Nickel(0)-catalyzed intramolecular reductive coupling of alkenes and aldehydes or ketones with hydrosilanes

Article abstract of DOI:10.1039/c6cc01915c

A nickel(0)-catalyzed reductive coupling of aldehydes and simple alkenes with hydrosilanes has been developed. A variety of silyl-protected 1-indanol derivatives were prepared in a highly diastereoselective manner (up to >99:1 dr) by employing a combination of nickel(0)/N-heterocyclic carbene and triethylsilane. The present system was also applied to a reductive coupling with ketones. Preliminary results of a nickel(0)-catalyzed asymmetric three-component coupling reaction of an aldehyde, an alkene, and triethylsilane are also shown.

Full text of DOI:10.1039/c6cc01915c

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DOI: 10.1039/C6CC01915C
Journal Name
COMMUNICATION
Nickel(0)-Catalyzed Intramolecular Reductive Coupling of Alkenes
and Aldehydes or Ketones with Hydrosilanes
Yukari Hayashi,a Yoichi Hoshimoto,ab Ravindra Kumar,a Masato Ohashia and Sensuke Ogoshi*a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
A nickel(0)-catalyzed reductive coupling of aldehydes and simple catalyzed reductive coupling reactions.2 Among them, the
alkenes with hydrosilanes has been developed. A variety of silyl-
protected 1-indanol derivatives were prepared in
diastereoselective manner (up to >99:1 dr) by employing a
combination of nickel(0)/N-heterocyclic carbene and
a highly
triethylsilane. The present system was also applied to a reductive
coupling with ketones. Preliminary results of a nickel(0)-catalyzed
asymmetric three-component coupling reaction of an aldehyde,
an alkene, and triethylsilane are also shown.
A high level of efficiency and wide applicability would make
the oxidative cyclization of two π components with nickel(0) a
key process in a variety of catalytic molecular transformations
proceeding through carbon–carbon bond formations. Indeed,
much progress has been realized in nickel(0)-catalyzed
molecular transformations, which were proposed to take place
through hetero-nickelacycle intermediates generated by
oxidative cyclization.1,2 We have also contributed to these
developments1a,b by the direct observation of the formation of
oxanickelacycles from (η2-aldehyde:η2-alkene)nickel complexes
through oxidative cyclization,3a and by the expansion of this
stoichiometric process to a catalytic hydroacylation yielding
five- and six-membered benzocyclic ketones (Scheme 1a).3b
This hydroacylation was proposed to proceed through β-
hydride elimination from the oxanickelacycle intermediate,
which was supported by the results of stoichiometric
experiments. Oxanickelacycles could efficiently react with a
reductant such as silanes, organoboranes, and organozincs,
and these have been the key process for many nickel(0)-
reactions of alkynes and aldehydes have been well-
developed.4,5 The use of 1,3-dienes6 or allenes7 instead of
alkynes was also reported. Nevertheless, the use of alkenes
has been rare, which probably is due to the difficulty of both
the simultaneous coordination of these two components to
nickel(0) and the following oxidative cyclization.2e Thus far, the
use of alkenes has been limited to the highly reactive ones
such as methylenecyclopropane,8 norbornene9 and
tetrafluoroethylene.10 Herein, we report an intramolecular
reductive coupling reaction of simple alkenes and aldehydes
with hydrosilanes catalyzed by nickel(0)/N-heterocyclic
carbene (NHC), yielding a variety of silyl-protected 1-indanol
derivatives in a diastereoselective manner (Scheme 1b). We
also demonstrate a corresponding reductive coupling reaction
with ketones instead of aldehydes.11
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DOI: 10.1039/C6CC01915C
comprising Ni(cod)2 and SIPr (entry 7 vs. 5). We thus used TNSI
for a further optimization since TNSI can be prepared through
a single-step, one-pot, and gram-scale method,12 and it readily
dissolves in a variety of solvents including alkane mediums,
unlike Ni(cod)2. In addition, the experimental manipulations
were simplified and made more accurate by using the
prepared nickel(0) complex. The reaction at 40 C resulted in
improvements in both yield and diastereoselectivity giving 2a
in 99% isolated yield (entry 8). Among the various solvents we
examined, toluene gave the highest yield and
diastereoselectivity (entries 8–11). The syn-conformation
between the silyl ether and the methyl groups in 2a was
confirmed by comparison with reports in the literature after
desilylation with TBAF (94% isolated yield).13,14
The impact of the steric and electronic nature of silanes on
both the yield and diastereoselectivity was not significant
(Table 2). Good to excellent yields and diastereoselectivities
were obtained across a broad range of silanes, with the
exception of (EtO)3SiH (entry 7). Other reducing reagents such
as diethylzinc or triethylborane were less effective in this
reaction.14
The reaction conditions were optimized through the use of
o-allylbenzaldehyde (1a) and triethylsilane (Table 1). The
formation of 1-triethylsiloxy-2-methylindan
(
2a
)
was
confirmed when NHC ligands were employed, whereas PPh3
and PCy3 were not effective (entries 1–6). Among the NHCs we
examined, SIPr gave 2a in a better yield at room temperature
(69%, entry 5). In this reaction system, (η6-toluene)Ni(SIPr)
(
TNSI) was generated as a precursor for an active nickel(0)/SIPr
catalyst.12 Indeed, the reaction conducted with TNSI provided
2a without a loss of the yield compared with the system
2 | J. Name., 2012, 00, 1-3
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The scope of the reaction was investigated with respect to metathesis and reductive elimination might giveVtiehweArptircloedOunlcinte.
DOI: 10.1039/C6CC01915C
o-allylbenzaldehyde derivatives
(1a–j) (Table 3). When Analogous mechanisms proceeding through oxanickelacycle
electron-donating groups were bonded to the benzene ring intermediates were proposed in the reductive coupling
1b–c), the reaction proceeded well to give the corresponding reaction of aldehydes and alkynes.18
silyl-protected 1-indanol derivatives in >97% isolated yields. In conclusion, the
(
nickel(0)/NHC-catalyzed
The fluorine substituted products (2d–f) were obtained in diastereoselective intramolecular reductive coupling of
>89% isolated yields; however, a trace amount of chlorine- alkenes and aldehydes with hydrosilanes was demonstrated. A
substituted product 2g was obtained. Both products with the variety of silyl-protected 1-indanol derivatives were prepared
o-benzyl group (2h) and the naphthyl structure (2i) were in excellent yields with perfect diastereoselectivities.
A
obtained in >99% isolated yields. In all of these reactions, the corresponding reductive coupling with ketones was also
syn-isomer was obtained with >99:1 dr. The substituted allyl achieved. The preliminary results on the enantioselective
group was also employed to afford 2j in >99% isolated yield.
reductive coupling were shown, in which the target indanol
The results of a reductive coupling of alkenes and ketones was obtained with a perfect diastereoselectivity and a
with triethylsilane are shown in Scheme 2. The reaction of o- promising enantioselectivity. Further development of this
allylacetophenone (1k) took place efficiently to afford the enantioselective process is ongoing in our group.
corresponding silyl-protected 1-methyl-1-indanol (2k) in 98%
This work was supported by Grants-in-Aid for Young
isolated yield and >99:1 dr. The syn-conformation between the Scientists (A) (25708018) and Grants-in-Aid for Scientific
silyl ether and the methyl groups in 2k was confirmed by Research on Innovative Area “Precise Formation of a Catalyst
comparison with reports in the literature after desilylation Having a Specified Field for Use in Extremely Difficult Substrate
with TBAF.14,15 The substituted allyl group was also employed Conversion Reactions” (15H05803) and “Stimuli-responsive
at 60

C, giving 2l in >99% isolated yield.
Chemical Species” (15H00943) from MEXT and by ACT-C from
Preliminary results of the expansion of the presented JST. Y.H. acknowledges support from the Frontier Research
reaction to an enantioselective version are given in Scheme Base for Global Young Researchers, Osaka University, on the
3.14 Chiral NHC ligands generated in situ by treating the Program of MEXT. Y.H. expresses her special thanks for the
imidazolinium salts (Ln•HBF4) with t-BuOK were applied in this Research Fellowship for Young Scientists from JSPS.
reaction. The reductive coupling of 1a and triethylsilane was
catalyzed by 5 mol% of Ni(cod)2 and L1 at room temperature
for 24 h in 1,4-dioxane and provided 2a in 92% isolated yield,
Notes and references
>99:1 dr, and 15% ee. The enantiomeric excess of 2a was
determined using supercritical fluid chromatography (SFC)
1
For selected recent reviews and books on the nickel(0)-
catalyzed reactions via nickelacycle intermediates, see: (a)
M. Ohashi, Y. Hoshimoto and S. Ogoshi, Dalton Trans., 2015,
44, 12060; (b) Y. Hoshimoto, M. Ohashi and S. Ogoshi, Acc.
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after converting it into 2-methyl-1-indanol
(3a) through
desilylation using TBAF.14 A novel ligand L2 was prepared
according to the procedures of L1 reported by Montgomery et
al.,16 and the system utilizing L2 afforded further improved
results (98% isolated yield, >99:1 dr, and 38% ee). The absolute
configuration of (1S,2S)-2a was confirmed by comparing the
specific rotation of corresponding desilylation product (1S,2S)-
3a with data found in the literature.13b
and T. F. Jamison, Nature, 2014, 509
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Hoboken, N.J., 2013, pp. 319–428; (e) J. C. Leung and M. J.
Krische, Chem. Sci., 2012, 3, 2202; (f) Modern Organonickel
Chemistry; ed. Y. Tamaru, Wiely-VCH, Weinheim, 2005.
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Jensen and T. F. Jamison, Acc. Chem. Res., 2015, 48, 1503; (b)
E. P. Jackson, H. A. Malik, G. J. Sormunen, R. D. Baxter, P.
Liu, H. Wang, A.-R. Shareef and J. Montgomery, Acc. Chem.
2
This intramolecular reductive coupling might proceed
through oxidative cyclization of an aldehyde and an alkene
affording an oxanickelacycle intermediate as shown in Scheme
1.17 The oxidative cyclization process would be promoted by a
Lewis acidic silane reagent.2e,3a The following σ-bond
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was confirmed by NMR spectroscopy.
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4 | J. Name., 2012, 00, 1-3
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