Selective C?O Bond Cleavage of Sugars with Hydrosilanes Catalyzed by Piers’ Borane Generated In Situ

Article abstract of DOI:10.1002/anie.201708109

Described herein is the selective reduction of sugars with hydrosilanes catalyzed by using Piers’ borane [(C₆F₅)₂BH] generated in situ. The hydrosilylative C?O bond cleavage of silyl-protected mono- and disaccharides in the presence of a (C₆F₅)₂BH catalyst, generated in situ from (C₆F₅)₂BOH, takes place with excellent chemo- and regioselectivities to provide a range of polyols. A study of the substituent effects of sugars on the catalytic activity and selectivity revealed that the steric environment around the anomeric carbon (C1) is crucial.

Full text of DOI:10.1002/anie.201708109

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
Chemie
International Edition
www.angewandte.org
Accepted Article
Title: In Situ Generated Piers' Borane-Catalyzed Selective C-O Bond
Cleavage of Sugars with Hydrosilanes
Authors: Sukbok Chang, Jianbo Zhang, and Sehoon Park
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201708109
Angew. Chem. 10.1002/ange.201708109
Link to VoR: http://dx.doi.org/10.1002/anie.201708109
http://dx.doi.org/10.1002/ange.201708109

10.1002/anie.201708109
Angewandte Chemie International Edition
COMMUNICATION
In Situ Generated Piers' Borane-Catalyzed Selective C–O Bond
Cleavage of Sugars with Hydrosilanes
Jianbo Zhang, Sehoon Park*, and Sukbok Chang*
Dedicated to Professor Hee-Yoon Lee on the occasion of his 60th birthday
Abstract: Described herein is the Piers' borane (C6F5)2BH-catalyzed
selective reduction of sugars with hydrosilanes. The hydrosilylative C–
O bond cleavage of silyl-protected mono- and disaccharides in the
presence of (C6F5)2BH catalyst, in situ generated from (C6F5)2BOH,
takes place with excellent chemo- and regioselectivities to provide a
range of polyols. Study of the substituent effects of sugars on the
catalytic activity and selectivity revealed that the steric environment
around the anomeric carbon (C1) is crucial.
A great number of hydrosilylation catalysts have been developed
over the past several decades.[1] In this context, organometallic
compounds based on precious metals such as Pt and Rh are
especially taking a superior position as selective and/or efficient
catalysts,[2] although poor recyclability and decomposition of the
catalysts are regarded as major drawbacks.[3] In addition,
B(C6F5)3 has drawn a notable attention as an alternative to the
metal catalysts for the hydrosilylative reduction of various
Scheme 1. (a) Defunctionalization within the catalytic B(C6F5)3/silane system.
functional groups, mainly due to its environmental-friendliness
and strong Lewis acidity.[4] However, the B(C6F5)3-promoted
hydrosilylation is known to exhibit excessive reduction reactivity
particularly toward C–O single bonds, which brings about the
formation of exhaustive reduction products.[5] Although there are
a handful of examples of the B(C6F5)3-catalyzed chemoselective
transformations using hydrosilanes as reducing agents, these
reactions often require specific conditions to achieve high
selectivity (Scheme 1a).[6] For instance, Gagné found that silyl-
protected polyols undergo selective C–O bond cleavage at the
primary position by tuning suitable stoichiometry and steric
bulkiness of hydrosilanes in the presence of catalytic B(C6F5)3.[6a-
c] Recently, a B(C6F5)3-catalyzed selective deoxygenation of 1,2-
diols was enabled by sequentially employing two different
(b) This work – Bis(pentafluorophenyl)borane-promoted hydrosilylative C–O
bond cleavage of sugars.
Aiming at uncovering
a selective boron catalyst, we
hypothesized that modulating Lewis acidity of boranes by
replacing pentafluorophenyl group(s) with other substituents(s)
may lead to harnessed catalytic reactivity suitable for
(chemo)selective hydrosilylative reduction of a certain range of
functional groups. Herein, we report the in situ generated
bis(pentafluorophenyl)borane-catalyzed selective C–O bond
cleavage
of
sugars
with
TMDS
(TMDS:
1,1,3,3-
tetramethyldisiloxane, Scheme 1b). This work represents the first
application of bis(pentafluorophenyl)borane, (C6F5)2BH (Piers'
borane) as
a single hydrosilylative reduction catalyst. A
silanes.[6d-e] Similarly, the Oestreich group reported
a
convenient synthetic route leading to the formation of Piers’
borane is also disclosed. The (C6F5)2BH/silane catalytic system
was found to promote the C–O bond cleavage of a series of silyl-
protected monosaccharides with excellent chemo- and
regioselectivities at room temperature. It was also elucidated that
the reaction rate is highly influenced by the relative
stereochemistry of carbon centers of sugars.
chemoselective C–O bond cleavage of primary alkyl tosylates
over ether functional groups using bulky silane Et3SiH.[6f]
Considering the stability and Lewis acidity of the
presupposed borane compounds, bis(pentafluorophenyl)borinic
acid (C6F5)2BOH 1[7] was envisioned at the outset of our study as
a potiential precatalyst for the desired late-stage hydrosilylative
transformations. In fact, we successfully established a one-pot
procedure leading to 1 with a slight modification of the Marks'
previous report [1.95 g, 27% yield, Scheme 2a (route a), see the
S.I. for details].[8a] Similarly, an additional synthetic route leading
to higher yield of 1 was developed by using (C6F5)MgBr and
PhBF3K on the basis of Soós’ report [0.66 g, 46% yield, Scheme
2a (route b)].[8b]
[*]
Dr. J. Zhang, Dr. S. Park, Prof. Dr. S. Chang
Center for Catalytic Hydrocarbon Functionalizations
Institute for Basic Science (IBS)
Daejeon 305-701, South Korea
E-mail: sehoonp@kaist.ac.kr
sbchang@kaist.ac.kr
Dr. J. Zhang, Dr. S. Park, Prof. Dr. S. Chang
Department of Chemistry
Korea Advanced Institute of Science & Technology (KAIST)
Daejeon 305-701, South Korea
Supporting information for this article is given via a link at the end of
the document.
This article is protected by copyright. All rights reserved.

10.1002/anie.201708109
Angewandte Chemie International Edition
COMMUNICATION
Having observed the facile formation of 2 in the presence of
excess silanes, we hypothesized that the Piers' borane 2 might
be utilized as a catalyst for the chemoselective CO bond
cleavage with hydrosilanes. In this regard, we next conceived
hydrosilylative reduction of sugars catalyzed by the in situ
generated borane 2 (Table 1). While a number of transition metal-
based heterogeneous catalytic protocols have been applied for
the hydrogenation of carbohydrates leading to linear polyols,[15] its
metal-free catalytic version remains less explored.[16]
Table 1: Scope of selective CO bond cleavage of sugars.[a]
Scheme 2. (a) One-pot synthesis of (C6F5)2BOH 1 from (C6F5)2BPh and H2O.
(b) In situ generation of (C6F5)2BH 2. (c) Trapping (C6F5)2BH 2 (Piers’ borane)
with base (2-SMe2 or 3). (d) ORTEP of 3 with thermal ellipsoids set at 50%
probability level. The bond length of two BH is 0.990 Å .
With a convenient protocol for the gram scale synthesis of
(C6F5)2BOH in hand, we initially examined feasibility of the
reactivity of 1 with hydrosilanes. A reaction of (C6F5)2BOH 1 with
PhMe2SiH (20 equiv) in CDCl3 proceeded smoothly with evolution
of H2 to quantitatively afford (C6F5)2BOSiPhMe2 1a at 25 oC within
10 min, in which the 11B chemical shift ( 39.2) was well matched
with that of its analogues[9] (Scheme 2b). Interestingly, 1a in the
presence of excess PhMe2SiH was observed to be slowly
converted to (C6F5)2BH 2 (Piers’ borane), during which the
corresponding new 19F signals appeared at  -131.6, -149.0, and
-160.5 in CDCl3.[10] Such transformation of 1 to 2 was highly
accelerated by employing more reactive silanes such as PhSiH3
(20 equiv) or TMDS (200 equiv), resulting in quantitative formation
of 2 within 10 min at 25 oC (see the S.I.).[11,12]
Upon the generation of 2, when excess SMe2 or NEt3 was
added into the crude solution of 2, the resulting products (2-SMe2
and 3) were found to form (Scheme 2c). The crude 19F NMR after
treating with SMe2 showed only a single set of signals at  -131.4,
-156.1, and -162.9, which agreed well with the reported chemical
shifts of (C6F5)2BHSMe2 (2-SMe2).[13] A borohydride bearing a
triethylammonium ion 3 was isolated from the crude solution after
6 h in CHCl3 (with excess PhSiH3) or 1,4-dioxane (with excess
TMDS) in 74% and 50% yield, respectively. The solid structure of
3 was determined by X-ray crystallography, where the BH bond
distances (0.990 Å) turned out to be shorter relative to the
corresponding 4-borane possessing only differed counter cations
(Scheme 2d).[13,14]
[a] Reaction conditions: (C6F5)2BOH (1, 1 mol%), substrate (0.4 mmol), and
TMDS (4 equiv, 1.6 mmol) in 1,4-dioxane (0.4 mL) for 1-14 days at 25 oC.
Following the catalytic hydrosilylation reaction, the crude solution was treated
with Dowex® in MeOH to give the corresponding alcohol products. Isolated
yield. [b] Conversion determined by 1H NMR. [c] 3 Mol% of 1 was used. The
structure of 5e is equal to 5f.
A hydrosilylative reduction of a silyl-protected anomeric
mixture of D-glucose 4a with TMDS proceeded slowly in the
presence of 1 (1 mol%) in 1,4-dioxane to furnish a ring-opening
product 5a-TMS albeit in low yield in 14 days. In contrast, 4b that
bears an opposite C2 configuration relative to 4a was found to be
more reactive under the identical conditions, giving 5b in 94%
yield in 7 days. Increasing a catalyst loading to 3 mol% led the
reaction to be completed in 4 days. In addition, C–O bond
cleavage of
a substrate 4c possessing an opposite C4
configuration relative to 4a took place in the presence of 1 (3
mol%) to afford the corresponding polyol 5c in 84% yield in 10
days. A silyl-protected 2-deoxy-glucose 4d and a series of five-
carbon glucose derivatives (4e-g) were highly reactive under the
standard conditions, being converted to the corresponding polyols
in 76-96% yields within 1-3 days (5d-g).[17] Notably, D-lyxose also
underwent the hydrosilylative ring-opening reduction under the
slightly modified conditions [1 (3 mol%), TMDS (8 equiv), CHCl3,
24 h, 25 oC], furnishing 5e in 63% isolated yield. Gratifyingly, silyl-
This article is protected by copyright. All rights reserved.

10.1002/anie.201708109
Angewandte Chemie International Edition
COMMUNICATION
Table 2: Study of regioselectivity for C–O bond cleavage of sugars.[a]
protected ribose 4h and 2-deoxy-ribose 4i were also cleanly
reduced to the polyols 5h and 5i with high efficacy. On the other
hand, B(C6F5)3-catalyzed hydrosilylation of 4b in 1,4-dioxane
caused the CO bond cleavage of the solvent, thereby being
unable to properly evaluate the reactivity of B(C6F5)3 in the present
procedure (see the S.I. for the crude NMR spectra).
The observed higher reactivity of 4b relative to 4a could be
rationalized by an SN2-type outer-sphere ionic mechanism[18]
involving the formation of a cyclic silyloxonium ion bearing a
-
borohydride anion (C6F5)2BH2 (Scheme 3a).[6a,b] Briefly, in the
case of presupposed -anomeric glucose 4a, the nucleophilic
-
attack by (C6F5)2BH2 is expected to be disfavored because of the
steric repulsion between the equatorial C2-silyloxy group on 4a-
-
Si+ and the approaching (C6F5)2BH2 (Scheme 3b). However,
-
unlike 4a, the hydride transfer from (C6F5)2BH2 to the -anomeric
C1 center of 4b-Si+ (possessing an axial C2-silyloxy group) is
presumed to take place without severe steric repulsions (Scheme
-
+
3c).[19] The isolated ion pair 3 [(C6F5)2BH2 HNEt3 ] was found to
be inactive as a catalyst for the present hydrosilylative reduction
of sugars.
[a] Reaction conditions: (C6F5)2BOH (1, 3 mol%), substrate (0.4 mmol), and
TMDS (8 equiv, 3.2 mmol) in CDCl3 (0.2 mL) for 0.3-15 h at 25 oC. Following the
catalytic hydrosilylation reaction, the crude solution was treated with Dowex® in
MeOH to give the corresponding alcohol products. Isolated yields. [b]
Determined by 1H NMR based on the isolated each diastereomers. The
structure of 5j is equal to 5p and 5q’, while the structure of 5k is same as 5g.
Scheme 3. (a) Proposed pathway of the sp3 C–O bond cleavage on the
presupposed silyloxonium intermediate. (b-c) Steric situations during the
-
hydride transfer from (C6F5)2BH2 to the -anomeric C1 center of the
silyloxonium intermediates (4a-Si+ and 4b-Si+).
To gain insights into the regioselectivity observed in the ring-
opening process, hydrosilylative reduction of a range of six-
membered monosaccharides having steric and/or electronic
variation was examined under newly optimized conditions [1 (3
However, a reaction of 2-deoxy substrate (4l) led to non-
selective C–O bond cleavage, resulting in a ca. 1:1 mixture of
cyclic (5l) and linear (5d and 5l′) polyols in >99% combined yield.
As expected, 4m possessing a sterically bulky isopropoxy group
at the C1 position was selectively ring-opened with TMDS, being
converted to a linear polyol 5m in 64%. Subsequently, additional
glucose derivatives with variable substituents at the C1 position
[OPh (4n), STol (4o), and F (4p)] were subjected to the identical
conditions: ring-opening products from 4n and 4o were formed in
63% (5n) and 93% (5o), respectively, while the C1-fluorinated
substrate 4p rapidly underwent defluorination within 15 min to
produce 5p in 76%. It is noteworthy that an enantiomerically pure
ketal substrate (4q) was reduced to the cyclic products 5q and 5q′
in 53% combined yield with a 1.4:1 diastereomeric ratio (d.r.),
o
mol%) and TMDS (8 equiv) in CHCl3 at 25 C] (Table 2). As a
reference substrate for the comparative selectivity study, 4a was
chosen and subjected to the conditions to give a linear product
sorbitol (5a), in 74% upon acidic work-up.[20] Substitution of
trimethylsiloxy at the C1 with a methoxy group caused a C1–OMe
bond cleavage, thus affording a cyclic product 5j in 81%.
Intriguingly, the C1-methoxy substrate, not having a C5 silyloxy
group (4k), selectively underwent the hydrosilylative ring-opening
to furnish a linear polyol 5k in 79%.
This article is protected by copyright. All rights reserved.

10.1002/anie.201708109
Angewandte Chemie International Edition
COMMUNICATION
[1]
[2]
For reviews on hydrosilylation, see: a) B. Marciniec, Coord. Chem. Rev.
2005, 249, 2374–2390; b) I. Ojima, Z. Li, J. Zhu, in The Chemistry of
Organic Silicon Compounds, Vol. 2 (Eds.: Z, Rappoport, Y, Apeloig),
John Wiley & Sons, New York, 1998, pp. 1687–1792; c) H. Nishiyama,
K. Itoh, in Catalytic Asymmetric Synthesis; (Ed.: I. Ojima), Wiley-VCH,
New York, 2000, pp. 111–144.
a) B. Marciniec, J. Guliński, W. Urbaniak, Z. W. Kornetka, in
Comprehensive Handbook on Hydrosilylation; (Ed.: B. Marciniec),
Pergamon, Oxford, 1992; b) T. K. Meister, J. W. Kück, K. Riener, A.
Pöthig, W. A. Herrmann, F. E. Kühn, J. Catal. 2016, 337, 157–166; c) J.
L. Speier, Adv. Organomet. Chem. 1979, 17, 407–447; d) I. E. Markó, S.
Stérin, O. Buisine, G. Mignani, P. Branlard, B. Tinant, J.-P. Declercq,
Science 2002, 298, 204–206.
a) A. J. Holwell, Platinum Metals Rev. 2008, 52, 243–246; b) C.-J. Yang,
Energy Policy 2009, 37, 1805–1808; c) C. H. Schuster, T. Diao, I.
Pappas, P. J. Chirik, ACS Catal. 2016, 6, 2632–2636; d) A. M. Tondreau,
C. C. H. Atienza, K. J. Weller, S. A. Nye, K. M. Lewis, J. G. P. Delis, P.
J. Chirik, Science 2012, 335, 567–570.
Selected examples for B(C6F5)3-catalyzed hydrosilylative reduction: a) W.
E. Piers, T. Chivers, Chem. Soc. Rev. 1997, 26, 345–354; b) M.
Oestreich, J. Hermeke, J. Mohr, Chem. Soc. Rev. 2015, 44, 22022220;
c) D. J. Parks, W. E. Piers, J. Am. Chem. Soc. 1996, 118, 9440–9441;
d) J. M. Blackwell, E. R. Sonmor, T. Scoccitti, W. E. Piers, Org. Lett. 2000,
2, 3921–3923; e) M. Rubin, T. Schwier, V. Gevorgyan, J. Org. Chem.
2002, 67, 1936–1940; f) D. Bézier, S. Park, M. Brookhart, Org. Lett. 2013,
15, 496–499; g) D. J. Harrison, R. McDonald, L. Rosenberg,
Organometallics 2005, 24, 1398–1400; h) N. Gandhamsetty, S. Joung,
S.-W. Park, S. Park, S. Chang, J. Am. Chem. Soc. 2014, 136, 16780–
16783.
suggesting that an SN1-type outer-sphere hydride-transfer
pathway is operative.[6b,21]
Pleasingly, the present catalytic conditions were applicable
for the hydrosilylative reduction of disaccharides. For instance, a
reaction of 4r with nBuSiH3 (16 equiv) in the presence of 1 (6 mol%)
o
proceeded at 25 C (1 day) to furnish the unprecedented ring-
opening product 5r in 67% yield [Eq. (1)].[20] Interestingly, the
reaction pattern for TMSO-sucrose 4s under the similar
conditions was distinctive from that of 4r. The resulting product
distribution in the reaction of 4s with TMDS strongly suggested
that the six-membered unit undergoes selective C–O bond
cleavage to give the respective cyclic polyol 5j (90%), while the
five-membered ring unit is converted to the linear product 5b (68%)
[Eq. (2)]. The use of nBuSiH3 instead of TMDS in the reaction of
4s led to the formation of products in poor selectivity [Eq. (3)].
[3]
[4]
[5]
[6]
a) V. Gevorgyan, M. Rubin, J.-X. Liu, Y. Yamamoto, J. Org. Chem. 2001,
66, 1672–1675; b) L. L. Adduci, M. P. McLaughlin, T. A. Bender, J. J.
Becker, M. R. Gagné, Angew. Chem. Int. Ed. 2014, 53, 1646–1649;
Angew. Chem. 2014, 126, 1672–1675; c) V. Gevorgyan, M. Rubin, S.
Benson, J.-X. Liu, Y. Yamamoto, J. Org. Chem. 2000, 65, 6179–6186;
d) M. Tan, Y. Zhang, Tetrahedron Lett. 2009, 50, 4912–4915.
a) L. L. Adduci, T. A. Bender, J. A. Dabrowski, M. R. Gagné, Nat. Chem.
2015, 7, 576–581; b) T. A. Bender, J. A. Dabrowski, M. R. Gagné, ACS
Catal. 2016, 6, 8399–8403; c) T. A. Bender, J. A. Dabrowski, H. Zhong,
M. R. Gagné, Org. Lett. 2016, 18, 4120–4123; d) N. Drosos, B. Morandi,
Angew. Chem. Int. Ed. 2015, 54, 8814–8818; Angew. Chem. 2015, 127,
8938–8942; e) N. Drosos, E. Ozkal, B. Morandi, Synlett 2016, 27, 1760–
1764; f) I. Chatterjee, D. Porwal, M. Oestreich, Angew. Chem. Int. Ed.
2017, 56, 3389–3391; Angew. Chem. 2017, 129, 3438–3441.
a) K. Ishihara, H. Yamamoto, Eur. J. Org. Chem. 1999, 527–538; b) T.
Beringhelli, D. Donghi, D. Maggioni, G. D’Alfonso, Coord. Chem. Rev.
2008, 252, 2292–2313; c) T. Beringhelli, G. D’Alfonso, D. Donghi, D.
Maggioni, P. Mercandelli, A. Sironi, Organometallics 2003, 22, 1588–
1590; d) T. Beringhelli, G. D’Alfonso, D. Donghi, D. Maggioni, P.
Mercandelli, A. Sironi, Organometallics 2004, 23, 5493–5502; e) E.
Dimitrijević, M. S. Taylor, ACS Catal. 2013, 3, 945962.
In conclusion, we have shown that the in situ generated
(C6F5)2BH displays unique catalytic reactivity in the hydrosilylative
reduction of sugars to provide a series of linear or cyclic polyols
with high chemo- and regioselectivities depending on the steric
and configuration of the stereogenic carbon centers of sugars.
Based on the observed structure-reactivity relationship, the
reaction leading to ring-opening products was proposed to
proceed via an SN2 mechanistic pathway involving a consecutive
silylium ion transfer followed by a nucleophilic attack by the
borohydride anion. The present findings would stimulate the
catalytic application of Piers' borane (C6F5)2BH in the field of
reduction chemistry.
[7]
[8]
[9]
a) P. A. Deck, C. L. Beswick, T. J. Marks, J. Am. Chem. Soc. 1998, 120,
1772–1784; b) Á . Gyömöre, M. Bakos, T. Földes, I. Pápai, A. Domján, T.
Soós, ACS Catal. 2015, 5, 53665372.
a) S. Krupski, G. Kehr, C. G. Daniliuc, G. Erker, Chem. Commun. 2016,
52, 2695–2697; b) D. J. Parks, W. E. Piers, G. P. A. Yap,
Organometallics 1998, 17, 5492–5503.
[10] D. J. Parks, R. E. von H. Spence, W. E. Piers, Angew. Chem. Int. Ed.
Engl. 1995, 34, 809–811; Angew. Chem. 1995, 107, 895–897.
[11] A similar facile in situ generation of a diaryl borane from the reaction of
a borinic acid with hydrosilanes containing PhSiH3, PMHS, and TMDS is
known; see: A. Chardon, T. Mohy El Dine, R. Legay, M. De Paolis, J.
Rouden, J. Blanchet, Chem. Eur. J. 2017, 23, 2005–2009.
[12] A stoichiometric treatment of (C6F5)3B with PhSiH3 (20 equiv) in CDCl3 or
C6D6 at 25 oC gave low conversion and intractable several borane
species including less than 10% yield of (C6F5)2BH 2 in 48 h; see: G. I.
Nikonov, S. F. Vyboishchikov, O. G. Shirobokov, J. Am. Chem. Soc.
2012, 134, 5488–5491.
Acknowledgements
This research was supported by the Institute for Basic Science
(IBS-R010-D1) in Korea.
[13] A. Schnurr, K. Samigullin, J. M. Breunig, M. Bolte, H.-W. Lerner, M.
Wagner, Organometallics 2011, 30, 2838–2843.
[14] a) R. E. Douthwaite, Polyhedron 2000, 19, 1579–1583; b) C. Jiang, O.
Blacque, H. Berke, Organometallics 2009, 28, 5233–5239.
Conflict of interest
[15] Selected examples for heterogeneous hydrogenation of carbohydrates:
a) K. van Gorp, E. Boerman, C. V. Cavenaghi, P. H. Berben, Catalysis
Today 1999, 52, 349–361; b) B. J. Arena, Appl. Catal. A 1992, 87, 219–
229; c) J. Wisniak, R. Simon, Ind. Eng. Chem. Prod. Res. Dev. 1979, 18,
50–57; d) J. Wisniak, M. Hershkowitz, S. Stein, Ind. Eng. Chem. Prod.
Res. Dev. 1974, 13, 232–236.
[16] a) M. Alonso-López, M. Bernabé, M. Martin-Lomas, S. Penadés-Ullate,
Carbohydr. Res. 1985, 142, 135–140; b) R. Köster, S. Penadés-Ullate,
W. V. Dahlhoff, Angew. Chem. Int. Ed. Engl. 1985, 24, 519–521; Angew.
Chem. 1985, 97, 508–510; c) A. Hernandez, M. Alonso-López, M.
Martin-Lomas, C. Pascual, S. Penades, Tetrahedron 1987, 43, 5457–
The authors declare no conflict of interest.
Keywords: Piers' borane • C–O Bond Cleavage •
Hydrosilylative Reduction • Sugar • Chemoselectivity
This article is protected by copyright. All rights reserved.

10.1002/anie.201708109
Angewandte Chemie International Edition
COMMUNICATION
5460; d) M. Bernabé, M. Martin-Lomas, S. Penadés, R. Köster, W. V.
Dahlhoff, J. Chem. Soc., Chem. Commun. 1985, 1001–1002.
[19] Also see the S.I. for a plausible steric situation of the -anomeric
silyloxonium intermediates of 4a and 4b during the hydride attack on the
[17] The 19F NMR spectra during the catalytic turnover of 4d exhibited a
single set of peaks assigned to (C6F5)2BH 2, suggesting 2 is in the
catalytic resting state (see the S.I.).
-
C1 centre by (C6F5)2BH2 .
[20] The same reaction using B(C6F5)3 as a catalyst in place of (C6F5)2BOH 1
gave rise to significant amounts of fully deoxygenated hydrocarbons
within 1.5 h.
[21] a) J. Yang, P. S. White, M. Brookhart, J. Am. Chem. Soc. 2008, 130,
17509–17518; b) S. Park, M. Brookhart, Chem. Commun. 2011, 47,
3643–3645.
[18] Selected examples for outer-sphere ionic catalysis: a) J. Hermeke, M.
Mewald, M. Oestreich, J. Am. Chem. Soc. 2013, 135, 17537–17546; b)
D. J. Parks, J. M. Blackwell, W. E. Piers, J. Org. Chem. 2000, 65, 3090–
3098; c) A. Y. Houghton, J. Hurmalainen, A. Mansikkamäki, W. E. Piers,
H. M. Tuononen, Nat. Chem. 2014, 6, 983–988; d) M. Iglesias, F. J.
Fernández-Alvarez, L. A. Oro, ChemCatChem 2014, 6, 2486–2489; e) S.
Park, M. Brookhart, Organometallics 2010, 29, 6057–6064; f) G. E.
Dobereiner, A. Nova, N. D. Schley, N. Hazari, S. J. Miller, O. Eisenstein,
R. H. Crabtree, J. Am. Chem. Soc. 2011, 133, 7547–7562.
This article is protected by copyright. All rights reserved.

10.1002/anie.201708109
Angewandte Chemie International Edition
COMMUNICATION
Entry for the Table of Contents
Jianbo Zhang, Sehoon Park,* and
Sukbok Chang*
Page No. – Page No.
In Situ Generated Piers' Borane-
Catalyzed Selective C–O Bond
Cleavage of Sugars with
Hydrosilanes
Piers’ borane in situ generated is for the first time demonstrated to promote the hydrosilylative reduction
of sugars, providing a series of linear or cyclic polyols with high chemo- and regioselectivities under
mild conditions. Studies of catalytic reactivity and regioselectivity with regard to the CO bond cleavage
with hydrosilane suggest an importance of the steric environment around the anomeric carbon centre
of sugars.
This article is protected by copyright. All rights reserved.