Enantioselective rhodium-catalyzed hydrogenation of enol carbamates in the presence of monodentate phosphines

Article abstract of DOI:10.1016/j.tetasy.2007.06.001

The rhodium-catalyzed asymmetric hydrogenation of different acyclic and cyclic enol carbamates to give optically active carbamates has been examined in the presence of chiral monodentate ligands based on a 4,5-dihydro-3H-dinaphthophosphepine motif 4. The

Full text of DOI:10.1016/j.tetasy.2007.06.001

Tetrahedron: Asymmetry 18 (2007) 1288–1298
Enantioselective rhodium-catalyzed hydrogenation of enol carbamates
in the presence of monodentate phosphines
Stephan Enthaler,a Giulia Erre,a Kathrin Junge,a Dirk Michalik,a Anke Spannenberg,a
Fabrizio Marras,b Serafino Gladialib and Matthias Bellera,*
aLeibniz-Institut fu¨r Katalyse e.V. an der Universita¨t Rostock, Albert-Einstein-Str. 29a, 18059 Rostock, Germany
b
`
Dipartimento di Chimica, Universita di Sassari, Via Vienna 2, 07100 Sassari, Italy
Received 27 March 2007; accepted 1 June 2007
Abstract—The rhodium-catalyzed asymmetric hydrogenation of different acyclic and cyclic enol carbamates to give optically active car-
bamates has been examined in the presence of chiral monodentate ligands based on a 4,5-dihydro-3H-dinaphthophosphepine motif 4.
The enantioselectivity is largely dependent upon the reaction conditions, the nature of substituents on the phosphorus ligand and struc-
ture of the enol carbamate. By applying the optimized reaction conditions, enantioselectivities of up to 96% ee have been achieved.
ꢀ 2007 Elsevier Ltd. All rights reserved.
1. Introduction
more attention.3,4 The advantages of monodentate phos-
phorus ligands compared to bidentate ligands are their eas-
ier synthesis, high tunability and even a higher efficiency in
the transfer of chiral information as observed in several
cases. Important contributions in this field with excellent
enantioselectivities for various classes of substrates were re-
ported by Feringa and de Vries et al.5 (phosphoramidites),
Reetz et al.6 (phosphites), Pringle and Claver et al.7 (phos-
phonites) and Zhou et al. (spiro phosphoramidites).8
The importance of enantiomerically pure compounds is
demonstrated by their widespread application as either
building blocks or intermediates for the synthesis of phar-
maceuticals, agrochemicals, polymers, natural compounds,
auxiliaries, ligands and synthons in organic syntheses.1 To
serve the growing demand for enantiomerically pure com-
pounds, various synthetic approaches have been developed.
Within the different molecular transformations to chiral
compounds, catalytic reactions offer an efficient and
versatile strategy and present a key technology for the
advancement of ‘green chemistry’, specifically for waste
prevention, reducing energy consumption, achieving high
atom efficiency and generating advantageous economics.2
In this regard, the use of molecular hydrogen in reductions
of C@C, C@O and C@N bonds is one of the most exten-
sively studied fields. For activation of the hydrogen and
transfer of chirality, the use of transition metal catalysts
containing chiral ligands are essential. Over a period of
nearly 30 years, the synthesis of new ligands focused mainly
on bidentate phosphorus systems, because of the promising
results in the first few years of homogeneous asymmetric
hydrogenation. However, at the end of the 20th century,
the situation changed and monodentate ligands received
Following the effort of one of us (S.G.)9 and parallel to the
work of Zhang,10 we constructed a ligand library of
approximately 25 different monodentate phosphines based
on a 4,5-dihydro-3H-dinaphtho[2,1-c;10,20-e]phosphepine
framework 4 (Scheme 1), which is reminiscent of the 1,10-
binaphthol core, which is present in the ligands mentioned
above (Scheme 1).11 The potential of this ligand class 4 in
asymmetric hydrogenation with molecular hydrogen, such
as the reduction of a-amino acid precursors, dimethyl
itaconate, enamides and b-ketoesters achieving enantio-
selectivities up to 95% ee was previously reported by us.11
Moreover, other groups demonstrated the usefulness of
these ligands in several catalytic asymmetric reactions.12
The promising results obtained in the asymmetric hydro-
genation of N-(1-phenylvinyl)acetamides with enantioselec-
tivities of up to 95% ee and catalyst activities up to
2000 hꢀ1 (TOF) motivated us to explore our ligand library
4 in the hydrogenation of structurally similar enol carba-
mates, which offer an alternative approach to chiral
*
Corresponding author. Tel.: +49 381 1281 113; fax: +49 381 1281
5000; e-mail: Matthias.Beller@catalysis.de
0957-4166/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2007.06.001

S. Enthaler et al. / Tetrahedron: Asymmetry 18 (2007) 1288–1298
1289
CH3
P
Ph
CH3
1.
n
-BuLi/
TMEDA
2. Cl2PNEt2
1.
n
-BuLi/
TMEDA
2. Cl2PR
1
HSiCl3
7
4'
5'
10'
3'
12'
O
6'
7'
2'
11'
11
2
9'
9
o
1'
5
8'
i
P
P
R
P
NEt2
m
p
8
7
6
12
4
2
3
10
5
4
RMgX
or RLi
6
H2O2
4a: R = Ph
4b: R = -CF3C6H4
HCl
LDA/MeI
O
p
4c: R = 3,5-(CH3)2C6H3
P
R
P
Cl
4d: R =
4e: R =
4f: R =
4g: R =
p
-CH3OC6H4
-CH3OC6H4
Pr
Bu
o
5a: R = Ph
5b: R = -CH3OC6H4
3
i
p
t
Scheme 1. General synthesis of ligands with 2,20-binaphthyl framework.
alcohols. Pioneering work in the field of enantioselective
hydrogenation of enol carbamates has been reported by
Feringa, de Vries and Minnaard et al. who have scored
enantioselectivities of up to 98% ee with rhodium-catalysts
containing monodentate phosphoramidites (MonoPhos-
family).
substituents on the aliphatic carbon at the a-position to
the phosphorus. The desired bis-methylated product 7 has
been obtained via a deprotonation–alkylation protocol.
After the preliminary step of oxidation of 4-phenyl-4,5-
dihydro-3H-dinaphtho[2,1-c;10,20-e]phosphepine 4a with
H2O2, lithiation and alkylation were performed by the addi-
tion of LDA (3 equiv) and CH3I (2 equiv) at room temper-
ature. The reaction is completely stereoselective, and only
one of the possible dialkylated products is obtained
(Scheme 1).
2. Results and discussion
2.1. Ligand synthesis
Recently, Widhalm et al. reported a similar approach to
the synthesis of compound 7, via the phosphepine sulfide
instead of the oxide.13 To compare the two procedures,
the stereochemistry of the new stereogenic centres in the
phosphepine oxide 6 was studied in detail.
In general, the ligands were prepared by double metallation
of 2,20-dimethylbinaphthyl 1 with 2 equiv of n-butyl lith-
ium, followed by quenching with diethylaminodichloro-
phosphine or with aryl and alkyl dichlorophosphines.
Deprotection of the diethylamino phosphine 2 with gaseous
HCl produced 4-chloro-4,5-dihydro-3H-dinaphtho[2,1-
c;10,20-e]phosphepine 3 in 80% yield. This enantiomerically
pure chlorophosphine is easily coupled with various Grig-
nard reagents or organo-lithium compounds to give a broad
selection of ligands 4. In order to expand the application of
this class of ligands, we prepared derivatives of 1, bearing
The stereochemistry of compound 6 was confirmed by
NMR spectroscopy. The initial 31P NMR measurements
displayed the occurrence of exclusively one enantiomer
for 6 and 7 in each case, since only one single signal was
found and racemization of the binaphthyl backbone over
the course of reactions was excluded. In a two-dimensional
˚
Table 1. Selected bond lengths [A] and angles [ꢁ] of the phosphepine oxides 5a, 5b and 6
5a
6
5ba
P1–C1
1.812(5)
1.813(4)
1.814(5)
1.481(3)
109.6(2)
104.0(2)
103.1(2)
P1–C25
1.799(3)
1.832(2)
1.834(2)
1.483(2)
108.6(1)
104.2(1)
108.8 (1)
P1–C1
[P2–C30]
P1–C29
[P2–C58]
P1–C8
[P2–C37]
P1–O1
[P2–O3]
C1–P1–C29
[C30–P2–C37]
C1–P1–C8
[C30–P2–C58]
C29–P1–C8
[C58–P2–C37]
1.824(4)
[1.825(4)]
1.833(4)
[1.846(4)]
1.837(4)
[1.819(4)]
1.444(3)
[1.407(5)]
107.9 (2)
[107.2 (2)]
105.4(2)
[103.0(2)]
102.3(2)
[100.8(2)]
P1–C7
P1–C22
P1–C28
P1–C1
P1–O1
P1–O1
C7–P1–C1
C28–P1–C1
C7–P1–C28
C25–P1–C22
C25–P1–C1
C22–P1–C1
a Values of the second molecule in the asymmetric unit are in brackets.

1290
S. Enthaler et al. / Tetrahedron: Asymmetry 18 (2007) 1288–1298
Figure 1. ORTEP plot of compounds 5a, 6 and 5b. Hydrogen atoms are omitted for clarity. The thermal ellipsoids correspond to 30% probability. With
respect to compound 5b, only one of the two symmetry-independent molecules of the asymmetric unit is depicted.
NOESY spectrum, correlations between the following pro-
tons were observed: o-Ph with H-30, H-110 and Me(12); H-3
with H-11 and H-30 with H-110, respectively, indicating the
bis-axial orientation of both methyl groups. The spatial
proximity of the methyl group Me(12) and of the phenyl
group is also reflected by the difference in 1H chemical shift
values of both methyl groups (dMe(12) = 0.61 and
Me(120) = 0.95). The high-field shift of the signal for the
methyl group Me(12) can be explained by the anisotropic
effect of the phenyl substituent on the phosphorus.
we used an in situ pre-catalytic mixture of 1.0 mol %
[Rh(cod)2]BF4 and 2.1 mol % of the ligand. All hydrogena-
tion reactions were carried out in an eightfold parallel reac-
tor array with a 3.0 ml reactor volume.15
First we investigated the influence of different solvents,
such as methylene chloride, methanol, ethanol and 2-pro-
panol in combination with a variation of the initial hydro-
gen pressure (1.0, 5.0, 10.0, 25.0 and 50.0 bar). Selected
results are presented in Figure 2.
In addition, useful structural data were gained by X-ray
crystallography of oxide 6. For comparison, X-ray struc-
ture analyses of the corresponding unsubstituted systems
5a and 5b were determined. Selected bond lengths and an-
gles are shown in Table 1. The molecular structures of the
three oxides are given in Figure 1. In the case of 5b, two
molecules have been found in the asymmetric unit with
similar structural features. As expected in all compounds
the substituents show an approximately tetrahedral
arrangement at the phosphorus atom. The a,a-disubsti-
tuted phosphepine oxide 6 features shorter exocyclic
N
N
[Rh(cod)2]BF4 + 2.1 (4a)
O
O
O
O
25 °C, 24 h, H2
8
8a
100
90
80
70
60
50
40
30
20
10
0
˚
(P1–C25 1.799(3) A) than the endocyclic P–C bonds
ee [90%]
˚
˚
(P1–C22 1.832(2) A and P1–C1 1.834(2) A) in comparison
with the unsubstituted system 5a where all P–C bonds are
equally long (Table 1). Furthermore, the a,a-substitution
promotes a pronounced expansion of the endocyclic
C–P–C angle up to 108.8(1)ꢁ (6) from 103.1(2)ꢁ (5a).
MeOH
EtOH
CH2Cl2
2-PrOH
1
5
10
25
50
pressure [bar]
In accordance with the NMR studies and the X-ray struc-
ture analysis, the configuration of compound 6 was assigned
to be (S,S,Sa). The stereochemistry of ligand 7 was allotted
in analogy to the one of the corresponding oxide.
Figure 2. Solvent and pressure variation. Reactions were carried out at
25 ꢁC for 24 h with 0.0024 mmol [Rh(cod)2]BF4, 0.005 mmol ligand 4a and
0.24 mmol 8 in 2.0 ml solvent.
Surprisingly, by applying toluene as solvent in the hydro-
genation of enol carbamate 8 no reaction occurred, while
in previous studies toluene was found to be the solvent of
choice for the hydrogenation of enamides and a-amino
acids.11c,e The best enantioselectivities of up to 96% ee were
obtained with methanol as solvent with a hydrogen pres-
sure of 25 bar.
2.2. Catalytic experiments
The synthesis of enol carbamates 8–14 was carried out in
analogy to literature protocols, by reacting the correspond-
ing ketone with NaH and subsequent addition of the corre-
sponding carbamoyl chloride.5m,14
Initial studies on the influence of reaction conditions were
performed with 1-phenylvinyl N,N-diethylcarbamate 8
as substrate and 4-phenyl-4,5-dihydro-3H-dinaphtho[2,1-
c;10,20-e]phosphepine 4a as our standard ligand. Typically,
Two different pressure-enantioselectivity-dependencies
have been noticed. In ethanol and 2-propanol, the enantio-
selectivity decreased when increasing the hydrogen pressure
(1 bar: ethanol: 74% ee, 2-propanol: 74% ee, 50 bar: ethanol:

S. Enthaler et al. / Tetrahedron: Asymmetry 18 (2007) 1288–1298
1291
64% ee, 2-propanol: 50% ee) whereas in methylene chloride
N
N
[Rh(cod)2]BF4 + 2.1 (4a)
and methanol, the reverse behaviour was observed (1 bar:
methanol: 72% ee, methylene chloride: 66% ee, 50 bar:
methanol: 92% ee, methylene chloride: 86% ee). With the
exception of 2-propanol (>99%), moderate to good conver-
sions (60–90%) were observed at lower pressures within a
reasonable time (24 h), while at higher pressure a complete
conversion was achieved. The results indicated methanol as
the solvent of choice (conversion: >99%; enantioselectivity:
96% ee). In addition, in order to estimate the effect of the
protic solvent on the product structure the reaction was
O
O
O
O
24 h, H2 (25 bar)
8
8a
100
90
80
70
60
50
40
30
20
10
0
ee
conversion
[%]
1
performed in methanol-d4. Analysis of the H NMR spec-
tra showed that no incorporation of deuterium in the prod-
uct had occurred. Therefore, one can rule out any
interference of the solvent in the catalytic cycle due to
transfer hydrogenation and/or protonolysis of Rh-C-
species.16
10
30
50
70
90
110
temperature [˚C]
Figure 4. Dependency of enantioselectivity versus temperature. Reactions
were carried out at corresponding temperature for 1–24 h with
0.0024 mmol [Rh(cod)2]BF4, 0.005 mmol ligand 4a and 0.24 mmol 8 in
2.0 ml methanol.
In order to assess the optimum reaction conditions, a
detailed pressure investigation was performed (Fig. 3).
The results illustrated a constant range of enantioselectivity
(ꢁ74% ee) between initial pressures of 1–18 bar, followed
by an increase of up to a maximum of 96% ee at 25 bar.
A further increase in the hydrogen pressure did not result
in any improvement while enantioselectivities ranged
between 92% and 94% ee in the region of 30–50 bar.
ylvinyl N,N-diethylcarbamate 8 in the presence of eight
different 4,5-dihydro-3H-dinaphtho[2,1-c;10,20-e]phosphe-
pines 4a–4g and 7 using the optimized reaction conditions
(2.5 bar hydrogen pressure, methanol, 30 ꢁC, 6 h). The
results are presented in Table 2. In the hydrogenation of
8, the best enantioselectivities of up to 90% and 72% ee,
respectively, were achieved with ligand 4a and 4d (Table
2, entries 1 and 4). The presence of electron-donating
groups, as well as electron-withdrawing groups onto the
P-aryl substituent, led to a significant decrease of the
stereoselectivity (Table 1, entries 2–5).
N
N
[Rh(cod)2]BF4 + 2.1 (4a)
25 ºC, 24 h, H2
O
O
O
O
8
8a
100
90
80
70
60
50
40
30
20
10
0
Table 2. Hydrogenation of compound 8 with different 4,5-dihydro-3H-
dinaphtho[2,1-c;10,20-e]phosphepines 4a–4g and ligand 7a
ee [%]
N
N
[Rh(cod)2]BF4 + 2.1 (4 or 7)
O
O
O
O
MeOH, 6 h, H2 (25 bar)
8
8a
Entry
Ligand
Conv. (%)
Yield (%)
ee (%)
1
5
10
12
15
18
20
25
30
40
50
1
2
3
4
5
6
7
8b
4a
4b
4c
4d
4e
4f
4g
7
>99
40
>99
>99
>99
40
>99
40
>99
>99
>99
40
96 (S)
28 (S)
66 (S)
72 (S)
51 (S)
12 (S)
50 (R)
42 (R)
pressure [bar]
Figure 3. Study of pressure-enantioselectivity-dependency. Reactions were
carried out at 25 ꢁC for 24 h with 0.0024 mmol [Rh(cod)2]BF4, 0.005 mmol
ligand 4a and 0.24 mmol 8 in 2.0 ml methanol.
41
>99
41
>99
The optimal reaction conditions devised in the solvent-
pressure investigation (methanol as solvent and 25 bar as
initial hydrogen pressure) were applied in a temperature
study (Fig. 4). With the model ligand 4a in the hydrogena-
tion of compound 8, we observed a high stability of the
enantioselectivity (94–96% ee) in the range of 10–90 ꢁC
albeit with a reduction of conversion at 90 ꢁC. A further
increase to 110 ꢁC produced a racemic mixture of 8a, pro-
bably as a result of ligand degradation.17
a All reactions were carried out at 25 ꢁC under 25 bar pressure of hydrogen
for 6 h with 0.0024 mmol [Rh(cod)2]BF4, 0.005 mmol ligand and
0.24 mmol 8 in methanol (2.0 ml).
b 24 h.
Catalysts containing alkyl-substituted phosphepines 4f or
4g gave a significant lower activity and enantioselectivity
compared to aryl-substituted phosphepines. Interestingly,
in the case of ligand 4g and 7, the opposite enantiomer is
formed during the reaction. A similar behaviour of the
In order to evaluate the substituent effect at the phosphorus
atom of the ligand, we studied the model reaction of 1-phen-

1292
S. Enthaler et al. / Tetrahedron: Asymmetry 18 (2007) 1288–1298
tert-butyl ligand 4g was previously reported for other
ent substituents on the carbamoyl nitrogen on the reaction
path.
asymmetric hydrogenations.11c,f
To explore the scope and limitation of our ligand toolbox,
the asymmetric hydrogenation of a range of enol carb-
amates was performed under optimized conditions (Tables
3 and 4). First the influence of the substitution at the car-
bamoyl-nitrogen was investigated (Table 3).
Finally, the sensitivity on the variations in the double bond
was investigated. Table 4 summarizes the results for three
substrates with different substitutions: substitution of the
phenyl-group by an alkyl-group 14, substitution in the 2-
position of the 1,1-olefin 12 and a cyclic substrate 13. Sub-
strate Z-12 was hydrogenated with excellent conversion
and good enantioselectivity by ligand 4d, while 13, which
is structurally related to the E-isomer of substrate 12, fails
to be hydrogenated with all the ligands but exceptionally
ligand 7 (Table 4, entry 8). The alkyl enol carbamate 14
is best hydrogenated by ligands 4a and 7, again leading
to an inversion of enantioselectivity with ligand 7. In gen-
eral the behaviour of substrates 12 and 14 is comparable
to that of the previous enol carbamates.
Table 3. Variation of the protecting group in the substrate moietya
R1
O
R2
O
R1
O
R2
O
N
N
[Rh(cod)2]BF4 + 2.1 (4 and 7)
MeOH, 24 h, H2 (25 bar)
9: R1=R2=Me
9a-11a
10: R1=Me R2=Ph
11: R1=Ph R2=Ph
Entry
Ligand
R1
R2
Conv. (%)
Yield (%)
ee (%)
Table 4. Variations of the substituent in the olefina
1
2
3
4
5
6
7
8
4a
4b
4c
4d
4e
4f
4g
7
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
>99
33
87
>99
99
26
>99
33
87
>99
99
26
68 (S)
26 (S)
65 (S)
75 (S)
40 (S)
17 (S)
33 (R)
27 (R)
N
N
N
O
O
O
O
O
O
14
12
13
44
80
44
80
Entry
Lig.
12a
13a
14a
Conv.
(%)
eeb
(%)
Conv.
(%)
ee
(%)
Conv.
(%)
ee
(%)
9
10
11
12
13
14
15
16
4a
4b
4c
4d
4e
4f
4g
7
Me
Me
Me
Me
Me
Me
Me
Me
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
>99
98
>99
>99
>99
53
>99
98
>99
>99
>99
53
58 (S)
37 (S)
61 (S)
65 (S)
42 (S)
4 (S)
1
2
3
4
5
6
7
8
4a
4b
4c
4d
4e
4f
4g
7
94
10
7
93
29
1
50 (S)
12 (R)
8 (S)
72 (S)
14 (S)
n.d.
<1
<1
<1
<1
<1
<1
<1
30
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
>99
24
90
89
81
39
44
98
48
1
39
48
Rac
11
42
ꢀ67
>99
>99
>99
>99
45 (R)
53 (R)
2
37
n.d.
6 (R)
17
18
19b
20
21
22
23
24
4a
4b
4c
4d
4e
4f
4g
7
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
>99
98
89
>99
>99
98
>99
>99
88
77
75
87
87
62
98
98
10 (S)
Rac
41 (S)
11 (S)
55 (S)
4 (S)
a All reactions were carried out at 25 ꢁC under 25 bar pressure of hydrogen
for 24 h with 0.0024 mmol [Rh(cod)2]BF4, 0.005 mmol ligand and
0.24 mmol substrate in methanol (2.0 ml).
b The absolute configuration was assigned by analogy.
70 (R)
76 (R)
3. Conclusions
a All reactions were carried out at 25 ꢁC under 25 bar pressure of hydrogen
for 24 h with 0.0024 mmol [Rh(cod)2]BF4, 0.005 mmol ligand and
0.24 mmol substrate in methanol (2.0 ml).
Monodentate phosphine ligands based on a 4,5-dihydro-
3H-dinaphtho[2,1-c;10,20-e]phosphepines structure 4 and 7
have been successfully exploited in the rhodium-catalyzed
asymmetric hydrogenation of various enol carbamates.
The influences of different reaction parameters have been
investigated. For the first time in this reaction a high
enantioselectivity (up to 96% ee) was obtained in the pres-
ence of monodentate phosphines.
b Reaction was carried out for 6 h.
All substrates were hydrogenated under the optimized con-
ditions with eight different ligands 4a–4g and 7. The enol
carbamates 9–11 undergo the reaction with good conver-
sion in most cases (Table 3). The negative influence on
the activity was again observed by the electron-withdraw-
ing substituent on the phenyl (entries 2, 10 and 18) and
by the alkyl group on the phosphorus, mainly i-Pr (Table
3, entries 6, 7, 14 and 22). On the other hand in some cases
a positive effect on the selectivity by substitution with elec-
tron donating groups was observed (Table 3, entries 4 and
12). Again the stereoselectivity was reversed in the case of
ligand 7 and 4g, with 7 being the higher inducer of chirality
for system 11. The overall results for the three substrates
9–11 are comparable, showing little influence of the differ-
4. Experimental
4.1. General
1H, 13C and 31P NMR spectra were recorded on Bruker
Spectrometer AVANCE 500, 400 and 300 (1H: 500.13
MHz, 400.13 MHz and 300.13 MHz; 13C: 125.8 MHz,
100.6 MHz and 75.5 MHz; 31P: 162.0 MHz). The calibration

S. Enthaler et al. / Tetrahedron: Asymmetry 18 (2007) 1288–1298
1293
1
of H and 13C spectra was carried out on solvent signals
64.6 min (30 m HP Agilent Technologies 50-8-260/5-8-280/
5-8-300/5).
(d(CDCl3) = 7.25 and 77.0). The 31P chemical shifts are
referenced to 85% H3PO4. Mass spectra were recorded on
an AMD 402 spectrometer. Optical rotations were
measured on a Gyromat-HP polarimeter. IR spectra were
recorded as KBr pellets or Nujol mulls on a Nicolet Magna
550. All manipulations with air sensitive compounds were
performed under argon atmosphere using standard
Schlenk techniques. Toluene was distilled from sodium
benzophenone ketyl under argon. Methanol was distilled
from Mg under argon. Ethanol and 2-propanol were
distilled from Na under argon. Methylene chloride was dis-
tilled from CaH2 under argon. Dimethyl sulfoxide (on
molecular sieves) and [Rh(cod)2]BF4 were purchased from
Fluka and used without further purifications. Ligands 4
were synthesized according to our previously published
protocols.11
4.2.2. (S)-4-(4-Methoxy)phenyl-4,5-dihydro-3H-dinaphtho-
[2,1-c:10,20-e]phosphepine oxide 5b. (S)-4-(4-Methoxy)-
phenyl-4,5-dihydro-3H-dinaphtho[2,1-c:10,20-e]phosphepine
4d (4.2 mmol) was dissolved in acetone (15 ml) and a mix-
ture of water (1.1 ml) and 35% sol. H2O2 (5.0 mmol) was
added carefully. After stirring for 4 h at room temperature,
the solvent was evaporated and the residue dissolved in
dichloromethane. The organic phase was washed with
water, brine and dried over MgSO4. The solvent was
removed to obtain an off-white foam. Yield: 99%. Mp:
112–115 ꢁC. 1H NMR (300 MHz, CDCl3) d = 8.03–7.89
(m, 4H); 7.69 (dd, 1H, J = 8.5 Hz, J = 1.2 Hz); 7.51–7.41
(m, 2H); 7.40–7.31 (m, 2H, C6H4); 7.29–7.15 (m, 5H);
6.89 (m, 2H, C6H4); 3.83 (s, 3H, OMe); 3.37–3.12
(m, 4H, CH2). 13C NMR (75.5 MHz, CDCl3) d = 162.5
(d, J = 3.0 Hz, C6H4); 133.9 (d, J = 3.8 Hz); 133.5 (d,
J = 3.8 Hz); 132.9 (d, J = 2.0 Hz); 132.7 (d, J = 2.0 Hz);
132.7 (d, J = 10.2 Hz, C6H4); 132.4 (d, J = 2.5 Hz); 132.1
(d, J = 2.0 Hz); 130.6 (d, J = 8.2 Hz); 129.8 (d,
J = 9.5 Hz); 129.3 (d, J = 1.8 Hz); 128.6 (d, J = 1.8 Hz);
128.4 (d, J = 3.8 Hz); 128.4; 128.3 (d, J = 4.5 Hz); 128.2;
127.1; 126.7; 126.5; 126.3; 125.8; 125.6; 123.0 (d,
J = 93.5 Hz, C6H4); 114.0 (d, J = 12.0 Hz, C6H4); 55.3
(OMe); 37.7 (d, J = 66.0 Hz, CH2); 36.3 (d, J = 64.2 Hz,
CH2). 31P NMR (121.5 MHz, CDCl3) d = 54.1. IR (KBr,
cmꢀ1): 3053 m; 2957 w; 2836 w; 1596 s; 1569 w; 1503 s;
1460 m; 1441 m; 1407 m; 1294 m; 1255 s; 1217 m; 1178 s;
1117 s; 1027 m; 931 w; 871 w; 816 s; 744 m; 684 w; 660
w; 623 w; 567 w; 544 m; 527 m; 496 w; 457 w; 419 w.
MS (EI): m/z (%) = 434 ([M+], 100); 282 (20); 279 (37);
4.2. Synthesis of ligands
4.2.1. (S)-4-Phenyl-4,5-dihydro-3H-dinaphtho[2,1-c:10,20-e]-
phosphepine oxide 5a. Ligand 4a (1.5 g, 3.86 mmol) were
dissolved in acetone (10 ml) and 7.7 ml of 10% sol. H2O2
(23 mmol) were added carefully, cooling with ice-bath.
After few minutes stirring at room temperature, the solu-
tion was refluxed at 100 ꢁC for 1 h. The solvent was evap-
orated and the resulting yellow oil taken up with CH2Cl2
and dried over MgSO4. Purification by column chromatog-
raphy (eluent: ethyl acetate/petroleum ether 4:1) yielded
1
1.17 g (75%) of white solid. Mp: 167–168 ꢁC. H NMR
(500 MHz, CDCl3) d = 8.02 (d, 1H, J3,4 = 8.5 Hz, H-4);
3
3
3
0
0
7.96, 7.95 (2d, 2H, J5,6 = 8.2 Hz, J5 ;6 ¼ 8:2 Hz, H-5,
H-50); 7.90 (d, 1H, J3 ;4 ¼ 8:5 Hz, H-40); 7.70 (d, 1H,
3
0
0
3J3,4 = 8.5 Hz, H-3); 7.53–7.35 (m, 7H, H-6, H-60, Ph);
266 (32); 121 (27). HRMS calcd for C29H23O2P:
22
3
7.29–7.21 (m, 3H), 7.16 (d, 1H, J = 8.5 Hz, H-7, H-70,
434.14302, found: 434.142805. ½aꢂD ¼ ꢀ293 (c 0.25,
H-8, H-80); 7.21 (d, 1H, J3 ;4 ¼ 8:5 Hz, H-30); 3.36 (dd,
CHCl3).
3
0
0
2
2
1H, JH,H = 14.2 Hz, JP,H = 8.2 Hz, H-11a); 3.32 (dd,
2
2
1H, JP,H = 22.5 Hz, JH,H = 14.2 Hz, H-110a); 3.22 (dd,
4.2.3.
(S,S,Sa)-3,5-Dimethyl-4-phenyl-4,5-dihydro-3H-di-
2
2
1H, JH,H = 14.2 Hz, JP,H = 13.0 Hz, H-11b); 3.21 (dd,
naphtho[2,1-c:10,20-e]phosphepine oxide 6. Phosphepine
oxide 5 (1.37 g, 3.4 mmol) is dissolved in 14 ml of THF,
followed by the addition of 0.42 ml (6.8 mmol) of methyl
iodide. To the well stirred solution, 22 ml of LDA
(11 mmol, 0.5 M) are added slowly at room temperature.
The dark red solution was stirred for 1 h and afterwards
quenched with few drops of water. The solvents were evap-
orated under reduced pressure. The product was taken up
with 50 ml of CH2Cl2, washed with 50 ml of H2O and the
water phase extracted with CH2Cl2 (2 · 50 ml). The organ-
ic phases are dried over MgSO4 and the solvents evapo-
rated, yielding 1.45 g of light yellow foam. Purification by
column chromatography on SiO2, eluting with acetone/
petroleum ether 1:1 yielded 0.56 g (38%) of a white solid.
Mp: 292–305 ꢁC. 1H NMR (500 MHz, CDCl3) d = 8.02
1H, JP,H = 16.0 Hz, JH,H = 14.2 Hz, H-110b). 13C NMR
(125.8 MHz, CDCl3): d = 134.0 (d, J = 4.0 Hz), 133.4 (d,
J = 4.0 Hz), 133.0 (d, J = 1.8 Hz), 132.9 (d, J = 1.8 Hz),
132.4 (d, J = 2.5 Hz), 132.2 (d, J = 1.8 Hz), 130.4 (d,
J = 8.2 Hz), 129.6 (d, J = 10.0 Hz, C-1, C-10, C-2, C-20,
C-9, C-90, C-10, C-100); 132.1 (d, J = 2.5 Hz, p-Ph); 132.0
(d, J = 88.0 Hz, i-Ph); 130.9 (d, J = 8.5 Hz, o-Ph); 129.4
(d, J = 1.8 Hz, C-4); 128.6 (d, J = 1.8 Hz, C-40); 128.5 (d,
J = 11.0 Hz, m-Ph); 128.5 (d, J = 3.5 Hz, C-3); 128.4,
128.2 (C-5, C-50); 128.3 (d, J = 4.5 Hz, C-30); 127.1,
126.7, 126.5, 126.3 (C-7, C-70, C-8, C-80); 125.9 (C-6);
125.6 (C-60); 37.4 (d, J = 65.0 Hz, C-110); 36.0 (d,
J = 64.0 Hz, C-11). 31P NMR (121.5 MHz, CDCl3)
d = 54.0. IR (KBr, cmꢀ1): 3052 m; 3008 w; 2951 w; 1618
w; 1592 w; 1508 m; 1435 m; 1405 m; 1359 w; 1328 w;
1251 m; 1221 s; 1199 m; 1159 m; 1114 m; 1102 m; 1061
w; 1026 w; 998 w; 973 w; 960 w; 931 w; 884 w; 866 w;
836 s; 833 m; 820 s; 802 w; 770 m; 752m; 742 s; 726 w;
713 w; 703 m; 694 m; 672 w; 661 m; 622 m; 586 w; 568
w; 544 m; 523 m; 496 w; 470 m; 436 w; 424 w. MS (ESI):
m/z (%) = 404 ([M+], 100); 365 (6); 266 (34); 202 (4); 139
2
2
3
3
(d, 1H, J3 ;4 ¼ 8:5 Hz, H-40); 7.97 (d, 1H, J3,4 = 8.5 Hz,
0
0
3
H-4); 7.95 (d, 1H, J5,6 = 8.2 Hz, H-5); 7.92 (d, 1H,
J5 ;6 ¼ 8:2 Hz, H-50); 7.72–7.68 (m, 2H, o-Ph); 7.65 (d,
3
0
0
3
3
0
0
1H, J3,4 = 8.5 Hz, H-3); 7.55 (d, 1H, J3 ;4 ¼ 8:5 Hz, H-
30); 7.50–7.39 (m, 5H, H-6, H-60, m-, p-Ph); 7.24–7.18 (m,
3
3H), 7.05 (d, 1H, J = 8.5 Hz, H-7, H-70, H-8, H-80); 3.62
2
(m, 1H, JP,H = 15.0 Hz, J11 ;12 ¼ 7:7 Hz, H-110); 3.43
3
0
0
2
3
(4); 73 (7). HRMS calcd for C28H21O1P: 404.13245, found:
404.132628. ½aꢂD ¼ þ79:0 (c 0.46, CHCl3). Retention time:
(dq, 1H, JP,H = 22.0 Hz, J11,12 = 7.7 Hz, H-11); 0.95
22
3
(dd, 1H, JP,H = 14.0 Hz, J11 ;12 ¼ 7:7 Hz, H-120); 0.61
3
0
0

1294
S. Enthaler et al. / Tetrahedron: Asymmetry 18 (2007) 1288–1298
(dd, 1H, JP,H = 16.1 Hz, J11,12 = 7.7 Hz, H-12). 13C
NMR (125.8 MHz, CDCl3): d = 135.2 (d, J = 3.2 Hz, C-
10); 134.5 (d, J = 5.0 Hz, C-20); 134.0 (d, J = 7.0 Hz, C-2);
133.9 (d, J = 3.0 Hz), 133.8 (d, J = 1.8 Hz), 133.4 (d,
J = 1.8 Hz), 133.0 (d, J = 1.5 Hz), 132.8 (d, J = 1.5 Hz,
C-1, C-9, C-90, C-10, C-100); 133.2 (d, J = 83.0 Hz, i-Ph);
131.7 (d, J = 2.5 Hz, p-Ph); 131.1 (d, J = 8.2 Hz, o-Ph);
130.1 (d, J = 5.0 Hz, C-3); 129.3 (d, J = 6.8 Hz, C-30);
129.2 (C-4); 129.1 (C-40); 128.2, 128.0 (C-5, C-50); 128.2
(d, J = 10.0 Hz, m-Ph); 127.0, 126.6, 126.5, 126.3 (C-7, C-
70, C-8, C-80); 126.1 (C-6); 125.7 (C-60); 46.4 (d,
J = 59.5 Hz, C-11); 43.2 (d, J = 63.0 Hz, C-110); 17.0 (C-
12); 14.6 (d, J = 4.5 Hz, C-120). 31P NMR (121.5 MHz,
CDCl3) d = 51.3. IR (KBr, cmꢀ1): 3039 m; 2990 m; 2931
m; 2874 w; 1618 w; 1594 m; 1568 w; 1504 m; 1455 w;
1436 m; 1375 w; 1341 w; 1325 w; 1292 w; 1253 m; 1225
w; 1184 m; 1166 s; 1112 m; 1092 m; 1057 m; 1028 w; 999
w; 957 w; 915 w; 896 m; 871 w; 838 m; 820 s; 796 w; 768
w; 756 m; 739 s; 711 m; 704 m; 689 m; 667 s; 632 w; 583
w; 564 s; 534 m; 520 w; 509 w; 482 m; 459 m; 418 w; 403
w. MS (ESI): m/z (%) = 432 ([M+], 44); 417 (2); 388 (2);
360 (1); 328 (2); 293 (15); 278 (100); 265 (15); 231 (4); 208
atmosphere of argon. The grey suspension was added drop-
wise to the corresponding ketone (0.1 mol) in 25 ml of di-
methyl sulfoxide at room temperature. The orange
solution was stirred for 15 min at room temperature and
then cooled to 10 ꢁC. The addition of the corresponding
carbamoyl chloride (0.11 mol) in dimethyl sulfoxide
(0.11 mol) was carried out in 30 min while maintaining
the temperature at 10 ꢁC. After stirring overnight at room
temperature, the solution was carefully quenched with
water (250 ml), extracted with n-hexane or heptane
(3 · 250 ml), washed with brine (250 ml) and dried over
MgSO4 or Na2SO4. The solvents were removed in vacuo
and the obtained yellow oil purified by column chromatog-
raphy or crystallization.
3
3
4.3.1. 1-Phenylvinyl N,N-diethylcarbamate 8. Purification
by column chromatography (eluent: ethylacetate/n-hexane
1:10) yielded a yellow oil. Yield: 18%. 1H NMR
(300 MHz, CDCl3) d = 7.44–7.39 (m, 2H, Ph); 7.30–7.19
(m, 3H, Ph); 5.35 (d, 1H, J = 2.0 Hz, @CH2); 4.96 (d,
1H, J = 2.0 Hz, @CH2); 3.35 (q, 2H, J = 7.0 Hz, CH2);
3.25 (q, 2H, J = 7.0 Hz, CH2); 1.20 (t, 3H, J = 7.0 Hz,
CH3); 1.10 (t, 3H, J = 7.0 Hz, CH3). 13C NMR
(75.5 MHz, CDCl3) d = 153.8; 153.4; 135.2; 128.6; 128.4;
124.8; 101.3; 42.0; 41.7; 14.3; 13.3. IR (KBr, cmꢀ1):
3059 w; 3027 w; 2975 m; 2934 m; 2876 w; 1719 s; 1641
m; 1600 w; 1577 w; 1495 m; 1474 m; 1457 m; 1420 s;
1380 m; 1351 w; 1314 w; 1255 s; 1225 m; 1158 s; 1097 m;
1076 m; 1050 m; 1027 w; 981 w; 902 w; 869 m; 787 m;
771 m; 759 m; 703 m; w; 638 w; 578 w. MS (ESI): m/z
(%) = 219 ([M+], 9); 103 (12); 100 (100); 77 (16); 72 (72);
44 (16). HRMS calcd for C13H17O2N: 219.1254, found:
219.1253. Retention time: 17.8 min (30 m HP Agilent
Technologies 50-8-260/5-8-280/5-8-300/5).
(12); 179 (2); 145 (16); 132 (33); 77 (7); 47 (4). HRMS calcd
22
for C30H25OP: 432.16375, found: 432.163562. ½aꢂD ¼ þ93:5
(c 0.25, CHCl3). Retention time: 58.6 min (30 m HP Agi-
lent Technologies 50-8-260/5-8-280/5-8-300/5).
4.2.4.
(S,S,Sa)-3,5-Dimethyl-4-phenyl-4,5-dihydro-3H-di-
naphtho[2,1-c:10,20-e]phosphepine 7. Phosphepine oxide 6
(0.08 g, 0.2 mmol) was dissolved in dry toluene (6 ml)
and triethylamine (0.2 ml, 1.4 mmol) was added to the
solution. The mixture was cooled to 0 ꢁC with an ice-bath
and HSiCl3 (0.1 ml, 1 mmol) was added. After the addition
was complete, the solution was refluxed for 4 h. The reac-
tion was quenched by 5 ml basic aqueous solution, and
the aqueous phase washed with toluene (2 · 5 ml). The
organic phase was dried over Na2SO4 and the solvent
evaporated under reduced pressure. Yield 70 mg (91%).
4.3.2. 1-Phenylvinyl N,N-dimethylcarbamate 9. Purifica-
tion by column chromatography on silica gel eluting with
hexane/ethyl acetate 4:1 yielded 6.4 g of an orange oil.
Yield: 34%. 1H NMR (300 MHz, CDCl3) d = 7.48–7.28
(m, 5H, Ph); 5.41 (1H, d, J = 2.0 Hz, @CH2); 5.02 (d,
1H, J = 2.0 Hz, @CH2); 3.10 (s, 3H, CH3); 2.96 (s, 3H,
CH3). 13C NMR (75.5 MHz, CDCl3) d = 154.5; 153.4;
135.1; 128.7; 128.5; 124.9; 101.6; 36.7; 36.4. IR (KBr,
cmꢀ1): 3084 w, 3058 w, 3023 w, 2934 m, 1958 w, 1724 s,
1643 m, 1601 w, 1577 m, 1494 s, 1445 s, 1391 s, 1313 m,
1295 m, 1262 s, 1168 s, 1098 m, 1076 m, 1030 m, 928 m,
875 m, 858 m, 772 s, 759 m, 708 m, 692 m, 641 w, 581 w.
MS (ESI): m/z (%) = 191 ([M+], 12); 103 (4); 91 (4); 77
(7); 72 (100); 51 (5). HRMS calcd for C11H13O2N:
191.09408, found: 191.09370. Retention time: 16.8 min
(30 m HP Agilent Technologies 50-8-260/5-8-280/5-8-300/
5).
1
Mp: 212 ꢁC. H NMR (300 MHz, CDCl3) d = 8.04–7.90
(m, 4H); 7.73–7.63 (m, 3H); 7.55 (d, 1H, J = 8.5 Hz);
7.51–7.38 (m, 5H); 7.26–7.16 (m, 3H); 7.06 (d, 1H, J =
8.5 Hz); 3.62 (m, 1H, JP,H = 15.5 Hz, JH,Me = 7.5 Hz,
CHMe); 3.43 (dq, 1H, JP,H = 22.0 Hz, JH,Me = 7.5 Hz,
2
3
2
3
3
3
CHMe); 0.95 (dd, 3H, JP,H = 13.9 Hz, JH,Me = 7.5 Hz,
3
3
Me); 0.61 (dd, 3H, JP,H = 16.0 Hz, JH,Me = .5 Hz, Me).
13C NMR (75.5 MHz, CDCl3) d = 141.2 (d, J = 2.5 Hz);
138.5 (d, J = 1.0 Hz); 138.5 (d, J = 25.8 Hz); 134.7 (d,
J = 5.8 Hz); 134.3; 133.9; 133.86 (d, J = 2.8 Hz); 132.8 (d,
J = 19.5 Hz); 132.7; 132.2; 128.9 (d, J = 3.0 Hz); 128.8;
128.6 (d, J = 1.0 Hz); 128.4; 128.3 (d, J = 3.2 Hz); 128.2;
128.1; 127.9; 126.6; 126.5; 126.0; 126.0; 125.2; 125.1; 39.3
(d, J = 20.0 Hz, CHMe); 36.6 (d, J = 20.0 Hz, CHMe);
22.3 (d, J = 35.5 Hz, Me); 14.0 (d, J = 3.5 Hz, Me). 31P
NMR d = 31.46 (s). MS (ESI): m/z (%): 416 ([M+], 100),
4.3.3. 1-Phenylvinyl N-methyl N-phenylcarbamate 10.
Purification by column chromatography on silica gel elut-
ing with n-hexane/ethyl acetate 1:1 followed by crystalliza-
tion with acetone/diethylether/n-hexane 1:2:4. Yield: 25%.
Mp: 56–59 ꢁC. 1H NMR (300 MHz, CDCl3) d = 7.42–
7.26 (m, 10H, Ph); 5.39 (1H, d, J = 1.7 Hz, @CH2); 5.06
(d, 1H, J = 1.7 Hz, @CH2); 3.38 (br s, 3H, CH3). 13C
NMR (75.5 MHz, CDCl3) d = 153.6; 153.4; 143.0; 134.9;
129.2; 128.8; 128.4; 126.7 (br); 126.0 (br); 125.0; 101.6;
360 (10), 265 (38), 149 (9). HRMS: calcd for C30H25P
416.16884, found: 416.167881. ½aꢂD ¼ þ87:5 (c 0.2,
25
CHCl3).
4.3. General synthesis of enol carbamate derivates 8–1414,5m
A solution of sodium hydride (0.11 mol) in dry dimethyl
sulfoxide (200 ml) was stirred for 2 h at 50 ꢁC under an

S. Enthaler et al. / Tetrahedron: Asymmetry 18 (2007) 1288–1298
1295
38.3. IR (KBr, cmꢀ1): 3762 w; 3407 w; 3119 w; 3085w; 3067
w; 3037 w; 2975 w; 2937 w; 2557 w; 1966w; 1891 w; 1813 w;
1717 s; 1643 m; 1592 m; 1578 w; 1493 s; 1446 m; 1420 m;
1370 s; 1294 m; 1257 s; 1180 w; 1146 s; 1088 m; 1072 m;
1050 w; 1025 m; 1004 w; 981 m; 916 w; 875 m; 840 w;
827 w; 771 m; 754 m; 705 s; 687 m; 602 w; 588 m; 563 w;
529 w; 429 w; 408 m. MS (ESI): m/z (%) = 253 ([M+], 4);
134 (100); 119 (4); 106 (37); 91 (6); 77 (38); 65 (4); 51
(10); 39 (3). HRMS calcd for C16H15O2N: 253.10973,
found: 253.10977. Retention time: 23.1 min (30 m HP Agi-
lent Technologies 50-8-260/5-8-280/5-8-300/5).
2934 m; 2890 m; 1726 s; 1653 w; 1616 m; 1605 m; 1577
m; 1474 m; 1459 m; 1420 s; 1380 m; 1361 m; 1316 m;
1267 s; 1235 m; 1223 m; 1204 m; 1172 s; 1156 s; 1118 m;
1098 m; 1076 m; 1017 w; 973 m; 953 m; 932 m; 915 w;
844 w; 761 s; 717 m; 635 w; 593 w; 553 w; 511 w; 467 w;
412 w. MS (ESI): m/z (%) = 231 ([M+], 6); 131 (10); 115
(6); 103 (11); 100 (100); 77 (14); 72 (62); 44 (17). HRMS
calcd for C14H17O2N: 231.12538; Found: 231.124840.
Retention time: 21.3 min (30 m HP Agilent Technologies
50-8-260/5-8-280/5-8-300/5).
4.3.7. 3,3-Dimethylbut-1-en-2-yl N,N-diethyl carbamate 14.
A colourless oil was obtained after column chromatogra-
phy (eluent: ethyl acetate/n-hexane 1:3). Yield: 27%. H
4.3.4. 1-Phenylvinyl N,N-diphenylcarbamate 11. Crystalli-
zation from acetone/diethylether/n-hexane 1:2:5 yielded
white-greenish crystals. Yield: 38%. Mp: 72–75 ꢁC. 1H
NMR (300 MHz, CDCl3) d = 7.26–7.21 (m, 15H, Ph);
5.40 (1H, d, J = 2.2 Hz, @CH2); 5.14 (1H, d, J = 2.2 Hz,
@CH2). 13C NMR (75.5 MHz, CDCl3) d = 153.2; 152.5;
142.2; 134.7; 129.1; 128.8; 128.4; 126.8; 126.5; 125.0;
101.6. IR (KBr, cmꢀ1): 3088 w; 3057 m; 1952 w; 1879 w;
1801 w; 1721 s; 1646 m; 1590 m; 1492 s; 1451 m; 1384 w;
1347 s; 1328 m; 1307 m; 1293 m; 1256 s; 1201 s; 1184 m;
1172 m; 1097 m; 1078 m; 1044 m; 1032 m; 1024 m; 913
w; 870 m; 836 w; 770 s; 761 s; 694 s; 638 m; 620 w; 597
m; 566 w; 530 m; 512 m; 443 w; 412 w. MS (ESI): m/z
(%) = 315 ([M+], 13); 196 (100); 168 (46); 103 (17); 91 (4);
77 (22); 51 (7). HRMS calcd for C21H17O2N: 315.12538,
found: 315.12538. Retention time: 28.2 min (30 m HP Agi-
lent Technologies 50-8-260/5-8-280/5-8-300/5).
1
NMR (400 MHz, CDCl3) d = 4.76 (d, 1H, J = 1.9 Hz,
@CH2); 4.64 (d, 1H, J = 1.9 Hz, @CH2); 3.31 (q, 4H,
J = 7.0 Hz, CH2CH3); 1.16–1.12 (br, 6H, CH2CH3);
1.10 (s, 9H, CH3). 13C NMR (100.6 MHz, CDCl3)
d = 163.0; 154.1; 96.2; 42.0; 41.6; 36.2; 27.9; 14.2; 13.4.
IR (KBr, cmꢀ1): 3125 w; 2973 s; 2936 m; 2876 m; 1720 s;
1653 m; 1555 w; 1506 w; 1474 m; 1461 m; 1419 s; 1380
m; 1362 m; 1317 m; 1264 s; 1225 m; 1148 s; 1097 m; 1054
m; 979 m; 938 w; 859 m; 786 m; 756 m; 703 w; 655 w;
593 w; 488 w. MS (ESI): m/z (%) = 199 ([M+], 1); 118
(1); 100 (100); 85 (2); 72 (50); 67 (3); 55 (5); 44 (15). HRMS
calcd for C11H21O2N: 199.15668, found: 199.155983.
Retention time: 11.5 min (30 m HP Agilent Technologies
50-8-260/5-8-280/5-8-300/5).
4.4. General procedure for the catalytic hydrogenation of
enol carbamates
4.3.5. (Z)-1-Phenylprop-1-enyl N,N-diethylcarbamate 12.18
Colourless oil was obtained after column chromatography
(eluent: ethyl acetate/n-hexane 1:10). Yield: 38%. 1H NMR
(500 MHz, CDCl3) d = 7.40 (m, 2H, o-Ph); 7.30 (m, 2H, m-
The catalyst was generated in situ by stirring [Rh(cod)2]-
BF4 (0.0024 mmol) and the corresponding 4,5-dihydro-
3H-dinaphthophosphepines ligand (0.005 mmol) in 1.0 ml
of solvent for a period of 10 min and afterwards transfer-
ring via syringe into the autoclave. A solution of the enol
carbamate (0.24 mmol) and 1.0 ml solvent was transferred
via syringe into the autoclave. Then, the autoclave was
charged with hydrogen and stirred at the required temper-
ature. After a predetermined time the hydrogen was re-
leased and the reaction mixture passed through a short
plug of silica gel. The conversion and enantioselecti-
vity were measured by GC and HPLC without further
modifications.
3
Ph); 7.23 (m, 2H, p-Ph); 5.85 (q, 1H, J1,2 = 7.0 Hz, H-2);
3
3.49, 3.36 (2q, 4H, H-5, H-50); 1.74 (d, 3H, J1,2=7.0 Hz,
3
3
0
0
H-1); 1.29, 1.17 (2t, 6H, J5,6 = 7.0 Hz, J5 ;6 ¼ 7:0 Hz,
H-6, H-60). 13C NMR (125.8 MHz, CDCl3) d = 153.4
(C@O); 147.3 (C–O); 136.0 (i-Ph); 128.3 (m-Ph); 127.6 (p-
Ph); 124.3 (o-Ph); 112.4 (C-2); 42.1, 41.7 (C-5, C-50);
14.4, 13.4 (C-6, C-60); 11.4 (C-1). IR (KBr, cmꢀ1): 3058
w; 2975 m; 2934 m; 2875 w; 1717 s; 1673 m; 1600 w;
1577 w; 1495 m; 1474 m; 1458 m; 1420 s; 1380 m; 1351
w; 1313 m; 1258 s; 1225 m; 1158 s; 1116 m; 1097 m; 1061
m; 1033 w; 1006 m; 972 w; 951 w; 926 w; 851 w; 793 w;
753 s; 692 m; 652 w; 637 w; 574 w. MS (ESI): m/z
(%) = 233 ([M+], 6); 115 (9); 105 (8); 100 (100); 77 (12);
72 (52); 44 (12). HRMS calcd for C14H19O2N: 233.14103,
found: 233.14101. Retention time: 19.3 min (30 m HP Agi-
lent Technologies 50-8-260/5-8-280/5-8-300/5). Retention
time (HPLC): 8.72 min (eluent: n-hexane/ethanol 98:2;
flow: 1.0 ml/min).
4.4.1. 1-Phenylethyl N,N-diethylcarbamate 8a. Colourless
1
oil. H NMR (300 MHz, CDCl3) d = 7.31–7.11 (m, 5H,
Ph); 5.73 (d, 1H, J = 6.5 Hz, CH); 3.20 (q, 4H,
J = 7.0 Hz, CH2); 1.44 (d, 3H, J = 6.5 Hz, CH3); 1.02 (t,
6H, J = 7.0 Hz, CH3). 13C NMR (75.5 MHz, CDCl3)
d = 155.1; 142.6; 128.2; 127.3; 125.7; 72.6; 41.5; 41.1;
22.7; 14.0; 13.4. IR (KBr, cmꢀ1): 3087 w; 3064 w; 3033
w; 2977 s; 2933 m; 2875 w; 1700 s; 1630 m; 1586 w; 1539
w; 1495 m; 1476 s; 1457 s; 1425 s; 1379 m; 1316 m; 2174
s; 1227 m; 1210 m; 1172 s; 1069 s; 1030 m; 1010 m; 998
m; 973 m; 940 w; 911 w; 877 w; 787 m; 766 m; 700 s; 630
w; 576 w; 535 m. MS (ESI): m/z (%) = 221 ([M+], 2); 105
(100); 100 (5); 77 (16); 72 (5); 58 (7); 51 (6); 44 (8). HRMS
4.3.6. 1H-Inden-3-yl N,N-diethyl carbamate 13. An
orange oil was obtained after column chromatography
(eluent: ethyl acetate/n-hexane 1:10). Yield: 58%. 1H
NMR (300 MHz, CDCl3) d = 7.34–7.10 (m, 4H); 6.19 (t,
1H, J = 2.3 Hz, CH); 3.41–3.27 (m, 4H, CH2CH3); 3.29
(d, 2H, J = 2.3 Hz, CH2CH); 1.22–1.08 (m, 6H, CH3).
13C NMR (75.5 MHz, CDCl3) d = 153.0; 149.4; 141.9;
139.7; 126.1; 125.4; 124.0; 117.8; 113.6; 42.3; 42.1; 34.8;
14.3; 13.4. IR (KBr, cmꢀ1): 3074 w; 3024 w; 2975 m;
calcd for C13H19O2N: 221.14103, found: 221.140593.
23
½aꢂD ¼ ꢀ146:1 (c 0.5, CH2Cl2/MeOH, 96% ee (S)). Conver-
sions were determined by GC (Agilent Technologies, 30 m,

1296
S. Enthaler et al. / Tetrahedron: Asymmetry 18 (2007) 1288–1298
50–300 ꢁC, (50-8-260/5-8-280/5-8-300/5)) and ees by HPLC
(Whelk (R,R), (S)-8a 8.29 min and (R)-8a 28.7 min (eluent:
n-hexane/ethanol 99:1; flow: 1.0 ml/min)).
1450 m; 1369 s; 1343 s; 1325 s; 1299 s; 1281 s; 1220 s;
1208 s; 1178 m; 1159 w; 1128 w; 1058 s; 1048 s; 1023 s;
1008 m; 993 m; 951 w; 913 w; 901 w; 860 m; 837 w; 814
w; 781 m; 764 s; 758 s; 693 s; 672 m; 642 w; 622 w; 603
w; 548 s; 516 m; 492 w. MS (ESI): m/z (%) = 317 ([M+],
2); 273 (2); 258 (2); 196 (1); 169 (41); 139 (1); 105 (100);
4.4.2. (S)-1-Phenylethyl N,N-diethylcarbamate 8a. To a
solution of (S)-1-phenylethanol (3.3 mmol) in THF
(10 ml) was added NaH (3.4 mmol). The solution was stir-
red for 30 min at room temperature under an argon atmo-
sphere. The solution was cooled to 0 ꢁC and N,N-diethyl
carbamoyl chloride (3.4 mmol) in THF (5 ml) was added.
After stirring for 2 h at room temperature the reaction
was quenched with water. The mixture was extracted with
ethylacetate/n-hexane (1:1), washed with brine and dried
over Na2SO4. The solvents were removed in vacuum and
the crude oil was purified by flash column chromatography
(ethylacetate/n-hexane 1:1) to yield a colourless oil (yield:
56%). The analytical data are in agreement with 8a
obtained by the hydrogenation protocol.
77 (12); 51 (5). HRMS calcd for C21H19O2N: 317.14103,
21
found: 317.141098. ½aꢂD ¼ ꢀ16:8 (c 0.33, CHCl3, 76% ee
(R)). Conversions were determined by NMR and ees by
HPLC (Chiralcel OD-H, (R)-11a 6.8 min and (S)-11a
9.6 min, eluent: n-hexane/ethanol 99.5:0.5; flow: 1.0 ml/
min). The absolute configuration was assigned by analogy.
4.4.6. 1-Phenylpropyl N,N-diethylcarbamate 12a. Colour-
less oil. Yield: 98%. 1H NMR (400 MHz, CDCl3)
d = 7.28–7.16 (m, 5H, Ph); 5.54 (1H, dd, J = 6.4 Hz,
J = 7.2 Hz, CHCH2); 3.23 (br, 4H, NCH2); 1.83 (m, 2H,
CHCH2CH3); 1.06 (br, 6H, NCH2CH3); 0.83 (t, 3H,
J = 7.4 Hz, CHCH2CH3). 13C NMR (100.6 MHz, CDCl3)
d = 155.5; 141.6; 128.3; 127.5; 126.4; 77.8; 41.8; 41.3;
29.9; 14.3; 13.6; 9.9. IR (KBr, cmꢀ1): 2972 m; 2934 m;
2877 w; 1700 s; 1475 m; 1457 m; 1424 m; 1380 w; 1273 s;
1226 w; 1171 s; 1063 m; 987 m; 903 w; 763 w; 700 m; 528
w. MS (ESI): m/z (%) = 235 ([M+], 9); 162 (15); 119 (54);
1
4.4.3. 1-Phenylethyl N,N-dimethylcarbamate 9a. Oil. H
NMR (400 MHz, CDCl3) d = 7.34–7.22 (m, 5H, Ph); 5.78
(q, 1H, J = 6.6 Hz, CH); 2.93 (br s, 3H, CH3); 2.88 (br s,
3H, CH3); 1.51 (d, 3H, J = 6.6 Hz, CH3). 13C NMR
(100.6 MHz, CDCl3) d = 156.0; 142.7; 128.5; 127.6; 125.9;
73.1; 36.4; 35.9; 22.9. IR (KBr, cmꢀ1): 3033 w; 2980 w;
2932 w; 1704 s; 1495 m; 1450 m; 1393 m; 1273 w; 1191 s;
1069 m; 1030 w; 1007 w; 995 w; 894 w; 844 w; 766 m;
700 m; 638 w; 569 w; 532 w. MS (ESI): m/z (%) = 193
([M+], 6); 134 (13); 121 (1); 105 (100); 90 (1); 77 (13); 63
100 (12); 91 (100); 77 (7). HRMS calcd for C14H19O2N:
23
235.15668, found: 235.157242. ½aꢂD ¼ ꢀ143:7 (c 0.5,
CH2Cl2/MeOH, 50% ee). Conversions and ees were deter-
mined by GC (Retention time: 17.9 min, 30 m HP Agilent
Technologies 50–300 ꢁC: 50-8-260/5-8-280/5-8-300/5) and
HPLC (Whelk (R,R), n-hexane/ethanol 98:2, flow 1.0 ml/
min, (S)-12a 4.84 min and (R)-12a 10.10 min).
(1); 51 (4). HRMS calcd for C11H15O2N: 193.10973, found:
22
193.109345. ½aꢂD ¼ ꢀ2:9 (c 0.3, CHCl3, 75% ee (S)). Con-
versions were determined by NMR and ees by HPLC
(Chiralpak AD-H, (R)-9a 23.6 min and (S)-9a 31.3 min,
eluent: n-hexane/ethanol 99:1; flow: 1.0 ml/min). The abso-
lute configuration was assigned by analogy.
4.4.7. 3,3-Dimethylbutan-2-yl N,N-diethylcarbamate 14a.
Oil. 1H NMR (300 MHz, CDCl3) d = 4.56 (q, 1H,
J = 6.4 Hz, CH); 3.25 (br d, 4H, CH2); 1.12 (d, 3H,
J = 6.4 Hz, CH3); 1.10 (t, 6H, CH2CH3); 0.90 (s, 9H,
CH3). 13C NMR (75.5 MHz, CDCl3) d = 155.9; 78.1;
41.6; 34.4; 25.9; 15.3; 14.2. IR (KBr, cmꢀ1): 2971 s; 2935
m; 2874 w; 1696 s; 1653 w; 1559 w; 1540 w; 1506 w; 1475
m; 1457 m; 1423 s; 1395 w; 1378 m; 1365 w; 1316 w;
1275 m; 1227 w; 1210 w; 1174 m; 1076 m; 1007 w; 972 w;
893 w; 824 w; 783 w; 768 w; 744 w; 697 w; 617 w; 537 w.
MS (ESI): m/z (%) = 201 ([M+], 7); 186 (3); 144 (2); 116
(16); 100 (100); 85 (44); 72 (25); 58 (21); 43 (46). HRMS
4.4.4. 1-Phenylethyl N-methyl N-phenylcarbamate 10a.
1
Oil. H NMR (300 MHz, CDCl3) d = 7.35–7.16 (m, 10H,
Ph); 5.83 (q, 1H, J = 6.5 Hz, CH); 3.28 (s, 3H, CH3);
1.47 (d, 3H, J = 6.5 Hz, CHCH3). 13C NMR (75.5 MHz,
CDCl3) d = 155.0; 143.4; 142.3; 128.8; 128.4; 127.6; 125.9
(br); 125.8; 125.7 (br); 73.8; 37.7; 23.0. IR (KBr, cmꢀ1):
3064 w; 3033 w; 3980 m; 2932 w; 1706 s; 1598 m; 1496 s;
1453 m; 1437 m; 1422 m; 1374 s; 1327 m; 1299 s; 1277 s;
1210 m; 1159 s; 1113 m; 1063 s; 1029 m; 1010 m; 997 m;
974 m; 912 w; 885 w; 819 w; 762 s; 698 s; 665 w; 625 w;
599 w; 544 m. MS (ESI): m/z (%) = 255 ([M+], 1); 211
(2); 196 (7); 151 (1); 134 (2); 105 (100); 91 (1); 77 (20); 65
calcd for C11H23O2N: 201.17233, found: 201.172292.
22
½aꢂD ¼ þ135 (c 0.04, CHCl3/MeOH, 67% ee). Conversions
and ees were determined by GC (50m Chiraldex b-PH, 50.0
m · 250 lm · 0.25 lm, 100/25-4-180/5, (ꢀ)-14a 25.6 min
and (+)-14a 26.0 min).
(2); 51 (7). HRMS calcd for C16H17NO2: 255.12538, found:
22
255.125229. ½aꢂD ¼ þ19:9 (c 0.26, CHCl3, 65% ee (S)).
Conversions were determined by NMR and ees by HPLC
(Chiralcel OD-H, (R)-10a 25.4 min and (S)-10a 47.2 min,
eluent: n-hexane/ethanol 99:1; flow: 1.0 ml/min). The abso-
lute configuration was assigned by analogy.
4.5. X-ray crystallographic studies of 5a, 5b and 6
Data were collected with a STOE-IPDS diffractometer
using graphite-monochromated Mo Ka radiation. The
structures were solved by direct methods19 and refined by
full-matrix least-squares techniques against F2.20 XP
(BRUKER AXS) was used for graphical representations.
The crystallographic data have been deposited with the
Cambridge Crystallographic Data Centre as supplemen-
tary publication no. CCDC 641493–641495. Copies of the
data can be obtained free of charge on application to
http://www.ccdc.cam.ac.uk/data_request/cif.
4.4.5. 1-Phenylethyl N,N-diphenylcarbamate 11a. Crys-
tals. Mp: 76–78 ꢁC. 1H NMR (300 MHz, CDCl3)
d = 7.32–7.14 (m, 15H, Ph), 5.88 (q, 1H, J = 6.5 Hz,
CH), 1.47 (d, 3H, J = 6.5 Hz, CH3). 13C NMR
(75.5 MHz, CDCl3) d = 154.1; 142.6; 141.9; 128.9; 128.4;
127.7; 127.0; 126.1; 125.9; 74.3; 22.9. IR (KBr, cmꢀ1):
3064 w; 3033 m; 2984 m; 2934 w; 1702 s; 1591 s; 1491 s;

S. Enthaler et al. / Tetrahedron: Asymmetry 18 (2007) 1288–1298
1297
Berg, M.; Haak, R. M.; Minnaard, A. J.; de Vries, A. H. M.;
de Vries, J. G.; Feringa, B. L. Adv. Synth. Catal. 2002, 344,
1003–1007; (f) van den Berg, M.; Minnaard, A. J.; Haak, R.
M.; Leeman, M.; Schudde, E. P.; Meetsma, A.; Feringa, B.
L.; de Vries, A. H. M.; Maljaars, C. E. P.; Willans, C. E.;
Hyett, D.; Boogers, J. A. F.; Henderickx, H. J. W.; de Vries,
4.5.1. Compound 5a. Space group P3121, trigonal, a =
3
˚
˚
11.174(2), c = 32.520(7) A, V = 3516(1) A , Z = 6,
q
calcd = 1.230 g cmꢀ3, 18,941 reflections measured, 3621
were independent of symmetry, of which 2550 were ob-
served (I > 2r(I)), R1 = 0.055, wR2 (all data) = 0.145, 281
parameters, Flack parameter x = 0.05(18).
J. G. Adv. Synth. Catal. 2003, 345, 308–323; (g) Pena, D.;
˜
Minnaard, A. J.; de Vries, A. H. M.; de Vries, J. G.; Feringa,
B. L. Org. Lett. 2003, 5, 475–478; (h) Jiang, X.; van den Berg,
M.; Minnaard, A. J.; Feringa, B. L.; de Vries, J. G.
Tetrahedron: Asymmetry 2004, 15, 2223–2229; (i) Eelkema,
R.; van Delden, R. A.; Feringa, B. L. Angew. Chem., Int. Ed.
2004, 43, 5013–5016; (j) Duursma, A.; Boiteau, J.-G.; Lefort,
L.; Boogers, J. A. F.; de Vries, A. H. M.; de Vries, J. G.;
Minnaard, A. J.; Feringa, B. L. J. Org. Chem. 2004, 69,
8045–8052; (k) Lefort, L.; Boogers, J. A. F.; de Vries, A. H.
M.; de Vries, J. G. Org. Lett. 2004, 6, 1733–1735; (l)
Bernsmann, H.; van den Berg, M.; Hoen, R.; Minnaard, A.
J.; Mehler, G.; Reetz, M. T.; de Vries, J. G.; Feringa, B. L. J.
Org. Chem. 2005, 70, 943–951; (m) Panella, L.; Feringa, B.
L.; de Vries, J. G.; Minnaard, A. J. Org. Lett. 2005, 7, 4177–
4180; (n) Hoen, R.; Boogers, J. A. F.; Bernsmann, H.;
Minnaard, A. J.; Meetsma, A.; Tiemersma-Wegman, T. D.;
de Vries, A. H. M.; de Vries, J. G.; Feringa, B. L. Angew.
Chem., Int. Ed. 2005, 44, 4209–4212; (o) Panella, L.;
Aleixandre, A. M.; Kruidhof, G. J.; Robertus, J.; Feringa,
B. L.; de Vries, J. G.; Minnaard, A. J. J. Org. Chem. 2006,
71, 2026–2036.
4.5.2. Compound 5b. Space group P21, monoclinic, a =
˚
7.985(2), b = 11.407(2), c = 12.625(3) A, b = 98.27(3)ꢁ,
3
˚
V = 1138.0(4) A , Z = 2,
q
calcd = 1.262 g cmꢀ3
,
15,617
reflections measured, 4452 were independent of symmetry,
of which 2645 were observed (I > 2r(I)), R1 = 0.034, wR2
(all data) = 0.059, 289 parameters, Flack parameter
x = 0.02(8).
4.5.3. Compound 6. Space group P21, monoclinic, a =
˚
9.445(2), b = 16.801(3), c = 14.081(3) A, b = 91.75(3)ꢁ,
3
˚
V = 2233.4(8) A , Z = 4,
q
calcd = 1.292 g cmꢀ3
,
13,676
reflections measured, 7244 were independent of symmetry,
of which 5881 were observed (I > 2r(I)), R1 = 0.047, wR2
(all data) = 0.118, 577 parameters, Flack parameter x =
ꢀ0.07(10).
Acknowledgements
6. (a) Reetz, M. T.; Sell, T. Tetrahedron Lett. 2000, 41, 6333–
6336; (b) Reetz, M. T.; Mehler, G. Angew. Chem., Int. Ed.
2000, 39, 3889–3891; (c) Reetz, M. T.; Mehler, G.; Meiswin-
kel, G.; Sell, T. Tetrahedron Lett. 2002, 43, 7941–7943; (d)
Reetz, M. T.; Mehler, G.; Meiswinkel, G.; Sell, T. Angew.
Chem., Int. Ed. 2003, 42, 790–793; (e) Reetz, M. T.; Mehler,
G. Tetrahedron Lett. 2003, 44, 4593–4596; (f) Reetz, M. T.;
Mehler, G.; Meiswinkel, A. Tetrahedron: Asymmetry 2004,
15, 2165–2167; (g) Reetz, M. T.; Li, X. G. Tetrahedron 2004,
60, 9709–9714; (h) Reetz, M. T.; Ma, J.-A.; Goddard, R.
Angew. Chem., Int. Ed. 2005, 44, 412–414; (i) Reetz, M. T.;
Fu, Y.; Meiswinkel, A. Angew. Chem. 2006, 118, 1440–1443;
(j) Reetz, M. T.; Li, X. Synthesis 2005, 3183–3185; (k) Reetz,
M. T.; Bondarev, O. G.; Gais, H.-J.; Bolm, C. Tetrahedron
Lett. 2005, 46, 5643–5646; (l) Reetz, M. T.; Meiswinkel, A.;
Mehler, G.; Angermund, K.; Graf, M.; Thiel, W.; Mynott,
R.; Blackmond, D. G. J. Am. Chem. Soc. 2005, 127, 10305–
10313; (m) Reetz, M. T.; Li, X. Angew Chem., Int. Ed. 2005,
44, 2959–2962; (n) Reetz, M. T.; Surowiec, M. Heterocycles
2006, 67, 567–574.
7. (a) Claver, C.; Fernandez, E.; Gillon, A.; Heslop, K.; Hyett,
D. J.; Martorell, A.; Orpen, A. G.; Pringle, P. G. Chem.
Commun. 2000, 961–962; (b) Martorell, A.; Naasz, R.;
Feringa, B. L.; Pringle, P. G. Tetrahedron: Asymmetry
2001, 12, 2497–2499.
8. (a) Hu, A.-G.; Fu, Y.; Xie, J.-H.; Zhou, H.; Wang, L.-X.;
Zhou, Q.-L. Angew. Chem. 2002, 114, 2454–2456; (b) Fu, Y.;
Guo, X.-X.; Zhu, S.-F.; Hu, A.-G.; Xie, J.-H.; Zhou, Q.-L. J.
Org. Chem. 2004, 69, 4648–4655; (c) Fu, Y.; Hou, G.-H.; Xie,
J.-H.; Xing, L.; Wang, L.-X.; Zhou, Q.-L. J. Org. Chem.
2004, 69, 8157–8160.
We thank Mrs. M. Heyken, Mrs. S. Buchholz and Dr. C.
Fischer (all Leibniz-Institut fur Katalyse e.V. an der Uni-
¨
versita¨t Rostock) for excellent technical and analytical
assistance. Dr. B. Hagemann is gratefully thanked for the
synthesis of ligand 4e. Generous financial support from
the state of Mecklenburg-Western Pomerania and the
BMBF as well as the Deutsche Forschungsgemeinschaft
(Leibniz-price) are gratefully acknowledged.
References
1. (a) Lennon, I. C.; Ramsden, J. A. Org. Process Res. Dev.
2005, 9, 110–112; (b) Hawkins, J. M.; Watson, T. J. N.
Angew. Chem. 2004, 116, 3286–3290; (c) Noyori, R.;
Ohkuma, T. Angew. Chem. 2001, 113, 40–75; Miyagi, M.;
Takehara, J.; Collet, S.; Okano, K. Org. Process Res. Dev.
2000, 4, 346–348; (d) Comprehensive Asymmetric Catalysis;
Jacobsen, E. N., Pfaltz, A., Yamamoto, H., Eds.; Springer:
Berlin, 1999; (e) Noyori, R. Asymmetric Catalysis in Organic
Synthesis; Wiley: New York, 1994.
2. (a) Anastas, P. T.; Kirchhoff, M. M. Acc. Chem. Res. 2002,
35, 686–694; (b) Anastas, P. T.; Kirchhoff, M. M.; William-
son, T. C. Appl. Catal. A: Gen. 2001, 221, 3–13.
3. Lagasse, F.; Kagan, H. B. Chem. Pharm. Bull. 2000, 48, 315–
324.
4. Komarov, I. V.; Bo¨rner, A. Angew. Chem. 2001, 113, 1237–
1240.
5. (a) Arnold, L. A.; Imobos, R.; Manoli, A.; de Vries, A. H.
M.; Naasz, R.; Feringa, B. Tetrahedron 2000, 56, 2865–2878;
(b) van den Berg, M.; Minnaard, A. J.; Schudde, E. P.; van
Esch, J.; de Vries, A. H. M.; de Vries, J. G.; Feringa, B. L. J.
Am. Chem. Soc. 2000, 122, 11539–11540; (c) Minnaard, A. J.;
van den Berg, M.; Schudde, E. P.; van Esch, J.; de Vries, A.
H. M.; de Vries, J. G.; Feringa, B. L. Chim. Oggi 2001, 19,
9. (a) Gladiali, S.; Dore, A.; Fabbri, D.; De Lucchi, O.;
Manassero, M. Tetrahedron: Asymmetry 1994, 5, 511–514;
(b) Gladiali, S.; Dore, A.; Fabbri, D.; De Lucchi, O.; Valle,
G. J. Org. Chem. 1994, 59, 6363–6371; (c) Gladiali, S.;
Fabbri, D. Chem. Ber./Recl. Trav. Chim. Pays-Bas 1997, 130,
543–554; (d) Charruault, L.; Michelet, V.; Taras, R.; Gladiali,
S.; Genet, J.-P. Chem. Commun. 2004, 850–851; (e) Zanoni,
G.; Gladiali, S.; Marchetti, A.; Piccinini, P.; Tredici, I.;
Vidari, G. Angew. Chem., Int. Ed. 2004, 43, 846–849; (f)
12–13; (d) Pena, D.; Minnaard, A. J.; de Vries, J. G.; Feringa,
˜
B. L. J. Am. Chem. Soc. 2002, 124, 14552–14553; (e) van den

1298
S. Enthaler et al. / Tetrahedron: Asymmetry 18 (2007) 1288–1298
Alberico, E.; Nieddu, I.; Taras, R.; Gladiali, S.. Helv. Chim.
Acta 2006, 89, 1716–1729.
12. (a) Wilson, J. E.; Fu, G. C. Angew. Chem., Int. Ed. 2006, 45,
1426–1429; (b) Wurz, R. P.; Fu, G. C. J. Am. Chem. Soc.
2005, 127, 12234–12235; (c) Vedejs, E.; Daugulis, O.; Diver,
S. T. J. Org. Chem. 1996, 61, 430–431.
10. (a) Chi, Y.; Zhang, X. Tetrahedron Lett. 2002, 43, 4849–4852;
(b) Tang, W.; Wang, W.; Chi, Y.; Zhang, X. Angew. Chem.,
Int. Ed. 2003, 42, 3506–3509; (c) Chi, Y.; Zhou, Y.-G.; Zhang,
X. J. Org. Chem. 2003, 68, 4120–4122; (d) Xiao, D.; Zhang,
X. Angew. Chem., Int. Ed. 2001, 40, 3425–3428; (e) Xiao, D.;
Zhang, Z.; Zhang, X. Org. Lett. 1999, 1, 1679–1681.
´
13. Kasak, P.; Mereiter, K.; Widhalm, M. Tetrahedron: Asym-
metry 2005, 16, 3416–3426.
14. (a) Olofson, R. A.; Cuomo, J.; Bauman, B. A. J. Org. Chem.
1978, 43, 2073–2075; (b) Jiang, X.-b.; van den Berg, M.;
Minnaard, A. J.; Feringa, B. L.; de Vries, J. G. Tetrahedron:
Asymmetry 2004, 15, 2223–2229.
11. (a) Junge, K.; Oehme, G.; Monsees, A.; Riermeier, T.;
Dingerdissen, U.; Beller, M. Tetrahedron Lett. 2002, 43,
4977–4980; (b) Junge, K.; Oehme, G.; Monsees, A.; Rierme-
ier, T.; Dingerdissen, U.; Beller, M. J. Organomet. Chem.
2003, 675, 91–96; (c) Junge, K.; Hagemann, B.; Enthaler, S.;
Spannenberg, A.; Michalik, M.; Oehme, G.; Monsees, A.;
Riermeier, T.; Beller, M. Tetrahedron: Asymmetry 2004, 15,
2621–2631; (d) Junge, K.; Hagemann, B.; Enthaler, S.;
Oehme, G.; Michalik, M.; Monsees, A.; Riermeier, T.;
Dingerdissen, U.; Beller, M. Angew. Chem. 2004, 116,
5176–5179; Angew. Chem., Int. Ed. 2004, 43, 5066–5069; (e)
Hagemann, B.; Junge, K.; Enthaler, S.; Michalik, M.;
Riermeier, T.; Monsees, A.; Beller, M. Adv. Synth. Catal.
2005, 347, 1978–1986; (f) Enthaler, S.; Hagemann, B.; Junge,
K.; Erre, G.; Beller, M. Eur. J. Org. Chem. 2006, 2912–
2917.
15. Institute of Automation (IAT), Richard Wagner Str. 31/H. 8,
18119 Rostock-Warnemunde, Germany.
¨
16. Tsukamoto, M.; Yoshimura, M.; Tsuda, K.; Kitamura, M.
Tetrahedron 2006, 62, 5448–5453.
17. The reaction is stopped after 1 h and a black precipitate
(rhodium-black) is formed.
18. During the synthesis the Z-isomer is formed exclusively,
which was characterized by NMR. In a NOESY spectrum a
correlation was observed between the ortho-hydrogen of the
phenyl group and the olefinic hydrogen.
19. Sheldrick, G. M. SHELXS-97, Program of Crystal Structure
Solution; University of Go¨ttingen: Germany, 1997.
20. Sheldrick, G. M. SHELXL-97, Program of Crystal Structure
Refinement; University of Go¨ttingen: Germany, 1997.