Ferrocene phosphane-carbene ligands in Cu-catalyzed enantioselective 1,4-additions of Grignard reagents to α,β-unsaturated carbonyl compounds

Article abstract of DOI:10.1016/j.jorganchem.2013.03.033

Chiral ferrocene phosphane-carbenes are good ligands for the copper-catalyzed 1,4-addition of Grignard reagents to various Michael acceptors. The products were obtained in high enantiomeric purity (up to e.r. = 95:5) and excellent regioselectivity (r.r. =

Full text of DOI:10.1016/j.jorganchem.2013.03.033

Journal of Organometallic Chemistry 737 (2013) 47e52
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Journal of Organometallic Chemistry
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Ferrocene phosphaneecarbene ligands in Cu-catalyzed enantioselective
1,4-additions of Grignard reagents to a,b-unsaturated carbonyl compounds
a
a
a
b
a,
*
ꢀ
ꢀ
Jana Csizmadiová , Mária Meciarová , Ambroz Almássy , Branislav Horváth , Radovan Sebesta
a Department of Organic Chemistry, Faculty of Natural Sciences, Comenius University, Mlynská dolina CH-2, SK-84215 Bratislava, Slovakia
b Institute of Chemistry, Faculty of Natural Sciences, Comenius University, Mlynská dolina CH-2, SK-84215 Bratislava, Slovakia
a r t i c l e i n f o
a b s t r a c t
Article history:
Chiral ferrocene phosphaneecarbenes are good ligands for the copper-catalyzed 1,4-addition of Grignard
reagents to various Michael acceptors. The products were obtained in high enantiomeric purity (up to
e.r. ¼ 95:5) and excellent regioselectivity (r.r. ¼ 99:1). These ligands are also useful for domino conjugate
addition followed by enolate trapping with imine and aldehyde.
Received 20 February 2013
Received in revised form
19 March 2013
Accepted 22 March 2013
Ó 2013 Elsevier B.V. All rights reserved.
Keywords:
Asymmetric catalysis
Ferrocene
Carbene ligand
Conjugate addition
1. Introduction
organoaluminium [26,27], alkylboranes [28], organosilanes [29] as
well as boron [30] and silicon [31,32] centered nucleophiles.
Conjugate additions of carbon nucleophiles to
a
,
b
-unsaturated
Bidentate heterodonor ligands often bring interesting new se-
lectivities to asymmetric catalytic reactions. Combining a strong
donor with a good -acceptor unit within the catalyst might be
carbonyl compounds ranks among the most valuable methods for
carbonecarbon bond formation in organic synthesis. Of particular
synthetic importance are asymmetric Cu-catalyzed additions of
organometallic reagents [1e8].
s-
p
beneficial for its catalytic activity, potentially showing rate accel-
eration for both oxidative addition and reductive elimination.
Therefore, NHC-ligands featuring adjacent phosphorus atom can
act as promising ligands for a variety of metal-catalyzed asym-
metric transformations. Surprisingly, only a few such ligands were
described (Fig. 1). Bappert and Helmchen prepared rigid naphthyl-
bridged ligand 1 for a Rh-catalyzed hydrogenation [33]. This ligand
was then successfully used also in Rh-catalyzed 1,4-addition of
arylboronic acids to enones [34]. Versatile ferrocene scaffold has
also been used for the construction of phosphaneecarbene ligands.
Togni and coworkers reported synthesis of a tridentate PCP ligand
2, based on a ferrocene scaffold [35,36]. Bolm and coworkers
described the synthesis of iridium complexes in which a bidentate
carbene-phosphane ligand 3 contains a chiral [2,2]paracyclophane
unit. These complexes efficiently catalyzed the asymmetric hy-
drogenation of functionalized as well as simple alkenes [37].
The synthesis of chiral ferrocene phosphane-NHC ligand 4 was
published by Chung’s group. This ligand was used in the hydroge-
nation of dimethyl itaconate, but enantioselectivity of the reaction
was low (18% ee) [38]. Shi and co-workers used this ligand in an
achiral Pd-catalyzed SuzukieMiyaura cross-coupling reaction,
which proceeded with excellent yields [39,40]. Visentin and Togni
tested another ligand of type 4 in a palladium-catalyzed allylic
The first application of an achiral N-heterocyclic carbene (NHC)
ligands in a copper-catalyzed conjugate addition to enones was re-
ported by Fraser and Woodward in 2001 [9]. The authors also
noticed strong acceleration of the Cu-catalyzed addition of dia-
lkylzinc reagents by the NHC-ligand. Later in the year 2001, an
asymmetric version of the conjugate addition using chiral NHC li-
gands was reported by the laboratories of Alexakis [10] and Roland
[11]. Enantioselectivities were only medium in these initial reports.
However, enantioselectivities of the Cu-catalyzed additions of dia-
lkyzinc to various Michael acceptors soon rose above e.r. 95:5 [12,13].
Further improvement was achieved by Mauduit and Hoveyda, who
introduced a weakly coordinating alkoxy or sulfonate group to car-
bene, which resulted in much improved performance of such ligands
[14e18]. Nowadays, CueNHC complexes are one of the most versa-
tile catalysts for conjugate additions of a wide range of nucleophiles
[19,20]. Apart from above mentioned dialkylzincs, CueNHC com-
plexes efficiently catalyze additions of Grignard [21e25],
* Corresponding author. Tel.: þ421 2 60296208.
ꢀ
E-mail address: radovan.sebesta@fns.uniba.sk (R. Sebesta).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.03.033

48
J. Csizmadiová et al. / Journal of Organometallic Chemistry 737 (2013) 47e52
Fig. 1. Phosphaneecarbene ligands.
Scheme 1. Synthesis of ligand precursors 4.
amination. However, only partial conversion of starting materials
was observed and the products were racemic [41]. Labande and
coworkers prepared a PeNHC ligand, similar to compound 4, only
up. This notion is also supported by the fact that enolate ion can be
successfully intercepted by an electrophile, such as imine or alde-
hyde, where higher yields were achieved than in the conjugate
addition itself (see below). No product of 1,4-addition was detected,
if the reaction proceeded under the same conditions in diethyl
ether. A decrease of the reaction temperature to ꢀ78 ꢁC had no
significant effect on the reaction course. On the other hand, an in-
crease of the reaction temperature resulted in decrease of yield to
25% and regioselectivity to 33:67 (8/9). The enantioselectivity was
only slightly affected (e.r. 9:91) (Table 1, Entries 1e4). Using
CuBr.Me2S instead of Cu(OTf)2 in 2-Me-THF at ꢀ78 ꢁC again led to
lower yield (35%) and enantiomeric purity (e.r. 9:91). Regiose-
lectivity remained the same (Table 1, Entry 5). The presence of the
methyl group on N(3) atom of imidazolylidene ring in an active
complex seems essential for the regioselectivity. Use of the phenyl
substituted ligand 4b led to the significantly lower regioselectivity
(8/9 63:37) while the satisfactory enantiomeric ratio 5:95 was
preserved (Table 1, entry 6). On the other hand, exchange of the
diphenylphosphano group in the ligand precursor 4a for bis(3,5-
dimethylfenyl)phosphano group in precursor 4c resulted in excel-
lent regioselectivity (8/9 99:1) at the expense of lower enantiose-
lectivity (e.r. 15:85) (Table 1, entry 7).
To assess catalytic profile of ferrocenyl phosphaneecarbene li-
gands in the Cu-catalyzed conjugate addition, we have screened a
range of Michael acceptors. The reactions were performed using the
best conditions (2-Me-THF as solvent, 6 mol% of the ligand pre-
cursor 4a, 6 mol% of Cu(OTf)2 at ꢀ78 ꢁC for 2.5 h). The results are
summarized in Table 2. In contrast to lactone 7, lactone 10 did not
undergo 1,4-addition of EtMgBr. The conjugate addition product 19
was detected in 5% (4a) and 7% (4b) yields, respectively. Enantio-
meric ratio was 24:76 (Table 2, Entry 2). Such low yields are
probably due to a ring opening and following side reactions.
Addition to cyclohex-2-enone (11) using 4a proceeded in 2-Me-THF
as well as in CH2Cl2 with synthetically useful yield (68%) albeit with
only medium enantioselectivity e.r. 79:21 and e.r. 62:38. A higher
without a-stereogenic center. The Pd-complex showed moderate
enantioselectivity in the asymmetric SuzukieMiyarua reaction
[42]. To the best of our knowledge, carbene-based bidentate P,C-
ligands were not used in asymmetric Cu-catalyzed conjugate
addition of hard organometallic reagents such as dialkylzinc or
Grignard reagents.
In this context, we decided to investigate catalytic efficiency of
ligands 4 in the Cu-catalyzed addition of Grignard reagents. Herein,
we report the result of this study e successful enantioselective Cu-
catalyzed 1,4-addition of Grignard reagents to
carbonyl compounds and lactones.
a,b-unsaturated
2. Results and discussion
Precursors to phosphanocarbene ligands 4a and 4b were pre-
pared according to the literature procedure [38], in which
commercially available Ugi amine (5) was ortho-lithiated with
nBuLi and then quenched with a chlorophosphane. The resulting
amino phosphanes 6a and 6b reacted with either 1-methyl or 1-
phenylimidazole in acetic acid. Finally, acetate anion was
exchanged to iodide by treatment with NaI in ethanol (Scheme 1).
The synthesis of compound 4c followed the similar path, using
amino phosphane 6b and 1-methylimidazole as building blocks.
Imidazolium phosphanes 4 were then used in the Cu-catalyzed
conjugated addition of Grignard reagents to
a,b-unsaturated
carbonyl compounds and lactones. We started our research with
optimization of asymmetric 1,4-addition of ethylmagnesium bro-
mide to lactone 7 (Schemes 2 and 3). The results are given in
Table 1. Reactions proceeded with 1.5 equiv. of EtMgBr, which is
also used as a base for deprotonation of the ligand precursor.
Catalyst loading was 6 mol%, both the ligand precursor 4 and
copper salt. The reactions were monitored by gas chromatography
(GC) and full conversion of starting material was usually achieved
in 2.5 h. Conversion, yield, ratio of 8/9, and enantiomeric purity of
compound 8 were determined by GC.
The conjugated addition using ligand precursor 4a, Cu(OTf)2 in
2-Me-THF at ꢀ60 ꢁC proceeded with 100% conversion, high regio-
selectivity of 99:1 (8/9) and enantioselectivity e.r. 5:95. Although
there was full conversion of the starting material, only 47% of the
product 8 was detected by GC. Usually, less than 20% of various side
products were detected by GC. The rest of the material can be
accounted by decomposition of the product during aqueous work-
Scheme 2. Conjugate addition of EtMgBr to lactone 7.

J. Csizmadiová et al. / Journal of Organometallic Chemistry 737 (2013) 47e52
49
Table 2
Cu-catalyzed 1,4-addition of ethylmagnesium bromide to
and carboxyl compounds.
a
,
b
-unsaturated carbonyl
Entry
Substrate
Conversion (%)
Yield (%)
e.r. (R:S)
2
10
11
100
5 (7c)
76:24
Scheme 3. Conjugate additions of EtMgBr to Michael acceptors 10e18.
3
100
68
79:21
yield (84%) and better enantioselectivity (e.r. 81:19) were achieved
when ligand precursor 4b was used in 2-Me-THF (Entries 3e5).
Cyclopent-2-enone (12) underwent 1,4-addition with ethyl-
magnesium bromide with 42% yield (Table 2, Entry 6). Somewhat
disappointing results were obtained when 3-methylcyclohexenone
(13) was used as a substrate for 1,4-addition of EtMgBr. The reaction
under established conditions proceeded with 78% conversion, but
only 7% of the product 22 was detected as a virtually racemic
mixture (Table 2, Entry 7). Chalcone (14) and ketone 15 afforded the
products of 1,4-addition in promising yields 60 and 43%, respec-
tively, but practically with no enantioselectivities (Table 2, Entries
8e9). Coumarin (16) again gave only traces of 1,4-addition product
25 with EtMgBr (Table 2, Entry 10). 1-Benzyl-1H-pyrrole-2,5-dione
(17) and 1-(cyclopent-1-en-1-yl)ethanone (18) were under estab-
lished reaction condition completely unreactive (Table 2, Entries
11e12).
4
5
99a
68
84
62:38
81:19
100c
6
7
12
13
100
78
42
7
n.d.
54:46
8
9
14
15
90
64
60b
43b
51:49
54:46
We also evaluated efficacy of the ligand precursor 4a in a
domino conjugate Grignard addition followed by a Mannich reac-
tion. A chiral enolate produced by the addition of ethylmagnesium
bromide to cyclohex-2-enone (11) reacted with imine N-benzyli-
denetoluenesulfonamide (26) (Scheme 4). Products of these
10
11
16
17
38
4
n.d.
e
e
e
domino reactions are b-amino ketones with three adjacent ster-
eocenters. Two diastereomers (S,R,R)-27 and (R,R,R)-27 were iso-
lated in 22 and 21% yield with enantiomeric ratios of e.r. 71:29 and
78:22, respectively. In comparison with originally developed con-
ditions from our laboratory, using Taniaphos ligand, yields were
similar but enantioselectivity was higher (32 and 28% yields; e.r.
95:5 and 97:3) [43].
Benzaldehyde was used as another acceptor for trapping of the
chiral enolate produced by Cu-catalyzed enantioselective Grignard
addition of ethylmagnesium bromide to lactone 7. The products
28e30 were first synthesized by Hoveyda using 1,4-addition of
dialkylzinc reagents and Cu-peptide complexes [44]. These prod-
ucts were formed in good yields also using our methodology with
ferrocenyl phosphaneecarbene ligands 4 and Grignard reagents
(Scheme 5, Table 3). Both ligands 4a and 4b provided similar results
in term of yield, diastereo- and enantioselectivity. Ratio of di-
12
18
e
e
e
a
CH2Cl2 was used as a solvent.
Isolated yields.
4b was used as a ligand precursor.
b
c
and e.r. was 97:3. The reaction worked well also with MeMgBr,
leading to product 29 (Table 3, entry 5). On the other hand, using
iPrMgCl, the product 30 was isolated only in 24% yield and with
only low e.r. of 57:43. The domino reaction with five-membered
lactone 10 (furan-2(5H)-one) did not proceed under these reac-
tion conditions (Table 3, entry 3).
Products of conjugate addition of organometallic reagents to
lactones are difficult to isolate. As Hoveyda described for the dia-
lkylzinc reagents [44], the domino conjugate addition and aldol
reaction can be used for obtaining products of conjugate addition
itself. Similarly, we subjected compound 28 to K2CO3 in boiling
toluene, what led to ketone 8 in 82% yield and with enantiomeric
purity of e.r. 98:2.
astereomers of b-hydroxy lactones (S,R,R)-28 and (R,R,R)-28 using
4a was 85:15 according to 1H NMR and the major diastereomer was
isolated in 63% yield with enantiomeric ratio 94:6. Using ligand
precursor 4b, the major isomer of 28 was isolated with 57% yield
Table 1
Screening of various reaction conditions in the asymmetric 1,4-addition of ethyl-
magnesium bromide to lactone 7.
Entry
Ligand
[Cu]
Temp
[ꢁC]
Conv.
[%]
Yield
[%]
r.r.
(8/9)
e.r.
1
2
3
4
5
6
7
4a
4a
4a
4a
4a
4b
4c
Cu(OTf)2
Cu(OTf)2
Cu(OTf)2
Cu(OTf)2
CuBr.Me2S
Cu(OTf)2
Cu(OTf)2
ꢀ60
ꢀ60
ꢀ78
ꢀ40
ꢀ78
ꢀ78
ꢀ78
100
81a
100
100
99
47
e
99:1
e
5:95
e
52
25
35
43
43
99:1
33:67
99:1
63:37
99:1
6:94
9:91
9:91
5:95
15:85
100
100
a
Reaction was performed in Et2O.
Scheme 4. Domino conjugate addition to 11 and reaction with imine 26.

50
J. Csizmadiová et al. / Journal of Organometallic Chemistry 737 (2013) 47e52
Unified chemical shift scale was used for 31P NMR with 85% H3PO4
as secondary standard (
d
¼ 0.0 ppm,
X
¼ 40.4807420). Specific
optical rotations were measured on Jasco instrument and are given
in deg cm3 gꢀ1 dmꢀ1. Gas chromatographic (GC) analysis was per-
formed in an Agilent Technologies 6890N and 6850 series instru-
ment equipped with an FID detector and a capillary column, HP-1
(30m ꢂ 0.32 ꢂ 0.25
m
m), Lipodex E (50 m ꢂ 0.25 mm ꢂ 0.2
mm) or
m). Enantiomeric ratios
BETA DEX (30 m ꢂ 0.25 mm ꢂ 0.25
m
were determined by HPLC on Chiralpak, OD-H, IA-H, AD-H, OJ-H
(Daicel Chemical Industries), column using hexane/iPrOH as a
mobile phase and detection with UV-detector at 254 and 218 nm.
Flash chromatography was performed on Merck silica gel 60.
Thin-layer chromatography was performed on Merck TLC-plates
silica gel 60, F-254. Diastereomeric ratios were determined by 1H
NMR and GC.
Precursors for ligands 4a, 4b and 4c are synthesized according to
the literature procedure [38,45,46]. See Supporting information for
NMR spectra.
Scheme 5. Domino conjugate addition to 7 and reaction with benzaldehyde.
We attempted to isolate and characterize catalytically active
copper-complexes. We tried several bases (EtMgBr, BuLi, tBuOK and
NaH) and copper salts for generation of the carbene complex. The
best results were obtained with NaH as base and Cu(MeCN)4PF6 as
copper source, because of its good solubility in the THF. The pro-
jected complex was precipitated with hexane, but resulting crystals
were not suitable for X-ray crystallographic analysis. Furthermore,
it was quite sensitive. The complex formation was followed by 1H,
13C and 31P NMR. Although we were not able to isolate a carbene
complex in pure form, Cu-complex formation is suggested by
following observations. In the 1H NMR, extinction of a signal cor-
responding to imidazolium 2-H proton at 9.3 ppm was observed. In
31P NMR, phosphorus signal in the free ligand is at ꢀ27.4 ppm. In
the complex, this signal shifts only slightly downfields (ꢀ25 ppm)
but its significant broadening suggests weak coordination and
presence of a dynamic equilibrium. The best evidence for Cuecar-
bene complex formation comes from 13C NMR. A new signal at
163 ppm appeared, what the expected position for Cu-bound car-
bene is. It is a combined signal due to coupling with both isotopes of
copper. In contrast, in the imidazolium compound 4a, the corre-
sponding carbon atom appears as a singlet at 136 ppm. This data
suggest coordination of carbon with copper.
4.1.1. 1-[(R)-1-((S)-2-(Bis(3,5-dimethylphenyl))phosphinoferrocenyl)
ethyl]3-phenylimidazolium iodide (4c)
A suspension of amine 6b (160 mg, 0.32 mmol) and 1-
methylimidazole (32 mg, 0.38 mmol) were dissolved in acetic acid
(2 mL) to give a clear orange solution. The solution was heated at
60 ꢁC for 5 h. After evaporating the solvent under vacuum, the
residue was dissolved in EtOH (4 mL) with NaI (144 mg, 0.96 mmol).
The resulting solution was stirred for 2 h, concentrated and chro-
matographed (silica gel, CH2Cl2 and CH3OH 2%). Yield: 100 mg (47%),
orange solid. M.p. ¼125e129 ꢁC, [
a
]D ¼ ꢀ144.77 (c ¼ 0.39, CHCl3),1H
NMR (600 MHz, CDCl3)
d
¼ 9.22 (s, 1H, CHimid), 7.05 (s, 1H, Ph), 7.04
(s, 1H, Ph), 7.02 (s, 1H, Ph), 6.83 (t, J ¼ 1.7 Hz, 1H, CHimid), 6.81 (s, 1H,
Ph), 6.66 (t, J ¼ 1.5 Hz, 1H, CHimid), 6.45 (s, 1H, Ph), 6.44 (s, 1H, Ph),
5.95 (dq, J ¼ 3.8 Hz, J ¼ 7.0 Hz, 1H, CH), 4.89 (m, 1H, Fc), 4.50 (t,
J ¼ 2.5 Hz, 1H, Fc), 4.13 (s, 5H, cp), 3.90 (m, 1H, Fc), 3.55 (s, 3H, CH3),
2.30 (s, 6H, CH3), 2.15 (s, 6H, CH3), 2.06 (d, J ¼ 7.0 Hz, 3H, CH3). 13
C
3. Conclusions
NMR (151 MHz, CDCl3)
d
¼ 138.21, 138.15, 134.63, 134.59 (2d, 2ꢂ
CqPh), 137.76, 137.70, 137.50, 137.45 (2d, 4ꢂ CqPh), 136.05 (d, J ¼ 1.5,
CHimid), 132.35 (d, J ¼ 20.8 Hz, CHPh), 131.31 (CHPh), 130.03 (CHPh),
129.74 (d, J ¼ 19.5 Hz, CHPh), 122.02 (CHimid), 118.76 (CHimid), 89.52
(d, J ¼ 24.5 Hz, CqFc), 76.72 (CqFc), 73.06 (d, J ¼ 4.3 Hz, CHFc), 70.49
(CHFc), 70.32 (CHCp), 69.52 (d, J ¼ 3.3 Hz, CHFc), 56.28 (d, J ¼ 10.9 Hz,
CH), 36.49 (CH3), 21.31 (2ꢂ CH3), 21.28 (2ꢂ CH3), 21.26 (CH3). 31P
Ferrocenyl phosphaneecarbene ligands are useful for Cu-
catalyzed 1,4-addition to 5,6-dihydro-2H-pyran-2-one and to
lesser extent to other substrates. The primary product of the con-
jugate additions, enolate ions can be trapped with electrophiles
such as imine or aldehyde.
NMR (CDCl3):
d
¼ ꢀ27.78 Hz. IR (ATR):
n 2963, 2960, 1579, 1248,
4. Experimental
Anal. Calcd for C32H36FeIN2P.CH2Cl2 (Mr ¼ 747.3): C 53.04, H 5.13, N
3.75; found: C 53.91, H 5.39, N, 3.87.
4.1. General information
4.2. General procedure for the addition of EtMgBr
All reactions were carried out in inert atmosphere of Ar. Solvents
were dried and purified by standard methods before use. NMR
spectra were recorded on Varian NMR System 300 (300 MHz for 1H,
75 MHz for 13C) and Varian NMR System 600 (600 MHz for 1H,
3.0 M Et2O solution of EtMgBr (0.26 mL, 0.77 mmol) was added
dropwise over 3 min at 0 ꢁC to a suspension of copper(II) triflate
(11.1 mg, 6 mol-%) and ferrocene phosphaneecarbene ligand 4a
(18.5 mg, 6 mol-%) in 2-Me-THF (3 mL) under argon atmosphere
and the mixture was stirred at 0 ꢁC for 1 h. Then the mixture was
cooled to ꢀ78 ꢁC and a solution of 5,6-dihydro-2H-pyran-2-one (7)
150 MHz for 13C and 242.8 MHz for 31P). Chemical shifts (
d) are
given in ppm relative to tetramethylsilane for 1H NMR and 13C NMR.
(44 mL, 0.51 mmol) in 2-Me-THF (2 mL) was added over 30 min.
Table 3
After stirring for 2.5 h at ꢀ78 ꢁC, the reaction was quenched with
saturated NH4Cl (3 mL). The aqueous layer was separated and
extracted with Et2O (3 ꢂ 3 mL). The organic layers were dried over
sodium sulfate. The data of the conversions and yield were deter-
mined by achiral-phase GC analysis using decaline as an internal
standard.
Cu-catalyzed domino addition of alkylmagnesium bromide to lactone 7 and 10 and
benzaldehyde.
Entry
Ligand
RMgX
Substrate
Yield [%]
d.r.
e.r.
1
2
3
4
5
6
7
4a
4b
4a
4a
4a
4a
4a
EtMgBr
EtMgBr
EtMgBr
EtMgCl
MeMgBr
MeMgI
iPrMgCl
7
7
10
7
7
63
57
e
85:15
84:16
e
94:6
97:3
e
63
55
60
24
75:25
85:15
83:17
82:18
98:2
88:12
64:36
57:43
4.2.1. (R)-4-Ethyl-tetrahydropyran-2-one (8)
7
7
1H NMR (300 MHz, CDCl3)
d
4.45e4.38 (m, 1H), 4.30e4.19 (m,
1H), 2.70 (ddd, J ¼ 17.3 Hz, J ¼ 5.9 Hz, J ¼ 1.6 Hz, 1H), 2.15 (dd,

J. Csizmadiová et al. / Journal of Organometallic Chemistry 737 (2013) 47e52
51
J ¼ 17.3 Hz, J ¼ 10.1 Hz, 1H), 2.04e1.79 (m, 2H), 1.61e1.46 (m, 1H),
4.3. Procedure for domino conjugate addition and Mannich
reaction of N-benzylidenetoluenesulfonamide
1.46e1.33 (m, 2H), 0.94 (t, J ¼ 7.4 Hz, 3H). NMR data agree with
literature [44]. Enantiomeric excess was determined by chiral GC
(Lipodex E,
(S), tR (major) ¼ 34.9 min (R), e.r. ¼ 5:95.
g
-cyclodextrin, 120 ꢁC, 196 kPa), tR (minor) ¼ 34.4 min
3.2 M solution of EtMgBr in 2-Me-THF (0.12 mL, 0.38 mmol) was
dropwise added over 3 min at 0 ꢁC under argon atmosphere to a
suspension of Cu(OTf)2 (5.4 mg, 6 mol%) and ferrocene phosphanee
carbene ligand 4a (9.1 mg, 6 mol%) in 2-Me-THF (3 mL) and the
mixture was stirred at 0 ꢁC for 1 h. Then the mixture was cooled to
4.2.2. (R)-4-Ethyl-dihydrofuran-2(3H)-one (19)
1H NMR (300 MHz, CDCl3)
d
¼ 4.44 (dd, J ¼ 7.3 Hz, J ¼ 9.4 Hz,1H),
3.94 (dd, J ¼ 7.6 Hz, J ¼ 9.4 Hz, 1H), 2.63 (dd, J ¼ 17.0 Hz, J ¼ 8.3 Hz,
1H), 2.49 (hept, J ¼ 7.3 Hz, 1H), 2.19 (dd, J ¼ 7.6 Hz, J ¼ 17.0 Hz, 1H),
1.81e1.38 (m, 2H), 0.98 (t, J ¼ 7.3 Hz, 3H). NMR data agree with
literature [47]. Enantiomeric excess was determined by chiral GC
ꢀ78 ꢁC and
a solution of cyclohex-2-enone (11) (35.2 mL,
0.38 mmol) in 2-Me-THF (2 mL) was added over 30 min. The
resulting mixture was stirred at ꢀ78 ꢁC for an additional 2.5 h.
Finally, N-benzylidenetoluenesulfonamide (65 mg, 0.25 mmol),
dissolved in 2-Me-THF (2 mL), was added, and the reaction mixture
was slowly allowed to reach room temperature overnight. The re-
action was then quenched with aq. NH4Cl (3 mL) and extracted
with Et2O (3 ꢂ 3 mL). The combined organic extracts were
concentrated. The crude product was purified by column chroma-
tography (silica gel, hexane/EtOAc/CH2Cl2, 83:14:3). Yield: (S,R,R)-
27a (21 mg, 22%) (R,R,R)-27b (20 mg, 21%).
(Lipodex E,
(S), tR (major) ¼ 37.3 min (R), e.r. ¼ 24:76.
g
-cyclodextrin, 120 ꢁC, 222 kPa), tR (minor) ¼ 36.8 min
4.2.3. (R)-3-Ethyl-cyclohexanone (20)
1H NMR (300 MHz, CDCl3)
d
¼ 2.48e2.38 (m, 1H), 2.37e2.30 (m,
1H), 2.28e2.20 (m, 1H), 1.92e1.85 (m, 1H), 1.72e1.57 (m, 2H), 1.45e
1.24 (m, 3H), 0.91 (t, J ¼ 7.4 Hz, 3H). NMR data agree with literature
[48]. Enantiomeric excess was determined by chiral GC (Lipodex E,
g
-cyclodextrin, 100 ꢁC, 122 kPa), tR (major) ¼ 12.5 min (R), tR
4.3.1. (S,R,R)-N-[(2-Ethyl-6-oxocyclohexyl)(phenyl)methyl]-4-
methyl-benzenesulfonamide (27a)
(minor) ¼ 12.8 min (S), e.r. ¼ 81:19.
1H NMR (300 MHz, CDCl3)
d
7.44 (d, J ¼ 8.3 Hz, 2H, Ar), 7.14e6.89
4.2.4. Ethyl-cyclopentanone (21)
(m, 7H, Ar), 6.15 (d, J ¼ 10.1 Hz, 1H, CH), 4.76 (dd, J ¼ 10.2 Hz, 4.2 Hz,
1H, CH), 2.58 (dd, J ¼ 9.2 Hz, 4.0 Hz, 1H, CH), 2.34e2.13 (m, 2H, CH),
2.29 (s, 3H, CH3), 2.07e1.84 (m, 3H, CH þ CH2), 1.80e1.63 (m, 2H,
CH2), 1.62e1.40 (m, 2H, CH2), 0.92 (t, J ¼ 7.4 Hz, 3H, CH3). 13C NMR
1H NMR (300 MHz, CDCl3)
d
¼ 2.10e2.44 (m, 5H), 1.75e1.85 (m,
1H), 1.41e1.58 (m, 3H), 0.96 (t, J ¼ 7.4 Hz, 3H). NMR data agree with
literature [49].
(151 MHz, CDCl3) d
213.39 (Cq),142.64 (Cq),139.64 (CPqh),138.06 (Cq),
4.2.5. (R)-3-Ethyl-3-methylcyclohexanone (22)
129.03 (CHPh), 127.93 (CHPh), 126.88 (CHPh), 126.82 (CHPh), 126.64
(CHPh), 61.38 (CH), 55.60 (CH), 42.36 (CH2), 42.02 (CH), 28.63 (CH2),
25.82 (CH2), 25.31 (CH2), 21.32 (CH3), 9.94 (CH3). NMR data agree
with literature [43]. HPLC (Diacel Chiralcel OD-H, hexane/propan-
2-ol, 90:10, 0.6 mL/min, 218 nm): tR (minor) ¼ 17.0 min (S), tR
(major) ¼ 23.7 min (R), e.r. ¼ 29:71.
1H NMR (300 MHz, CDCl3)
d
¼ 2.28 (t, J ¼ 6.8 Hz, 2H), 2.14 (d,
J ¼ 12.6 Hz, 1H), 2.00 (d, J ¼ 12.6 Hz, 1H), 1.90e1.81 (m, 2H), 1.61e
1.46 (m, 2H), 1.31 (q, J ¼ 7.6 Hz, 2H), 0.90 (s, 3H), 0.84 (t, J ¼ 7.4 Hz,
3H). NMR data agree with literature [22]. Enantiomeric excess was
determined by chiral GC (BETA DEX,
b
-cyclodextrin, 110 ꢁC,
171 kPa), tR (major) ¼ 7.8 min (R), tR (minor) ¼ 8.1 min (S),
e.r. ¼ 54:46.
4.3.2. (R,R,R)-N-[(2-Ethyl-6-oxocyclohexyl)(phenyl)methyl]-4-
methyl-benzenesulfonamide (27b)
4.2.6. (R)-1,3-Diphenyl-pentan-1-one (23)
1H NMR (300 MHz, CDCl3)
d
7.46 (d, J ¼ 8.3 Hz, 2H), 7.14e6.95
1H NMR (300 MHz, CDCl3)
d
¼ 7.96e7.84 (m, 2H), 7.53e7.49
(m, 7H), 6.31 (d, J ¼ 10.1 Hz,1H), 4.67 (dd, J ¼ 10.1 Hz, J ¼ 5.8 Hz,1H),
2.63 (dd, J ¼ 8.8 Hz, J ¼ 6.2 Hz, 1H), 2.32 (s, 3H), 2.30e2.24 (m, 1H),
2.23e2.09 (m, 1H), 1.93e1.82 (m, 2H), 1.68e1.23 (m, 5H), 0.88 (t,
(m, 1H), 7.48e7.37 (m, 2H), 7.30e7.13 (m, 5H), 3.30e3.23 (m, 3H),
1.87e1.72 (m, 1H), 1.66e1.60 (m, 1H), 0.80 (t, J ¼ 7.3 Hz, 3H).
13C NMR (151 MHz, CDCl3)
d
199.19 (Cq), 144.64 (CPqh), 137.26
J ¼ 7.3 Hz, 3H). 13C NMR (151 MHz, CDCl3)
d 213.15 (Cq), 142.66 (Cq),
(CqPh), 132.86 (CHPh), 128.49 (CHPh), 128.37 (CHPh), 128.03 (CHPh),
127.61 (CHPh), 126.23 (CHPh), 45.59 (CH2), 42.99 (CH), 29.19
(CH2), 12.06 (CH3). NMR data agree with literature [50]. HPLC
(Diacel Chiralcel OJ-H, hexane/propan-2-ol, 99.5:0.5, 1 mL/min,
254 nm): tR (minor) ¼ 29.9 min (S), tR (major) ¼ 43.0 min (R),
e.r. ¼ 49:51.
138.07 (Cq), 137.46 (Cq), 129.13 (CHPh), 128.50 (CHPh), 128.17 (CHPh),
127.41 (CHPh), 126.82 (CHPh), 59.50 (CH), 57.01 (CH), 41.80 (CH2),
40.12 (CH), 28.05 (CH2), 25.63 (CH2), 23.39 (CH2), 21.36 (CH3), 10.21
(CH3). NMR data agree with literature [43]. HPLC (Diacel Chiralcel
OD-H, hexane/propan-2-ol, 90:10, 0.6 mL/min, 218 nm): tR
(major) ¼ 14.8 min (R), tR (minor) ¼ 17.9 min (S), e.r. ¼ 78:22.
4.2.7. (R)-1-Benzyloxycarbonyl-2-ethyl-4-piperidone (24)
4.4. Procedure for domino conjugate Grignard addition and aldol
reaction with benzaldehyde
1H NMR (300 MHz, CDCl3)
d
¼ 7.43e7.30 (m, 5H), 5.26e5.10 (m,
2H), 4.58 (br, 1H), 4.40 (br, 1H), 3.31e3.13 (m, 1H), 2.65 (dd,
J ¼ 14.6 Hz, J ¼ 6.6 Hz, 1H), 2.59e2.40 (m, 1H), 2.38e2.20 (m. 1H),
1.65e1.41 (m, 2H), 0.87 (t, J ¼ 7.3 Hz, 3H). 13C NMR (151 MHz, CDCl3)
3.2 M solution of EtMgBr in 2-Me-THF (0.18 mL, 0.57 mmol) was
dropwise added over 3 min at 0 ꢁC under argon atmosphere to a
suspension of Cu(OTf)2 (8.2 mg, 6 mol%) and ferrocene phosphanee
carbene ligand 4a or 4b (6 mol-%) in 2-Me-THF (3 mL) and the
mixture was stirred at 0 ꢁC for 1 h. Then the mixture was cooled to
d
207.60 (Cq), 155.46 (Cq), 136.40 (CPqh), 128.55 (CHPh), 128.17 (CHPh),
127.94 (CHPh), 67.57 (CH2), 53.77 (CH), 45.21 (CH2), 40.59 (CH2),
38.38 (CH2), 25.39 (CH2), 10.14 (CH3). NMR data agree with litera-
ture [51]. HPLC (Diacel Chiralcel AD-H, hexane/propan-2-ol, 90:10,
1 mL/min): tR (major) ¼ 5.6 min (R), tR (minor) ¼ 6.5 min (S),
e.r. ¼ 54:46.
ꢀ78 ꢁC and a solution of 5,6-dihydro-2H-pyran-2-one (7) (48.2
mL,
0.57 mmol) in 2-Me-THF (2 mL) was added over 30 min. The
resulting mixture was stirred at ꢀ78 ꢁC for additional 2.5 h. Finally,
benzaldehyde (38.4 mL, 0.38 mmol), dissolved in 2-Me-THF (2 mL),
4.2.8. 4-Ethyl-chroman-2-one (25)
was added, and the reaction mixture was slowly allowed to reach
room temperature overnight. The reaction was then quenched with
aq. NH4Cl (3 mL) and extracted with Et2O (3 ꢂ 3 mL). The combined
organic extracts were concentrated. The crude product was purified
1H NMR (300 MHz, CDCl3)
d
¼ 6.90e7.10 (m, 4H), 2.67e3.10 (m,
3H),1.63 (q, J ¼ 7 Hz, 2H), 0.98 (t, J ¼ 7 Hz, 3H). NMR data agree with
literature [52].

52
J. Csizmadiová et al. / Journal of Organometallic Chemistry 737 (2013) 47e52
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by column chromatography (silica gel, hexane/EtOAc, 7:3). Yield:
55 mg (63%), white solid.
4.4.1. 4-Ethyl-3-(hydroxy(phenyl)methyl)-tetrahydropyran-2-one (28)
1H NMR (300 MHz, CDCl3)
d 7.44e7.29 (m, 5H), 5.25 (dd,
J ¼ 6.8 Hz, J ¼ 3.7 Hz, 1H), 4.25e4.13 (m, 1H), 4.01 (ddd, J ¼ 2.4 Hz,
J ¼ 10.0 Hz, J ¼ 12.6 Hz, 1H), 3.76 (d, J ¼ 6.8 Hz, 1H), 2.72 (dd,
J ¼ 7.4 Hz, J ¼ 3.7 Hz, 1H), 1.98e1.75 (m, 2H), 1.16e1.01 (m, 2H), 0.75
(t, J ¼ 7.4 Hz, 3H). 13C NMR (75 MHz, CDCl3)
d 174.08 (s, Cq),141.07 (s,
Cq), 128.47 (s, CH), 127.90 (s, CH), 126.24 (s,CH), 74.04 (s, CH), 67.91
(s, CH2), 53.33 (s, CH), 33.26 (s, CH), 27.73 (s, CH2), 27.66 (s, CH2),
10.85 (s, CH3). NMR data agree with literature [44]. HPLC (Diacel
Chiralcel IA-H, hexane/propan-2-ol, 90:10, 0.8 mL/min, 218 nm): tR
(major) ¼ 10.6 min (R), tR (minor) ¼ 11.3 min (S), e.r. ¼ 97:3.
4.4.2. 3-(Hydroxy(phenyl)methyl)-4-methyltetrahydropyran-2-one
(29)
1H NMR (300 MHz, CDCl3)
d 7.45e7.26 (m, 5H), 5.27 (s, 1H),
4.36e4.24 (m, 1H), 4.06 (td, J ¼ 10.7 Hz, J ¼ 2.7 Hz, 1H), 3.87 (d,
J ¼ 6.0 Hz, 1H), 2.68 (dd, J ¼ 8.4, 3.7 Hz, 1H), 2.10e1.93 (m, 1H), 1.81
(dtd, J ¼ 14.2, 4.7, 2.8 Hz, 1H), 1.67e1.44 (m, 2H), 0.79 (d, J ¼ 6.6 Hz,
3H). 13C NMR (75 MHz, CDCl3)
d 173.86 (s, Cq), 141.07 (s, Cq), 128.50
(s, CH), 127.84 (s, CH), 126.26 (s, CH), 73.51 (s, CH), 68.00 (s, CH2),
55.03 (s, CH), 31.38 (s, CH2), 27.05 (s, CH), 21.06 (s, CH3). NMR data
agree with literature [44]. HPLC (Diacel Chiralcel IA-H, hexane/
propan-2-ol, 90:10, 0.8 mL/min, 218 nm): tR (major) ¼ 12.7 min (R),
tR (minor) ¼ 13.5 min (S), e.r. ¼ 88:12.
4.4.3. 3-(Hydroxy(phenyl)methyl)-4-isopropyl-tetrahydropyran-2-
one (30)
1H NMR (300 MHz, CDCl3)
d
7.40e7.29 (m, 5H), 5.15 (d, J ¼ 3.9 Hz,
1H), 4.24 (dt, J ¼ 10.9 Hz, J ¼ 3.8 Hz,1H), 3.84 (td, J ¼ 11.0 Hz, J ¼ 2.5 Hz,
1H), 2.90 (dd, J ¼ 7.7 Hz, J ¼ 4.0 Hz,1H), 1.92e1.78 (m, 1H), 1.76e1.66
(m,1H),1.64e1.45 (m, 5H),1.43e1.31 (m,1H), 0.80 (dd, J ¼ 9.0, 6.8 Hz,
4H).13C NMR (75 MHz, CDCl3)
d 174.20 (s, Cq),141.03 (s, Cq),128.52 (s,
CH),128.07(s, CH),126.40(s, CH), 74.74 (s, CH), 68.08(s, CH2), 51.59 (s,
CH), 37.88 (s, CH), 29.88 (s, CH), 23.08 (s, CH2), 20.59 (s, CH3),16.75 (s,
CH3). NMR data agree with literature [44]. HPLC (Diacel Chiralcel IA-
H, hexane/propan-2-ol, 90:10, 0.8 mL/min, 218 nm): tR
(major) ¼ 9.7 min (R), tR (minor) ¼ 10.9 min (S), e.r. ¼ 54:43.
Acknowledgments
Financial support from Slovak Grant Agency VEGA, grant no.
VEGA 1/0623/12 is gratefully acknowledged. This publication is the
result of the project implementation: 26240120025 supported by
the Research & Development Operational Programme funded by
the Research & Development Operational Programme funded by
the European Regional Development Fund. NMR measurements
were provided by The Slovak State Programme project no.
2003SP200280203.
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Appendix A. Supplementary data
ꢀ
ꢀ
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Supplementary data related to this article can be found at http://
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