Journal of the American Chemical Society
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drogenation of Aromatic, Aliphatic, and a,b-Unsaturated Acyl Silanes
Catalyzed by Tol-binap/Pica Ruthenium(II) Complexes: Practical Synthe-
sis of Optically Active a-Hydroxysilanes. Angew. Chem. Int. Ed. 2008,
47, 1770.
In conclusion, asymmetric reactions between aromatic alde-
hydes and aryl bromides with a silylboronate occurred with
high enantioselectivities to yield the three-component coupling
products, chiral silyl-protected secondary alcohol derivatives.
The reaction was enabled by the merging of a new chiral cop-
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per–N-heterocyclic carbene catalyst and
a
palladium–
bisphosphine catalyst in a synergistic manner. Preliminary
results showed that this palladium/copper catalysis is also
amenable to the reaction of an allylic carbonate as the cou-
pling partner. Our method features the catalytic generation of
enantioenriched chiral a-alkoxyalkylcopper(I) intermediates
from aldehydes and their subsequent palladium-catalyzed ste-
reospecific cross-coupling with aryl or allyl electrophiles. This
protocol provides a new umpolung strategy for catalytically
forming a chiral a-alkoxyalkyl anion from an aromatic alde-
hyde for use in asymmetric synthesis. Mechanistic investiga-
tions aided by theoretical calculations are currently ongoing in
our laboratory.
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ASSOCIATED CONTENT
Supporting Information. Experimental details and characteriza-
tion data for all new compounds (PDF). This material is available
AUTHOR INFORMATION
Corresponding Author
(6) (a) Takeda, M.; Yabushita, K.; Yasuda, S.; Ohmiya, H. Synergistic palladi-
um/copper-catalyzed Csp3–Csp2 cross-couplings using aldehydes as latent
a-alkoxyalkyl anion equivalents. Chem. Commum. 2018, 54, 6776. See
also: (b) Takeda, M.; Nagao, K.; Ohmiya, H. Reductive Coupling be-
tween Aldehydes and Ketones by Copper Catalysis. Submitted.
ORCID
Hirohisa Ohmiya: 0000-0002-1374-1137
Kazunori Nagao: 0000-0003-3141-5279
(7) For non-enantioselective reaction involving catalytic generation of a-
oxygenated enolates from a-ketoesters through [1,2]-phospha-Brook re-
arrangement, followed by an SNAr reaction, see: Kondoh, A.; Aoki, T.;
Terada, M. Efficient Synthesis of Polysubstituted Pyrroles Based on
[3+2] Cycloaddition Strategy Utilizing [1,2]-Phospha-Brook Rearrange-
ment under Brønsted Base Catalysis. Chem. Eur. J. 2018, 24, 15246.
(8) For reviews on enantioselective preparation of chiral diarylmethanols, see:
(a) Ameen, D.; Snape, T. J. Chiral 1,1-diaryl compounds as important
pharmacophores. Med. Chem. Commun. 2013, 4, 893. (b) Schmidt, F.;
Stemmler, R. T.; Rudolph, J.; Bolm, C. Catalytic asymmetric approaches
towards enantiomerically enriched diarylmethanols and diarylmethyla-
mines. Chem. Soc. Rev. 2006, 35, 454. For selected recent papers, see: (c)
Touge, T.; Nara, H.; Fujiwhara, M.; Kayaki, Y.; Ikariya, T. Efficient Ac-
cess to Chiral Benzhydrols via Asymmetric Transfer Hydrogenation of
Unsymmetrical Benzophenones with Bifunctional Oxo-Tethered Ruthe-
nium Catalysts. J. Am. Chem. Soc. 2016, 138, 10084−10087. (d) Lee, T.;
Wilson, T. W.; Berg, R.; Ryberg, P.; Hartwig, J. F. Rhodium-Catalyzed
Enantioselective Silylation of Arene C–H Bonds: Desymmetrization of
Diarylmethanols. J. Am. Chem. Soc. 2015, 137, 6742. (e) Salvi, L.; Kim, J.
G.; Walsh, P. J. Practical Catalytic Asymmetric Synthesis of Diaryl-, Aryl
Heteroaryl-, and Diheteroarylmethanols. J. Am. Chem. Soc. 2009, 131,
12483.
(9) Chiral bisphosphine ligand such as DTBM-SEGPHOS resulted in no reac-
tion. See ref 4c.
(10) Scholl, M.; Ding, S.; Lee, C. W.; Grubbs, R. H. Synthesis and Activity of
a New Generation of Ruthenium-Based Olefin Metathesis Catalysts Co-
ordinated with 1,3-Dimesityl-4,5-dihydroimidazol-2-ylidene Ligands.
Org. Lett. 1999, 1, 953.
(11) Faller, J. W.; Fontaine, P. P. Stereodynamics and Asymmetric Hydrosi-
lylation with Chiral Rhodium Complexes Containing a Monodentate N-
Heterocyclic Carbene. Organometallics 2006, 25, 5887.
(12) Lillo, V.; Prieto, A.; Bonet, A.; Díaz-Requejo, M. M.; Ramírez, J.; Peŕez,
P. J.; Fernańdez, E. Asymmetric b-Boration of a,b-Unsaturated Esters
with Chiral (NHC)Cu Catalysts. Organometallics 2009, 28, 659.
(13) To test the assumption, we investigated the reaction without NHC ligand
for a copper under conditions shown in Table 1, entry 10. The coupling
product was obtained in a low yield.
ACKNOWLEDGMENT
This work was supported by JSPS KAKENHI Grant Number
JP18H01971 to Scientific Research (B), JSPS KAKENHI Grant
Number JP17H06449 (Hybrid Catalysis), Kanazawa University
SAKIGAKE project 2018 and the Uehara Memorial Foundation.
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