Readily Accessible Unsymmetrical Unsaturated 2,6-Diisopropylphenyl N-Heterocyclic Carbene Ligands. Applications in Enantioselective Catalysis

Article abstract of DOI:10.1021/acs.joc.6b02888

A new multicomponent procedure was applied to the synthesis of (a)chiral bulky unsymmetrical unsaturated 2,6-diisopropylphenyl N-heterocyclic carbene (NHC) precursors with excellent selectivity (up to 95%) and good yields. This approach offers access to new chiral NHC ligands, which have found successful applications in both copper-catalyzed asymmetric allylic alkylation and copper-catalyzed asymmetric borylation.

Full text of DOI:10.1021/acs.joc.6b02888

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Featured Article
Readily Accessible Unsymmetrical Unsaturated 2,6-Diisopropylphenyl-N-
Heterocyclic Carbene Ligands. Applications in Enantioselective Catalysis.
Robert Tarrieu, Adrien Dumas, Jompol Thongpaen, Thomas Vives, Thierry
Roisnel, Vincent Dorcet, Christophe Crévisy, Olivier Baslé, and Marc Mauduit
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b02888 • Publication Date (Web): 18 Jan 2017
Downloaded from http://pubs.acs.org on January 19, 2017
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Readily Accessible Unsymmetrical Unsaturated 2,6-
Diisopropylphenyl-N-Heterocyclic Carbene Ligands.
Applications in Enantioselective Catalysis.
Robert Tarrieu, a Adrien Dumas, a Jompol Thongpaen, a Thomas Vives, a Thierry
Roisnel, b Vincent Dorcet, b Christophe Crévisy,*a Olivier Baslé,*a and Marc Mauduit*a
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a Ecole Nationale Supérieure de Chimie de Rennes, CNRS UMR 6226, Institut des
Sciences Chimiques de Rennes, 11 Allée de Beaulieu, 35708 Rennes Cedex 7
(France),
e-mail: christophe.crevisy@enscꢀrennes.fr
olivier.basle@ensc-rennes.fr
marc.mauduit@ensc-rennes.fr
b Université de Rennes 1, CNRS, UMR 6226, Institut des Sciences Chimiques de
Rennes, Centre de Diffractométrie X, Bat 10B, Campus de Beaulieu, 35042 Rennes
Cedex (France)
Graphical Abstract:
Cu-catalyzed AAA:
Glyoxal
PF6
Folmaldehyde
AcOH, ZnCl2, MgSO4
R
R1
R2
R
Et
NH2
+
H2N
N
N
R'
R'
ꢀ cyclic amines
ꢀ chiral amines
ꢀ aminoꢀalcohols/acids
up to >98% SN2'
and 95:5 er
up to >95% selectivity
up to 89% isolated yield
Chiral Cu/NHC complex
Abstract: A new multicomponent procedure was applied to the synthesis of (a)chiral
bulky unsymmetrical unsaturated 2,6ꢀdiisopropylphenylꢀNꢀheterocyclic carbene
(NHC) precursors with excellent selectivity (up to 95%) and good yields. This
approach offers access to new chiral NHCs ligands, which found successful
applications in both copperꢀcatalyzed asymmetric allylic alkylation and copperꢀ
catalyzed asymmetric borylation.
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Introduction
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During the past two decades, NꢀHeterocyclic Carbenes (NHCs) have broken
through in the field of coordination chemistry.1 These species have been used as
ligands to kinetically stabilize highly reactive, lowꢀvalent transition metals complexes
and enable high catalytic activity to be achieved.2 Among the large variety of NHCs
described in the literature, C2ꢀsymmetrical ligands bearing the sterically encumbered
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2,6ꢀdiisopropylphenyl
(Dipp)
nitrogen
substituent,
i.e.
bis(2,6ꢀ
diisopropylphenyl)imidazolꢀ2ꢀylidene (IPr) and bis(2,6ꢀdiisopropylphenyl) imidazolidinꢀ
2ꢀylidene (SiPr), have on numerous occasions demonstrated significant benefits in
multiple modern chemistry applications.3 On the other hand, unsymmetrical NHCs
with increased steric discrimination and distinctive electronic properties have
witnessed growing interest in the recent years.4 Indeed, transition metal bearing
Dippꢀbased unsymmetrical NHC have found considerable advantages in terms of
reactivity and selectivity towards challenging processes.5,6 A related type of carbene
ligand, the family of cyclic(alkyl)(amino)carbenes (CAACs) developed by Bertrand
and coworkers, has allowed important achievements by stabilizing unusual both
transition metal and main group element complexes.7 However, the strategies to
construct unsymmetrical NHC precursors require multiple steps syntheses that, due
to time consumption and cost, may limit their industrial applications.8 Recently, we
described an elegant and practical multicomponent strategy, providing access to
various unsymmetrical unsaturated (a)chiral Nꢀheterocyclic carbene (U2ꢀNHC)
ligands precursors with high selectivity and good yield.9 Indeed, by simply mixing an
arylamine, an alkylamine, formaldehyde and glyoxal in acetic acid for few minutes, a
wide range of imidazolium salts were obtained with high selectivity (up to 93%). The
corresponding U2ꢀNHC ligands were evaluated and evidenced strong electron donor
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ability, high steric discrimination, and modular steric demand. This methodology was
also successfully applied for the construction of chiral bidentate hydroxyalkylꢀ and
carboxyalkylꢀNHC ligands, which demonstrated excellent transfer of the
stereoinduction from the chiral center to the metal.10 Despite the efficiency and
flexibility of this multicomponent procedure, the introduction of highly hindered pattern
such as the Dipp fragment appeared as a major limitation, affording the desired bulky
U2ꢀNHC precursors with poor yields and selectivities.9,10 Herein, we disclose a novel
multicomponent procedure leading to a wide range of (a)chiral unsymmetrical
unsaturated 1ꢀ(2,6ꢀdiisopropylphenyl)ꢀ3ꢀalkylꢀimidazolium salts with high selectivities
(up to 95%) and good yields (figure 1). Moreover, evaluation of this ligand family in
copper catalysis demonstrated utility in asymmetric CꢀB and CꢀC bond formation.
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Multicomponent synthesis:
U2-NHCs
Multi-step synthesis:
C2-symmetrical
X
R
H2N
NH2
N
N
R'
+
formaldehyde /glyoxal / AcOH
ZnCl2/MgSO4
IPr and SIPr
Unsymmetrical
X
X
N
N
n
N
N
X
or
R
N
N
X
OH
R
N
N
R'
N
R = Me, iPr, iBu
Cl
CAAC
R' = Aryl, CH2OH, CO2H
This work
Figure 1. Examples of Dippꢀbased NHC ligands (left) and new synthetic route to
Dippꢀbased U2ꢀNHC ligands (right)
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Results and Discussion
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With the objective to reach the exclusive formation of the unsymmetrical 1ꢀ
(2,6ꢀdiisopropylphenyl)ꢀ3ꢀcycloalkyꢀimidazolium salts 3, we decided to reꢀinvestigate
our initial multicomponent procedure by probing various reaction conditions (Table 1).
An important point to be taken into consideration when using 2,6ꢀdiisopropylaniline
(1) in such approach, is the inherent low reactivity of this sterically congested amine
under typical operational conditions for the synthesis of imidazolium salts.11 First,
using cyclododecanamine as the second partner of the reaction, the modest
selectivity and poor yield observed at 40°C were improved with a slight increase of
the temperature to 60°C (Table 1, entries 1ꢀ2). Importantly, a major improvement in
both selectivity and yield could be obtained after addition of a stoichiometric amount
of hydrochloric acid (Table 1, entry 4).12 During the screening of Lewis acids, the
addition of zinc chloride (1 equiv.) in diethylether appeared highly beneficial affording
the unsymmetrical NHC precursors with very high selectivity (>95%) and excellent
NMR yield (Table 1, entry 7).13 Interestingly, without affecting selectivity, the addition
of magnesium sulfate (MgSO4) could improve the NMR yield to >95% and allowed
isolation of the 1ꢀ(2,6ꢀdiisopropylphenyl)ꢀ3ꢀcyclodedecylꢀimidazolium salt 3a in 76%
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ꢀ
ꢀ
yield (table 1, entry 9). Finally, replacement of the BF4 anion by PF6 facilitated the
purification procedure and afforded the corresponding imidazolium.PF6 salts with
high 89% isolated yield (table 1, entry 10).
Table 1. Optimization of the conditions for the multicomponent process.
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Entry
Additives
T (°C) Selectivity (%)a
Yield (%)b
1
2
3
4
5
6
7
NAc
40
60
60
60
60
60
60
57
69
35
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89
73
83
88
NAc
HCl (1 mol%)d
HCl (1 equiv.)d
MgCl2(s) (1 equiv.)
ZnCl2(s) (1 equiv.)
ZnCl2 (1 equiv.)d
73
89
88
93
>95
8
9
ZnCl2 (1.2 equiv.)d
60
60
>95
>95
94
MgSO4 (2 equiv.), ZnCl2 (1.2
equiv.)d
>95 (76)
MgSO4 (2 equiv.), ZnCl2 (1.2
equiv.)d
10e
60
>95
>95 (89)
11
12
MgSO4 (2 equiv.)
60
60
65
45
46
Et2O
30
aDetermined by H NMR using tetrachloroethane as an internal standard. NMR
yields using tetrachloroethane as an internal standard; Isolated yields presented in
parentheses. cNot applicable.d1M in Et2O . eKPF6 was used instead of KBF4.
1
b
Under the optimized reaction conditions, we extended the scope of the
reaction using first a variety of cycloalkylamines (Scheme 1). Similarly to the results
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obtained with cyclododecanamine, the desired U2ꢀNHC precursors bearing the
cyclooctylꢀ, cyclopentylꢀ fragments were obtained with excellent selectivity and good
isolated yields. Interestingly, the polycyclic adamantylamine could be efficiently
employed in this strategy and afforded perfect selectivity in the preparation of 3e; the
unsaturated analogue of the most effective NHC ligand precursor employed in
rutheniumꢀcatalyzed Zꢀselective metathesis.5 Moreover, while cyclobutylamine
reacted quite smoothly (86% selectivity and 66% isolated yield), a noticeable
decrease of selectivity was observed with cyclopropylamine leading to a modest 42%
isolated yield of the corresponding imidazolium salt 3f. Importantly, this approach
was also applicable to the use of alpha substituted chiral amines such as (S)ꢀαꢀ
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methylbenzylamine,
(R)ꢀ1ꢀ(1ꢀnaphthyl)ethylamine,
(1R,
2R,
3R,
5S)ꢀ
isopinocampheylamine and (R)ꢀindanamine allowing for a simple and efficient access
to bulky chiral NHC precursors with strong propensity for new applications in
selective catalysis (figure 2).14,5g In effort to further extend the synthetic utility of this
multicomponent procedure, the synthesis of chiral bidentate NHC ligand precursors
was investigated. Pleasantly, the bulky chiral imidazolium salts 3k and 3l derived
from (L)ꢀleucinol and (L)ꢀvalinol were formed with excellent selectivity and isolated in
reasonable yields. Under the same conditions, modest selectivity and isolated yield
could be obtained with (L)ꢀleucine.
Scheme 1. Scope of the multicomponent procedure.
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O
O
H
O
H
R
H2N
NH2
H
H
R'
7
8
9
AcOH, ZnCl2, MgSO4,
60 °C, 25 min,
then HCl 3M and KX
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X
R
N
N
R'
(Selectivitya / Yieldb)
PF6
N
N
N
N
n
PF6
3d (86% / 66%)
n = 7 3a (> 95% / 89%)
n = 3 3b
(91% / 70%)
n = 0 3c (> 95% / 78%)
PF6
N
N
N
N
BF4
3e-BF4 (94% / 75%)c
3f (70% / 42%)
PF6
PF6
N
N
N
N
3h (83% / 65%)
PF6
3g (94% / 71%)
PF6
N
N
N
N
3i (93% / 65%)
3j (91% / 51%)
PF6
R
PF6
N
N
N
N
OH
O
HO
3k: R = iꢀBu (91% / 65%)
3l: R = iꢀPr (93% / 46%)
3m (66% / 37%)
a Determined by 1H NMR analysis. b Isolated Yields. c The purification
procedure is facilitated with BF4ꢀ instead of PF6 .
ꢀ
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Figure 2. Solidꢀstate structure of a selection of imidazolium salts from single crystal
Xꢀray diffraction. Displacement ellipsoids are drawn at 50% probability. Most
hydrogen atoms and PF6 anions have been omitted for clarity (N in blue, C in grey, P
in orange, F in yellow, H in white.
In order to get a better understanding of the reaction mechanism and to
provide insight into the factors governing the selectivity of the multicomponent
procedure, we decided to adopt a twoꢀstep approach. Importantly, preliminary
experiments demonstrated that the procedure involving the combination of DippNH2
1 and adamantylamine 2a could be greatly simplified, since ZnCl2 and MgSO4
additives had no significant impact on the outcomes of this specific reaction.15
Therefore, this simplified protocol was selected as a model for the following
mechanistic study. First, a stoichiometric amount of DippNH2 1, AdNH2 2a and
aqueous glyoxal were reacted in presence of an excess of acetic acid (9 equiv.). The
1H NMR analysis of the resulting crude mixture (< 5 min reaction) showed the
preferential formation of the diarylꢀdiimine 4 (>95%) without unequivocal identification
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of diimine 5 and no detectable amount of dialkylꢀdiimine 6 (Scheme 2, A).16 The
subsequent addition of 1 equivalent of aqueous formaldehyde afforded the desired
unsymmetrical imidazolium salt 3e-OAc with high >95% selectivity along with <5% of
the symmetrical dialkyl imidazolium salt 7e-OAc and no detectable amount of the IPr
imidazolium salt precursors (scheme 2, B). Besides, it was observed that the
sterically congested diarylꢀdiimine 4 was poorly reactive towards cyclisation under
our reactions conditions, whereas the dialkylꢀdiimine 6 was able to afford easily the
corresponding cyclized imidazolium salt 7e-OAc.16 Nevertheless, when the
cyclisation of the dialkylꢀdiimine 6 was performed in the presence of DippNH2 1 (2
equiv.), the major product was the unsymmetrical salt 3e-OAc (3e-OAc/7e-OAc ratio
= 94:6).16 Consequently, the high selectivity in favor of the unsymmetrical salt 3e-
OAc may be explained by the fact that the cyclizations of the symmetrical diimines
are slower than i) the equilibration reactions between the three diimines17 and ii) than
the cyclisation of the unsymmetrical diimine 5.18
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Scheme 2. Mechanistic investigation of unsymmetrical salts synthesis. (A) Ratio in
diimines after condensation with aqueous glyoxal and excess acetic acid (< 5 min
reaction). (B) Selectivity of the cyclization procedure in presence of aqueous
formaldehyde. a Not identified b not detected
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The asymmetric conjugate addition of nucleophiles to electron deficient
alkenes represents one of the most powerful methods to form CꢀC and Cꢀ
heteroelement bond.19 In the recent years, enantioselective conjugate addition of
diboron reagents to α,βꢀunsaturated carbonyl compounds catalyzed by Cuꢀbased
NHC/complexes has attracted considerable interest.20 With our new series of
unsymmetrical chiral imidazolium salts in hand, we decided to evaluate their potential
as chiral ligands in copperꢀcatalyzed borate addition to ethyl cinnamate (8). The
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chiral NHC precursor 3h displaying demanding steric environment was initially
selected and the in situ generated Cu/NHC complex afforded the desired product 9 in
good 67% isolated yield and 87:13 enantiomeric ratio (scheme 3). On the other hand,
the use of the C2 symmetrical ligand precursor analogue 7h allowed for poor
enantiocontrol (67.5:32.5 er), which demonstrates unambiguously the advantage
provided by the sterically congested unsymmetrical chiral ligand. Moreover, it should
be noted that the isolated and fully characterized, including Xꢀray diffraction analysis,
Cu/NHC complex 3hꢀCuCl catalyzed efficiently the transformation to form product 9
with 82:18 enantiomeric ratio.21
3
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Scheme 3. Copper/NHCꢀCatalyzed asymmetric borylation.a
1)
Cu(OTf)2 (4 mol%)
NHC (12 mol%)
NaOtBu (20 mol%)
O
OH
O
THF, MeOH, −50 °C
+
B2Pin2
Ph
OEt
Ph
OEt
2) NaBO3 .4H2O
9
8
3h
with
:
7h
with :
PF6
N
PF6
N
N
N
67 % yield, 87:13 er
60 % yield, 67.5:32.5 er
3h
with .CuCl:
N
N
Cu
Cl
76 % yield, 82:18 er
aEnantiomeric ratios were obtained from chiral HPLC analysis.
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To further demonstrate the potential of newly developed ligand family, the
chiral bidentate hydroxyalkyl ligand precursor 3k was evaluated in copperꢀcatalyzed
asymmetric allylic alkylation to form allꢀcarbon quaternary centers.6c,10 Interestingly
the catalytic system prepared in situ by deprotonation of the imidazolium salt 3k with
nꢀbutyllithium in presence of copper(I) triflate promoted efficiently the reaction
between diethylzinc and allylphosphates 10 to form the desired quaternary carbon
centers with excellent regioꢀ (>96% SN2’) and high enantioꢀselectivity (up to 95:5 er)
(Scheme 4).
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Scheme 4. Copperꢀcatalyzed AAA with allylphosphates.a,b
a Conversions and SN2’ ratios were determined by 1H NMR analysis of the crude
mixture. bEnantiomeric ratios were obtained from GC and HPLC analysis of the
substitution product.
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In conclusion,
a
multicomponent synthesis of sterically congested
4
5
6
7
8
unsymmetrical unsaturated imidazolium salts has been developed. This practical, low
cost and efficient methodology allows for the preparation in high yields and high
selectivities of a large variety of NHC ligand precursors bearing the sterically
hindered 2,6ꢀdiisopropylphenyl moieties. The new chiral monodentate ligands have
found application in copper catalyzed asymmetric boronate conjugate addition to
unsaturated esters. Significantly, with unsymmetrical chiral monodentate ligand, the
chirality transfer is enhanced by the presence of the 2,6ꢀdiisopropylphenyl fragment.
Moreover, the multicomponent procedure was also successfully applied for the
construction of chiral bidentate ligands, which demonstrated excellent control in
copperꢀcatalyzed allylic substitution with allyl phosphates to form allꢀcarbon
quaternary centers with high regioꢀ and enantioselectivities. The use of this ligand
family to construct new transitionꢀmetal catalysts along with their applications in
asymmetric transformations is currently under intensive investigation in our laboratory
and will be reported in due course.
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Experimental section
General Experimental Procedures. All commercial chemicals were used as
received unless otherwise noted. 1,4ꢀBis(2,6ꢀdiisopropylphenyl)ꢀ1,4ꢀdiazaꢀ1,3ꢀ
butadiene11a 4 and N,N'ꢀBis(1ꢀadamantyl)ethanediimine22 6 were obtained following
already described procedures.
Reactions were monitored by thinꢀlayer
chromatography (TLC) carried out on silica gel plates (60F254) using UV light as
visualizing agent, KMnO4/K2CO3/NaOH in water for staining. Column
chromatography was performed with Silica Gel (spherical, particle size 40 ꢀm,
neutral). The eluents employed are reported as volume (volume percentages).
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Melting points were measured on a standard melting point apparatus in open
capillary tubes and are uncorrected. Optical rotations were recorded on a polarimeter
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and are uncorrected. H (400 MHz), 13C (101 MHz), 19F (376 MHz), 31P (162 MHz)
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and 11B (128 MHz) NMR spectra were recorded on a NMR spectrometer with
complete proton decoupling for nucleus other than 1H. Chemical shifts are reported in
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1
parts per million with the solvent resonance as the internal standard (CDCl3, H: δ
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7.26 ppm, 13C: δ 77.16 ppm; CD3OD, H: δ 3.31 ppm, 13C: δ 49.00 ppm); 19F
chemical shifts are reported with CFCl3 (δ = 0.0 ppm) as the internal standard; 31P
chemical shifts are reported with H3PO4 (δ = 0.0 ppm) as the internal standard; 11B
chemical shifts are reported with BF3.Et2O (δ = 0.0 ppm) as the internal standard.
Coupling constants (J) are reported in Hertz (Hz). Multiplicities are reported using
following abbrevations: s = singlet, br. s = broad singlet, d = doublet, dd = double
doublet, ddd = double double doublet, dt = double triplet, t = triplet, q = quartet, quint
= quintet, sept = septet, m = multiplet. Highꢀresolution mass spectroscopy (HMRS)
were recorded on a QꢀTOF .
General Procedure for the Multicomponent Synthesis of Unsymmetrical
Imidazolium Salts 3. The reaction was performed in open vessel under air
atmosphere. In a roundꢀbottomed flask were placed 2,6ꢀdiisopropylaniline (1 mmol,
1.0 equiv.), alkylamine (1 mmol, 1.0 equiv.) and acetic acid (4.5 mmol, 4.5 equiv.),
then the mixture was heated at 60 °C for 5 minutes and MgSO4 (2 mmol, 2 equiv.)
was added (mixture A). In another roundꢀbottomed flask were placed glyoxal (1
mmol, 1.0 equiv., 40 % weight in aqueous solution), formaldehyde (1 mmol, 1.0
equiv., 37 % weight in aqueous solution) and acetic acid (4.5 mmol, 4.5 equiv.), then
the mixture was heated at 60 °C for 5 minutes and ZnCl2 (1.2 mmol, 1.2 equiv., 1M in
Et2O) was added (mixture B). At 60 °C mixture B was added to mixture A and the
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resulting mixture was stirred at 60 °C for 25 minutes then cooled down to room
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temperature. An aliquot of the crude reaction mixture was taken and a H NMR was
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recorded to determine the selectivity of the reaction, which was calculated by
integration of characteristic signals of the different compounds. Dichloromethane (25
mL) and 3M aqueous solution of HCl (50 mL) were added and the resulting mixture
was stirred at room temperature for 1 hour. Then the organic layer was separated.
Water (50 mL) and potassium hexafluorophosphate or potassium tetrafluoroborate
(1.0 mmol, 1.0 equiv.) was added and the mixture was stirred at room temperature
for 1 hour. The organic layer was separated, dried over magnesium sulfate, filtered
and the solvents were evaporated under reduced pressure. The desired imidazolium
salt was isolated either by flash chromatography on silica gel or recrystallization.
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General Procedure for the Multicomponent Synthesis of Unsymmetrical
Imidazolium Salts 7. In a roundꢀbottomed flask were placed alkylamine (0.53 mmol,
1 equiv.) and acetic acid (1.20 mmol, 2.25 equiv.) then the mixture was heated at
40 °C for 5 min (mixture A). In another roundꢀbottomed flask were placed glyoxal
(0.26 mmol, 0.5 equiv., 40 % wt in aqueous solution), formaldehyde (0.026 mmol, 0.5
equiv., 37 % wt in aqueous solution) and acetic acid acid (1.20 mmol, 2.25 equiv.)
then the mixture was heated at 40 °C for 5 min (mixture B). At 40 °C mixture B was
added to mixture A and the resulting mixture was stirred at 40 °C for 25 min then
cooled down to room temperature. Dichloromethane (25 mL) was added and the
organic layer was washed with brine (3 x 10 mL). The organic layer was separated,
then water (5 mL) and potassium hexafluorophosphate (48 mg, 0.26 mmol) were
added and the mixture was stirred at room temperature for 1 hour. The organic layer
was separated, dried over magnesium sulfate, filtered and the solvents were
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evaporated under reduced pressure. The desired imidazolium salt 7 was isolated
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without further purification.
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General Procedure for the Synthesis of Copper Complexes 3.CuCl.
Hexafluorophosphate salt 3 (0.24 mmol, 1 equiv.) was loaded on an anion exchange
resin Dowex® 1x2 chloride form (2.4 ml of resin for 0.24 mmol of
hexafluorophosphate salt) with milliꢀQ water / acetone (1/1) as an eluent. After
removal of solvents under reduced pressure, the residue was dissolved in
dichloromethane, dried over MgSO4, filtered and concentrated under reduced
pressure to give the corresponding chloride salt. In a dry Schlenk, under argon
atmosphere, were placed Ag2O (0.24 mmol, 1 equiv.), chloride imidazolium salt (0.24
mmol, 1 equiv.), dichloromethane (25 mL) and 4Å molecular sieves. The mixture was
stirred at room temperature overnight in darkness (alumina foil) then CuCl (0.24
mmol, 1 equiv.) was added and the resulting mixture was stirred at room temperature
for 4 h in darkness. The mixture was then filtered on a celite bed with
dichloromethane and the solvent was removed under reduced pressure. The crude
solid was precipitated in dichloromethane/pentane (1/5) to afford the desired copper
complex 3.CuCl.
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General Procedure for Copper-Catalyzed Asymmetric Borylation. Starting
from the imidazolium salts (3h and 7h): In the glove box, Cu(OTf)2 (4 mol%), ligand
(12 mol%), NaOtBu (20 mol%) and THF (1 mL) were added in a flameꢀdried
microwave flask. The resulting mixture was stirred at room temperature for 10
minutes and bis(pinacolato)diboron (0.55 mmol, 1.1 equiv.) was added. The mixture
was stirred for an extra 10 minutes and the solution was cooled down to ꢀ50 °C.
Then, a solution containing MeOH (1.0 mmol, 2 equiv.), ethyl cinnamate (0.5 mmol, 1
equiv.) and THF (1 mL) was slowly added and the mixture was stirred 3 hours at ꢀ
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50 °C. Then, the oxidation step was carried out with the successive addition of
NaBO3.4H2O (2.5 mmol, 5 equiv.) and water (2 mL), after which the mixture was
stirred at room temperature for 3 hours. Water (10 mL) was added and the aqueous
layer was extracted with ethyl acetate (3x20 mL). The organics layers were
combined, washed with brine (20 mL), dried over MgSO4, filtered and concentrated
under reduced pressure. The crude product was purified by silica gel
chromatography (pentane/diethyl ether, 8/2) to give the corresponding product 9 as a
colorless oil.
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Starting from the isolated copper complex (3h.CuCl): In the glove box, 3h.CuCl (4
mol%), Cs2CO3 (8 mol%), bis(pinacolato)diboron (0.55 mmol, 1.1 equiv.) and THF (1
mL) were added in a microwave flask. The resulting mixture was stirred at room
temperature for 10 minutes and the solution was cooled down to ꢀ50 °C. Then, a
solution containing MeOH (1.0 mmol, 2 equiv.), ethyl cinnamate (0.5 mmol, 1 equiv.)
and THF (1 mL) was slowly added at ꢀ50 °C and the mixture was stirred 3 hours at ꢀ
50 °C. Then, the oxidation step was carried out with the successive addition of
NaBO3.4H2O (1 mmol, 5 equiv.) and water (1 mL), after which the mixture was stirred
at room temperature for 3 hours. Water (5 mL) was added and the aqueous layer
was extracted with ethyl acetate (3x10 mL). The organics layers were combined,
washed with brine (10 mL), dried over MgSO4, filtered and concentrated under
reduced pressure. The crude product was purified by silica gel chromatography
(pentane /diethyl ether: 8/2) to give the corresponding product 9 as a colorless oil.
General Procedure for Copper-Catalyzed Asymmetric Allylic Alkylation.
A flameꢀdried Schlenk tube, under an argon atmosphere, was charged with
[Cu(OTf)2].C6H6 (0.5 mol%) and 3k (1 mol%). Freshly distillated ethyl acetate (0.25
mL) was then added and the reaction mixture was stirred 10 minutes at room
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temperature followed by the addition of nꢀBuLi (1.6M in hexanes, 2.5 mol%). The
reaction was stirred 10 minutes at room temperature and Et2Zn (1.5 mmol, 3 equiv.)
was added. After cooling the reaction vessel to 0 °C, the phosphate (0.5 mmol, 1
equiv.) was added. As soon as the addition of the substrate was completed, the ice
bath was removed. The reaction mixture was stirred at room temperature until total
consumption of the phosphate. Upon completion of the reaction, a 1M aqueous
solution of HCl was added and the compound was extracted with diethyl ether. The
combined organic layers were then washed with a saturated aqueous solution of
NaHCO3, brine and dried over MgSO4. The solvents were carefully removed under
vacuum. The crude product was purified by silica gel chromatography (pentane) to
isolate the corresponding product 11 as a colorless oil.
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Characterization Data of Isolated Compounds. 3-cyclododecyl-1-(2,6-
diisopropylphenyl)imidazolium hexafluorophosphate (3a): Selectivity 3aꢀOAc/bisC12
ꢀ
OAc/IPrꢀOAc = >95/traces/traces. Purification over silica gel (dichloromethane then
dichloromethane/ethyl acetate: 9/1). Pale brown solid (481 mg, 89%). m. p.: 173 °C.
1H NMR (400 MHz, Chloroformꢀd) δ 8.61 (dd, J = 1.7, 1.7 Hz, 1H), 7.66 (dd, J = 1.8,
1.8 Hz, 1H), 7.49 (t, J = 7.8 Hz, 1H), 7.33–7.17 (m, 3H), 4.73ꢀ4.67 (m, 1H), 2.21–2.06
(m, 4H), 1.95–1.70 (m, 2H), 1.61–1.18 (m, 18H), 1.13 (d, J = 7.6 Hz, 6H), 1,11 (d, J =
7.6 Hz, 6H). 13C NMR (101 MHz, Chloroformꢀd) δ 145.4, 135.7, 132.0, 130.15, 125.4,
124.7, 121.7, 59.7, 30.2, 28.9, 24.3, 24.0, 23.8, 23.5, 23.3, 23.3, 21.3. 19F NMR (376
31
MHz, Chloroformꢀd) δ ꢀ72.16 (d, J = 713 Hz). P NMR (162 MHz, Chloroformꢀd) δ ꢀ
+
144.32 (sept, J = 713 Hz). HRMS (ESI) calcd. for C27H43N2 (MꢀPF6): m/z 395.34207,
found: 395.3422 (0 ppm). Anal. Calcd. for C27H43F6N2P: C, 59.99%; H, 8.02%; N,
5.18%; found: C, 59.85%; H, 7.77%; N, 4.99%
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3-cyclooctyl-1-(2,6-diisopropylphenyl)imidazolium
hexafluorophosphate
(3b):
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Selectivity 3bꢀOAc/bisC8ꢀOAc/IPrꢀOAc = 91/9/0. Purification over silica gel
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(dichloromethane) followed by recrystallization in dichloromethane/cyclohexane.
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White solid (339 mg, 70%). m. p.: 196 °C. H NMR (400 MHz, Chloroformꢀd) δ 8.63
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(dd, J = 1.7, 1.7 Hz, 1H), 7.67 (dd, J = 1.9, 1.9 Hz, 1H), 7.52 (t, J = 7.8 Hz, 1H), 7.30
(s, 1H), 7.28 (s, 1H), 7.25 (dd, J = 1.5, 1.5 Hz, 1H), 4.82 (quint., J = 7.3 Hz, 1H),
2.28–2.01 (m, 6H), 1.91–1.52 (m, 10H), 1.17 (d, J = 6.8 Hz, 6H), 1.14 (d, J = 6.8 Hz,
6H). 13C NMR (101 MHz, Chloroformꢀd) δ 145.5, 135.3, 132.0, 130.2, 125.3, 124.7,
121.3, 62.4, 33.9, 28.9, 26.4, 25.4, 24.4, 24.0, 23.8. 19F NMR (376 MHz, Chloroformꢀ
d) δ ꢀ72.20 (d, J = 713 Hz). 31P NMR (162 MHz, Chloroformꢀd) δ ꢀ144.29 (sept, J =
+
713 Hz). HRMS (ESI) calcd. for C23H35N2 (MꢀPF6): m/z 339.27947, found: 339.2798
(1 ppm). Anal. Calcd. for C23H35F6N2P: C, 57.02%; H, 7.28%; N, 5.78%; found: C,
57.05%; H, 6.87%; N, 5.68%
3-cyclopentyl-1-(2,6-diisopropylphenyl)imidazolium
hexafluorophosphate
(3c):
Selectivity 3cꢀOAc/bisC5ꢀOAc/IPrꢀOAc = 96/4/0. Purification over silica gel
1
(dichloromethane). Pale brown solid (345 mg, 78%). m. p.: 172 °C. H NMR (400
MHz, Chloroformꢀd) δ 8.55 (dd, J = 1.7, 1.7 Hz, 1H), 7.68 (dd, J = 1.9, 1.9 Hz, 1H),
7.51 (t, J = 7.8 Hz, 1H), 7.32–7.24 (m, 3H), 4.98 (quint, J = 7.1 Hz, 1H), 2.55–2.32
(m, 2H), 2.21 (sept, J = 6.7 Hz, 2H), 2.09–1.67 (m, 6H), 1.15 (d, J = 6.8 Hz, 6H), 1.12
(d, J = 6.8 Hz, 6H). 13C NMR (101 MHz, Chloroformꢀd) δ 145.4, 135.5, 132.0, 130.1,
125.5, 124.7, 121.5, 62.1, 33.5, 28.8, 24.3, 23.9, 23.8. 19F NMR (376 MHz,
Chloroformꢀd) δ ꢀ72.44 (d, J = 713 Hz). 31P NMR (162 MHz, Chloroformꢀd) δ ꢀ144.37
+
(sept, J = 713 Hz). HRMS (ESI) calcd. for C20H29N2 (MꢀPF6): m/z 297.23307, found:
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297.2331 (0 ppm). Anal. Calcd. for C20H29F6N2P: C, 54.30%; H, 6.61%; N, 6.33%;
found: C, 54.72%; H, 6.77%; N, 6.39%
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3-cyclobutyl-1-(2,6-diisopropylphenyl)imidazolium
hexafluorophosphate
(3d):
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Selectivity 3dꢀOAc/bisC4ꢀOAc/IPrꢀOAc = 86/14/0. Purification over silica gel
(dichloromethane/pentane: 8/2 then dichloromethane). Pale brown solid (283 mg,
66%). Singleꢀcrystals of 3d were obtained by slow evaporation of a saturated
solution in dichoromethane/pentane. m. p.: 161 °C. 1H NMR (400 MHz, Chloroformꢀd)
δ 8.55 (dd, J = 1.7, 1.7 Hz, 1H), 7.78 (dd, J = 1.8, 1.8 Hz, 1H), 7.52 (t, J = 7.8 Hz,
1H), 7.30 (s, 1H), 7.28 (s, 1H), 7.27–7.24 (m, 1H), 5.13 (quint, J = 8.5 Hz, 1H), 2.74 –
2.62 (m, 2H), 2.58–2.44 (m, 2H), 2.22 (sept, J = 6.8 Hz, 2H), 2.06–1.88 (m, 2H), 1.16
(d, J = 6.8 Hz, 6H), 1.12 (d, J = 6.8 Hz, 6H). 13C NMR (101 MHz, Chloroformꢀd) δ
145.5, 135.1, 132.0, 130.1, 125.4, 124.7, 121.4, 54.0, 30.7, 28.7, 24.4, 23.9, 14.6. 19F
NMR (376 MHz, Chloroformꢀd) δ ꢀ72.47 (d, J = 713 Hz). 31P NMR (162 MHz,
+
Chloroformꢀd) δ ꢀ144.35 (sept, J = 713 Hz). HRMS (ESI) calcd. for C19H27N2 (Mꢀ
PF6): m/z 283.21687, found: 283.2169 (0 ppm). Anal. Calcd. for C19H27F6N2P: C,
53.27%; H, 6.35%; N, 6.54%; found: C, 53.75%; H, 6.38%; N, 6.29%
3-adamantyl-1-(2,6-diisopropylphenyl)imidazolium
tetrafluoroborate
(3e-BF4):
Selectivity 3eꢀOAc/7eꢀOAc/IPrꢀOAc 94/6/0. Purification over silica gel
=
(dichloromethane then dichloromethane/ethyl acetate: 9/1) following by
recrystallization in ethyl acetate. White solid (1.9 g, 75% from 5.6 mmol of
1
corresponding alkylamine). m. p.: 218 °C. H NMR (400 MHz, Chloroformꢀd) δ 8.83
(dd, J = 1.7, 1.7 Hz, 1H), 7.94 (dd, J = 1.9, 1.9 Hz, 1H), 7.51 (t, J = 7.8 Hz, 1H), 7.31
(dd, J = 1.9, 1.9 Hz, 1H), 7.29 (s, 1H), 7.27 (s, 1H), 2.36–2.25 (m, 9H), 2.20 (sept, J =
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6.8 Hz, 2H), 1.87–1.74 (m, 6H), 1.18 (d, J = 6.8 Hz, 6H), 1.14 (d, J = 6.8 Hz, 6H). 13C
NMR (101 MHz, Chloroformꢀd) δ 145.4, 134.5, 131.8, 130.54, 125.1, 124.6, 120.4,
61.6, 42.6, 35.2, 29.6, 28.8, 24.3, 24.0. 19F NMR (376 MHz, Chloroformꢀd) δ ꢀ151.57.
9
+
11B NMR (128 MHz, Chloroformꢀd) δ ꢀ1.02. HRMS (ESI) calcd. for C25H35N2 (Mꢀ
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BF4): m/z 363.28002, found: 363.2799 (0 ppm)
3-cyclopropyl-1-(2,6-diisopropylphenyl)imidazolium
hexafluorophosphate
(3f):
Selectivity 3fꢀOAc/bisC3ꢀOAc/IPrꢀOAc = 70/26/4. Purification over silica gel
(dichloromethane/pentane: 8/2 then dichloromethane). Pale brown solid (174 mg,
1
42%). m. p.: 69 °C. H NMR (400 MHz, Chloroformꢀd) δ 8.62 (dd, J = 1.6, 1.6 Hz,
1H), 7.63 (dd, J = 1.9, 1.9 Hz, 1H), 7.53 (t, J = 7.9 Hz, 1H), 7.31 (s, 1H), 7.29 (s, 1H),
7.21 (dd, J = 1.9, 1.8 Hz, 1H), 4.02–3.94 (m, 1H), 2.23 (sept, J = 6.8 Hz, 2H), 1.33–
1.22 (m, 4H), 1.17 (d, J = 6.8 Hz, 6H), 1.13 (d, J = 6.8 Hz, 6H). 13C NMR (101 MHz,
Chloroformꢀd) δ 145.5, 137.2, 132.1, 130.0, 125.0, 124.7, 123.7, 32.1, 28.7, 24.4,
23.9, 7.4. 19F NMR (376 MHz, Chloroformꢀd) δ ꢀ72.58 (d, J = 714 Hz). 31P NMR (162
+
MHz, Chloroformꢀd) δ ꢀ144.42 (sept, J = 713 Hz). HRMS (ESI) calcd. for C18H25N2
(MꢀPF6): m/z 269.20177, found: 269.2018 (0 ppm)
(S)-1-(2,6-diisopropylphenyl)-3-(1-phenylethyl)imidazolium hexafluorophosphate (3g):
Selectivity 3gꢀOAc/bisPhEtꢀOAc/IPrꢀOAc = 94/6/0. Purification over silica gel
(dichloromethane). Pale brown solid (341 mg, 71%). m. p.: 178 °C. [ꢀ]ꢂꢁꢃ : ꢀ25.4 (c =
1
1, chloroform). H NMR (400 MHz, Chloroformꢀd) δ 8.53 (dd, J = 1.7, 1.7 Hz, 1H),
7.66 (dd, J1 = 1.9, 1.9 Hz, 1H), 7.51 (t, J = 7.9 Hz, 1H), 7.46–7.35 (m, 5H), 7.32 –
7.23 (m, 3H), 5.98 (q, J = 7.0 Hz, 1H), 2.26 (sept, J = 6.8 Hz, 1H), 2.11 (sept, J = 6.8
Hz, 1H), 2.02 (d, J = 7.0 Hz, 3H), 1.15 (d, J = 6.8 Hz, 3H), 1.13 (d, J = 6.8 Hz, 3H),
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1.11 (d, J = 6.8 Hz, 3H), 1.06 (d, J = 6.8 Hz, 3H). 13C NMR (101 MHz, Chloroformꢀd)
δ 145.5, 145.3, 137.9, 132.1, 130.1, 129.8, 126.9, 125.2, 124.8, 124.7, 121.8, 60.6,
28.8, 28.8, 24.4, 24.1, 23.9, 20.7. 19F NMR (376 MHz, Chloroformꢀd) δ ꢀ72.28 (d, J =
713 Hz). 31P NMR (162 MHz, Chloroformꢀd) δ ꢀ144.27 (sept, J = 713 Hz). HRMS
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(ESI) calcd. for C23H29N2 (MꢀPF6): m/z 333.23252, found: 333.2330 (1 ppm)
(R)-1-(2,6-diisopropylphenyl)-3-((1-(naphthalen-1-yl)ethyl)imidazolium
hexafluorophosphate (3h): Selectivity 3hꢀOAc/7hꢀOAc/IPrꢀOAc = 83/17/0. Purification
over silica gel (diethyl ether/dichloromethane: 9/1). Pale brown solid (346 mg, 65%).
Singleꢀcrystals of 3h were obtained by slow evaporation of a saturated solution in
1
dichloromethane/pentane. m. p.: 214 °C. [ꢀ]ꢂꢁꢃ : ꢀ 36.2 (c = 1, chloroform). H NMR
(400 MHz, Chloroformꢀd) δ 8.43 (dd, J = 1.7, 1.7 Hz, 1H), 7.94 – 7.87 (m, 3H), 7.74–
7.71 (m, 1H), 7.63 (dd, J = 1.9, 1.9 Hz, 1H), 7.58–7.49 (m, 3H), 7.45 (t, J = 7.8 Hz,
1H), 7.23–7.19 (m, 3H), 6.71 (q, J = 6.8 Hz, 1H), 2.17 (d, J = 6.9 Hz, 3H), 2.14–2.03
(m, 2H), 1.07 (d, J = 6.8 Hz, 3H), 1.04 (d, J = 6.8 Hz, 3H), 1.03 (d, J = 6.8 Hz, 3H),
0.91 (d, J = 6.8 Hz, 3H). 13C NMR (101 MHz, Chloroformꢀd) δ 145.4, 145.2, 135.7,
134.2, 132.1, 131.9, 131.0, 130.4, 129.9, 129.6, 127.8, 126.6, 125.6, 125.2, 125.2,
124.7, 124.7, 122.3, 121.8, 57.0, 28.7, 28.7, 24.1, 24.1, 24.1, 23.8, 20.8. 19F NMR
(376 MHz, Chloroformꢀd) δ ꢀ72.11 (d, J = 713 Hz). 31P NMR (162 MHz, Chloroformꢀd)
+
δ ꢀ144.16 (sept, J = 713 Hz). HRMS (ESI) calcd. for C27H31N2 (MꢀPF6): m/z
383.24817, found: 383.2485 (1 ppm). Anal. Calcd. for C27H31F6N2P: C, 61.36%; H,
5.91%; N, 5.30%; found: C, 61.74%; H, 5.91%; N, 5.24%
(R)-3-(2,3-dihydro-inden-1-yl)-1-(2,6-diisopropylphenyl)imidazolium
hexafluorophosphate (3i): Selectivity 3iꢀOAc/bisIndꢀOAc/IPrꢀOAc = 93/7/0. Purification
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dichloromethane/cyclohexane. White solid (320 mg, 65%). Singleꢀcrystals of 3i were
obtained by slow evaporation of a saturated solution in dichloromethane/pentane. m.
p.: 205 °C. [ꢀ]ꢂꢁꢃ : +13.3 (c = 1, chloroform). 1H NMR (400 MHz, Chloroformꢀd) δ 8.54
(dd, J = 1.7, 1.7 Hz, 1H), 7.53 (t, J = 7.8 Hz, 1H), 7.45–7.35 (m, 3H), 7.32 – 7.23 (m,
5H), 6.29 (dd, J = 7.8, 4.2 Hz, 1H), 3.27–2.90 (m, 3H), 2.41–2.17 (m, 3H), 1.18 (d, J
= 6.8 Hz, 3H), 1.16 (d, J = 6.8 Hz, 3H), 1.15 (d, J = 6.8 Hz, 6H). 13C NMR (101 MHz,
Chloroformꢀd) δ 145.6, 145.3, 144.5, 137.8, 135.7, 132.2, 130.6, 130.0, 128.2, 125.9,
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125.6, 125.0, 124.9, 124.8, 121.7, 66.0, 34.5, 30.4, 28.9, 28.8, 24.3, 24.1. F NMR
(376 MHz, Chloroformꢀd) δ ꢀ72.30 (d, J = 713 Hz). 31P NMR (162 MHz, Chloroformꢀd)
+
δ ꢀ144.27 (sept, J = 713 Hz). HRMS (ESI) calcd. for C24H29N2 (MꢀPF6): m/z
345.23252, found: 345.2327 (0 ppm). Anal. Calcd. for C24H29F6N2P: C, 58.77%; H,
5.96%; N, 5.71%; found: C, 58.64%; H, 6.24%; N, 5.50%
(1R,2R,3R,5S)-1-(2,6-diisopropylphenyl)-3-(isopinocampheyl)imidazolium
hexafluorophosphate (3j): Selectivity 3jꢀOAc/bisCCamphꢀOAc/IPrꢀOAc = 91/9/0.
Purification over silica gel (diethyl ether/dichloromethane: 9/1). White solid (260 mg,
51%). m. p.: 177 °C. [ꢀ]ꢂꢁꢃ : ꢀ 3.5 (c = 1, chloroform). 1H NMR (400 MHz, Chloroformꢀ
d) δ 8.78 (dd, J = 1.7, 1.7 Hz, 1H), 7.74 (dd, J = 1.9, 1.9 Hz, 1H), 7.52 (t, J = 7.8 Hz,
1H), 7.35 (dd, J1 = 1.9, 1.9 Hz, 1H), 7.34–7.24 (m, 2H), 5.08 (dt, J = 10.2, 7.2 Hz,
1H), 2.97–2.85 (m, 1H), 2.68–2.57 (m, 1H), 2.39–2.20 (m, 2H), 2.19–2.01 (m, 3H),
2.03–1.94 (m, 2H), 1.29 (s, 3H), 1.20–1.11 (m, 15H), 1.09 (s, 3H). 13C NMR (101
MHz, CDCl3) δ 145.7, 145.3, 136.9, 132.1, 130.0, 126.3, 124.9, 124.6, 120.6, 60.8,
47.4, 45.8, 41.4, 39.1, 36.2, 35.4, 29.0, 28.9, 28.1, 24.5, 24.4, 24.0, 23.7, 23.1, 19.7.
19F NMR (376 MHz, Chloroformꢀd) δ ꢀ72.05 (d, J = 713 Hz). 31P NMR (162 MHz,
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Chloroformꢀd) δ ꢀ144.28 (sept, J = 714 Hz). HRMS (ESI) calcd. for C25H37N2 (Mꢀ
PF6): m/z 365.29512, found: 365.2953 (0 ppm). Anal. Calcd. for C25H37F6N2P: C,
58.81%; H, 7.31%; N, 5.49%; found: C, 58.94%; H, 7.57%; N, 5.79%
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(S)-1-(2,6-diisopropylphenyl)-3-(1-hydroxy-4-methylpentan-2-yl)-imidazolium
hexafluorophosphate (3k): Selectivity 3kꢀOAc/bisLeuOHꢀOAc/IPrꢀOAc = 91/4.5/4.5.
Purification over silica gel (dichloromethane/acetone: 9/1). Brown glassy solid (309
1
mg, 65%). [ꢀ]ꢂꢁꢃ : ꢀ 4.8 (c = 1, chloroform). H NMR (400 MHz, Chloroformꢀd) δ 8.52
(dd, J = 1.8, 1.8 Hz, 1H), 7.73 (dd, J = 1.8, 1.8 Hz, 1H), 7.53 (t, J = 7.8 Hz, 1H), 7.36–
7.24 (m, 3H), 4.77–4.65 (m, 1H), 3.95 (dd, J = 12.2, 3.4 Hz, 1H), 3.71 (dd, J = 12.2,
7.6 Hz, 1H), 2.90 (br. s, 1H), 2.34–2.16 (m, 2H), 1.96–1.89 (m, 1H), 1.76–1.64 (m,
1H), 1.52–1.36 (m, 1H), 1.16 (d, J = 6.8 Hz, 3H), 1.14 (d, J = 6.9 Hz, 3H), 1.12 (d, J =
6.7 Hz, 6H), 0.94 (d, J = 6.5 Hz, 3H), 0.93 (d, J = 6.7 Hz, 3H). 13C NMR (101 MHz,
Chloroformꢀd) δ 145.7, 145.3, 136.6, 132.1, 130.0, 125.1, 124.8, 124.6, 121.4, 64.2,
62.0, 38.5, 28.8, 28.6, 25.0, 24.2, 24.0, 24.0, 23.9, 22.5, 21.7. 31P NMR (162 MHz,
Chloroformꢀd) δ ꢀ144.32 (sept, J = 713 Hz). 19F NMR (376 MHz, Chloroformꢀd) δ ꢀ
71.83 (d, J = 713 Hz). HRMS (ESI) calcd. for C21H33N2O+ (MꢀPF6): m/z 329.25929,
found: 329.2596 (0 ppm). Anal. Calcd. for C21H33F6N2OP: C, 53.16%; H, 7.01%; N,
5.90%; found: C, 53.40%; H, 7.11%; N, 5.98%
(S)-1-(2,6-diisopropylphenyl)-3-(1-hydroxy-4-methylpentan-2-yl)-imidazolium
hexafluorophosphate (3l): Selectivity 3lꢀOAc/bisValOHꢀOAc/IPrꢀOAc
=
92/4/4.
Purification over silica gel (dichloromethane/acetone: 95/5) then washing with Et2O.
Brown glassy solid (1.05 g, 46% from 5.0 mmol of corresponding alkylamine). [ꢀ]ꢁꢂꢃ
:
ꢀ10.2 (c = 0.5, chloroform). 1H NMR (400 MHz, Chloroformꢀd) δ 8.51 (dd, J = 1.5, 1.5
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Hz, 1H), 7.75 (dd, J = 1.8, 1.8 Hz, 1H), 7.53 (t, J = 7.8 Hz, 1H), 7.33–7.28 (m, 3H),
4.31 (ddd, J = 10.1, 6.9, 3.2 Hz, 1H), 4.06 (dd, J = 12.3, 3.2 Hz, 1H), 3.95 (dd, J =
12.3, 7.0 Hz, 1H), 2.77 (br. s, 1H), 2.38–2.16 (m, 3H), 1.19–1.11 (m, 12H), 1.09 (d, J
= 6.7 Hz, 3H), 0.85 (d, J = 6.7 Hz, 3H). 13C NMR (101 MHz, Chloroformꢀd) δ 145.7,
145.3, 136.6, 132.1, 130.0, 125.0, 124.8, 124.7, 122.1, 77.5, 69.4, 61.7, 29.3, 28.8,
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28.7, 24.2, 24.1, 23.9, 19.1. P NMR (162 MHz, Chloroformꢀd) δ ꢀ144.32 (sept, J =
713 Hz). 19F NMR (376 MHz, Chloroformꢀd) δ ꢀ71.90 (d, J = 713 Hz). HRMS (ESI)
calcd. for C20H31N2O+ (MꢀPF6): m/z 315.24309, found: 315.2431 (0 ppm)
(S)-3-(1-carboxy-3-methylbutyl)-1-(2,6-diisopropylphenyl)imidazolium
hexafluorophosphate (3m): Selectivity 3mꢀOAc/bisLeuCOOHꢀOAc/IPrꢀOAc = 79/3/18.
Purification: Chromatography on silica gel (dichloromethane/MeOH: 95/5) and
extraction with a saturated aqueous solution of NaHCO3. The aqueous solution was
neutralized with 1M aqueous solution of HCl and extracted with dichloromethane.
1
Orange glassy solid (181 mg, 37%). [ꢀ]ꢂꢁꢃ : +31.5 (c = 1, chloroform). H NMR (400
MHz, Chloroformꢀd) δ 9.20 (dd, J = 1.5, 1.5 Hz, 1H), 7.95 (dd, J = 1.6, 1.6 Hz, 1H),
7.51 (t, J = 7.8 Hz, 1H), 7.32–7.26 (m, 2H), 7.12 (dd, J = 1.9, 1.9 Hz, 1H), 5.19 (dd, J
= 10.6, 4.7 Hz, 1H), 2.38–2.25 (m, 2H), 2.20 (ddd, J = 14.0, 9.0, 4.7 Hz, 1H), 1.97
(ddd, J = 14.9, 10.6, 5.0 Hz, 1H), 1.46–1.30 (m, 1H), 1.27–1.06 (m, 12H), 0.98 (d, J =
6.6 Hz, 3H), 0.92 (d, J = 6.6 Hz, 3H). 13C NMR (101 MHz, chloroformꢀd) δ 170.6,
145.8, 145.4, 137.1, 131.8, 130.6, 124.7, 124.6, 123.8, 123.1, 122.8, 65.5, 43.8,
31
28.7, 28.7, 24.4, 24.3, 24.2, 24.1, 23.1, 21.7. P NMR (162 MHz, Chloroformꢀd) δ ꢀ
144.33 (sept, J = 713 Hz). 19F NMR (376 MHz, Chloroformꢀd) δ ꢀ72.20 (d, J = 713
+
Hz). HRMS (ESI) calcd. for C21H31N2O2 (MꢀPF6): m/z 343.238, found: 343.2376 (1
ppm)
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1,3-bis((R)-1-(naphthalen-1-yl)ethyl)imidazol-3-ium hexafluorophosphate (7h): Yellow
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8
1
powder (492 mg, 97%). m.p.: 103 °C. [ꢀ]ꢂꢁꢃ : ꢀ118.0 (c = 0.1, chloroform). H NMR
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(400 MHz, Chloroformꢀd) δ 8.90 (dd, J = 1.7, 1.7 Hz, 1H), 8.02–7.68 (m, 6H), 7.58 –
7.35 (m, 8H), 6.98 (d, J = 1.7 Hz, 2H), 6.43 (q, J = 6.9 Hz, 2H), 2.06 (d, J = 6.9 Hz,
6H). 13C NMR (101 MHz, Chloroformꢀd) δ 134.5, 134.1, 132.5, 130.6, 130.3, 129.4,
127.9, 126.6, 125.5, 124.7, 121.7, 121.3, 56.7, 21.0. 31P NMR (162 MHz, Chloroformꢀ
d) δ ꢀ144.03 (sept, J = 713 Hz). 19F NMR (376 MHz, Chloroformꢀd) δ ꢀ71.78 (d, J =
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+
713 Hz). HRMS (ESI) calcd. for C27H25N2 (MꢀPF6): 377.20122 m/z, found: 377.2013
(0 ppm)
(R)-1-(2,6-diisopropylphenyl)-3-((1-(naphthalen-1-yl)ethyl)imidazol-2-ydene)copper
chloride complex (3h.CuCl): White solid (99 mg, 86%). m.p.: 214 °C. [ꢀ]ꢂꢁꢃ : +85.4 (c
1
= 1, chloroform). H NMR (400 MHz, Chloroformꢀd) δ 8.13–8.07 (m, 1H), 7.96–7.87
(m, 2H), 7.81–7.73 (m, 1H), 7.63–7.41 (m, 4H), 7.30–7.19 (m, 2H), 6.76–6.71 (m,
2H), 6.68 (q, J = 6.9 Hz, 1H), 2.45 (sept, J = 6.8 Hz, 1H), 2.27 (sept, J = 6.9 Hz, 1H),
2.14 (d, J = 6.9 Hz, 3H), 1.32 (d, J = 6.9 Hz, 3H), 1.27 (d, J = 6.9 Hz, 3H), 1.13 (d, J =
6.9 Hz, 3H), 0.99 (d, J = 6.9 Hz, 3H). 13C NMR (101 MHz, Chloroformꢀd) δ 178.4,
145.8, 145.7, 134.8, 134.2, 133.9, 131.3, 130.5, 130.2, 129.2, 127.0, 126.4, 125.2,
124.6, 124.2, 124.2, 123.3, 123.2, 118.5, 56.9, 28.6, 28.4, 25.0, 24.7, 24.3, 24.0,
22.5. HRMS (ESI) calcd. for C27H30N235ClNa63Cu+ (M+Na) : 503.12857 m/z , found :
503.1291 (1 ppm)
Ethyl (S)-3-hydroxy-3-phenylpropanoate (9): With 3h: Colorless oil (65 mg, 67%), e.r
= 87 : 13. [ꢀ]ꢂꢁꢃ : ꢀ35.8 (c = 1, chloroform), [Litt19f : [ꢀ]ꢁꢂꢃ= ꢀ49.2 (c = 0.1, chloroform),
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e.r.= 98:2]. With 7h: Colorless oil (58 mg, 60%), e.r = 67.5 : 32.5. With 3h.CuCl:
Colorless oil (74 mg, 76%), e.r.= 82 : 18. Enantiomeric excess was measured by
chiral HPLC:23 ODꢀH column, Hexane / 2ꢀpropanol (90% / 10%) – 1 mL/min, λ=254
9
1
nm, T=25°C, Rt1 = 7.8 min, Rt2 = 10.1 min. H NMR (400 MHz, Chloroform-d) δ
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7.48–7.12 (m, 5H), 5.14 (dt, J = 8.5, 3.6 Hz, 1H), 4.19 (q, J = 7.1 Hz, 2H), 3.26 (d, J =
3.4 Hz, 1H), 2.88–2.59 (m, 2H), 1.27 (t, J = 7.1 Hz, 3H), 13C NMR (101 MHz,
Chloroformꢀd) δ 172.6, 142.6, 128.7, 127.9, 125.8, 70.4, 61.0, 43.5, 14.3.
(S)-(3-methylpent-1-en-3-yl)benzene (11a): Colorless oil (58 mg, 73%, conversion
>95%). SN2’/SN2 selectivity: 96/4. e.r = 92:8 (S). [ꢀ]ꢂꢁꢃ : +10.5 (c = 1, chloroform)
[Litt10 : [ꢀ]ꢂꢁꢃ= +10.1 (c = 1, chloroform), e.r.= 91:9]. Enantiomeric excess was
measured by chiral GC: Betaꢀdex column, helium (30.9 cm/sec), 80°Cꢀ55minꢀ
1
10°C/minꢀ160°Cꢀ10 min, Rt1 = 43.7 min (R), Rt2 = 44.3 min (S). H NMR (400 MHz,
Chloroform-d): δ = 7.37−7.16 (m, 5H), 6.04 (dd, J = 17.4, 10.8 Hz, 1H), 5.10 (dd, J =
10.8, 1.4 Hz, 1H), 5.04 (dd, J = 17.4, 1.4 Hz, 1H), 1.90−1.74 (m, 2H), 1.38 (s, 3H,
13
CH3), 0.80 (t, J = 7.6 Hz, 3H). C NMR (101 MHz, Chloroform-d): δ = 147.6, 147.0,
128.1, 126.8, 125.8, 111.9, 44.7, 33.5, 24.5, 9.0.
1-bromo-2-(3-methylpent-1-en-3-yl)benzene (11b): Colorless oil (81 mg, 68%,
conversion >95%). SN2’/SN2 selectivity: >98/<2. e.r = 91:9 (S). [ꢀ]ꢂꢁꢃ : +1.7 (c = 1,
chloroform). [Litt10 : [ꢀ]ꢂꢁꢃ = +2.4 (c = 1, chloroform), e.r. = 95:5]. Enantiomeric excess
was measured by chiral GC: GTA column, helium (33.2 cm/sec), 80°Cꢀ60minꢀ110°Cꢀ
15minꢀ1°C/minꢀ160°Cꢀ10minꢀ10°C/min, Rt1(major) = 94.7 min (R), Rt2(minor) = 96.7
min (S). 1H NMR (400 MHz, Chloroform-d) δ 7.57 (dd, J = 7.9, 1.4 Hz, 1H), 7.40 (dd,
J = 8.0, 1.7 Hz, 1H), 7.29−7.22 (m, 1H), 7.05 (ddd, J = 7.9, 7.2, 1.7 Hz, 1H), 6.20 (dd,
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J = 17.6, 10.7 Hz, 1H), 5.10 (dd, J = 10.7, 1.1 Hz, 1H), 4.93 (dd, J = 17.6, 1.1 Hz,
1H), 2.41−2.29 (m, 1H), 1.94–1.82 (m, 1H), 1.49 (s, 3H), 0.71 (t, J = 7.5 Hz, 3H). 13C
NMR (101 MHz, Chloroformꢀd) δ 146.5, 145.1, 135.6, 129.9, 127.8, 127.0, 123.5,
112.6, 46.4, 31.3, 25.8, 9.1.
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1-(3-methylpent-1-en-3-yl)naphthalene (11c): Colorless oil (74 mg, 71%, conversion
78%). SN2’/SN2 selectivity: 96/4. e.r = 95 : 5. [ꢀ]ꢂꢁꢃ : ꢀ6.5 (c = 1, chloroform). [Litt10
[ꢀ]ꢂꢁꢃ = ꢀ8.0 (c = 1, chloroform), e.r. = 96:4]. Enantiomeric excess was measured by
chiral HPLC: OJꢀH column, hexane (100%) – 0.3 mL/min, λ=254 nm, T=25°C,
Rt1(minor) = 17.9 min, Rt2(major) = 18.5 min. 1H NMR (400 MHz, Chloroform-d): δ =
8.38 (d, J = 8.6 Hz, 1H), 7.86 − 7.83 (m, 1H), 7.74 (d, J = 8.0 Hz, 1H), 7.50−7.37 (m,
4H), 6.32 (dd, J = 17.7, 10.7 Hz, 1H), 5.13 (d, J = 10.8 Hz, 1H), 5.03 (d, J = 17.6 Hz,
1H), 2.35−2.26 (m, 1H), 2.04−1.95 (m, 1H), 1.57 (s, 3H), 0.67 (t, J = 7.4 Hz, 3H). 13C
NMR (101 MHz, Chloroform-d) δ 149.0, 142.5, 135.0, 131.8, 129.2, 127.8, 127.7,
125.2, 125.1, 124.9, 124.4, 112.1, 45.7, 32.9, 27.5, 9.1.
Acknowledgements
We are grateful to the CNRS, the Ecole Nationale Supérieure de Chimie de Rennes.
This work was supported by Omega Cat System and the region Bretagne (ARED
n°COH14007 “NHCꢀMET” grant to RT) and the Agence Nationale de la Recherche
(N° ANRꢀ15ꢀCE07ꢀ0012ꢀ01 ”CHADOC”).
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