Palladium-Catalyzed Asymmetric Allylic Alkylation of Alkyl-Substituted Allyl Reagents with Acyclic Amides

Article abstract of DOI:10.1021/acs.orglett.7b02927

A wide range of alkyl-substituted allyl reagents, as well as nonstabilized carbon nucleophiles, was successfully used for the first time in the palladium-catalyzed asymmetric allylic alkylation reaction, affording the corresponding allylic alkylated produ

Full text of DOI:10.1021/acs.orglett.7b02927

Letter
pubs.acs.org/OrgLett
Cite This: Org. Lett. XXXX, XXX, XXX-XXX
Palladium-Catalyzed Asymmetric Allylic Alkylation of Alkyl-
Substituted Allyl Reagents with Acyclic Amides
Yang-Jie Jiang,† Gao-Peng Zhang,† Jian-Qiang Huang,† Di Chen,† Chang-Hua Ding,*,†
and Xue-Long Hou*,†,‡
‡
†State Key Laboratory of Organometallic Chemistry and Shanghai−Hong Kong Joint Laboratory in Chemical Synthesis, Shanghai
Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
S
* Supporting Information
ABSTRACT: A wide range of alkyl-substituted allyl reagents, as
well as nonstabilized carbon nucleophiles, was successfully used
for the first time in the palladium-catalyzed asymmetric allylic
alkylation reaction, affording the corresponding allylic alkylated
products in high yields with high enantioselectivities. The
usefulness of the protocol has been demonstrated by the
enantioselective synthesis of an important chiral building block
and enantiomer of Dubiusamine A.
alladium-catalyzed asymmetric allylic alkylation (AAA)
Preaction, one of the most important protocols to form
carbon−carbon bond and carbon−heteroatom bond enantiose-
lectively in organic synthesis, has attracted great attention for
decades.1 Tremendous efforts have been made to address the
challenging issues of the reaction, such as the use of nonstabilized
carbon nucleophiles and alkyl-substituted allyl reagents, since its
discovery about 40 years ago.2 So far, enormous achievements
have been made in many aspects of those challenging issues,
including the use of nonstabilized carbon nucleophiles3−6 and
regio- and enantioselectivities in the reaction of monosubstituted
allyl reagents and 1,3-unsymmetric substituted ones.7,8 However,
the allyl reagents have been limited to those with aryl and methyl
as substituents in most cases, in addition to the cyclic allyl ones
such as cyclohex-2-en-1-yl acetate.1 Only a few examples used
alkyl substituted allyl reagents in Pd-catalyzed AAA reaction with
the limitation of employing stabilized carbanions and oxygen as
nucleophiles (Scheme 1).9 No report has appeared regarding the
use of nonstabilized carbon nucleophiles in the reactions with
alkyl-substituted allyl reagents. These limitations have severely
hampered the applications of the Pd-catalyzed AAA reaction.
Obviously, the use of alkyl substituted allyl reagents in Pd-
catalyzed AAA, especially with nonstabilized carbanion, is a great
challenge that remains to be addressed. During our studies on
Pd-catalyzed AAA reactions, we realized regio- and enantiose-
lectivities in the reaction using aryl-substituted allyl reagents and
successfully utilized nonstabilized carbanions as nucleophiles.10
Further studies showed that a wide range of alkyl-substituted allyl
reagents could also be used in Pd-catalyzed AAA reaction with
nonstabilized carbon nucleophiles. In this Letter, we report our
preliminary investigations on the Pd-catalyzed AAA reaction of
alkyl-substituted allyl reagents with acyclic aliphatic amides to
afford corresponding products in high yields with high
enantioselectivity. The utility of the method was demonstrated
in a formal catalytic asymmetric synthesis of an enantiomer of
Dubiusamine A.
Initially, phenylethyl allyl carbonate 2a was used as a reagent to
react with three nucleophiles, such as propiophenone, ethyl 2-
methyl-3-oxobutanoate, and N,N-diphenylpropionamide, using
Pd(OAc)2 and (R)-BINAP (L1) as the catalyst with LDA as the
base in THF (Scheme 2). Only β-H elimination of 2a was
observed for the reaction with propiophenone, while the
corresponding product, in 80% yield but with very low er
(54:46), was afforded only if ethyl 2-methyl-3-oxobutanoate was
the nucleophile. Pleasingly, the reaction of N,N-diphenylpropio-
namide (1a) and allyl reagent 2a provided allylic alkylation
product 3a in 66% yield with 63.5:36.5 er. This preliminary result
Scheme 1. Palladium-Catalyzed AAA Reaction of Alkyl-
Substituted Allyl Reagents
Received: September 19, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.7b02927
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
er was acquired (entry 3). The screening of solvents including
Et2O and toluene and bases including NaHMDS indicated that
dimethoxyethane (DME) and LiHMDS were the best choices,
providing 3a in 94% yield with 73:27 er (entry 5, Table 1) (for
detail, see Supporting Information (SI)). Then the effect of the
chiral ligand on the reaction was investigated. The palladium
complexes of several chiral ligands that show high catalytic
activity in Pd-catalyzed AAA including SIOCPhox-L2,10a
(S)-iPrPHOX-L3,7b and Trost’s ligand (R,R)-DACH-phenyl
L44a could not catalyze the reaction since no conversion of 2a
was observed (entries 6−8). The utilization of chiral bi-
sphosphine ligands L5L7 with C2-symmetry and different
scaffolds did not improve the enantioselectivity (entries 9−11 vs
entry 5). Pleasingly, the use of a commercially available ligand L8
containing bis(3,4,5-trimethoxyphenyl)phosphine group led to
higher er (83.5:16.5), although the yield decreased to 57% due to
lower conversion of the amide 1a (entry 12). Further
investigation revealed that when LiCl was added as an additive
99% yield with 93.5:6.5 er of product 3a could be reached (entry
13). The importance of both lithium cation and chloride anion
was confirmed by using NaCl, LiBr, or LiI as the additive (entries
14−16 vs entry 13).10f Replacing LiHMDS with NaHMDS as
base afforded 3a in 75% yield with low er (63:37), further
confirming the importance of lithium cation (entry 17). Finally,
allylic alkylation product 3a in >90% yield with 95:5 er was
provided by changing the leaving group of allyl substrate 2 to
OAc or OPO(OEt)2 (entries 18 and 19 vs entry 13). It was found
also that the presence of two phenyl groups was important.10e
Only 63% yield with 68:32 er of product was obtained if N-
methyl-N-phenylpropionamide instead of amide 1a was the
substrate (for detail, see SI).
Scheme 2. Palladium-Catalyzed AAA Reaction of Allyl
Reagent 2a with Different Nucleophiles
prompted us to study the influence of the reaction parameters on
the reaction to improve its efficiency (Table 1). Lowering the
reaction temperature was beneficial for the yield of the reaction
(entries 2−4). When the reaction was conducted at a
temperature of −25 °C, 97% yield of product 3a in 66.5:33.5
Table 1. Optimization of Reaction Conditions for the Pd-
Catalyzed Asymmetric Allylic Alkylation of Amide 1a with
a
Allyl Reagents 2a
With the above optimum reaction conditions established, a
survey of the substrate scope was conducted (Table 2). In
general, the reaction tolerated a variety of alkyl substituents on
Table 2. Substrate Scope for the Pd-Catalyzed Asymmetric
Allylic Alkylation of Amides 1 with Alkyl-Substituted Allyl
Reagents 2
b
c
entry
L
t (°C)
additive
yield (%)
er
a
1
L1
L1
L1
L1
L1
L2
L3
L4
L5
L6
L7
L8
L8
L8
L8
L8
L8
L8
L8
rt
66
91
97
83
94
nr
63.5:36.5
62:38
2
0
3
−25
−40
−25
−25
−25
−25
−25
−25
−25
−25
−25
−25
−25
−25
−25
−25
−25
66.5:33.5
51.5:48.5
73:27
4
5
6
b
c
entry
R1 (1)
R2 (2)
yield (3, %)
er
7
nr
1
Me (1a)
Me (1a)
Me (1a)
Me (1a)
Me (1a)
Me (1a)
Me (1a))
Me (1a)
Me (1a)
Et (1b)
Ph(CH2)2 (2a)
Et (2b)
95 (3a)
84 (3b)
92 (3c)
82 (3d)
83 (3e)
89 (3f)
90 (3g)
91 (3h)
88 (3i)
91 (3j)
97 (3k)
74 (3l)
80 (3m)
72 (3n)
79 (3o)
95:5
8
nr
2
95.7:4.3
96:4
9
99
92
79
57
99
86
63
27
75
92
99 (95)
72:28
3
nPr (2c)
10
11
12
13
14
15
16
69.5:30.5
67:33
4
nPentyl (2d)
Bn (2e)
94.6:5.4
95.5:4.5
96.4:3.6
96:4
5
83.5:16.5
93.5:6.5
72.5:27.5
88.5:11.5
73:27
6
iBu (2f)
LiCl
NaCl
LiBr
LiI
7
iPr (2g)
8
BnO(CH2)3 (2h)
TBSO(CH2)3 (2i)
Ph(CH2)2 (2a)
Ph(CH2)2 (2a)
Et (2b)
96:4
9
92.8:7.2
94.7:5.3
95:5
d
10
11
12
13
14
15
17
63:37
e
nPr (1c)
Et (1b)
18
f
LiCl
LiCl
95:5
92.4:7.6
91.3:8.7
92.9:7.1
94.4:5.6
19
95:5
Et (1b)
nPr (2c)
a
Et (1b)
iBu (2f)
Molar ratio of 1a/2a/base/[Pd]/ligand/additive = 130/100/130/5/
5/100; entries 1−4: LDA as base and THF as solvent. The yield was
determined by H NMR using mesitylene as internal standard. The
number in parentheses of entry 18 being isolated yield. Determined
by chiral HPLC. NaHMDS used as base. Leaving group of 2a being
b
OMe (1e)
Ph(CH2)2 (2a)
1
c
a
Molar ratio of 1/2/LiHMDS/Pd(OAc)2/L8/LiCl = 130/100/130/
5/5/100. The leaving group of 2 is OBoc for entries 2, 8, and 12−14.
d
e
f
b
c
OAc. Leaving group of 2a being OPO(OEt)2.
Isolated yield. Determined by chiral HPLC.
B
DOI: 10.1021/acs.orglett.7b02927
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
allyl reagents 2, leading to the corresponding allylic alkylation
products 3 in high yields with high enantioselectivities (entries
1−9). The length of linear alkyl substituents of the allyl reagents
2 had little effect on enantioselectivity, though the yield varied to
some extent when the alkyl chain was changed (entries 1−5).
The allyl reagent 2 with a steric substituent such as iso-butyl and
iso-propyl also led to high enantioselectivities in 96.4:3.6 er and
96:4 er, respectively (entries 6 and 7). Notably, the reaction of
allyl reagent 2 containing a BnO- or TBSO-ether functional
group, which can be readily deprotected, provided also the
corresponding 3h and 3i in 96:4 er and 92.8:7.2 er, respectively
(entries 8 an 9). In terms of amides 1, when R1 group is a linear
alkyl substituent, the yield and enantioselectivity remained high
(entries 10−14). Interestingly, amide 1f with an α-methoxy
group is tolerated, leading to product 3o in 79% yield with
94.4:5.6 er (entry 15). However, no desired product was
observed if an amide with α-chloride was used (for detail, see SI).
The synthetic utility of the protocol is demonstrated in the
preparation of alcohol 5 (Scheme 3) as well as the efficient
enantioselective formal total synthesis of an enantiomer of
Dubiusamine A (Scheme 4).
of the crude product). The pure major isomer of 7 was isolated in
61% yield. Deiodination of 7 with nBu3SnH/Et3B led to lactone 8
in 94% yield and 93.8:6.2 er. Debenzylation of lactone 8 by
hydrogenation furnished alcohol 9 in 99% yield, the enantiomer
of an advanced intermediate in the total synthesis of Dubius-
amine A.12 Our enantioselective synthesis of alcohol 9 was
realized in 56% overall yield for three steps, constituting a
substantial improvement over reported synthesis (nine steps,
40%;12a five steps, 33%12b) (Scheme 4).
The absolute configuration of the reaction products was
determined by conversion of alcohol 5 to its ester 6, the er of
which was determined to be 93.7:6.3, thus indicating the optical
purity remained unchanged during the transformations of 3d to
6. The absolute configuration of the alcohol 5 was assigned as S
by comparing its sign of optical rotation with that reported in the
literature.13 Accordingly, the absolute configuration of the
allylated product 3d was assigned as S (Scheme 3).
In conclusion, the enantioselective reaction of a variety of
alkyl-substituted allyl reagents with acyclic amides as non-
stabilized carbon nucleophile was accomplished under Pd-
catalysis for the first time, affording allylic alkylation products in
high yields with high enantioselectivities. The usefulness of the
protocol has been demonstrated by conversion of the products to
the important chiral building block and enantiomer of Dubius-
amine A.
Scheme 3. Transformation of the Allylated Product 3d and Its
Determination of Absolute Configuration
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.orglett.7b02927.
Screening of reaction conditions, experimental proce-
dures, NMR, and HPLC spectra (PDF)
AUTHOR INFORMATION
Corresponding Authors
■
*E-mail: xlhou@sioc.ac.cn.
*E-mail: dingch@sioc.ac.cn.
ORCID
Scheme 4. Enantioselective Formal Synthesis of an
Enantiomer of Dubiusamine A
Xue-Long Hou: 0000-0003-4396-3184
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support by National Natural Science Foundation of
China (NSFC) (21532010, 21372242, 21472214, 21421091),
the Strategic Priority Research Program of the Chinese Academy
of Sciences (XDB20030100), the NSFC and the Research
Grants Council of Hong Kong Joint Research Scheme
(21361162001), the Technology Commission of Shanghai
Municipality, and the Croucher Foundation of Hong Kong is
acknowledged. This paper is dedicated to Professor Chi Ming
Che of the University of Hong Kong on the occasion of his 60th
birthday.
Alcohol 5 was the key intermediate in the synthesis of the
pheromone of Neodipirion sertifer, a pest on Scandinavian pine
trees.11 The alkylated product 3d was efficiently converted to
alcohol 5 after amide reduction with LiAlH4 followed by Pd/C-
catalyzed hydrogenation of the double bond in 83% yield for two
steps (Scheme 3).
Dubiusamine A is an alkaloid isolated from the crude base of P.
dubius.12a The compound 3h underwent an iodolactonization to
afford butyrolactone 7 with 5/1 dr (determined by the 1H NMR
REFERENCES
■
(1) For reviews, see: (a) Helmchen, G. J. Organomet. Chem. 1999, 576,
203. (b) Trost, B. M.; Crawley, M. L. Chem. Rev. 2003, 103, 2921. (c) Lu,
Z.; Ma, S. Angew. Chem., Int. Ed. 2008, 47, 258. (d) Ding, C.-H.; Hou, X.-
L. Top. Organomet. Chem. 2011, 36, 247. (e) Guerrero Rios, I.; Rosas-
Hernandez, A.; Martin, E. Molecules 2011, 16, 970. (f) Poli, G.; Prestat,
G.; Liron, F.; Kammerer-Pentier, C. Top. Organomet. Chem. 2011, 38, 1.
C
DOI: 10.1021/acs.orglett.7b02927
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
(g) Ding, C.-H.; Hou, X.-L. Nucleophiles with Allyl Metal Complexes In
Comprehensive Organic Synthesis, 2nd ed.; Molander, G. A., Knochel, P.,
Eds.; Elsevier: Oxford, 2014; Vol 4, pp 648.
(2) (a) Tsuji, J.; Takahashi, H.; Morikawa, M. Tetrahedron Lett. 1965,
6, 4387. (b) Trost, B. M.; Fullerton, T. J. J. Am. Chem. Soc. 1973, 95, 292.
(3) For selected examples using aldehyde as nucleophile: (a) Ibrahem,
M. J. Am. Chem. Soc. 2000, 122, 3785. (f) Kuwano, R.; Uchida, K.; Ito, Y.
Org. Lett. 2003, 5, 2177. (g) Nemoto, T.; Matsumoto, T.; Masuda, T.;
Hitomi, T.; Hatano, K.; Hamada, Y. J. Am. Chem. Soc. 2004, 126, 3690.
(10) (a) You, S.-L.; Zhu, X.-Z.; Luo, Y.-M.; Hou, X.-L.; Dai, L.-X. J. Am.
Chem. Soc. 2001, 123, 7471. (b) Zheng, W.-H.; Sun, N.; Hou, X.-L. Org.
Lett. 2005, 7, 5151. (c) Yan, X. X.; Liang, C. G.; Zhang, Y.; Hong, W.;
Cao, B. X.; Dai, L. X.; Hou, X. L. Angew. Chem., Int. Ed. 2005, 44, 6544.
(d) Zheng, W.-H.; Zheng, B.-H.; Zhang, Y.; Hou, X.-L. J. Am. Chem. Soc.
2007, 129, 7718. (e) Zhang, K.; Peng, Q.; Hou, X.-L.; Wu, Y. D. Angew.
Chem., Int. Ed. 2008, 47, 1741. (f) Chen, J.-P.; Ding, C.-H.; Liu, W.; Hou,
X.-L.; Dai, L.-X. J. Am. Chem. Soc. 2010, 132, 15493. (g) Chen, J.-P.;
Peng, Q.; Lei, B.-L.; Hou, X.-L.; Wu, Y.-D. J. Am. Chem. Soc. 2011, 133,
14180. (h) Chen, T.-G.; Fang, P.; Dai, L.-X.; Hou, X.-L. Synthesis 2015,
47, 134. (i) Bai, D.-C.; Yu, F.-L.; Wang, W.-Y.; Chen, D.; Li, H.; Liu, Q.-
R.; Ding, C.-H.; Chen, B.; Hou, X.-L. Nat. Commun. 2016, 7, 11806.
(j) Li, X.-H.; Wan, S.-L.; Chen, D.; Liu, Q.-R.; Ding, C.-H.; Fang, P.;
Hou, X.-L. Synthesis 2016, 48, 1568.
́
I.; Cordova, A. Angew. Chem., Int. Ed. 2006, 45, 1952. (b) Mukherjee, S.;
List, B. J. Am. Chem. Soc. 2007, 129, 11336. (c) Jiang, G.; List, B. Angew.
Chem., Int. Ed. 2011, 50, 9471. (d) Zhao, X.; Liu, D.; Xie, F.; Liu, Y.;
Zhang, W. Org. Biomol. Chem. 2011, 9, 1871. (e) Yoshida, M.; Terumine,
T.; Masaki, E.; Hara, S. J. Org. Chem. 2013, 78, 10853. (f) Zhou, H.;
Wang, Y.; Zhang, L.; Cai, M.; Luo, S. J. Am. Chem. Soc. 2017, 139, 3631.
(4) For selected examples using ketone as nucleophile: (a) Trost, B.
M.; Schroeder, G. M. J. Am. Chem. Soc. 1999, 121, 6759. (b) Braun, M.;
Laicher, F.; Meier, T. Angew. Chem., Int. Ed. 2000, 39, 3494. (c) Burger,
E. C.; Tunge, J. A. Org. Lett. 2004, 6, 4113. (d) Behenna, D. C.; Stoltz, B.
́
M. J. Am. Chem. Soc. 2004, 126, 15044. (e) Bel
́
anger, E.; Cantin, K.;
(11) (a) Jewett, D. M.; Matsumura, F.; Coppel, H. C. Science 1976, 192,
51. (b) Bystrom, S.; Hogberg, H. E.; Norin, T. Tetrahedron 1981, 37,
2249.
(12) (a) Tan, M. A.; Kitajima, M.; Kogure, N.; Nonato, M. G.;
Takayama, H. Tetrahedron 2010, 66, 3353. (b) Kawasumi, M.; Iwabuchi,
Y. Org. Lett. 2013, 15, 1788.
Messe, O.; Tremblay, M.; Paquin, J.-F. J. Am. Chem. Soc. 2007, 129,
1034. (f) Zhao, X.; Liu, D.; Guo, H.; Liu, Y.; Zhang, W. J. Am. Chem. Soc.
2011, 133, 19354. (g) Huo, X.; Quan, M.; Yang, G.; Zhao, X.; Liu, D.;
Liu, Y.; Zhang, W. Org. Lett. 2014, 16, 1570. (h) Numajiri, Y.; Pritchett,
B. P.; Chiyoda, K.; Stoltz, B. M. J. Am. Chem. Soc. 2015, 137, 1040.
(5) For selected examples using carboxylic acid derivative as
nucleophile: (a) Genet, J.-P.; Juge, S.; Achi, S.; Mallart, S.; Ruiz-
Montes, J.; Levif, G. Tetrahedron 1988, 44, 5263. (b) Trost, B. M.; Lee,
C. B. J. Am. Chem. Soc. 1998, 120, 6818. (c) Kazmaier, U.; Zumpe, F. L.
Angew. Chem., Int. Ed. 1999, 38, 1468. (d) Nakoji, M.; Kanayama, T.;
Okino, T.; Takemoto, Y. J. Org. Chem. 2002, 67, 7418. (e) Weiß, T. D.;
Helmchen, G.; Kazmaier, U. Chem. Commun. 2002, 1270. (f) Deska, J.;
Kazmaier, U. Angew. Chem., Int. Ed. 2007, 46, 4570. (g) Trost, B. M.;
Lehr, K.; Michaelis, D. J.; Xu, J.; Buckl, A. K. J. Am. Chem. Soc. 2010, 132,
8915. (h) Trost, B. M.; Michaelis, D. J.; Charpentier, J.; Xu, J. Angew.
Chem., Int. Ed. 2012, 51, 204. (i) Starkov, P.; Moore, J. T.; Duquette, D.
C.; Stoltz, B. M.; Marek, I. J. Am. Chem. Soc. 2017, 139, 9615.
(13) Cardillo, G.; D’Amico, A.; Orena, M.; Sandri, S. J. Org. Chem.
1988, 53, 2354.
(6) For selected examples using other nonstabilized carbon
nucleophile: (a) Trost, B. M.; Thaisrivongs, D. A. J. Am. Chem. Soc.
2008, 130, 14092. (b) Trost, B. M.; Thaisrivongs, D. A. J. Am. Chem. Soc.
2009, 131, 12056. (c) Trost, B. M.; Thaisrivongs, D. A.; Hartwig, J. J.
Am. Chem. Soc. 2011, 133, 12439. (d) Sha, S.-C.; Zhang, J.; Carroll, P. J.;
Walsh, P. J. J. Am. Chem. Soc. 2013, 135, 17602. (e) Mao, J.; Zhang, J.;
Jiang, H.; Bellomo, A.; Zhang, M.; Gao, Z.; Dreher, S. D.; Walsh, P. J.
Angew. Chem., Int. Ed. 2016, 55, 2526.
(7) (a) Hayashi, T.; Kawatsura, M.; Uozumi, Y. Chem. Commun. 1997,
́ ̂
561. (b) Pretot, R.; Pfaltz, A. Angew. Chem., Int. Ed. 1998, 37, 323.
(c) Trost, B. M.; Bunt, R. C.; Lemoine, R. C.; Calkins, T. L. J. Am. Chem.
Soc. 2000, 122, 5968. (d) Cook, G. R.; Yu, H.; Sankaranarayanan, S.;
Shanker, P. S. J. Am. Chem. Soc. 2003, 125, 5115. (e) Watson, I. D. G.;
Styler, S. A.; Yudin, A. K. J. Am. Chem. Soc. 2004, 126, 5086. (f) Pam
̀
ies,
O.; Dieguez, M.; Claver, C. J. Am. Chem. Soc. 2005, 127, 3646.
́
(g) Waetzig, S. R.; Tunge, J. A. J. Am. Chem. Soc. 2007, 129, 4138.
(h) Johns, A. M.; Liu, Z.; Hartwig, J. F. Angew. Chem., Int. Ed. 2007, 46,
7259. (i) Hu, Z.; Li, Y.; Liu, K.; Shen, Q. J. Org. Chem. 2012, 77, 7957.
(j) Wang, X.; Wang, X.; Han, Z.; Wang, Z.; Ding, K. Angew. Chem., Int.
Ed. 2017, 56, 1116.
(8) (a) Itami, K.; Koike, T.; Yoshida, J.-i. J. Am. Chem. Soc. 2001, 123,
6957. (b) Krafft, M. E.; Sugiura, M.; Abboud, K. A. J. Am. Chem. Soc.
2001, 123, 9174. (c) Benfatti, F.; Cardillo, G.; Gentilucci, L.; Mosconi,
E.; Tolomelli, A. Org. Lett. 2008, 10, 2425. (d) Du, L.; Cao, P.; Xing, J.;
Lou, Y.; Jiang, L.; Li, L.; Liao, J. Angew. Chem., Int. Ed. 2013, 52, 4207.
(e) Le, H.; Batten, A.; Morken, J. P. Org. Lett. 2014, 16, 2096. (f) Jia, T.;
Cao, P.; Wang, B.; Lou, Y.; Yin, X.; Wang, M.; Liao, J. J. Am. Chem. Soc.
2015, 137, 13760. (g) Wu, X.; Lin, H.-C.; Li, M.-L.; Li, L.-L.; Han, Z.-Y.;
Gong, L.-Z. J. Am. Chem. Soc. 2015, 137, 13476. (h) Lin, H.-C.; Wang,
P.-S.; Tao, Z.-L.; Chen, Y.-G.; Han, Z.-Y.; Gong, L.-Z. J. Am. Chem. Soc.
2016, 138, 14354.
(9) (a) Von Matt, P.; Pfaltz, A. Angew. Chem., Int. Ed. Engl. 1993, 32,
566. (b) Kuwano, R.; Nishio, R.; Ito, Y. Org. Lett. 1999, 1, 837.
(c) Kuwano, R.; Ito, Y. J. Am. Chem. Soc. 1999, 121, 3236. (d) Hayashi,
T. J. Organomet. Chem. 1999, 576, 195. (e) Trost, B. M.; Schroeder, G.
D
DOI: 10.1021/acs.orglett.7b02927
Org. Lett. XXXX, XXX, XXX−XXX