Solvent and substituent effects on the photochemistry of norbornadiene-diarylacetylene pauson-khand adducts

Article abstract of DOI:10.1002/chem.201001037

The photochemistry of Pauson-Khand cycloadducts of norbornadiene with a series of bis-aryl alkynes has been studied. Two types of photochemical transformation take place: photorearrangement to tricyclic ketones or photochemical 6π electrocyclization. High

Full text of DOI:10.1002/chem.201001037

DOI: 10.1002/chem.201001037
Solvent and Substituent Effects on the Photochemistry of Norbornadiene-
Diarylacetylene Pauson–Khand Adducts
Yining Ji, Xavier Verdaguer,* and Antoni Riera*[a]
Abstract: The photochemistry of Pauson–Khand cycloadducts of norbornadiene
with a series of bis-aryl alkynes has been studied. Two types of photochemical
Keywords: cyclopentenones · elec-
transformation take place: photorearrangement to tricyclic ketones or photochem-
trocyclic reactions · photochemistry ·
ical 6p electrocyclization. High selectivity levels have been attained for each path-
rearrangement · solvent effects
way, controlled by the polarity of the solvent, irradiation wavelength, and presence
(or absence) of oxygen.
Introduction
Although this novel photorearrangement tolerates a wide
variety of functional groups and affords the rearranged
products in high yields, irradiation of the PK adduct of di-
phenylacetylene (1a) gives exclusively the phenanthrene de-
rivative 2a, instead of the expected rearranged product 3a[5]
(Scheme 2). In this case, a stilbene fragment is suitably
Enones[1] are among the most synthetically useful substrates
in photochemical reactions because high levels of selectivity
are observed in reactions such as [2+2] cycloadditions,[2] re-
arrangements,[3] and conjugate additions.[4] Some years ago,
we reported a novel enone photoreaction by irradiation of
cyclopentenones I at 365 nm, which afforded the rearranged
products II in excellent yields[5] (Scheme 1). Cyclopente-
Scheme 1. Photochemical rearrangement of Pauson–Khand adducts I.
nones I are widely available substrates; they can be ob-
tained in one step by a Pauson–Khand (PK) reaction[6] be-
tween norbornadiene and the appropriate acetylene. Com-
pounds I are also accessible in enantiomerically enriched
form through an asymmetric version of the reaction devel-
oped recently by our group.[7]
This rearrangement is mostly general for norbornadiene
PK adducts.[5] The compounds have the exo stereochemistry
required to prevent the well-known intramolecular [2+2] cy-
cloaddition that occurs in endo tricyclic alkenyl enones.[8]
Scheme 2. Electrocyclization of the Pauson–Khand adduct of norbornene
and phenylacetylene (1a).
placed in the cis configuration and can undergo conrotatory
electrocyclic ring closure to afford 2a via an unstable dihy-
drophenanthrene intermediate. It must be pointed out that
the aromatization to the thermodynamically favored deriva-
tive 2a takes place without any extra source of oxidant; the
most probable oxidative reagent is the oxygen solved in the
solution. Several precedents of this 1,6-electrocyclization
have been described in the photochemistry of stilbenes,[9] as
well as in the synthesis of photochromic compounds.[10]
More recently, this type of 6p-electrocycloreversion oxida-
tive aromatization reaction has been reported with norbor-
nene PK adducts of 4-(phenylethynyl)-2-pyrone.[11]
Based on the absence of the rearranged product 3a in the
crude reaction mixture, we initiated an exploration of this
photochemical reaction to establish the impact of the sol-
vent and irradiation wavelength on the reaction outcome.
To pursue the synthesis of the photorearranged product 3a,
[a] Y. Ji, Prof. X. Verdaguer, Prof. A. Riera
Unitat de Recerca en Sꢀntesi Asimꢁtrica (URSA)-PCB
Institute for Research in Biomedicine (IRB) Barcelona
Departament de Quꢀmica Orgꢂnica
Universitat de Barcelona, c/Baldiri Reixac 10
08028 Barcelona (Spain)
Fax : (+34)934037095
E-mail: antoni.riera@irbbarcelona.org
xavier.verdaguer@irbbarcelona.org
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201001037.
3942
ꢃ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 3942 – 3948

FULL PAPER
we reasoned that the two possible photochemical pathways
(namely rearrangement and electrocyclization) take place
through two different mechanistic pathways and, therefore,
should be sensitive to the reaction conditions. Here we
report a study of the scope of the photochemical transfor-
mations of aromatic PK cycloadducts and the optimized
conditions that ultimately lead to the formation of either the
phenanthrene or the photorearranged products with com-
plete selectivity.
could not be reversed (Table 1, entry 5). This is in agree-
ment with our mechanistic study of the rearrangement,[12] in
which we observed that the energy transfer from the benzo-
phenone triplet was not very efficient.
We then proceeded to study the solvent effect. Photoirra-
diation of 1a in non-degassed CH2Cl2 afforded mixtures of
2a and 3a with very low conversions and selectivities. In
these reactions, the amount of solvated oxygen was critical.
When we undertook the reaction at 300 nm in degassed
CH2Cl2 a 1:1 mixture of 2a and 3a was obtained, in only
81% conversion after
5 days of irradiation (Table 1,
Results and Discussion
entry 6). Most pleasingly, the reaction performed in de-
gassed CH2Cl2 at 365 nm provided photorearranged com-
pound 3a as the main product (3a/2a=96:4, 83%; Table 1,
entry 7). Therefore, a strong solvent dependence of the reac-
tion product was clearly revealed in this photochemical
transformation. Thus, we concluded that irradiation at
365 nm in degassed CH2Cl2 were the best conditions for the
photorearrangement to 3a. Two more solvents were tested.
Acetone gave the rearranged product 3a with a slightly
lower selectivity (3a/2a=90:10; Table 1, entry 8). Hexane
gave similar selectivity to CH2Cl2 (Table 1, entry 9), al-
though a much longer reaction time was required because
highly diluted solutions (5ꢄ10À3 m) of the reagent were nec-
essary to overcome poor solubility. On the basis of the
above results, we concluded that a shorter wavelength
(300 nm) and non-degassed MeOH favor the pericyclic reac-
tion, whereas a longer wavelength (365 nm) and degassed
apolar solvents favor the photorearrangement.
To gain a deeper insight into these photochemical pro-
cesses, we undertook a kinetic study of the photoconversion
of 1a into either 2a or 3a. We found that temperature is
critical to the pericyclic reaction rate and is even more sig-
nificant in the photorearrangement. To achieve significant
conversion in short reaction times, we performed the kinetic
experiments at 508C, which forced us to use dichloroethane
(DCE) as the solvent instead of CH2Cl2.
For exploratory purposes, we used diphenylacetylene as a
benchmark internal symmetric alkyne. As described in our
preliminary communication,[5] irradiation of 1a at 365 nm in
methanol afforded the phenanthrene product 2a (Table 1,
Table 1. Photochemical reactions of Pauson–Khand adduct 1a, derived
from norbornadiene and diphenylacetylene
Entry
Solvent
hn
[nm]
O2
t
Conv.
[%]
2a/3a[b]
Yield[c]
[%]
[h][a]
1
2
3
4
5
6
7
8
9
MeOH
MeOH
MeOH
MeOH
MeOH[d]
CH2Cl2
CH2Cl2
acetone
hexane
365
365
300
300
365
300
365
365
365
no
yes
yes
no
no
no
no
no
no
15
15
7
100
100
100
100
100
81
100
100
100
96:4
100:0
100:0
98:2
85:15
56:44
4:96
54
quant
quant
30
7
15
120
26
38
72[e]
n.m.[f]
[f]
n.m.
83
80
82
10:90
5:95
[a] Reactions were performed at 30–358C. [b] Ratio measured by
1H NMR spectroscopy of the crude material. [c] Combined yield of 2 and
3. [d] Benzophenone (1 equiv) was added. [e] Dilute solution due to low
solubility of 1a. [f] Not measured
The plots of the concentration of electrocyclization prod-
uct 2a versus time during the initial 3 h of the reaction are
shown in Figure 1. The formation of 2a in MeOH (both de-
gassed and non-degassed) was much faster than in DCE.
entry 1) in a modest 54% yield. Moreover, careful analysis
identified a small amount of 3a (4%) in the crude material.
Assuming that oxygen was the oxidant, the reaction was
conducted without degassing the solution. Gratifyingly, in
non-degassed methanol we obtained 2a in quantitative yield
(Table 1, entry 2). Under irradiation with a shorter wave-
length (300 nm) in non-degassed methanol, the same phen-
anthrene derivative 2a was formed exclusively, at a higher
reaction rate—the reaction time was reduced to half
(Table 1, entry 3). In the absence of oxygen (Table 1,
entry 4), the reaction gave a poor 30% yield, although the
selectivity towards 2a was still very high. Clearly, in metha-
nol oxygen plays an essential role to obtain high yields but
has little influence on the ratio 2a/3a. The addition of ben-
zophenone as triplet sensitizer significantly increased the
amount of photorearranged product 3a, but the selectivity
Figure 1. Reaction rates for the electrocyclization of 1a to 2a. (l=
365 nm; initial concentration of 1a=4.2ꢄ10À3 m; MeOH non-degassed;
*
~
&
^
MeOH degassed; DCE non-degassed; DCE degassed).
Chem. Eur. J. 2011, 17, 3942 – 3948
ꢃ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3943

A. Riera, X. Verdaguer, and Y. Ji
Table 2. Pauson–Khand reaction of norbornadiene with internal aromatic
alkynes 1b–f.
Non-degassed MeOH proved to be more advantageous for
the pericyclic transformation, not only because the oxidative
photocyclized product 2a was generated efficiently, but also
because the formation of 3a was suppressed (Figure 2). Al-
Entry
R
Solvent
T [8C]
t [h]
Product
Yield [%]
1
2
3
4
5
F
Cl
CO2Me
tBu
OMe
hexane
toluene
CH2Cl2
hexane
toluene
60
75
RT
60
60
24
1b
1c
1d
1e
1 f
99
98
56
77
69
21
[a]
72[b]
96
96
[a] Activated with NMO. [b] 89% conversion.
gioisomers 1g and 1g’ (2.5:1), which were easily separable
by chromatography on silica gel. As reported in the litera-
ture,[14] the regiochemistry was governed by the electronic
nature of the substituents. In the major isomer, the electron-
releasing group (ERG) was settled at the a-position, the
electron-withdrawing group (EWG) at the b-position
(Scheme 3).
Figure 2. Reaction rates of the photochemical rearrangement of 1a to 3a.
(l=365 nm; initial concentration of 1a=4.2ꢄ10À3 m;
MeOH non-de-
*
~
&
^
gassed; MeOH degassed; DCE non-degassed; DCE degassed).
though the reaction took place initially at the same rate in
degassed methanol, the reaction could not go further after
1.5 h. At this point, the formation of 3a became significant
(Figure 2). It appears that oxygen was not totally excluded
from the solvent by degassing (2 h of nitrogen bubbling),
which then allowed initial rapid conversion of 1a to 2a. The
reaction stopped when all of the oxygen present in the
medium was consumed. This behavior indicates that oxygen
is required for the dehydrogenation step after the photocyc-
lization.
As illustrated in Figure 2, degassed DCE was clearly the
solvent of choice for the formation 3a. In degassed MeOH,
the rearrangement to 3a was quite slow and the formation
of the phenanthrene product 2a was clearly favored. In non-
degassed solvents, the rearrangement was completely inhib-
ited, probably because oxygen acts as efficient triplet
quencher.
With suitable reaction conditions identified for both reac-
tion courses, we studied the scope of the reaction. We per-
formed experiments to determine the influence of the sub-
stituents in the aromatic ring. First, a set of tricyclic cyclo-
pentenones (1b–f) was prepared by stoichiometric intermo-
lecular PK reactions of norbornadiene with a range of di-
versely substituted alkynes. Symmetrical alkynes 4b–f were
synthesized by following a reported procedure based on So-
nogashira couplings between trimethylsilylacetylene and the
corresponding iodobenzenes.[13] The stoichiometric PK reac-
tions took place uneventfully to afford compounds 1b–f in
good yields (Table 2). All reactions were promoted thermal-
ly except the reaction of the electron-deficient acetylene 4d
(R=CO2Me), which was activated with N-methylmorpho-
line N-oxide (NMO).
Scheme 3. Pauson–Khand reaction of the unsymmetrical diarylacetylene
4g.
With diaryl PK cycloadducts 1b–g in hand, we performed
a series of photochemical reactions with a range of solvents
(CH2Cl2, hexane, MeOH) and irradiation wavelengths (300,
365 nm). The results are summarized in Table 3. The corre-
sponding phenanthrene derivatives 2b, 2c, and 2e–g were
obtained in quantitative yields with high purity (>95%)
when the substrates were irradiated in non-degassed MeOH
at 300 nm (Table 3, entries 1–5). The reaction could not be
performed with cycloadduct 1d due to its low solubility in
MeOH. Notably, all the products precipitated from the reac-
tion medium and the pure products were isolated after
simple filtration. Cycloadducts 1b and 1c (R=Rꢅ=EWG;
Table 3, entries 1 and 2) reacted more slowly than PK ad-
ducts 1e and 1 f (R=Rꢅ=ERG; Table 3, entries 3 and 4).
Two days were required for the reactions of 1b and 1c to
reach completion, whereas seven hours were sufficient in
the case of 1e. Remarkably, the reaction of cycloadduct 1 f
was very fast and the compound was fully converted into 2 f
after three hours of irradiation. We next considered the PK
adduct 1g, which bears an ERG and EWG. The deleterious
Unsymmetrical acetylene 4g was prepared in a similar
fashion, from two different aryl iodides. The thermal PK re-
action of 4g with norbornadiene afforded a mixture of re-
3944
www.chemeurj.org
ꢃ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 3942 – 3948

Photochemistry of Pauson–Khand Adducts
FULL PAPER
Table 3. Photochemical reactions of diaryl Pauson–Khand adducts 1b–g.
vent, it is necessary to analyze both reaction mechanisms.
We have recently reported a detailed theoretical and experi-
mental study of the photorearrangement of compounds I
into the tricyclic ketones II.[12] From this study, it was con-
cluded that, although there is a non-adiabatic pathway that
starts on the 1
tion product is formed through the
energy barrier involved in the initial C C g-bond cleavage
of the enone is much lower in the
3(pp*) PES than in the
1(np*) PES. The 3
(pp*) PES can be easily accessed in the re-
actant region through intersystem crossing (ISC) from the
1(np*) to the 3(pp*) state.
Although a detailed mechanistic study of the transforma-
tion of 1 into 2 has not yet been performed, several theoreti-
cal and experimental studies on related systems (hexa-
trienes[15] and diarylethenes[16]) have established that the
conrotatory 6p electrocyclization is allowed under photo-
chemical activation and that the reaction occurs in the sin-
glet manifold.[17]
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
Entry
R
R’
hn
[nm]
Solvent
t
Ratio Product Yield
À
[h] 2/3
[%]
AHCTUNGTRENNUNG
1
2
3
4
5
6
7
8
F
Cl
tBu
OMe
OMe
F
F
Cl
tBu
OMe
300 MeOH[a] 48 100:0 2b
quant
quant
quant
quant
quant
quant
quant
68
G
ACHTUNGTRENNUNG
300 MeOH[a] 48 100:0 2c
300 MeOH[a]
300 MeOH[a]
7
3
100:0 2e
100:0 2 f
R
ACHTUNGTRENNUNG
CO2Me 300 MeOH[a] 144 100:0 2g
[b]
F
Cl
365 CH2Cl2
365 CH2Cl2
26 0:100 3b
26 0:100 3c
22 0:100 3d
72 0:100 3g
72 50:50 2d/3d
[b]
[b]
[b]
Cl
CO2Me CO2Me 365 CH2Cl2
OMe CO2Me 365 CH2Cl2
CO2Me CO2Me 365 MeOH/
9
10
58[c]
79[d]
[b]
CH2Cl2
[b]
11
12
13
tBu
tBu
OMe
tBu
tBu
OMe
365 CH2Cl2
72 40:60 2e/3e
47[d]
66[d]
7
365 hexane[b] 72 16:84 2e/3e
In both reaction pathways, the strong solvent dependence
of the photochemical reactions of PK adducts 1 can be ex-
plained by the assumption that the 6p electrocyclization to 2
[b]
365 CH2Cl2
23 n.d.[e] 2 f
[a] Non-degassed solution. [b] Degassed solution. [c] 26% of starting ma-
terial (1g) was recovered. [d] Combined yield of 2 and 3. [e] Compound
3 f was not detected by NMR spectroscopy.
takes place through the
ment to 3 occurs through the
apolar solvents, such as hexanes or CH2Cl2, facilitate ISC
from the 1(np*) to the 3
(pp*) state and strongly favor the re-
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
effect of the EWG appeared to predominate over the reac-
tion rate because the reaction was slowed down dramatically
relative to that of cycloadduct 1 f. The selectivity towards
2g, however, was complete when working at 300 nm.
A
ACHTUNGTRENNUNG
arrangement to 3. It is well-documented that the ISC rate
constant depends strongly on the polarity of the solvent, the
rate being higher in less polar solvents.[18] Conversely, be-
cause the pericyclic reaction occurs through a singlet excited
state it is more favored in polar reaction mediums, such as
MeOH,[19] in which the rate of ISC is very low.
Oxygen plays two essential roles: as an enone triplet
quencher and an oxidant in the tandem electrocyclization/
oxidative aromatization reaction. Thus, oxygen should be
present in the medium to favor the pathway to phenan-
threne compounds 2. Conversely, oxygen should be removed
from the reaction medium for the photorearrangement to
compounds 3 because it quenches the triplet enone through
which the transformation occurs.
In addition, to achieve the most favorable conditions for
the rearrangement, PK adducts 1b–g were irradiated at
365 nm in degassed CH2Cl2. The reaction was completely se-
lective for PK adducts 1b–d and 1g (Table 3, entries 6–9).
Selectivity dropped dramatically when a mixture of solvents
was used. Thus, irradiation of 1d in degassed CH2Cl2/MeOH
(1:1) at 365 nm gave a 1:1 mixture of 2d and 3d (Table 3,
entry 10). This result could be attributed to the presence of
MeOH. The presence of an ERG on the aryl ring lowered
the rate and the selectivity of the reaction (Table 3, en-
tries 11 and 12). For instance, a mixture of 2e and 3e was
obtained when the cycloadduct 1e, which bears tert-butyl
groups at the para positions of the aromatic rings, was sub-
jected to irradiation in CH2Cl2 at 365 nm (Table 3, entry 11).
Interestingly, selectivity in favor of 3e increased from 40:60
to 16:84 when hexane was used instead of CH2Cl2 (Table 3,
entry 12). It became clear that ERGs do not favor the pho-
torearrangement, which is almost completely suppressed in
the case of methoxy-substituted cycloadduct 1 f (Table 3,
entry 13). After 23 h of irradiation, we observed a complex
mixture of products, from which only 7% of 2 f could be iso-
lated. In the case of the unsymmetrical PK adduct 1g, the
reaction proceeded at a slow rate (26% of starting material
was recovered after 3 days of irradiation), although the pho-
torearranged compound 3g was the only product observed
(Table 3, entry 9).
The effect of the aromatic ring substituents can be easily
1(np*) state
explained. We assume that ERGs stabilize the CAHTUNGRTENNGUN
by acceleration of the 6p-electrocyclization, whereas EWGs
displace the electron density, thus disfavoring this process.
Our results fully support this interpretation.[20]
Conclusion
We have reported the diverse photochemical behavior of
the PK adducts of bis-aryl alkynes 1a–g in response to sev-
eral solvents, oxygen, and irradiation wavelengths. Several
trends emerge from these experimental results. For degassed
CH2Cl2, a longer wavelength (365 nm) and an electron-re-
leasing group favor the formation of photorearranged prod-
ucts 3a–g; for non-degassed MeOH, a shorter wavelength
(300 nm) and an electron-withdrawing group are the condi-
To explain the experimental findings and rationalize the
strong dependence of selectivity on the nature of the sol-
Chem. Eur. J. 2011, 17, 3942 – 3948
ꢃ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3945

A. Riera, X. Verdaguer, and Y. Ji
8.6 Hz; CH), 128.5 (d, J
4.0 Hz; C), 132.8 (C), 135.4 (dd, J
138.6 (CH), 158.0 (C), 162.0 (d, J
N
ACHTUNGTRENNUNG(C,F)=8.2,
tions of choice for the preparation of phenanthrene products
2a–g. We have recently developed the first asymmetric in-
termolecular PK reaction for internal symmetric alkynes
and it is worth noting that both products 2 and 3 can be ob-
tained in their optically pure form and, in most cases, in
high yield and complete selectivity.
AHCTUNGTRENNUNG
G
ACHTUNGTRENNUNG
333.1083 [M+H]+; elemental analysis calcd (%) for C22H14F2O·1= H2O: C
78.10, H 4.37; found: C 78.20, H 4.34.
3
(1S*,2S*,6R*,7R*)-1,9-Bis(4-fluorophenyl)tricyclo[5.2.1.02,6]deca-3,8-
dien-10-one (3b): Following the general procedure, a solution of 1b
(37 mg, 0.11 mmol) in CH2Cl2 was irradiated at 365 nm for 26 h. Purifica-
tion by flash chromatography on SiO2 (hexanes/AcOEt, gradient elution)
afforded 3b (37 mg, quant) as a white solid. M.p. 1518C; 1H NMR
(400 MHz, CDCl3): d=2.28–2.40 (m, 1H; CH2), 2.68–2.80 (m, 1H; CH
and 1H; CH2), 3.00 (d, J=3.9 Hz, 1H; CH), 3.65–3.73 (m, 1H; CH),
5.70–5.76 (m, 1H; CH), 5.79–5.84 (m, 1H; CH), 6.75 (d, J=3.9 Hz, 1H;
CH), 6.77–6.84 (m, 2H; CH), 6.87–6.94 (m, 2H; CH), 6.96–7.04 (m, 2H;
CH), 7.29–7.35 ppm (m, 2H; CH); 13C NMR (100 MHz, CDCl3): d=36.7
Experimental Section
General: All reactions were carried out under nitrogen atmosphere in
solvents dried with a solvent purification system (SPS). Chromatographic
purifications performed on a Combiflash (Teledyne Isco) automated
chromatography system with silica gel RediHep columns. 1H, 13C and
19F NMR spectra were recorded at room temperature on a Varian Mercu-
ry 400 spectrometer and were referenced to residual solvent peaks.
Signal multiplicities in the 13C NMR spectra have been assigned with the
aid of DEPT and HSQC experiments. Melting points were measured by
differential scanning calorimetry. Compounds 4b–j were prepared by de-
scribed procedures; compounds 1a–c are known.[7]
(CH2), 43.1 (CH), 53.2 (CH), 54.6 (CH), 63.4 (C), 115.1 (d, J
18.8 Hz, 2ꢄCH), 115.4 (d, J(C,F)=18.5 Hz, 2ꢄCH), 128.4 (CH), 128.7
(d, J(C,F)=1.0 Hz; CH), 128.8 (d, J(C,F)=8.1 Hz, 2ꢄCH), 130.5 (d, J-
(C,F)=3.3 Hz; C), 131.8 (d, J(C,F)=3.4 Hz; C), 131.9 (d, J(C,F)=7.9 Hz,
2ꢄCH), 134.7 (CH), 148.4 (C), 161.8 (d, J(C,F)=246.3 Hz; C), 162.3 (d,
(C,F)=247.7 Hz; C), 201.9 ppm (C=O); 19F NMR (376 MHz, CDCl3):
ACHTUNGTRENNUNG(C,F)=
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
General procedure for the photochemical reactions: The PK cycloadduct
1 was dissolved into the volume of solvent necessary to reach a 0.018m
concentration or until a totally homogeneous solution was formed. When
stated, the solvent was previously degassed with a stream of bubbling ni-
trogen for 1 h. The solution was placed into a flask provided with mag-
netic stirring and irradiated at 365 or 300 nm in a Rayonet-type reactor
provided with seven lamps (8 W). The temperature inside the reactor
was measured to be 30–358C. The reaction was monitored by TLC.
JACHTUNGTRENNUNG
d=À114.5 (br), À115.65 ppm (br); IR (film): n˜ =2909, 1775, 1511, 1226,
1160, 813 cmÀ1; elemental analysis calcd (%) for C22H16F2O (334.36): C
79.03, H 4.82; found: C 78.81, H 4.84.
(9aS*,10S*,13R*,13aR*)-3,6-Dichloro-10,13-methano-9a,10,13,13a-tetra-
hydro-[9H]-indenoACHTNUTGRNEUNG[1,2-l]phenanthren-9-one (2c): Following the general
procedure, a solution of 1c (50 mg, 0.14 mmol) in MeOH was irradiated
at 300 nm for 2 d. Filtration afforded 2c (50 mg, quant) as a white solid.
M.p. 2138C; 1H NMR (400 MHz, CDCl3): d=1.11 (d, J=9.5 Hz, 1H;
CH2), 1.44 (d, J=9.5 Hz, 1H; CH2), 2.83 (d, J=5.6 Hz, 1H; CH), 3.13 (s,
1H; CH), 3.22 (s, 1H; CH), 3.63 (d, J=5.6 Hz, 1H; CH), 6.40 (dd, J=
5.5, 2.9 Hz, 1H; CH), 6.52 (dd, J=5.5, 3.0 Hz, 1H; CH), 7.67 (dd, J=8.8,
2.0 Hz, 1H; CH), 7.71 (dd, J=8.6, 1.9 Hz, 1H; CH), 8.22 (d, J=8.6 Hz,
1H; CH), 8.50 (d, J=1.9 Hz, 1H; CH), 8.58 (d, J=1.8 Hz, 1H; CH),
9.25 ppm (d, J=8.8 Hz, 1H; CH); 13C NMR (100 MHz, CDCl3): d=44.6
(CH2), 45.4 (CH), 45.9 (CH), 55.2 (CH), 122.6 (CH), 123.8 (CH), 126.2
(C), 126.8 (CH), 127.3 (C), 127.4 (CH), 128.5 (CH), 129.4 (CH), 130.8
(C), 133.4 (C), 134.0 (C), 134.0 (C), 136.9 (C), 138.1 (CH), 138.6 (CH),
158.6 (C), 207.3 ppm (C=O); IR (film): n˜ =2976, 1695, 1604, 1514, 1400,
1175 cmÀ1; HRMS (ESI): m/z calcd for C22H15Cl2O: 365.0500; found:
Reaction products 2 precipitated from the reaction mixture. Simple filtra-
tion after cooling the solution afforded pure products. In the preparation
of rearranged products 3, the solvent was removed in vacuo and the
crude product was purified by flash chromatography.
(1S*,2S*,6R*,7R*)-1,9-Diphenyltricyclo[5.2.1.02,6]deca-3,8-dien-10-one
(3a): Following the general procedure,
a solution of 1a (30 mg,
0.10 mmol) in degassed CH2Cl2 was irradiated at 365 nm for 26 h. Purifi-
cation by flash chromatography on SiO2 (hexanes/AcOEt, gradient elu-
tion) afforded both 2a[5] (1 mg, 3%) and 3a (24 mg, 80%) as white
solids. M.p. 1648C; 1H NMR (400 MHz, CDCl3): d=2.30–2.40 (m, 1H;
CH2), 2.69–2.79 (m, 1H; CH and 1H; CH2), 3.00 (d, J=3.9 Hz, 1H; CH),
3.72–3.76 (m, 1H; CH), 5.78–5.85 (m, 2H; CH), 6.79 (d, J=3.9 Hz, 1H;
CH), 6.96–7.00 (m, 2H; CH), 7.07–7.12 (m, 3H; CH), 7.16–7.22 (m, 1H;
CH), 7.26–7.31 (m, 2H; CH), 7.35–7.38 ppm (m, 2H; CH); 13C NMR
(100 MHz, CDCl3): d=36.7 (CH2), 43.2 (CH), 53.0 (CH), 54.7 (CH), 64.0
(C), 126.9 (CH), 127.0 (2ꢄCH), 127.5 (CH), 128.0 (2ꢄCH), 128.2 (2ꢄ
CH), 128.6 (CH), 128.9 (CH), 130.5 (2ꢄCH), 134.3 (CH), 134.7 (C),
135.8 (C), 149.5 (C), 202.3 ppm (C=O); IR (film): n˜ =3054, 1768, 1496,
1444, 756, 743 cmÀ1; HRMS (ESI): m/z calcd for C22H19O: 299.1430;
found: 299.1436 [M+H]+; m/z calcd for C22H22NO: 316.1695; found:
316.1693 [M+NH4]+; m/z calcd for C22H18ONa: 321.1249; found:
365.0491 [M+H]+; elemental analysis calcd (%) for C22H14Cl2O·1= H2O:
4
C 71.46, H 3.95; found: C 71.39, H 3.90.
(1S*,2S*,6R*,7R*)-1,9-Bis(4-chlorophenyl)tricyclo[5.2.1.02,6]deca-3,8-
dien-10-one (3c): Following the general procedure, a solution of 1c
(45 mg, 0.12 mmol) in CH2Cl2 was irradiated at 365 nm for 26 h. Purifica-
tion by flash chromatography on SiO2 (hexanes/AcOEt, gradient elution)
afforded 3c (45 mg, quant) as a white solid. M.p. 1778C; 1H NMR
(400 MHz, CDCl3): d=2.28–2.38 (m, 1H; CH2), 2.68–2.79 (m, 1H; CH
and 1H; CH2), 3.01 (d, J=3.9 Hz, 1H; CH), 3.65–3.70 (m, 1H; CH),
5.70–5.73 (m, 1H; CH), 5.79–5.83 (m, 1H; CH), 6.79 (d, J=3.9 Hz, 1H;
CH), 6.85–6.91 (m, 2H; CH), 7.07–7.13 (m, 2H; CH), 7.28 ppm (s, 4H;
CH); 13C NMR (100 MHz, CDCl3): d=36.7 (CH2), 43.1 (CH), 53.1 (CH),
54.6 (CH), 63.4 (C), 128.3 (CH), 128.3 (2ꢄCH), 128.5 (2ꢄCH), 128.6 (2ꢄ
CH), 129.3 (CH), 131.7 (2ꢄCH), 133.1 (C), 133.1 (C), 133.7 (C), 134.0
(C), 134.8 (CH), 148.1 (C), 201.4 ppm (C=O); IR (film): n˜ =2901, 1774,
1493, 1092, 1013, 802 cmÀ1; elemental analysis calcd (%) for C22H16Cl2O
(367.27): C 71.95, H 4.39; found: C 71.91, H 4.41.
321.1250 [M+Na]+; elemental analysis calcd (%) for C22H18O·1= H2O: C
87.50, H 6.14; found: C 87.77, H 6.14.
5
(9aS*,10S*,13R*,13aR*)-3,6-Bis
ACHTUNGTREN(NUNG fluoro)-10,13-methano-9a,10,13,13a-tet-
rahydro-[9H]-indeno[1,2-l]phenanthren-9-one (2b): Following the gener-
ACHTUNGTRENNUNG
al procedure, a solution of 1b (50 mg, 0.15 mmol) in MeOH was irradiat-
ed at 300 nm for 2 d. Filtration afforded 2b (50 mg, quant) as a white
solid. M.p. 1988C; 1H NMR (400 MHz, CDCl3): d=1.13 (d, J=9.5 Hz,
1H; CH2), 1.44 (d, J=9.5 Hz, 1H; CH2), 2.82 (d, J=5.6 Hz, 1H; CH),
3.14 (s, 1H; CH), 3.22 (s, 1H; CH), 3.64 (d, J=5.5 Hz, 1H; CH), 6.40
(dd, J=5.5, 2.9 Hz, 1H; CH), 6.52 (dd, J=5.5, 2.9 Hz, 1H; CH), 7.46 (dt,
J=8.7, 2.4 Hz, 1H; CH), 7.51 (dt, J=8.5, 2.4 Hz, 1H; CH), 8.11 (dd, J=
10.8, 2.5 Hz, 1H; CH), 8.19 (dd, J=10.8, 2.4 Hz, 1H; CH), 8.30 (dd, J=
8.9, 5.9 Hz, 1H; CH), 9.33 ppm (dd, J=9.0, 6.2 Hz, 1H; CH); 13C NMR
(100 MHz, CDCl3): d=42.7 (CH2), 44.6 (CH), 45.3 (CH), 45.9 (CH), 55.1
(9aS*,10S*,13R*,13aR*)-3,6-Bis(methoxycarbonyl)-10,13-methano-
9a,10,13,13a-tetrahydro-[9H]-indenoACTHNUGRTNEUNG[1,2-l]phenanthren-9-one (2d): Fol-
lowing the general procedure, a solution of 1d (72 mg, 0.17 mmol) in
MeOH (plus a small amount of CH2Cl2 to achieve a totally homogeneous
solution) was irradiated at 365 nm for 3 d. Purification by flash chroma-
tography on SiO2 (hexanes/AcOEt, gradient elution) afforded 2d (27 mg,
39%) as a yellow solid and 3d (28 mg, 40%) as a white solid. M.p.
2468C; 1H NMR (400 MHz, CDCl3): d=1.16 (d, J=9.5 Hz, 1H; CH2),
(CH), 108.4 (d, J
117.0 (d, J(C,F)=23.7 Hz; CH), 117.7 (d, J
(C,F)=1.7 Hz; C), 125.8 (d, J(C,F)=1.7 Hz; C), 127.7 (d, JACHTUNGRTENNUGN
G
ACHTUNGTREN(NUGN C,F)=22.7 Hz; CH),
R
ACHTUNGTRENNUNG
J
G
A
3946
www.chemeurj.org
ꢃ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 3942 – 3948

Photochemistry of Pauson–Khand Adducts
FULL PAPER
1.46 (d, J=9.6 Hz, 1H; CH2), 2.88 (d, J=5.6 Hz, 1H; CH), 3.20 (br, 1H;
CH), 3.26 (br, 1H; CH), 3.73 (d, J=5.6 Hz, 1H; CH), 4.06 (s, 3H; CH3),
4.09 (s, 3H; CH3), 6.42 (dd, J=5.5, 3.0 Hz, 1H; CH), 6.56 (dd, J=5.6,
3.0 Hz, 1H; CH), 8.34 (dd, J=8.5, 1.6 Hz, 1H; CH), 8.35 (d, J=0.9 Hz,
1H; CH), 9.38 (d, J=8.4 Hz, 1H; CH), 9.46 (d, J=1.5 Hz, 1H; CH),
9.52 ppm (brs, 1H; CH); 13C NMR (100 MHz, CDCl3): d=42.7 (CH2),
44.8 (CH), 45.4 (CH), 46.2 (CH), 52.7 (CH3), 52.9 (CH3), 55.2 (CH),
125.1 (CH), 125.4 (CH), 126.1 (CH), 126.3 (CH), 127.8 (CH), 128.8
(CH), 129.1 (C), 130.3 (C), 130.6 (C), 131.5 (C), 131.6 (C), 133.5 (C),
134.9 (C), 138.1 (CH), 138.7 (CH), 160.4 (C), 166.9 (C=O), 167.2 (C=O),
149.1 (C), 149.6 (C), 150.4 (C), 203.1 ppm (C=O); IR (film): n˜ =2961,
1776, 1518, 1363, 1269, 837 cmÀ1; HRMS (ESI): m/z calcd for C30H35O:
411.2682; found: 411.2685 [M+H]+; m/z calcd for C30H38NO: 428.2947;
found: 428.2951 [M+NH4]+; m/z calcd for C60H72NO2: 838.5557; found:
838.5555 [2M+NH4]+; elemental analysis calcd (%) for C30H34O·H2O: C
84.07, H 8.47; found: C 84.15, H 8.29.
(9aS*,10S*,13R*,13aR*)-3,6-Bis
ACHTUNGTRENUN(NG methoxy)-10,13-methano-9a,10,13,13a-
tetrahydro-[9H]-indeno[1,2-l]phenanthren-9-one (2 f): Following the
AHCTUNGTRENNUNG
general procedure, a solution of 1 f (55 mg, 0.15 mmol) in MeOH was ir-
radiated at 300 nm for 3 h. Filtration afforded 2 f (55 mg, quant) as a
yellow solid. M.p. 2218C; 1H NMR (400 MHz, CDCl3): d=1.15 (d, J=
9.4 Hz, 1H; CH2), 1.40 (d, J=9.4 Hz, 1H; CH2), 2.78 (d, J=5.6 Hz, 1H;
CH), 3.13 (s, 1H; CH), 3.19 (s, 1H; CH), 3.61 (d, J=5.6 Hz, 1H; CH),
4.02 (s, 3H; CH3), 4.06 (s, 3H; CH3), 6.38 (dd, J=5.6, 3.0 Hz, 1H; CH),
6.50 (dd, J=5.5, 3.0 Hz, 1H; CH), 7.33 (dd, J=3.9, 2.5 Hz, 1H; CH),
7.35 (dd, J=3.8, 2.6 Hz, 1H; CH), 7.94 (d, J=2.5 Hz, 1H; CH), 7.98 (d,
J=2.4 Hz, 1H; CH), 8.20 (d, J=8.9 Hz, 1H; CH), 9.24 ppm (d, J=
9.0 Hz, 1H; CH); 13C NMR (100 MHz, CDCl3): d=42.7 (CH2), 44.4
(CH), 45.4 (CH), 45.8 (CH), 55.1 (CH), 55.7 (CH3), 55.8 (CH3), 105.5
(CH), 105.8 (CH), 116.9 (CH), 117.1 (CH), 122.5 (C), 123.5 (C), 126.8
(CH), 127.8 (CH), 131.5 (C), 131.7 (C), 135.3 (C), 138.0 (CH), 138.6
(CH), 157.2 (C), 158.7 (C), 161.0 (C), 207.5 ppm (C=O); IR (film): n˜ =
2933, 1680, 1612, 1514, 1402, 1236 cmÀ1; HRMS (ESI): m/z calcd for
C24H21O3: 357.1485; found: 357.1486 [M+H]+; m/z calcd for C48H41O6:
713.2898; found: 713.2899 [2M+H]+; elemental analysis calcd (%) for
207.4 ppm (C=O); IR (film): n˜ =2963, 1691, 1614, 1409, 1263, 827 cmÀ1
;
HRMS (ESI): m/z calcd for C26H21O5: 413.1383; found: 413.1370
[M+H]+, m/z calcd for C52H41O10: 825.2694; found: 825.2674 [2M+H]+;
m/z calcd for C52H44NO10: 842.2959; found: 842.2929 [2M+NH4]+.
(1S*,2S*,6R*,7R*)-1,9-Bis(4-methoxycarbonylphenyl)tricy-
clo[5.2.1.02,6]deca-3,8-dien-10-one (3d): Following the general procedure,
a solution of 1d (41 mg, 0.10 mmol) in CH2Cl2 was irradiated for 22 h.
Purification by flash chromatography on SiO2 (hexanes/AcOEt, gradient
elution) afforded 3d (28 mg, 68%) as
a white solid. M.p. 1898C;
1H NMR (400 MHz, CDCl3): d=2.35–2.45 (m, 1H; CH2), 2.72–2.82 (m,
1H; CH and 1H; CH2), 3.07 (d, J=3.9 Hz, 1H; CH), 3.75–3.80 (m, 1H;
CH), 3.84 (s, 3H; CH3), 3.89 (s, 3H; CH3), 5.76–5.86 (m, 2H; CH), 6.92
(d, J=3.9 Hz, 1H; CH), 7.02 (d, J=8.5 Hz, 2H; CH), 7.43 (d, J=8.5 Hz,
2H; CH), 7.76 (d, J=8.5 Hz, 2H; CH), 7.96 ppm (d, J=8.5 Hz, 2H;
CH); 13C NMR (100 MHz, CDCl3): d=36.7 (CH2), 43.1 (CH), 52.2 (2ꢄ
CH3), 52.9 (CH), 54.8 (CH), 64.2 (C), 126.9 (2ꢄCH), 128.3 (CH), 128.9
(C), 129.2 (C), 129.5 (2ꢄCH), 129.6 (2ꢄCH), 130.5 (2ꢄCH), 130.6 (CH),
135.0 (CH), 139.8 (C), 139.9 (C), 148.3 (C), 166.8 (C=O), 167.0 (C=O),
C24H20O3·1= H2O: C 78.88, H 5.79; found: C 78.75, H 5.67.
2
(9aS*,10S*,13R*,13aR*)-3-Methoxycarbonyl-6-methoxy-10,13-methano-
9a,10,13,13a-tetrahydro-[9H]-indenoACTHNUGRTNEUNG[1,2-l]phenanthren-9-one (2g): Fol-
200.9 ppm (C=O); IR (film): n˜ =2943, 1779, 1722, 1610, 1435, 1281 cmÀ1
;
HRMS (ESI): m/z calcd for C26H23O5: 415.1540; found: 415.1540
[M+H]+, m/z calcd for C26H22O5Na: 437.1359; found: 437.1361 [M+Na]+;
m/z calcd for C52H45O10: 829.3007; found: 829.3019 [2M+H]+; m/z calcd
for C52H44O10Na: 851.2827; found: 851.2834 [2M+Na]+; elemental analy-
lowing the general procedure, a solution of 1g (40 mg, 0.10 mmol) in
MeOH was irradiated at 300 nm for 6 d. Filtration afforded 2g (40 mg,
quant) as a yellow solid. M.p. 2218C; 1H NMR (400 MHz, CDCl3): d=
1.13 (d, J=9.5 Hz, 1H; CH2), 1.42 (d, J=9.5 Hz, 1H; CH2), 2.82 (d, J=
5.6 Hz, 1H; CH), 3.15 (s, 1H; CH), 3.22 (s, 1H; CH), 3.64 (d, J=5.6 Hz,
1H; CH), 4.05 (s, 3H; CH3), 4.07 (s, 3H; CH3), 6.39 (dd, J=5.6, 2.9 Hz,
1H; CH), 6.53 (dd, J=5.5, 3.0 Hz, 1H; CH), 7.36 (dd, J=9.0, 2.5 Hz,
1H; CH), 8.08 (d, J=2.5 Hz, 1H; CH), 8.30 (br, 2H; CH), 9.23 (d, J=
9.0 Hz, 1H; CH), 9.33 ppm (s, 1H; CH); 13C NMR (100 MHz, CDCl3):
d=42.7 (CH2), 44.7 (CH), 45.2 (CH), 45.8 (CH), 52.7 (CH3), 55.2 (CH),
55.8 (CH3), 105.1 (CH), 118.0 (CH), 122.1 (C), 126.0 (CH), 126.1 (CH),
126.8 (CH), 127.1 (CH), 130.4 (C), 131.8 (C), 132.5 (C), 132.8 (C), 135.3
(C), 138.0 (CH), 138.8 (CH), 155.7 (C), 159.4 (C), 167.1 (C=O),
sis calcd (%) for C26H22O5·1= H2O: C 74.54, H 5.41; found: C 74.83, H
4
5.39.
(9aS*,10S*,13R*,13aR*)-3,6-Bis(tert-butyl)-10,13-methano-9a,10,13,13a-
tetrahydro-[9H]-indenoACHTUNGTRENNUNG[1,2-l]phenanthren-9-one (2e): Following the
general procedure, a solution of 1e (60 mg, 0.15 mmol) in MeOH was ir-
radiated at 300 nm for 7 h. Filtration afforded 2e (60 mg, quant) as a
yellow solid. M.p. 1858C; 1H NMR (400 MHz, CDCl3): d=1.14 (d, J=
9.3 Hz, 1H; CH2), 1.39 (d, J=9.6 Hz, 1H; CH2), 1.51 (s, 9H; CH3), 1.54
(s, 9H; CH3), 2.86 (d, J=5.5 Hz, 1H; CH), 3.18 (br, 1H; CH), 3.20 (br,
1H; CH), 3.66 (d, J=5.6 Hz, 1H; CH), 6.38 (dd, J=5.6, 2.9 Hz, 1H;
CH), 6.52 (dd, J=5.5, 3.0 Hz, 1H; CH), 7.76–7.81 (m, 2H; CH), 8.23 (d,
J=8.5 Hz, 1H; CH), 8.66 (d, J=1.9 Hz, 1H; CH), 8.74 (d, J=1.8 Hz,
1H; CH), 9.22 ppm (d, J=8.6 Hz, 1H; CH); 13C NMR (100 MHz,
CDCl3): d=31.5 (3ꢄCH3), 31.6 (3ꢄCH3), 35.4 (C), 35.7 (C), 42.6 (CH2),
44.5 (CH), 45.3 (CH), 45.9 (CH), 55.1 (CH), 118.1 (CH), 119.3 (CH),
124.9 (CH), 125.3 (CH), 125.6 (C), 125.8 (CH), 126.4 (CH), 126.7 (C),
130.3 (C), 133.8 (C), 134.0 (C), 138.0 (CH), 138.7 (CH), 150.0 (C), 153.1
(C), 158.6 (C), 207.9 ppm (C=O); IR (film): n˜ =2963, 1691, 1614, 1409,
1263, 827 cmÀ1; HRMS (ESI): m/z calcd for C30H33O: 409.2525; found:
409.2516 [M+H]+, m/z calcd for C60H65O2: 817.4979; found: 817.4971
[2M+H]+.
(1S*,2S*,6R*,7R*)-1,9-Bis(4-tert-butylphenyl)tricyclo[5.2.1.02,6]deca-3,8-
dien-10-one (3e): Following the general procedure, a solution of 1e
(248 mg, 0.60 mmol) in CH2Cl2 was irradiated for 3 d. Purification by
flash chromatography on SiO2 (hexanes/AcOEt, gradient elution) provid-
ed 2e (46 mg, 19%) as a yellow solid and 3e (69 mg, 28%) as a white
solid. M.p. 1538C; 1H NMR (400 MHz, CDCl3): d=1.21 (s, 9H; CH3),
1.28 (s, 9H; CH3), 2.28–2.38 (m, 1H; CH2), 2.66–2.74 (m, 1H; CH and
1H; CH2), 2.97 (d, J=3.9 Hz, 1H; CH), 3.69–3.74 (m, 1H; CH), 5.78
(dd, J=5.8, 1.9 Hz, 1H; CH), 5.87 (dd, J=5.8, 2.1 Hz, 1H; CH), 6.79 (d,
J=3.9 Hz, 1H; CH), 6.92 (d, J=8.4 Hz, 2H; CH), 7.10 (d, J=8.5 Hz,
2H; CH), 7.27–7.33 ppm (m, 4H; CH); 13C NMR (100 MHz, CDCl3): d=
31.3 (3ꢄCH3), 31.5 (3ꢄCH3), 34.6 (2ꢄC), 36.7 (CH2), 43.4 (CH), 52.8
(CH), 54.5 (CH), 63.6 (C), 124.9 (2ꢄCH), 125.2 (2ꢄCH), 126.5 (2ꢄCH),
127.8 (CH), 129.2 (CH), 130.2 (2ꢄCH), 131.6 (C), 132.8 (C), 134.1 (CH),
208.0 ppm (C=O); IR (film): n˜ =2923, 1720, 1691, 1515, 1256, 762 cmÀ1
;
HRMS (ESI): m/z calcd for C25H21O4: 385.1440; found: 385.1435
[M+H]+; m/z calcd for C50H40O8Na: 791.2621; found: 791.2635
[2M+Na]+; elemental analysis calcd (%) for C25H20O4·1= H2O: C 76.91, H
3
5.34; found: C 76.89, H 5.26.
(1S*,2S*,6R*,7R*)-1-(4-Methoxyphenyl)-9-(4-methoxycarbonylphenyl)-
tricyclo[5.2.1.02,6]deca-3,8-dien-10-one (3g): Following the general proce-
dure, a solution of 1g (50 mg, 0.13 mmol) in CH2Cl2 was irradiated for
3 d. Purification by flash chromatography on SiO2 (hexanes/AcOEt, gra-
dient elution) afforded 3g (29 mg, 58%) as a white solid and 1g (26%).
M.p. 1928C; 1H NMR (400 MHz, CDCl3): d=2.29–2.40 (m, 1H; CH2),
2.69–2.79 (m, 1H; CH and 1H; CH2), 3.02 (d, J=4.0 Hz, 1H; CH), 3.70–
3.73 (m, 1H; CH), 3.76 (s, 3H; CH3), 3.85 (s, 3H; CH3), 5.81 (s, 2H;
CH), 6.84 (d, J=8.8 Hz, 2H; CH), 6.90 (d, J=4.0 Hz, 1H; CH), 7.06 (d,
J=8.5 Hz, 2H; CH), 7.26 (d, J=8.8 Hz, 2H; CH), 7.78 ppm (d, J=
8.5 Hz, 2H; CH); 13C NMR (100 MHz, CDCl3): d=36.7 (CH2), 43.2
(CH), 52.2 (CH3), 53.1 (CH), 54.7 (CH), 55.3 (CH3), 63.4 (C), 113.9 (2ꢄ
CH), 126.3 (C), 126.9 (2ꢄCH), 128.8 (CH), 128.9 (C), 129.4 (2ꢄCH),
130.3 (CH), 131.4 (2ꢄCH), 134.4 (CH), 140.3 (C), 148.7 (C), 158.6 (C),
166.9 (C=O), 202.4 ppm (C=O); IR (film): n˜ =2953, 1773, 1721, 1609,
1516, 1282 cmÀ1; HRMS (ESI): m/z calcd for C25H21O4: 387.1591; found:
387.1593 [M+H]+; m/z calcd for C55H44O8Na: 773.3109; found: 773.3112
[2M+H]+; m/z calcd for C55H44O8Na: 795.2928; found: 791.2933
[2M+Na]+; elemental analysis calcd (%) for C25H22O4·1= H2O: C 76.81,
4
H, 5.80; found: C 76.61, H 5.74.
Chem. Eur. J. 2011, 17, 3942 – 3948
ꢃ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
3947

A. Riera, X. Verdaguer, and Y. Ji
2005, 26–41; g) D. Strꢆbing, M. Beller, Top Organomet. Chem. 2006,
18, 165–178; h) H.-W. Lee, F.-Y. Kwong, Eur. J. Org. Chem. 2010,
789–811.
Acknowledgements
We thank MICINN (CTQ2008–00763/BQU), IRB Barcelona and the
Generalitat de Catalunya (2009SGR 00901) for financial support. Y.J.
thanks the MEC for a predoctoral fellowship.
[7] Y. Ji, A. Riera, X. Verdaguer, Org. Lett. 2009, 11, 4346–4349.
[8] T. Ogino, F. Wada, T. Murayama, S. Aoki, K. Ohshima, Tetrahedron
Lett. 1996, 37, 7065–7068.
[9] a) F. B. Mallory, C. W. Mallory, Org. React. 1984, 30, 1; b) C. S.
Wood, F. B. Mallory, J. Org. Chem. 1964, 29, 3373–3377; c) J. R.
Davy, P. J. Jessup, J. A. Reiss, J. Chem. Educ. 1975, 52, 747–748;
d) S. Amin, J. Camanzo, K. Huie, S. S. Hecht, J. Org. Chem. 1984,
49, 381–384.
[10] K. Matsuda, M. Irie, Chem. Lett. 2006, 35, 1204–1209.
[11] B. E. Moulton, H. Dong, C. T. OꢅBrien, S. B. Duckett, Z. Lin, I. J. S.
Fairlamb, Org. Biomol. Chem. 2008, 6, 4523–4532.
[1] a) N. Hoffmann, Chem. Rev. 2008, 108, 1052; b) A. G. Griesbeck, J.
Mattay, Mol. Supramol. Photochem. 2005, 12, 1; c) CRC Handbook
of Organic Photochemistry and Photobiology, (Eds.: W. Horspool, F.
Lenci), CRC Press, Boca Raton, 2004; d) J. P. Hehn, C. Mꢆller, T.
Bach in Handbook of Synthetic Photochemistry, (Eds.: A. Albini, M.
Fagnoni), Wiley-VCH, Weinheim, 2009, 171.
[2] Recent examples: a) W. D. Shipe, E. J. Sorensen, J. Am. Chem. Soc.
2006, 128, 7025–7035; b) M. Fleck, T. Bach, Angew. Chem. 2008,
120, 6284–6286; Angew. Chem. Int. Ed. 2008, 47, 6189–6191; c) M.
Le Liepvre, J. Ollivier, D. J. Aitken, Eur. J. Org. Chem. 2009, 5953–
5962; d) L. M. Tedaldi, J. R. Baker, Org. Lett. 2009, 11, 811–814;
e) P. Selig, E. Herdtweck, T. Bach, Chem. Eur. J. 2009, 15, 3509–
3525; f) D. Albrecht, F. Vogt, T. Bach, Chem. Eur. J. 2010, 16, 4284–
4296; g) M. Fleck, T. Bach, Chem. Eur. J. 2010, 16, 6015–6032.
[3] Recent examples: a) L. A. Paquette, J. D. Pettigrew, Synthesis 2009,
379–384; b) G. A. Abakumov, N. N. Vavilina, L. N. Zakharov, Y. A.
Kurskii, V. I. Nevodchikov, A. S. Shavyrin, Russ. Chem. Bull. 2004,
53, 2276–2280; c) L. A. Paquette, Z. Zhao, F. Gallou, J. Liu, J. Am.
Chem. Soc. 2000, 122, 1540–1541; d) I. Marchueta, S. Olivella, L.
Sola, A. Moyano, M. A. Pericas, A. Riera, Org. Lett. 2001, 3, 3197–
3200; e) K. Tanaka, R. Nagahiro, Z. Urbanczyk-Lipkowska, Chirali-
ty 2002, 14, 568–572.
[4] Recent examples: a) A. Vazquez-Romero, J. Rodriguez, A. Lledo,
X. Verdaguer, A. Riera, Org. Lett. 2008, 10, 4509–4512; b) N. Mase,
Y. Watanabe, T. Toru, Bull. Chem. Soc. Jpn. 1998, 71, 2957–2965;
c) R. Mosca, M. Fagnoni, M. Mella, A. Albini, Tetrahedron 2001, 57,
10319–10328.
[5] A. Lledꢇ, J. Benet-Buchholz, A. Sole, S. Olivella, X. Verdaguer, A.
Riera Angew. Chem. 2007, 119, 6047–6050; Angew. Chem. Int. Ed.
2007, 46, 5943–5946.
[12] S. Olivella, A. Sole, A. Lledo, Y. Ji, X. Verdaguer, R. Suau, A.
Riera, J. Am. Chem. Soc. 2008, 130, 16898–16907.
[13] M. J. Mio, L. C. Kopel, J. B. Braun, T. L. Gadzikwa, K. L. Hull,
R. G. Brisbois, C. J. Markworth, P. A. Grieco, Org. Lett. 2002, 4,
3199–3202.
[14] a) F. Robert, A. Milet, Y. Gimbert, D. Konya, A. E. Greene, J. Am.
Chem. Soc. 2001, 123, 5396–5400; b) T. J. M. de Bruin, A. Milet, F.
Robert, Y. Gimbert, A. E. Greene, J. Am. Chem. Soc. 2001, 123,
7184–7185; c) T. J. M. de Bruin, C. Michel, K. Vekey, A. E. Greene,
Y. Gimbert, A. Milet, J. Organomet. Chem. 2006, 691, 4281–4288.
[15] a) H. Tamura, S. Nanbu, H. Nakamura, T. Ishida, Chem. Phys. Lett.
2005, 401, 487–491; b) P. Celani, F. Bernardi, M. A. Robb, M. Oli-
vucci, J. Phys. Chem. 1996, 100, 19364–19366; c) D. A. Harris, M. B.
Orozco, R. J. Sension, J. Phys. Chem. A 2006, 110, 9325–9333.
[16] a) U. Mazzucato, A. Spalletti, J. Phys. Chem. A 2009, 113, 14521–
14529; b) H. R. Talele, M. J. Gohil, A. V. Bedekar, Bull. Chem. Soc.
Jpn. 2009, 82, 1182–1186; c) F. B. Mallory, C. S. Wood, J. T. Gordon,
J. Am. Chem. Soc. 1964, 86, 3094–3102.
[17] a) T. Ogino, F. Wada, T. Murayama, S. Aoki, K. Ohshima, Tetrahe-
dron Lett. 1996, 37, 7065–7068; b) F. B. Mallory, C. W. Mallory, J.
Am. Chem. Soc. 1972, 94, 6041–6048.
[18] E. V. Sitzmann, J. Langan, K. B. Eisenthal, J. Am. Chem. Soc. 1984,
106, 1868–1869.
[19] P. Lupattelli, M. D’Auria, N. Di Blasio, F. Lenti, Eur. J. Org. Chem.
2009, 141–145.
[20] S. M. Pearson Morwenna, D. R. Carbery, J. Org. Chem. 2009, 74,
5320–5325.
[6] For selected general reviews, see: a) S. Laschat, A. Becheanu, T.
Bell, A. Baro, Synlett 2005, 2547–2570; b) S. E. Gibson, N. Mainolfi,
Angew. Chem. 2005, 117, 3082–3097; Angew. Chem. Int. Ed. 2005,
44, 3022–3037; c) S. E. Gibson, A. Stevenazzi, Angew. Chem. Int.
Ed. 2003, 42, 1800–1810; d) L. V. R. Bonaga, M. E. Krafft, Tetrahe-
dron 2004, 60, 9795–9833; e) T. Shibata, Adv. Synth. Catal. 2006,
348, 2328–2336; f) M. R. Rivero, J. Adrio, J. C. Carretero, Synlett
Received: April 20, 2010
Revised: October 19, 2010
Published online: March 4, 2011
3948
www.chemeurj.org
ꢃ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 3942 – 3948