 1c,f, the 1H NMR spectrum of the crude oily
residues indicated the presence of some other photoproduct
to the extent of 55% in case of photoltsyate derived from 1c
and 80% in case of 1f, respectively.
3-(E-2′-ar yleth en yl)-oxabicyclo[4.4.0]-deca-3,5-dien es (3a -
e) in Aqu eou s Meth a n ol, Recor d in g of th e 1H NMR
Spectr a of th e Cr u de 11-(exo)-Ar yl-1,7,7-tr im eth yl-tr icyclo-
[4.4.0.12,4]u n d ec-5-en -3-on es (8a -c), a n d Isola tion of 8d ,e.
Solutions of 3a -e (400 mg) in a mixture of methanol (250 mL)
and water (5 mL) were irradiated under above said conditions.
1
The photolyzate was concentrated under vacuum, and the H
NMR spectrum of the crude oily residue was recorded. In the
case of photolyzates derived from 3d ,e, the residual oil when
triturated with hexane yielded solids, which were recrystal-
lized from hexane to obtain pure 8d ,e, for which complete
spectroscopic data was collected.
11-(exo)-p -P h en yl-1,7,7-t r im et h yl-t r icyclo[4.4.0.12,4]-
u n d ec-5-en -3-on e (8a ). 1H NMR (CDCl3, 200 MHz, based on
the spectrum of crude photolyzate): δ 7.36-7.12(m, arom.-Hs),
5.68(d, 1H, J ) 7.6 Hz, C5-H), 3.28(t, 1H, J ≈ 8.1 Hz, C4-H),
3.15(s, 1H, C11-H), 2.74(d, 1H, J ) 8.5 Hz, C2-H), 1.89-0.82-
(overlapping multiplets with sharp singlets at δ1.41, 1.16,
1.12).
1- (exo)-p-Tolyl-1,7,7-tr im eth yl-tr icyclo[4.4.0.12,4]u n d ec-
5-en -3-on e (8b). 1H NMR (CDCl3, 200 MHz, based on the
spectrum of crude photolyzate): δ 7.10(s, 4H, arom.-Hs), 5.97-
(d, 1H, J ) 7.8 Hz, C5-H), 3.29(t, 1H, J ≈ 8.1 Hz, C4-H), 3.11-
(s, C11-H), 2.77(d, J 2,4 ) 8.4 Hz, C2-H), 2.29(s, 3H, -PhCH3),
1.86-0.87(overlapping multiplets with sharp singlets at δ 1.40,
1.15, 1.09).
Column chromatographic (silica gel 100-200 mesh, 30 g,
packed in hexane) separation of the photolyzate derived from
1c (hexane-chloroform 95:5, eluent) yielded 5c (40%) and 12-
(exo)-p-a n isyl-8,8-d im eth yl-tr icyclo[5.4.0.13,6]d od ec-1(7)-
en e-4-on e (9c) (55%) as colorless oil. IR (CHCl3)/cm-1: 3517(m),
2940(s), 2043(w), 1893(w), 1872(w), 1739(s), 1662(s), 1619(s),
1590(m), 1568(w), 1547(w), 1521(s), 1470(s), 1449(s), 1410(w),
1393 (w), 1367(m), 1312(w), 1295(w), 1269(s), 1184(s), 1140(m),
1119(m), 1043(s), 948(m), 906(m), 863(w), 837(s), 803(w), 794-
(m), 782(m), 765(w), 735(w), 713(w), 683(m), 670(m), 645(w),
602(w), 563(m), 534(m), 491(m), 474(m), 453(m), 444(m),
11-(exo)-p-An isyl-1,7,7-tr im eth yl-tr icyclo[4.4.0.12,4]u n dec-
5-en -3-on e (8c). 1H NMR (CDCl3, 200 MHz, based on the
spectrum of crude photolyzate): δ 7.15-7.03(m, arom.-Hs),
6.88-6.72(m, arom.-Hs), 5.97 (d, 1H, J ) 7.8 Hz, C5-H), 3.78-
(s, 3H, -OCH3), 3.28(t, 1H, J ≈ 8.1 Hz, C4-H), 3.11(s, 1H, C11
-
H), 2.70(d, J 2,4 ) 8.3 Hz, C2-H), 1.93-1.00(broad multiplet with
sharp singlets at δ1.40, 1.15, 1.11).
1
11-(exo)-p -B r o m o p h e n y l-1,7,7-t r im e t h y l-t r ic y c lo -
[4.4.0.12,4]u n d ec-5-en -3-on e (8d ). Colorless solid, yield 80%,
mp 108-109 °C (hexane). IR (KBr)/cm-1: 1770.5(CdO), 1593(s),
1491(s), 1460(m), 1421(w), 1393(w), 1375(w), 1361(m), 1242(w),
1221(w), 1190(w), 1150(w), 1105(w), 1043(m-s), 1071(m-s),
1009(s), 978(w), 895(m), 864(w), 837(w), 810(s), 769(w), 703(w),
669(m). 1H NMR (CDCl3, 300 MHz): δ 7.41(d, 2H, J ) 8.4 Hz,
arom.-Hs), 7.08(d, 2H, J ) 8.4 Hz, arom.-Hs), 5.97(d, 1H, J )
431(m). H NMR (CDCl3, 200 MHz): δ 7.04(dd, 2H, J ) 6.7,
2.0 Hz, arom.-Hs), 6.82(dd, 2H, J ) 6.7, 2.0 Hz, arom.-Hs),
3.78(s, 3H, -OCH3), 3.29 (br s, J 3,12 ≈ J 6,12 ≈ 0, 1H, C12-H),
2.85(br d, 1H, J 3,2a ) 5.7 Hz, J 3,2b ≈ 0, C3-H), 2.78(br d, 1H,
J 6,5a ) 6.4 Hz, J 6,5b ≈ 0, C6-H), 2.45(dd, 1H, J 2a,2b ) 15.7, J 3,2a
) 5.7 Hz, C2-Ha), 2.27(dd, 1H, J 5a,5b ) 17.8 Hz, J 6,5a ) 6.4 Hz,
C5-Ha), 2.17 (d, 1H, J ) 15.7 Hz, C2-Hb), 2.01(dd, J ) 17.8, 1.8
Hz, C5-Hb), 1.88-1.81 (m, 2H, C11-Hs), 1.67-1.44 (m, 2H),
1.43-1.34(m, 2H), 1.12(s, 3H, -CH3), 0.96(s, 3H, -CH3). 13C
NMR (CDCl3, 50 MHz): δ 220.11(C4), 158.32(C4′), 143.53 (C7),
7.8 Hz, C5-H), 3.25(t, 1H, J ) 8.0 Hz, C4-H), 3.09(s, 1H, C11
-
H), 2.75(d, 1H, J 2,4 ) 8.5 Hz, C2-H), 1.93-1.78(m, 2H, -CH2),

2240 J . Org. Chem., Vol. 67, No. 7, 2002
Ishar et al.
134.51(C1′), 127.92(C2′, C6′), 124.88(C1), 114.09(C3′, C5′), 55.22-
(-OCH3), 49.79(C3), 49.64(C12), 44.77(C5), 39.80(C6), 39.23(C9),
37.55(C2), 34.45(C8), 29.97(C11), 27.82, 27.64(2 × -CH3), 19.41-
(C10). MS: m/z 311(M+ + 1), 310(M+), 296(6), 253(5), 192(9),
171(9), 162 (12), 161(100). Anal. Calcd for C21H26O2: C, 81.25;
H, 8.44. Found: C, 81.16; H, 8.49.
Hz, C5-Ha), 2.15(overlapping dds, 2H, C2-Hb, C5-Hb), 1.82(m,
2H, C11-Hs), 1.74-1.56(m, 2H), 1.43-1.34(m, 2H), 1.11(s, 3H,
-CH3), 1.00(s, 3H, -CH3). 13C NMR (CDCl3, 50 MHz): δ 220.96-
(C4), 156.56(C1′), 143.14(C7), 142.18(C4′), 125.32(C1), 110.60-
(C2′), 106.04(C3′), 49.98(C3), 45.80(C5), 45.18(C12), 39.57(C9),
36.98(C2), 36.69(C6), 34.75(C8), 30.28(C11), 28.05, 27.87(2 ×
-CH3), 19.63(C10). MS: m/e 271(M+ + 1, 10), 270(M+, 21),
269(19), 256(26), 255(39), 254(11), 242(10), 241(33), 240(26),
226(17), 169(87), 111(46), 98(15), 97(21), 96(21), 94(29), 93(28)
79(50). Anal. Calcd for C18H22O2: C, 79.96; H, 8.20. Found:
C, 79.87; H, 8.27.
Similarly, column chromatographic (silica gel 100-200
mesh, 30 g, packed in hexane) separation of the photolyzate
derived from 1f (hexane-chloroform eluent) yielded 5f (10%)
and 12-(exo)-(fu r a n -2-yl)-8,8-d im eth yl-tr icyclo[5.4.0.13,6]-
d od ec-1(7)-en e-4-on e (9f) (80%) as colorless oil. IR (CHCl3)/
cm-1: 2924(s), 2854(s), 2362(m), 1743(s), 1560(w), 1539(w),
1508(w), 1464(m), 1456(m), 1438(w), 1411(w), 1363(m), 1216(m),
Su p p or tin g In for m a tion Ava ila ble: X-ray crystallo-
graphic data including ORTEP diagram for compound 5b,
details of instrumental analysis, and NMR spectra including
2D NMR spectra for compounds 9c,f. This material is available
free of charge via the Internet at http://pubs.acs.org.
1
823(w), 758(s), 667(w). H NMR (CDCl3, 200 MHz): δ 7.41(d,
1H, J ) 1.8 Hz, C4′-H), 6.35(dd, 1H, J ) 3.1, 1.8 Hz, C3′-H),
6.05(d, 1H, J ) 3.1 Hz, C2′-H), 3.33(br s, J 3,12 ≈ J 6,12 ≈ 0, 1H,
C
12-H), 3.09(d, 1H, J 6,5a ) 6.2 Hz, J 6,5b ≈ 0, C6-H), 2.83(d, 1H,
J 3,2a ) 5.50 Hz, J 3,2b ≈ 0, C3-H), 2.56(dd, 1H, J 2a,2b ) 15.88,
J 3,2a ) 5.5 Hz, C2-Ha), 2.35(dd, 1H, J 5a,5b ) 18.6, J 6,5a ) 6.2
J O010963W