Regioselective reductions of β,β-disubstituted enones catalyzed by nonracemically ligated copper hydride

Article abstract of DOI:10.1016/j.tet.2011.10.056

CuH-catalyzed 1,2-additions to β,β-disubstituted α,β-unsaturated ketones have been further explored. Asymmetric reductions of enones lacking an α-substituent can be achieved with CuH complexed by DTBM-SEGPHOS in Et₂O at -25 °C leading to the ge

Full text of DOI:10.1016/j.tet.2011.10.056

Tetrahedron 68 (2012) 3410e3416
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Regioselective reductions of
ligated copper hydride
b,b-disubstituted enones catalyzed by nonracemically
*
*
Karl R. Voigtritter, Nicholas A. Isley, Ralph Moser, Donald H. Aue , Bruce H. Lipshutz
Department of Chemistry, University of California, Santa Barbara, CA 93106, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 July 2011
Received in revised form 7 October 2011
Accepted 14 October 2011
Available online 3 November 2011
CuH-catalyzed 1,2-additions to
b
,
b
-disubstituted
a
,
b
-unsaturated ketones have been further explored.
Asymmetric reductions of enones lacking an
a-substituent can be achieved with CuH complexed by
DTBM-SEGPHOS in Et2O at ꢀ25 ꢁC leading to the generation of highly valuable nonracemic allylic
alcohols. The corresponding 1,4-reductions can also be achieved using the same reaction conditions by
switching the ligand to a JOSIPHOS analog affording nonracemic b,b-disubstituted ketones. DFT calcu-
lations of the enone conformations and transition-state energies for model 1,2- and 1,4-additions were
carried out to clarify the factors affecting the product ratios.
Warmly dedicated to Professor Gerhard
Bringmann on the occasion of his 60th
birthday
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Copper hydride
Asymmetric 1,2-addition
Hydrosilylation
a,b-Unsaturated ketones
Nonracemic ligands
1. Introduction
under mild reducing conditions, as recently highlighted by Mal-
kov.5b Following a recent report on the asymmetric copper-
Control of regioselectivity is oftentimes a problem in transition
metal catalyzed reactions. The ability to predictably change the
mode of reactivity via the expediency of a change in ligand is a goal,
that is, highly sought after within the synthetic community. In the
case of CuH, aside from its capability to reduce aromatic ketones1
and imines,2 the reduction pathway toward Michael acceptors
strongly favors delivery of hydride in a conjugate addition sense
catalyzed 1,2-reduction of benzylidene acetone,6 we questioned
whether
a
-substitution is required for the observed shift in regio-
-disubstituted
selectivity. The asymmetric 1,2-reduction of
b,b
enones, in particular, would provide nonracemic allylic alcohols
that, e.g., after SN20 displacements7 or Claisen rearrangements,8
would provide access to chiral quaternary centers.
(Scheme 1).3 The reduction of
racemically ligated CuH complexes has been extensively studied,
providing facile access to valued
-disubstituted chiral ketones.3a
Re-direction of CuH reactions with enones to form allylic alcohols
in an enantioselective fashion, on the other hand, is quite rare.
Stryker first recognized, in the achiral series, that electronic and
steric changes can have a major impact on ligands so as to alter
their mode of hydride delivery to Michael acceptors.4 Our recent
findings employing nonracemically ligated CuH have shown similar
regioselectivities with enones leading to chiral allylic alcohols.5a In
a,b-unsaturated ketones with non-
2. Results and discussion
b,b
To begin a study on the effect of various ligand classes on the
regioselective outcome with enone substrates lacking
a-sub-
stitution, educt 1 was exposed to our previously optimized
hydrosilylation conditions employing diethoxymethylsilane
(DEMS) as the stoichiometric source of hydride9 (Table 1). Within
the ligands screened, both the SEGPHOS10 and BIPHEP11a series
favored 1,2-reductions, while selected ligands among the JOSI-
PHOS12 WALPHOS, or P-PHOS13 series (Fig. 1) favored 1,4-
,
that prior study, the enones all possessed an
a-substituent that
reduction. Notably, DTBM-SEGPHOS-complexed CuH demon-
strated high regioselectivities for, and enantioselectivity in, the 1,2-
reduced product 2 (Table 1, entry 3). Modified JOSIPHOS ligand L6,
on the other hand, led to the expected conjugate reduction to
provide chiral ketone 3. Alternative hydride sources were also
assisted with the observed enantio- and regioselectivities realized
* Corresponding authors. Tel.: þ1 805 893 2521; fax: þ1 805 893 8265; e-mail
addresses: aue@chem.ucsb.edu (D.H. Aue), lipshutz@chem.ucsb.edu (B.H. Lipshutz).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.10.056

K.R. Voigtritter et al. / Tetrahedron 68 (2012) 3410e3416
3411
Scheme 1. Reduction pathways of CuH with a,b-unsaturated ketones.
screened; only phenylsilane (entry 4) afforded similar results in
terms of reactivity, albeit with some erosion in regioselectivity. A
copper source (e.g., copper nitrate) other than copper acetate led to
only low conversion to the desired product (entries 5 and 9).
With optimized conditions established, substrate scope was
examined so as to gauge the generality of this methodology (Table
2). Good regio- and stereoselectivities for 1,2-reductions were ob-
served for most cases of E-b-aryl-substituted enones (educts 4e11).
Ratios of 1,2- to 1,4-addition mediated by (DTBM-SEGPHOS)CuH
were found to be between 70:30 and 94:4. Enantiomeric excesses
of the resulting allylic alcohols tended to be high (ꢂ92%), although
both the ortho-bromo example (8) and substituted chalcone (9) led
to lower ees. Neither the regioselectivity nor the stereoselectivity
seemed to be impacted by the nature of the substituent on the b-
aryl ring. One example bearing a heteroaromatic ring in thiophene
analog 7 displayed similar selectivities. Substitution of methyl for
a phenyl or butyl substituent in 9 and 10 provided substrates that,
likewise, exhibited good regioselectivities, although aromatic ke-
tone 9 showed lower levels of stereo-induction for the 1,2-mode of
addition. Geometrical isomers 11 and 12 showed a reversal in
regioselectivity, as well as a considerable reduction in ee for the Z-
olefin. Substrate 14 demonstrated the inherent need for an aro-
Fig. 1. Summary of the reactivity of ligands screened with CuH catalysts.
matic ring in the b-position to afford good regioselectivities, al-
though the stereoselectivity for the minor product allylic alcohol
was very high.
Table 2
Substrate scope
Entry
Substrate
Liganda
Ratio (a/b)b
[1,2- vs 1,4-]
eec (a)
eec (b)
Table 1
Influence of chiral ligands on regio- and stereoselectivitya
1
2
L3
L6
L3
L6
L3
L6
L3
L6
L3
L6
77/23
1/99
96
6
n.d.
97
99
25
98
11
86
36
96
n.d.
92
Entry
Chiral ligand
Ratio (2/3)b
Yield (%)c
eed (2)
eed (3)
3
76/24
1/99
1
2
3
4
5
6
7
8
L1
L2
L3
L3
L3
L4
L5
L6
L6
L7
L8
91/9e
80/20
98/2
88
94
97 (R)
97
d
76
85
78
36
d
92
4
n.d.
92
94/6f
n.d.g
73/27
84:16
5/95
93
95
38
d
87
86
99 (R)
d
5
79/21
1/99
90
9
10
11
n.d.g
6
n.d.
94
16/84
25/75
19
92
92
42
7
82/18
18/82
96/4
a
Reaction conditions: Cu(OAc)2$H2O (0.003 mmol), ligand (0.003 mmol), DEMS
(0.3 mmol), enone (0.1 mmol), 24 h at ꢀ25 ꢁC in Et2O (0.33 M), NH4F quench.
b
Determined by GC/FID.
Isolated yields of the major regioisomer for reactions run on a 0.25 mmol scale.
Determined by GC or HPLC on chiral stationary phases. Absolute stereochem-
8
n.d.
82
c
d
istry determined by comparison of optical rotation to a reported value.
9
e
Low conversion.
Using PhSiH3 as a hydride source.
Using Cu(NO3)2 as an alternative Cu source led to only low conversion.
f
g
10
19/81
21
(continued on next page)

3412
K.R. Voigtritter et al. / Tetrahedron 68 (2012) 3410e3416
Table 2 (continued )
resolution to give enantiopure allylic alcohol 16. Exposure of
Liganda
Ratio (a/b)b
[1,2- vs 1,4-]
eec (a)
eec (b)
enone 15 to (DTBM-SEGPHOS)CuH led to the same intermediate
16 in 97% ee.
Entry
Substrate
Density functional theory (DFT) calculations at the B3LYP/aug-
cc-pVTZ//B3LYP/6-311G(d,p) level including an SMD B3LYP/6-
31þG(d,p)//B3LYP/6-311G(d,p) free-energy term for ether solva-
tion were carried out to establish the conformations of the starting
olefins with the hope that they could shed light on the reactivity
differences between the substrates. Fig. 2 shows the major con-
formational equilibrium that exists in enone 1. Enone 1 shows
a 2.34 kcal/mol preference for the s-cis conformation and experi-
mentally yields excellent regioselectivity for the 1,2 adduct 2 (Table
1, entry 3). Comparing this substrate to the cyclic analog 13, which
is locked in the s-trans conformation, shows no such preference for
1,2-addition. This might suggest that the desired 1,2 adduct will be
favored using the DTBM-SEGPHOS ligand system when the s-cis
conformation is favored. This generalization can be roughly applied
to other cases: 8, 11, and 12. For 11, the ethyl group decreases the
preference for the s-cis enone to 2.19 kcal/mol and results in a 70:30
preference for 1,2-addition. Geometrical isomers 11 and 12 showed
a reversal in regioselectivity. In 12, the s-trans conformer is pre-
ferred by 0.21 kcal/mol, while substitution of an ethyl group for the
less bulky methyl in 12, reduces this difference to 0.20 kcal/mol.
Enone 8, like 1, shows a strong preference, 2.12 kcal/mol, for the s-
cis conformer and affords good 1,2-selectivity. Thus, it appears that
the olefin substitution pattern that affects the s-cis/s-trans equi-
librium is a major factor for the observed regioselectivity with some
examples using the DTBM-SEGPHOS ligand. The situation must be
more complicated, however, since other ligands fail to show this
trend.
11
12
13
14
15
16
17
18
19
20
21
L3
L6
L3
L6
L3
L6
L3
L6
L3
L6
L3
L6
81/19
5/95
63
n.d.
94
45
97
n.d.
9
30
97
62
99
20
99
62
94
98
3
88/12
5/95
70/30
3/97
22/88
8/92
n.d.
55
2
53/47
75/25
38/62
1/99
97
85
99
To shed more light on the factors affecting the regioselectivity,
we carried out DFT calculations directly on the transition states for
the 1,2- and 1,4-additions to 2-butenone (17), and E-enone 1 and its
Z-isomer, 1z. We take these as good models for the E and Z ethyl
derivatives 11 and 12 for which the reversal in regiochemistry is
observed experimentally. These calculations were done for addition
of monomeric CuH with a simple, non-bulky cis-PH2eCH]CHePH2
ligand 18. In all three enones, there was a strong preference for 1,4-
addition to the C]C bond.
22
n.d.
a
Reaction conditions: Cu(OAc)2$H2O (0.003 mmol), ligand (0.003 mmol), DEMS
(0.3 mmol), enone (0.1 mmol), 24 h at ꢀ25 ꢁC in Et2O (0.33 M), NH4F quench.
b
Determined by GC/FID.
Determined by GC or HPLC on chiral stationary phases.
c
This methodology could be utilized in a formal, enantiose-
lective synthesis of isoaminile (PeraconÒ), an antitussive agent
(Scheme 2).14 Previous routes to this target relied on a kinetic
The transition-state calculations considered four types of tran-
sition states (see Scheme 3): (a) TSA: conjugate addition (1,4-) by
a 4-centered addition to the C]C; (b) TSB: conjugate addition by
a 6-centered mechanism involving coppereoxygen chelation; (c)
TSC: 1,2-addition to the C]O of the s-trans-enone; and (d) TSD: 1,2-
addition to the s-cis-enone. For all enones, transition state TSA is
preferred over TSB, both of which were preferred over TSC, and then
TSD (see Supplementary data for details). The difference in energy
between the better 1,4-transition state, TSA, and the better 1,2-
transition state, TSC, predict that 1,4-addition would be preferred
over 1,2-addition with the simple ligand 18, in qualitative dis-
agreement with the experimental results with SEGPHOS. It is not
expected that the theoretical energies with ligand 18, would agree
well with experiment. Rather, the theoretical energies give an
Scheme 2. Regio-, and enantioselective route to a key intermediate 16 in the synthesis
of isoaminile.
Fig. 2. Conformational analysis of enones.

K.R. Voigtritter et al. / Tetrahedron 68 (2012) 3410e3416
3413
18
Scheme 3. Transition states for copper-catalyzed reductions of 1.
indication of what would happen in the absence of the bulky li-
gands used experimentally, so that one may deduce what the
quantitative role of the bulky ligands is. Table 3 shows that the
differences in free energies of activation (from transition-state
energy differences) lead to a strong preference of 6.59 kcal/mol for
1,4-addition to the E-isomer of 1 with ligand 18, while the experi-
mental free-energy difference with SEGPHOS is in the opposite
direction by 0.42 kcal/mol for the E-enone 11. Thus, the bulky
SEGPHOS ligand dramatically shifts the regioselectivity of the re-
action toward 1,2-addition. For 2-butenone, the differences are
even larger. The calculated structures of the two relevant transition
states TSA1 and TSC1 in Fig. 3 suggest a reasonable explanation for
this behavior. The 1,2-addition transition state has the copper li-
gand held further away from the rest of the enone substituents than
in the 1,4-addition transition state, which could explain how in-
creasing the steric bulk of the ligand could destabilize the 1,4-
addition transition state to eventually make 1,2-addition the pre-
ferred path for some ligands.
Fig. 3. Structures of the most favorable 1,4-addition and 1,2-addition transition states.
Detailed analysis of the data shows that solvation effects, modeled
by a continuous dielectric mimicking diethyl ether, play some role
in the energy differences, as well as inherent steric and electronic
effects.
3. Conclusion
The trends in product ratios for the E- and Z-isomers, however,
show a reasonable correlation with one another, as one changes the
nature of the ligand from 18 to SEGPHOS. The experimental free-
energy differences in Table 3 show a 1.1 kcal/mol shift toward 1,4-
addition for the product reversal seen in 11 and 12 as one
changes from the E- to Z-enones. The predicted energies in Table 3
for 1 and 1z show the same 1.1 kcal/mol shift in the same direction,
perhaps suggesting that this experimental reversal may result from
structural differences inherent in the model transition states with
ligand 18. The fact that this reversal in regiochemistry between 11
and 12 is not observed when other ligands are used experimentally
and is not predicted at all of the higher theoretical levels (see
Supplementary data for details), indicates, however, that the
regioselectivity trends likely result from subtle and complex in-
teractions between the substrate, solvent, and bulky ligands, and
not necessarily from trends inherent simply in the substrate.
In summary, a method has been developed that shifts the in-
herent bias of copper(I) hydride from the conjugate reduction to
a 1,2-addition manifold, which is mainly applicable to acyclic
b-
arylated enones. This alteration in regioselectivity is accompanied
by enantioselectivities associated with the resulting nonracemic
allylic alcohols. Thus, using catalytic amounts of CuH ligated by
Takasago’s DTBM-SEGPHOS, good yields and ees were obtained
from 1,2-reductions of
stituents at the -site.
b,b-disubstituted enones lacking sub-
a
DFT calculations of the enone conformations and transition-
state energies for model 1,2- and 1,4-additions help to gain an
understanding of the factors involved in determining the regio-
chemistry and the reversal from 1,4-addition to 1,2-addition from E
to Z-isomers (e.g., 11 and 12) with some ligands. The calculated
transition-state energies indicate what product ratios would be
expected with just simple ligand 18 and predict that 1,4-addition
prefers a 4-centered C]C transition state, which is about 7 kcal/
mol more stable than an s-cis transition state for the corresponding
1,2-addition to the C]O bond. The small experimental preference
for the 1,2-product from the E-enone 11 shows that ligands much
bulkier than 18 behave very differently. The transition-state
structures suggest the bulky ligands employed experimentally
would disfavor the more congested 1,4-transition state, and could
then make the 1,2-transition state more favorable. The trends in
energy differences for 1,4- and 1,2-addition for E- and Z-enones are
consistent with experimental data with the SEGPHOS ligand for 11
and 12, but not with other bulky ligands, suggesting that these
shifts in regioselectivity likely result from subtle and complex in-
teractions between the substrate, solvent, and bulky ligands, rather
than necessarily trends inherent in the substrate alone.
Table 3
Relative free energies of activation for 1,2-addition vs 1,4-addition for LCuH addition
to enones from quantum calculations at 298 K (L¼cis-PH2eCH]CHePH2), and ex-
periment values at 248 K with the SEGPHOS ligand (all values in kcal/mol)
DDG≠
ether
Calculated at the M06/6-311þG(d,p) level (L¼cis-PH2eCH]CHePH2)
From enone 15
From E-enone 1
From Z-enone 1z
11.89
6.59
7.31
Experimental (L¼SEGPHOS)
From E-enone 1
From E-enone 11
ꢀ1.92
ꢀ0.42
0.68
From Z-enone 12

3414
K.R. Voigtritter et al. / Tetrahedron 68 (2012) 3410e3416
4. Experimental
J¼1.0 Hz, 3H), 2.28 (s, 3H); 13C NMR (100 MHz, CDCl3):
d 198.3,
146.1, 145.8, 128.2, 127.5, 127.4, 121.4, 32.2, 17.6. IR (neat): 3103,
3002, 2920,1673,1583,1424, 1361,1220,1183, 706 cmꢀ1; HRMS (EI)
calcd for C9H10OS (Mþ): 166.0452, found: 166.0444.
4.1. General
Unless otherwise noted, all reactions were performed under an
atmosphere of argon. Low temperature reactions were cooled in an
acetone or isopropanol bath, held at the indicated temperature
using a cryostat. DEMS and Et2O were used as received. Analytical
thin layer chromatography (TLC) was performed using Silica Gel 60
F254 plates (Merck, 0.25 mm thick). Flash chromatography was
performed with glass columns using Silica FlashÒ P60 (SiliCycle,
4.3. General procedure for the enantioselective CuH-
catalyzed 1,2-reduction of b,b-disubstituted enones
A conical 3 mL microwave vial containing a conical stir bar was
charged with fine powdered Cu(OAc)2$H2O (0.5 mg, 3 mol %,
3
m
mol) and ligand (3 mol %, 3
a rubber septum and placed under an Argon atmosphere, followed
by the addition of 200 L of Et2O added via syringe. At rt, the silane
mmol). The vial was capped with
40e63
m
m). An HP-5 column (30 mꢃ0.250 mm, 0.25
m, Agilent
Technologies) was employed for conversion analysis. General
temperature program: 50 ꢁC for 5 min; heating rate 5 ꢁC/min;
280 ꢁC for 10 min; split-inlet at 200 ꢁC and 8.97 psi (H2, constant
pressure) with 40:1 split ratio, FID at 290 ꢁC. Chiral GC analysis was
performed using a Restek RT-betaDEXcst column (30 mꢃ0.250 mm,
m
(0.3 mmol) was introduced and the mixture stirred for 30 min. The
vial was then placed into a pre-cooled acetone bath set to ꢀ25 ꢁC
and stirred for an additional 5 min. The enone (0.1 mmol) was
subsequently introduced via syringe. The side of the reaction vial
0.25
m
). Retention times (tR) are from compound dependant tem-
was rinsed with Et2O (2ꢃ50
mL). The extent of conversion was
perature programs; split-inlet at 200 ꢁC at 11.60 psi (H2, constant
pressure) with 20:1 split ratio, FID at 290 ꢁC.1H and 13C spectra were
recorded at 22 ꢁC on a Varian UNITY INOVA 400, 500, or 600 MHz
instrument. Chemical shifts in 1H NMR spectra are reported in parts
monitored by TLC. All reactions were run to completion in ꢄ 24h.
The reaction was quenched at ꢀ25 ꢁC after 24 h by the addition of
0.5 mL satd NH4F/MeOH. The reaction vial was removed from the
cooling bath and warmed to rt. After filtration through SiO2, the
solvent was evaporated in vacuo and the crude reaction mixture
was analyzed by NMR and GC/FID. This was followed by purifica-
tion by column chromatography on silica gel. The purified product
was analyzed by chiral HPLC or GC for the determination of ee.
per million (ppm) on the
d scale from an internal standard of re-
sidual chloroform (7.27 ppm). Data are reported as follows: chem-
ical shift, multiplicity (s¼singlet, d¼doublet, t¼triplet, q¼quartet,
p¼pentet, sep¼septet, m¼multiplet, br¼broad), coupling constant
in hertz (Hz), and integration. Chemical shifts of 13C NMR spectra
are reported in ppm from the central peak of CDCl3 (77.23 ppm) on
23
4.3.1. (E)-4-Phenylpent-3-en-2-ol (2). Pale yellow oil; [
a
]
¼þ26.9
D
the
d
scale. High-resolution mass analyses were obtained using a PE
(c 1.9, EtOH); 1H NMR (400 MHz, CDCl3):
d 7.39e7.44 (m, 2H),
Sciex QStar Pulsar quadrupole/TOF instrument (API) for ESI, or a GCT
Premier TOF MS (Waters Corp) for FI.
7.31e7.36 (m, 2H), 7.25e7.29 (m, 1H), 5.80e5.83 (m, 1H), 4.76e4.79
(m, 1H), 2.13 (d, J¼1.35, 3H), 1.48 (s, 1H), 1.35e1.37 (m, 3H). Spectral
data match previously reported data.21 HPLC separation conditions:
CHIRALCEL OB-H, 242 nm, 2% IPA/hexanes, 1.0 mL/min, tR¼11.7 and
14.0 min.
4.2. Starting materials
Starting olefins were synthesized by procedures found in the lit-
erature: 1,15 4,15 5,15 6,15 7,15 8,16 9,17 10,18 11,16 12,16 13,19 14,20 and 15.16
23
4.3.2. 4-Phenylpentan-2-one (3). Pale yellow oil. [
a
]
¼ꢀ22.8 (c 1.0,
D
CHCl3). 1H NMR (400 MHz, CDCl3):
d
7.28e7.32 (m, 2H), 7.18e7.23
4.2.1. (E)-4-(4-Bromophenyl)pent-3-en-2-one (4). White solid, mp
(m, 3H), 3.26e3.36 (m, 1H), 2.77 (dd, J¼16.3, 6.5, 1H), 2.67 (dd,
J¼16.4, 7.7, 1H), 2.06 (s, 3H) 1.28 (d, J¼7.0, 3H). Spectral data match
previously reported data.22 Chiral GC conditions: 110 ꢁC for 10 min;
heating 1 ꢁC/min; 120 ꢁC for 3 min, tR¼19.88 and 20.40 min.
49e51 ꢁC; 1H NMR (400 MHz, CDCl3):
d
7.50e7.53 (m, 2H),
7.34e7.38 (m, 2H), 6.49 (m, 1H), 2.51 (d, J¼1.2 Hz, 3H), 2.30 (s, 3H);
13C NMR (100 MHz, CDCl3):
199.0, 152.6, 141.5, 131.9, 128.3, 124.9,
d
123.5, 32.5, 18.4. IR (thin film): 3013, 2957, 2921, 1914, 1680, 1600,
1558, 1487, 1421, 1400, 1356, 1264, 1179, 1108, 1080, 1008, 962, 818,
672 cmꢀ1; HRMS (FI) calcd for C11H11BrO (Mþ): 237.9993, found:
237.9986.
4.3.3. (E)-4-(4-Bromophenyl)pent-3-en-2-ol (4a). Yellow oil; 1H
NMR (400 MHz, CDCl3):
d 7.44e7.46 (m, 2H), 7.26e7.29 (m, 2H),
5.80 (m, J¼8.0, 1.0 Hz, 1H), 4.75 (dq, J¼13.0, 6.0 Hz, 1H), 2.08 (d,
J¼1.0 Hz, 3H), 1.48 (br s, 1H), 1.35 (d, J¼6.0 Hz, 3H); 13C NMR
4.2.2. (E)-4-(4-Methoxyphenyl)pent-3-en-2-one (5). Yellow solid;
(125 MHz, CDCl3):
d
¼142.0, 135.4, 132.6, 131.5, 127.6, 121.4, 65.4,
mp 48e49 ꢁC; 1H NMR (400 MHz, CDCl3):
d
7.45e7.49 (m, 2H),
23.7, 16.2. IR (neat): nmax 3348, 2966, 2925, 2855, 1483, 1449, 1400,
1074, 1008, 817, 637 cmꢀ1; C11H13BrO (Mþ): 240.0150, found:
240.0143. HPLC separation conditions: CHIRALCEL OD-H, 210 nm,
2% IPA/hexanes, 1.0 mL/min, tR¼16.3 and 28.3 min.
6.88e6.92 (m, 2H), 6.50 (d, J¼1.2 Hz, 1H), 3.84 (s, 3H), 2.53 (d,
J¼1.2 Hz, 3H), 2.28 (s, 3H); 13C NMR (100 MHz, CDCl3):
d 199.0,160.7,
153.5, 134.6, 128.0, 122.9, 114.1, 35.5, 32.4, 16.2. IR (thin film): 2967,
2914, 2843, 1896, 1677, 1598, 1512, 1356, 1182, 1025, 822 cmꢀ1
HRMS (FI) calcd for C12H14O2 (Mþ): 190.0994, found: 190.0973.
;
4.3.4. 4-(4-Bromophenyl)pentan-2-one (4b). Yellow oil; 1H NMR
(400 MHz, CDCl3):
d 7.40e7.43 (m, 2H), 7.08e7.12 (m, 2H), 3.29
4.2.3. (E)-4-(3-(Trifluoromethyl)phenyl)pent-3-en-2-one (6). Yellow
oil; 1H NMR (500 MHz, CDCl3):
7.72 (m, 1H), 7.63e7.67 (m, 2H),
(dqd, J¼14.0, 7.2, 6.8 Hz, 1H), 2.73 (dd, J¼16.8, 6.8 Hz, 1H), 2.67 (dd,
J¼16.4, 7.6 Hz, 1H), 2.08 (s, 3H), 1.25 (d, J¼6.8 Hz, 3H). Spectral data
match previously reported data.23 Chiral GC conditions: 110 ꢁC for
10 min; heating 1 ꢁC/min; 160 ꢁC for 0 min, tR¼55.11 and
55.80 min.
d
7.52e7.54 (m, 1H), 6.53, (s, 1H), 2.55 (s, 3H), 2.33 (s, 3H); 13C NMR
(125 MHz, CDCl3):
d
198.9,152.2,143.5,131.6,131.2 (q, 2JCF¼31.6 Hz),
129.9, 129.3, 125.8 (q, 3JCF¼3.5 Hz), 124.1 (q, 1JCF¼271.1 Hz), 123.4 (q,
3JCF¼4.1 Hz), 32.4, 18.5. IR (neat): 3359, 3006, 2923, 1685, 1604,
1488, 1433, 1332, 1168, 1126, 1072, 801, 699 cmꢀ1; HRMS (FI) calcd
for C12H11F3O (Mþ): 228.0762; found: 228.0759.
4.3.5. (E)-4-(4-Methoxyphenyl)pent-3-en-2-ol (5a). Colorless oil;
1H NMR (400 MHz, CDCl3):
d
7.35 (m, 2H), 6.88 (d, J¼10.0 Hz, 2H),
5.75 (dd, J¼8.0, 1.0 Hz, 1H), 4.76 (dq, J¼12.5, 8.5, 6.5 Hz, 1H), 3.82 (s,
4.2.4. (E)-4-(Thiophen-2-yl)pent-3-en-2-one (7). Yellow oil; 1H
3H), 2.09 (d, J¼1.5 Hz, 3H), 1.47 (br, 1H), 1.35 (d, J¼6.5 Hz, 3H); 13C
NMR (400 MHz, CDCl3):
J¼5.2, 1.0 Hz, 1H), 7.06 (dd, J¼5.2, 3.9 Hz, 1H), 6.63 (s, 1H), 2.57 (d,
d
7.36 (dd, J¼3.9, 1.2 Hz, 1H), 7.34 (dd,
NMR (125 MHz, CDCl3): d 159.2, 135.9, 135.5, 130.5, 127.0, 113.8,
65.5, 55.5, 23.8, 16.3. IR (neat): 3389, 3060, 2967, 2914, 2843, 1896,

K.R. Voigtritter et al. / Tetrahedron 68 (2012) 3410e3416
3415
1677, 1598, 1182, 1025, 822 cmꢀ1; HRMS (FI) calcd for C12H16O2
(Mþ): 192.1150; found: 192.1154; HPLC separation conditions:
CHIRALCEL OB-H, 242 nm, 2% IPA/hexanes,1.0 mL/min, tR¼33.9 and
36.4 min.
(d, J¼6.8 Hz, 3H). Spectral data match previously reported data.16
HPLC separation conditions: CHIRALCEL OD-H, 210 nm, 2% IPA/
hexanes, 1.0 mL/min, tR¼8.9 and 9.7 min.
4.3.13. (E)-1,3-Diphenylbut-2-en-1-ol (9a). Yellow oil; 1H NMR
(400 MHz, CDCl3): d 7.25e7.47 (m, 10H), 5.98e6.04 (m, 1H),
4.3.6. 4-(4-Methoxyphenyl)pentan-2-one (5b). Yellow oil; 1H NMR
(400 MHz, CDCl3):
d
7.13 (d, J¼7.2 Hz, 2H), 6.84 (d, J¼8.4 Hz, 2H),
5.62e5.72 (m, 1H), 2.19 (d, J¼0.5 Hz, 3H) 1.97 (s, 1H). Spectral data
match previously reported data.26 HPLC separation conditions:
CHIRALCEL OD-H, 274 nm, 10% IPA/hexanes, 1.0 mL/min, tR¼9.5 and
14.1 min.
3.79 (s, 3H), 3.27 (ddq, 1H), 2.73 (dd, J¼12.8, 10.8 Hz, 1H), 2.63 (dd,
J¼12.0, 10.8 Hz, 1H), 1.56 (s, 3H), 1.25 (d, J¼7.2 Hz, 3H). Spectral data
match previously reported data.24 Chiral GC conditions: 110 ꢁC for
10 min; heating 1.00 ꢁC/min; 160 for 0 min, tR¼46.8 and 47.4 min.
4.3.14. 1,3-Diphenylbutan-1-one (9b). Yellow oil; 1H NMR
4.3.7. (E)-4-(3-(Trifluoromethyl)phenyl)pent-3-en-2-ol (6a). Yellow
(600 MHz, CDCl3): d 7.93e7.95 (m, 2H), 7.54e7.57 (m, 1H),
oil; 1H NMR (500 MHz, CDCl3):
d
7.43e7.64 (m, 4H), 5.85
7.44e7.47 (m, 2H), 7.28e7.33 (m, 4H), 7.19e7.22 (m, 1H), 3.52 (dq,
J¼14.0, 7.0 Hz, 1H), 3.31 (dd, J¼16.4, 5.7 Hz, 1H), 3.20 (dd, J¼16.4,
8.3 Hz, 1H), 1.35 (d, J¼7.0 Hz, 3H). Spectral data match previously
reported data.27 HPLC separation conditions: CHIRALCEL OD-H,
242 nm, 2% IPA/hexanes, 0.5 mL/min, tR¼13.4 and 16.0 min.
(d, J¼8.5 Hz, 1H), 4.78 (m, 1H), 2.13 (s, 3H), 1.52 (br, 1H), 1.37
(d, J¼6 Hz, 3H); 13C NMR (125 MHz, CDCl3):
d 143.9, 135.2, 133.6,
2
131.8 (q, JCF¼32.4 Hz), 130.0 (q, 1JCF¼235.4 Hz), 129.3, 128.9, 124.1
3
3
(q, JCF¼2.1 Hz), 122.8 (q, JCF¼4.1 Hz), 65.4, 23.7, 16.3. IR (neat):
3349, 2966, 2925, 1654, 1448, 1334, 1166, 1126, 1074, 800,
700 cmꢀ1; HRMS (FI): calcd for C12H13F3O (Mþ): 230.0918; found:
230.0908; HPLC separation conditions: CHIRALCEL OB-H, 242 nm,
1% IPA/hexanes, 1.0 mL/min, tR¼7.0 and 8.2 min.
4.3.15. (E)-2-Phenyloct-2-en-4-ol (10a). Colorless oil; 1H NMR
(600 MHz, CDCl3):
d
7.26e7.43 (m, 5H), 5.78 (dq, J¼8.61, 1.33 Hz,
1H), 4.56 (q, J¼7.41 Hz, 1H), 2.09e2.15 (m, 3H), 1.68e1.74 (m, 1H),
1.54e1.60 (m, 1H), 1.50 (s, 1H), 1.32e1.44 (m, 4H), 0.93 (t, J¼6.97 Hz,
4.3.8. 4-(3-(Trifluoromethyl)phenyl)pentan-2-one (6b). Yellow oil;
3H); 13C NMR (150 MHz, CDCl3):
d 143.2, 137.3, 131.2, 128.5, 127.5,
1H NMR (500 MHz, CDCl3):
d
7.41e7.47 (m, 4H), 3.40 (ddq, J¼14.0,
126.0, 69.3, 37.6, 27.8, 22.9, 16.5, 14.3. IR (neat): 3337, 2956, 2929,
2859, 1494, 1445, 1379, 1026, 757, 695 cmꢀ1; HRMS (EI) calcd for
C14H20O (Mþ): 204.1514, found: 204.1523; HPLC separation condi-
tions: CHIRALCEL AD-H, 242 nm, 2% IPA/hexanes, 1.0 mL/min,
tR¼15.6 and 18.7 min.
7.5, 5.4 Hz, 1H), 2.77 (dd, J¼14.0, 7.5 Hz, 1H), 2.71 (dd, J¼9.0, 7.5 Hz,
1H), 2.10 (s, 3H), 1.29 (d, J¼7 Hz, 3H); 13C NMR (125 MHz, CDCl3):
2
d
207.2, 147.4, 131.1 (q, JCF¼32.1 Hz), 130.6, 129.2, 124.4
(q, 1JCF¼270.5 Hz),123.6 (q, 3JCF¼4.1 Hz),123.4 (q, 3JCF¼3.6 Hz), 51.8,
35.2, 30.7, 22.0. IR (neat): 3361, 2957, 2926, 2855, 1723, 1685, 1604,
1433, 1357, 1331, 1254, 1168, 1127, 1073, 801 cmꢀ1; HRMS (FI): calcd
for C12H13F3O (Mþ): 230.0918; found: 230.0928. Chiral GC condi-
tions: 110 ꢁC for 10 min; heating 1.00 ꢁC/min; 160 ꢁC for 0 min,
tR¼24.6 and 25.4 min.
4.3.16. 2-Phenyloctan-4-one (10b). Colorless oil; 1H NMR
(400 MHz, CDCl3): d 7.18e7.31 (m, 5H), 3.30e3.36 (m, 1H), 2.72 (dd,
J¼16.1, 6.6 Hz, 1H), 2.62 (dd, J¼16.1, 7.8 Hz, 1H), 2.26e2.36 (m, 2H),
1.47e1.52 (m, 2H), 1.25 (d, J¼6.8 Hz, 3H), 1.23 (tq, J¼7.3, 2H), 0.86
(t, J¼7.3 Hz, 3H). Spectral data match previously reported data.28
Chiral GC conditions: 110 ꢁC for 10 min; heating rate 1 ꢁC/min;
180 ꢁC for 3 min, tR¼20.51 and 21.50 min.
4.3.9. (E)-4-(Thiophen-2-yl)pent-3-en-2-ol (7a). Yellow oil; 1H NMR
(500 MHz, CDCl3):
d
7.16 (d, J¼5.0 Hz,1H), 7.05 (d, J¼3.6 Hz,1H), 6.98
(dd, J¼5.0, 3.6, 1H), 5.95 (dd, J¼8.3, 1.0 Hz, 1H), 4.46e4.80 (m, 1H),
2.12 (d, J¼1 Hz, 3H), 1.67 (s, 1H), 1.33 (d, J¼7.2 Hz, 3H); 13C NMR
4.3.17. (E)-4-Phenylhex-3-en-2-ol (11a). Colorless oil; 1H NMR
(125 MHz, CDCl3):
d
147.0, 130.4, 130.3, 127.5, 124.1, 123.5, 65.1, 23.7,
(400 MHz, CDCl3):
d
7.25e7.39 (m, 5H), 5.66 (d, J¼8.4 Hz, 1H), 4.77
16.2. IR (neat): 3342, 3104, 2971, 2925, 1637, 1435, 1369, 1241, 1057,
849, 821, 695 cmꢀ1; HRMS (FI) calcd for C9H12OS (Mþ): 168.0609,
found: 168.0581. HPLC separation conditions: CHIRALCEL OB-H,
242 nm, 2% IPA/hexanes, 1.0 mL/min, tR¼15.4 and 18.6 min.
(m, 1H), 2.52e2.64 (m, 2H), 1.58 (br, 1H), 1.36 (d, J¼6.4 Hz, 3H), 0.99
(t, J¼7.6 Hz, 3H); 13C NMR (100 MHz, CDCl3):
d 143.5, 142.1, 131.8,
128.5, 127.4, 126.7, 65.1, 24.1, 23.5, 14.3. IR (neat): 3337, 3081, 3058,
3023, 2968, 2873, 1726, 1466, 1056 cmꢀ1; HRMS (FI): calcd for
C12H16O (Mþ): 176.1201; found: 176.1208. HPLC separation condi-
tions: CHIRALCEL OB-H, 242 nm, 2% IPA/hexanes, 1.0 mL/min,
tR¼9.5 and 10.7 min.
4.3.10. 4-(Thiophen-2-yl)pentan-2-one (7b). Yellow oil; 1H NMR
(500 MHz, CDCl3):
d 7.12 (m, 1H), 6.91 (m, 1H), 6.81 (m, 1H), 3.64
(m, 1H), 2.82 (dd, J¼16.6, 7.8 Hz, 1H), 2.68 (dd, J¼16.6, 7.8, 1H), 2.10
(s, 3H), 1.34 (d, J¼6.8 Hz, 3H). Spectral data match previously
reported data.25 Chiral GC conditions: 110 ꢁC for 10 min; heating
rate 1 ꢁC/min; 180 ꢁC for 3 min, tR¼20.51 and 21.50 min.
4.3.18. 4-Phenylhexan-2-one (11b). Colorless oil; 1H NMR
(400 MHz, CDCl3):
d 7.25e7.32 (m, 2H), 7.14e7.24 (m, 3H), 3.03
(m, 1H), 2.74 (dd, J¼16.6, 7.3 Hz, 1H), 2.70 (dd, J¼16.6, 7.1 Hz, 1H),
2.01 (s, 3H), 1.67 (ddq, J¼12.9, 7.6, 7.3 Hz, 1H), 1.55 (ddq, J¼12.9, 7.4,
7.3 Hz, 1H), 0.77 (t, J¼7.3 Hz, 3H). Spectral data match previously
reported data.16 Chiral GC conditions: 100 ꢁC for 0 min; heating
1.00 ꢁC/min; 130 for 0 min, tR¼42.6 and 43.3 min.
4.3.11. (E)-4-(2-Bromophenyl)pent-3-en-2-ol (8a). Colorless oil; 1H
NMR (400 MHz, CDCl3):
5.42 (dd, J¼8.0,1.2 Hz,1H), 4.75 (dq, J¼12.8, 6.4 Hz,1H), 2.03 (s, 3H),
1.61 (br, 1H), 1.36 (d, 3H); 13C NMR (100 MHz, CDCl3):
145.5, 137.8,
d
7.55 (d, J¼8 Hz, 1H), 7.10e7.29 (m, 3H),
d
134.7, 132.9, 129.9, 128.5, 127.5, 122.2, 65.1, 23.4, 18.1. IR (neat):
3349, 3053, 2968, 2925, 2854, 1468, 1058, 1027, 754 cmꢀ1; HRMS
(FI): calcd for C11H13BrO (Mþ): 240.0150; found: 240.0144; HPLC
separation conditions: CHIRALCEL OD-H, 210 nm, 2% IPA/hexanes,
1.0 mL/min, tR¼16.3 and 28.3 min.
4.3.19. (Z)-4-Phenylhex-3-en-2-ol (12a). Colorless oil; 1H NMR
(400 MHz, CDCl3):
d
7.06e7.29 (m, 5H), 5.40 (d, J¼9.2 Hz, 1H), 4.17
(dq, J¼8.8, 6.4 Hz, 1H), 2.28 (q, J¼7.2 Hz, 2H), 1.47 (br, 1H), 1.16
(d, J¼6.4 Hz, 3H), 0.92 (t, J¼7.2 Hz, 3H). Spectral data match pre-
viously reported data.29 HPLC separation conditions: CHIRALCEL
OB-H, 242 nm, 1% IPA/hexanes, 0.5 mL/min, tR¼15.5 and 17.5 min.
4.3.12. 4-(2-Bromophenyl)pentan-2-one (8b). Colorless oil; 1H NMR
(400 MHz, CDCl3):
(dt, J¼2.0, 7.6, 1H), 3.78 (ddq, J¼8.8, 5.4, 6.8 Hz, 1H), 2.80 (dd,
J¼16.4, 5.4 Hz, 1H), 2.59 (dd, J¼16.4, 8.8 Hz, 1H), 2.13 (s, 3H), 1.26
d
7.55 (d, J¼8.0 Hz, 1H), 7.20e7.30 (m, 2H), 7.06
4.3.20. 3,4,5,6-Tetrahydro-[1,10-biphenyl]-3-ol (13a). Yellow oil; 1H
NMR (400 MHz, CDCl3):
d 7.39e7.46 (m, 2H), 7.31e7.36 (m, 2H),
7.25e7.30 (m, 1H), 6.14 (dt, J¼3.6, 1.8 Hz, 1H), 4.41e4.45 (m, 1H),

3416
K.R. Voigtritter et al. / Tetrahedron 68 (2012) 3410e3416
2.44e2.54 (m, 1H), 2.33e2.42 (m, 1H), 1.87e2.02 (m, 2H), 1.65e1.83
(m, 2H), 1.53 (s, 1H). Spectral data match previously reported
data.30 HPLC separation conditions: CHIRALCEL OD-H, 242 nm, 2%
IPA/hexanes, 1.0 mL/min, tR¼17.0 and 23.8 min.
References and notes
1. Lipshutz, B. H.; Noson, K.; Chrisman, W. J. Am. Chem. Soc. 2001, 123, 12917.
2. Lipshutz, B. H.; Shimizu, H. Angew. Chem., Int. Ed. 2004, 43, 2228.
3. (a) Deutsch, C.; Krause, N.; Lipshutz, B. H. Chem. Rev. 2008, 108, 2916; (b) Yun, J.;
Kim, D.; Lee, D. Angew. Chem., Int. Ed. 2006, 45, 2785; (c) Lipshutz, B. H.; Ser-
vesko, J. M.; Taft, B. R. J. Am. Chem. Soc. 2004, 126, 8352; (d) Buchwald, S. L.; Aye,
Y.; Rainka, M. P. Proc. Natl. Acad. Sci. U.S.A. 2004, 101, 5821; (e) Czekelius, C.;
Carreira, E. M. Angew. Chem., Int. Ed. 2003, 42, 4793.
4.3.21. 3-Phenylcyclohexanone (13b). Yellow oil; 1H NMR
(400 MHz, CDCl3):
d 7.38e7.29 (m, 2H), 7.28e7.17 (m, 3H), 3.00 (m,
1H), 2.66e2.32 (m, 4H), 2.24e2.00 (m, 2H), 1.95e1.70 (m, 2H).
Spectral data match previously reported data.31 HPLC separation
conditions; CHIRALCEL OD-H, 210 nm, 2% IPA/hexanes, 1.0 mL/min,
tR¼12.1 and 13.4 min.
4. Chen, J.-X.; Daeuble, J. F.; Brestensky, D. M.; Stryker, J. M. Tetrahedron 2000, 56,
2153.
5. (a) Moser, R.; Boskovic, Z. V.; Crowe, C. S.; Lipshutz, B. H. J. Am. Chem. Soc. 2010,
132, 7852; (b) Malkov, A. V. Angew. Chem., Int. Ed. 2010, 49, 9814.
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2009, 19, 3143.
7. (a) Modern Organocopper Chemistry; Krause, N., Ed.; Wiley-VCH: Weinheim,
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B. L. Chem. Rev. 2008, 108, 2824.
8. Martin Castro, A. M. Chem. Rev. 2004, 104, 2939.
9. Nishiyama, H.; Shiomi, T.; Tsuchiya, Y.; Matsuda, I. J. Am. Chem. Soc. 2005, 127,
4.3.22. (E)-4-Methyldec-3-en-2-ol (14a). Colorless oil; 1H NMR
(400 MHz, CDCl3):
d
5.20 (m, 1H), 4.60 (m, 1H),1.97 (t, J¼7.6 Hz, 2H),
1.67 (s, 3H), 1.23e1.43 (m, 12H), 0.88 (t, J¼6.7 Hz, 3H). Spectral data
match previously reported data.32 Chiral GC conditions: 85 ꢁC for
10 min; heating rate 0.1 ꢁC/min; 117 ꢁC for 0 min, tR¼56.01 and
57.47 min.
6972.
10. Saito, T.; Yokozawa, T.; Moroi, T.; Sayo, N.; Miura, T.; Kumobayashi, H. Adv.
Synth. Catal. 2001, 343, 264.
11. (a) Schmid, R.; Broger, E. A.; Cereghetti, M.; Crameri, Y.; Foricher, J.; Lalonde, M.;
Mueller, R. K.; Scalone, M.; Schoettel, G.; Zutter, U. Pure Appl. Chem. 1996, 68,
131; (b) Schmid, R.; Foricher, J.; Cereghetti, M.; Schonholzer, P. Helv. Chim. Acta
1991, 74, 370.
12. Blaser, H.-U.; Brieden, W.; Pugin, B.; Spindler, F.; Studer, M.; Togni, A. Top. Catal.
2002, 19, 3.
13. Wu, J.; Chan, A. S. C. Acc. Chem. Res. 2006, 39, 711.
14. Antonietti, F.; Brenna, E.; Fuganti, C.; Gatti, F. G.; Giovenzana, T.; Grande, V.;
Malpezzi, L. Synthesis 2005, 7, 1148.
15. Guthrie, J. P.; Wang, X. eP. Can. J. Chem. 1992, 70, 1055.
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17. Kanazawa, Y.; Tsuchiya, Y.; Kobayashi, K.; Shiomi, T.; Itoh, J.-I.; Kikuchi, M.;
Yamamoto, Y.; Nishiyama, H. Chem.dEur. J. 2006, 12, 63.
18. Kojima, S.; Hidaka, T.; Yamakawa, A. Chem. Lett. 2005, 34, 470.
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Helv. Chim. Acta 2004, 87, 765.
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23. Biswas, S.; Maiti, S.; Jana, U. Eur. J. Org. Chem. 2010, 2861.
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25. Lopez, F.; Harutyunyan, S. R.; Minnaard, A. J.; Feringa, B. L. J. Am. Chem. Soc.
2004, 126, 12784.
4.3.23. 4-Methyldecan-2-one (14b). Colorless oil; 1H NMR
(400 MHz, CDCl3):
d
2.41 (dd, J¼15.6, 5.7 Hz, 1H), 2.21 (dd, J¼15.6,
8.0 Hz, 1H), 2.13 (s, 3H), 1.95 (m, 1H), 1.20e1.35 (m, 10H), 0.88 (t,
J¼6.4 Hz, 3H), 0.82 (d, J¼6.6 Hz, 3H). Spectral data match previously
reported data.33 Chiral GC conditions: 85 ꢁC for 10 min; heating rate
0.1 ꢁC/min; 117 ꢁC for 0 min, tR¼39.44 and 40.19 min.
23
4.3.24. 5-Methyl-4-phenylhexan-2-one (16). [
a
]
¼þ16.5 (c 1.12,
D
CHCl3). Colorless oil; 1H NMR (400 MHz, CDCl3):
d 7.12e7.32 (m,
5H), 5.31 (d, J¼8.3 Hz, 1H), 4.83 (dq, J¼8.4, 6.1 Hz, 1H), 3.10 (sep,
J¼7.0 Hz, 1H), 1.55 (br s, 1H), 1.34 (d, J¼6.1 Hz, 3H), 1.01e1.11 (m,
6H). Spectral data match previously reported data.14 HPLC separa-
tion conditions: CHIRALCEL OD-H, 242 nm, 2% IPA/hexanes, 1.0 mL/
min, tR¼13.5 and 28.6 min.
Acknowledgements
We are pleased to warmly acknowledge financial support from
theNSF (CHE0948479), and theNational Center forSupercomputing
Applications NSF (CHE100123) utilizing the NCSA Ember system.
Ligands were generously provided by Roche (BIPHEP), Takasago
(SEGPHOS) and Solvias (JOSIPHOS), for which we are most grateful.
26. Arai, N.; Azuma, K.; Nii, N.; Ohkuma, T. Angew. Chem., Int. Ed. 2008, 47,
7457.
27. Inagaki, T.; Phong, L. T.; Furuta, A.; Ito, J. i; Nishiyama, H. Chem.dEur. J. 2010, 16,
3090.
28. Sakai, M.; Hayashi, H.; Miyaura, N. Organometallics 1997, 16, 4229.
29. Chou, S. S. P.; Kuo, H. L.; Wang, C. J.; Tsai, C. Y.; Sun, C. M. J. Org. Chem. 1989, 54,
872.
30. Uyanik, M.; Fukatsu, R.; Ishihara, K. Org. Lett. 2009, 15, 3470.
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Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tet.2011.10.056.