Nickel-catalyzed enantio- and diastereoselective three-component coupling of 1,3-dienes, aldehydes, and a silylborane leading to α-chiral allylsilanes

Article abstract of DOI:10.1002/anie.201107360

Three-in-one: The nickel-catalyzed asymmetric three-component coupling of 1,3-dienes, aldehydes, and a silylborane in the presence of a chiral phosphoroamidite ligand has been realized. The reaction proceeds by σ-bond metathesis of an oxanickelacycle intermediate with the silylborane to afford the corresponding α-chiral allylsilane derivative in a highly diastereo- and enantioselective manner. Copyright

Full text of DOI:10.1002/anie.201107360

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DOI: 10.1002/anie.201107360
a-Chiral Allylsilanes
Nickel-Catalyzed Enantio- and Diastereoselective Three-Component
Coupling of 1,3-Dienes, Aldehydes, and a Silylborane Leading to a-
Chiral Allylsilanes**
Nozomi Saito,* Ayami Kobayashi, and Yoshihiro Sato*
Transition metal-catalyzed addition of the metal–metal link-
age of bimetallic compounds (1: X, Y= B, Si, Sn, Ge, etc.) to
unsaturated bonds (i.e., bismetalation) is an indispensable
strategy for the synthesis of various types of organometallic
compounds.[1] Bismetalation of simple unsaturated com-
pounds 2, such as alkenes, alkynes, and allenes, has been
established as a promising method for the preparation of 1,2-
dimetallo-organic compounds 3 (Scheme 1, type A). On the
Nickel-catalyzed intra- and intermolecular couplings of
1,3-dienes and aldehydes have attracted much attention
because the coupling reaction has been recently employed
as an efficient synthetic method for the generation of homo-
and bis-homoallylic alcohols.[5,6] We have also contributed to
the development of the field of nickel-catalyzed couplings and
cyclizations of 1,3-dienes and carbonyl groups.[7,8] A key
intermediate in diene–aldehyde coupling is oxanickelacycle
8,[9] generated by the oxidative cycloaddition of 1,3-diene 6
and aldehyde 7 to a nickel(0) complex, which is known to
react with various organometallic reagents.[10] Thus, trans-
metalation or s-bond metathesis between nickelacycle 8 and
organometallic compounds (R-M) proceeds to give bis-
homoallylic alcohol derivatives 9 (Scheme 2a) or homoallylic
alcohols 10 (Scheme 2b) depending on the substrate struc-
Scheme 1. Transition-metal-catalyzed simple bismetalation of unsatu-
rated compounds (Type A) and multicomponent coupling of unsatu-
rated compounds with a bimetallic reagent (Type B).
other hand, the multicomponent coupling of different unsa-
turated compounds 2 and 4 with a bimetallic reagent, wherein
À
a C C bond forming reaction accompanied by bismetalation
occurs, should also be an attractive method to synthesize
dimetallo compounds 5 (type B). Such an approach would
give a wide variety of 1,n-dimetallo species by combining
various types of bimetallic reagents 1 with unsaturated
compounds 2 and 4. However, in contrast to extensive studies
that have been carried out on type A reactions, type B
reaction systems are still limited and this coupling therefore
remains a frontier in organometallic chemistry.[2] An enantio-
selective version of the type A bismetalation has also been
extensively investigated as a practical method for the
preparation of optically active organometallic compounds,[3]
whereas an enantioselective type B multicomponent coupling
has not been reported to date.[4]
Scheme 2. Nickel-catalyzed coupling of 1,3-dienes and aldehydes via
an oxanickelacycle intermediate. pin=pinacolato.
ture, class of organometallic reagent, and type of ligand
employed. We envisaged that, if a heterobimetallic com-
pound, such as silylborane,[1e,h] is employed for the diene–
aldehyde coupling, the reaction of oxanickelacycle 8 and the
silylborane would proceed by a highly oxophilic boron atom
interacting with an oxygen atom, giving the coupling product
[*] Dr. N. Saito, A. Kobayashi, Prof. Dr. Y. Sato
Faculty of Pharmaceutical Sciences, Hokkaido University
Sapporo 060-0812 (Japan)
E-mail: biyo@pharm.hokudai.ac.jp
[**] This work was supported by a Grant-in-Aid for Science Research on
Priority Areas (Nos. 19027005 and 20036005, Synergy of Elements)
from MEXT (Japan) and a Grant-in-Aid for Scientific Research (B)
(No. 23390001) from JSPS. N.S. acknowledges the NOVARTIS
Foundation (Japan) for the Promotion of Science and the Takeda
Science Foundation for financial support.
À
À
11 through three different bond forming reactions (C C, C
À
Si, and O B) in one pot. We also expected that the coupling
reaction would provide a new method for the synthesis of a-
chiral allylsilanes.[11] Herein, we describe a novel three-
component coupling of 1,3-dienes and aldehydes with com-
mercially available (dimethylphenylsilyl)pinacolatoboron
(PhMe2SiB(pin), 12)[12] and its development into an enantio-
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201107360.
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selective reaction,[13] leading to enantioenriched a-chiral
allylsilanes.
3,3’-bis(diphenylmethyl) analogue (R)-17 f gave 13aa in 71%
yield and 81% ee (entry 11). Finally, (R)-17g[15e] was found to
be the most effective ligand, with 13aa being produced in
71% yield and 97% ee (entry 12).[16]
To study the feasibility of a three-component coupling of
1,3-dienes, aldehydes, and a silylborane, we first investigated
the reaction using achiral ligands. Thus, the reaction of 1,3-
diene 6a, benzaldehyde (7a), and PhMe2SiB(pin) (12) was
carried out in the presence of 10 mol% of [Ni(cod)2] and
10 mol% of PPh3 in DMF at room temperature for 3 hours
(Scheme 3). As a result, the coupling product 13aa was
With optimized conditions in hand, we explored the scope
of the enantioselective coupling (Table 2). Reaction of 6a
with 7b and 7c, bearing an electron-donating group on the
aromatic ring, afforded the corresponding products 13ab and
13ac in high yield and enantiopurity (entries 1 and 2). When
1,3-diene 6a was reacted with p-trifluorobenzaldehyde (7d),
the yield of 13ad decreased to 29%, although the ee remained
high (entry 3). Coupling reactions of bicyclic aromatic
aldehydes 7e and 7 f with 6a also proceeded to afford the
corresponding products 13ae and 13af in high yield and
enantiopurity (entries 4 and 5). Aliphatic aldehydes 7g–7i
were also suitable for coupling with 6a, giving allylsilanes
13ag–13ai in a highly enantioselective manner (entries 6–8).
The coupling of siladiene 6b with 7a gave 13ba in 80% yield
and 82% ee (entry 9). Also, alkyl substituted diene 6c was
coupled with 7a and the corresponding product 13ca was
obtained in moderate yield and enantiopurity as a single
diastereomer (entry 10). Next, the asymmetric coupling
reaction of internal dienes with 7a was investigated
(entries 11 and 12). When the reaction of unsymmetrical
diene 6d and 7a was carried out under optimized conditions,
the corresponding coupling product 13da was obtained in
Scheme 3. Three-component coupling of 1,3-diene 6a, benzaldehyde
(2a), and silylborane 12 and determination of product stereochemistry
at C1 and C3. cod=1,5-cyclooctadiene, pin=pinacolato, MOM=me-
thoxymethyl, PPTS= pyridinium p-toluenesulfonate.
Table 1: Screening of chiral ligands.[a]
obtained in 94% yield as a single diastereomer. The relative
stereochemistries of the hydroxy group at the C1 position and
the PhMe2Si group at the C3 position of 13aa were
1
determined by H NMR spectroscopy and NOESY experi-
ments on 14 (derived from 13aa) to be 1,3-syn orientation.
This result indicated that the reaction of oxanickelacycle 8
with silylborane 12 proceeded to give the cross-coupling
product 11aa exclusively, as expected, from which 13aa was
produced by hydrolysis of the boron–oxygen bond.[14]
Entry
Ligand
t [h]
Yield [%]
ee [%]
1
2
3
4
5
6
7
8
(R)-BnO-MOP
NMDPP
(R,R)-15
(R,R)-16
24
3
54
57
26
37
70
29
51
56
59
57
71
71
12[b]
1[b]
24
16
24
26
18
13
18
26
24
22
6[b]
2[b]
Encouraged by this result, we set out to conduct a screen
of various chiral ligands for the realization of an enantiose-
lective version of the 1,3-diene and aldehyde coupling
(Table 1). The coupling reaction of 6a, 7a, and 12 using
chiral phosphine ligands, (R)-BnO-MOP,[15a] NMDPP, (R,R)-
15,[15b] or phosphoroamidite ligand (R,R)-16,[15c] gave 13aa in
moderate yield and low ee (entries 1–4). However, the use of
(R)-MonoPhos provided 13aa in 70% yield, although the
enantioselectivity was still low (entry 5). Based on these
results, MonoPhos seemed to be a good starting point, so we
decided to modify it and apply its analogues to the coupling
reaction (entries 6–11). When N,N-diisopropyl and N,N-
dibenzyl analogues (R)-17a and (R)-17b[15d] were employed,
both the yield and ee of 13aa decreased (entries 6 and 7). On
the other hand, modification of the 3,3’ positions of the
binaphthyl skeleton was found to be effective for improving
the enantioselectivity (entries 8–12). Introduction of a methyl
group ((R)-17c)[15d] and a phenyl group ((R)-17d)[15d] at the
3,3’-positions increased the ee of 13aa to 52% and 58%,
respectively (entries 8 and 9). The reaction using 3,3’-dime-
sityl derivative (R)-17e provided the coupling product 13aa in
57% yield and 94% ee (entry 10). The coupling reaction using
(R)-MonoPhos
À19[c]
À4[c]
À9[c]
À52[c]
À58[c]
94[b]
81[b]
97[b]
(R)-17a (R1 =H, R2 =iPr)
(R)-17b (R1 =H, R2 =Bn)
(R)-17c (R1 =R2 =Me)
(R)-17d (R1 =Ph, R2 =Me)
(R)-17e (R1 =mesityl, R2 =Me)
(R)-17 f (R1 =CHPh2, R2 =Me)
(R)-17g (R1 =CHPh2, R2 =Bn)
9
10
11
12
[a] cod=1,5-cyclooctadiene, MOM=methoxymethyl. [b] (1S,3R)-13aa
was formed as the major enantiomer. [c] (1R,3S)-13aa was formed as the
major enantiomer. The absolute configuration of 13aa was determined
by transformation to a known compound. For details, see the Supporting
Information.
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Table 2: Asymmetric coupling of various dienes and aldehydes with silylborane 12.[a]
[1] For reviews on the bismetalation of unsaturated bonds,
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1,3-dienes with a chiral diboron reagent followed by
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Morgan, J. P. Morken, Org. Lett. 2003, 5, 2573.
Entry Diene
Aldehyde
Product: yield, ee (t)
1
2
3
6a
7b: R1 =Me
13ab: 89%, 96% ee (20 h)
7c: R1 =OMe 13ac: 92%, 92% ee (5 h)
7d: R1 =CF3
13ad: 29%, 85% ee (48 h)
4
5
13ae: 72%, 92% ee (24 h)
13af: 82%, 92% ee (18 h)
6
7
13ag: 68%, 96% ee (18 h)
13ah: 56%, 97% ee (20 h)
8
9
13ai: 74%, 94% ee (18 h)
7a
7a
10
11
7a
7a
[5] For reviews on the nickel-catalyzed coupling of 1,3-
dienes and carbonyl groups, see: a) M. Kimura, Y.
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12
[a] Reaction conditions: Diene 6 (1 equiv), aldehyde 7 (2.5 equiv), [Ni(cod)2]
(10 mol%), (R)-17g (10 mol%), PhMe2SiB(pin) (12, 2.5 equiv), DMF, RT.
[6] For recent examples of diene–aldehyde couplings
catalyzed by other transition metals and leading to
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22% yield and 92% ee (entry 11). When (E,E)-1,4-diphenyl-
buta-1,3-diene (6e) was employed for the coupling with 7a
and 12, 13ea was produced in 51% yield and 20% ee as a
single diastereomer (entry 12).
In summary, we have succeeded in developing an enantio-
and diastereoselective three-component coupling of 1,3-
dienes, aldehydes, and a silylborane. This coupling reaction
is the first example of an asymmetric coupling of two different
types of unsaturated compounds with a bimetallic reagent and
represents a new synthetic approach to optically active a-
chiral allylsilane derivatives. Further studies, including a
mechanistic investigation, are in progress.
Received: October 19, 2011
Published online: December 15, 2011
Keywords: aldehydes · asymmetric catalysis · dienes · nickel ·
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silylborane
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T. Takanashi, M. Hoshiba, M. Mori, J. Organomet. Chem. 2003,
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À
À
dienes and aldehydes through the formation of C C, C B, and
À
O Si bonds in one pot; see: M. Suginome, H. Nakamura, T.
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