An efficient direct activation method transferring diastereopure platinum complex of BIPHEP to highly efficient Lewis acid catalyst for enantioselective carbonyl-ene reaction

Article abstract of DOI:10.1016/j.molcata.2005.12.006

An efficient direct activation method was developed to transfer diastereopure λ-[(BIPHEP)Pt(S-BINOL)] to highly active and selective enantiopure Lewis acid λ-[(BIPHEP)Pt](SbF₆)₂ by silver hexafluoroantimonate(AgSbF₆) for t

Full text of DOI:10.1016/j.molcata.2005.12.006

Journal of Molecular Catalysis A: Chemical 248 (2006) 42–47
An efficient direct activation method transferring diastereopure platinum
complex of BIPHEP to highly efficient Lewis acid catalyst for
enantioselective carbonyl-ene reaction
He-Kuan Luoa,∗, Herbert Schumannb
a Institute of Chemical and Engineering Sciences(ICES), 1 Pesek Road,
Jurong Island, Singapore 627833, Singapore
b Institut fu¨r Chemie, Technischen Universita¨t Berlin (TU-Berlin), Straße des 17,
Juni 135, D-10623 Berlin, Germany
Received 6 November 2005; received in revised form 3 December 2005; accepted 8 December 2005
Available online 19 January 2006
Abstract
An efficient direct activation method was developed to transfer diastereopure ␭-[(BIPHEP)Pt(S-BINOL)] to highly active and selective
enantiopure Lewis acid ␭-[(BIPHEP)Pt](SbF6)2 by silver hexafluoroantimonate(AgSbF6) for the enantioselective carbonyl-ene reactions. Both
enantioselective glyoxylate-ene reactions between ethyl glyoxylate and alkenes, and enantioselective carbonyl-ene reactions between phenylgly-
oxal and alkenes were studied demonstrating good catalytic activity and enantioselectivity. Particularly, for the enantioselective carbonyl-ene
reaction between phenylglyoxal and 2,3-dimethyl-1-butene, the Lewis acid catalyst ␭-[(BIPHEP)Pt](SbF6)2 generated with this direct activation
method by silver hexafluoroantimonate(AgSbF6) could give excellent ee values high up to 94%.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Enantioselectivity; Carbonyl-ene; BIPHEP; Platinum; Activation
oxylate and methylenecyclohexane to give (S)-ethyl 3-(1ꢀ-
cyclohexenyl)-2-hydroxypropionate with 96% ee, similarly, the
complex[Cu(S,S)-tert-butylbis(oxazolinyl)](OTf)2 gave 86% ee
for the same reaction. Optically active ␤-ketoiminato cationic
cobalt(III) complex was reported by Yamada and co-workers
[6] to be an efficient catalyst for enantioselective carbonyl-ene
reaction to gave 88% ee in the carbonyl-ene reaction between
phenylglyoxal and ␣-methylstyrene, and 94% ee in the carbonyl-
enereactionbetweenphenylglyoxalandmethylenecyclohexane.
Ding and co-workers [3d] reported an extremely efficient Ti
catalyst of modified BINOL ligands. Under nearly solvent-free
conditions, 6,6ꢀ-I2-or6,6ꢀ-(CF3)2-BINOL-Ti-catalystcouldcat-
alyze the enantioselective carbonyl-ene reaction of glyoxylate
ester with a variety of olefins at very low catalyst loadings (up
to 0.01 mol%) affording the corresponding ␣-hydroxy esters in
high yields and excellent enantioselectivities.
1. Introduction
The enantioselective carbonyl-ene reaction catalyzed by chi-
ral Lewis acid is an important methodology for carbon–carbon
bond construction to prepare optically active homoallylic alco-
hols [1] which could then be transferred into more function-
alized compounds by further reaction on its carbon–carbon
double bond, hydroxyl and carbonyl groups. The key of this
topic is searching for highly efficient and selective chiral cat-
alyst to gain high ee values. Up to now, a variety of transi-
tion metal complexes have been studied involving Al [2], Ti
[3], Ln [4], Cu [5], Co [6], Pd and Pt [7], etc., among which
some could achieve high efficiency and enantioselectivity in the
carbonyl-ene reaction. Evans et al. [5b] reported that the C2-
symmetric complex [Cu(S,S)-tert-butylbis(oxazolinyl)](SbF6)2
could catalyze the glyoxylate-ene reaction between ethyl gly-
Chiral diphosphine-palladium and platinum complexes
which are usually highly efficient and selective catalysts for
Diels–Alder reaction [7a,8], have also been proved to be
highly efficient and selective catalysts for enantioselective
∗
Corresponding author. Tel.: +65 6796 3827; fax: +65 6316 6182.
E-mail address: luo hekuan@ices.a-star.edu.sg (H.-K. Luo).
1381-1169/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.molcata.2005.12.006

H.-K. Luo, H. Schumann / Journal of Molecular Catalysis A: Chemical 248 (2006) 42–47
43
carbonyl-ene reaction. Mikami and co-workers [7b] reported
that {Pd(CH3CN)2[(S)-Tol-BINAP]}(SbF6)2 could catalyze
the glyoxylate-ene reaction between ethyl glyoxylate and
methylenecyclohexane to give (S)-ethyl-3-(1ꢀ-cyclohexenyl)-2-
hydroxypropionate with 78% ee and 88% yield under room tem-
perature. More recently, {[(S)-MeOBIPHEP]Pt}(SbF6)2 was
reported by Gagne and co-workers [7c] to be efficient and selec-
tive catalysts for the same glyoxylate-ene reaction to give 77%
ee and 67% conversion under −50 ◦C for 5 h run.
Besides BINAP (atropos), BIPHEP (tropos) is another pop-
ular diphosphine ligand with potential application in asymmet-
ric catalysis. There are two methodologies have been reported
to resolve palladium or platinum complexes of BIPHEP to
chiral catalyst. Mikami et al. reported that palladium com-
plexes of BIPHEP could be resolved with 3,3ꢀ-dimethyl-2,2ꢀ-
diamino-1,1ꢀ-binaphthyl (DM-DABN) [8d] to give enantiop-
ure Lewis acid (R)-[(BIPHEP)Pd(CH3CN)2](SbF6)2 which was
proved to be an efficient catalyst for the Hetero Diels–Alder
reaction between ethyl glyoxylate and 1,3-cyclohexadiene
to give 82% ee. Mikami et al. further reported that the
diastereopure (R)-[(BIPHEP)Pd(R-DABN)(SbF6)2[R-DABN:
(R)-diaminobinaphthyl]] was an activated highly efficient and
enantioselective catalyst [8e] for the Hetero Diels–Alder reac-
tion between ethyl glyoxylate and 1,3-cyclohexadiene to give
92% ee and 75% yield under room temperature, the key of this
catalyst is the chiral activator DABN which could completely
control the BIPHEP-Pd chirality and significantly increase
the catalytic activity. In another methodology, Gagne and co-
workers [7a] demonstrated that platinum complex of BIPHEP
could be resolved with (S)-BINOL, the ␦- and ␭-[(BIPHEP)Pt(S-
BINOL)] could be each isolated to give corresponding sin-
gle diastereoismer. After liberation of (S)-BINOL, the ␦- or
␭-[(BIPHEP)Pt]2+ fragment was proved to be an efficient cat-
alyst for Diels–Alder reaction and glyoxylate-ene reaction. In
this approach BIPHEP was used as the sole source of chi-
rality to achieve high ee in asymmetric catalysis since coor-
dination of BIPHEP with platinum slows the atropintercon-
version. After diastereopure ␦- or ␭-[(BIPHEP)Pt(S-BINOL)]
is isolated, the key of this methodology is to find an effi-
cient activator or method to liberate S-BINOL from plat-
inum center to give the ␦- or ␭-[(BIPHEP)Pt]2+ fragment and
the activator should have minimum influence to the reaction.
Two methods were used by Gagne. The first method (method
3 in Scheme 1) is a two-step activation, firstly to convert
diastereopure ␦- or ␭-[(BIPHEP)Pt(S-BINOL)] to enantiop-
ure ␦- or ␭-[(BIPHEP)PtCl2] which was then transferred to
activated catalyst [(BIPHEP)Pt](SbF6)2 or [(BIPHEP)Pt](OTf)2
by reaction with corresponding silver salt. The resulting ␭-
[(BIPHEP)Pt](SbF6)2 could catalyze the glyoxylate-ene reac-
tion between ethyl glyoxylate and methylenecyclohexane to
give 70% ee. The second method (method 2 in Scheme 1)
is a treatment of ␦- or ␭-[(BIPHEP)Pt(S-BINOL)] solution
with trifluoromethanesulfonic acid (HOTf) to give enantiop-
ure catalyst ␦- or ␭-[(BIPHEP)Pt](OTf)2 which could catalyze
the Diels–Alder reaction between oxazolidinone and cyclopen-
tadiene to give cycloadduct with 92–94% ee (93:7 endo:
exo).
Scheme 1. Three activation methods transferring ␭-[(BIPHEP)Pt(S-BINOL)] to
activated catalyst.
In the enantioselective glyoxylate-ene reaction studies
between ethyl glyoxylate and methylenecyclohexane using
␭-[(BIPHEP)Pt(S-BINOL)] as catalyst precursor, we found
that the in situ activated catalyst system by treatment of ␭-
[(BIPHEP)Pt(S-BINOL)] solution with stoichiometric amount
of HOTf, demonstrated unexpected low enantioselectivity and
low yield (see Table 1, entry 3, 10% ee, 25% yield), fur-
Table 1
Glyoxylate-ene reactions between ethyl glyoxylate and alkenes
Entry
Alkene
Activator
Yielda (%)
eeb (%)
1
2
3
4
5
6
7c
8d
1a
1a
1a
1b
1b
1b
1a
1a
AgSbF6
AgOTf
HOTf
AgSbF6
AgOTf
HOTf
88
52
25
85
73
7
70
76
10
52
58
1
–
HOTf
HCl
0
16
Racemic
Reaction conditions: all reactions were run at room temperature for 5 h. Catalyst,
0.0125 mmol (5 mol%); ethyl glyoxylate, 0.5 mmol; alkene, 0.25 mmol.
a
Isolated yield with flash chromatography.
Determined by GC with a CYCLODEX-B column in case of methylenecy-
b
clohexane, by HPLC with a Chiracel AS column in case of ␣-methylstyrene.
c
␭-[(BIPHEP)Pt(S-BINOL)] was not added, only 0.025 mmol HOTf was used
to carry out the reaction.
d
0.025 mmol HCl was used as catalyst instead of platinum catalyst.

44
H.-K. Luo, H. Schumann / Journal of Molecular Catalysis A: Chemical 248 (2006) 42–47
Scheme 2. Proposed equilibration in the reaction of ␭-[(BIPHEP)Pt(S-BINOL)] with HOTf.
thermore, side reactions were always found to give impuri-
ties. The reason is probably because when the molar ratio of
HOTf/Pt is approaching to 2, the reaction of ␭-[(BIPHEP)Pt(S-
BINOL)] with HOTf is not complete and is slightly reversible
(see Scheme 2), which may result in the existence of a small
amount of HOTf. A small amount of free HOTf could signifi-
cantly influence this reaction. In fact, a comparative reaction by
using the same amount of HOTf showed that no product was
found, but only some impurities were formed (see Table 1, entry
7). While, inorganic acid HCl could catalyze the glyoxylate-ene
reaction between ethyl glyoxylate and methylenecyclohexane to
give clean product, of course the product is racemic (see Table 1,
entry 8). Therefore, it is necessary to find an alternative effi-
cient activator or method to transfer ␭-[(BIPHEP)Pt(S-BINOL)]
directly to highly efficient and highly enantioselective catalyst
␭-[(BIPHEP)Pt]2+ for the enantioselective carbonyl-ene reac-
tion, and the activator should has no evident negative influence
on the reaction.
cate that AgSbF6 and AgOTf are efficient activators for ␭-
[(BIPHEP)Pt(S-BINOL)].
2.2. Enantioselective carbonyl-ene reactions between
phenylglyoxal and alkenes
So far, the platinum complexes of BIPHEP have been
shown to be efficient catalyst for the glyoxylate-ene reac-
tions between ethyl glyoxylate and alkenes, but this catalyst
has not been explored for the enantioselective carbonyl-ene
reaction of phenylglyoxal. The significant improvement with
AgSbF6/AgOTf activation method encouraged us to carry out
the enantioselective carbonyl-ene reactions between phenylgly-
oxal and various alkenes, including methylenecyclohexane, 2,3-
dimethyl-1-butene and 2,4,4-trimethyl-1-pentene. As expected
a significant improvement was also achieved for both catalytic
activity and enantioselectivity. For all the three carbonyl-ene
reactions between phenylglyoxal and the three alkenes, the
AgSbF6 activation method gives the best results (see Table 2,
entry 1 corresponding to methylenecyclohexane, 80% yield,
83% ee; entry 4 corresponding to 2,3-dimethyl-1-butene, 73%
Here, we report an efficient direct activation method using
hexafluoroantimonate (AgSbF6) or silver trifluoromethanesul-
fonate (AgOTf) as activators to transfer diastereopure ␭-
[(BIPHEP)Pt(S-BINOL)] to highly active and selective enan-
tiopure Lewis acid for enantioselective carbonyl-ene reactions
with ee values as high as 94%.
Table 2
Carbonyl-ene reactions between phenylglyoxal and alkenes
2. Results and discussions
2.1. Enantioselective glyoxylate-ene reactions between
ethyl glyoxylate and alkenes
Instead of HOTf, the ␭-[(BIPHEP)Pt(S-BINOL)] solution
was treated with two equivalent silver hexafluoroantimonate
(AgSbF6) or silver trifluoromethanesulfonate (AgOTf). After
25 min stirring under room temperature, a purple solution
was given, then 0.50 mmol ethyl glyoxylate and 0.25 mmol
methylenecyclohexane were added. After routine work up, we
surprisingly found that both catalytic activity and enantioselec-
tivity were enhanced significantly relative to HOTf activation
method. The isolated yield was increased from 25% to 88% and
52%, respectively; the enantioselectivity was increased from
10% ee to 70% ee and 76% ee, respectively (see Table 1,
entries 1–3). For the glyoxylate-ene reaction between ethyl gly-
oxylate and ␣-methylstyrene, the isolated yield was increased
from 7% to 85% and 73%, respectively; the enantioselectivity
was increased from 1% ee to 52% ee and 58% ee, respec-
tively (see Table 1, entries 4–6). These results clearly indi-
Entry
Alkene
Activator
Yielda (%)
eeb (%)
1
2
3
4
5
6
7
8
9
1a
1a
1a
1c
1c
1c
1d
1d
1d
AgSbF6
AgOTf
HOTf
AgSbF6
AgOTf
HOTf
AgSbF6
AgOTf
HOTf
80
45
Littlec
73
22
12
65
44
83
69
–
94
93
78
86
67
35
23
Reaction conditions: all the reactions were run at room temperature for 5 h.
Catalyst, 0.0125 mmol (5 mol%); phenylglyoxal, 0.5 mmol; alkene, 0.25 mmol.
a
Isolated yield with flash chromatography.
Determined by HPLC with a Chiralcel OD-H column.
Not pure enough to get ee.
b
c

H.-K. Luo, H. Schumann / Journal of Molecular Catalysis A: Chemical 248 (2006) 42–47
45
Table 3
enantioselectivity is still excellent because the chiral platinum
catalyst is expensive.
Effect of catalyst loading in the enantioselective carbonyl-ene reaction between
phenylglyoxal and 2,3-dimethyl-1-butene
2.4. The effect of anions
Generally, for all the enantioselective carbonyl-ene reactions
including ethyl glyoxylate and phenylglyoxal, ␭-[(BIPHEP)Pt]
(SbF6)2 gave better yield than ␭-[(BIPHEP)Pt](OTf)2. This
Entry
Catalyst loading (mol%)
Yielda (%)
eeb (%)
2+
1
2
3
4
5
6
5
2
1
0.5
0.2
0.1
73
72
64
54
53
40
94
94
94
93
91
91
result is consistent with the result of {[(S)-MeOBIPHEP]Pt}
catalyst[7c]. ThereasonisprobablybecauseSbF6 isagoodleav-
ing group, while OTf has relatively stronger coordination capa-
bility with platinum center, which may result in the decrease of
coordination opportunities between platinum center and phenyl-
glyoxal (see Scheme 3).
All the reactions were run for 5 h under room temperature.
a
Isolated yield with flash chromatography.
Determined by HPLC with a Chiralcel OD-H column.
b
3. Summary
yield, 94% ee; entry 7 corresponding to 2,4,4-trimethyl-1-
pentene, 65% yield, 86% ee). The AgOTf activation method
gives lower yield and ee’s (see Table 2, entry 2 corresponding
to methylenecyclohexane, 45% yield, 69% ee; entry 5 corre-
sponding to 2,3-dimethyl-1-butene, 22% yield, 93% ee; entry
8 corresponding to 2,4,4-trimethyl-1-pentene, 44% yield, 67%
ee). Obviously both of AgSbF6 and AgOTf activations are much
better than the HOTf activation method (see Table 2, entries 3,
6 and 9 corresponding to methylenecyclohexane, 2,3-dimethyl-
1-butene and 2,4,4-trimethyl-1-pentene, respectively).
An efficient direct activation method was developed to trans-
fer diastereopure ␭-[(BIPHEP)Pt(S-BINOL)] to highly active
and selective enantiopure Lewis acid ␭-[(BIPHEP)Pt](SbF6)2
by silver hexafluoroantimonate (AgSbF6). With this activation
method the enantioselective glyoxylate-ene reactions between
ethyl glyoxylate and alkenes, and the carbonyl-ene reac-
tions between phenylglyoxal and alkenes were studied. ␭-
[(BIPHEP)Pt](SbF6)2 was proved to be particularly highly effi-
cient and enantioselective catalyst for the carbonyl-ene reaction
between phenylglyoxal and 2,3-dimethyl-1-butene with ee as
high as 94%, even at very low catalyst loading (0.1 mol%),
the ee% was still as high as 91%. This efficient activation
method made the methodology to resolve racemic catalyst with
S-BINOL more valuable, and provided an alternative activa-
tion way in the asymmetric catalysis when using diastereopure
diphosphine/platinum/S-BINOL complex as catalyst precursor.
2.3. Study on catalyst loading
In order to test the capability of this unique catalyst acti-
vation method and the catalyst system generated, the catalyst
loading was dropped from 5 mol% down to 0.1 mol% for the
carbonyl-ene reaction between phenylglyoxal and 2,3-dimethyl-
1-butene, see Table 3. It was found that the isolated yield was
decreased from 73% to 40%, while the enantioselectivity was
only slightly dropped, even at 0.1 mol% catalyst loading, the
ee is still excellent (91%), demonstrating a highly efficient and
highly enantioselective catalyst system. It is very important for
industrial applications by using low catalyst loading while the
4. Experimental
4.1. General considerations
All manipulations involving air and/or moisture sensitive
materials were carried out under an atmosphere of nitrogen
Scheme 3. Ligand/counterion exchange equilibrations.

46
H.-K. Luo, H. Schumann / Journal of Molecular Catalysis A: Chemical 248 (2006) 42–47
by using standard Schlenk line techniques in dried glassware.
Dichloromethane was distilled from CaH2. Ethyl glyoxylate was
freshly distilled prior to use. Pure phenylglyoxal was obtained
by drying phenylglyoxal hydrate at 90 ◦C under vacuum and was
used freshly. ␭-[(BIPHEP)Pt(S-BINOL)] was prepared accord-
ing to a reported method [7a].
(R)enantiomer tr = 25 min (minor), (S)enantiomer tr = 26 min
(major)).
4.5. Preparation of ethyl
2-hydroxy-4-phenyl-4-pentenoate (3b)
4.2. Catalyst activation
Two methods of catalyst activation were used and com-
pared. In method A, a small Schlenk was charged with 12.5 mg
(0.0125 mmol) ␭-[(BIPHEP)Pt(S-BINOL)] and AgSbF6 (or
AgOTf) (2.0 equiv.), after 2 mL dichloromethane was added, the
resulting mixture was stirred for 25 min under nitrogen atmo-
sphere at room temperature, the color changed from pale yellow
to deep purple gradually. In method B, a small Schlenk was
firstly charged with 12.5 mg (0.0125 mmol) ␭-[(BIPHEP)Pt(S-
BINOL)], then 2 mL dichloromethane was added and stirred
until platinum complex ␭-[(BIPHEP)Pt(S-BINOL)] was dis-
solved completely, the solution was then treated with HOTf
(2.2 ␮L, 2.0 equiv.), resulting in an immediate color change from
light yellow to near colorless. The resulting mixture was stirred
for 5 min under nitrogen atmosphere at room temperature before
substrates were added.
The title compound was prepared according to the gen-
eral procedure using 0.5 mmol freshly distilled ethyl glyoxylate
and 0.25 mmol ␣-methylstyrene. Pure product was obtained
by column chromatography over silica gel eluted with hex-
ane/ethyl acetate (5:1). 1H NMR (CDCl3, 300 MHz, δ): 1.26 (t,
–CH2CH3), 2.79 (OH), 2.90, 3.10 (dd,dd, –CH2–), 4.05–4.15
(m, –OCH2CH3), 4.28–4.32 (m, –CH(OH)), 5.25, 5.44 (s,s,
–C CH2), 7.31–7.47 (m, Ph–H). 13C NMR (CDCl3, 300 MHz,
δ): 14.5, 41.0, 62.0, 69.6, 116.6, 126.9, 128.1, 128.8, 140.8,
144.0, 174.8. Enantiomeric excess was determined by HPLC
with a Chiralcel AS column (5.0% 2-propanol in hexane, flow
1.0 mL/min, (S)enantiomer RT = 11 min (major), (R)enantiomer
RT = 17 min (minor)).
4.6. Preparation of 3-(1ꢀ-cyclohexenyl)-2-hydroxy-1-
phenylpropan-1-one (3c)
4.3. General procedure for enantioselective carbonyl-ene
reactions
To a solution of the in situ prepared catalyst in dichlo-
romethane according to activation method A or B, was added
0.5 mmol freshly distilled ethyl glyoxylate or freshly dried
phenyloxal and 0.25 mmol alkylene. The resulting mixture was
stirred for 5 h at room temperature, then the mixture was directly
loaded onto a silica gel, and eluted with hexane/ethyl acetate
mixture to give the corresponding compound [5,6].
The title compound was prepared according to the gen-
eral procedure using 0.5 mmol freshly dried phenylglyoxal and
0.25 mmol methylenecyclohexane. Pure product was obtained
by column chromatography over silica gel eluted with hex-
ane/ethyl acetate (9:1). 1H NMR (CDCl3, 300 MHz, δ):
1.57–1.63 (m, –CH2CH2–), 2.01–2.03 (m, –CH2–C C–),
2.18, 2.50 (dd,dd, –CH2CH(OH)), 3.67 (OH), 5.20–5.26 (m,
–OCH2CH3 and –CH(OH)), 5.50 (s, –C CH–), 7.53 (t), 7.65
(t), 7.95 (d) (Ph–H). 13C NMR (CDCl3, 300 MHz, δ): 22.6,
23.2, 25.7, 29.2, 45.0, 72.6, 125.5, 129.0, 129.2, 133.7, 134.3,
134.4, 202.4. Enantiomeric excess was determined by HPLC
with a Chiralcel OD-H column (1.0% 2-propanol in hexane, flow
1.0 mL/min, (S)enantiomer RT = 13 min (major), (R)enantiomer
RT = 20 min (minor)).
4.4. Preparation of ethyl
3-(1ꢀ-cyclohexenyl)-2-hydroxypropionate (3a)
The title compound was prepared according to the gen-
eral procedure using 0.5 mmol freshly distilled ethyl glyoxy-
late and 0.25 mmol methylenecyclohexane. Pure product was
obtained by column chromatography over silica gel eluted
4.7. Preparation of 2-hydroxy-4-isopropyl-1-phenyl-4-
penten-1-one (3d)
1
with hexane/ethyl acetate (4:1). H NMR (CDCl3, 300 MHz,
δ): 1.31 (t, –CH2CH3), 1.58–1.63 (m, –CH2CH2–), 1.95–2.05
(m, –CH2–C C–), 2.30, 2.45 (dd,dd, –CH2CH(OH)), 2.76
(OH), 4.23–4.28 (m, –OCH2CH3 and –CH(OH)–), 5.55 (s,
–C CH–). 13C NMR (CDCl3, 300 MHz, δ): 14.2, 22.2, 22.8,
25.3, 28.4, 43.2, 61.4, 69.2, 125.3, 133.0, 174.9. Enantiomeric
excess was determined by GC with a CYCLODEX-B column
(10.8 psi, 107 ◦C, at t = 50 min, rate 5 ◦C/min, final T = 160 ◦C,
The title compound was prepared according to the gen-
eral procedure using 0.5 mmol freshly dried phenylglyoxal and

H.-K. Luo, H. Schumann / Journal of Molecular Catalysis A: Chemical 248 (2006) 42–47
47
0.25 mmol2,3-dimethyl-1-butene. Pureproductwasobtainedby
Acknowledgement
column chromatography over silica gel eluted with hexane/ethyl
1
acetate (5:1). H NMR (CDCl3, 300 MHz, δ): 1.05, 1.07 (d,d,
This work was supported by Institute of Chemical and Engi-
neering Sciences (ICES) A-STAR, Singapore.
–CH3), 2.23 (dd, –CH2CH(OH)), 2.34 (m, –CH(CH3)3), 2.65
(dd, –CH2CH(OH)), 3.71 (OH), 4.93, 4.97 (s, s, –C CH2),
5.23–5.29 (m, –CH(OH)), 7.53 (t), 7.65 (t), 7.95 (d) (Ph–H).
13C NMR (CDCl3, 300 MHz, δ): 22.0, 22.2, 34.0, 41.4, 72.8,
110.2, 129.0, 129.3, 134.2, 134.4, 151.7, 202.2. Enantiomeric
excess was determined by HPLC with a Chiralcel OD-H column
(0.8% 2-propanol in hexane, flow 0.5 mL/min, (S)enantiomer
RT = 28 min (major), (R)enantiomer RT = 59 min (minor)).
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[5] (a) D.A. Evans, C.S. Burgey, N.A. Paras, T. Vojkovsky, S.W. Tregay, J.
Am. Chem. Soc. 120 (1998) 5824;
(b) D.A. Evans, S.W. Tregay, C.S. Burgey, N.A. Paras, T. Vojkovsky, J.
Am. Chem. Soc. 122 (2000) 7936.
[6] S. Kezuka, T. Ikeno, T. Yamada, Org. Lett. 3 (2001) 1937.
[7] (a) J.J. Becker, P.S. White, M.R. Gagne, J. Am. Chem. Soc. 123 (2001)
9478;
(b) J. Hao, M. Hatano, K. Mikami, Org. Lett. 2 (2000) 4059;
(c) J.H. Koh, A.O. Larsen, M.R. Gagne, Org. Lett. 3 (2001) 1233.
[8] For palladium catalyzed Diels–Alder reactions, see:
(a) A.K. Ghosh, H. Matsuda, Org. Lett. 1 (1999) 2157;
For palladium catalyzed Hetero-Diels–Alder reactions, see:
(b) S. Oi, E. Terada, K. Ohuchi, T. Kato, Y. Tachibana, Y. Inoue, J. Org.
Chem. 64 (1999) 8660;
The title compound was prepared according to the gen-
eral procedure using 0.5 mmol freshly dried phenylglyoxal and
0.25 mmol 2,4,4-trimethyl pentene. Pure product was obtained
by column chromatography over silica gel eluted with hex-
1
ane/ethyl acetate (9:1). H NMR (CDCl3, 300 MHz, δ): 0.90
(s, –CH3), 2.02, 2.04 (d, –CH2C(CH3)3), 2.26, 2.65 (dd,dd,
–CH2CH(OH)), 3.72 (OH), 4.90, 5.04 (s,s, –C CH2), 5.21–5.26
(m, –CH(OH)), 7.53 (t), 7.65 (t), 7.95 (d) (Ph–H). 13C NMR
(CDCl3, 300 MHz, δ): 30.3, 32.0, 44.5, 49.9, 73.0, 116.8,
129.0, 129.3, 134.2, 134.4, 143.4, 202.1. Enantiomeric excess
was determined by HPLC with a Chiralcel OD-H column
(1.0% 2-propanol in hexane, flow 1.0 mL/min, (S)enantiomer
RT = 10 min (major), (R)enantiomer RT = 14 min (minor)).
(c) J.J. Becker, L.J.V. Orden, P.S. White, M.R. Gagne, Org. Lett. 4 (2002)
727;
(d) K. Mikami, K. Aikawa, Y. Yusa, M. Hatano, Org. Lett. 4 (2002) 91;
(e) K. Mikami, K. Aikawa, Y. Yusa, Org. Lett. 4 (2002) 95.