Cross-coupling reaction of alcohols for carbon-carbon bond formation using pincer-type NHC/palladium catalysts

Article abstract of DOI:10.1039/b914618k

A cross-coupling reaction of different alcohols was achieved using a pincer-type NHC/PdBr complex as the catalyst precursor, and the reaction, under either Ar or H₂ gas, displayed a broad substrate scope with respect to both primary and secondary alcohol components, with high alcohol product selectivity. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/b914618k

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PAPER
www.rsc.org/obc | Organic & Biomolecular Chemistry
Cross-coupling reaction of alcohols for carbon–carbon bond formation using
pincer-type NHC/palladium catalysts†
Osamu Kosea and Susumu Saito*a,b
Received 20th July 2009, Accepted 11th November 2009
First published as an Advance Article on the web 17th December 2009
DOI: 10.1039/b914618k
A cross-coupling reaction of different alcohols was achieved using a pincer-type NHC/PdBr complex
as the catalyst precursor, and the reaction, under either Ar or H2 gas, displayed a broad substrate scope
with respect to both primary and secondary alcohol components, with high alcohol product selectivity.
alcohols within a range of alcohol–alcohol coupling reactions
(Scheme 1).
Introduction
In an effort to minimize salt waste by-products in the field
of carbon–carbon bond-forming reactions, transition metal-
catalyzed direct coupling between two different alcohols was
recently reconsidered.1 The homo-coupling of primary alcohols,
where two different carbon atoms are coupled, was first rec-
ognized as the Guerbet reaction, which was discovered around
19002 using heterogeneous transition metal catalysts at a high
pressure/temperature (~220 ◦C) in the presence of excess alkali
metal hydroxides or alkoxides. A stepwise process, involving
a dehydrogenation/aldol condensation/hydrogenation sequence,
was proposed. Thus far, the most frequently used metal sources
Scheme 1 General: NHC/Pd-catalyzed cross-coupling of alcohols.
are Ir3,4,5 or Ru,6,7,8 which showed a high reactivity with subtle
modification from original conditions; however, the reaction
frequently utilized a stoichiometric amount of alkaline metal base
Results and discussion
(1–3 equiv. with respect to one of the two alcohols), with some
exceptions.3 In contrast, heterogeneous9,10,11 and homogeneous10,11
Pd complexes were tested earlier and more recently, but showed
scant catalytic activity or were limited to a special case, such as
those in which MeOH, n-PrOH and n-BuOH were coupled using
We first chose secondary alcohol 1a as a model substrate, since a
considerable amount of ketone 4aa was generated as a side product
using Ir4 or Ru6 complexes. Treatment of secondary (2◦) alcohol
1a (2 mmol) with primary (1◦) alcohol 2a (1 mmol) in p-xylene
(1 mL) at 125 ◦C for 12 h in the presence of Pd2(dba)3 (1 mol%),
ligand precursor 5a (2 mol%) and CsOH (40 mol%), afforded, after
the mixture was purified by column chromatography on silica gel,
coupling product alcohol 3aa in an isolated yield of 47% (Table 1,
◦
1 equiv. of base at a high temperature (200 C)10,11 and pressure
(30 atm).11 Recently, heterogeneous Pd/AlO(OH) catalysts,12 Pd-
NP (nanoparticles)/viologen13 and Ni-NPs14 were examined for
ketone–alcohol coupling, allowing ketones to become major
products. Here, the carbonyl functionality remained intact and
thus the corresponding secondary alcohols were rarely produced.
Even though a PdH species was supposedly generated during the
dehydrogenation from alcohols, the reduction of ketone carbonyls
1
entry 2). Formation of ketone 4aa was undetected (<1%) by H
NMR analysis. Scant reactivity was observed (entry 1) when either
one of these three species, Pd2(dba)3, 5a, or the base, was lacking.
The 1a : 2a ratio of 2 : 1 proved to be the best mixing ratio, as the
1 : 1 ratio gave the product in a lower yield (76%) and selectivity
(entry 7). The NHC/PdBr complex 718 was also synthesized in a
separate experiment, and it was examined whether this species is
the most responsible for the catalytic cycle (entry 3). As expected,
the reaction completed under otherwise identical conditions to
give product 3aa in near quantitative yield in the presence of not
more than 4 mol% of 7 (entry 4). In this case, homo-coupling of 1a
was not detected. Doubling the molar amount of 7 (or Pd2(dba)3
and 5a) from 2 to 4 mol% ensured the best smooth conversion
(entries 3 and 4; entries 2 and 7). Other alkaline metal hydroxides
were totally unsatisfactory to give ketone 4aa as the major product
(entries 8–10). The solvent screening with Pd2(dba)3 (2 mol%)/5a
was highly unlikely owing to the relative inertness of the PdH
15
=
species towards the C O double bonds. The Ag/Al2O3 system
was very recently highlighted in the selective synthesis of the
corresponding ketones, but not the alcohols, by alcohol–alcohol
coupling.16 We report here that pincer-type N-heterocyclic carbene
(NHC)/Pd complexes17,18 are effective catalyst precursors in the
presence of alkaline metal base for the selective formation of
aDepartment of Chemistry, Graduate School of Science, Nagoya University,
Chikusa, Nagoya, 464-8602, Japan. E-mail: saito.susumu@f.mbox.nagoya-
u.ac.jp; Fax: 81 52 789 5945; Tel: 81 52 789 5945
bInstitute for Advanced Research, Nagoya University, Chikusa, Nagoya, 464-
8601, Japan. E-mail: saito.susumu@f.mbox.nagoya-u.ac.jp; Fax: 81 52 788
6140; Tel: 81 52 788 6140
◦
(4 mol%) (an initial concentration of Pd: 0.04 M; 125 C, 24 h)
suggested that polar solvents including DMSO, DMF and 1,4-
dioxane were not promising (3aa: 0–20%). When we used ligand
† Electronic supplementary information (ESI) available: General experi-
mental information, synthetic procedure for NHC precursors and spectral
data of new and known compounds. See DOI: 10.1039/b914618k
896 | Org. Biomol. Chem., 2010, 8, 896–900
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Table 1 NHC/Pd complex-catalyzed coupling between secondary (2◦)
alcohol 1a and primary (1◦) alcohol 2a (2 : 1 ratio) to give 3aa + 4aaa
Table 2 NHC/Pd complex-catalyzed cross-coupling reaction of sec-
ondary (2◦) and primary (1◦) alcohols 1 and 2 (2 : 1 ratio)a
Main
Yield (%)
Entry 2◦ Alcohol 1 1◦ Alcohol 2 Base
product (3 : 4)b
1
2
3
4
5
6
7
8
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
1b
1c
1c
1d
1e
1e
2a
2b
2c
2d
2d
2e
2f
CsOH
CsOH
CsOH
CsOH
CsOH
NaOH
CsOH
NaOH
NaOH
CsOH
NaOH
NaOH
CsOH
CsOH
3ba
3bb
3bc
3bd
3bd
3be
3bf
3bf
3bf
3bg
3bg
3bg
3ca
3ca
97 (48 : 1)
99 (21 : 1)
99 (24 : 1)
55 (4.0 : 1)
82 (15 : 1)d
26 (>99 : 1)
26 (3.3 : 1)
78 (3.3 : 1)c
92 (9.2 : 1)c,d
50 (6.0 : 1)
78 (3.3 : 1)c
99 (9.0 : 1)c,d
94 (3.6 : 1)
95 (4.3 : 1)d
50 (>99 : 1)c
73 (1.6 : 1)c
81 (2.7 : 1)c,d
2f
Catalyst precursors
Entry (mol%)
Base (MOH)
(mol%)b
Yield (%)c 3aa : 4aad
9
2f
10
11
12
13
14
15
16
17
2g
2g
2g
2a
2a
2a
2a
2a
1
2
3
4
5
6
7
8
Pd2(dba)3 (1)
Pd2(dba)3 (1), 5a (2)
7 (2)
CsOH (40)
CsOH (40)
CsOH (40)
CsOH (40)
7
47
47
97
78
80
99 : 1
99 : 1
99 : 1
18 : 1
38 : 1
1.8 : 1
7 (4)
KOt-Bu 3da
KOt-Bu 3ea
KOt-Bu 3ea
Pd2(dba)3 (1.5), 5a (3) CsOH (40)
Pd2(dba)3 (2), 5a (4)
Pd2(dba)3 (2), 5a (4)
Pd2(dba)3 (2), 5a (4)
Pd2(dba)3 (2), 5a (4)
Pd2(dba)3 (2), 5a (4)
Pd2(dba)3 (2), 5b (4)
Pd2(dba)3 (2), 5c (4)
Pd2(dba)3 (2), 5d (4)
CsOH (20)
CsOH (40)
KOH (40)
NaOH (40)
LiOH (40)
CsOH (40)
CsOH (40)
CsOH (40)
99 (76)e
87
13 : 1 (2.5 : 1)e
0.67 : 1
0.65 : 1
0.28 : 1
5.5 : 1
a Pd2(dba)3 : 5a : base : 1 : 2 = 0.025 : 0.05 : 0.4 : 2 : 1. Conditions: 125 ◦C,
12–24 h in anhydrous p-xylene under argon (initial concentration of Pd:
0.05 M). b Of isolated, purified products 3 and 4 (Fig. 2 and 3) based on
the conversion (%) of 2. The ratio 3 and 4 was determined by 1H NMR.
c 5 mol% of 6 was used instead of 5a. d Reactions were performed under 1
atm pressure of H2.
9
79
68
97
89
10
11
12
13
4.6 : 1
4.5 : 1
99
a Pd2(dba)3 : ligand precursor : 2◦ alcohol 1a : 1◦ alcohol 2a = 0.01–
0.02 : 0.02–0.04 : 2 : 1. Conditions: 125 ◦C, 12 h in anhydrous p-xylene
under argon (initial concentration of Pd: 0.02–0.04 M). Diastereoselec-
tivity was consistently ca. 1 : 1. b With respect to 2a. c Of isolated, purified
1
products based on the conversion (%) of 2a. d Determined by H NMR.
e 1 equiv. of 1a was used.
5b in place of 5a, the reaction was less selective, suggesting that
it could be controlled by precise adjustment of electronic and
steric environments around inner and outer spheres of the Pd
center. Other NHC precursors 5c or 5d additionally tested so far
also did not improve the productivity but lowered the selectivity
(3aa : 4aa = 4.5 : 1–5.5 : 1) (entries 11–13).
Although NHC/PdBr complex 7 (Fig. 1) was able to be
synthesized according to literature procedure,18 for a practical
reason we utilized the general procedure for further screening,
in which Pd2(dba)3 and NHC precursor 5a were mixed just before
running the coupling reaction. Subsequently, the substrate scope
was investigated under optimal conditions (Pd2(dba)3 (2.5 mol%);
5a (5 mol%) in p-xylene; 125 ◦C for 12–24 h).
Table 2 summarizes representative examples of cross-coupling
between 1◦ and 2◦ alcohols. The combinations of benzylic alcohol
derivatives were well suited for this general procedure (entries
1–3), and the product alcohols were produced selectively and in
good to excellent yields in many cases. Although alcohols were
consistently the major products, a substantial amount of ketone
was generated in some cases. For instance, when we used aliphatic
alcohols as 1◦ alcohol counterparts (entries 7–12), selectivities
and/or conversions were rather lower under argon atmosphere
(entries 4, 8, 11, 13 and 16); in sharp contrast, under H2 gas (1
atm), productivities and/or selectivities were reasonably increased
(entries 5, 9, 12, 14 and 17). In some cases, the use of NHC
precursor 6 was better suited for reactivity (entries 8, 11, 15
and 16), and the combination with KOt-Bu was more favorable
(entries 15–17). In the other cases, conversion of 1◦ alcohols was
satisfactory using NaOH in place of CsOH (entries 7 and 8, and
Fig. 1 NHC precursors 5a–d and 6; NHC/PdBr complex 7.
10 and 11), so that the reactivity and selectivity strongly depended
on structure of substrates, as well as NHC ligands and alkaline
metals.
Coupling between 2◦ alcohols was also successful without
purging H2 (1 atm), which is one of the advantages overriding
other methods previously reported.1,3–12 Thus, optically pure (S)-
1b (>98% ee) was utilized to see whether the present catalysis is
supportive of the conventional mechanistic model (Scheme 2). We
identified little preservation of chirality in 8, so that a main process
supported the redox/acid–base cooperative mechanism (Fig. 4),
although other pathways could not be fully ruled out.
Based on this working hypothesis, several issues were to be
addressed in the present coupling, which consisted of two different
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Fig. 2 A series of product alcohols 3.
Fig. 4 Simplified plausible mechanism.
transfer upon reduction of product ketone 4ba leading to 3ba (eqn
(3) and (4)), so that LnPd–OCH(R)(Ph) might prevail over LnPdH-
like species for the reduction of the ketone carbonyl; (iv) to
summarize the points so far, 2◦ alcohol 1b has two important
roles: one is for providing a partial structure of 3ba and 4ba,
=
and the other is for smooth reduction of the C O, so that an
excess amount of 1b was necessary for both a higher productivity
and alcohol selectivity; otherwise an equilibrium between 3ba
and 4ba, involving LnPd(OR)-promoted hydrogen (H2) transfer,
would reach an apparent static point, eventually giving a mixture
of 3ba and 4ba in a lower selectivity (Table 1, entry 7); (v)
these speculations have some relevance to a notable effect of H2,
which helps enhancing high alcohol selectivity in some examples
(Table 2, entries 5, 9 and 12), although the way of additional H2
to participate in this multi-steps sequence, redox and acid–base
cooperative reactions, should be far more complicated than would
be expected.
Fig. 3 A series of product ketones 4.
Scheme 2 Coupling reaction between 2◦ alcohols. The yield of 8 was
calculated based on the conversion (%) of (S)-1b.
hydrogen sources: one is a 1◦ alcohol and the other is a 2◦ alcohol.
Why were 2 molar amounts of 2◦ over 1◦ alcohols required to
ensure high yields of product alcohols as well as high alcohol
(1)
(2)
(3)
=
selectivity in products? Why were C O bonds reduced in the
catalysis, likely by involving the PdH species? To get further insight
into these mechanistic aspects, we carried out a set of experiments
separately. The results are summarized in eqn (1)–(4), from which
several characteristic features are discussed. (i) The mechanistic
scenario shown in Fig. 4 was further supported, since a coupling to
give alcohol 3ba proceeded whether the ketone and aldehyde, or the
corresponding 2◦ and 1◦ alcohols, were used as starting materials
(eqn (1) and (2)); (ii) not only 2◦ alcohol 1b, but also 1◦ alcohol 2a
=
can promote the reduction of C C bonds of trans-chalcone (9),
in which both LnPd–OCHR(Ph)- and LnPdH-like species may
have chance to participate (eqn (3) and (4)). The former Pd-
alkoxide, while might being in an equilibrium with LnPdH-like
species, probably was involved in the Meerwein–Ponndorf–Verley
(MPV)-type reduction; (iii) in contrast, 2◦ alcohol 1b seems to
be the only species that is most responsible for smooth hydrogen
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stirred at 125 ◦C for 24 h. The mixture was cooled down to 25 ◦C
and was directly purified by column chromatography on silica gel
(EtOAc–n-hexane = from 1 : 100 to 1 : 30) to give alcohol 3aa and
ketone 4aa in a ratio of 13 : 1 (236 mg, 99% yield). The structure
and diastereoselectivity were determined by comparing with the
data in literatures (also see the ESI†).6
(4)
Representative procedure for the alcohol–alcohol coupling under
H2 (1 atm)
Conclusions
To a 30 mL flask stoppered by a Young’s stopcock was added
Pd2(dba)3 (22.5 mg, 0.025 mmol), 6 (35 mg, 0.05 mmol), 1b
(244 mg, 2 mmol), 2f (74 mg, 1 mmol), NaOH (16 mg, 0.4 mmol)
and anhydrous p-xylene (1.0 mL) at 25 ◦C. The flask was degassed
and subsequently filled with H2, and was stoppered again by
a Young’s stopcock to make a closed system. The resulting
suspension was immediately heated and stirred at 125 ◦C for 24 h.
The mixture was cooled down to 25 ◦C and was directly purified
by column chromatography on silica gel (EtOAc–n-hexane = from
1 : 100 to 1 : 30) to give alcohol 3bf and ketone 4bf in a ratio of 9.2 : 1
We have demonstrated that Pd-catalysts, derived from pincer-
type NHCs, were useful for the cross-coupling reaction of two
different alcohols in the absence or in the presence of H2, which
was complementary to related methods.3–11 To the best of our
knowledge, this is essentially the first successful example showing
a wider substrate scope in the coupling reaction of alcohols via
Pd-catalysis. No more than 40 mol% of base was required without
any extra additives including olefinic substrates.3,7 The reaction
was selective, providing the corresponding alcohols in good to
high yields, especially under the conditions of an H2 atmosphere.
The search for the mechanistic aspects, including the ab initio
calculation, of the present catalysis is now under way in our
laboratories.
1
(92% H NMR total yield, using 1,1,2,2-tetrachloroethane as an
internal standard).
1-Phenyl-3-thiophenylpropan-1-ol (3be). Yield (57 mg, 26%).
IR (ATR): n/cm-1 = 3388, 2920, 1721, 1492, 1451, 1276, 1056,
1
Experimental
914, 849, 752, 694. H NMR (600 MHz, CDCl3) d (ppm): 7.35–
7.25 (m, 5H), 7.09 (d, J = 4.1 Hz, 1H), 6.90 (dd, J = 5.2 Hz,
3.4 Hz, 1H), 6.78 (t, J = 1.7 Hz, 1H), 4.68 (t, J = 5.9 Hz, 1H),
2.95–2.85 (m, 2H), 2.18–2.12 (m, 1H), 2.07–2.02 (m, 2H). 13C
NMR (600 MHz, CDCl3) d (ppm): 144.9, 144.7, 128.9, 128.0,
127.1, 126.2, 124.6, 123.4, 73.8, 41.0, 26.5. HRMS (EI) Calcd for
C13H14OS (M+): 218.0765. Found m/z = 218.0756.
General
All reactions were carried out under either argon or H2 atmosphere
and in dried glassware by means of standard Schlenk techniques
unless otherwise noted. All reagents were purchased from Aldrich,
Wako, TCI or Kanto and used without further purification, except
for benzyl alcohol, which was simply distilled under reduced
pressure. Column chromatography was performed using silica gel
(silica gel 60, 230-400 mesh, Merck). TLC was performed using
pre-coated silica gel plates (silica gel 60 F254, Merck) and products
were observed under UV light or with phosphomolybdic acid
reagent. 1H NMR and 13C NMR spectra were recorded on a JEOL
ECA-600 spectrometer, operating in CDCl3 at 600 MHz. Chemical
shifts and coupling constants are presented in ppm (d) relative
to tetramethylsilane (TMS) and Hz, respectively. High resolution
mass spectra were obtained on JEOL JMS-700. Chiral high
performance liquid chromatography analysis was conducted using
Shimadzu LC-10AD coupled with photo diode array-detector
SPD-M20A and chiral column of CHIRALCEL OD-H (Daicel
chemical industries, LTD.). Alcohols 3aa,6,19 3ba,6,19 3bb,4 3bc,4
3bd,7,20 3bf,4 3bg,4 3ca6 and 3ea,21 as well as ketones 4aa,22 4ba,23
4bb,24 4bd,24 4bf,4 4ca25 and 4ea,26 are all known compounds, and
their 1H and 13C NMR data measured this time, as well as synthetic
procedures and full spectral or analytical data for NHC precursors
1,5-Diphenylpentan-3-ol (3da). Yield (120 mg, 50%). IR
(ATR): n/cm-1 = 3364, 3024, 2919, 1602, 1595, 1454, 1029, 911,
743, 696. 1H NMR (600 MHz, CDCl3) d (ppm): 7.29–7.26 (m, 4H),
7.19–7.17 (m, 6H), 3.68–3.65 (m, 1H), 2.81–2.76 (m, 2H), 2.69–
2.64 (m, 2H), 1.85–1.74 (m, 4H), 1.44 (s, 1H). 13C NMR (600 MHz,
CDCl3) d (ppm): 142.4 (2C), 128.8 (8C), 126.2 (2C), 71.2, 39.5,
32.4. HRMS (EI) Calcd for C17H22 (M+–H2O): 222.1408. Found
m/z = 222.1406.
3-(4-Methylphenyl)-1-phenylpropan-1-one
(4bc). Yield
(8.9 mg, 4%). IR (ATR): n/cm-1 = 2922, 1683, 1596, 1514, 1447,
1360, 1290, 1202, 972, 808, 741, 688. 1H NMR (600 MHz, CDCl3)
d (ppm): 7.97 (d, J = 7.6 Hz, 2H), 7.55 (t, J = 7.6 Hz, 1H), 7.45
(t, J = 7.5 Hz, 2H), 7.16 (d, J = 7.6 Hz, 2H), 7.12 (d, J = 8.2 Hz,
2H), 3.28 (t, J = 7.9 Hz, 2H), 3.04 (t, J = 7.6 Hz, 2H), 2.33 (s,
3H). 13C NMR (600 MHz, CDCl3) d (ppm): 199.7, 138.7, 137.3,
136.1, 133.5, 129.7, 129.1, 128.8, 128.5, 41.0, 30.2, 21.5. HRMS
(FAB) Calcd for C16H16O (M+): 224.1201. Found m/z = 224.1200.
5a–d and 6 are presented in the ESI† (scans of raw H and 13C
NMR spectral charts are also available).
1
1-Phenyl-3-thiophenylpropan-1-one (4be). Yield (~1%). IR
(ATR): n/cm-1 = 3103, 2922, 1682, 1594, 1446, 1363, 1207, 971,
1
852, 748, 707, 692. H NMR (600 MHz, CDCl3) d (ppm): 7.97
Representative procedure for the alcohol–alcohol coupling under Ar
(1 atm)
(d, J = 8.3 Hz, 2H), 7.57 (t, J = 7.6, 1H), 7.47 (t, J = 7.6 Hz,
2H), 7.13–7.12 (m, 1H), 6.93–6.91 (m, 1H), 6.87 (t, J = 1.4 Hz,
1H), 3.38–3.35 (m, 2H), 3.32–3.29 (m, 2H). 13C NMR (600 MHz,
CDCl3) d (ppm): 198.9, 144.2, 137.1, 133.5, 129.0, 128.4, 127.2,
125.0, 123.7, 40.9, 24.5. HRMS (FAB) Calcd for C13H12OS (M+):
216.0609. Found m/z = 216.0607.
To a degassed, and argon-filled suspension of Pd2(dba)3 (18 mg,
0.02 mmol) in anhydrous p-xylene (1.0 mL) was added 5a (40 mg,
0.04 mmol), 1a (294 mg, 2 mmol), 2a (108 mg, 1 mmol) and CsOH
(60 mg, 0.4 mmol) at 25 ◦C, and the mixture was immediately
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1-Phenyldecan-1-one (4bg). Yield (23 mg, 10%). IR (KBr):
n/cm-1 = 2918, 2846, 1686, 1596, 1473, 1447, 1375, 1256, 1220,
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1
1193, 970, 733, 688. H NMR (600 MHz, CDCl3) d (ppm): 7.96
(d, J = 7.6 Hz, 2H), 7.55 (t, J = 7.2 Hz, 1H), 7.46 (t, J = 7.6 Hz,
2H), 2.96 (t, J = 7.6 Hz, 2H), 1.76–1.71 (m, 2H), 1.39–1.28 (m,
12H), 0.88 (t, J = 7.2 Hz, 3H). 13C NMR (600 MHz, CDCl3)
d (ppm): 201.0, 137.5, 133.2, 128.9, 128.4, 39.0, 32.2, 29.7, 24.7,
23.0, 14.4. HRMS (EI) Calcd for C16H24O (M+): 232.1827. Found
m/z = 232.1818.
1,3-Diphenyl-3-methylpropan-1-ol (8) (cis and trans).
Diastereomer. Yield (158 mg, 70% (for two diastereomers)). IR
(ATR): n/cm-1 = 3401, 3025, 2956, 1492, 1452, 1069, 1021, 762,
1
697. H NMR (600 MHz, CDCl3) d (ppm): 7.33–7.29 (m, 4H),
7.25–7.20 (m, 6H), 4.41–4.39 (m, 1H), 3.05–2.99 (m, 1H), 2.06–
2.01 (m, 1H), 1.94–1.90 (m, 1H), 1.78 (d, J = 3.4 Hz, 1H), 1.28
(d, J = 6.8 Hz, 3H). 13C NMR (600 MHz, CDCl3) d (ppm): 146.9,
145.5, 128.9, 128.8, 127.8, 127.5, 126.5, 126.0, 72.6, 48.0, 37.0,
23.4.
Another diastereomer. IR (ATR): n/cm-1 = 3357, 3026, 2925,
1602, 1492, 1452, 1051, 1015, 908, 760, 697. 1H NMR (600 MHz,
CDCl3) d (ppm): 7.36–7.19 (m, 10H), 4.58–4.56 (m, 1H), 2.76–2.70
(m, 1H), 2.21–2.16 (m, 1H), 1.97–1.92 (m, 1H), 1.71 (d, J = 2.8 Hz,
1H), 1.27 (d, J = 6.9 Hz, 3H). 13C NMR (600 MHz, CDCl3) d
(ppm): 147.3, 144.9, 128.7, 128.1, 127.4, 126.5, 73.3, 47.6, 37.0,
22.9. HRMS (EI) Calcd for C16H18O (M+, two diastereomers):
226.1358. Found m/z = 226.1361. The chiral HPLC analytical
data for 8 were obtained using i-PrOH/hexane (2.5/97.5) as eluent
at a flow rate of 1.0 mL min-1. Column: OD-H, tR = 10.7 min and
11.9 min for the two enantiomers of either cis or trans isomer;
14.8 min and 15.5 min for the two enantiomers of either cis or
trans isomer.
Acknowledgements
16 K.-i. Shimizu, R. Sato and A. Satsuma, Angew. Chem., Int. Ed., 2009,
48, 3982–3986.
This work was supported by a Grant-in-Aid for Basic Research
(B) from JSPS and Scientific Research on Priority Areas “Ad-
vanced Molecular Transformations of Carbon Resource” from the
Ministry of Education, Culture, Sports, Science and Technology,
Japan, as well as Asahi Glass Foundation. S.S. also greatly
appreciates Professor R. Noyori (Nagoya Univ. (NU) & RIKEN)
for his valuable suggestions and fruitful discussions. HR-MS was
measured by Dr K. Oyama (Chemical Instrument Room of RCMS
at NU).
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