(HMe 2 SiCH 2) 2: A Useful Reagent for B(C 6 F 5) 3 -Catalyzed Reduction-Lactonization of Keto Acids: Concise Syntheses of (-)- cis -Whisky and (-)- cis -Cognac Lactones

Article abstract of DOI:10.1055/s-0036-1588488

(HMe ₂ SiCH ₂) ₂ has been utilized as a useful reagent for B(C ₆ F ₅) ₃ -catalyzed reduction-lactonization of keto acids to synthesize γ- and δ-lactones. The process led concisely to (-)- cis -whisky and (-)- cis -cognac lactones in respective overall yields of 32% and 36%.

Full text of DOI:10.1055/s-0036-1588488

SYNLETT
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2017, 29, A–G
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(HMe2SiCH2)2: A Useful Reagent for B(C6F5)3-Catalyzed Reduction–
Lactonization of Keto Acids: Concise Syntheses of (–)-cis-Whisky
and (–)-cis-Cognac Lactones
Hengmu Xiea
Si
Si
Ji Lua
Yingying Guia
Lu Gaoa
H H
R2
O
(–)-cis-whisky lactone
Me
R
n
(1.1 equiv)
O
[4 step, 32%]
R1
n
O
O
R2
(n = 1, 2)
B(C6F5)3 (1 mol%)
CH2Cl2, r.t., 10 min
68–92%
O
R1
O
OH
(–)-cis-cognac lactone
Zhenlei Song*a,b
0
0
0
0
0-
0
0
2
7-
2
2
8
1-
5
7
2
[4 step, 36%]
dr up to ≥ 95:5
a Key Laboratory of Drug-Targeting and Drug Delivery System
of the Education Ministry, West China School of Pharmacy,
Sichuan University, Chengdu, 610041,, P. R. of China
zhenleisong@scu.edu.cn
b State Key Laboratory of Elemento-organic Chemistry, Nankai
University, Tianjin, 300071, P. R. of China
R1, R2 = alkyl, aryl
Published as part of the Cluster Silicon in Synthesis and Catalysis
Received: 23.04.2017
Accepted after revision: 10.06.2017
Published online: 19.07.2017
a) Traditional methods
Method A: one-step, but
using transition metals at
high T (°C) under high P
(MPa)
R
R
O
DOI: 10.1055/s-0036-1588488; Art ID: st-2017-b0284-c
Method A:
H2/transition metal (cat.)
O
Abstract (HMe2SiCH2)2 has been utilized as a useful reagent for
B(C6F5)3-catalyzed reduction–lactonization of keto acids to synthesize γ-
and δ-lactones. The process led concisely to (–)-cis-whisky and (–)-cis-
cognac lactones in respective overall yields of 32% and 36%.
Method B:
(1) M–H; (2) H+
HO
O
O
Method B: inconvenient two-
step approach
γ-keto acids
b) This work
γ-lactones
Key words lactonization, reduction, silanes, B(C6F5)3, keto acids
Si
Si
R2
O
(1.1 equiv)
H
H
n
O
n
R1
O
R2
B(C6F5)3 (1 mol%)
CH2Cl2, r.t., 10 min
69–92%
The γ-lactone and its variants are important core struc-
tures that occur often in a broad range of natural products
and biologically active compounds.1 Therefore, it is highly
demanded to develop efficient methods for constructing γ-
lactones.2 The simple substrates γ-keto acids are easily ac-
cessible and so are one of the most practical starting points
to generate γ-lactones, usually via a sequential hydrogena-
tion–lactonization process (Scheme 1, a, method A).3 The
synthesis occurs in one step, but it requires a homo- or het-
erogeneous transition-metal catalyst as well as high tem-
perature, high pressure and reaction time of several hours.
An alternative approach is to first reduce the ketone using
various hydride reagents, followed by an acid-promoted
lactonization (Scheme 1, a, method B), but this two-step
process is inconvenient.4 Therefore, one of the major chal-
lenges in this field is to develop a one-step synthesis of γ-
lactones from γ-keto acids under mild reaction conditions.
OH
1 (n = 1, 2)
R1
O
3 (dr up to ≥ 95:5)
Scheme 1 (a) Traditional methods to synthesize γ-lactones from γ-
keto acids; (b) (HMe2SiCH2)2 as a useful reagent for B(C6F5)3-catalyzed
one-step reduction–lactonization of keto acids
bond cleavage.8 The B(C6F5)3-catalyzed reaction has sub-
stantially expanded possibilities for transition-metal-free
catalysis,9 making it compatible with both sustainable
chemistry and pharmaceutical synthesis. Moreover, the ap-
proach using hydrosilanes is a safer and easier-to-handle
process compared with traditional methods using H2 or M–
H reagents. Hydrosilanes exploited in this approach have
so far been limited to those with only one silicon center
(RnSiH4–n). Little attention has been paid to bis(silyl) species
such as (HMe2SiCH2)210 or its analogues. As part of our con-
tinuing interest in bis(silyl) chemistry,11 we are intrigued by
the bifunctionality of (HMe2SiCH2)2 and its potential in the
discovery of unique transformations. Herein, we report a
B(C6F5)3-catalyzed reduction–lactonization process of keto
acids 1 using (HMe2SiCH2)2 (Scheme 1, b, 2) . The approach
leads to an one-step synthesis of diverse γ- and δ-lactones 3
The
Lewis
acid
tris(pentafluorophenyl)borane
[B(C6F5)3]5 has recently emerged as an attractive catalyst
because of its ability to activate H–H and Si–H bonds
through η1coordination.6 This unique activation mecha-
nism allows several transformations involving hydrosilane,
such as C=X bond reduction (X = O, N, S, and C) 5n,7 and C−O
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 29, A–G

B
H. Xie et al.
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in good yield at room temperature.12 It also allowed us to
synthesize (–)-cis-whisky and (–)-cis-cognac lactones in
four steps.
substantial amount of hydroxyl product formed from the
reduction (17% yield), without undergoing subsequent lac-
tonization. Since the ketone moiety in the reduction is acti-
vated by silicon rather than boron,6 we reasoned that the
reaction with a monohydrosilane could only proceed via an
intermolecular silicon–ketone coordination. This mechanis-
tic consideration led us to envision that switching to intra-
molecular silicon–ketone coordination might improve the
reduction, and that the switch could occur if the initially
formed silyl ester served as a linkage. To this end, we tested
a range of dihydro- and trihydrosilanes containing one sili-
con center (Table 1, entries 3–5). Unfortunately, these reac-
tions led to yields that were comparable or even lower than
those obtained using Et3SiH. While no reaction occurred us-
ing disilane HMe2SiSiMe2H (Table 1, entry 6), HMe2SiO-
SiMe2H was partially effective to generate GVL in 67% yield
(Table 1, entry 7). Next we tested disilanes, respectively,
containing a phenyl ring (Table 1, entry 8) and a –CH2CH2–
group (Table 1, entry 9) as linkage. To our delight, the con-
formationally more flexible (HMe2SiCH2)2 led to complete
consumption of LA within ten minutes and generated GVL
in 86% yield.
Table 1 Screening of Reduction–Lactonization Conditionsa
O
silane (equiv)
O
OH
Me
O
B(C6F5)3 (1 mol%)
Me
O
CH2Cl2, r.t., t
levulinic acid (LA)
γ-valerolactone (GVL)
Entry
Silane (equiv)
Time (min)
GVL (conv., %)c
1
Ph3SiH (2.1)
60
60
N.R.
2b
3b
4b
5
Et3SiH (2.1)
34 (78)
44 (68)
34 (88)
N.R.
Ph2SiH2 (1.1)
60
Et2SiH2 (1.1)
60
PhSiH3 (0.7)
300
300
20
6
HMe2SiSiMe2H (1.1)
HMe2SiOSiMe2H (1.1)
N.R.
7
67 (100)
Si
H
With the optimal reaction conditions in hand, the scope
of our approach was explored. The reaction tolerated γ-keto
acid 1a with a branched i-Pr group and 1b with a cyclohex-
yl ring (Table 2, entries 1 and 2). However, substitution with
the sterically more hindered t-Bu group completely inhibit-
ed reduction of ketone and the subsequent formation of 3c
(Table 2, entry 3). Lewis basic functionalities, such as Br and
PhO groups, were tolerated. No debromination or deoxy-
genation occurred during formation of the desired γ-lac-
tones 3d and 3e (Table 2 entries 4 and 5). The reaction of
1,4-diketo acid 1f generated 3f in 83% yield as an 8:1 mix-
ture of two diastereomers, and competitive eight-mem-
bered lactonization was not observed (Table 2, entry 6). The
approach was also suitable for keto acids 1g–i containing a
phenyl group or an electron-deficient or electron-rich phe-
nyl ring (Table 2, entries 7–9). It is noteworthy that Lewis
basic MeO group, which generally undergoes facile Me–O
bond cleavage,7j did not interfere with the reaction, giving
3i in 68% yield (Table 2, entry 9). For α,β-unsaturated keto
acids, 1,2-reduction proceeded regioselectively to afford 3j
and 3k in good yields (Table 2, entries 10 and 11). In addi-
tion, reaction of γ-keto acid 1l, in which the ketone and car-
boxyl groups are tethered to a phenyl ring, gave bicyclic lac-
tone 3l in 75% yield (Table 2, entry 12).
8
300
10
N.R.
H
Si
(1.1)
Si
H
Si
H
9d
86 (100)
(1.1)
a Reaction conditions: 0.34 mmol of LA, B(C6F5)3 (1 mol%), and hydrosilane
in dry CH2Cl2 at r.t.
b 15–20% of the hydroxyl product was obtained in these cases, indicating
that the reaction stopped at the reduction step without further lactoniza-
tion.
c Isolated yields after purification by silica gel column chromatography.
d 2,2,5,5-Tetramethyl-1-oxa-2,5-disilacyclopentane was isolated in 56%
yields as byproduct.
Our model scaffold was levulinic acid (LA), an important
platform molecule among lignocellulosic biomass-based
chemicals.13 Reduction–lactonization of LA would generate
γ-valerolactone (GVL), which has been proposed as feed-
stock for producing alkenes and transportation fuels.14 The
reaction was initially examined using monohydrosilane and
1 mol % of B(C6F5)3 as catalyst in CH2Cl2 at room tempera-
ture. Et3SiH proved more efficient than Ph3SiH in the reduc-
tion–lactonization, yet GVL was still obtained in only 34%
yield after one hour (Table 1, entries 1 and 2). In addition, a
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Table 2 Scope of γ-Keto Acids with Terminal Substituentsa
Si
Si
O
(1.1 equiv)
H
H
O
OH
R1
R1
O
B(C6F5)3 (1 mol%), CH2Cl2
r.t., 10 min
O
1
3
Entry
1
γ-Keto acid
γ-Lactone
Yield (%)b
82
O
OH
OH
OH
O
1a
3a
3b
3c
i-Pr
O
i-Pr
O
O
O
2
3
4
5
1b
90
Cy
O
Cy
O
O
O
f
1c
1d
1e
–
t-Bu
O
t-Bu
O
O
Br
OH
O
3d
3ec
80
80
Br
O
O
O
PhO
OH
OH
O
PhO
HO
Ph
O
O
O
O
6
7
1f
3fd
3g
83
92
O
O
Ph
Ph
O
OH
O
1g
Ph
O
O
O
O
OH
8
9
1h
1i
3h
3ie
71
68
p-BrC6H4
O
p-BrC6H4
O
O
OH
O
p-MeOC6H4
O
p-MeOC6H4
O
O
O
OH
O
10
1j
3j
70
O
Ph
Ph
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Table 2 (continued)
Entry
γ-Keto acid
γ-Lactone
Yield (%)b
75
O
O
OH
O
11
1k
1l
3k
3l
O
Ph
Ph
12
75
O
Me
OH
O
O
O
Me
a Reaction conditions: 0.34 mmol of keto acid, 0.38 mmol of (HMe2SiCH2)2, and B(C6F5)3 (1 mol%) in 4 mL of dry CH2Cl2 at r.t. for 10 min.
b Isolated yields after purification by silica gel column chromatography.
c 0.58 mmol of (HMe2SiCH2)2.
d 0.61 mmol of (HMe2SiCH2)2. 3f was an 8:1 mixture of two diastereomers.
e 0.34 mmol of (HMe2SiCH2)2 and B(C6F5)3 (3 mol%).
f The initially formed γ-keto silyl ester of 1c is easy to hydrolyze. Thus, 1c was recovered nearly completely based on the crude 1H NMR analysis.
Next we tested γ-keto acids substituted with a range of
internal R2 groups. Substitution such as Me, Ph, allyl, or
propargyl group at the α-position of the ketone led to com-
plete 1,2-cis diastereoselectivity in the formation of 3m–p
(Table 3, entries 1–4). Moreover, the reaction of 1q and 1r
efficiently generated cis-fused 5,5- and 5,6-bicyclic lactones
3q and 3r (Table 3, entries 5 and 6). In a similar manner,
substitution of R2 group at the β-position of ketone resulted
in 1,3-cis selectivity, although cis/trans ratios were moder-
ate (Table 3, entries 7 and 8). This lower diastereoselectivity
of the reduction probably reflects that 1,3-induction is gen-
erally less effective than 1,2-induction.
the reaction of 1w led only to slow ketone reduction, with
no subsequent lactonization to 3w observed. The failure to
form 3w probably reflects the greater strain in seven- or
eight-membered rings, which are therefore more difficult
to construct than five- and six-membered rings.
n
O
Si
Si
n
(1.1 equiv)
H
H
R1
R1
O
O
B(C6F5)3 (1 mol%), CH2Cl2
r.t., 10 min
HO
O
1u (n = 1; R1 = Me)
1v (n = 1; R1 = Ph)
1w (n = 2 or 3; R1 = Me)
3u (84%)
3v (73%)
3w ( ⎯ )
We attempted to use our approach to synthesize lac-
tones with larger rings (Scheme 2). The δ-lactones 3u and
3v formed readily in good yields within ten minutes, but
Scheme 2 Synthesis of δ-lactones 3u and 3v
Table 3 Scope of γ-Keto Acids with Internal Substituentsa
R2
Si
Si
O
(1.1 equiv)
H
H
OH
O
R1
R2
R1
O
B(C6F5)3 (1 mol%), CH2Cl2
r.t., 10 min
O
1
3
Entry
1
γ-Keto acid
γ-Lactoneb
Yield (%)c
83
drd
O
Me
OH
O
1m
3m
3n
3o
≥95:5
Me
O
Me
Me
O
O
O
Ph
OH
OH
O
2
3
1n
1o
68
77
≥95:5
≥95:5
Me
Me
O
Me
Ph
O
O
O
Me
O
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Table 3 (continued)
Entry
γ-Keto acid
γ-Lactoneb
Yield (%)c
drd
O
OH
O
Me
O
4
1p
3p
79
≥95:5
Me
O
Me
Me
O
OH
O
5
6
1q
1r
3q
3r
81
80
≥95:5
≥95:5
O
O
O
OH
O
O
O
Me
O
O
Me
OH
OH
7
8
1s
1t
3s
3t
78
75
75:25
80:20
Me
Me
O
O
O
O
Me
Me
Ph
Ph
O
O
a Reaction conditions: 0.34 mmol of keto acid, 0.38 mmol of (HMe2SiCH2)2, and B(C6F5)3 (1 mol%) in 4 mL of dry CH2Cl2 at r.t. for 10 min.
b The compounds 3m,15d 3n,15b 3q,15b 3r,15c and 3s15a with cis stereochemistry are known, and the spectroscopic data of our samples were in accordance with the
data reported in ref. 15a–d.
c Isolated yields after purification by silica gel column chromatography.
d The ratios were determined based on crude 1H NMR analysis of the products.
(a)
O
OSi
intermolecular silicon–ketone coordination is still involved,
the initially formed silyl ester 6 might serve as a linkage, al-
lowing an intramolecular silicon–ketone coordination to
promote the reduction step (Scheme 3, b). It is also possible
that this intramolecular silicon–ketone coordination bene-
fits subsequent lactonization, since in the predicted cyclic
intermediate 7, the carboxyl and hydroxyl groups, tethered
to a bis(silyl) moiety, lie close to each other. Lactonization
by transannular nucleophilic attack should therefore pro-
ceed smoothly to give GVL.
Si
Si
Me
Me
H
H
O
4 (20%)
+
OEt
+
O
B(C6F5)3
CH2Cl2, r.t.
10 min
OEt
Me
O
O
4
GVL (23%)
5 (57%)
(b)
H
BH(C6F5)3
H
Me
O
Si
Me
Si
Si
O
Si
reduction
H
H
lactonization
LA
GVL
O
Si
B(C6F5)3
O
O
Si
O
This methodology allowed us to achieve a concise syn-
thesis of (–)-cis-whisky lactone and (–)-cis-cognac lactone
from the known acid 816 (Scheme 4). Although many syn-
theses of trans isomers have been achieved,17 far fewer re-
ports of enantioselective syntheses of cis isomers have been
published.18 Transformation of 8 into the corresponding
Weinreb amide19 followed by addition with n-BuLi or n-
PentMgBr led, respectively, to 9 in 63% yield or 9′ in 70%
yield. Direct cleavage of the terminal alkene using
NaIO4/RuCl3·3H2O20 generated the key precursor acids 10
and 10′ in respective yields of 71% and 75%. Finally, reduc-
tion–lactonization mediated by B(C6F5)3/(HMe2SiCH2)2 gen-
erated (–)-cis-whisky lactone in 72% yield, and (–)-cis-co-
gnac lactone in 69% yield with complete cis stereocontrol.
B(C6F5)3
6
7
Scheme 3 (a) Reaction of keto ester 4 with (HMe2SiCH2)2, the ratios
were determined by the 1H NMR spectroscopy of the crude products;
(b) proposed intramolecular silicon activation in the reaction of LA with
(HMe2SiCH2)2.
To gain a deeper insight into the mechanism of the ap-
proach, we performed a control experiment using 4, in
which the carboxyl group was masked as an ethyl ester
(Scheme 3, a). In sharp contrast to that of LA, reaction of 4
afforded 23% of GVL together with 57% of the reduced prod-
uct 5 and 20% of unreacted 4. These contrasting results sug-
gest that in the reaction of LA with (HMe2SiCH2)2, while the
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 29, A–G

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Spectroscopic data of our synthetic samples were in full ac-
cordance with those reported18 for the naturally occurring
compounds.
(4) (a) Ramachandran, P. V.; Pitre, S.; Brown, H. C. J. Org. Chem.
2002, 67, 5315. (b) Frenette, R.; Kakushima, M.; Zamboni, R.;
Young, R. N.; Verhoeven, T. R. J. Org. Chem. 1987, 52, 304.
(5) For selected reviews, see: (a) Nikolaos, D.; Erhan, O.; Bill, M.
Synlett 2016, 27, 1760. (b) Oestreich, M.; Hermeke, J.; Mohr, J.
Chem. Soc. Rev. 2015, 44, 2202. (c) Robert, T.; Oestreich, M.
Angew. Chem. Int. Ed. 2013, 52, 5216. (d) Hatano, M.; Ishihara, K.
Chem. Commun. 2012, 48, 4273. (e) Erker, G. Chem. Commun.
2003, 13, 1469. (f) Chen, E. Y.-X.; Marks, T. J. Chem. Rev. 2000,
100, 1391. (g) Ishihara, K.; Yamamoto, H. Eur. J. Org. Chem. 1999,
527. (h) Piers, W. E.; Chivers, T. Chem. Soc. Rev. 1997, 26, 345.
For selected seminal works on B(C6F5)3, see: (i) Massey, A. G.;
Park, A. J.; Stone, F. G. A. Proc. Chem. Soc. 1963, 212. (j) Yang, X.;
Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1991, 113, 3623.
(k) Ishihara, K.; Hananki, N.; Yamamoto, H. Synlett 1993, 577.
(l) Ishihara, K.; Hananki, N.; Yamamoto, H. Synlett 1995, 721.
(m) Temme, B.; Erker, G.; Karl, J.; Luftmann, H.; Fröhlich, R.;
Kotila, S. Angew. Chem., Int. Ed. Engl. 1995, 34, 1755. (n) Parks, D.
J.; Piers, W. E. J. Am. Chem. Soc. 1996, 118, 9440. (o) Welch, G. C.;
Juan, R. R. S.; Masuda, J. D.; Stephan, D. W. Science 2006, 314,
1124. (p) Spies, P.; Erker, G.; Kehr, G.; Bergander, K.; Fröhlich, R.;
Grimme, S.; Stephan, D. W. Chem. Commun. 2007, 5072.
a) Cl(CO)2Cl, DMF (cat.)
NaIO4, RuCl3•H2O
O
O
R
H2O/MeCN/EtOAc
r.t.
then MeOMeN•HCl, NEt3, CH2Cl2
b) RM, THF
Me
OH
Me
RM = n-BuLi for 9
9 (63%)
9' (70%)
8
RM = n-PentMgBr for 9'
Me
O
Si
Si
O
(–)-cis-whisky lactone
(1.1 equiv)
O
O
O
H
H
n-Bu
(72%)
HO
Me
R
B(C6F5)3 (1 mol%)
CH2Cl2, r.t., 10 min
Me
10 (71%)
10' (75%)
(–)-cis-cognac lactone
O
dr ≥ 95:5
n-Pent
(69%)
Scheme 4 Total syntheses of (–)-cis-whisky and (–)-cis-cognac lac-
tones
In summary, (HMe2SiCH2)2 has been explored as a use-
ful reagent for B(C6F5)3-catalyzed reduction–lactonization
of keto acids to synthesize γ- and δ-lactones. (HMe2SiCH2)2-
assisted intramolecular silicone–ketone coordination of ke-
tone was proposed to facilitate both the reduction and lac-
tonization steps. This one-step approach also led to a con-
cise synthesis of (–)-cis-whisky and (–)-cis-cognac lactones
in respective overall yields of 32% and 36%. More detailed
studies and applications of this approach are currently un-
der way.
(6) (a) Houghton, A. Y.; Hurmalainen, J.; Mansikkamäki, A.; Piers,
W. E.; Tuononen, H. M. Nat. Chem. 2014, 6, 983. (b) Hermeke, J.;
Mewald, M.; Oestreich, M. J. Am. Chem. Soc. 2013, 135, 17537.
(c) Sakata, K.; Fujimoto, H. J. Org. Chem. 2013, 78, 12505.
(d) Piers, W. E.; Marwitz, A. J. V.; Mercier, L. G. Inorg. Chem.
2011, 50, 12252. (e) Rendler, S.; Oestreich, M. Angew. Chem. Int.
Ed. 2008, 47, 5997. (f) Parks, D. J.; Blackwell, J. M.; Piers, W. E.
J. Org. Chem. 2000, 65, 3090.
(7) (a) Kim, Y. C.; Chang, S. Angew. Chem. Int. Ed. 2016, 55, 218.
(b) Ma, Y. H.; Wang, B. L.; Zhang, L.; Hou, Z. M. J. Am. Chem. Soc.
2016, 138, 3663. (c) Wübbolt, S.; Oestreich, M. Angew. Chem. Int.
Ed. 2015, 54, 15876. (d) Kim, D. W.; Joung, S.; Kim, J. G.; Chang,
S. Angew. Chem. Int. Ed. 2015, 54, 14805. (e) Chatterjee, I.;
Oestreich, M. Angew. Chem. Int. Ed. 2015, 54, 1965.
(f) Gandhamsetty, N.; Park, S.; Chang, S. J. Am. Chem. Soc. 2015,
137, 15176. (g) Zhang, Z.; Du, H. Angew. Chem. Int. Ed. 2015, 54,
623. (h) Gandhamsetty, N.; Joung, S.; Park, S.-W.; Park, S.;
Chang, S. J. Am. Chem. Soc. 2014, 136, 16780. (i) Liu, Y.; Du, H.
J. Am. Chem. Soc. 2013, 135, 6810. (j) Bézier, D.; Park, S.;
Brookhart, M. Org. Lett. 2013, 15, 496. (k) Mewald, M.;
Oestreich, M. Chem. Eur. J. 2012, 18, 14079. (l) Geier, S. J.; Chase,
P. A.; Stephan, D. W. Chem. Commun. 2010, 46, 4884.
(m) Shchepin, R.; Xu, C.; Dussault, P. Org. Lett. 2010, 12, 4772.
(n) Harrison, D. J.; McDonald, R.; Rosenberg, L. Organometallics
2005, 24, 1398. (o) Chandrasekhar, S.; Reddy, C. R.; Babu, B. N.
J. Org. Chem. 2002, 67, 9080. (p) Rubin, M.; Schwier, T.;
Gevorgyan, V. J. Org. Chem. 2002, 67, 1936. (q) Blackwell, J. M.;
Morrison, D. J.; Piers, W. E. Tetrahedron 2002, 58, 8247.
(r) Blackwell, J. M.; Sonmor, E. R.; Scoccitti, T.; Piers, W. E. Org.
Lett. 2000, 2, 3921.
Funding Information
We are grateful for financial support from the National Natural Sci-
ence Foundation of China (21290180, 21622202, 21502125).
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Supporting Information
Supporting information for this article is available online at
https://doi.org/10.1055/s-0036-1588488.
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References and Notes
(1) For selected reviews, see: (a) Alonso, D. M.; Wettstein, S. G.;
Dumesic, J. A. Green Chem. 2013, 15, 584. (b) Lorente, A.;
Merketegi, J. L.; Albericio, F.; Álvarez, M. Chem. Rev. 2013, 113,
4567.
(2) For selected reviews, see: (a) Kitson, R. R. A.; Millemaggi, A.;
Taylor, R. J. K. Angew. Chem. Int. Ed. 2009, 48, 9426. (b) Salvador,
G.; Margarita, P.; Pablo, R.; Jose, S. Mini-Rev. Org. Chem. 2009, 6,
345.
(3) (a) Fábos, V.; Mika, L. T.; Horváth, I. T. Organometallics 2014, 33,
181. (b) Shimizu, K.-I.; Kanno, S.; Kon, K. Green Chem. 2014, 16,
3899. (c) Yang, Z.; Huang, Y.-B.; Guo, Q.-X.; Fu, Y. Chem.
Commun. 2013, 49, 5328.
(8) (a) Hazra, C. K.; Gandhamsetty, N.; Park, S.; Chang, S. Nat.
Commun. 2016, 7, 13431. (b) Bender, T. A.; Dabrowski, J. A.;
Zhong, H. Y.; Gagne, M. R. Org. Lett. 2016, 18, 4120. (c) Adduci, L.
L.; Bender, T. A.; Dabrowski, J. A.; Gagné, M. R. Nat. Chem. 2015,
7, 576. (d) Drosos, N.; Morandi, B. Angew. Chem. Int. Ed. 2015,
54, 8814. (e) Mack, D. J.; Guo, B.; Njardarson, J. T. Chem.
Commun. 2012, 48, 7844. (f) Chojnowski, J.; Rubinsztajn, S.;
Cella, J. A.; Fortuniak, W.; Cypryk, M.; Kurjata, J.; Kaźmierski, K.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 29, A–G

G
H. Xie et al.
Cluster
Synlett
Organometallics 2005, 24, 6077. (g) Gevorgyan, V.; Liu, J.-X.;
Rubin, M.; Benson, S.; Yamamoto, Y. Tetrahedron Lett. 1999, 40,
8919.
(15) (a) Korpaka, M.; Pietruszkaa, J. Adv. Synth. Catal. 2011, 353,
1420. (b) Adrio, L. A.; Quek, L. S.; Taylor, J. G.; Hii, K. K. (M.). Tet-
rahedron 2009, 65, 10334. (c) Müller, P.; Lacrampe, F.;
Bernardinelli, G. Tetrahedron: Asymmetry 2003, 14, 1503.
(d) Fang, J.-M.; Hong, B.-C.; Liao, L.-F. J. Org. Chem. 1987, 52, 855.
(16) Chatterjee, B.; Mondal, D.; Bera, S. Tetrahedron: Asymmetry
2012, 23, 1170.
(9) Sun, C.-L.; Shi, Z.-J. Chem. Rev. 2014, 114, 9219.
(10) (a) Hreczycho, G. Eur. J. Inorg. Chem. 2015, 67. (b) Hanada, S.;
Motoyama, Y.; Nagashima, H. Eur. J. Org. Chem. 2008, 4097.
(11) Liu, Z. J.; Lin, X. L.; Yang, N.; Su, Z. S.; Hu, C. W.; Xiao, P. H.; He, Y.
Y.; Song, Z. L. J. Am. Chem. Soc. 2016, 138, 1877; and references
cited therein.
(17) Koschker, P.; Kähny, M.; Breit, B. J. Am. Chem. Soc. 2015, 137,
3131; and references cited therein.
(12) For related works, see: (a) Sakai, N.; Horikawa, S.; Ogiwara, Y.
RSC Adv. 2016, 6, 81763. (b) Bercot, E. A.; Kindrachuk, D. E.;
Rovis, T. Org. Lett. 2005, 7, 107. (c) Mukaiyama, T.; Izumi, J.;
Shiina, I. Chem. Lett. 1997, 187.
(13) Corma, A.; Iborra, S.; Velty, A. Chem. Rev. 2007, 107, 2411.
(14) Horváth, I. T.; Mehdi, H.; Fábos, V.; Boda, L.; Mika, L. T. Green
Chem. 2008, 10, 238.
(18) (a) Pisani, L.; Superchi, S.; D’Elia, A.; Scafato, P.; Rosini, C. Tetra-
hedron 2012, 68, 5779. (b) Ghosh, M.; Bose, S.; Ghosh, S. Tetra-
hedron Lett. 2008, 49, 5424. (c) Zhang, Y.; Wang, Y.-Q.; Dai, W.-
M. J. Org. Chem. 2006, 71, 2445. (d) Ozeki, M.; Hashimoto, D.;
Nishide, K.; Kajimoto, T.; Node, M. Tetrahedron: Asymmetry
2005, 16, 1663.
(19) Nahm, S.; Weinreb, S. M. Tetrahedron Lett. 1981, 22, 3815.
(20) Craig, R. A. II; Loskot, S. A.; Mohr, J. T.; Behenna, D. C.; Harned, A.
M.; Stoltz, B. M. Org. Lett. 2015, 17, 5160.
© Georg Thieme Verlag Stuttgart · New York — Synlett 2017, 29, A–G