Divergence in photoinduced electron transfer (PET) reactions: A useful strategy towards identifying route-selectivity in mixed ketones

Article abstract of DOI:10.1016/j.tet.2010.12.064

The work utilized photoinduced electron transfer (PET) reactions to identify the preferred photoreaction route in molecules having juxtaposed α,β and β,γ-enones. Such process directly converted 2-hydroxyimino derivatives of 5-benzoylbicyclo[2.2.2]octenone

Full text of DOI:10.1016/j.tet.2010.12.064

Tetrahedron 67 (2011) 1689e1695
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Divergence in photoinduced electron transfer (PET) reactions: a useful strategy
towards identifying route-selectivity in mixed ketones
*
Ananya Sengupta, Indrajit Chakraborty, Asitanga Ghosh, Saswati Lahiri
Department of Organic Chemistry, Indian Association for the Cultivation of Science, Kolkata-700032, India
a r t i c l e i n f o
a b s t r a c t
Article history:
The work utilized photoinduced electron transfer (PET) reactions to identify the preferred photoreaction
Received 20 November 2010
Received in revised form 18 December 2010
Accepted 23 December 2010
Available online 8 January 2011
route in molecules having juxtaposed
imino derivatives of 5-benzoylbicyclo[2.2.2]octenones to the corresponding bicyclo[3.2.1]octane
derivatives. First evidence of Type B rearrangement in -enones having acyl substitution at C -position
a,b and b,g-enones. Such process directly converted 2-hydroxy-
a,
b
g
has been depicted in this work. In rigid mixed enones, this has been found to be generally the preferred
photoreaction route.
Keywords:
Ó 2011 Elsevier Ltd. All rights reserved.
Photoinduced electron transfer (PET)
d-Keto-a,b-enone
Type B rearrangement
Oxime photoreaction
1. Introduction
the b,g-enone part and till now the preference for either of the
routes could not be ascertained conclusively. In the present work
we applied PET reactions to ascertain, which of these photo-
transformation routes is followed in such mixed enones. For this
Recent reports have shown that photoinduced electron transfer
(PET) processes are increasingly becoming useful for constructing
complex molecules because of their chemo-, regio-, and stereo-
selectivity.1 With the emergence of a comprehensive picture of
such reactions using amines,2e4 photochemical reactions involving
amines and chromophores like ketones in their triplet excited
states, have become one of the much popular methods in organic
syntheses. Electron transfer takes place from amine to an elec-
tronically excited ketone-acceptor to form radical ions and to avoid
the reversible back electron transfer (BET) at this stage polar sol-
vents are used to solvate such ion pairs, which then may eventually
undergo different types of reactions depending on the substrates.5
We have reported applications of such reactions in presence of
triethylamine (TEA) to prepare bicyclo[3.2.1]octanones from tricy-
clo[3.3.0.02,8]octanones6 and from bicyclo[2.2.2]octanones7 and for
efficient trans-reduction of C]C bonds.8 In all these cases the
purpose the
imino group (4aec) and that of 3 was replaced by methylene
group (5) and the -enone part in 1c, d and 3 have also been
b,g-enones in 1aec have been replaced by hydroxy-
a,b
replaced by methylene groups (6a,b, 7) (Fig. 2).
2. Results and discussion
2.1. Syntheses of 5-benzoyl-2-hydroxyiminobicyclo[2.2.2]oct-
5-enes (4aec)
The 5-benzoylbicyclo[2.2.2]oct-5-en-2-ones (1aec) prepared7
from the respective silyloxyhexa-1,3-dienes and 1-phenylprop-2-
yn-1-one (monobenzoylacetylene, MBA), were heatedwithw1 equiv
molecules contained
manner (Fig. 1).
While under PET condition such molecules like 1 underwent
one-pot conversion to bicyclo[3.2.1]octanones,7 on direct irradia-
tion quantitative yields of tricyclo[3.3.0.02,8]octanones (2) were
obtained from them (Scheme 1). The 1 to 2 conversion may
a,b- as well as b,g-enones in juxtaposed
β,γ−
enone
O
follow either a Type B rearrangement route from the
part or an oxa-di-pi-methane (ODPM) rearrangement route from
a,b-enone
Ph
O
α,β−
enone
* Corresponding author. E-mail address: ocsl@iacs.res.in (S. Lahiri).
Fig. 1. Model mixed enones.
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.12.064

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A. Sengupta et al. / Tetrahedron 67 (2011) 1689e1695
2.2. Syntheses of 5 and 7
*3
O
O
O
O
Compound 39 on Wittig reaction using 1 equiv of triphenyl
phosphonium methylide following the reported procedure10 gave 5
selectively (Scheme 3). On the other hand, protection of the bridge-
ketone (8), gave the wittig product 9,10 which on hydrolysis yielded
7 in quantitative quantity (Scheme 3).
ODPM via
β.γ−
enone
Ph
Ph
1
O
X
O
α,β−
Type B via
O
enone
Ph 3P=CH 2
1 eq, 73%
Ph
O
Ph
Ph
O
H
H
Y
(O
COPh
3
5 (X= CH2,Y= O)
7
(X= O, Y= CH2)
O
Ethylene glycol,
D-CSA,Toluene,
3h
2
Ph
O
Ph
CAN,
Reflux, 97%
O
Scheme 1.
O
O
O
O
Ph 3P=CH 2
where,
1a:
X
X= O; R1= R2= R3=H
1 eq, 85%
Ph
Ph
1b: X= O; R1= R3= H; R2= Me
R1
R3
R3
H
H
1c:
X= O; R1= H; R2= R3= Me
O
9
8
1d: X= O; R1= R2= Me; R3= H
4a:
Scheme 3.
X= NOH; R1= R2= R3=H
X= NOH; R1= R3= H; R2= Me
R2
1a-d
COPh
4b:
4c: X= NOH; R1= H; R2= R3= Me
2.3. Syntheses of 6a,b
4a-c
Using the same procedure,10 non-enolizable carbonyls in 1c and
1dwereolefinatedtogive6aand6bin48%and41%yields(Scheme4).
These reactions were sluggish presumably because of overall mo-
lecular steric congestion and the starting materials were recovered in
w40% yields in both cases.10 A small amount of 10 (11%) was also
obtained from 1d.
X
O
R1
R3
R3
Ph
R2
6a-b
Ph
H
Y
3,5,7
O
O
where,
3:
where,
a:
R1
X= Y= O
R3
R3
R1
R3
R3
R1= H; R2= R3= Me
b: R1= R2= Me; R3= H
5: X= CH2; Y= O
Ph3P=CH2
1 eq
+
7:
X= O; Y= CH2
R2
6a,b
R2
1c-d
Ph
COPh
COPh
Fig. 2. Enones used for this work.
10
of hydroxylamine hydrochloride in pyridine at 80ꢀ to give quantita-
tive yields of the corresponding monooxime derivatives 4aec
(Scheme 2). Interestingly, the hydroxyimino group in the oxime
was formed exclusively as the thermodynamically stable E-isomer in
the products, which on keeping isomerized to mixtures of EeZ
isomers.
c: R1= H; R2= R3= Me
a: R1= H; R2= R3= Me
d
: R1= R2= Me; R3= H
b
: R1= R2= Me; R3= H
Scheme 4.
2.4. PET reactions of 4aec
The parent compounds 1aec on irradiation are known to give
corresponding tricyclic derivatives of 2.7 However the preferred
route to this transformation is not yet very clear (Scheme 1), If such
O
NOH
transformation originated from the b,g-enone part of the molecule,
R3
R3
R3
R3
along with the general EeZ isomerization at the C]N bond11 the
triplet sensitized aza-di-pi-methane (ADPM) rearrangement, as
observed in similar bridged systems,12,13 were also expected to take
place giving 11aec from 4aec (Scheme 5). When 4aec were irra-
diated in benzene, acetonitrile, methanol or acetone, the product
was solely from the EeZ isomerization at C]N bonds in 4aec. No
NH2OH, HCl (1.2eq)
pyridine, 80º
COPh
R2
1a-c
R2
4a-c
COPh
Scheme 2.

A. Sengupta et al. / Tetrahedron 67 (2011) 1689e1695
1691
trace of the ADPM products 11aec could be identified from these
reactions even on irradiation in presence of sensitizers like aceto-
phenone or benzophenone. In suitable examples, oximes are
known to undergo photo-Beckmann rearrangement in meth-
anol14aed or, cyclization via iminyl radicals14e,f and no such products
could be identified from these reactions. When the irradiation of
4aec were carried out in presence of TEA at 254 nm as well as at
300 nm, similar to their 2-oxo-analogs 1aec7 these compounds
also underwent phototransformation to 8-anti bicyclo[3.2.1]octane
derivatives 12aec (Scheme 6). The 8-anti geometry was confirmed
by the X-ray crystallographic picture of 12c (Fig. 3).15 Unlike their
oxa-counterparts, to accomplish such rearrangements from the
oximes 4aec under comparable reaction conditions, a much longer
time of 5e6 h was needed and yields of the rearranged products
were also much poor compared to their corresponding oxa-analogs.
One of the possible reasons for the inefficiency of these processes in
these oximes may be attributed to the dissipation of a major part of
the excited state energy via ‘free rotor effect’ of the C]N bonds
leading to the EeZ isomerization. Similar to the cases of 1aec,7
formation of 12aec may also occur from 4aec via either of the
three routes. In route ‘a’ the initially formed ketyl radical A may
undergo bond formation to give A0 or, bond migration to give A00. In
route ‘b’ similarly the radical ion B may undergo bond formation to
give B0. Both A0 and B0 then could undergo bond migration followed
by back electron transfer (BET) to give 11aec, which then by PET
mediated tandem bond migration could give 12aec (Scheme 6).
But experimentally it has been shown that 11aec are not formed
from 1aec on irradiation.
Fig. 3. Molecular structure of 12c with thermal ellipsoid drawn at the 50% proba-
bility level (oxime hydroxyl group is disordered over two positions); color code:
C-grey; H-white; O-red.
Furthermore, separately prepared 11b from 2b (Scheme 5) when
subjected to PET reaction in presence of TEA, the product was pri-
marily an EeZ mixture of the 3-hydroxyimino group along with some
unidentified mass and no trace of 12b was identified from the re-
action mixture. On the basis of this observation one can eliminate the
intermediacy of 11aec and hence paths ‘b’ and ‘c’ for the conversion
of 4aec to 12aec. This will then leave only A00 as the intermediate,
X
COPh
formed from the a,b-enone part by path ‘a’, towards the formation of
R3
R3
the rearranged product 12aec. These observations would also sup-
port our earlier proposition that the conversion of 1aec to the cor-
responding bicyclo[3.2.1]octanones follow a similar route.7 For
further confirmation, we carried out the following experiments.
R3
R3
ν
h
O
X= O
R2
1a-c
4a-c
R2
COPh
2a-c
2.5. PET reactions of 5, 6a, b and 7
COPh
R3
R3
ν
h
It was known that 3 on direct irradiation gave a quantitative yield
NOH
X= NOH
of 13 (Scheme 7). On the other hand, when the
was replaced by a methylene group (5)9 it becomes an
with a vinyl group at C- as well as a di-pi-methane systemwith a 4-
b,
g-enone part in 3
a,b-enone
R2
11a-c
g
keto conjugation. Photoreactivity of this compound was found to be
reduced considerably and a prolonged irradiation of 39 h yielded
only 46% of the tetracyclic compound 14 (Scheme 7). Quenching of
Scheme 5.
NOH
NOH
NOH
R3
R3
R3
R3
R3
R3
i. H+
ii. H.
Ph
or,
Ph
R2
R2
'a'
R2
A'
Ph
A''
A
O
O
O
BET with bond
migration
NOH
ET
H
COPh
COPh
R3
R3
R3
R3
'c'
TEA:MeOH
i.ET
R3
R3
NOH
ii. H+
(1:1), hν
iii. H .
R2
4a-c
R2
12a-c
COPh
R2
11a-c
ET
'b'
BET with
NOH
bond migration
NOH
NOH
R3
R3
R3
R3
R2
B'
Ph
R2
B
COPh
O
Scheme 6.

1692
A. Sengupta et al. / Tetrahedron 67 (2011) 1689e1695
X
COPh
H
COPh
X
ν
h , 254 nm
ν
h , TEA-MeOH
(for 3, 5)
2 d (for 5)
Ph
H
Y
3: X=O; Y= O
13: X=O
14:
ν
h , 300 nm, 3h or,
5:
X=CH2; Y= O
15
X=CH2
7
TEA-MeOH (for
)
7
: X= O; Y= CH2
ν
h , 300 nm or,
5': X= Y= CH2
Ph
5'
)
TEA-MeOH (for
O
No reaction
H
16
Scheme 7.
the formation of 14 by triplet quenchers like anthracene confirmed
the reaction as a triplet one and from the phosphorescence band of 5
at 440 nm showed ET¼65 kcal molꢁ1. Lifetime of the triplet was
When the totally olefinated derivative 50, a di-pi-methane sys-
tem was irradiated, only the starting material was recovered in
quantitative yields. This further confirmed the earlier proposition
of facile dissipation of the excited energy via a free rotor mecha-
nism of the exo-methylene group.
Direct irradiation as well as irradiation in presence of TEA gave
the 1,3-acyl shift products 17a, b from 6a,b in 75%, 63%, and 55%,
68% yields, respectively (Scheme 8). Involvement of triplets in
direct irradiation was confirmed from quenching experiments.
found to be 10.6 ms and that suggested an n,
*
p nature of the triplet.
This strongly suggested a Type B route for this transformation
originated from the -enone moiety. This was further verified from
a
,
b
the attempted PET reaction of 5 in presence of TEA. The exo-meth-
ylene moiety is known to dissipate the triplet energy via a rapid
radiationless free rotational decay.16 This would then compete with
the bond migration of the triplet ketyl radicals of 5 formed from its
PET reaction with TEA to give 14 or, 15. In fact, irradiation for 2 days
did not bring about any change in 5, which confirmed the non-in-
Although in b,g-enones the 1,3-acyl shifts on irradiation are known
generally to take place from the singlet states, the present examples
provide some of the less observed 1,3-acyl shifts presumably from
volvement of the
That the -enone in 3 did not really take part in the PET-
rearrangements were further verified from the following reactions.
When the -enone part in 3 was methylated to give 7, the ir-
b
,g-enone part in this rearrangement.
the T1 (n,
p
*
) states.18
b,g
O
Ph
a,b
R1
R3
R3
R1
R3
O
ν
h , 300 nm or,
radiation experiment for 3 h in acetonitrile yielded a 1,3-acyl shift
product 16 in 52% yield (Scheme 7). Quenching experiments
showed this to be a triplet reaction however; failure to observe any
emission band from 7 could not suggest a probable configuration of
the excited state. The structure of 16 was confirmed from its ana-
lytical, spectral and X-ray crystallographic structure (Fig. 4).17
Attempted PET reaction in presence of TEA/MeOH yielded the
same product in 65% yields.
ν
h , TEA-MeOH
R2
6a,b
Ph
R3
17a,b
R2
a: R1= H; R2= R3= Me
a: R1= H; R2= R3= Me
b
b
: R1= R2= Me; R3= H
: R1= R2= Me; R3= H
Scheme 8.
All the above-mentioned examples strongly suggest, in mixed
enones ( - and -) the reaction route in the excited state orig-
inated from the T1(n, ) states of -enones and thus preferably
follow a Type B route instead of an oxa-di-pi-methane route from
the -enone part. Only one example of such Type B rearrange-
a
,b
b,g
p
*
a,b
b,g
ment in non-cyclic system has so far been reported in the litera-
ture19 and the present reactions provide additional examples. The
observation also supports our earlier proposition where we had
preferred a similar route for the PET-induced transformation of
bicyclo[2.2.2]octenones to bicyclo[3.2.1]octanones.7
3. Conclusion
With the help of PET reaction we have identified that in
a mixed
is selectively from the
that, Type B rearrangement, so far observed only in cyclo-
hexenones, is a general process for geometrically rigid -enones
a
,
b
- and
b
,
g
-enone system the photorearrangement route
a,b
-enone part. We have also confirmed
Fig. 4. Molecular structure of 16 with thermal ellipsoid drawn at the 50% probability
level; C-grey; H-white; O-red.
a,b

A. Sengupta et al. / Tetrahedron 67 (2011) 1689e1695
1693
and this route predominates over other probabilities in mixed
enones. While exo-C]C at -position of the enone retards the
2.42 (d, J 18 Hz, 1H), 3.42e3.44 (m, 1 Hz), 6.56 (d, J 7 Hz, 1H),
7.35e7.45 (m, 2H), 7.54e7.57 (m, 1H), 7.77e7.78 (m, 2H). 13C NMR
g
reaction presumably via a ‘free rotor effect’, C]O can actually
facilitates the process. To the best of our knowledge presumably
this is the first example of Type B rearrangement having an acyl
substitution at Cg position.
(125 MHz): d (ppm) 22.5 (CH3), 26.04 (CH2), 33.30 (CH2), 38.13
(CH), 38.44 (CH2), 38.7 (C), 128.49 (CH), 130.07 (CH), 133.05 (CH),
137.76 (C), 138.03 (CH), 148.99 (C), 162.59 (C]N), 195.39 (C]O).
HRMS (ESI) calcd for C16H17NO2: 256.1332; found: [ MþH ]þ
256.1328.
4. Experimental
4.1. General
4.2.3. 5-Benzoyl-2-hydroxyimino-4,7,7-trimethylbicyclo[2.2.2]oct-5-
ene (4c). A solid was obtained from 1c (268 mg, 1 mM). Elution of
the column with 8% EA in PE gave a yellow solid of 4c (241 mg, 90%),
All melting points were measured in a Gallenkamp melting
point apparatus. The IR spectra were recorded on an FTIR-8300
Shimadzu spectrometer. The NMR spectra were recorded in CDCl3
solution and CD3OD solution at 300 and 500 MHz for 1H NMR and
at 75 and 125 MHz for 13C NMR on a Brucker AC-300 spectrometer
and Brucker AC-500 spectrometer, respectively using tetrame-
thylsilane as an internal standard. Elemental analyses were per-
formed with a Heraeus Combustion apparatus or on a 2400 series-II
PerkineElmer CHN analyzer. High Resolution Mass Spectra (HRMS)
were recorded on a Qtof Micro YA263 spectrometer using Elec-
trospray ionization (ESI) technique. UV absorption spectra were
recorded on a Shimadzu UV-2401 PC spectrophotometer. Column
Chromatography was performed using silica gel (60e120 mesh)
under normal pressure. Flash column chromatography was per-
formed using silica gel of mesh 230e400 under nitrogen pressure.
Petroleum ether (PE) used was of the boiling range 60e80 ꢀC.
Spectral grade solvents were used for recording UV spectra.
Triethylamine was dried over KOH. Ether refers to diethyl ether.
Irradiation experiments were carried out in a Rayonet Photo-
chemical Reactor using lamps of desired wavelength.
mp 98e100 ꢀC. Rf (8% EA/PE) 0.4, UV (CH3CN) lmax (nm): 247 (log
e
2.86); IR: 3277, 2956, 1649, 1597 cmꢁ1. 1H NMR (500 MHz):
d (ppm)
1.0 (s, 3H), 1.05 (s, 3H), 1.32 (s, 3H), 1.36 (d, J 13 Hz, 1H), 1.44 (dd, J
13 Hz, 1H), 2.16 (d, J 15 Hz, 1H), 2.34 (dd, J 15 Hz, 1H), 2.93 (d, J 7 Hz,
1H), 6.54 (d, J 7 Hz, 1H), 7.46e7.49 (m, 2H), 7.58e7.61 (m, 1H),
7.75e7.77 (m, 2H). 13C NMR (125 MHz):
d (ppm) 20.3 (CH3), 28.7
(CH3), 30.0 (CH3), 35.9 (C), 40.4 (C), 45.0 (CH2), 47.9 (CH2), 61.2 (CH),
125.5 (CH), 126.4 (CH), 128.1 (CH), 128.8 (CH), 135.8 (C), 146.5 (C),
155.2 (C]N), 213.7 (C]O). HRMS (ESI) calcd for C18H21NO2Na:
306.1470; found: [MþNa]þ 306.1471.
4.2.4. 1-Benzoyl-3-hydroxyimino-5-methyltricyclo[3.3.0.02,8]octane
(11b). A thick liquid was obtained from 2b (240 mg, 1 mmol).
Elution of the column with 12% EA in PE gave a thick liquid of 11b
(204 mg, 80%). Rf (12% EA/PE) 0.4, UV (CH3CN) lmax (nm): 287 (log
e
3.0); IR: 3257, 2970, 1662, 1597 cmꢁ1. 1H NMR (500 MHz):
d
(ppm)
1.20 (s, 3H), 1.69e1.84 (m, 3H), 2.11 (d, J 18 Hz, 1H), 2.27e2.39 (m,
2H), 2.50 (br s 1H), 2.61 (d, J 18 Hz, 1H), 7.45e7.50 (m, 2H),
7.56e7.61 (m, 1H), 7.86e7.89 (m, 2H). 13C NMR (125 MHz):
d (ppm)
23.14 (CH3), 23.85 (CH2), 35.57 (CH), 39.66 (CH), 45.59 (CH2), 49.40
(CH2), 51.90 (C), 54.54 (C), 128.9 (CH), 133.16 (CH), 138.05 (C), 164.01
(C]N), 199.07 (C]O). HRMS calcd for C16H17NO2Na: 278.1157;
found [MþNa]þ: 278.1156.
The 5-benzoylbicyclo[2.2.2]oct-5-en-2-ones (1aed),7 tricyclo
[3.3.0.02,8]octan-3-onederivatives (2b,7 1320), methylenederivatives
3, 5, 50, 6a, b, 9, 10 and 1110 were prepared according to reported
procedures.
4.3. Synthesis of 4-(1-phenylvinyl)-1,5,6,7,8,8a-hexahydro-2H-
4.2. Synthesis of hydroxyimino derivative (4aec, 11b)
2,4a-ethanonapthalen-10-one (7)
A mixture of the starting materials (1aec, 2b 1 mM), and hy-
droxylamine hydrochloride (1.2 mM) in pyridine (3 mL) was heated
at 80 ꢀC (at 55 ꢀC for 2b) for 10 h stirring under argon atmosphere.
The temperature of the reaction was brought down to room tem-
perature. The reaction mixture was extracted with ether and excess
pyridine was washed by dilute HCl solution. Then it was washed
throughly by saturated NaHCO3 solution and brine and dried over
anhydrous Na2SO4, and evaporated in vacuo. The residue was flash
chromatographed over a silica gel column.
To a well stirred solution of the compound 40-(1-phenylvinyl)-
10,50,60,70,80,8a0-hexahydro-20H-spiro[1,3-dioxolane-2,100-[2,4a]etha-
nonaapthalene] (9, 1 gm, 3.1 mmol) in 20 mL acetonitrile/water
mixture (3:1, v/v) cerric ammonium nitrate (CAN) (64 mg,
w10 mol%) was added and the reaction mixture was refluxed for
next 1 h. Then it was cooled to room temperature, and was
extracted with ether and washed with brine and dried over
anhydrous sodium sulfate, filtered, and concentrated. The residue
was chromatographed over silica gel column. Elution with 6% EA
in PE gave a white solid, which on recrystallization from diethyl
ether and petroleum ether (1:8) gave white crystals of 4-(1-phe-
nylvinyl)-1,5,6,7,8,8a-hexahydro-2H-2,4a-ethanonapthalen-10-one
(7, 837 mg, 97%), mp 63e65 ꢀC. Rf (15% EA/PE) 0.5, Anal. Calcd for
C20H22O: C, 86.29; H, 7.97. Found C, 86.39; H, 7.79; IR: 3035,
4.2.1. 5-Benzoyl-2-hydroxyiminobicyclo[2.2.2]oct-5-ene (4a). A thick
liquid was obtained from 1a (226 mg, 1 mM). Elution of the column
with 8% EA in PE gave a thick liquid of 4a (203 mg, 90%). Rf (8% EA/PE)
0.4, UV (CH3CN) lmax (nm): 245 (log
e
4.3), 340 (3.5); IR: 3259, 2958,
1
1650, 1597 cmꢁ1. H NMR (300 MHz):
d
(ppm) 1.24e2.47 (m, 6H),
1724 cmꢁ1. UV (CH3CN) lmax (nm): 246 (log
1H NMR (300 MHz)
(ppm): 1.08e1.38 (m, 7H), 1.57e1.65 (m, 2H),
e 3.77), 297 (2.48).
3.40e3.44 (m, 1H), 3.57 (br s, 1H), 6.93 (dd, J 1 Hz, 1H), 7.43e7.50 (m,
d
2H), 7.54e7.58 (m, 1H), 7.65e7.74 (m, 2H). 13C NMR (75 MHz):
1.78 (br d, J 18 Hz, superimposed with a multiplet 1.75e1.80, 2H),
2.03 (ddd, J 12, 9, 3 Hz, 1H), 2.59 (d, J 18 Hz, 1H), 3.12e3.15 (m, 1H),
5.04 (s, 1H), 5.36 (s, 1H), 6.14 (d, J 6 Hz, 1H), 7.22e7.31 (m, 5H).
d
(ppm) 23.9 (CH2), 24.2 (CH2), 30.3 (CH2), 30.6 (CH), 38.4 (CH),128.6
(CH),129.8 (CH),132.1 (CH),144.6 (C),146.7 (CH),155.2 (C),161.0 (C]
N), 194.1 (C]O). HRMS (ESI) calcd for C15H15NO2Na: 264.1000;
found: [MþNa]þ 264.0998.
13C NMR (75 MHz)
d (ppm): 21.5 (CH2), 25.7 (CH2), 30.1 (CH2), 31.2
(CH2), 31.4 (CH2), 37.8 (CH), 39.0 (CH2), 42.9 (C), 48.9 (CH), 115.0
(CH2), 124.7 (CH), 126.5 (CH), 127.7 (CH), 128.4 (CH), 140.2 (C),
148.2 (C), 154.9 (C), 212.3 (C]O).
4.2.2. 5-Benzoyl-2-hydroxyimino-4-methylbicyclo[2.2.2]oct-5-ene
(4b). An oil was obtained from 1b (240 mg, 1 mM). Elution of the
column with 8% ethyl acetate (EA) in petroleum ether (PE) gave
an oil of 4b (201 mg, 84%). Rf (8% EA/PE) 0.4, UV (CH3CN) lmax
4.4. PET reactions of 4aec
(nm): 325 (log
e
1.9); IR 3254, 2931, 1651, 1595 cmꢁ1
.
1H NMR
Methanol solution (5 mL) of the hydroxyimino derivative of
bicyclo compound (30 mg) in triethylamine (TEA, 5 mL), was
(500 MHz): (ppm) 1.43 (s, 3H), 1.58e1.97 (m), 2.32 (d, J 18 Hz),
d

1694
A. Sengupta et al. / Tetrahedron 67 (2011) 1689e1695
degassed and then irradiated in desired wavelength. After which
the solvents were removed under reduced pressure. The residue
was then purified by flash column chromatography to yield the
product.
ne (5, 139 mg, 0.5 mmol) in dry benzene was irradiated at 254 nm
for 39 h. Elution of the column with 2% EA in PE gave 14 (55 mg,
46%) as yellowish thick liquid. Rf (5% EA/PE) 0.5, UV (CH3CN) lmax
(nm): 243 (log
e
2.75), 288 (4.01), 320 (2.94); IR: 3053, 2929, 1773,
(ppm): 0.80e1.20 (m, 5H),
1614 cmꢁ1 1H NMR (300 MHz)
.
d
4. 4.1. 8-Benzoyl-3-hydroxyi minobi cyclo[3. 2.1]octane
(12a). Compound 4a (30 mg, 1 mM) was irradiated at 300 nm
wavelength for 5 h. Elution of the column with 10% PE, EA gave
a yellow solid of 12a (4.5 mg, 15%), mp 148e150 ꢀC. Rf (10% EA/PE)
1.33e1.53 (m, 4H), 1.86e1.99 (m, 2H), 2.15 (ddd, J 9, 6 and 3 Hz, 1H),
2.37 (td, J 18 and 3 Hz, 1H), 2.54 (d, J 18 Hz, superimposed with
another doublet (J 9 Hz) at 2.55, total 2H), 4.93 (dd, J 3 Hz), 4.99 (dd,
J 3 Hz), 7.19e7.48 (m, 3H), 7.76e7.79 (m, 2H). 13C NMR (75 MHz)
0.4, UV (CH3CN) lmax (nm): 278 (log
e
2.65); IR: 3277, 2956, 1649,
d (ppm): 22.9 (CH2), 25.3 (CH2), 26.7 (CH2), 27.7 (CH2), 30.6 (CH), 35.9
1597 cmꢁ1. 1H NMR (500 MHz)
d
(ppm): 0.407 (m, 2H), 0.97e01.08
(CH2), 41.2 (CH2), 44.0 (CH), 54.7 (C), 55.9 (C), 56.2 (CH), 106.5 (CH2),
128.3 (CH), 128.7 (CH), 132.5 (CH), 138.7 (C), 150.0 (C), 200.3 (C]O).
HRMS calcd for C20H22ONa: 301.1568; found [MþNa]þ: 301.1563.
Further elution of the column with 2% EA in PE gave back 5
(35 mg, 25%) with superimposible spectra.
(m, 2H), 1.32e1.75 (m, 4H), 3.66 (br s, 1H), 6.58e6.61 (m, 2H),
6.68e6.69 (m, 1H), 7.06e7.07 (m, 2H). 13C NMR (125 MHz)
d
(ppm): 24.1 (CH2), 25.6 (CH2), 26.7 (CH), 29.4 (CH2), 31.9 (CH),
43.0 (CH2), 100.1 (CH), 128.1 (CH), 128.5 (CH), 132.8 (CH), 160.4
(C]N). HRMS (ESI) calcd for C15H17NO2Na 266.1157; found:
[MþNa]þ 266.1156.
4.5.2. 1,3,3-Trimethyl-6-(1-phenylvinyl)bicyclo[4.2.0]oct-4-en-7-one
(17a). (i) In benzene: A solution of 4,7,7-trimethyl-5-(1-phenyl-
vinyl)bicyclo[2.2.2]oct-5-en-2-one (6a, 80 mg, 0.3 mmol) in dry
benzene was irradiated at 300 nm for 45 min. Elution of the column
with 5% EA in PE gave a yellow thick liquid of 17a (60 mg, 75%). Rf
Further elution of the column with 10% EA in PE gave unreacted
starting material (4a, 18 mg, 60%) with superimposible spectra.
4.4.2. 8-Benzoyl-3-hydroxyimino-1-methylbicyclo[3.2.1]octane
(12b). Compound 4b (30 mg, 1 mM) was irradiated at 300 nm
wavelength for 3 h. Elution of the column with 10% PE, EA gave
a yellow solid (12b, 4.8 mg,16%), mp 148e150 ꢀC. Rf (10% EA/PE) 0.4,
(10% EA/PE) 0.8, UV (CH3CN) lmax (nm): 235 (log
e 4.1), 310 (2.95);
IR: 2956, 1772, 1616 cmꢁ1. 1H NMR (300 MHz)
d
(ppm): 1.06 (s, 3H),
1.18 (s, 3H), 1.37 (d, J 15 Hz, 1H), 2.46 (d, J 17 Hz, 1H), 3.47 (d, J 17 Hz,
1H), 5.32 (d, J 1 Hz, 1H), 5.6 (d, J 10 Hz, 1H), 5.82 (d, J 10 Hz)
superimposed with 5.81 (d, J 1 Hz) total 2H, 7.23e7.25 (m, 3H),
7.34e7.37 (m, 2H). 13C NMR (75 MHz): 27.6 (CH3), 28.8 (CH3),
32.2 (C), 32.9 (CH3), 34.9 (C), 43.3 (CH2), 54.2 (CH2), 71.9 (C), 117.3
(]CH2), 125.5 (CH), 127.7 (CH), 128.1 (CH), 128.2 (CH), 140.3 (CH),
141.6 (C), 146.3 (C), 208.2 (C]O). HRMS calcd for C19H22ONa:
289.1568; found [MþNa]þ: 289.1579.
UV (CH3CN) lmax (nm): 248 (log
e 3.7); IR: 3163, 2937, 1662,
1597 cmꢁ1. 1H NMR (500 MHz):
d
(ppm) 1.14 (s, 3H), 1.28e1.63 (m,
2H), 1.86 (d, J 15 Hz), 1.97 (d, J 15 Hz), 2.02e2.06 (m), 2.66 (hextet, J
4 Hz, 1H), 2.97 (d, J 16 Hz, 1H), 3.15 (d, J 16 Hz, 1H), 3.55 (d, J 4 Hz,
1H), 7.48e7.51 (m, 2H), 7.58e7.61 (m, 1H), 7.97e7.98 (m, 2H). 13C
NMR (125 MHz):
d (ppm) 24.2 (CH3), 27.5 (CH2), 28.2 (CH2), 37.4
(CH2), 39.3 (C), 40.1 (CH2), 42.7 (CH), 55.78 (CH), 127.8 (CH), 128.52
(CH), 132.8 (CH), 138.6 (C), 158.1 (C), 202.7 (C]O). HRMS (ESI) calcd
for C16H19NO2Na: 280.1313; found [MþNa]þ 280.1313.
Further elution of the column with same solvent gave back (6a,
13 mg, 16%) as colorless semi-solid (superimposable IR spectrum).
(ii) In acetonitrile: Follow up of the above mentioned procedure
in acetonitrile solution yielded the same compound (17a, 58 mg,
72%), which was identified by superimposible spectra.
Further elution of the column with 10% EA in PE gave unreacted
starting material (4b, 15 mg, 50%) with superimposible spectra.
4.4.3. 8-Benzoyl-3-hydroxyimino-1,6,6-trimethylbicyclo[3.2.1]octane
(12c). Compound 4c (30 mg, 1 mM) was irradiated at 254 nm
wavelength for 7 h. Elution of the column with 10% PE, EA gave
a white crystal of 12c (6.0 mg, 20%) Rf (10% EA/PE) 0.4, mp
168e170 ꢀC after crystallization from DCM-PE mixture (1:8). UV
4.5.3. 1,4-Dimethyl-6-(1-phenylvinyl)bicyclo[4.2.0]oct-4-en-7-one
(17b). (i) In benzene: A solution of 1,4-dimethyl-5-(1-phenylvinyl)
bicycle[2.2.2]oct-5-en-2-one (6b, 90 mg, 0.36 mmol) in dry ben-
zene was irradiated at 300 nm for 40 min. Elution of the column
with 3% EA in PE gave a colorless liquid of 17b (62 mg, 69%). Rf (10%
(CH3CN) lmax (nm): 249 nm (log
e 4.0); IR: 3281, 2926, 1672,
1595 cmꢁ1. 1H NMR (500 MHz):
d
(ppm) 0.97 (s, 3H), 1.15 (s, 3H),
EA/PE) 0.8, UV (CH3CN) lmax (nm): 238 (log 4.41), 308 (3.26); IR:
e
1.27 (s, 3H), 1.41 (d, J 15 Hz, 1H), 1.53 (dd, J 15 Hz, 1H), 1.66 (dd, J
20 Hz, 1H), 1.98 (d, J 15 Hz, 1H), 2.12 (q, J 5 Hz, 1H) 3.13 (dd, J
15 Hz, 1H), 3.25 (d, J 15 Hz, 1H), 3.89 (d, J 4 Hz, 1H), 7.48e7.51
(m, 2H), 7.57e7.6 (m, 1H), 7.92e7.94 (m, 2H). 13C NMR
2962, 1766, 1466 cmꢁ1 1H NMR (300 MHz)
.
d (ppm): 0.94 (s, 3H),
1.18e1.34 (m, 1H), 1.47e1.53 (m, 1H), 1.75 (s, 3H), 1.97e2.09 (m, 1H),
2.17 (dd, J 18, 6 Hz,1H), 2.35 (d, J 17,1H), 2.90 (d, J 17 Hz,1H), 5.24 (d,
J 1 Hz, 1H), 5.30 (s, 1H), 5.76 (d, J 1 Hz, 1H), 7.15e7.19 (m, 3H),
(125 MHz):
d
(ppm) 23.5 (CH2), 24.2 (CH3), 25.0 (CH3), 32.5
7.27e7.30 (m, 2H). 13C NMR (75 MHz)
d (ppm): 24.3 (CH2), 25.45 (C),
(CH3), 38.6 (C), 40.2 (CH2), 43.2 (C), 49.9 (CH), 53.9 (CH2), 54.9
(CH), 127.7 (CH), 128.5 (CH), 132.7 (CH), 139 (C), 158.4 (C]N),
202.4 (C]O). HRMS (ESI) calcd for C18H23NO2Na: 308.1627;
found [MþNa]þ 308.1627.
25.49 (CH3), 27.2 (CH2), 28.3 (CH3), 33.5 (C), 51.8 (CH2), 116.4
(]CH2), 122.2 (CH), 127.3 (CH), 127.7 (CH), 137.3 (C), 141.4 (C), 146.7
(C), 206.7 (C]O). HRMS calcd for C18H20ONa: 275.1412; found
[MþNa]þ: 275.1413.
Further elution of the column with 10% EA in PE gave a solid of
unreacted starting material (4c, 15 mg, 50%), mp 98e100 ꢀC (mmp
98 ꢀC).
Further elution of the column with same solvent gave back (6b,
19 mg, 21%) as colorless thick liquid (superimposable IR spectrum).
(ii) In acetonitrile: Follow up of the above mentioned procedure
in acetonitrile solution yielded the same compound (17b, 44 mg,
63%), which was identified by superimposible spectra.
4.5. Irradiation of 5, 6a, 6b, and 7 in solution
A 50 mL solution of the compound in solution was degassed
with argon for 10 min and then irradiated at suitable wavelength.
Solvent was removed under reduced pressure and the residue was
subjected to flash column chromatography.
4.5.4. 2A-(1-phenylvinyl)-5,5a,6,7,8,9-hexahydro-1H-cyclobuta[d]
naphthalene-2(2aH)-one (16). A solution of 4-(1-phenylvinyl)-
1,5,6,7,8,8a-hexahydro-2H-2,4a-ethanonapthalen-10-one (7, 139 mg,
0.5 mmol) in dry acetonitrile was irradiated at 300 nm for 3 h. Elution
with2%EA inPEgave16 (72mg, 52%)asawhitesolid,mp128e130 ꢀC.
Rf (5% EA/PE) 0.6, Anal. Calcd for C20H22O: C, 86.29; H, 7.97. Found: C,
86.11; H, 8.09; IR: 3053, 3024, 1773 cmꢁ1; UV (CH3CN) lmax (nm):
4.5.1. 2-Methylenedecahydro-7bH-benzo[g]cyclopropa[cd]pentalen-
7b-yl(phenyl)methanone (14). A solution of 10-methylene-1,5,6,7,
8,8a-hexahydro-2H-2,4a-ethanonapthalen-4-yl(phenyl)methano
239 nm (log
e d (ppm):
3.52), 305 nm (2.42). 1H NMR (300 MHz)

A. Sengupta et al. / Tetrahedron 67 (2011) 1689e1695
1695
0.83e0.95 (m, 2H),1.02e1.33 (m, 3H),1.45 (ddt, J 12, 6, 3 Hz,1H),1.60
References and notes
(brd, J 9 Hz, 3H),1.78 (tdd, J 18,12 and 3 Hz,1H), 2.3 (td, J 18 and 1.2 Hz,
1H), 2.53 (d, J 18 Hz, 1H), 2.87 (dd, J 18 and 1.2 Hz,1H), 5.38 (s,1H), 5.6
(dd, J 12 and 3 Hz, 1H), 5.76 (s, 1H), 6.00 (ddd, J 12, 6, 3 Hz, 1H),
1. Some of the reviews are: (a) Cossy, J.; Belotti, D. Tetrahedron 2006, 62, 6459;
(b) Oelgemoller, M.; Griesbeck, A. G. In CRC Handbook of Organic Photochem-
€
istry and Photobiology; Horsepool, W. M., Lenci, F., Eds.; CRC: Boca Raton, FL,
2004; p 84; (c) Cossy, J. In Radicals in Organic Synthesis; Renaud, P., Sibi, M. P.,
Eds.; Wiley-VCH: Weinheim, 2001; Vol. 1, p 229; (d) Albini, A.; Fagnoni, M.;
Mella, M. Pure Appl. Chem. 2000, 72, 1321; (e) Santamaria, J. Pure Appl. Chem.
1995, 67, 141.
2. (a) Simon, J. D.; Peters, K. S. J. Am. Chem. Soc. 1982, 104, 6542; (b) Schaefer, C. G.;
Peters, K. S. J. Am. Chem. Soc. 1980, 102, 7566.
3. (a) Schuster, D. I.; Insogna, A. M. J. Org. Chem. 1991, 56, 1879; (b) Weir, D.;
Scaiano, J. C.; Schuster, D. I. Can. J. Chem. 1988, 66, 2595.
7.25e7.27 (m, 3H), 7.39e7.42(m, 2H).13C NMR (75MHz)
d(ppm):22.9
(CH2),26.0(CH2), 29.5(CH2),29.8(C),30.8(CH2),33.7(CH2),33.9(CH),
39.7 (C), 47.8 (CH2), 117.5 (CH2), 127.4 (CH2), 127.8 (CH), 127.9 (CH),
128.0 (CH), 129.2 (CH2),142.0 (C),145.5 (C), 206.3 (C]O). HRMS calcd
for C20H22ONa: 301.1568; found 301.1563.
4. (a) Yoon, U. C.; Kim, J. U.; Hasegawa, E.; Mariano, P. S. J. Am. Chem. Soc. 1987, 109,
4421; (b) Hasegawa, E.; Xu, W.; Mariano, P. S.; Yoon, U. C.; Kim, J. U. J. Am. Chem.
Soc. 1988, 110, 8099; (c) Yoon, U. C.; Marino, P. S. Acc. Chem. Res. 1992, 25, 233.
5. Mattay, J.; Vondenhof, M. Top. Curr. Chem. 1991, 159, 219; (b) Mattay, J. Synthesis
1989, 233; (c) Mattay, J. Angew. Chem., Int. Ed. Engl. 1987, 26, 825.
6. Maiti, B. C.; Lahiri, S. Tetrahedron 1998, 54, 9111.
4.6. Irradiation of 6a, 6b, and 7 under PET condition
Methanol solution (5 mL) of the methylene derivatives in trie-
thylamine (TEA, 5 mL), was degassed and then irradiated at 300 nm
wavelength for 5 h. After which the solvent was removed under
reduced pressure. The residue was then purified by flash column
chromatography on silica gel to yield the product.
7. Yadav, S.; Banerjee, S.; Maji, D.; Lahiri, S. Tetrahedron 2007, 63, 10979.
8. Banerjee, S.; Yadav, S.; Lahiri, S. Org. Lett. 2009, 11, 3494.
9. Maiti, B. C.; Singh, R.; Lahiri, S. J. Chem. Res., Synop. 1993, 500.
10. Ghosh, A.; Chakraborty, I.; Adarsh, N. N.; Lahiri, S. Tetrahedron 2010, 66, 164.
11. (a) Padwa, A. Chem. Rev. 1977, 77, 37; (b) Yang, M.-S.; Lu, S.-S.; Rao, C. P.; Tsai, Y.-
F.; Liao, C.-C. J. Org. Chem. 2003, 68, 6543.
12. (a) Nitta, M.; Kasahara, I.; Kobayashi, T. Bull. Chem. Soc. Jpn. 1981, 54, 1275; (b)
Nitta, M.; Inoue, O.; Tada, M. Chem. Lett. 1977, 1065.
13. (a) Armesto, D.; Ortiz, M. J.; Agarrabeitia, A. R. In Synthetic Organic Photo-
chemistry; Griesbeck, A. G., Mattay, J., Eds.; Marcell Dekker: NY, 2005; p 161; (b)
Armesto, D.; Ramos, A.; Ortiz, M. J.; Horspool, W. M.; Mancheno, M. J.; Cabal-
lero, O.; Mayoral, E. P. J. Chem. Soc., Perkin Trans. 1 1997, 1535.
14. (a) Constantino, M. G.; De Oliveira, K. T.; Beatriz, A.; Da Silva, G. V. J. Tetrahedron
Lett. 2003, 44, 2641; (b) Suginome, H.; Furukawa, K.; Orito, K. J. Chem. Soc., Perkin
Trans.11991, 917; (c) Yates, P.; Wong, J.; McLean, W. Tetrahedron1981, 37, 3357; (d)
Suginome, H.; Shea, C.-M. J. Chem. Soc., Perkin Trans. 11980, 2268; (e) Alonso, R.;
Campos, P. J.; García, B.; Rodríguez, M. A. Org. Lett. 2006, 8, 3521; (f) Alonso, R.;
Campos, P. J.; Rodríguez, M. A.; Sampedro, D. J. Org. Chem. 2008, 73, 2234.
4.6.1. 2A-(1-phenylvinyl)-5,5a,6,7,8,9-hexahydro-1H-cyclobuta[d]
naphthalene-2(2aH)-one (16). Residue obtained from 4-(1-phenyl-
vinyl)-1,5,6,7,8,8a-hexahydro-2H-2,4a-ethanonapthalen-10-one (7,
30 mg, 0.1 mmol) on elution with pet ether gave 10 mg of an un-
identified decarbonylated compound. Further elution with 4% EA in
PE gave a white solid of 16 (20 mg, 68%), identified by super-
imposible spectra. Further elution of the column with same solvent
gave back 7 (3 mg, 10%).
4.6.2. 1,3,3-Trimethyl-6-(1-phenylvinyl)bicyclo[4.2.0]oct-4-en-7-one
(17a). Residue obtained from 4,7,7-trimethyl-5-(1-phenyvinyl)
bicyclo[2.2.2]oct-5-en-2-one (6a, 30 mg, 0.1 mmol) on elution
with pet ether gave 7 mg of an unidentified decarbonylated
compound. Further elution with 3% EA in PE gave a yellow thick
liquid of 17a (16.5 mg, 55%), identified by superimposible spectra.
Further elution of the column with same solvent gave back 6a
(3 mg, 12%).
15. X-ray single crystal data of a single crystal of 12c was collected using Mo K
a
ꢀ
(
l
¼0.7107 A) radiation on an SMART APEX II diffractometer equipped with
CCD area detector. Data collection, data reduction, structure solution/re-
finement were carried out using the software package of SMART APEX. The
structure was solved by direct method and refined in a routine manner. The
non-hydrogen atoms were treated anisotropically except oxime hydroxyl
oxygen atom. The hydroxyl group of oxime moiety was found to be disorderd
over two positions and thus treated as two position disorder by FVAR facility
of Shelxl-97. The positions of all hydrogen atoms were generated by their
idealized geometry and refined using a riding model. Crystal dimension: 0.
32ꢂ0.24ꢂ0.12 mm; T¼100(2) K; orthorhombic, space group Pca21; a¼12.949
¼1.180 gcmꢁ3
;
m
¼0.
4.6.3. 1,4-Dimethyl-6-(1-phenylvinyl)bicyclo[4.2.0]oct-4-en-7-one
(17b). Residue obtained from 1,4-dimethyl-5-(1-phenylvinyl)bicy-
clo[2.2.2]oct-5-en-2-one (6b, 30 mg, 0.1 mmol) on elution with pet
ether gave 10 mg of an unidentified decarbonylated compound.
Further elution with 3% EA in PE gave a colorless liquid of 17b
(20 mg, 68%), identified by superimposible spectra. Further elution
of the column with same solvent gave back 6b (3 mg, 10%).
(6), b¼7.867(4), c¼31.438(14) Ǻ; V¼3203(2) Ǻ3; Z¼8,
r
076 mmꢁ1; F(000)¼1224; qmin
/
qmax/ꢀ¼5.76/32.28; Rint¼0.0810; Range of h, k,
l¼ꢁ19/19, ꢁ11/11, ꢁ46/46; 45207 reflections collected of which 11066 were
unique, 6714 observed [I>2s(I)] reflections, 383 parameters were refined;
R1¼0.0630, wR2¼0.1776; Goodness of fit on F2¼0.994; CCDC-798095 contains
the supplementary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
16. Zimmerman, H. E. In Rearrangements in Ground and Excited States; De Mayo, P.,
Ed.; Academic: NY, 1980; vol. 3, p 137.
17. Using the above-mentioned instrument and software the single crystal struc-
ture of 16 was solved by direct method and refined. The non-hydrogen atoms
were treated anisotropically. All hydrogen atoms were located and refined.
Crystal dimension: 0.37ꢂ0.27ꢂ0.18 mm; T¼100(2) K; orthorhombic, space
Acknowledgements
Single crystal X-ray diffraction was performed with the help of
Mr. P. Sahoo at the DST-funded National Single Crystal Diffrac-
tometer Facility at the Department of Inorganic Chemistry. Finan-
cial support was received from the Department of Science and
Technology, Govt. of India.
3
ꢀ
ꢀ
group P21/c; a¼8.9712(7), b¼24.4263(19), c¼7.1014(6) A; V¼1511.7(2) A ; Z¼4,
rcalcd¼1.223 gcmꢁ3
;
m
¼0.073 mmꢁ1
;
F(000)¼600; qmin
/
qmax/ꢀ¼1.67/27.00;
Rint¼0.0458; range of h, k, l¼ꢁ11/11, ꢁ31/31, ꢁ9/9; 16250 reflections collected
of which 3299 were unique, 2544 observed [I>2s(I)] reflections, 278 parame-
ters were refined; R1¼0.0435, wR2¼0.1019; Goodness of Fit on F2¼1.033; CCDC-
801061 contains the supplementary crystallographic data for this paper. These
data can be obtained free of charge from the Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
18. (a) Demuth, M. In Organic Photochemistry; Padwa, A., Ed.; Marcell-Dekker: NY,
1991; Vol 11, p 37; (b) Demuth, M. In Comprehensive Organic Synthesis; Trost, B.
M., Ed.; Pergamon: NY, 1991; Vol. 5, p 217.
19. Scheffer, J. R.; Vishnumurthy, K. Can. J. Chem. 2003, 81, 705.
20. Maiti, B. C.; Singh, R.; Lahiri, S. J. Photochem. Photobiol., A 1995, 91, 27.
Supplementary data
Supplementary data related to this article can be found online at
doi:10.1016/j.tet.2010.12.064.