ACS Catalysis
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Acidity. Polymer 1996, 37, 4629–4631.
CF3H has diagnostic spectral signatures, and it is not
observed during in situ catalysis experiments. In
hydrogenations with Hantzsch ester, BAr3,5-CF3 was found
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(5)
Childs, R. F.; Mulholland, D. L.; Nixon, A. The Lewis Acid
Complexes of α,β-Unsaturated Carbonyl and Nitrile
Compounds. A Nuclear Magnetic Resonance Study. Can. J.
Chem. 2006, 60, 801–808.
Sivaev, I. B.; Bregadze, V. I. Lewis Acidity of Boron
Compounds. Coord. Chem. Rev. 2014, 270–271, 75–88.
Morgan, M. M.; Marwitz, A. J. V; Piers, W. E.; Parvez, M.
6 5 3
to also not build up the borohydride while B(C F )
29,38
does.
the catalysts speciate quite differently. The consequences
of these behaviors are that B(C catalyzed reactions
The above in situ observations demonstrate that
(6)
(
7)
6 5 3
F )
Comparative Lewis Acidity in Fluoroarylboranes: B(o-HC
, B(p-HC , and B(C . Organometallics 2013, 32, 317–
22.
Ishihara,
Tris(Pentafluorophenyl)Boron as
6
F
have little free boron Lewis acid but concomitantly high
concentrations of silylium. In contrast, the BAr3,5-CF3
catalyst rests in the Lewis acidic form of the borane and
the concentration of any generated silylium species will
be small and likely transient. The higher nucleophilicity
and lower steric profile of a putative BAr3,5-CF3H almost
certainly contributes to this behavior. The inversion in
steady state ‘B’ vs ‘Si ’ Lewis acids for the two catalysts
4
)
3
F
6 4
)
3
6 5 3
F )
3
(8)
K.;
Hananki,
N.;
Yamamoto,
H.
a
New Efficient, Air
0
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0
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0
Stable, and Water Tolerant Catalyst in the Aldol-Type and
Michael Reactions. Synlett 1993, 577.
Christmann, M.; Kalesse, M. Vinylogous Mukaiyama Aldol
Reactions with Triarylboranes. Tetrahedron Lett. 2001, 42,
1269–1271.
–
(
9)
+
may be the ultimate source of the observed differences in
selectivity. Mechanistic studies are ongoing.
(10)
(11)
Ishihara, K.; Funahashi, M.; Hananki, N.; Miyata, M.;
Yamamoto, H. Tris(Pentafluorophenyl)Boran as an
Efficient Catalyst in the Aldol-Type Reaction of Ketene Silyl
Acetals with Imines. Synlett 1994, 963.
Ishihara, K.; Hananki, N.; Funahashi, M.; Miyata, M.;
Yamamoto, H. Tris(Pentafluorophenyl)Boran as an
Efficient, Air Stable, and Water Tolerant Lewis Acid
Catalyst. Bull. Chem. Soc. Jpn. 1995, 68, 1721.
Ishihara, K.; Yamamoto, H. Arylboron Compounds as Acid
Catalysts in Organic Synthetic Transformations. European
J. Org. Chem. 1999, 527–538.
Parks, D. J.; Blackwell, J. M.; Piers, W. E. Studies on the
Mechanism of B(C F ) -Catalyzed Hydrosilation of
6 5 3
Carbonyl Functions. J. Org. Chem. 2000, 65, 3090–3098.
Adduci, L. L.; Bender, T. A.; Dabrowski, J. A.; Gagné, M. R.
Chemoselective Conversion of Biologically Sourced Polyols
into Chiral Synthons. Nat. Chem. 2015, 7, 576–581.
Drosos, N.; Morandi, B. Boron-Catalyzed Regioselective
Deoxygenation of Terminal 1,2-Diols to 2-Alkanols Enabled
In summary, the two reported fluoroarylboranes are
highly complementary in their ability to site-selectively
activate the CO bonds of pentoses and hexoses for
hydrosilylative reduction. Catalyst control over these
processes in complex environments is therefore one step
closer, and provides one potential path to generating
diverse high-value chemicals from a limited number of
(
12)
3
9
renewable feedstocks.
(13)
(14)
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ASSOCIATED CONTENT
Supporting Information. Experimental procedure, analysis
data and NMR spectra for products (1-19), and details of the
computational studies of Si-1-deoxysugars’ conformations, in
addition to Figures S1-S4.
All 1H and 13C NMR spectra (and data files) reported herein
by the Strategic Formation of
Intermediate. Angew. Chemie - Int. Ed. 2015, 54, 8814–8818.
Chatterjee, I.; Porwal, D.; Oestreich, M. B(C -Catalyzed
a
Cyclic Siloxane
(
16)
6 5 3
F )
Chemoselective Defunctionalization of Ether-Containing
Primary Alkyl Tosylates with Hydrosilanes. Angew. Chemie
resolution spectra and raw FID files for 75+ biomass derived,
partially deoxygenated, hexoses and pentoses.
-
Int. Ed. 2017, 56, 3389–3391.
(17)
(18)
Hazra, C. K.; Gandhamsetty, N.; Park, S.; Chang, S. Borane
Catalysed Ring Opening and Closing Cascades of Furans
Leading to Silicon Functionalized Synthetic Intermediates.
Nat. Commun. 2016, 7, 13431–13439.
Parks, D. J.; Piers, W. E.; Yap, G. P. A. Synthesis, Properties,
and Hydroboration Activity of the Highly Electrophilic
AUTHOR INFORMATION
Corresponding Author
*mgagne@unc.edu
Borane
Bis(Pentafluorophenyl)Borane,
6 5 2
HB(C F ) .
Organometallics 2002, 17, 5492–5503.
ACKNOWLEDGMENT
(
(
(
19)
20)
21)
Parks, D. J.; Spence, R. E.; Piers, W. E.
Bis(Pentafluorophenyl)Borane: Synthesis, Properties, and
Hydroboration Chemistry of a Highly Electrophilic Borane
Reagent. Angew. Chemie - Int. Ed. 1995, 34, 809–811.
Zhang, J.; Park, S.; Chang, S. Selective C−O Bond Cleavage
of Sugars with Hydrosilanes Catalyzed by Piers’ Borane
Generated In Situ. Angew. Chemie - Int. Ed. 2017, 56, 13757–
This work was exclusively supported by the Department of
Energy (Basic Energy Science, DE-FG02-05ER15630). We
thank UNC’s Department of Chemistry Mass Spectrometry
Core Laboratory, especially Dr. Brandie Ehrmann, for her
assistance with the mass spectrometry analysis.
1
3761.
Bender, T. A.; Payne, P. R.; Gagné, M. R. Late-Stage
Chemoselective Functional-Group Manipulation of
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