Enantioselective silicon-boron additions to cyclic 1,3-dienes catalyzed by the platinum group metal complexes

Article abstract of DOI:10.1016/j.jorganchem.2008.08.029

Silaborations of 1,3-cyclohexadiene and 1,3-cycloheptadiene were achieved using catalysts prepared from different combinations of phosphorus ligands and group 10 metal compounds. For the six-membered compound, 1,4-adducts with up to 82% ee were obtained e

Full text of DOI:10.1016/j.jorganchem.2008.08.029

Journal of Organometallic Chemistry 693 (2008) 3519–3526
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Enantioselective silicon–boron additions to cyclic 1,3-dienes catalyzed
by the platinum group metal complexes
*
Martin Gerdin, Maël Penhoat, Raivis Zalubovskis, Claire Pétermann, Christina Moberg
KTH School of Chemical Science and Engineering, Organic Chemistry, SE 10044 Stockholm, Sweden
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 2 June 2008
Received in revised form 12 August 2008
Accepted 20 August 2008
Available online 28 August 2008
Silaborations of 1,3-cyclohexadiene and 1,3-cycloheptadiene were achieved using catalysts prepared
from different combinations of phosphorus ligands and group 10 metal compounds. For the six-mem-
bered compound, 1,4-adducts with up to 82% ee were obtained employing Pt(0) and phosphoramidite
ligands. For the seven-membered diene optimal conditions were found using catalysts based on Ni(0),
but the highest selectivity observed was merely 22% ee. No improvement of the chiral induction was
obtained using chiral silylboranes in combination with chiral phosphoramidite ligands in the additions
to 1,3-cyclohexadiene. The adduct obtained from cyclohexadiene was used in allylborations of aldehydes
under microwave irradiation to produce homoallylic alcohols with moderate to good diastereoselectivity.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords:
Silaboration
Interelement
Enantioselective
Diastereoselective
Catalysis
1. Introduction
Although conditions were at hand defining the relative configu-
ration of the two new stereocenters formed in additions to cyclic
Additions of homo- and heteroelement–element linkages to
unsaturated organic compounds catalyzed by the platinum group
metals constitute synthetically highly versatile processes provid-
ing access to a variety of functionalized species for further transfor-
1,3-dienes, control of the absolute configuration is desirable in or-
der to obtain non-racemic synthetic building blocks. So far this has
been achieved in rather few interelement additions. Stereochemi-
cal control in silaborations was first achieved with 1,2-dienes as
substrates. By using a combination of a chiral catalyst and chiral
non-racemic silylboranes, high diastereoselectivities were ob-
served in silaborations of achiral [8] and chiral [9] 1,2-dienes. Later
enantioselective silaboration of 1,2-dienes was also achieved
employing chiral phosphoramidites [10]. We decided to study
the possibility to induce asymmetry in the silaboration of 1,3-
dienes. After screening a multitude of metal–ligand combinations,
we were able to report that platinum(0) together with chiral phos-
phoramidites served as useful catalyst precursors for enantioselec-
tive additions to 1,3-cyclohexadiene [11].
mations [1]. The insertion of 1,3-dienes into interelement
r bonds
has emerged as a powerful route for the preparation of compounds
containing two equal or different allylic functions in one step. The
silaboration of 1,3-dienes, which normally proceeds in a 1,4-fash-
ion, is particularly useful affording compounds containing at the
same time allylsilane [2] and allylborane [3] functions [1c,e], which
both serve as synthetically versatile structural motifs. The reac-
tions were first studied by Suginome, Ito and coworkers, who
found that whereas a Pt(0) catalyst resulted in 1:1 mixtures of E
and Z olefins [4], pure Z isomers were obtained using a catalyst
generated from Ni(acac)2 and DIBALH [5]. The regioselectivity in
reactions with unsymmetrically substituted dienes was poor, how-
ever. From cyclic substrates, cis-1,4-disubstituted adducts were ob-
tained as the major products. The mechanism involves oxidative
addition of the interelement linkage to the metal, insertion of the
unsaturated moiety into an element–metal bond, and reductive
elimination. The ease of oxidative addition has been shown to be
highly dependent on the structure of the phosphine ligand and
We have now further optimized this reaction and found condi-
tions to include seven-membered cyclic dienes. The results of this
study are presented here together with results from reactions of
the adducts from cyclohexadiene with aldehydes.
2. Results and discussion
2.1. 1,3-Cyclohexadiene
the silylborane [6]. The
p-allyl complex resulting from insertion
of the diene was recently detected by NMR spectroscopy [7].
Although it was shown by Ito and Suginome that Ni catalysts
were superior to those based on Pt [5], their studies and our previ-
ous results indicated that using Ni(acac)2 only a narrow range of
electron-rich phosphines are able to provide active catalysts for
* Corresponding author. Fax: +46 8 791 2333.
E-mail address: kimo@kth.se (C. Moberg).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.08.029

3520
M. Gerdin et al. / Journal of Organometallic Chemistry 693 (2008) 3519–3526
tries 3 and 4, Table 1), we decided to use dibenzylsubstituted
O
O
ligand 4e. Gratifyingly, the catalyst prepared with this ligand fur-
nished the product in 84% yield and with the highest ee obtained
so far, 77% (entry 1, Table 2).
PhMe2Si
B
O
O
2
PhMe2Si
B
"M(0)L"
We then proceeded by modifying the reaction conditions. First
the ligand to metal ratio was varied using ligand 4d at 110 °C. A
2:1 ratio proved to be most beneficial. A lower ligand/Pt ratio re-
sulted in decreased reaction rate, possibly due to catalyst decom-
position, while an increased ratio, 3:1, effectively inhibited the
reaction (entries 2–4, Table 2). Since the catalysts containing ligand
4e and 4d seemed to exhibit higher activity than those with previ-
ously used ligands, reactions at lower temperatures were tested.
Using ligand 4d a decrease in reaction temperature to 80 °C evi-
dently resulted in a moderate yield, but an increase in the enantio-
meric excess to 78% ee. Encouraged by these results we performed
the reaction using 4e at 80 °C. Gratifyingly, an enantiomeric excess
of 82% was recorded without too serious decrease in reactivity
(58% yield, entry 6, Table 2). Under these conditions little differ-
ence was found between a 1:1 and a 2:1 ligand/Pt ratio, even
though the 1:1 ratio gives the most reactive catalyst system (en-
tries 6 and 7, Table 2). It is possible that catalyst decomposition
is a less serious problem at 80 °C and that the reaction therefore
works satisfactorily using a 1:1 ratio. Increasing the ratio to 3:1
again effectively inhibited the reaction (entry 8). It seems likely
that an excess of amidite ligand inhibits the formation of some cat-
alytically active species. On a 1 mmol scale, the conditions of entry
6 (except reaction time: 48 h) gave compound 3 in 73% isolated
yield.
In order to further attempt to optimize the phosphoramidite
ligand structure, ligands 6, (R,R)-7, and (S,R)-7 (see Fig. 2) were
synthesized by a slight modification of the Feringa protocol [12].
During the course of our work the synthesis of 7 was also reported
by Eberhartdt et al. [13]. These ligands are structurally similar to
4e, but have a more rigid amine part. Ligand 6 can exist as two dia-
stereomers due to the tropos nature of the biphenyl moiety.
Once these new amidites were at hand, they were tested in the
silaboration of 1,3-cyclohexadiene. The results are summarized in
Table 3. To our disappointment, no increase in enantioselectivity
was observed and the reactivity was considerably lower than that
3
1
Scheme 1.
the silaboration of 1,3-cyclohexadiene (Scheme 1). In the search for
asymmetric catalysts, we therefore decided to evaluate not only Ni
but also Pd and Pt complexes with a wide range of ligands under
different conditions (room temperature, 80 °C and 110 °C). Using
Ni(0) complexes we could confirm that electron-rich ligands
seemed to be required, and with palladium complexes we could
never observe any product formation. In contrast, catalysts pre-
pared from Pt(acac)2/DIBALH proved to provide the product using
a wide range of ligands [11].
2.1.1. Phosphoramidite Pt complexes
In contrast to the situation with Ni, essentially all ligands tested
together with Pt(acac)2 provided the desired product, exceptions
being o-(dicyclohexylphosphino)biphenyl and bidentate ligands,
e.g. binap. The product was in fact formed even in the absence of
ligand (16% yield, 20 h, 110 °C). The reactions were rather slow at
80 °C and were therefore usually run at 110 °C [11].
In our previous study we found that among the chiral ligands
tested, phosphoramidites resulted in highest enantioselectivities
[11]. The most interesting results are summarized in Table 1. It
was obvious that the structure of the amine part of the ligand as
well as the relative configuration of the two parts of the ligand play
a major role for both the yield and the enantioselectivity. The high-
est enantiomeric excess was achieved using ligand 4a (70% ee and
61% yield, entry 1). Using (S)-binaphthyl and chiral (R,R)- and (S,S)-
bis(2-phenylethyl)amine gave the product with 28 and 69% ee,
respectively (entries 2 and 3). The methylbenzyl substituted ami-
dite afforded the product in 84% yield and 69% ee (entry 4). Replac-
ing the binaphthyl part of the ligand with a substituted analogue
did not improve the enantioselectivity of the reaction, the best re-
sult being a small increase in yield when using 3,30-dimethyl
substituted 5 (entry 5), although at the expense of the enantiose-
lectivity (see Fig. 1).
Table 2
Lowering of reaction temperature and catalyst optimization
Considering the promising results obtained using amidites de-
rived from methylbenzylamine and bis(2-phenylethyl)amine (en-
Entry
Ligand
L/Pt ratio
Temperature (°C)
Time (h)
Yield (%)a
ee (%)
1
2
3
4
5
6
7
8
4e
4d
4d
4d
4d
4e
4e
4e
2:1
1:1
2:1
3:1
2:1
1:1
2:1
3:1
110
110
110
110
80
80
80
80
24
24
24
24
48
24
48
48
84
50
84
<5
69
58b
53
<5
77
69
69
Table 1
Silaboration with phosphoramidite Pt complexes
n.d.
78
Entry
Ligand
Time (h)
Yield (%)a
ee (%) (product)
1
2
3
4
5
(S)-4a
(S)-4b
(S)-4c
(S)-4d
(R)-5
41
30
48
48
48
61
40
58
84
92
70 (3)
28 (3)
69 (3)
69 (3)
82c
81
n.d.
Reactions performed in toluene using 5% Pt(acac)2 (reduced to Pt(0) by DIBALH).
58 (ent-3)
Determined by 1H NMR using 1-methoxynaphthalene as internal standard.
Average of three runs.
Average of three runs. Deviation 1%.
a
b
Reactions performed in toluene using 5% Pt(acac)2 and 10% of the ligand at 110 °C.
a
c
Determined by 1H NMR using 1-methoxynaphthalene as internal standard.
Ph
Ph
Ph
Ph
Ph
N
O
O
R
N
N
P N
P N
N
N
R'
O
O
Ph
Ph
Ph
a
b
c
d
e
(S)-4
(R)-5
Fig. 1. Phosphoramidite ligands.

M. Gerdin et al. / Journal of Organometallic Chemistry 693 (2008) 3519–3526
3521
O
P
O
O
O
N
P
N
P
N
O
O
(R,R)-7
(S,R
(
R
)-6
)-7
Fig. 2. Phosphoramidite ligands.
Table 3
Silaboration using phosphoramidite ligands
Table 4
Silaboration using chiral tropos P-ligands
Entry
Ligand
Time (h)
Yield (%)a
ee (%) (product)
Entry
Ligand
Time (h)
Yield (%)a
ee (%)
1
2
3
(R)-6
(R,R)-7
(S,R)-7
48
48
48
51
38
20
58 (ent-3)
53 (ent-3)
56 (3)
1
2
10
11
20
16
60
<5
4
n.d.
Reactions performed in toluene using 5% Ni(acac)2, 10% ligand, 80 °C.
a
Reactions performed in toluene using 5% Pt(acac)2, 10% ligand, 80 °C.
Determined by 1H NMR using 1-methoxynaphthalene as internal standard.
Determined by 1H NMR using 1-methoxynaphthalene as internal standard.
a
to apply this strategy by mixing 4e with achiral phosphines and
tropoisomeric 8, obtained as an intermediate in the synthesis of
10 and 11, proved unsuccessful and never provided enantioselec-
tivities higher than those observed with the chiral ligands alone.
using 4e. The biphenyl ligand gave the highest yield, suggesting
that the binaphthyl ligands are too sterically hindered for satisfac-
tory performance.
2.1.2. Nickel complexes
2.2. 1,3-Cycloheptadiene
We decided to also further study catalysts based on Ni. Being
limited to electron-rich phosphines when performing the reaction
under Ni catalysis, we synthesized tropos ligands 10 and 11, having
electronic properties that were expected to be suitable for the reac-
tion under study. The ligands were then tested in the silaboration
of cyclohexadiene. The reaction using 11 gave only trace amounts
of products, while 10 gave an appreciable yield, but a disappoint-
ingly low ee of merely 4% (see Scheme 2 and Table 4).
In our effort to widen the scope of the asymmetric reaction we
also turned our attention to 1,3-cycloheptadiene, which has previ-
ously been successfully silaborated by Ito and Suginome using
Ni(0)/PPh2Cy [5] (see Scheme 3).
We again started our investigation by screening combinations
of metals and ligands. To our surprise, using Pt(acac)2 and
Pt2(dba)3 together with PPh3 or PPh2Cy at 80 °C and 110 °C, the ex-
pected product was not obtained. Instead small amounts of some
other silaboration product that was not fully characterized were
observed. When Pd(acac)2 was tested under the same conditions
as the platinum complexes, no product was observed. Finally we
fine-tuned the reaction conditions using Ni(acac)2 (Table 5). Tri-
phenylphosphine was found to be a superior ligand to PPh2Cy
2.1.3. Ligand mixtures
Recently mixtures of chiral monodentate P-ligands have
emerged as a new principle in asymmetric catalysis [14]. Combina-
tions of chiral and achiral ligands have also been used successfully
in rhodium catalyzed asymmetric hydrogenations [15]. Attempts
L-Menthol, BuLi,
THF
O
P
P
10
dry HCl,
cyclohexane
P
P Cl
N
8
9
NH
11
(R
)-2-Phenylethylamine,
Et3N, THF
Scheme 2. Synthesis of tropos ligands.
O
O
O
O
Ni(0)/PPh2Cy
PhMe2Si
B
PhMe2Si
B
+
Toluene, 80 °C
2
13
93% yield, cis/trans >99:1
12
Scheme 3.

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M. Gerdin et al. / Journal of Organometallic Chemistry 693 (2008) 3519–3526
Table 5
Table 6
Silaboration of cycloheptadiene using Ni complexes
Silaboration of cycloheptadiene using chiral Ni complexes
Entry
Metal
Ligand
Concentration (M)
Yield (%)a
Entry
Ligand
Yielda (%)
ee (%)
1
2
3
4
5
6
7
Ni(acac)2 (5%)
Ni(acac)2 (5%)
Ni(acac)2 (10%)
Ni(acac)2 (5%)
Ni(acac)2 (5%)
Ni(acac)2 (5%)
Ni(acac)2 (5%)
PPh2Cy (10%)
PPh2Cy (10%)
PPh2Cy (20%)
PPh2Cy (20%)
PPhMe2 (10%)
PPh3 (10%)
0.5
0.8
0.8
0.5
0.5
0.5
0.5
61
50
73
84
–
1
2
3
4
5
6
7
8
9
4f
4g
4a
4c
16
17
18
19
60
55
–
8
8
17
87
30
11
12
22
10
n.d.
n.d.
10
14
n.d.
97
83
PPh3 (20%)
Reactions performed in toluene for 24 h at 80 °C.
Binap
Determined by 1H NMR using 1-methoxynaphthalene as internal standard.
a
Reactions performed in toluene, 80 °C 5% Ni(acac)2, 2:1 P/Ni ratio, 24 h.
a
Determined by 1H NMR using 1-methoxy-naphthalene as internal standard.
and the reaction was best performed using a 2:1 PPh3/Ni(acac)2 ra-
tio. Decreasing the amount of solvent did not increase the reaction
rate (entries 1 and 2). Since a complex with triphenylphosphine
catalyzed the reaction, we hoped that we could use a variety of
monodentate, chiral phosphines as ligands.
In order to determine the enantioselectivity of the reaction, 13
was oxidized to allylic alcohol 14 [16] and then transformed
into the (S)-Mosher ester. As the 1H NMR spectra of the two
diastereomers were very similar and their 19F NMR signals over-
lapped, the enantiomeric excess was assessed by chiral HPLC (see
Scheme 4).
2.3. Chiral silylboranes
Chiral analogues of 2 can easily be synthesized by reacting a
chiral diol with PhMe2SiBCl(NEt2) [8]. Such compounds have suc-
cessfully been applied in the asymmetric silaboration of allenes
[8,9]. Three structurally different silylboranes, 20–22, were synthe-
sized and applied in the silaboration of cyclohexadiene and cyclo-
heptadiene (see Fig. 4).
2.3.1. 1,3-Cyclohexadiene
The three silylboranes 20, 21, and 22 were employed in the
silaboration of 1,3-cyclohexadiene together with several metal
complexes and ligands. Ni(acac)2 and Pt(acac)2 were used in com-
bination with the most reactive achiral ligands. The most interest-
ing results are summarized in Table 7. Under nickel catalysis
promising selectivities (up to 58% de) were observed using PPh2Cy
as the ligand. Replacing it by tropos ligand 8 resulted in somewhat
lower yields and unaltered or diminished selectivities. Combining
platinum and PPh3 as catalyst resulted in a 1:1 mixture of two
Phosphoramidites were first used as ligands as they gave
superior induction in the silaboration of 1,3-cyclohexadiene. As ex-
pected, they did indeed give the desired product but, disappoint-
ingly, the highest ee observed was 22% (entries 1–4, Table 6). It
seems that small substituents on nitrogen are beneficial for the
reactivity of the complex. Then a variety of other chiral ligands were
examined. The ee values were not higher than 20% and many of the
ligands reacted sluggishly, although most of them provided the
product (entries 5–9, Table 6 and Fig. 3).
O
(S)-MTPA-Cl,
DMAP (cat.)
pyridine, rt
O
O
H2O2/NaOH
THF, rt
CF3
OMe
PhMe2Si
O
PhMe2Si
B
PhMe2Si
OH
Ph
15
13
14
Scheme 4.
Ph
Ph
N
P
O
P N
O
R
PPh2
Ph
O
N
N
16
17
N
R'
Ph
a
c
f
g
P
P
(S)-4
18
19
Fig. 3. Chiral ligands employed in silaboration of 1,3-cycloheptadiene.
O
O
O
O
O
O
O
O
PhMe2Si
B
PhMe2Si
B
PhMe2Si
B
O
O
20
21
22
Fig. 4. Chiral silylboranes.

M. Gerdin et al. / Journal of Organometallic Chemistry 693 (2008) 3519–3526
3523
Table 7
Silaboration of 1,3-cyclohexadiene using 20, 21, and 22
Table 8
Allylboration of aldehydes
Entry Silylborane Metal
Ligand
Temperature Time
Yield
(%)a
de
(%)
Entry
Aldehyde
Yielda (%)
d.r.b
Product
(°C)
(h)
1
2
3
4
5
6
7
8
Benzaldehyde
Valeraldehyde
Furfural
Pivalaldehyde
p-Anisaldehyde
4-Fluorobenzaldehyde
Cyclohexanal
77
88
76
0
72:28
71:29
87:13
–
23a
23b
23c
–
1
2
3
4
5
6
7
20
21
22
22
22
22
22
Ni(acac)2 PPh2Cy 80
Ni(acac)2 PPh2Cy 80
Ni(acac)2 PPh2Cy 80
Pt(acac)2 (R)-4f
Pt(acac)2 (S)-4f
Pt(acac)2 (R)-4d
Pt(acac)2 (R)-4e
24
24
24
48
48
48
48
40
86
46
72
62
78
86
58
44
19
37
21
59
71
110
0
–
–
110
110
80
90
72
64
65:35
90:10
72:28
23d
23e
23f
p-(Trifluoromethyl)benzaldehyde
Reactions performed in toluene using 5% M(acac)2, 10% ligand.
Reaction performed for 2 h in 1,2-dichlorobenzene at 240 °C in
a
microwave
a
Determined by 1H NMR using 1-methoxynaphthalene as internal standard.
reactor.
Determined by 1H NMR using 1-methoxynaphthalene as internal standard. Sum
a
of the two diastereomers.
b
Estimated from crude 1H NMR spectrum.
diastereomers, while combinations with phosphoramidite ligands
exclusively resulted in lowered selectivities. Silylborane 22 gave
the highest yields and selectivities and it was shown that (R)-con-
figuration on the binol gave the matched complex (Table 7, entries
4–5).
PhMe2Si
OH
H
Ph
H
2.3.2. 1,3-Cycloheptadiene
1,3-Cycloheptadiene was reacted with 20 and 21 using
Ni(acac)2 and achiral phosphines. The best results were obtained
with 21, yielding 70% of the desired product, with poor diastere-
oselectivity (7% de), employing PPh2Cy as the ligand.
Fig. 5. NOESY correlation observed.
180 °C product started appearing, and after 5 h at 240 °C it could
be isolated in 75% yield (sum of isomers). A screening of different
aldehydes was then undertaken to investigate the scope and limi-
tations of this reaction. Heating at 240 °C for 2 h was chosen as
standard conditions (see Table 8).
We were pleased to find that the reaction proceeded with both
aliphatic and aromatic aldehydes, although the sterically demand-
ing pivaldehyde and the electronically deactivated p-anisaldehyde
failed to react. The diastereoselectivities obtained were good to
modest. The yields were generally good. A cis configuration of
the PhMe2Si– and Ph(OH)CH-groups was confirmed by a strong
NOESY correlation between the corresponding cis protons for both
isomers of 23a. The two diastereomers therefore differ in relative
configuration at the hydroxy-substituted carbon atom (see Fig. 5).
2.4. Synthetic applications
We decided to investigate the reactivity of compound 3 in ally-
lboration reactions, as these usually proceed with good to excellent
diastereoselectivities, especially when catalyzed by Lewis acids
[3,17]. Among the Lewis acids employed, Sc(OTf)3 stands out as
being the most efficient [18]. The 1,4-silaboration products of sily-
lborane 2 and butadiene and 2,3-dimethylbutadiene have been
subjected to allylboration reactions, and found to give the expected
alcohols under mild reaction conditions [5]. The use of cyclic allyl-
boronates in allylboration reactions has also been reported [19]
(see Scheme 5).
2.4.1. Allylboration of aldehydes
As model substrate benzaldehyde was chosen and the reaction
was first tested at room temperature in DCM, although without
any noticeable conversion. Changing solvent to toluene and/or
increasing the temperature (80 °C, 110 °C) did not result in any
conversion of the starting materials. Using Sc(OTf)3 (10 mol%) as
Lewis acid in DCM, toluene or hexane at room temperature re-
sulted in decomposition of the starting material, even in the ab-
sence of benzaldehyde and no allylboration product was
observed. BF3 ꢀ OEt2 was also tested at room temperature and
ꢁ78 °C but still no product formation was observed. Considering
the sterically demanding nature of our substrate, with the bulky
dimethylphenylsilyl group blocking the access of the electrophile,
we assumed that more forcing reaction conditions were required.
Therefore we switched solvent to 1,2-dichlorobenzene, increased
the amount of benzaldehyde from a slight excess to 10 equiv.
and heated the reaction mixture in a microwave reactor. At
3. Conclusion
Silaborations of 1,3-cyclohexadiene and 1,3-cycloheptadiene
require different types of catalysts, containing Pt and Ni, respec-
tively, in order to proceed efficiently. In contrast to the situation
with linear 1,4-disubstituted 1,3-dienes, which provide 1:1
mixtures of dienylboranes and hydrosilylated products [20], only
1,4-silaborated adducts were obtained from the cyclic substrates.
The product from addition of 2-(dimethylphenylsilyl)-4,4,5,5-
tetrametyl-1,3,2-dioxaborolane to 1,3-cyclohexadiene was formed
with 82% ee using a catalyst obtained by reduction of Pt(acac)2 in
the presence of a phosphoramidite with (R)-binaphthyl and dib-
enzylamino groups. Attempts to improve the enantioselectivity
by using mixtures of phosphoramidites and achiral phosphines
were unsuccessful. The conditions employed for reactions of
cyclohexadiene did not provide the desired product from
R
HO
O
O
O
PhMe2Si
B
+
PhMe2Si
R
3
23
Scheme 5.

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M. Gerdin et al. / Journal of Organometallic Chemistry 693 (2008) 3519–3526
1,3-cycloheptadiene. Instead, Ni(0) and phosphoramidites gave the
1,4-cis adduct with up to 22% ee. The allylboration of aldehydes
using the product from silaboration of 1,3-cyclohexadiene was suc-
cessfully performed in a microwave reactor at 240 °C.
was stirred at r.t. for 16 h. The resulting product was taken up in
EtOAc (20 mL) and washed with sat. NaHCO3 (2 ꢂ 10 mL) and
NH4Cl (2 ꢂ 10 mL) solutions and brine (2 ꢂ 10 mL). The organic
phase was dried over MgSO4, filtered, and the solvents were evap-
orated in vacuo to yield the title compound. The enantiomeric ex-
cess was determined by HPLC [CHIRALCEL OD-H, 0.025% i-PrOH/
hexane, 1 mL/min]. 1H NMR (CDCl3) d 7.52–7.48 (m, 4H), 7.39–
7.36 (m, 6H), 5.75–5.67 (m, 2.5H), 5.61–5.55 (m, 0.5H), 0.27 (s, 6H).
4. Experimental
4.1. General remarks
4.5. Synthesis of phosphoramidite ligands
All transition metal catalyzed reactions were prepared inside a
nitrogen filled glovebox using oven dried glassware. After the reac-
tion flask had been sealed, heating was performed outside the
glovebox. Toluene, THF, Et2O, and hexane were dried using a
Glass-contour solvent dispensing system. The microwave heating
4.5.1. Synthesis of the chlorophosphite
Under an N2-atmosphere (R)- or (S)-binol (287 mg, 1 mmol)
was suspended in toluene (3 mL) and THF was added until the bi-
nol dissolved (0.5 mL). The binol solution was slowly added to a
TM
was performed using a Smith Creator single mode cavity from Bio-
cooled (ꢁ60 °C) solution of Et3N (278
lL, 2 mmol) and PCl3
tage. Cyclohexane was distilled from CaH2 prior to use. Compounds
2 [21], 4 [12], 5 [11], 8–10 [22], 17–18 [23], 19 [24], 20–22 [8], and
(S)-MTPA-Cl [25] were synthesized according to literature proce-
dures. Ni(acac)2 was dried in vacuo (1 mm Hg, 110 °C) prior to
use. Benzaldehyde, p-anisaldehyde, furfural, and cyclohexanal
used in allylboration reactions were freshly distilled. All other
chemicals were of at least 97% purity and used as received. 1H
NMR spectra were recorded at 500 or 400 MHz, 13C spectra at
125 MHz, and 31P spectra at 202 MHz. The 1H and 13C chemical
shifts are reported relative to CHCl3; 31P chemical shifts were not
calibrated.
(87
l
L, 1 mmol) and the resulting mixture was stirred at ꢁ60 °C
for 2 h and then transferred into a nitrogen filled glovebox and fil-
tered through celite to remove Et3NꢀHCl. The solution was diluted
to 10.00 mL with toluene to obtain a 0.10 M solution of the chloro-
phosphite that was stored in the glovebox at ꢁ35 °C.
4.5.2. Synthesis of phosphoramidite ligands
Inside a nitrogen filled glovebox a 0.1 M solution of the chloro-
phosphite (1.76 mL, 0.176 mmol) was added to a solution of amine
(52.0 mg, 0.176 mmol) and Et3N (24.7 lL, 0.176 mmol) in toluene
(0.6 mL) at ꢁ35 °C. The resulting mixture was stirred at r.t. for
18 h and filtered through celite using toluene as eluent. The result-
ing mixture was removed from the glovebox and the solvent was
removed in vacuo. The crude amidite was purified on deactivated
silica gel (prepared by suspending SiO2 (250 g) and NaHCO3 (5 g)
in MeOH and then evaporating the solvent until dryness) using a
gradient of hexane–DCM mixtures.
4.2. General procedure for silaboration of 1,3-dienes
Inside
0.2 mmol) was weighed into a vial. M(acac)2 (0.01 mmol), ligand
(0.02 mmol), toluene (0.20 mL), 1-methoxynaphtalene (29 L,
a nitrogen filled glovebox: silylborane 2 (52.2 mg,
l
0.2 mmol), and diene (0.50 mmol) were then added. The resulting
mixture was cooled in a freezer at ꢁ35 °C for approx 10 min. DI-
4.5.3. (R)-6
1H and 31P NMR spectra were in accordance with literature data
[27].
BALH (1 M) in cyclohexane (20 lL, 0.02 mol) was added via a syr-
inge and the solution was allowed to warm to room temperature
over 30 min. Heating was then performed outside the glovebox.
The yield was monitored by taking out 20 lL samples, evaporating
4.5.4. (R,R)-7
the solvents, recording the 1H NMR spectrum and comparing the
integrals from 1-methoxynaphthalene (d 4.0, –OMe) and com-
pound 3 (d 0.27 and 0.29, –SiMe2Ph). The enantiomeric excess of
compound 3 was determined as previously described [11].
1H and 31P NMR spectra were in accordance with literature data
[13].
4.5.5. (S,R)-7
1H and 31P NMR spectra were in accordance with literature data
[13].
4.3. Compound 14
Compound 13 [5] (crude product [26], maximum 0.2 mmol)
was dissolved in THF (15 mL). NaOH (2 M, 1.5 mL, 3 mmol) and
H2O2 (50% w/w, 0.7 mL, 1 mmol) were added via a syringe. The
resulting mixture was stirred vigorously for 2.5 h and then diluted
with 30 mL of Et2O, washed with brine (2 ꢂ 10 mL), dried over
MgSO4, filtered, and purified by flash chromatography on silica
gel using 5% EtOAc in hexane as eluent, yielding the desired prod-
uct as a colorless oil in 71% yield (over 2 steps using PPh3 as ligand
for formation of 13); 1H NMR (CDCl3): d 7.52–7.50 (m, 2H), 7.37–
7.35 (m, 2H), 5.76–5.72 (m, 1H), 5.66–5.62 (m, 1H), 4.40 (s, 1H),
1.9–1.25 (m, 9H), 0.32 (s, 3H), 0.30 (s, 3H); 13C NMR (CDCl3): d
138.3, 137.7, 134.4, 131.3, 129.6, 128.2, 72.0, 37.2, 29.9, 28.4,
27.7, ꢁ3.9, ꢁ4.0.
4.6. Compound 11
Et3N (50.8
lL, 365
l
mol) was added to a solution of 9 (30 mg,
122 mol) and (R)-(+)-1-phenylethylamine (14.7 mg, 122
l
lmol)
in THF (1 mL), and the mixture was stirred at r.t. for 18 h and then
filtered through celite. After evaporation of the solvents, 11 (16 mg,
40%) was obtained as a colourless oil. MS (EI, 70 eV): m/z 330
[M+ꢁ1] (76), 288 (100), 226 (8), 212 (24), 197 (82), 178 (40), 165
(40), 152 (8), 136 (6), 120 (12), 105 (24); 1H NMR (CDCl3) (mixture
of two diastereomers) d 1.46 (d, J = 6.7 Hz, 3H), 1.49 (d, J = 6.7 Hz,
3H), 1.61 (br t, J = 8.2 Hz, 2 ꢂ 1H), 2.36–2.17 (m, 4 ꢂ 1H), 2.48–
2.58 (m, 2 ꢂ 1H), 2.77 (dd, JH–H = 12.4, JP–H = 14.6 Hz, 1H), 2.88
(app t, J = 13.3 Hz, 1H), 4.10–4.27 (m, 2 ꢂ 1H), 6.70 (d, J = 7.5 Hz,
1H), 7.01–7.05 (m, 1H), 7.17–7.42 (m, 2 ꢂ 12H); 13C NMR (CDCl3)
d 147.3 (d, JC–P = 3.0 Hz), 146.9 (d, JC–P = 4.8 Hz), 140.8, 140.7,
140.6, 140.5, 140.4, 135.7, 135.5, 134.5 (d, JC–P = 6.8 Hz), 129.1,
129.0, 128.8, 128.7, 128.6, 128.5, 128.4, 128.3, 127.3, 127.2,
4.4. Compound 15
Inside
a nitrogen filled glovebox compound 14 (6.74 mg,
0.027 mmol) was weighed into
a
flask. DMAP (1.77 mg,
127.0, 126.8, 126.7, 126.6, 126.3, 126.2, 126.1, 126.0, 56.5 (d, JC–P
=
0.016 mmol) and (S)-MTPA-Cl (12
added. Pyridine (120 lL) was added via a syringe and the solution
ll, 0.035 mmol) were then
22.0 Hz), 55.7 (d, JC–P = 22.0 Hz), 36.6 (d, JC–P = 29.1 Hz), 36.5 (d,
JC–P = 27.3 Hz), 35.9 (d, JC–P = 23.4 Hz), 35.3 (d, JC–P = 25.5 Hz), 26.1

M. Gerdin et al. / Journal of Organometallic Chemistry 693 (2008) 3519–3526
3525
(d, JC–P = 6.5 Hz), 25.4 (d, JC–P = 8.8 Hz); 31P NMR (202 MHz, CDCl3)
4.8.3. Compound 23c
d 61.0, 59.2.
Compound 23c was purified on silica gel using a gradient of 2–
5% Et2O in hexane. Yield 20%, major isomer. 1H NMR (CDCl3) d 0.41
(s, 3H), 0.43 (s, 3H), 1.35–1.42 (m, 1H), 1.70–1.76 (m, 1H), 1.84 (d,
J = 9.7 Hz, 1H), 1.92–2.18 (m, 3H), 2.71–2.80 (m, 1H), 4.87 (d,
J = 9.6 Hz, 1H), 5.44–5.51 (m, 1H), 6.00 (dt, J = 3.2, 0.9 Hz, 1H),
6.03–6.10 (m, 1H), 6.27 (dd, J = 3.20, 1.82 Hz, 1H), 7.27–7.30 (m,
1H), 7.32–7.40 (m, 3H), 7.52–7.61 (m, 2H). Spectrum contains
around 24% of the minor isomer.
4.7. Compound 16
Inside
0.027 mmol) was weighed into a flask. DMAP (0.77 mg, 6.2
and (S)-MTPA-Cl (10 l, 62 L) were then added. Pyridine
(120 L) was added via a syringe and the solution was stirred at
a
nitrogen filled glovebox compound 15 (6.74 mg,
l
L)
l
l
l
r.t. for 16 h. The resulting product was taken up in EtOAc (20 mL)
and washed with sat. NaHCO3 (2 ꢂ 10 mL) and NH4Cl (2 ꢂ 10 mL)
solutions and brine (2 ꢂ 10 mL). The organic phase was dried over
MgSO4, filtered, and the solvents were evaporated in vacuo to yield
the title compound. The enantiomeric excess was determined by
HPLC [CHIRALCEL OD-H, 0.025% i-PrOH/hexane, 1 mL/min]. 1H
NMR (CDCl3) d 7.52–7.48 (m, 4H), 7.39–7.36 (m, 6H), 5.75–5.67
(m, 2.5H), 5.61–5.55 (m, 0.5H), 0.27 (s, 6H).
4.8.4. Compound 23d
Compound 23d was purified on silica gel using gradient of 5–
40% DCM in hexane. Yield 82%, major (maj) + minor (min) isomer
(65:35 d.r.). 1H NMR (CDCl3) d 0.38 (s, 3H, maj), 0.42 (s, 3H, min),
0.44 (s, 3H, min), 0.51 (s, 3H, maj), 1.18–1.59 (m, overlapping),
1.71–2.28 (m, overlapping), 2.40–2.48 (m, 1H, maj), 2.53–2.65
(m, 1H, min), 4.36 (dd, J = 10.0, 4.1 Hz, 1H, min), 4.84 (d,
J = 8.8 Hz, 1H, maj), 4.99 (ddt, J = 10.0, 4.3, 2.1 Hz, 1H, min), 5.18–
5.28 (m, 1H, maj), 5.56–5.64 (m, 1H, min), 6.02–6.12 (m, 1H,
maj), 6.63–6.78 (m, 2H, maj), 6.81–6.91 (m, 2H, maj), 6.92–7.03
(m, 2H, min), 7.13–7.22 (m, 2H, min), 7.30–7.68 (m, overlaping),
7.78–7.82 (m, 1H, min). 13C NMR (CDCl3) d ꢁ4.80 (maj), ꢁ2.90
(min), ꢁ2.76 (maj), ꢁ1.86 (min), 20.5 (maj), 21.3 (min), 24.8
(maj), 25.7 (min), 26.1 (maj), 26.3 (min), 26.4 (maj), 42.5 (maj),
44.7 (min), 74.5 (maj), 75.5 (min), 114.5 (maj), 114.6 (maj), 114.9
(min), 115.1 (min), 123.9 (maj), 126.3 (maj), 126.4 (maj), 127.77
(min), 127.84 (maj), 128.1 (maj), 128.42 (min), 128.49 (min),
128.53 (min), 128.66 (min), 129.1 (maj), 129.2 (min), 133.5
4.8. General procedure for allylboration of aldehydes
Inside
0.15 mmol) was weighed into a vial [28]. 1,2-Dichlorobenzene
(500 L) and aldehyde (1.5 mmol) were then added and the vial
a nitrogen filled glovebox compound 3 (51.3 mg,
l
was capped. Heating was performed outside the glovebox in a
microwave reactor. 1-Methoxynapthalene (23.7 mg, 0.15 mmol)
and 2 mL of water were then added and the mixture stirred for
15 min. Et2O (10 mL) was added and the phases separated. The
water phase was then repeatedly extracted with Et2O
(3 ꢂ 10 mL) and the combined organic phases dried over MgSO4,
filtered, the solvents were evaporated and a 1H NMR spectrum
was recorded. The crude product was then dried under vacuum
to remove remaining 1,2-dichlorobenzene. Purification was per-
formed using gradient chromatography yielding the products as
colorless oils.
2
2
(maj), 133.9 (d, JC–F = 25.4 Hz, maj), 134.1 (d, JC–F = 23.6, min),
3
3
138.4 (maj), 139.5 (d, JC–F = 3.1 Hz, min), 140.4 (d, JC–F = 3.1 Hz,
maj), 141.0 (min), 161.5 (d, JC–F = 244.3 Hz, maj), 162.8 (d, JC–F
245.4 Hz, min).
1
1
=
4.8.5. Compound 23e
Compound 23e was purified on silica gel using a gradient of
11–50% DCM in hexane. Yield 66%, major + minor isomer. Major
isomer: 1H NMR (CDCl3) d 0.33 (s, 3H), 0.37 (s, 3H), 0.52 (app.
qd, J = 12.2, 3.8 Hz, 1H), 0.76 (app. qd, J = 12.5, 3.3 Hz, 1H), 1.04
(d, J = 9.5 Hz, 1H), 1.06–1.34 (m, 6H), 1.39–1.49 (m, 1H), 1.52–
1.61 (m, 2H), 1.63–1.77 (m, 2H), 1.89–2.18 (m, 4H), 2.45–2.50
(m, 1H), 3.27 (app t, J = 9.0 Hz, 1H), 5.63–5.70 (m, 1H), 5.99–
6.07 (m, 1H), 7.32–7.39 (m, 3H), 7.50–7.57 (m, 2H); 13C NMR
(CDCl3) d ꢁ3.9, ꢁ3.3, 20.6, 25.9, 26.1, 26.2, 26.3, 26.7, 29.3, 29.6,
36.1, 42.6, 78.7, 125.5, 127.7, 128.8, 132.6, 133.85, 138.94.
Anal. Calc. for C21H32OSi: C, 76.77; H, 9.82. Found: C, 76.65; H,
9.77%.
4.8.1. Compound 23a
Compound 23a was purified on alumina (activity grade II) using
gradient of 1–5% EtOAc in hexane. Yield 75%, major + minor isomer
(5 h r ꢂ n time). Major and minor isomer were then separated on
silica using a gradient of 2–5% EtOAc in hexane. Major isomer:
1H NMR (CDCl3) d 0.39 (s, 3H), 0.51 (s, 3H), 1.35–1.50 (m, 1H),
1.70–1.90 (m, 1H), 1.83 (d, J = 8.9 Hz, 1H), 1.95–2.30 (m, 3H)
2.43–2.55 (m, 1H), 4.89 (d, J = 8.9 Hz,1H), 5.18–5.30 (m, 1H),
5.97–6.10 (m, 1H), 6.70–6.88 (m, 2H), 7.10–7.22 (m, 3H), 7.58–
7.70 (m, 3H), 7.87–7.98 (m, 2H); 13C NMR (CDCl3) d ꢁ4.6, ꢁ2.9,
20.5, 26.2, 26.6, 42.4, 75.0, 124.2, 124.8, 126.4, 127.8, 128.1,
129.0, 133.1, 134.0, 138.5, 144.7. Anal. Calc. for C21H26Osi: C,
78.21; H, 8.13. Found: C, 78.11; H, 8.09%.
Minor isomer: 1H NMR (CDCl3) d 0.30 (s, 3H), 0.34 (s, 3H), 0.78
(d, J = 7.2 Hz, 1H), 0.83–1.90 (m, 14H), 1.93–2.11 (m, 2H), 2.30–
2.37 (m, 1H), 3.20–3.27 (m, 1H), 5.63–5.67 (m, 1H), 5.68–5.75
(m, 1H), 7.32–7.38 (m, 3H), 7.52–7.58 (m, 2H); 13C NMR (CDCl3)
d ꢁ2.4, ꢁ2.3, 21.0, 24.4, 25.4, 26.4, 26.70, 26.76, 26.82, 31.2, 39.0,
40.1, 127.9, 128.6, 128.8, 129.6, 133.8, 141.4. Signal from
RCH(OH)Cy obscured by residual solvent peak.
Minor isomer: 1H NMR (CDCl3) d 0.41 (s, 3H), 0.44 (s, 3H), 1.49
(d, J = 4.9 Hz, 1H), 1.50–1.56 (m, 1H), 1.78–1.90 (m, 2H), 1.92–2.12
(m, 2H), 2.61–2.67 (m, 1H), 4.37 (dd, J = 10.0, 4.9 Hz, 1H), 4.97–5.02
(m, 1H), 5.54–5.61 (m, 1H), 7.19–7.39 (m, 8H), 7.59–7.68 (m, 2H).
13C NMR (CDCl3) d ꢁ2.9, ꢁ1.9, 21.4, 25.7, 26.3, 44.6, 76.2, 126.9,
127.6, 127.8, 128.28, 128.33, 128.6, 129.4, 133.8, 141.2, 143.7.
4.8.6. Compound 23f
4.8.2. Compound 23b
Compound 23f was purified on silica gel using a gradient of 0–
10% Et2O in hexane. Yield 29%, major isomer. 1H NMR (CDCl3) d
0.38 (s, 3H), 0.53, (s, 3H), 1.40–1.51 (m, 1H), 1.77–1.88 (m, 1H),
1.91 (d, J = 9.0 Hz, 1H), 1.96–2.12 (m, 2H), 2.13–2.27 (m, 1H),
2.43–2.50 (m, 1H), 4.88 (d, J = 9.0 Hz, 1H), 5.12–5.19 (m, 1H),
6.04–6.12 (m, 1H), 6.76–6.82 (m, 2H), 7.39–7.48 (m, 5H), 7.61–
7.66 (m, 2H); 13C NMR (CDCl3) d ꢁ5.0, ꢁ2.7, 20.4, 26.1, 26.4, 42.4,
Compound 23b was purified on alumina (activity grade II) using
a gradient of 1–10% Et2O in hexane. Yield 67%, major isomer (91:9
d.r.). Major isomer: 1H NMR (CDCl3) d 0.33 (s, 3H), 0.37 (s, 3H),
0.79–0.85 (t, J = 7.1 Hz, 3H), 1.02–1.42 (m, 8H), 1.65–1.75 (m,
1H), 1.92–2.16 (m, 3H), 2.20–2.26 (m, 1H), 3.60–3.68 (m, 1H),
5.67–5.78 (m, 1H), 5.99–6.08 (m, 1H), 7.29–7.40 (m, 3H), 7.49–
7.59 (m, 2H). 13C NMRCDCl3) d ꢁ3.99, ꢁ3.29, 14.0, 20.6, 22.5,
26.3, 26.8, 28.2, 36.9, 39.6, 74.2, 125.3, 127.8, 128.8, 132.7, 133.8,
138.9. Anal. Calc. for C19H30OSi: C, 75.43; H, 10.00. Found: C,
75.32; H, 9.88%.
1
3
74.5, 123.4, 124.2 (q, JC–F = 271.7 Hz), 124.7 (q, JC–F = 3.7 Hz),
3
125.2, 128.2, 128.7 (q, JC–F = 32.3 Hz), 129.2, 133.96, 134.00,
138.3, 148.8.

3526
M. Gerdin et al. / Journal of Organometallic Chemistry 693 (2008) 3519–3526
[12] L.A. Arnold, R. Imbos, A. Mandoli, A.H.M. de Vries, R. Naasz, B.L. Feringa,
Acknowledgments
Tetrahedron 56 (2000) 2865–2878.
[13] L. Eberhardt, D. Armspach, D. Matt, L. Toupet, B. Oswald, Eur. J. Org. Chem.
(2007) 5395–5403.
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(2003) 790–793;
(b) D. Peña, A.J. Minnaard, J.A.F. Boogers, A.H.M. de Vries, J.G. de Vries, B.L.
Feringa, Org. Biomol. Chem. 1 (2003) 1087–1090;
(c) M.T. Reetz, Angew. Chem., Int. Ed. 47 (2008) 2556–2588.
[15] R. Hoen, J.A.F. Boogers, H. Bernsmann, A.J. Minaard, A. Meetsma, T.D.
Tiemersma-Wegman, A.H.M. de Vries, J.G. de Vries, B.L. Feringa, Angew.
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This work was supported by the Swedish Research Council and
by the Carl Trygger Foundation. We are grateful to Dr Nina Kann
and Dr Magnus Johansson for generous gifts of ligands 18 and
19. We would also like to thank Mr. Michael Holzwarth for his ef-
fort on the allylboration reactions and Dr. Zoltan Szabo for running
NOESY spectra.
[16] The oxidation of organoboranes using H2O2/NaOH is known to proceed with
retention of configuration. See: H.C. Brown, C. Snyder, B.C.S. Rao, G. Zweifel,
Tetrahedron 42 (1986) 5505–5510.
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12 (2006) 3132–3142;
(d) X. Gao, D.G. Hall, J. Am. Chem. Soc. 127 (2005) 1628–1629;
(e) G. Hilt, W. Hess, K. Harms, Org. Lett. 8 (2006) 3287–3290.
[20] M. Gerdin, C. Moberg, Org. Lett. 8 (2006) 2929–2932.
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Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2008.08.029.
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use of schlenck techniques. As it slowly decomposes in air we chose to store
and handle it inside the glovebox.
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