Use of Planar Chiral Ferrocenylphosphine-Gold(I) Complexes in the Asymmetric Cycloisomerization of 3-Hydroxylated 1,5-Enynes

Article abstract of DOI:10.1002/ejoc.201501121

Chiral monodentate phosphines based on ortho-disubstituted ferrocene units have been prepared and used for the synthesis of gold(I) complexes. These complexes are highly active catalysts for the cycloisomerization of 3-hydroxy-1,5-enynes into bicyclo[3.1.0]hexanones. Their high catalytic activity is ascribed to their structural analogy to the biaryl-based Buchwald phosphines. This paper discloses the first enantioselective variant of these reactions based on gold catalysis (ee's up to 80 %).

Full text of DOI:10.1002/ejoc.201501121

DOI: 10.1002/ejoc.201501121
Full Paper
Gold Catalysis
Use of Planar Chiral Ferrocenylphosphine-Gold(I) Complexes in
the Asymmetric Cycloisomerization of 3-Hydroxylated 1,5-
Enynes
Zhiyong Wu,[a,b] Pascal Retailleau,[a] Vincent Gandon,[a,b] Arnaud Voituriez,*[a] and
Angela Marinetti*[a]
Abstract: Chiral monodentate phosphines based on ortho-di- is ascribed to their structural analogy to the biaryl-based Buch-
substituted ferrocene units have been prepared and used for
the synthesis of gold(I) complexes. These complexes are highly
active catalysts for the cycloisomerization of 3-hydroxy-1,5-en-
ynes into bicyclo[3.1.0]hexanones. Their high catalytic activity
wald phosphines. This paper discloses the first enantio-
selective variant of these reactions based on gold catalysis (ee's
up to 80 %).
Introduction
intermediates, either by steric effects, or by weak coordination
of the pendant aryl unit to the gold centre.[4] With this in mind,
it would be an attractive idea to apply an analogous design to
chiral ligands in which a biaryl unit would ensure both high
catalytic activity and enantiocontrol. However, gold complexes
of such ligands (II, L = phosphine or carbene, including chiral
variants of Buchwald phosphines themselves) have hardly been
used in catalysis. The most common strategy for building chiral
ligands of this class involves the use of NHC's (N-heterocyclic
carbenes) or NAC's (nitrogen acyclic carbenes) as ligands, com-
bined with binaphthyl units. This is typified by compounds III,
in which flexible NAC units are connected to a binaphthyl scaf-
fold bearing an additional aryl substituent.[5] High asymmetric
induction is driven here by an appropriate conformation of the
triaryl scaffold, which gives the so-called “in” rotamer in which
the phenyl group becomes closer to the gold centre and cre-
ates a suitable chiral pocket. Alternatively, high enantioselectiv-
ity has been achieved with ligands containing rigid NHC units
fused to a biaryl scaffold, as in IV.[6] In terms of biaryl-based
phosphorus ligands, gold complexes of chiral biaryl-monophos-
phines (II with L = PR2) have only recently been investigated
as catalysts for intramolecular hydroamination reactions, with
moderate success in terms of chiral induction (eemax = 29 %).[7]
The biarylphosphines I (Figure 1), initially developed by Buch-
wald,[1] represent a privileged family of ligands in both palla-
dium and gold catalysis, due to the exceptional catalytic activity
of the corresponding metal complexes. The use of these ligands
in gold catalysis was first reported by Echavarren,[2] and their
scope has subsequently been investigated further by many re-
search groups.[3]
Figure 1. Biaryl ligands and gold complexes.
At the start of our studies, we noticed that a three-dimen-
sional arrangement analogous to that of biarylmonophosphines
could be generated in gold complexes by pseudobiaryl ferro-
cene-based phosphines with planar chirality (see V in Figure 2;
aryl-MOPFs = aryl-monophosphino ferrocenes).
The increased catalytic activity of complexes containing
these ligands is mainly due to the stabilization of cationic gold
[a] Institut de Chimie des Substances Naturelles, CNRS UPR 2301, Université
Paris-Sud, Université Paris-Saclay,
Although several palladium– and copper–MOPF complexes
have been synthesized and used in catalysis,[8] the use of gold–
MOPF complexes is extremely rare. Only Echavarren has re-
cently reported on two complexes of this family, which gave up
to 50 % ee in a [4+2] cycloaddition reaction.[9]
1, av. de la Terrasse, 91198 Gif-sur-Yvette, France
E-mail: arnaud.voituriez@cnrs.fr
angela.marinetti@cnrs.fr
http://www.icsn.cnrs-gif.fr/
[b] ICMMO (UMR CNRS 8182), Université Paris-Sud,
91405 Orsay, France
In this context, we were interested in a more extended inves-
tigation of the potential of gold complexes V in enantioselect-
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/ejoc.201501121.
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substituted phosphines, which were isolated as the correspond-
ing borane complexes (i.e., 3b and 3c), after in-situ protection
with BH3. The phosphorus substituents were varied, going from
phenyl (3a–3c) to more bulky aryl groups in 3d (R = 3,5-
Me2C6H3), or to cyclohexyl substituents in 3e. Phosphine bor-
anes 3d and 3e were isolated in moderate yields.[14]
With these five phosphines in hand, we turned our attention
to the synthesis of gold complexes (S)-4a–4e (Scheme 1). Start-
ing with trivalent phosphine (S)-3a, gold complex (S)-4a was
obtained in 70 % yield after complexation with AuCl·thiodi-
ethanol, obtained in situ by the reaction of NaAuCl4·(H2O)2 and
2,2′-thiodiethanol. Phosphine boranes (S)-3b–3e were con-
verted into the corresponding gold complexes (S)-4b–4e by in
situ deprotection of the borane (2 h at 80 °C in a THF/EtOH
solution), followed by reaction with the same gold precursor at
0 °C. Overall yields of 32–75 % were obtained over these two
steps.
Figure 2. MOPF–gold(I) complexes.
ive catalysis. In this paper, we report the results of our system-
atic screening of new MOPF–gold complexes in the cyclo-
isomerization of 1,5-enynes into bicyclo[3.1.0]hexanones. Enan-
tioselective variants of these reactions[10] have not been re-
ported to date with gold catalysts. Our previous work has
shown that MonoPhos–platinum(II) complexes promote these
skeletal rearrangements with moderate to good efficiency.[11]
Results and Discussion
This work started with the synthesis of a series of MOPF ligands,
following an established strategy.[8a] The method makes use of
(S,Rpl)-1-iodo-2-p-tolylsulfinylferrocene (1) as the starting mate-
rial. This compound was easily obtained in enantiopure form
by diastereoselective ortho-directed lithiation/iodination of (S)-
p-tolylsulfinylferrocene.[12] Palladium-catalysed Suzuki coup-
lings of (S,Rpl)-1 with three different boronic acids allowed us
to introduce various aromatic groups onto the ferrocene back-
bone. Disubstituted chiral ferrocenyl sulfoxides (S,Spl)-2a–2c
were obtained in 70–90 % yield, depending on the aryl group
used [Ar = phenyl, 70 %; Ar = 9-anthracenyl (Anth), 89 %; Ar =
9-phenanthryl (Phen), 90 %; step a] (Table 1).
Scheme 1. Synthesis of gold complexes (S)-4a–4e.
The structure and absolute configuration of complex (S)-4c
was ascertained by an X-ray diffraction study. An ORTEP view
of this complex is shown in Figure 3.
Table 1. Synthesis of planar chiral ferrocenyl-phosphines [(S)-3a] or their BH3
complexes [(S)-3b–3e].
Product
Ar
R
X
Yield [%]
3a
3b
3c
3d
3e
Ph
Ph
Ph
Ph
–
77
28
39
25
35
9-anthracenyl
9-phenanthryl
9-phenanthryl
9-phenanthryl
BH3
BH3
BH3
BH3
3,5-Me2C6H3
cyclohexyl
[a] Reaction conditions: Pd(SPhos)2Cl2 (Sphos = 2-dicyclohexylphosphino-2′
,6′-dimethoxybiphenyl), ArB(OH)2, Cs2CO3, toluene/THF, 80 °C, 16 h.
[b] (i) tBuLi, THF, R2PCl; (ii) BH3·DMS (DMS = dimethyl sulfide).
The desired phosphines [(S)-3a] or their borane adducts [(S)-
3b–3e] could be synthesized then through sulfoxide/lithium ex-
change by the addition of tBuLi, followed by trapping of the
carbanionic ferrocenyl intermediate with a chlorodiaryl- or a
chlorodialkylphosphine (step b).[13] Ferrocenyl diphenylphos-
phine (S)-3a[8a] was isolated in 77 % yield. The same procedure
was used for the synthesis of 9-anthracenyl and 9-phenanthryl-
Figure 3. X-ray crystal structure of (S)-4c showing one molecule in the asym-
metric unit. Ellipsoids are drawn at the 50 % probability level, H atoms are
not shown for clarity. Selected bond lengths [Å]: Au–P, 2.229(2); Au–Cl,
2.029(2); P–C-5, 1.792(6); Au–C-11, 3.198; Au–C-12, 3.477; Au–C-24, 3.430. Se-
lected bond angles [°]: P–Au–Cl, 178.55(7); Au–P–C-5, 113.1(2); P–C-5–C-4,
126.3(5); C-5–C-1–C-11, 128.1(6).
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For neutral gold chloride complex (S)-4c, the distance be- hexan-3-one (6a), in good yields, but with very low enantio-
tween the AuI centre and the nearest carbon of the phenanthryl meric excess (Table 2, entries 1 and 2).
group, C-11, is 3.198 Å. The adjacent carbons, C-24 and C-12
are at 3.430 and 3.477 Å, respectively, from the gold. The meas-
ured Au–C distances are longer than the maximum estimated
length for significant arene–Au interactions (2.95 Å).[4c] Based
on these structural data, we can only postulate a weak localized
gold–π(arene) interaction between the metal centre and the
phenanthryl group in 4c, but, as shown below, the high cata-
lytic activity of the corresponding cationic complexes suggests
an effective stabilization of the gold centre by these ligands.
The enantiomeric excess could be improved to about 31 %
ee by using catalyst 4c, which contains a 9-phenanthryl substit-
uent on the ferrocene backbone (Table 2, entry 3). The enantio-
meric excess did not improve further by moving to catalysts 4d
and 4e, in which the diphenylphosphino unit of 4c was re-
placed either by a bulkier bis(3,5-dimethylphenyl)phosphino
unit (in 4d) or a more electron-rich dicyclohexylphosphino unit
(in 4e) (Table 2, entries 4 and 5; 30 and 17 % ee, respectively).
In attempts to optimize the enantioselectivity with catalyst 4c,
The five gold complexes [i.e., (S)-4a–4e] were investigated as we screened several silver salts (AgPF6, AgSbF6, AgNTf2, AgOTf),
catalysts for the cycloisomerization of 3-hydroxy-1,5-enynes solvents (dichloroethane, dichloromethane, chloroform, aceto-
into bicyclo[3.1.0]hexan-3-ones, as shown in Table 2.[10] In spite nitrile, THF), and reaction temperatures. The highest enantiose-
of the established synthetic utility of these reactions, their lectivity was obtained when the reaction was run in dichloro-
asymmetric variants are still rare. Asymmetric variants have methane at room temperature, with AgOTf as the activating
been carried out with platinum catalysts,[11] but, as far as we silver salt (Table 2, entry 7, 85 % isolated yield, 46 % ee). De-
are aware, they have not been explored with chiral gold cata- creasing the reaction temperature to 0 °C for this substrate did
lysts. From a more general point of view, we can also note that, not improve the enantiomeric excess, but good catalytic activity
unlike phosphorus ligands with central, axial, or helical chirality, was still observed (Table 2, entry 8).
ligands with planar chirality have been poorly exploited to date
in gold catalysis.[15b,16] Enantioselective reactions[17] are com-
monly carried out with catalysts based on bimetallic gold com-
plexes of atropisomeric diphosphines,[15] chiral counterions
(mainly chiral phosphoric acid derivatives),[18] phosphoramidite
ligands with bulky and extended substituents,[19] as well as
monodentate phosphahelicene ligands.[20] The preliminary
screening of monodentate phosphine–gold complexes 4 are re-
ported in Table 2.
The same conditions were then used for the cycloisomeriza-
tion of other 3-hydroxy-1,5-enynes with catalyst (S)-4c, as
shown in Table 3.
Table 3. Cycloisomerization of 3-hydroxylated 1,5-enynes catalysed by gold
complex (S)-4c.
Table 2. Screening of gold catalysts (S)-4a–4e in the cycloisomerization of 3-
hydroxy-1,5-enynes.
Entry Substrate Ar
R
T [°C]
Yield [%] ee [%][a]
1
2
3
4
5
6
7
8
9
5a
5b
5c
5d
5e
5e
5e
5f
Ph
Me
Me
Me
Me
Me
Me
Me
Ph
20
0
0
0
20
0
–40
0
–40
85
87
91
88
67
82
72
76
79
46
43
29
20
56
64
66
71
80
3,4-Cl2-C6H3
3-OMe-C6H4
2-OMe-C6H4
4-OMe-C6H4
4-OMe-C6H4
4-OMe-C6H4
4-OMe-C6H4
4-OMe-C6H4
Entry
[Au*]
AgX
Conv. [%][a]
ee [%][b]
1
2
3
4
5
6
4a
4b
4c
4d
4e
4c
4c
4c
AgBF4
AgBF4
AgBF4
AgBF4
AgBF4
AgOTf
AgOTf
AgOTf
93
95
98
100
98
95
100 (85)
95 (80)
13
2
5f
Ph
31
30
17
44
46
46
[a] Enantiomeric excesses determined using chiral HPLC.
Enynes 5b–5e, which have substituted aryl rings on the
alkyne group and a methyl group on the olefin moiety (R =
Me) gave the corresponding bicyclo[3.1.0]hexan-3-ones in high
yields and with moderate enantioselectivities when the reac-
tions were carried out at room temperature or at 0 °C (20–64 %
ee; Table 3, entries 1–6). Substrate 5f, in which R = Ph, was
converted into the desired bicyclo[3.1.0]hexan-3-one with a
higher 71 % ee under the same reaction conditions (Table 3,
entry 8).[21]
7[c]
8[c,d]
[a] Conversions determined by 1H NMR spectroscopy. Isolated yields in paren-
theses. [b] Determined by HPLC on a chiral stationary phase. [c] In CH2Cl2.
[d] At 0 °C.
5-Methyl-1-phenylhex-5-en-1-yn-3-ol (5a) was chosen as an
initial substrate. The experiments were carried out at room tem-
perature in toluene by using the gold(I) catalyst (4 mol-%) and
AgBF4 (8 mol-%). Under these conditions, the reaction pro-
It must be noted here that all these MOPF–gold complexes
ceeded with over 90 % conversion after 16 h. Gold catalysts 4a gave high catalytic activity, and total conversion was reached
and 4b, where Ar = phenyl and 9-anthracenyl, respectively, gave for all substrates after 16 h at 0 °C. Given the efficiency of the
the corresponding product, 1-methyl-5-phenylbicyclo[3.1.0]- catalyst, we envisioned that the reaction temperature could be
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decreased to –40 °C. As a result, the enantiomeric excesses im-
In terms of enantioselectivity, the enantiomeric excesses of
proved to 66 and 80 % ee for 6e and 6f, respectively (Table 3, up to 80 % ee obtained with these catalysts are promising, es-
entries 7 and 9). Overall, decreasing the reaction temperature pecially when considering that enynes 6a–6f have a stereo-
resulted in a beneficial effect for these reactions (Table 3, en- genic carbon at their propargylic position, which means that
tries 5–7, and entries 8 and 9).
the substrate might compete with the chiral catalyst for stereo-
chemical control of the cyclization. Indeed, according to the
generally assumed mechanism for the cycloisomerization of
1,5-enynes,[22] the stereochemistry of the substrate might be
transferred, at least in part, into the product. In our previous
work, as well as in literature reports, it has been demonstrated
that this is indeed the case with platinum catalysts;[10a,11,23] par-
tial chirality transfer has also been observed by Gagosz in the
gold-promoted cycloisomerization of some diastereomeric sub-
strates.[24] Thus, to gain information about the stereochemical
control of these cycloisomerization reactions, we carried out the
additional experiments shown in Table 4.
The high catalytic activity of complexes 4 might be due to
stabilization of the catalyst through gold–arene interactions.
However, the X-ray data in Figure 3 above show long Au–C
distances, which preclude strong metal–arene interactions. In
spite of this unambiguous structural feature, we cannot exclude
the possibility that the Au–arene interactions increase when
moving from the neutral complex [i.e., (S)-4c] to the corre-
sponding cationic gold complex, in which the stabilizing effect
of π-arene complexation becomes crucial. This hypothesis was
actually corroborated by DFT (density functional theory) calcu-
lations. Complex (S)-4c was optimized using the Gaussian 09
software package at the M06-2X level (see Supporting Informa-
tion for further details). This functional is known to properly
describe noncovalent interactions. SDD (Stuttgart–Dresden ba-
sis set) relativistic effective core potentials were used to de-
scribe the Au and Fe atoms. The other atoms were described
by the 6-31+G(d,p) basis set (Figure 4).
Table 4. Stereochemical effect of the stereogenic centre of the substrate.
The calculated gas-phase Au–C-11 distance is slightly longer
than in the solid state (3.286 vs. 3.198 Å, respectively). On the
other hand, the gas-phase Au–C-24 distance was found to be
slightly shorter than the solid-state distance (3.385 vs. 3.430 Å,
respectively). In the corresponding cationic complex, i.e., after
the removal of Cl– in the calculations, the Au–C-11 distance
shortens significantly to become 3.050 Å. More strikingly, the
Au–C-24 distance shortens drastically to become as low as
2.802 Å. The maximum electron density along the Au–C-24 axis
Entry
Substrate
Catalyst
ee [%]
1
2
3
4
5
(R)-5a
(S)-5a
rac-5a
(R)-5a
(R)-5a
(S)-4c
(S)-4c
(S)-4c
7
50 (–)
38 (–)
46 (–)
36 (–)
21 (–)
PtCl2
is indicative of quite a strong noncovalent interaction (ρmax
=
0.023 e Å–3) in the cationic complex. For comparison, the maxi-
mum electron density in (S)-4c is found along the Au–C-11 axis,
and is very modest (ρmax = 0.009 e Å–3). Clearly the phenanthryl
moiety is well-suited to protecting the active gold centre in the
cationic complex, both sterically and electronically, by transfer-
ring electron density. This might account for the stability of the
cationic gold complex towards reduction to Au0.
We prepared enantiomerically pure substrates (R)-5a and (S)-
5a,[11a] and submitted them separately to cycloisomerization,
Figure 4. Geometries of calculated complex (S)-4c (left) and its cationic counterpart (right) (selected distances in Å).
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30:70) gave gold complex 4b (21 mg, 75 %) as an orange solid. Rf =
0.29 (dichloromethane/heptane, 70:30). 1H NMR (500 MHz, CDCl3):
δ = 10.36 (d, J = 8.5 Hz, 1 H), 8.32 (s, 1 H), 7.93 (d, J = 8.0 Hz, 1 H),
7.90–7.80 (m, 3 H), 7.70 (dd, J = 8.5, 6.5 Hz, 1 H), 7.53–7.42 (m, 4 H),
7.34 (d, J = 8.5 Hz, 1 H), 7.28–7.21 (m, 1 H), 7.13–7.05 (m, 3 H), 6.95–
6.89 (m, 1 H), 6.76–6.68 (m, 2 H), 4.88 (s, 1 H), 4.84 (s, 1 H), 4.65 (s,
using either enantiopure complex (S)-4c or the achiral gold
complex [(2-biphenyl)di-tert-butylphosphine]gold(I)(aceto-
nitrile) hexafluoroantimonate (7) as the catalyst. When the chi-
ral catalyst [i.e., (S)-4c) was used in the cycloisomerization of
(R)-5a and (S)-5a, enantiomeric excesses of 50 and 38 % ee, re-
spectively, were obtained (Table 4, entries 1 and 2). These re-
sults are consistent, in terms of enantiomeric excess, with the
ee obtained starting from the racemic substrate rac-5a (Table 4,
entry3,46 %ee).TheexperimentsinTable4,entries1and2gavebi-
1 H), 4.40 (s, 5 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 134.5 (d, JC,P
14.6 Hz, CH), 133.6 (d, JC,P = 14.6 Hz, CH), 133.3 (C), 131.8 (d, JC,P
=
=
65.0 Hz, C), 131.7 (CH), 131.3 (C), 131.0 (C), 130.8 (CH), 129.7 (d,
C,P = 19.2 Hz, C), 128.9 (d, JC,P = 4.4 Hz, CH), 128.8 (CH), 128.5 (CH),
J
cyclo[3.1.0]hexanone 6a with the same absolute configuration, 128.3 (CH), 127.9 (CH), 127.7 (CH), 127.3 (C), 126.7 (CH), 125.2 (d,
JC,P = 4.6 Hz, CH), 125.3 (CH), 124.5 (CH), 77.0 (d, JC,P = 8.0 Hz, CH),
73.9 (d, JC,P = 10.1 Hz, CH), 72.3 (C), 69.8 (d, JC,P = 8.0 Hz, CH) ppm.
which means that the stereochemical control of the chiral cata-
lyst overcomes the effect of the chirality of the substrate. The
gap of 12 % ee between the two experiments indicates that the
stereogenic centre of the substrate has only a rather moderate
effect on the stereocontrol. A “matched effect” is observed be-
tween (R)-5a and (S)-4c (Table 4, entry 1).
31P NMR (121 MHz, CDCl ): δ = 27.4 ppm. IR: ν = 3049, 2986, 1518,
˜
3
1481, 1437, 1333, 1158, 1101, 1001, 889, 829, 740, 694 cm–1. [α]D25
=
–28 (c = 1.0, CHCl3). HRMS (ESI): calcd. for C38H30AuFeNP [M – Cl +
CH3CN]+ 784.1131; found 784.1210.
General Procedure for the Enantioselective Cycloisomerization
Reactions: Silver salt (8 mol-%) and the substrate (0.10 mmol, in
1.0 mL of CH2Cl2) were added sequentially to a solution of the AuI
complex (4 mol-%) in CH2Cl2 (0.5 mL) under argon. The mixture was
stirred for 16 h. The solvent was removed under reduced pressure,
and the crude mixture was checked by NMR spectroscopy. The mix-
ture was then purified by column chromatography on silica gel
(heptane/EtOAc, 90:10) to give the final product.
On the other hand, starting from enantiomerically pure alco-
hol (R)-5a, the achiral gold catalyst
7 gave bicyclo-
[3.1.0]hexanone 6a with 36 % ee, and PtCl2 gave the same prod-
uct with 21 % ee (Table 4, entries 4 and 5). Overall, these results
demonstrate that enantiopure substrates give partial chirality
transfer to the product under gold catalysis, but the chiral gold
catalysts (S)-4, as well as the chiral platinum catalysts reported
previously, overcome the effect of the substrate.
1-(4-Methoxyphenyl)-5-phenylbicyclo[3.1.0]hexan-3-one (6f):
1
79 % yield, 80 % ee. H NMR (500 MHz, CDCl3): δ = 7.20–7.10 (m, 2
H), 7.18–7.05 (m, 3 H), 7.01 (d, J = 8.5 Hz, 2 H), 6.70 (d, J = 8.5 Hz,
2 H), 3.72 (s, 3 H), 3.22 (d, J = 19.0 Hz, 1 H), 3.15 (d, J = 18.5 Hz, 1
H), 2.77 (d, J = 19.0 Hz, 1 H), 2.75 (d, J = 18.5 Hz, 1 H), 1.99 (m, 1
H), 1.05 (d, J = 6.5 Hz, 1 H) ppm. HPLC [CHIRALPAK® IB, 20 °C, iPrOH/
n-heptane (0.5:99.5), 0.8 mL/min, 231 nm]: tR = 36.3 min (major)
and 39.3 min (minor).
Conclusions
In conclusion, we have shown that aryl-substituted, planar chi-
ral ferrocenylphosphines give very active gold catalysts for the
cycloisomerization of 3-hydroxy-1,5-enynes into bicyclo[3.1.0]-
hexanones. These ligands can be considered to be chiral ana-
logues of Buchwald's phosphines. Their good catalytic activity
can be ascribed to a stabilizing effect of the aryl-substituted
ferrocene unit, which behaves as a pseudo-biaryl unit. In terms
of enantioinduction, these ligands give moderate to good en-
antiomeric excesses, which are strongly modulated by varia-
tions in the aryl substituents on the ferrocene backbone. These
results open the way to further optimization of target reactions
through structural modification of the chiral ligands.
CCDC-1400309 [for (S)-4c] contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
Acknowledgments
The authors thank the Chinese Scholarship Council (CSC) for a
PhD grant to Z. W., V. G. thanks the Institut Universitaire de
France (IUF) for support. We used the computational facilities
of the CRIHAN (project 2006-013).
Experimental Section
Keywords: Asymmetric catalysis · Cycloisomerization ·
Homogeneous catalysis · Gold · Ligand design · P ligands
Gold Complex 4b: Compound 3b (20 mg, 0.036 mmol, 1 equiv.)
was put into a mixture of ethanol and THF (2:1; 9 mL). The mixture
was stirred and heated to reflux (80 °C) for 2 h under an argon
atmosphere. The yellow solution was then cooled to room tempera-
ture. The volatiles were removed under reduced pressure to give
the crude phosphine as a yellow solid, which was used directly in
the next step.
[1] a) S. D. Walker, T. E. Barder, J. R. Martinelli, S. L. Buchwald, Angew. Chem.
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NaAuCl4·2H2O (16 mg, 0.04 mmol, 1.1 equiv.) was dissolved in water
(2 mL) under argon, and the solution was cooled to 0 °C. 2,2′-Thiodi-
ethanol (14 mg, 0.11 mmol, 3 equiv.) was then added to the solu-
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(1 equiv.) in CHCl3 (2 mL). The mixture was stirred for 10 min at
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Received: August 26, 2015
Published Online: November 30, 2015
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© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim