Control of reaction pathways in the photochemical reaction of a quinone with tetramethylethylene by metal binding

Article abstract of DOI:10.1039/c4ob00659c

The present study reports a novel supramolecular photochemical reaction that focuses on the direct electronic interactions between a host reaction substrate and guest metal salts. The reaction pathways in the photochemical reactions of quinone derivatives bearing a methoxy group and a long oligoether sidearm QE_n (n = 0 and 3) with tetramethylethylene (TME) are changed upon noncovalent complexations of the host reactant with alkali and alkaline earth metal ions and a transition metal salt. The photochemical reaction of QE_n with TME provides a mixture of [2 + 2] cycloadducts 1aE _n and 1bE_n, hydroquinone H₂QE_n, and monoallyl ether adducts of hydroquinones 2aE_n and 2bE_n. The photochemical reaction proceeds by the photoinduced electron transfer mechanism, where photoirradiation brings about formation of a radical ion pair [QE_n^-, TME⁺] as the primary intermediate. We found that the yields and selectivity of these photoproducts are changed upon electronic interactions of QE_n^- with the metal salts. The photochemical reaction in the absence of metal salts provides H ₂QE_n as its major product, whereas QE₃, having the long sidearm, dominantly produces 2aE₃ at the expense of 1aE ₃, 1bE₃, and H₂QE₃ when it forms a size-favorable host-guest complex with divalent Ca²⁺. In contrast, QE_n selectively provides oxetanes 1aE_n and 1bE_n in the presence of Pd(OAc)₂, which can form complexes with the quinone through metal-olefin and coordination interactions in the ground and photoexcited states of the quinone. This journal is the Partner Organisations 2014.

Full text of DOI:10.1039/c4ob00659c

Volume 12 Number 36 28 September 2014 Pages 6955–7168
Organic &
Biomolecular
Chemistry
www.rsc.org/obc
ISSN 1477-0520
PAPER
Akihiko Tsuda et al.
Control of reaction pathways in the photochemical reaction of a quinone
with tetramethylethylene by metal binding

Organic &
Biomolecular Chemistry
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PAPER
Control of reaction pathways in the
photochemical reaction of a quinone with
tetramethylethylene by metal binding†
Cite this: Org. Biomol. Chem., 2014,
2, 7004
1
a
b
c
b
Hiroaki Yamamoto, Kei Ohkubo, Seiji Akimoto, Shunichi Fukuzumi and
Akihiko Tsuda*
a
The present study reports a novel supramolecular photochemical reaction that focuses on the direct elec-
tronic interactions between a host reaction substrate and guest metal salts. The reaction pathways in the
photochemical reactions of quinone derivatives bearing a methoxy group and a long oligoether sidearm
QE
host reactant with alkali and alkaline earth metal ions and a transition metal salt. The photochemical reac-
tion of QE with TME provides a mixture of [2 + 2] cycloadducts 1aE and 1bE , hydroquinone H QE
and monoallyl ether adducts of hydroquinones 2aE and 2bE . The photochemical reaction proceeds by
the photoinduced electron transfer mechanism, where photoirradiation brings about formation of a
radical ion pair [QE
•−, TME•+] as the primary intermediate. We found that the yields and selectivity of
these photoproducts are changed upon electronic interactions of QE
chemical reaction in the absence of metal salts provides H QE as its major product, whereas QE
the long sidearm, dominantly produces 2aE3 at the expense of 1aE , 1bE , and H QE when it forms a
n
(n = 0 and 3) with tetramethylethylene (TME) are changed upon noncovalent complexations of the
n
n
n
2
n
,
n
n
n
•
−
n
with the metal salts. The photo-
, having
2
n
3
Received 28th March 2014,
Accepted 29th May 2014
3
3
2
3
2+
size-favorable host–guest complex with divalent Ca . In contrast, QE
and 1bE in the presence of Pd(OAc) , which can form complexes with the quinone through metal–olefin
and coordination interactions in the ground and photoexcited states of the quinone.
n n
selectively provides oxetanes 1aE
DOI: 10.1039/c4ob00659c
n
2
www.rsc.org/obc
1
–13
fined cavities of the host molecules
or by noncovalent
Introduction
1
4–17
binding with the template molecule or metal.
The host
Photochemical synthesis is a complementary method of and the template allow specific reactions of the reactant mole-
synthesizing molecules that are difficult to obtain through cules with highly restricted structures and orientations in the
thermal reactions. Precise control of the photochemical reac- molecular assemblies (Fig. 1a). However, less attention has
tion is, however, more difficult to achieve than that of the been paid to the direct electronic interactions between the
thermal reaction, because the excited states are short-lived host and the guest, especially for those that can be seen in the
1
8
with high reactivity even at low temperatures. In general, steric noncovalently linked metal–host complexes.
and electronic modifications of the reactant molecule result in One of the authors reported a metal-catalyzed photochemi-
changes in reaction pathways of the photochemical reactions. cal reaction, where a magnesium ion promotes the photo-
On the other hand, supramolecular photochemical reactions chemical reaction of organosilane with an aromatic carbonyl
occur by accommodation of the reactant molecules in the con- compound that proceeds through a photoinduced electron
1
9
2+
transfer mechanism. Mg –carbonyl interaction exhibited a
remarkable increase in the redox reactivity of carbonyl com-
pounds. On the other hand, Kochi and coworkers reported a
a
20
Department of Chemistry, Graduate School of Science, Kobe University,
-1 Rokkodai-cho, Nada-ku, Kobe 657-8501, Japan. E-mail: tsuda@harbor.kobe-u.ac.jp
1
b
salt-inhibited photochemical reaction, where tetra-n-butyl-
ammonium hexafluorophosphate suppresses the [2 + 2] cyclo-
addition of p-chloranil with stilbene that also proceeds
Department of Material and Life Science, Graduate School of Engineering, Osaka
University, ALCA, Japan Science and Technology Agency, 2-1 Yamada-oka, Suita,
Osaka 565-0871, Japan
2
1
c
Molecular Photoscience Research Center, Kobe University, 1-1 Rokkodai-cho,
through a photoinduced electron transfer mechanism. The
added salt interacts with the intermediate radical ion pair by
ion exchange to separate the p-chloranil anion and the stilbene
cation. Subsequently, we hypothesized that a strong site-selec-
tive metal binding by the reaction substrate itself in the photo-
induced electron transfer reaction dramatically changes the
Nada-ku, Kobe 657-8501, Japan
†
1
13
Electronic supplementary information (ESI) available: H and C NMR spectro-
scopies, HPLC analyses, X-ray crystallography, mass spectrometry, and ESR
spectroscopies, and further details of computational calculations. CCDC 894295.
For ESI and crystallographic data in CIF or other electronic format see DOI:
1
0.1039/c4ob00659c
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Scheme 1 2-Substituted quinones QE
0
and QE
3
and their metal-com-
plexations in the ground state.
Fig. 1 Concepts of supramolecular photochemical reactions through
(
a) inclusion of reactants in a host cavity and (b) metal binding of the
photoinduced electron transfer complex.
Scheme 2 Photochemical reaction of p-benzoquinone with TME.
2
2
photochemical reaction pathways (Fig. 1b). Such a control of
the photochemical reaction pathways by strong metal–host
interactions has not yet been reported.
There are some reports on thermal supramolecular reac-
tions using the noncovalent metal complexes as the reaction
above, photochemical reactions of QE (n = 0 or 3) with tetra-
n
methylethylene (TME) have been examined in the absence and
+
2+
2+
presence of metal ions (Na , Mg , Ca , and transition metal
salts of Pd(OAc) ). We have found that the product selectivity
2
2
3,24
of oxetanes, hydroquinone, and monoallylether of hydro-
quinones and the quantum yield are changed by complexa-
substrates.
tive QE (Scheme 1), bearing a long oligoether sidearm,
dramatically accelerates [4 + 2] cycloaddition with cyclopenta-
We previously reported that a quinone deriva-
3
•
−
tions of QEn and the radical anions (QEn ) with the metal
2
3
salts in the course of the photochemical reactions. The
diene upon noncovalent complexation with metal ions. This
is an example of the thermal supramolecular reaction,
•
−
2
4–27
binding modes of metal salts with QE
n
are clarified by the
direct detection of metal salt complexes by ESR spectroscopy.
where the bound metal ion lowers the LUMO of the quinone
with respect to the HOMO of cyclopentadiene. We herein
anticipated that QE
3
can form metal complexes with the
1
oligoether and/or the quinone moiety in both the ground H NMR spectroscopy of QE with or
3
and photoexcited states, which change the photoinduced
without metal salts
electron transfer reaction pathways by steric and electronic
interactions.
Although QE0 in the ground state rarely forms metal com-
It is known that the photochemical reaction of a quinone plexes with alkaline metal and alkaline earth metal ions in
with olefin provides [2 + 2] adducts such as cyclobutane and MeCN, QE3 bearing a long oligoether sidearm can form the
2
8
23
oxetane. The reactions forming the latter oxetane usually metal complexes.
QE , having a podand-type structure,
3
+
2+
proceed through the photoinduced electron transfer mechan- forms size-favorable complexes with Na and Ca with the
ism, being called Paterno–Büchi reactions.
2
9,30
−1
Oshima and binding constant K = 120 and 4900 M , respectively, in 1 : 1
coworkers reported that photochemical reaction of p-benzo- stoichiometry at 20 °C, but forms a size-mismatch complex
2
+
quinone with TME gave not only the oxetane but also monoallyl- with the smaller Mg with a relatively lower binding constant
−
1
ethers of hydroquinone in the photoinduced electron transfer K = 69 M
mechanism (Scheme 2). With our hypothesis described
(Table 1 and Fig. S1†). Representatively, the
3
1
1
H NMR spectrum of QE in CD CN exhibited large downfield
3
3
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a
3
Table 1 Photochemical reactions of QE with TME in the absence or presence of metal salts
c
Yield (%)
b
Kd (M−1)
+
ΔGET (kcal mol−1
e
g
Entry
Metal salt
1aE
3
1bE
3
H QE
2 3
2aE
3
2bE
3
E
red vs. Fc/Fc (V)
)
Quantum yield (Φ)
1
2
3
4
5
None
NaClO
Mg(ClO
Ca(ClO
Pd(OAc)
10
5
9
1
19
10
11
8
1
20
24
33
26
11
—
6
17
21
42
—
5
8
5
7
−0.81
−10.9f
0.21
0.24
0.27
0.32
0.06
4
120
69
h4900
−0.62
−17.8
h
h
4
)
2
f
4
)
2
−0.18
−0.83
−28.2f
2
—
−7.1
a
MeCN solution containing 10 mM of QE
3
and 40 mM of TME (4 eq.) without or with metal salts upon photoirradiation at λ > 420 nm at 20 °C.
Metal salt concentration and reaction time: 100 mM and 20 min for NaClO , Mg(ClO , Ca(ClO , and 10 mM and 150 min for Pd(OAc)
Determined by HPLC and H NMR. Determined at 20 °C. Calculated using the Weller free energy relationship for photoinduced electron
b
c
4
)
4 2
)
4 2
2
.
1
d
e
f
g
h
transfer (eqn (1)). Observed value. Determined by ferrioxalate actinometry. The value could not be determined.
logous palladium–olefin bond and/or
a π-allylpalladium
3
6
1
complex, its H NMR signal of methyl protons, observed at
δ = 1.66 ppm, showed no change upon mixing with Pd(OAc)2
under the same conditions (Fig. S2†). The four methyl groups
of TME may sterically hinder the possible metal–olefin inter-
action. As expected, even in the 1 : 1 : 1 ternary mixture of QE3,
TME, and Pd(OAc) , QE showed the same spectral changes
2
3
without any changes of TME signals (Fig. S3†).
Redox potentials of QE in the
3
absence and presence of metal salts
The one-electron reduction potentials of QE3 in the absence
and presence of metal salts in MeCN containing 0.1 M
1
Fig. 2 H NMR spectral changes of QE
CD CN. (a) QE , (b) a 1 : 3 mixture of QE
: 3 mixture of QE and Pd(OAc) . [QE ] = 10 mM.
3
upon mixing with metal salts in
3
3
3
and Ca(ClO , and (c) a
4 2
)
Bu
cyclic voltammetry (Fig. S4† and Table 1). The cyclic voltammo-
gram of QE showed the one-electron redox couple at E1/2
shifts (Fig. 2a and b) upon complexation with Ca . The −0.81 V vs. Fc/Fc , corresponding to QE /QE . With reference
4 4
NClO as a supporting electrolyte were determined by
1
3
2
3
37
3
=
2
+
+
•−
3
3
signals observed at δ = 4.1–3.3 and 6.8–6.0 ppm, corresponding to p-benzoquinone, which provided the redox couple at E1/2
=
to the oligoether sidearm and the quinone moiety, respecti- −0.70 V, the observed lower potential of QE indicates that the
3
vely, showed downfield shifts with Δδ = 0.19–0.29 and oligoether group attached at the C2 position donates electrons
0
.20–0.22 ppm, respectively. These observed peak shifts indi- to the quinone moiety. When Ca(ClO ) , having the largest
4 2
2
+
cate that Ca binds QE at its carbonyl group and oligoether binding constant with QE3 in the series of metal ions, was
sidearm, where the guest Ca strongly withdraws electrons added into the sample solution, a large positive shift (ΔE1/2
through oxygen atoms (Scheme 1a).
3
2
+
=
3
2
+0.63 V) of the redox couple was observed. As indicated by the
H NMR spectroscopic study described above, Ca signifi-
3
3
1
2+
When QE was mixed with Pd(OAc)2 however, the two sets
3
of signals at δ = 6.69 and 6.73 ppm, corresponding to the vinyl cantly withdraws electrons from QE through electronic inter-
3
protons of C5 and C6 positions, respectively, notably broaden actions with carbonyl and ether oxygens in the complex
into a unified single peak at δ = 6.67 ppm (Fig. 2c). In sharp (Scheme 1a). A smaller positive shift of the reduction potential
+
contrast, no notable change was observed in the other protons, of QE was observed with monovalent Na (ΔE = +0.19 V).
3
1/2
2
+
including those in the oligoether sidearm. This characteristic Although Mg also brought about a positive shift of the
peak shift suggests the formation of a metal–olefin complex at reduction potential, the redox profile becomes irreversible. In
3
4,35
C5–C6 olefin (Scheme 1b).
The observed preference of the contrast, a very small negative shift of the redox (ΔE1/2
=
complexation at C5–C6 olefin rather than C2–C3 olefin can be −0.02 V) was observed without a notable change of the redox
explained by their different π-electronic structures and steric profile of the quinone upon mixing with Pd(OAc) , having the
2
+
38
hindrance caused by the presence of either the methoxy or the irreversible reduction peak at around −0.52 V vs. Fc/Fc . This
3
5
oligoether group. Since the metal–olefin complexation is result indicates that Pd(OAc) is electrically rather neutral for
2
usually very weak in the neutral state, we could not determine the one-electron redox process of the quinone. This agrees
1
the binding constant between QE3 and Pd(OAc) . Although with the results obtained in the H NMR spectroscopic study
2
TME, having a double bond, is also expected to form an ana- described above.
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The free energy change for electron transfer (ΔGET) from
Photochemical reactions of QE with
TME
n
3
−1
TME to QE * is estimated to be −8.1 kcal mol by the Weller
0
0
equation (eqn (1)) using the reduction potential of QE (Ered =
+
−
0.81 V vs. Fc/Fc ), the one-electron oxidation potential of
When the photochemical reaction of QE0 with TME was
performed in MeCN at 20 °C upon photoirradiation (>420 nm)
for 20 min with a 500 W xenon lamp, a mixture of oxetanes
4
0
TME (E = 1.21 V) (Fig. S8†), the triplet excitation energy of
ox
3
QE
0
( E(T)* = 2.36 eV), which was evaluated from its phos-
phorescence spectrum with λmax at 525 nm taken at 77 K
1
aE0 and 1bE , hydroquinone H QE , and monoallyl ether
0 2 0
4
1–43
(
Fig. S9†).
0 0
adducts of hydroquinones 2aE and 2bE were obtained in 14,
1
7, 23, 3, and 5% yields, respectively (Scheme 3, entry 6 in
3
ΔGET ðin eVÞ ¼ eðEox ꢀ EredÞ ꢀ EðTÞ* þ wp
ð1Þ
Table 2, and Fig. S5a†). No notable change in the product
yields was observed upon further photoirradiation of the
sample solution. The products, isolated by column chromato-
graphy or preparative HPLC, were characterized by means of
This result indicates that the photochemical reaction pro-
ceeds by the photoinduced electron transfer mechanism in
which the photoirradiation brings about formation of the
•
−
•+
1
13
radical ion pair [QE0 , TME ] as the primary reaction inter-
mediate, which then allows a biradical formation (path A), a
proton transfer (PT) reaction (path B), and a hydrogen transfer
H and C NMR spectroscopy (see ESI†), IR spectroscopy, elec-
trospray ionization (ESI) mass spectrometry, and elemental
analysis. 2aE0 was further characterized by X-ray crystallo-
graphy (Fig. S6†). In the reference reaction without TME, a 40%
decrease of QE was observed after photoirradiation for 20 min
2
8–30,44
39
(
HT) reaction (path C) (Scheme 4a).
tanes 1aE and 1bE , while paths B and C give hydroquinone
0
QE and monoallyl ether of hydroquinones 2aE and 2bE .
Path A provides oxe-
0
0
0
1
H
2
0
0
in both the H NMR spectroscopy and the HPLC analysis
After the PT reaction in path B, the final products are produced
through hydrogen transfer (HT) and radical coupling reactions
of the tertiary allyl radical with the semiquinone radical
(
Fig. S7†). Since there was no detectable product in these ana-
lyses, QE may gradually decompose upon photoirradiation.
0
•
•
(
4-HQE0 or 1-HQE ). On the other hand, after the HT reaction
0
in path C, proton transfer and ion coupling reactions of the
−
tertiary allyl cation with the hydroquinone anion (4-HQE
0
or
−
1
-HQE0 ) provide the same products. QE , having an oligo-
3
ether sidearm, affords dominantly the PT/HT products
Fig. S5b†). The observed difference in the ratio of the [2 + 2]
adducts to the PT and HT products in the reactions of QE and
(
3
0
QE can be explained by the slightly different electric charac-
teristics of the attached substituent groups (entry 1 in Table 1
and entry 6 in Table 2).
Photochemical reactions of metal ion
complexes of QE with TME
n
Scheme 3 Photochemical reactions of QE
n
with TME.
In the absence of a metal salt, [2 + 2] cycloaddition and PT/HT
0
reactions equally occur with QE , whereas the PT/HT reaction
dominantly occurs with QE (Tables 1 and 2). Both the reac-
3
tions give the hydroquinone as the major product. The
Table 2 Photochemical reactions of QE
presence of metal salts
0
with TME in the absence or product yields and selectivity of the reactions are changed
a
upon addition of alkaline and alkaline earth metal ions into
the reaction systems. The photochemical reactions of QE
n
(n =
c
Yield (%)
0
or 3) with TME were performed in MeCN containing
b
Entry
Metal salt
1aE
0
1bE
0
2
H QE
0
2aE
0
2bE
0
10 equiv. of the metal ion for 20 min. In the case of QE0,
without an oligoether sidearm, the yield of hydroquinone
6
7
8
9
None
NaClO
Mg(ClO
Ca(ClO
Pd(OAc)
14
12
10
6
17
13
11
5
23
27
21
20
—
3
4
11
19
—
5
5
2
3
+
H
2
QE
0
was slightly increased with monovalent Na , while the
4
4
)
2
yield of 2aE0 increased at the expense of other products in
2
+
2+
4
)
2
cases with divalent ions Mg and Ca (entries 6–9 in Table 2,
1
0
2
22
27
—
and Fig. 3a). The selectivity (%) of the PT/HT products for
a
MeCN solution containing 10 mM of QE
0
and 40 mM of TME (4 eq.) [2 + 2] adducts, defined as [(H QE + 2aEn + 2bEn − 1aEn
2
n
without or with metal salts upon photoirradiation at λ > 420 nm at
−
1bE
n
)/(H
2
QE
n
+ 2aE
n
+ 2bE
n
n n
+ 1aE + 1bE )] × 100, is
b
2
2
0 °C. Metal salt concentration and reaction time: 100 mM and
0 min for NaClO , Mg(ClO , Ca(ClO , and 10 mM and 150 min for
Determined by HPLC and H NMR.
+
increased in the following order: without metal (0%) < Na
(18%) < Mg (24%) < Ca (58%) (Fig. 3c, black bars). In the
4
4
)
2
4 2
)
1
c
2+
2+
Pd(OAc)
2
.
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2+
n 2
Scheme 4 Reaction pathways of QE with TME in the absence and presence of Ca and Pd(OAc) .
2
+
case with Ca , the total yield of the PT/HT products (H
2
QE
0
,
Table 1) was further photoirradiated upon mixing with
2
aE , and 2bE ) was slightly increased from 31% to 42% at the Ca(ClO ) , no notable changes of the product yields were
0
0
4 2
expense of [2 + 2] adducts (1aE and 1bE ) from 31% to 11% observed. No photoisomerization from oxetane to monoallyl
0
0
(
entries 6 and 9 in Table 2). Interestingly, this observed trend ether adduct occurred upon photoirradiation of the isolated
2
+
dramatically stands out in QE , which can bind a metal ion 1aE in the presence of Ca , either.
(
relatively high selectivity of H QE , while Mg and Ca
2 3
increased mainly 2aE3 at the expense of [2 + 2] adducts
3
3
+
Fig. 3b). Na increased the yields of most of the products with
2
+
2+
Mechanistic study for the
m+
2
+
(
entries 1–4 in Table 1 and Fig. 3b). In the case with Ca , the photochemical reactions of QE /M
3
total yield of PT/HT products increased from 35% to 60%,
while oxetanes decreased from 20% to 2%, where the main
with TME
product was 2aE in 42% yield (Fig. S5c†). The selectivity of The observed trend in the above photochemical reactions of
3
the PT/HT products increased in the following order: without QE with TME, where yields of the PT/HT products increased
3
2
+
+
2+
metal (27%) < Mg (51%) < Na (57%) < Ca (94%) (Fig. 3c, at the expense of the oxetanes in the presence of metal ions,
purple bars). When the resulting sample solution after the indicates that the bound metal ion electronically stabilizes the
•
−
•+
19,20
reaction of QE
3
and TME without metal ions (entry 1 in initial radical ion pair [QE3 , TME ] (Scheme 4b)
to
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Scheme 5 Possible interactions of [QE
n
•−, TME•+] photoinduced electron
2+
2
transfer complex with (a) Ca or (b) Pd(OAc) .
3
m+
from TME to [QE
3
. M ]* (Table 1). The quantum yields (Φ)
of the reactions also increased in the presence of metal ions.
2
+
Here, the combination of QE and Ca , which forms the most
stable divalent complex QE
3
2
+
3
. Ca , shows the largest change
in the one-electron reduction potential, the driving force
2
+
(
−ΔGET) and the quantum yield. The size-favorable QE . Ca
3
complexation may efficiently decelerate the back electron
transfer by electronic interaction between the semiquinone
radical anion and the bound metal ion in the radical ion pair
•
−
2+
•+
20
[QE
3
. Ca , TME ] (Scheme 4b and 5a) (vide infra). This
electronic interaction withdraws the anionic charge of the
quinone radical anion with decreasing the charge density,
especially at C1 oxygen, but increases the spin density at C4
oxygen. It may subsequently decelerate both the O–C bond for-
mation and the PT reaction in paths A and B, respectively, but
accelerates the HT reaction in path C.
The PT/HT reactions occur at either oxygen of quinone, and
the pathway must be highly dependent on the electron and
spin densities of the carbonyl groups. We performed DFT
calculations at the UB3LYP/6-31+G(d,p) level to evaluate the
Fig. 3 Changes in yields of products when varying added metal salts in
the photochemical reaction of QE
Selectivity (%) of PT/HT products (H
cycloadducts (1aE and 1bE ).
n
with TME; (a) n = 0, (b) n = 3. (c)
2
QE , 2aE , and 2bE ) for [2 + 2] atomic charge and spin densities of the radical anion of the
n
n
n
•
−
n
n
host quinone QE
4 2
in the absence or presence of Ca(ClO )
The results show that both the anionic
3
4
5,46
(
Fig. 4 and ESI†).
charge and the spin densities of the quinone oxygens are
decelerate the O–C bond formation, when the PT/HT reaction higher than those of the six-membered ring. Although no
is the major reaction pathway. Here, the oligoether sidearm notable difference in the charges between the two oxygens of
•
−
may assist complexation of the host substrate with the metal quinone in QE
is observed without the metal ion, the
3
•
−
2+
ion in the course of photoinduced electron transfer reaction. QE
The proposed electronic interaction in the initial radical ion charge of QE
3
. Ca complex shows a larger decrease of the anionic
•
−
, especially at C1 oxygen (from −0.71 to −0.53
3
pair is supported by the fact that metal ions bring about posi- at C1 oxygen, from −0.73 to −0.68 at C4 oxygen). The spin
tive shifts of the one-electron reduction potential of QE3, density also decreases at C1 oxygen (from 0.26 to 0.21),
which increase the driving force of electron transfer (−ΔGET
)
whereas it increases at C4 oxygen (from 0.22 to 0.25). These
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reaction, a transition metal salt of Pd(OAc)
tive formation of oxetanes with increases in the product yields
Tables 1 and 2, and Fig. 3). The reactions of QE with TME
were carried out in MeCN containing 1.0 equiv. of Pd(OAc) for
.5 h. In comparison with the reactions without or with
Pd(OAc) , the total yields of the oxetanes 1aE and 1bE
2
allowed the selec-
(
n
2
2
2
n
n
increased from 31% to 49% and from 20% to 39% at the
expense of all the other products in QE and QE , respectively
0
3
(
entry 10 in Table 2 and entry 5 in Table 1, respectively, and
Fig. S11†). The starting quinone and formation of other pro-
•
−
•−
Fig. 4 Calculated electron potential maps of (a) QE
3
and QE
3
3
. Ca- ducts were not observed after the reactions. When the reaction
•−
1
(
(
ClO
ClO
4
4
)
)
2
, with the atomic charge and spin density ratios of QE
. Ca-
was monitored by H NMR spectroscopy, dominant formations
•−
2
to QE
3
on O(1) and O(4) by DFT calculation with the UB3LYP/
of the oxetanes were also observed in the course of the reaction
Fig. S12 and S13†). Furthermore, no isomerization reaction
from the monoallyl ether to the oxetane occurred upon photo-
results are reasonably explained by the size-favorable com- irradiation of the isolated 2aE by mixing with Pd(OAc)
plexation, which includes the strong electronic interaction Therefore, the observed changes in the yields and selectivity of
6
-31+G(d,p) level.
(
3
2
.
2
+
between C1 oxygen and Ca . Since both [2 + 2] and PT reac- the products can also be explained by the complexations of Pd-
•
−
•+
tions (paths A and B, respectively) may be decelerated by (OAc)
2
with QE
n
and with [QE
n
, TME ] (Scheme 4b). Since
•
−
3
decreasing the charge density of QE
3
upon the complexation, the driving force of electron transfer from TME to QE
3
* in the
1
the HT reaction (path C) dominantly occurs at C4 oxygen, presence of Pd(OAc)
2
(−ΔGET = 7.1 kcal mol− ) is smaller than
having a higher spin density, to form an intermediate that without the metal ion and Pd(OAc)
2
absorbs visible light,
−
4
-HQE
3
. The subsequent bond forming reaction with the allyl the quantum yield of the reaction decreased to 0.06 (entry 5 in
1
cation provides 2aE
3
. Otherwise, proton transfer from the allyl Table 1). As discussed in the H NMR spectroscopic study
most likely forms a metal–olefin
in rapid equilibrium in the ground state,
is electronically neutral. In such a case, Pd-
cation would allow formation of H QE . The resulting product described above, Pd(OAc)
2
2
3
of 2,3-dimethyl-1,3-butadiene in the reaction mixture was actu- complex with QE
3
1
ally detected in the H NMR spectroscopic measurements where Pd(OAc)
2
•
−
(
Fig. S10†). The unreacted TME and the water included in the (OAc)
solvent may be the candidates for the hydrogen source in the TME ], formed through photoinduced electron transfer reac-
2
+
may stabilize the semiquinone radical anion in [QE
n
,
•
formation of H
In this mechanism, the observed differences in yields of QE
hydroquinone and its monoallyl ether adducts can also be (Schemes 4b and 5b).
2
QE
3
.
tion, by coordination bonding without a large separation of
•
−
•+
n
and TME to accelerate the O–C bond formation
3
3
explained by considering the charge density of hydroquinone
DFT calculations with the UB3PW91/LANL2DZ level of the
•
−
anions formed in the possible intermediate metal complex of possible complex of QE
0
2
and Pd(OAc) , with a hypothesis
−
−
m+
4
4
-HQE
-HQE
3
. M . Here, the resulting ionic interaction of that Pd(OAc)
coordinates to C4 oxygen when it catalyze O–C
2
with the metal ion reduces the charge density of C1 bond formation, show an increase and a decrease of the
3
oxygen. This may decelerate the subsequent proton transfer atomic charge and spin density, respectively, at C4 oxygen, and
4
5,46
reaction, resulting in the observed increase in 2aE
3
−
formed vice versa at C1 oxygen (Fig. 5 and ESI†).
Pd(OAc) may
2
through the bond forming reaction between 4-HQE
3
and the interact with the anion to allow charge and spin localizations
without decreases in their densities and, thus, become a tem-
With these proposed mechanisms, monovalent Na , which plate for O–C bond formation, resulting in selective formation
allyl cation.
+
1
6
also forms a size-favorable complex with QE
3
, may stabilize the of the oxetanes to increase the yields. Since no notable
•
−
+
•+
initial radical ion pair of [QE3 /Na , TME ] (Schemes 4 and change of the product ratio of 1aE
n
and 1bE
n
is observed in
5
), but the interaction may be electrically too weak to affect the the reactions with or without Pd(OAc)
2
, it can be expected that
subsequent reactions, resulting in increments of the reaction there is no preference in interactions of Pd(OAc)
2
with C1 or
products, except for 1aE (Table 1). Actually, the driving force C4 oxygen.
3
3
of electron transfer from TME to QE
mol ) in the presence of Na and the redox potential of
QE . Na are smaller than those of QE . Ca .
3
* (−ΔGET = 17.8 kcal
−
1
+
+
2+
3
3
2+
Detections of Ca and Pd(OAc)
2
complexes of the semiquinone radical
anion
•−/Ca2+ and QE •−/Pd(OAc)
The QE complexes were success-
3 3 2
Photochemical reactions of Pd(OAc)2-
complexes of QE with TME
n
In sharp contrast to the cases with alkaline or alkaline earth fully detected by absorption spectroscopy and ESR in
metal ions, which act as Lewis acids in the photochemical photoinduced electron transfer from dimeric 1-benzyl-1,4-
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•
−
Fig. 5 Calculated electron potential maps of QE
0
and a possible
QE
atomic charge and spin density ratios of QE
(1) and O(4) by DFT calculation with the UB3PW91/LANL2DZ level.
0 2
•−/Pd(OAc)
complex formed through O(4)–Pd interaction with the
•−
•−
0
/Pd(OAc)
2
to QE
0
on
O
dihydronicotinamide [(BNA)
2 3
] to QE in the presence of
2
0,47
Ca(ClO ) or Pd(OAc) , respectively, in MeCN (eqn (2)).
The
BNA) is known to act as a two-electron donor to produce the
4
2
2
(
2
4
8
radical anions of electron acceptors.
hv
QE3 þ ðBNAÞ2 ꢀ! 2QE3 þ 2BNAþ
•
ꢀ
ð2Þ
2
The difference spectrum of the UV/Vis absorption spectra
•
−
of QE
3
3
and QE provided λmax at 420 nm with a shoulder
around 450–550 nm (Fig. 6a). The spectral profile dramatically
changed in the presence of Ca(ClO ) or Pd(OAc) (Fig. 6b and
4
2
2
c, respectively). The absorption bands were red-shifted to
27 nm and 550–800 nm with Ca(ClO , while a broad absorp-
4
4 2
)
tion band appeared in the range of 400–800 nm with Pd(OAc)2.
These different spectra strongly indicate formation of the
•
−
metal complexes of QE
3
, generated upon photoirradiation
2
+
with Ca or Pd(OAc)2.
The ESR spectrum of QE
•
−
3
in the absence of the metal salt
was also observed at g = 2.0055 with hyperfine splitting due to
three inequivalent protons with a(3H) = 0.98, 2.14, and 3.63 G
•
−
and two equivalent protons with a(2H) = 0.86 G of QE
43 K in Fig. 7a. These hyperfine coupling constants are deter-
mined by a computer-simulated spectrum that agrees well Fig. 6 Difference spectra in UV/Vis absorption of (a) QE
3
at
2
3
, (b) QE
after photoirradiation in
] = 0.33 mM, Ca(ClO = 3.3 mM,
3
/
Ca(ClO
deaerated MeCN at 293 K. [QE
(BNA) ] = [Pd(OAc) ] = excess.
4 2 3 2 2
) , or (c) QE /Pd(OAc) with (BNA)
with the observed spectrum. Further, these constants are con-
sistent with those predicted by the DFT calculation at the
UB3LYP/6-311G(d) level (Fig. S14†). The ESR spectrum was
changed to the spectra at g = 2.0049 with a(3H) = 1.13, 1.80,
3
4 2
)
[
2
2
and 3.66 G, a(2H) = 0.80 G in the presence of Ca(ClO
98 K (Fig. 7b), or g = 2.0057 with a(3H) = 2.75, 0.90, and 1.07 complex by the DFT calculation at the UB3LYP/LANL2DZ level
G, a(2H) = 1.95 G in the presence of Pd(OAc)
at 243 K (Fig. 7c). also suggest that Pd(OAc) interacts with the radical anion
These results also indicate that the radical anion of quinone of quinone mainly through C5–C6 bonds of the quinone
4 2
) at
2
2
2
2
+
forms metal complexes with Ca and Pd(OAc) , respectively. (Fig. S14†). Electrospray Ionization Fourier Transform Mass
2
The smaller or larger g values observed with Ca(ClO
Pd(OAc)
, respectively, suggest a decrease or an increase in the the QE
π-electron spin density of the radical anion of quinone when it of a mixture of QE
)
4 2
or Spectrometry (ESI-FT-MS) for the sample solution, containing
•
−
3 2
/Pd(OAc)
complex, prepared upon photoirradiation
, Pd(OAc) , and (BNA) in the negative ion
forms the complex. The results agree well with those revealed mode showed a peak at m/z = 495.04 in a complicated mass
by the DFT calculations as shown in Fig. 4 and 5. The evalu- profile owing to the clusters of Pd(OAc) , which correspond
ated hyperfine coupling constants for the QE3 /Pd(OAc)2 to its hydrogenated form with the calculated mass of 495.05
2
3
2
2
4
9
2
•
−
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Fig. 7 ESR spectra of (a) QE
3
•−, (b) QE
3
•−/Ca(ClO
4
)
2
complex, and (c) QE
or 5.0 mM Pd(OAc)
hyperfine coupling constants, and the maximum slope line widths (ΔHmsl). The spectral measurements of (a) and (c), and (b) were demonstrated at
43 K and 298 K, respectively.
3
•−/Pd(OAc)
2
complex generated by photo-irradiation of QE
in deaerated MeCN with the computer simulation spectra, the
3
(5.0 mM) with
(
BNA)
2
(excess) in the absence or presence of 50.0 mM Ca(ClO
4
)
2
2
2
(Fig. S15†). The observed isotope pattern is almost consistent The g value was shifted to 2.0048 or 2.0054 in the presence of
with the calculated one. 10 equiv. Ca(ClO ) or 1.0 equiv. Pd(OAc) , respectively. Since
4
2
2
•
−
•+
2+
[
QE3 , TME ] as an intermediate of photoinduced electron the observed shifts of g values in the presence of Ca and
agree with those observed in QE
ing a 1 : 4 mixture of QE and TME under exposure to light at Pd(OAc)2 complexes generated by (BNA) , the [QE , TME ]
•
−
2+
•−
•+
transfer was also detected by ESR in a MeCN solution contain- Pd(OAc)
2
3
/Ca and QE
3
/
•
−
3
2
3
2
+
7
7 K. The ESR spectrum in the absence of the metal salt was complex most likely forms the ternary complexes with Ca or
observed at g = 2.0050 without hyperfine splitting (Fig. S16†). Pd(OAc)
2
.
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Measurements
Conclusion
1
13
H and C NMR spectra were recorded on a Varian INOVA 400
Photochemical reactions of QE
proceed through the photoinduced electron transfer mechan-
ism, provide multi-photoproducts of oxetanes 1aE and 1bE ,
and hydroquinone H
ether adducts of hydroquinones 2aE
long oligoether sidearm, selectively provides 2aE3 when it
n
(n = 0 and 3) with TME, which
1
13
spectrometer (400 MHz for H and 100 MHz for C) or a
1
Bruker AVANCE 500 spectrometer (500 MHz for H and
13
n
n
1
25 MHz for C). Chemical shifts (δ in ppm) were reported
2
QE
n
as major products, and monoallyl
with respect to tetramethylsilane as the internal standard.
Infrared absorption spectra (IR) were recorded on a JASCO FT/
IR-4200 Fourier transform infrared spectrometer. Electronic
absorption spectra were recorded using a Hewlett-Packard
HP8453 diode array spectrophotometer. Phosphorescence
spectra were recorded using a JASCO FP-6600 fluorescence
n
and 2bE . QE , having a
n
3
2
+
forms a size-favorable host–guest complex with Ca . The
oxetanes are selectively produced when QE forms metal–
NMR spectroscopy
binds Ca and Pd(OAc) through electro-
static interaction and metal–olefin interaction, respectively.
n
1
olefin complexes with Pd(OAc) .
H
2
2
+
revealed that QE
3
2
spectrometer. Elemental analyses were performed on
a
YANACO CHN Corder MT-5. Fourier transform mass spectro-
metry was performed on a Thermo Fisher Scientific LTQ
Orbitrap Discovery. Analytical HPLC was performed at 20 °C
on a COSMOSIL 5C -MS-II column (Ø 4.6 mm × 250 mm)
using a JASCO PU-2080 HPLC pump equipped with a
UV-2015 multi-wavelength UV-Vis detector, with MeOH–H O
2
+
Cyclic voltammetry also showed that Ca strongly withdraws
electrons from the quinone moiety, whereas Pd(OAc) has no
electronic effect on the quinone reduction. DFT calculations
also indicated that such metal complexations of QE resulted
in changing electronic structures of the intermediate semi-
2
1
8
n
2
•−
2+
quinone radical anion QE
from the quinone through C1 oxygen in both the QE . Ca
n
. Ca strongly withdraws electrons
(
100 : 0, 80 : 20, or 65 : 35) as an eluent.
2
+
3
•
−
2+
•+
complex and the [QE
transfer complex to reduce the electron density of the quinone.
Pd(OAc) allows localization of the anionic charge around the Electrochemical measurements were made with an ALS 1210A
3
. Ca , TME ] photoinduced electron
Cyclic voltammetry
2
•
−
coordination bond with Pd(OAc)
2
in the [QE
n
/Pd(OAc)
2
,
electrochemical analyzer using a glassy carbon working
TME ] complex without a decrease of the charge density of electrode, a platinum wire counter electrode, and an Ag/Ag
the quinone radical anion. The Ca and Pd(OAc) complexes [0.01 M AgNO , 0.1 M Bu NClO (MeCN)] reference electrode.
3 4 4
•
+
+
2
+
2
•
−
−1
of QE
3
have been successfully characterized by the absorp- The scan rate was 100–20 mV s . The CV curves were cali-
•
−
+
tion and ESR spectroscopy. The ternary complex [QE
3
/metal, brated using the ferrocene/ferrocenium (Fc/Fc ) redox couple
TME ] formed upon photoirradiation, thus, determines the as an external standard, which was measured under the same
favorable reaction pathway of the [2 + 2] cycloaddition, PT and conditions before and after the measurement of samples. The
•
+
+
HT reactions. The present supramolecular photochemical reac- half-wave potential of Fc/Fc was found to be 0.09 V related to
+
tions suggest their importance for the design of the electronic the Ag/Ag reference electrode.
interactions of reaction substrates and the intermediate
radical ion pair with the catalyst in controlling a variety of Theoretical calculations
photochemical reaction pathways that proceed by the photo-
induced electron transfer mechanism.
For the calculation of the structures and electron potential
•−
•−
•−
•−
maps of QE
Pd(OAc) density functional theory (UB3LYP/6-31+G(d,p)
and UB3PW91/LANL2DZ, respectively) was employed as
3
and QE
3
. Ca(ClO
4
)
2
, and QE
0
0
and QE /
2
,
4
5
implemented in the Gaussian 09 set of programs. Stationary
structures were identified as those structures where all of the
harmonic frequencies were real.
Experimental section
Materials
Unless otherwise noted, reagents and solvents were used as
received from Tokyo Kasei Co., Ltd (TCI) [methoxy-p-benzo-
ESR measurements
0
quinone QE (>99%) and tetramethylethylene TME (>96%)], Wako The ESR spectra were recorded on a JEOL X-band ESR spectro-
Pure Chemical Industries, Ltd [sodium perchlorate (>95%), meter (JES-RE1XE). A quartz ESR tube (internal diameter:
acetonitrile (>99.5) and acetonitrile-d3 (>99.8%)], Sigma 1.8 mm and 4.5 mm) containing a sample at 298, 243, or 77 K
Aldrich [calcium perchlorate tetrahydrate (>99%) and mag- was irradiated in the cavity of the ESR spectrometer with the
nesium perchlorate], and Kishida Chemical Co., Ltd [chloro- focused light of a 1000 W high-pressure Hg lamp (Ushio-
form (>99%) and hexane (>95%)]. QE3 was prepared as USH1005D) through an aqueous filter. The ESR spectra were
described in our previous report. All products were unambigu- measured under nonsaturating microwave power conditions.
1
13
ously characterized by means of H and C NMR and IR The amplitude of modulation was chosen to optimize the
spectroscopies, and electrospray ionization Fourier transform resolution and the signal-to-noise (S/N) ratio of the observed
2+
mass spectrometry. Oxetanes 1aE
ether adducts of hydroquinones 2aE
characterized by reference to ref. 29d and 31 respectively.
n
and 1bE
n
and monoallyl spectra. The g values were calibrated with a Mn marker.
were also Simulations of ESR signals were performed using the WinSIM
n
and 2bE
n
5
0
program.
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A typical procedure for photochemical reactions of QE
and 3)
n
(n = 0
1H, J = 10.9, 2.9 Hz), 6.15 (d, 1H, J = 10.9 Hz), 6.06 (d, 1H, J =
2.8 Hz), 3.72 (s, 3H), 1.51 (s, 3H), 1.48 (s, 3H), 1.23 (s, 3H), 1.17
1
3
(5 × 10−3 mmol)
was added 4 equiv. TME (20 × 10 mmol) with or without
3
(s, 3H); C NMR (125 MHz, CDCl , 20 °C): δ 180.4, 150.9,
To an acetonitrile solution (0.5 mL) of QE
n
−
3
149.9, 127.1, 116.0, 85.6, 81.7, 55.0, 49.2, 27.1, 27.0, 22.6, 21.8;
IR (KBr): 2924, 2360, 2341, 1674, 1638, 1609, 1455, 1369, 1209,
+
2+
2+
1
0 equiv. metal perchlorate (Na , Mg , or Ca ) or 1 equiv.
−
1
1
+
106, 935, 882, 629 cm ; HRMS (ESI): m/z calcd for (C13
H
18
O
3
Pd(OAc) in a Pyrex glass tube, and the mixture solution was
2
+
H ) 223.1334, found 223.1332.
degassed by argon bubbling for 5 min. The solution was
irradiated by a 500 W xenon lamp (USHIO SPAX Inc.,
SX-UID502XAM) equipped with a >420 nm optical filter
3
-Methoxy-4-[(1,1,2-trimethyl-2-propene-1-yl)oxy]-phenol
1
(
0 3
2aE ). H NMR (500 MHz, CDCl , 20 °C): δ 6.80 (d, 1H, J =
8
5
.7 Hz), 6.41 (d, 1H, J = 2.9 Hz), 6.23 (dd, 1H, J = 8.7, 2.8 Hz),
.05 (s, 1H, –OH), 4.94 (s, 1H), 4.90 (s, 1H), 3.75 (s, 3H), 1.93
(Kansai Chemical Engineering Co. Ltd, GG420). The reactions
were performed for 20 min in the cases with or without the
metal perchlorate and for 150 min in the case with Pd(OAc)2.
The sample solution was then analyzed using a HPLC
equipped with a COSMOSIL 5C18-MS-II column (Ø 4.6 mm ×
1
3
(
s, 3H), 1.41 (s, 6H); C NMR (125 MHz, CDCl
3
, 20 °C):
δ 153.4, 151.3, 150.3, 138.8, 122.2, 111.1, 105.9, 100.5, 81.9,
5
1
8
5.7, 26.0, 19.0; IR (KBr): 3343, 2988, 2965, 1603, 1510, 1452,
382, 1366, 1347, 1298, 1203, 1163, 1110, 1037, 957, 907, 850,
2
50 mm), with MeOH–H O (100 : 0, 80 : 20, or 65 : 35) as an
2
32, 815, 663 cm− ; Anal. Calcd for C13
1
H
O
: C, 70.24;
18
3
eluent.
H, 8.16; Found: C, 69.39; H, 8.30. HRMS (ESI): m/z calcd for
+
(
C
13
H
18
O
3
+ H ) 223.1334, found 223.1330.
Isolation of H
2
QE
n
, 2aE
n
, and 2bE
n
(n = 0 and 3)
(1.45 mmol) was
2
-Methoxy-4-[(1,1,2-trimethyl-2-propene-1-yl)oxy]-phenol
To an acetonitrile solution (6 mL) of QE
n
1
(
2bE0). H NMR (500 MHz, CDCl , 20 °C): δ 6.73 (d, 1H, J =
3
added 4 equiv. TME (5.80 mmol) in a Pyrex glass tube, and the
mixture solution was degassed by argon bubbling for 10 min.
The solution was irradiated by a 500 W xenon lamp (USHIO
SPAX Inc., SX-UID502XAM) equipped with a >420 nm optical
filter (Kansai Chemical Engineering Co. Ltd, GG420) for 3 h.
The sample solution was then evaporated to dryness. The
brown oil was obtained, and the residue was separated using a
preparative HPLC equipped with a COSMOSIL 5C -MS-II
8
5
.5 Hz), 6.53 (d, 1H, J = 2.5 Hz), 6.48 (dd, 1H, J = 8.7, 2.5 Hz),
.25 (s, 1H, –OH), 4.96 (s, 1H), 4.93 (s, 1H), 3.82 (s, 3H), 1.90
13
(
s, 3H), 1.44 (s, 6H); C NMR (125 MHz, CDCl , 20 °C):
3
δ 150.6, 149.6, 146.3, 140.4, 113.6, 112.1, 111.1, 104.6, 88.8,
5
1
5.8, 26.7, 18.9; IR (KBr): 3423, 2982, 1609, 1509, 1450, 1376,
263, 1230, 1198, 1156, 1135, 1037, 965 cm ; HRMS (ESI): m/z
−1
+
calcd for (C13
H
18
O
3
+ H ) 223.1332, found 223.1330.
1
8
5
-(2′-(2″-(2′′′-Methoxyethoxy)ethoxy)ethoxy)-2,2,3,3-tetramethyl-
column (Ø 10.0 mm × 250 mm), with MeOH–H
2
O (80 : 20) as
1
1
-oxaspiro[3.5]nona-5,8-dien-7-one (1aE3). H NMR (500 MHz,
CDCl , 20 °C): δ 7.04 (d, 1H, J = 10.2 Hz), 6.05 (dd, 1H, J = 10.2,
.6 Hz), 5.41 (d, 1H, J = 1.6 Hz), 4.10–3.54 (m, 12H), 3.38 (s,
H), 1.51 (s, 3H), 1.48 (s, 3H), 1.20 (s, 3H), 1.13 (s, 3H);
an eluent.
3
1
3
Isolation of 1aE
To an acetonitrile solution (5 mL) of QE
added 8 equiv. TME (0.288 mmol) and 1 equiv. Pd(OAc)
0.036 mmol) in a Pyrex glass tube, and the mixture solution 27.4, 25.0, 22.5, 20.9; IR (KBr): 3504, 2926, 1656, 1623, 1585,
n n
and 1bE (n = 0 and 3)
1
3
n
(0.036 mmol) was
3
C NMR (125 MHz, CDCl , 20 °C): δ 187.1, 173.7, 147.7, 126.9,
2
102.4, 86.8, 82.7, 72.0, 70.8, 70.7, 70.6, 68.8, 67.7, 59.1, 50.8,
(
−
1
was degassed by argon bubbling for 10 min. The solution was 1415, 1374, 1349, 1226, 1097, 1057, 983, 946, 851, 803 cm
irradiated by a 500 W xenon lamp (USHIO SPAX Inc., Anal. Calcd for C19 : C, 64.38; H, 8.53. Found: C, 64.45;
SX-UID502XAM) equipped with a >420 nm optical filter H, 8.24; HRMS (ESI): m/z calcd for (C H O + H ) 355.2121,
;
30 6
H O
+
1
9
30 6
(Kansai Chemical Engineering Co. Ltd, GG420) for 4 h. The found 355.2111.
sample solution was then evaporated to dryness. A brown oil
was obtained and the residue was separated by flash silica gel 1-oxaspiro[3.5]nona-5,8-dien-7-one (1bE3). H NMR (500 MHz,
column chromatography with hexane–chloroform (30 : 70) and CDCl , 20 °C): δ 7.26 (dd, 1H, J = 10.1, 2.9 Hz), 6.13 (d, 1H, J =
6-(2′-(2″-(2′′′-Methoxyethoxy)ethoxy)ethoxy)-2,2,3,3-tetramethyl-
1
3
hexane–ethyl acetate (20 : 80) as eluents for 1aE
0
and 1bE
0
, and 10.1 Hz), 6.11 (d, 1H, J = 2.8 Hz), 4.00–3.98 (m, 2H), 3.88–3.85
(m, 2H), 3.74–3.72 (m, 2H), 3.68–3.63 (m, 4H), 3.57–3.55 (m,
1
aE and 1bE , respectively.
3 3
5
-Methoxy-2,2,3,3-tetramethyl-1-oxaspiro[3.5]nona-5,8-dien- 2H), 3.38 (s, 3H), 1.50 (s, 3H), 1.47 (s, 3H), 1.21 (s, 3H), 1.16 (s,
1
13
7
0 3 3
-one (1aE ). H NMR (500 MHz, CDCl , 20 °C): δ 7.06 (d, 1H, 3H); C NMR (125 MHz, CDCl , 20 °C): δ 181.1, 150.5, 149.2,
J = 10.1 Hz), 6.05 (dd, 1H, J = 10.1, 2.0 Hz), 5.45 (d, 1H, J = 127.2, 117.3, 85.5, 81.7, 71.9, 70.9, 70.6, 70.5, 69.0, 67.3, 59.0,
1
.9 Hz), 3.83 (s, 3H), 1.50 (s, 6H), 1.17 (s, 3H), 1.13 (s, 3H); 49.3, 27.0, 26.9, 22.5, 21.8; IR (KBr): 2921, 1675, 1637, 1608,
1
3
C NMR (125 MHz, CDCl
3
, 20 °C): δ 187.1, 174.5, 147.7, 126.8, 1457, 1375, 1272, 1236, 1194, 1091, 1020, 876, 630, 524,
02.0, 86.7, 82.8, 55.4, 50.7, 27.2, 25.2, 22.3, 20.9; IR (KBr): 504 cm− ; HRMS (ESI): m/z calcd for (C H O + H ) 355.2121,
1
+
1
3
9
1
9
30 6
449, 2965, 1657, 1588, 1459, 1360, 1227, 1165, 1096, 1059, found 355.2117.
80, 851 cm− ; Anal. Calcd for C13
1
H
18
O
: C, 70.24; H, 8.16.
2-(2′-(2″-(2′′′-Methoxyethoxy)ethoxy)ethoxy)-hydroquinone
3
1
Found: C, 68.32; H, 8.59; HRMS (ESI): m/z calcd for (C H O
+
(H QE ). H NMR (500 MHz, CDCl , 20 °C): δ 6.74 (d, 1H, J =
1
3
18
3
2
3
3
+
H ) 223.1334, found 223.1327.
8.5 Hz), 6.49 (d, 1H, J = 2.9 Hz), 6.37 (dd, 1H, J = 8.5, 2.9 Hz),
6
-Methoxy-2,2,3,3-tetramethyl-1-oxaspiro[3.5]nona-5,8-dien- 4.09–4.07 (m, 2H), 3.79–3.78 (m, 2H), 3.71–3.58 (m, 6H),
1
13
7
-one (1bE0). H NMR (500 MHz, CDCl , 20 °C): δ 7.29 (dd, 3.58–3.56 (m, 2H), 3.38 (s, 3H); C NMR (125 MHz, CDCl3,
3
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2
7
1
0 °C): δ 149.4, 146.3, 140.6, 115.4, 108.5, 103.0, 71.9, 70.5,
5 Y. Inoue, F. Dong, K. Yamamoto, L.-H. Tong, H. Tsuneishi,
T. Hakushi and A. Tai, J. Am. Chem. Soc., 1995, 117, 11033;
Y. Inoue, T. Wada, N. Sugahara, K. Yamamoto, K. Kimura,
L. H. Tong, X. M. Gao, Z. J. Hou and Y. Liu, J. Org. Chem.,
2000, 65, 8041; C. Yang, A. Nakamura, T. Wada and
Y. Inoue, Org. Lett., 2006, 8, 3005; C. Yang, T. Mori,
Y. Origane, Y. H. Ko, N. Selvapalam, K. Kim and Y. Inoue,
J. Am. Chem. Soc., 2008, 130, 8574.
0.4, 70.3, 69.6, 69.2, 58.9; IR (KBr): 3269, 2898, 1616, 1515,
−
1
457, 1351, 1293, 1201, 1171, 1110, 986, 840, 801 cm ; HRMS
+
(ESI): m/z calcd for (C13
20 6
H O + H ) 273.1338, found 273.1335.
3
-(2′-(2″-(2′′′-Methoxyethoxy)ethoxy)ethoxy)-4-[(1,1,2-trimethyl-
1
2
-propene-1-yl)oxy]-phenol (2aE
3 3
). H NMR (500 MHz, CDCl ,
2
0 °C): δ 6.79 (d, 1H, J = 8.6 Hz), 6.57 (d, 1H, J = 2.8 Hz), 6.30
(dd, 1H, J = 8.6, 2.8 Hz), 6.06 (s, 1H, –OH), 4.95 (s, 1H), 4.89 (s,
1
3
1
1
6
1
9
3
H), 4.10–4.08 (m, 2H), 3.77–3.75 (m, 2H), 3.72–3.70 (m, 2H),
6 W. Herrmann, S. Wehrle and G. Wenz, Chem. Commun.,
1997, 1709; H. Ikeda, T. Nihei and A. Ueno, J. Org. Chem.,
2005, 70, 1237.
7 Y. Ishida, Y. Kai, S. Y. Kato, A. Misawa, S. Amano,
Y. Matsuoka and K. Saigo, Angew. Chem., Int. Ed., 2008, 47,
8241.
8 M. Yoshizawa, Y. Takeyama, T. Kusukawa and M. Fujita,
Angew. Chem., Int. Ed., 2002, 41, 1347; M. Yoshizawa,
Y. Takeyama, T. Okano and M. Fujita, J. Am. Chem. Soc.,
2003, 125, 3243; M. Yoshizawa, S. Miyagi, M. Kawano,
K. Ishiguro and M. Fujita, J. Am. Chem. Soc., 2004, 126,
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.68–3.65 (m, 4H), 3.63–3.60 (m, 2H), 3.41 (s, 3H), 1.93 (s, 3H),
1
3
.39 (s, 6H); C NMR (125 MHz, CDCl , 20 °C): δ 152.5, 151.9,
3
50.3, 139.3, 123.2, 110.9, 107.4, 104.3, 81.9, 72.0, 70.6, 70.2,
9.6, 68.9, 58.9, 25.9, 19.0; IR (KBr): 3366, 2981, 2921, 1646,
599, 1508, 1455, 1376, 1361, 1298, 1216, 1176, 1132, 990, 933,
09, 862 cm− ; HRMS (ESI): m/z calcd for (C19
1
+
30 6
H O + H )
55.2121, found 355.2111.
2
-(2′-(2″-(2′′′-Methoxyethoxy)ethoxy)ethoxy)-4-[(1,1,2-trimethyl-
1
2
3 3
-propene-1-yl)oxy]-phenol (2bE ). H NMR (500 MHz, CDCl ,
2
0 °C): δ 6.74 (d, 1H, J = 8.8 Hz), 6.56 (d, 1H, J = 2.9 Hz), 6.52
(dd, 1H, J = 8.8, 2.6 Hz), 6.36 (s, 1H, –OH), 4.95 (s, 1H), 4.91 (s,
1
3
H), 4.11–4.09 (m, 2H), 3.81–3.79 (m, 2H), 3.73–3.72 (m, 2H),
.70–3.68 (m, 2H), 3.67–3.65 (m, 2H), 3.57–3.55 (m, 2H), 3.38
1
3
(s, 3H), 1.89 (s, 3H), 1.42 (s, 6H); C NMR (125 MHz, CDCl3,
9 S. Y. Jon, Y. H. Ko, S. H. Park, H.-J. Kim and K. Kim, Chem.
Commun., 2001, 1938; R. Wang, L. Yuan and
D. H. Macartney, J. Org. Chem., 2006, 71, 1237.
2
8
3
1
0 °C): δ 150.5, 149.2, 145.6, 142.3, 114.7, 114.3, 111.1, 108.5,
0.8, 71.9, 70.7, 70.6, 70.5, 69.7, 69.5, 59.0, 26.7, 18.9; IR (KBr):
434, 2981, 2925, 1646, 1604, 1509, 1455, 1376, 1234, 1200, 10 L. S. Kaanumalle and V. Ramamurthy, Chem. Commun.,
170, 1132, 989, 902, 857 cm ; HRMS (ESI): m/z calcd for
−
1
2007, 1062.
+
(C
19
H
30
O
6
+ H ) 355.2121, found 355.2121.
11 K. Fujimoto, S. Matsuda, N. Takahashi and I. Saito, J. Am.
Chem. Soc., 2000, 122, 5646; K. Fujimoto, H. Yoshino,
T. Ami, Y. Yoshimura and I. Saito, Org. Lett., 2008, 10,
3
97.
2 G. Agati and A. F. McDonagh, J. Am. Chem. Soc., 1995, 117,
425; T. Wada, N. Sugahara, M. Kawano and Y. Inoue,
Acknowledgements
1
4
The present work was sponsored by a Grant-in-Aid for Scienti-
fic Research (B) (no. 25286017 to A.T. and 26288037 to K.O.)
and a Challenging Exploratory Research (no. 24655125 to
A.T. and 26620154 to K.O.) from the Ministry of Education,
Science, Sports, and Culture, Japan, and a Toray Science and
Technology Grant.
Chem. Lett., 2000, 1174.
1
3 V. Ramamurthy, J. Shailaja, L. S. Kaanumalle, R. B. Sunoj
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Y. V. Pol, R. Suau, E. Perez-Inestrosa and D. Bassani, Chem.
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