π-extended DPCB for activation-free homogeneous gold catalysis

Article abstract of DOI:10.1002/cctc.201402158

The catalytic properties of bis[chlorogold(I)] complexes that bear the 3,4-bis(2,4,6-tri-tert-butylphenyl)-3,4-diphosphinidenecyclobutene (DPCB) ligand could be improved by suitable extension of the π-conjugation. If the 1-naphthyl substituent was employed in the 1,2-positions in the kinetically stabilized DPCB skeleton, high catalytic activity of the DPCB-bis(chlorogold) complex was induced in the intermolecular alkoxycyclization of 1,6-enyne without activation by a Ag cocatalyst. DFT calculations of the 1,2-diaryl-substituted DPCB derivatives indicated that both suitable energetic reduction of the LUMO level and steric characteristics of the ligand structure are important for the high catalytic activity. The optimized 1-naphthyl-substituted DPCB-chlorogold(I) complex was further employed for catalytic intramolecular cyclizations to afford heterocyclic structures by the activation of terminal acetylene and allene moieties and the hydration of terminal acetylene under the mild conditions.

Full text of DOI:10.1002/cctc.201402158

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DOI: 10.1002/cctc.201402158
p-Extended DPCB for Activation-Free Homogeneous Gold
Catalysis**
Shigekazu Ito,* Masaki Nanko, and Koichi Mikami[a]
The catalytic properties of bis[chlorogold(I)] complexes that
bear the 3,4-bis(2,4,6-tri-tert-butylphenyl)-3,4-diphosphinidene-
cyclobutene (DPCB) ligand could be improved by suitable ex-
tension of the p-conjugation. If the 1-naphthyl substituent was
employed in the 1,2-positions in the kinetically stabilized DPCB
skeleton, high catalytic activity of the DPCB-bis(chlorogold)
complex was induced in the intermolecular alkoxycyclization of
1,6-enyne without activation by a Ag cocatalyst. DFT calcula-
tions of the 1,2-diaryl-substituted DPCB derivatives indicated
that both suitable energetic reduction of the LUMO level and
steric characteristics of the ligand structure are important for
the high catalytic activity. The optimized 1-naphthyl-substitut-
ed DPCB-chlorogold(I) complex was further employed for cata-
lytic intramolecular cyclizations to afford heterocyclic structures
by the activation of terminal acetylene and allene moieties and
the hydration of terminal acetylene under the mild conditions.
Introduction
In the past decades the chemistry of homogenous Au catalysts
has grown tremendously. Various homogenous Au catalysts
have been employed widely for organic synthesis,[1–8] and con-
sequently, precise mechanistic analyses have been devel-
oped.[9–13] One of the popular procedures for the generation of
the catalytically active Au species is the exchange of the chlo-
ride in LAuCl precursors [L=phosphine, N-heterocyclic carbene
(NHC), etc] by treatment with Ag salts as the LAuCl species
normally showed low or almost no catalytic functionality be-
cause of the insufficient activity of the Cl-coordinated Au cen-
ters except for a few examples.[14–16] This conventionally utilized
procedure for homogeneous Au catalysis, however, often ex-
hibits remarkable dependence on the “Ag effect”. Shi and co-
workers proved that several Au-catalyzed organic transforma-
tions scarcely worked in the absence of silver halides.[17] One of
the effective procedures that excludes the Ag effect is to
employ isolable and catalytically active LAuX complexes such
as Gagosz-type complexes [LAu(NTf2)].[18,19] Recently Nolan and
co-workers reported Ag- and acid-free procedures by using
a diaurated structure for highly catalytically active Au spe-
cies.[20] These “Ag-free” processes still require the addition of
a Ag salt to exchange the chloride of the LAuCl precursors
with anionic ligands X, and the Ag effect could exist unless the
resultant Ag salt was removed properly in the purification of
the catalysts.[21,22]
An alternative method for Ag-free homogeneous Au cataly-
sis is to use LAuCl complexes directly. Previously, we found
that several phosphaalkene-chlorogold(I) structures could ex-
hibit catalytic activity for molecular transformations through
the activation of the terminal alkyne without exchange of the
chloride anion.[23–25] This unique catalytic activity would corre-
spond to the strong p-accepting ability of the P=C bond
based on its low LUMO level.[26,27] 3,4-Diphosphinidenecyclobu-
tenes (DPCBs) possess a unique, almost planar p-conjugate
system that includes two P=C moieties and provides relatively
rigid and suitable chelate structures for remarkable catalytic ac-
tivity. To date, Ozawa and Yoshifuji have utilized DPCB chelate
complexes for unique transition-metal catalysis.[28] Moreover,
DPCBs can also be utilized for bis(chlorogold) complexes to
induce considerable distortion of the planar ligand skele-
ton,[23,29] and homogeneous catalytic activity is displayed in
1,6-enyne cycloisomerizations without any Ag activator
(Figure 1).[23] The remarkable short AuÀAu distance caused by
the DPCB distortion reinforces the aurophilic interaction,[30]
which leads to the resultant catalytic activity.
As Ozawa and co-workers have revealed, the catalytic activi-
ty of the mononuclear DPCB chelate complexes depends con-
siderably on the 1,2-diaryl substituents.[31,32] Therefore, the
tuning of the 1,2-diaryl groups is a promising approach to im-
prove and understand the catalytic activity of DPCB-bis(chloro-
gold) complexes. Furthermore, the tuning method for the ho-
[a] Prof. S. Ito, M. Nanko, Prof. K. Mikami
Department of Applied Chemistry
Graduate School of Science and Engineering
Tokyo Institute of Technology
2-12-1 Ookayama, Meguro, Tokyo 152-8552 (Japan)
Fax: (+81)3-5734-2143
E-mail: ito.s.ao@m.titech.ac.jp
[**] DCPB=3,4-bis(2,4,6-tri-tert-butylphenyl)-3,4-diphosphinidenecyclobutene
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/cctc.201402158.
Figure 1. A catalytically active DPCB-bis(chlorogold) complex.
ChemCatChem 2014, 6, 2292 – 2297 2292
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mogeneous chlorogold catalysis is expected to be applicable
to other DPCB-coordinated transition-metal catalysts.
Table 1. Synthesis of 2 and 3 via 2-bromo-1-phosphapropene 1.
In this paper we demonstrate the synthesis of various 1,2-
diaryl-substituted DPCB derivatives, and their structural and
physical properties are discussed based on the observed cata-
lytic activity of the DPCB-bis(chlorogold) complexes in the al-
koxycyclization of 1,6-enyne, the intramolecular cyclization of
propargylic amide and allenyl alcohol, and the acetyl-assisted
hydration of terminal alkynes without activation. The structural
and physicochemical properties suggest that moderate exten-
sion of the p conjugation of the 1,2-diaryl substituents and the
corresponding steric effects were able to improve the catalytic
activity. In addition to the 1,2-diaryl-substituted DPCB deriva-
tives, the related 1,2-cycloalkyl-substituted derivatives were
also employed for activation-free chlorogold catalysis.
Compound
R
Yield of
1 [%]
Yield of
Yield of
3 [%]
2 [%][a]
a
85
96
80
97
83
82
b
c
77
87
85
d
e
83
97
85
85
89
80
f
86
95
66
90
21
14
82
82
86
g
h
Results and Discussion
As displayed in Scheme 1, 2-bromo-1-phosphapopenes 1 were
synthesized by the regioselective halogen–metal exchange of
a kinetically stabilized 2,2-dibromo-1-phosphaethene (dibromo-
methylenephosphine; Mes*=2,4,6-tBu3C6H2),[33] and the subse-
quent coupling of the anionic organophosphorus intermedi-
[a] Combined yield of E,E and E,Z isomers.
confirmed by X-ray crystallography (Figures 2 and 3). The
metric parameters of the DPCB skeleton are compared in
Table 2.[34] Most of the metric parameters of 2b are comparable
to the 1,2-diaryl DPCB derivatives reported previously.[34,36]
However, the P1ÀC1ÀC2ÀP2 skeleton of 2b showed a slightly
twisted conformation, and correspondingly, the four aryl rings
formed a propeller-like structure. Although the Mes* groups
are nearly perpendicular to the PÀC1ÀC2ÀP2 plane (A), the di-
hedral angles between the 1-naphthyl planes (C and D) and
the four-membered ring B indicate the possible extension of
the conjugation effect. The LUMO plots of 2b show the re-
markable contribution of the 1-naphthyl groups (Figure 4), and
the UV/Vis spectroscopic study also supports a reduction of
the HOMO–LUMO energetic difference (Figure S1). The X-ray
structure of 3b indicated that the dual coordination of the
AuCl moiety induced a remarkable distortion of the P=CÀC=P
skeleton to construct the C2-type structure.[23,29] The increase of
the P1ÀC1ÀC2 and P2ÀC2ÀC1 angles also indicates the effect
Scheme 1. Preparation of DPCB derivatives.
ates afforded the corresponding DPCB derivatives (2) together
with small amounts of the E,Z isomers.[23,29] Aromatic hydrocar-
bons and the related aliphatic cyclic structures were employed
as the substituents at the 1,2-positions (R; Table 1). Additional-
ly, the 4-methoxyphenyl derivative 2 f that was successful to
improve the catalytic activity of chelate Pd complexes[31,32,34,35]
was also examined. Although yields of the 1,2-cycloalkyl-substi-
tuted 2g[29] and 2h were low, probably because of the instabil-
ity of the organophosphorus intermediates, the 1,2-diaryl de-
rivatives 2a–f were obtained in high yields. DPCBs 2 were suc-
cessfully converted to the corresponding bis(chlorogold(I))
complexes (3) by reaction with two equivalents of (tht)AuCl
(tht=tetrahydrothiophene) in good yields. The E,Z isomers
were consumed in the course of complexation.
The structures of 2 and 3 were determined from the spec-
troscopic data, and the structures of 2b and 3b were further
Figure 2. An ORTEP drawing of 2d (40% probability levels). Hydrogen atoms
are omitted for clarity. The torsion angle of P1ÀC1ÀC2ÀP2 is 7.7(4)8.
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Figure 3. An ORTEP drawing of 3b (50% probability levels). One of the two
independent molecules is shown. Hydrogen atoms and solvent molecules
(acetonitrile) are omitted for clarity. Bond distances [ꢁ]: P1ÀAu1 2.232(1)/
2.231(1), P2ÀAu2 2.228(1)/2.229(1), Au1ÀCl1 2.283(1)/2.286(1), Au2ÀCl2
2.285(1)/2.281(1), Au1ÀAu2 2.9719(3)/3.0014(2). The torsion angle of P1ÀC1À
C2ÀP2 is 18.3(4)/21.4(7)8
Table 2. Comparison of bond distances [ꢁ] and angles [8] in the DPCB
skeleton.
Figure 4. Plots of the LUMO and LUMO+1 for 2b [M06-2X/6-31G(d)].[37]
ture of methanol and dichloromethane, 3a afforded the cycli-
zation product 5 but in a low yield (Table 3, Entry 1), whereas
the intramolecular cycloisomerization of 4 was catalyzed quan-
titatively.[23] The p-extended 1,2-substituents were then em-
ployed for the chlorogold catalysis. To our delight, 1-naphthyl-
substituted 3b showed quite a high activity for the alkoxycycli-
zation, and 5 was obtained almost quantitatively (Entry 2).
Conversely, 3c, which bears 2-naphthyl groups, showed
a lower catalytic activity than 3b (Entry 3), although the levels
of the frontier orbitals of 2c were almost same as those of 2b
(Supporting Information). However, the extension of the conju-
gation was basically effective, and complexes 3d and 3e
showed a high activity (Entries 4 and 5). 4-Methoxyphenyl-sub-
stituted DPCB was also effective, and 3 f catalyzed the alkoxy-
cyclization to afford 5 in good yield (Entry 6). Cyclopropyl-sub-
stituted DPCB 3g improved the catalytic activity in comparison
with 3a (Entry 7), whereas 3h, which bears cyclohexyl groups,
showed a comparable activity to 3a (Entry 8). Therefore, the
cyclopropyl conjugation effect[39] would be somewhat useful
for the activation-free Au-catalyzed reaction. DFT calculation of
2g indicated a large contribution of the cyclopropyl group to
the LUMO (Supporting Information). The most active catalyst
3b permitted the reduction of the catalytic amount up to
0.5 mol%, although an extension of the reaction time was re-
quired (Entries 9 and 10; turnover number (TON)=92 and 170,
respectively). Very recently Hashmi and co-workers developed
quite active Au catalysts by the use of sterically bulky phos-
phite ligands and accomplished TONs up to 420 for the rele-
Description
2b
1.679(3)
3b
1.670(5)/1.668(4)
P1ÀC1
P2ÀC2
1.669(3)
1.843(2)
1.851(3)
1.521(4)
1.480(4)
1.483(4)
1.397(3)
1.468(4)
1.468(4)
1.684(4)/1.675(4)
1.828(4)/1.818(4)
1.818(4)/1.826(4)
1.504(6)/1.508(5)
1.470(6)/1.481(6)
1.467(6)/1.467(6)
1.399(6)/1.400(5)
1.466(6)/1.456(6)
1.461(6)/1.477(6)
110.5(2)/110.3(2)
110.7(2)/112.5(2)
131.6(3)/129.9(3)
128.2(3)/129.0(3)
134.8(4)/133.7(4)
134.2(4)/135.1(4)
7.6/7.7
P1ÀMes*1
P2ÀMes*2
C1ÀC2
C1ÀC3
C2ÀC4
C3ÀC4
C3ÀC5
C4ÀC6
C1ÀP1ÀMes*1
C2ÀP2ÀMes*2
P1ÀC1ÀC2
P2ÀC2ÀC1
C3ÀC4ÀC6
C4ÀC3ÀC5
AÀB
104.6(1)
105.3(2)
124.4(2)
124.4(2)
134.6(2)
135.8(2)
3.3
75.1
77.4
47.0
42.9
AÀMes*1
BÀMes*2
BÀC
84.5/80.2
78.4/80.4
53.9/43.8
47.4/45.3
BÀD
of the dual coordination of Au, whereas the chelation of DPCB
reduced the corresponding parameters.[34]
The catalytic activity of 3 was monitored in the Ag-activator-
free (phosphaalkene)AuCl-catalyzed alkoxycyclization of 1,6-
enyne 4.[38] Under the reaction conditions that used a 1:1 mix-
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ysis because of the suitable level of conjugation and steric hin-
drance to the Au catalyst (Supporting Information).[44,45]
Table 3. Catalytic activity of 3.
Next we attempted to develop intermolecular reactions by
using 3b and we found that the acetyl-supported hydration of
6[46] was catalyzed successfully under the mild conditions. The
corresponding methylketone derivative 7 was obtained in
a moderate yield (Scheme 2). Although activation with Ag salts
Entry
Catalyst
R
Yield of
Recovery of
5 [%]
4 [%]
1
2
3
4
5
6
7
8
3a
3b
3c
3d
3e
3 f
3g
3h
3b[a]
3b[b]
3b[c]
Ph
45
99
67
88
92
87
75
55
92
85
81
55
<1
32
8
1-Naph
2-Naph
4-PhC6H4
2-PhC6H4
4-MeOC6H4
cPr
6
11
20
45
7
15
18
Scheme 2. Acetyl-assisted hydration of terminal acetylene.
cHex
9
10
11
1-Naph
1-Naph
1-Naph
such as AgSbF6 normally accompanies the Au-catalyzed hydra-
tion reaction, the use of small Au clusters was developed re-
cently and achieved high TONs.[47] However, the Au-catalyzed
processes without any activation process would also be attrac-
tive synthetic approaches in terms of simplified reaction condi-
tions and the avoidance of residual contamination of the prod-
ucts.
[a] 1 mol% of 3b, 4 h. [b] 0.5 mol% of 3b, 24 h. [c] Reaction without di-
chloromethane for 24 h.
vant 1,6-enyne cycloisomerization.[40] Thus, 3b, which shows
a comparable catalytic efficiency to the phosphite-gold cata-
lysts, might be effective for practical homogeneous Au cataly-
sis. Additionally, 3b catalyzed the alkoxycyclization in the ab-
sence of dichloromethane (Entry 11). The dual coordination of
Au with the DPCB ligand is also decisive for the Ag-free Au-cat-
alyzed reaction.[41]
Conclusions
Adequate p-conjugation effects were effective to enforce activ-
ity of the homogeneous chlorogold catalyst that bears the 3,4-
bis(2,4,6-tri-tert-butylphenyl)-3,4-diphosphinidenecyclobutene
(DPCB) ligand system. The 1-naphthyl structure could be em-
ployed as the optimized DPCB ligand, which enables several
activation-free Au-catalyzed cyclization and hydration reac-
tions. The structural characteristics of the 1-naphthylated DPCB
derivatives would also be advantageous to understand the de-
tailed mechanism of the activation-free Au-catalyzed reactions.
Phosphaalkene-chlorogold complexes have not catalyzed reac-
tions by the activation of inner alkynes to date, which is an im-
portant aspect of these particular homogeneous Au-catalyzed
reactions. However, the bis(chlorogold) structure of 3 is appli-
cable for further development based on dual Au catalysis[5,8,21]
and the helically distorted molecular skeleton. The exploration
of Au-catalyzed reactions by using complexes 3 and the relat-
ed phosphaalkene-gold complexes under the activation-free
conditions is in progress.
As described above, the remarkable difference of catalytic
activity between 3b and 3c could not be explained only by
the electronic properties. UV/Vis spectra of 3c show larger ab-
sorption coefficients and indicate a higher planarity between
the four-membered ring and 2-naphthyl groups, whereas 3b
displayed slightly redshifted absorptions. However, 3b showed
somewhat better solubility under the conditions employed in
comparison with other DPCB-bis(chlorogold) complexes. Com-
plex 3b showed enough solubility in methanol, which would
be advantageous for catalytic activity under CH2Cl2-free condi-
tions (Table 1, Entry 11). However, the possibly more planar
skeleton and relatively rigid structure of 2c indicates the disad-
vantageous character of 3c for the homogeneous reaction
conditions.
The results of the alkoxycyclization, which include the inter-
molecular formation of the CÀO bond stimulated us to use 3b
for other reactions, and we next examined intramolecular cycli-
zations that afford heterocyclic structures. A propargylic amide
could be cyclized in the presence of 3b to give the corre-
sponding methylene-3-oxazoline derivative[42] under AgX-free
conditions at 258C, although a low yield (29%) was observed
(Table S1). The intramolecular cyclization of a hydroxyallene
(hexa-4,5-dien-1-ol) could also be catalyzed by 3b without
a AgX cocatalyst, and the corresponding furan derivative[43]
was isolated in 26% yield (Table S2). Almost every 3 except 3b
showed a low catalytic activity. However, the catalytic activity
of 3e was slightly superior in comparison with other DCPB-
bis(chlorogold) complexes, and thus the 2-phenylphenyl group
might also be available to the phosphaalkene-chlorogold catal-
Experimental Section
All manipulations with organolithium reagents were performed
under an Ar atmosphere using standard Schlenk techniques, and
the solvents were dried by appropriate methods. 1H, 13C{1H}, and
31P{1H} NMR spectra were recorded by using a Bruker AV300M
spectrometer in CDCl3 at 298 K with internal Me4Si (1H, 13C) or ex-
ternal 85% H3PO4 (31P) standards. MS spectra were taken by using
a JEOL T100 LC spectrometer. XRD data were collected by using
a Rigaku RAXIS-Rapid diffractometer, and structures were solved by
direct methods (SHELXL-97).[48] The X-ray structure solution and re-
finement were performed by using the Yadokari-XG software.[49]
DFT calculations for a single isolated species were performed by
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using the Gaussian 09 program package.[50] UV/Vis spectra were re-
corded by using a Jasco V570 spectrometer. 2,2-Dibromo-1-(2,4,6-
tri-tert-butylphenyl)-1-phosphaethene was synthesized according
to our previous report.[33]
arom.), 7.17 (t, J=2.1 Hz, 4H, arom.), 7.00 (t, J=7.8 Hz, 2H, arom.),
6.84 (t, J=7.2 Hz, 2H, arom.), 6.76 (d, J=8.7 Hz, 2H, arom.), 6.71 (d,
J=6.9 Hz, 2H, arom.), 6.58 (t, J=8.3 Hz, 2H, arom.), 1.57 (s, 36H, o-
tBu), 1.21 ppm (s, 18H, p-tBu); 31P{1H} NMR (121 MHz, CDCl3): d=
132.9 ppm; 13C{1H} NMR (75 MHz, CDCl3): d=167.9 (dd, JPC
29.4 Hz and 8.5 Hz), 157.1 (d, JPC =13.0 Hz), 156.9, 132.6, 130.4,
129.0, 128.0, 127.3, 126.4, 125.8 (d, JPC =4.1 Hz), 124.7 (d, JPC
=
=
Preparation of 1b
2.3 Hz), 123.2 (t, JPC =5.0 Hz), 120.5 (t, JPC =14.3 Hz), 39.3, 35.2, 34.7,
31.1 ppm; HRMS (APCI): m/z: calcd for C60H73Au2Cl2NaP2: 1341.3715
[M+Na]+; found: 1341.3749.
To a solution of 2,2-dibromo-1-(2,4,6-tri-tert-butylphenyl)-1-phos-
phaethene (Mes*P=CBr2; 2.24 g, 5.00 mmol) in THF (40 mL) was
added butyllithium (5.50 mmol, 1.6m solution in hexane, 1m=
1 moldmÀ3) at À788C, and the mixture was stirred for 15 min. 1-
Naphthaldehyde (5.50 mmol) was added at À788C, and the mix-
ture was stirred for 15 min. After the reaction mixture was warmed
to 08C, chlorotrimethylsilane (0.58 mL, 6.0 mmol) was added, and
the reaction mixture was stirred for 3 h at 408C. After the residue
was extracted with hexane, and the solvent was removed in vacuo.
The resultant residue was purified by silica-gel column chromatog-
raphy (hexane/AcOEt=30:1) to afford 1b as a colorless solid (2.9 g,
Alkoxycyclization of 4 (Table 3, Entry 1–8)
To a solution of 3 (3 mol%) in dichloromethane (0.5 mL) and meth-
anol (0.5 mL) was added a solution of 4 (25.3 mg, 0.10 mmol) in
methanol (0.5 mL) at RT. After it was stirred for 2 h, the reaction
mixture was loaded directly onto a silica-gel column (hexane/ethyl
1
acetate 6:1) to give 5 as a colorless oil. H NMR (300 MHz, CDCl3):
1
96%). H NMR (300 MHz, CDCl3): d=8.50 (d, J=8.2 Hz, 1H, arom.),
d=5.02 (s, 1H, =CH), 4.96 (s, 1H, =CH), 3.70 (s, 6H, CO2Me), 3.17 (s,
3H, OMe), 2.79–2.92 (m, 3H, CH2), 2.53 (dd, J=13.4 Hz and 8.6 Hz,
1H, CH2), 1.98 (dd, J=13.4 Hz and 9.4 Hz, 1H, CH2), 1.16 (s, 3H,
Me), 1.10 ppm (s, 3H, Me); 13C{1H} NMR (75 MHz, CDCl3): d=172.0,
171.9, 148.2, 110.5, 58.6, 52.69, 52.65, 49.1, 49.0, 43.4, 36.0, 22.6,
22.2 ppm.
7.98–7.92 (m, 2H, arom.), 7.86 (d, J=8.4 Hz, 1H, arom.), 7.63–7.52
(m, 3H, arom.), 7.44 (d, J=14.7 Hz, 2H, arom.), 6.51 (d, J=13.5 Hz,
1H, CH), 1.52 (s, 9H, o-tBu), 1.38 (s, 9H, o-tBu), 1.35 (s, 9H, p-tBu),
0.25 ppm (s, 9H, TMS); 31P{1H} NMR (121 MHz, CDCl3): d=
1
258.1 ppm; 13C{1H} NMR (75 MHz, CDCl3): d=167.4 (d, JPC
=
63.6 Hz, P=C), 153.4 (d, JPC =2.5 Hz), 153.3 (d, JPC =2.2 Hz), 150.8,
140.8, 137.6, 137.1 (d, JPC =10.4 Hz), 136.9, 133.7, 130.3, 128.9,
126.0, 125.9, 125.2 (d, JPC =13.2 Hz), 124.2 (d, JPC =4.9 Hz), 122.2 (d,
Hydration of 6
J
PC =5.3 Hz), 71.4, 37.9 (d, JPC =13.4 Hz), 35.1, 32.8 (d, JPC =7.1 Hz),
To a solution of 3b (4.0 mg, 3 mmol) in 1,4-dioxane (0.5 mL) was
32.5 (d, JPC =6.9 Hz), 31.4, 0.33 ppm; HRMS (atmospheric pressure
chemical ionization; APCI): m/z: calcd for C33H47BrOPSi: 597.2317
[P+H]+; found 597.2362.
added
a solution of 1-phenylprop-2-yn-1-yl acetate (17.4 mg,
0.10 mmol) in 1,4-dioxane (0.25 mL) and H2O (0.25 mL) at 258C.
After it was stirred for 24 h, the reaction mixture was loaded direct-
ly onto a silica-gel column and eluted with hexane/ethyl acetate
10:1 to give 2-oxo-1-phenylpropyl acetate as a colorless oil.
1H NMR (300 MHz, CDCl3): d=7.40 (brs, 5H, arom.), 5.97 (s, 1H, CH),
2.19 (s, 3H, CH3), 2.11 ppm (s, 3H, CH3); 13C{1H} NMR (75 MHz,
CDCl3): d=201.7, 170.3, 133.1, 129.4, 129.1, 128.1, 81.0, 26.2,
20.8 ppm.
Preparation of 2b
To a solution of 1b (0.600 g, 1.00 mmol) in THF (15 mL) was added
tert-butyllithium (2.1 mmol, 1.55m solution in pentane) at À788C,
and the mixture was stirred for 15 min. The reaction mixture was
warmed to 08C, and 1,2-dibromoethane (43 mL, 0.5 mmol) was
added. The reaction mixture was warmed to 408C and stirred for
4 h. After concentration in vacuo, the residue was extracted with
hexane, and the solvent was removed in vacuo. The crude residue
was purified by silica-gel column chromatography (hexane/ethyl
acetate=20:1) to give 2b (0.83 g, 97%, (E,E)/(E,Z)=76:24) as
X-ray crystallography of 2b
C60H72P2, yellow prisms (CH2Cl2), MW =855.12, crystal dimensions=
0.38ꢂ0.35ꢂ0.23 mm3, monoclinic, space group P21/a (#14), a=
19.9929(6), b=12.9744(4), c=20.4275(6) ꢁ, b=100.2460(10)8, V=
1
a yellow solid. H NMR (300 MHz, CDCl3): d=7.38 (d, J=7.8 Hz, 4H,
5214.3(3) ꢁ3, Z=4, l=0.71075 ꢁ, T=123 K, 1calcd =1.089 gcmÀ3
,
arom.), 7.26 (s, 4H, arom.), 7.05 (d, J=8.6 Hz, 2H, arom.), 6.95 (t,
J=7.2 Hz, 2H, arom.), 6.89 (t, J=7.7 Hz, 2H, arom.), 6.73 (d, J=
7.1 Hz, 2H, arom.) 6.63 (t, J=7.7 Hz, 2H, arom.), 1.62 (s, 36H, o-
mMoK =0.119 mmÀ1, F000 =1848, 49892 total reflections (2qmax
=
a
54.968), index ranges=À25 ꢀ h ꢀ 25, À16 ꢀ k ꢀ 16, À26 ꢀ l ꢀ
26, 11948 unique reflections (Rint =0.0712), R1=0.0908 (I>2s(I)),
0.1023 (all data), wR2=0.2806 (I>2s(I)), 0.2873 (all data), S=2.000
(812 parameters).
tBu), 1.36 ppm (s, 18H, p-tBu); 31P{1H} NMR (121 MHz, CDCl3): d=
3
168.3 [(E,Z) isomer: 193.1 (d, 3JP,P =13.3 Hz), 173.5 ppm (d, JP,P
=
13.3 Hz)]; 13C{1H} NMR (75 MHz, CDCl3): d=177.0 (dd, JPC =16.8 Hz
and 9.2 Hz), 156.7 (d, 2JPC =5.0 Hz), 154.7, 150.1, 124.5–130.3 (m,
8C), 121.5, 119.5, 38.4, 34.9, 33.4, 31.5 ppm; HRMS (APCI): m/z:
calcd for C60H73P2: 855.5188 [P+H]+; found: 855.5225.
X-ray Crystallography of 3b
C60H72P2Au2Cl2·C2H3N, yellow prisms (CH2Cl2/MeCN), MW =1361.00,
3
¯
crystal dimensions=0.28ꢂ0.22ꢂ0.15 mm , triclinic, space group P1
Preparation of 3b
(#2), a=14.6352(5), b=16.4465(5), c=25.2864(7) ꢁ, a=90.0373(8),
A mixture of 2b (86.0 mg, 0.100 mmol), (tht)AuCl (0.195 mmol),
and CH2Cl2 (1 mL) was stirred for 1 h at RT. After evaporation under
reduced pressure, the resultant residue was dissolved in CH2Cl2
(0.2 mL), and the resulting mixture was recrystallized from hexane
to afford 3b (108 mg, 82%) as a red solid. 1H NMR (300 MHz,
CDCl3): d=7.48 (d, J=8.4 Hz, 2H, arom.), 7.43 (d, J=8.1 Hz, 2H,
b=95.3300(11), g=107.1027(12)8, V=5789.6(3) ꢁ3, Z=4, l=
0.71075 ꢁ, T=123 K, 1calcd =1.561 gcmÀ3, mMoK =5.248 mmÀ1, F000
=
a
2704, 52162 total reflections (2qmax =54.968), index ranges=À18
ꢀ h ꢀ 18, À18 ꢀ k ꢀ 21, À32 ꢀ l ꢀ 32, 25865 unique reflections
(Rint =0.0680), R1=0.0412 (I>2s(I)), 0.0501 (all data), wR2=0.1136
(I>2s(I)), 0.1290 (all data), S=0.814 (1368 parameters).
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 2292 – 2297 2296

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Acknowledgements
This work was supported in part by Grants-in-Aid for Scientific
Research (Nos. 22350058, 23655173, and 25109518) from the
Ministry of Education, Culture, Sports, Science and Technology,
Japan, the Collaborative Research Program of Institute for Chem-
ical Research, Kyoto University (grant # 2013-10), and Nissan
Chemicals Co. Ltd. The authors thank Prof. Dr. Hiroharu Suzuki
and Prof. Dr. Masataka Oishi of the Tokyo Institute of Technology
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Published online on July 10, 2014
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ChemCatChem 2014, 6, 2292 – 2297 2297