Copper-Catalyzed γ-Selective and Stereospecific Allylic Cross-Coupling with Secondary Alkylboranes

Article abstract of DOI:10.1002/chem.201501055

The scope of the copper-catalyzed coupling reactions between organoboron compounds and allylic phosphates is expanded significantly by employing triphenylphosphine as a ligand for copper, allowing the use of secondary alkylboron compounds. The reaction proceeds with complete γ-E-selectivity and preferential 1,3-syn stereoselectivity. The reaction of γ-silicon-substituted allylic phosphates affords enantioenriched α-stereogenic allylsilanes.

Full text of DOI:10.1002/chem.201501055

DOI: 10.1002/chem.201501055
Communication
&
CÀC Coupling
Copper-Catalyzed g-Selective and Stereospecific Allylic Cross-
Coupling with Secondary Alkylboranes
Yuto Yasuda,[a] Kazunori Nagao,[a] Yoshinori Shido,[a] Seiji Mori,[b] Hirohisa Ohmiya,*[a] and
Masaya Sawamura*[a]
Abstract: The scope of the copper-catalyzed coupling re-
actions between organoboron compounds and allylic
phosphates is expanded significantly by employing triphe-
nylphosphine as a ligand for copper, allowing the use of
secondary alkylboron compounds. The reaction proceeds
with complete g-E-selectivity and preferential 1,3-syn
stereoselectivity. The reaction of g-silicon-substituted allyl-
ic phosphates affords enantioenriched a-stereogenic
allylsilanes.
Copper-catalyzed allylic substitutions with organoboron com-
pounds are of interest due to their broad substrate scope.[1,2]
Previous reports have shown that sp3-alkylboron compounds,
such as B-alkyl-9-borabicyclo[3.3.1]nonane (alkyl-9-BBN), can be
coupled with internal allylic systems with complete g-selectivi-
ty by using a catalytic amount of a copper(I) salt and a stoichio-
metric potassium alkoxide base.[3–5] Interestingly, the stereo-
chemistry of the cross-coupling between enantioenriched
Scheme 1. Previous work:[3c] a) Reaction of primary alkylboranes; b) reaction
of secondary alkylboranes.
chiral allylic phosphates and alkylboranes could be switched
between the 1,3-anti and 1,3-syn forms relative to the leaving
group by choosing the appropriate achiral alkoxide base with
a specific steric demand; tBuOK and MeOK led to 1,3-anti and
1,3-syn stereochemistry, respectively.[3c] Acyclic and cyclic bimo-
dal participation of alkoxyborane species generated in situ in
an organocopper addition–elimination sequence was proposed
to account for the phenomenon of the anti/syn stereochemical
reversal (Scheme 1a). However, only primary alkylboron com-
pounds could be used as nucleophilic coupling partners.
Neither the 1,3-anti nor the 1,3-syn form was effective in the
reaction of secondary alkylboranes, probably due to increased
steric demands of the transferring groups (Scheme 1b).
enabled copper-catalyzed allylic cross-coupling between sec-
ondary alkylboron compounds, such as alkyl-9-BBN, and (Z)-
acyclic or cyclic allylic phosphates. These ligand effects were
most pronounced when the ligands were used as additives for
the 1,3-syn-selective protocol (CuOAc/MeOK/toluene) in
a
previous study.[6] This new copper catalysis using secondary al-
kylboranes proceeded with complete g-E-selectivity and pre-
ferential 1,3-syn stereoselectivity. These methods significantly
broaden the scope of allylic CÀC cross-coupling reactions.
In numerous studies for finding reaction conditions enabling
the regio- and stereoselective coupling between secondary al-
kylboron compounds and chiral secondary allylic electrophiles,
we found critical effects of phosphine ligands for promoting
this transformation. Specifically, the reaction between cyclo-
hexylborane 2a, which was prepared by hydroboration of cy-
clohexene (1a), and an enantioenriched chiral g-silylated allylic
phosphate, (S)-(Z)-3a (99% ee) containing a diisopropyl phos-
phate leaving group afforded allylsilane (R)-(E)-4aa with
97% ee and 88% yield with complete g- and E-selectivities
(Scheme 2 and Table 1, entry 3).[7] The absolute configuration
of the coupling product indicated that the reaction occurred
with 1,3-syn stereochemistry (syn/anti 99:1). The reported
phosphine-free conditions, which gave 1,3-syn (CuOAc/MeOK/
The present study describes the dramatic ligand effects of
tertiary monophosphines such as Ph3P, Cy3P, and tBu3P, which
[a] Y. Yasuda, K. Nagao, Y. Shido, Prof. Dr. H. Ohmiya, Prof. Dr. M. Sawamura
Department of Chemistry, Faculty of Science
Hokkaido University, Sapporo 060-0810 (Japan)
;http://wwwchem.sci.hokudai.ac.jp/~orgmet/index.php
E-mail: ohmiya@sci.hokudai.ac.jp
sawamura@sci.hokudai.ac.jp
[b] Prof. Dr. S. Mori
Faculty of Science, Ibaraki University
Mito 310-8512 (Japan)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201501055.
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(Table 1, entry 5). Use of PMe3 produced a very low
yield with moderate syn selectivity (syn/anti 88:12;
Table 1, entry 6). The phosphine ligands PEt3 and
PBu3 both promoted the coupling efficiently, but syn
selectivity was slightly decreased compared to the
excellent selectivity obtained with PPh3 (Table 1, en-
tries 7 and 8). Interestingly, the bulkier monodentate
trialkylphosphines, such as PCy3 and PtBu3, were as
effective as PPh3 in terms of both product yield and
syn selectivity (Table 1, entries 9 and 10). In contrast,
bisphosphines such as DPPE and Xantphos, produced
no reaction (Table 1, entries 11 and 12). Monodentate
N-heterocyclic carbene (NHC) ligands, such as IMes,
SIMes, IPr, and SIPr, did not promote the reaction either
(Table 1, entries 13–16). Thus, PPh3 was selected as the most
useful additive for cost-effectiveness and ease of handling
(Scheme 2 and Table 1, entry 3).[9]
Scheme 2. Hydroboration/copper-catalyzed g-syn-selective allylic cross-
coupling sequence.
toluene) or 1,3-anti (CuOAc/tBuOK/THF) stereochemical out-
comes in a previous study on the reaction of primary alkyl-
boranes (Scheme 1a), produced no coupling product, leaving
the substrates almost unreacted (Table 1, entries 1 and 2).[3c,8]
The effect of ligands on the reaction between 2a and 3a
are shown in Table 1. Use of tri(4-methoxyphenyl)phosphine
resulted in a significantly lower product yield and syn-stereo-
selectivity compared to PPh3 (Table 1, entry 4). No reaction oc-
curred with the electron-deficient P[3,5-(CF3)C6H3]3 ligand
The effect of the stoichiometric base is also shown in
Table 1. The use of EtOK instead of MeOK in the presence of
PPh3 resulted in a slight decrease in the syn-stereoselectivity
(Table 1, entry 17). No reaction occurred with the sterically
more demanding base tBuOK, which induced 1,3-anti stereo-
chemistry under phosphine-free conditions in the reaction of
primary alkylboranes (Table 1, entry 18).[10]
Table 1. Effects of ligands and bases.[a,b]
To gain understanding of the mechanism of Cu-catalyzed
cross-coupling with secondary alkylboranes, the effect of PPh3
on the stoichiometric reaction of CuOAc, MeOK, and cyclohex-
ylborane 2a was investigated [Eq. (1)]. Reaction in the pres-
ence of PPh3 caused the complete disappearance of the signal
for 2a (d=86.4 ppm), confirmed by 11B NMR spectroscopy, and
a new signal for 9-BBNÀOMe appeared at a higher magnetic
field (d=55.5 ppm). In contrast, reaction in the absence of
PPh3 did not result in formation of 9-BBNÀOMe, indicating that
PPh3 is essential for B/Cu transmetalation.
Entry
Ligand
Base
MeOK
Yield [%][c,d]
syn/anti[e]
1
2
3[f]
4
5
6
7
8
none
none
PPh3
0
0
88
55
0
13
95
90
93
83
0
0
0
0
0
0
99
0
–
–
tBuOK
MeOK
MeOK
MeOK
MeOK
MeOK
MeOK
MeOK
MeOK
MeOK
MeOK
MeOK
MeOK
MeOK
MeOK
EtOK
99:1
96.5:3.5
P(4-MeOC6H4)3
P[3,5-(CF3)C6H3]3
PMe3
–
88:12
98.5:1.5
92:8
99:1
99:1
–
–
–
–
–
–
98:2
–
PEt3
PBu3
PCy3
PtBu3
9
10
11
12
13
14
15
16
17
18
DPPE
Xantphos
IMes
SIMes
IPr
SIPr
PPh3
PPh3
tBuOK
Molecular modeling studies suggested that tertiary mono-
phosphines would not be able to coordinate to the copper
center in the cyclic organocopper addition–elimination transi-
tion state due to steric effects (Scheme 1a).[11] Therefore, a cata-
lytic cycle for the copper-catalyzed g-syn-selective allylic cross-
coupling with secondary alkylboranes should involve coordina-
tion and dissociation of the phosphine ligand as shown in
Scheme 3. According to these considerations, the reduction of
yield and syn selectivity in the reaction with PMe3 may suggest
that the Cu–P interaction would be persistent in the addition–
elimination step. This should be reasonable, considering the
higher coordination ability of PMe3 as a compact ligand. The
marginal reduction of the syn selectivity in the reactions with
PEt3 and PBu3 may be due to partial coordination of these
ligands in the addition–elimination step. In this context, the
[a] Reaction conditions: 3 (0.15 mmol), alkylborane 2 (0.24 mmol), CuOAc
(10 mol%), ligand (11 mol%), and base (0.225 mmol) in toluene at 608C
for 24 h; [b] alkylborane 2 was prepared in advance by hydroboration of
alkene 1 with 9-BBN dimer in toluene at 708C for 1 h and used without
purification. [c] yield of isolated product based on 3; [d] isomeric ratios
(g/a>99:1, E/Z>99:1) determined by 1H NMR spectroscopy or GC of the
crude product; [e] selectivity was determined by HPLC; [f] see Scheme 2.
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Table 2. (Continued)
Entry Borane
Phosphate Product
Yield syn/anti[e]
[%][c,d]
(S)-(Z)-3a
99% ee
3
94
98.5:1.5
98:2
(S)-(Z)-3a
99% ee
4[f]
47[f]
94
5
>99.5:0.5
>99.5:0.5
Scheme 3. Proposed catalytic cycle for the copper-catalyzed g-syn-selective
allylic cross-coupling between secondary alkylboranes and secondary allylic
phosphates.
(S)-(Z)-3b
99% ee
6
7
2b
2d
93
common features of PPh3, PCy3, and PtBu3, showing the high
product yields and syn selectivities, may be due to their
moderate coordination abilities toward Cu, allowing timely
coordination/dissociation equilibria.
(S)-(Z)-3b
99% ee
88
93
>99.5:0.5
The scope of copper-catalyzed regioselective and stereospe-
cific cross-coupling reaction between secondary alkylboranes
and enantioenriched chiral g-silylated allylic phosphates to
afford enantioenriched a-stereogenic chiral allylsilanes is sum-
marized in Table 2.[12–14] Cyclic secondary alkylboranes 2b and
c, with five- and seven-membered carbocycles, underwent re-
action with excellent syn-stereoselectivities (Table 2, entries 1
and 2). Acyclic isopropylborane 2d was also tolerated, with
a high level of stereoselectivity retained (Table 2, entries 3 and
7). The heterocyclic secondary alkylborane 2e, with a carba-
mate group, underwent stereospecific reaction resulting in
a moderate product yield (Table 2, entry 4).
8
99.5:0.5
(S)-(Z)-3c
99% ee
9
2b
2c
96
38
99.5:0.5
99:1
(S)-(Z)-3c
99% ee
10
11
12
13
31
75
61
97:3
Table 2. Synthesis of chiral allylsilanes.[a,b]
(S)-(Z)-3d
99% ee
2b
2c
96.5:3.5
98.5:1.5
(S)-(Z)-3d
99% ee
Entry Borane
Phosphate Product
Yield syn/anti[e]
[%][c,d]
[a] Reaction conditions: 3 (0.15 mmol), alkylborane 2 (0.24 mmol), CuOAc
(10 mol%), PPh3 (11 mol%), and MeOK (0.225 mmol) in toluene at 608C for
24 h; [b] alkylborane 2 was prepared in advance by hydroboration of alkene
1 with 9-BBN dimer in toluene at 708C for 1 h and used without purification;
[c] yield of the isolated product based on 3; [d] isomeric ratios (g/a>99:1,
E/Z>99:1) determined by 1H NMR spectroscopy or GC of the crude
product; [e] enantiomeric excess was determined by HPLC; [f] diastereomeric
ratio=1:1.
(S)-(Z)-3a
99% ee
1
93
80
97.5:2.5
99:1
(S)-(Z)-3a
99% ee
2
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Communication
tion proceeded with complete g-E-selectivity and pref-
erential 1,3-syn stereoselectivity. This is the first catalytic
allylic substitution reaction with secondary alkylboron
derivatives.
Table 3. Allyl–alkyl coupling with non-silicon-substituted allylic phosphates.[a,b]
Experimental Section
Entry
1
Borane
Product
Yield [%][c,d]
syn/anti[e]
Scheme 2 shows
a
representative reaction. (9-BBNÀH)2
(30.2 mg, 0.12 mmol) was placed in a vial containing a mag-
netic stirring bar. The vial was sealed with a Teflon-coated
silicon rubber septum followed by evacuation of the vial,
which was then filled with argon. Cyclohexene 1a
(0.027 mL, 0.27 mmol) and toluene (0.3 mL) were added to
the vial, and the mixture stirred at 708C for 1 h to prepare
2a
88
96:4
2
3
2b
2c
98
78
84:16
a
secondary alkylborane. Then, CuOAc (1.8 mg,
0.015 mmol), PPh3 (4.0 mg, 0.0165 mmol), and MeOK
(15.7 mg, 0.225 mmol) were placed in another vial, which
was sealed with a Teflon-coated silicon rubber septum,
evacuated, and filled with argon. Next, the alkylborane so-
lution was transferred to the vial containing the Cu salt, fol-
lowed by addition of (S)-(Z)-3a (55.6 mg, 0.15 mmol). After
24 h stirring at 608C, the mixture was filtered through
a short plug of aluminum oxide, which was then washed
with diethyl ether (5 mL). After the solvent was removed
under reduced pressure, flash chromatography on silica gel
(hexane) gave (R)-(E)-4aa (35.6 mg, 0.132 mmol) in 88%
yield.
74.5:25.5
[a] Reaction conditions:
5 (0.15 mmol), alkylborane 2 (0.24 mmol), CuOAc
(10 mol%), PPh3 (11 mol%), and MeOK (0.225 mmol) in toluene at 608C for 24 h;
[b] alkylborane 2 was prepared in advance by hydroboration of alkene 1 with 9-
BBN dimer in toluene at 708C for 1 h and used without purification; [c] yield of the
isolated product based on 5; [d] isomeric ratios (g/a>99:1, E/Z>99:1) determined
by 1H NMR spectroscopy or GC of the crude product; [e] enantiomeric excess was
determined by HPLC.
The methyl group at the a-position of 3a could be re-
Table 4. Allyl–alkyl coupling with cyclic allylic phosphates.[a,b]
Entry Borane Phosphate Product
placed with n-pentyl (3b) or isopropyl (3c) groups with ex-
cellent syn selectivity retained (Table 2, entries 5–10). The
allylic phosphate (S)-(Z)-3d, with a BnMe2Si group at the g-
position, reacted with cyclic secondary alkylboranes con-
taining five-, six-, and seven-membered carbocycles with
excellent syn selectivities (Table 2, entries 11–13).
Yield syn/
[%][c,d] anti[e]
1
2
2a
2b
85 >99:1
90 >99:1
The usefulness of this protocol was not limited to allylsi-
lane synthesis but could also be applied to reactions of
non-silicon-substituted acyclic allylic phosphates (Table 3).
For example, the reaction between allylic phosphate (S)-
(Z)-5a (97% ee) and cyclohexylborane 2a occurred with
96% syn selectivity to produce the Me-branched product
(R)-(E)-6aa (Table 3, entry 1). Reaction of cyclic secondary
alkylboranes with a five- or a seven-membered ring also
occurred, but 1,3-syn stereoselectivity was only moderate
(Table 3, entries 2 and 3).
7a
7a
3
4
2c
2a
73 >99:1
49
93:7
Cyclic allylic phosphates also could serve as substrates
(Table 4). Coupling reactions between trans-2-cyclohexene-
1,4-diol derivative 7a and 2a proceeded with excellent g-
selectivity and 1,3-syn selectivity relative to the leaving
group, giving trans-1,2-isomer 8aa (Table 4, entry 1). Reac-
tions with cyclopentyl or cycloheptylboranes also occurred
with excellent 1,3-syn selectivity (Table 4, entries 2 and 3).
Trans-3-cyclohexene-1,2-diol derivative 7b also underwent
coupling with excellent 1,3-syn selectivity (Table 4, entry 4).
In summary, the scope of copper-catalyzed coupling re-
actions between organoboron compounds and allylic
phosphates was broadened significantly by employing triphe-
nylphosphine as a ligand for copper, allowing the use of sec-
ondary alkylboron compounds such as alkyl-9-BBN. The reac-
[a] Reaction conditions:
7 (0.15 mmol), alkylborane 2 (0.24 mmol), CuOAc
(10 mol%), PPh3 (11 mol%), and MeOK (0.225 mmol) in toluene at 608C for
24 h; [b] alkylborane 2 was prepared in advance by hydroboration of alkene
1 with 9-BBN dimer in toluene at 708C for 1 h and used without purification;
[c] yield of the isolated product based on 7; [d] isomeric ratios (g/a>99:1,
E/Z>99:1) determined by 1H NMR or GC of the crude product; [e] syn/anti
1
selectivity was determined by H NMR.
Acknowledgements
This work was supported by Grants-in-Aid for Young Scientists
(A) and Challenging Exploratory Research (JSPS) to H.O., ACT-C,
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[7] Reaction of (S)-(E)-3a proceeded with significantly decreased E-selectivi-
ty (E/Z 59:41), consistent with the concept of allylic 1,3-strain in acyclic
stereocontrol. See: R. W. Hoffmann, Chem. Rev. 1989, 89, 1841–1860.
[8] The use of Cu(acac)2 or copper(I) thiophene-2-carboxylate instead of
CuOAc under phosphine-free conditions (Table 1, entry 1) resulted in no
reaction.
[9] The effect of ligands on the reaction of primary alkylborane also was
examined (CuOAc/MeOK/toluene/608C). Reaction between 2-phenyl-
ethyl-9-BBN and (S)-(Z)-3a with PPh3 or PCy3 gave moderate 1,3-syn se-
lectivity (syn/anti 79:21, 81% yield and syn/anti 89:11, 84% yield, re-
spectively). In contrast, phosphine-free conditions resulted in greater
1,3-syn selectivity (syn/anti 97.5:2.5, 95% yield).
[10] Several observations concerning the optimum reaction conditions
should be noted. Reaction with cyclohexylboronic acid and its pinaco-
late ester instead of secondary alkyl-9-BBN reagents did not produce
any coupling product, leaving unreacted substrates. Using diethyl phos-
phate instead of diisopropyl phosphate as a leaving group was useful,
although it produced a slightly decreased stereoselectivity (syn/anti
98:2, 87%).
[11] Details of the DFT calculations will be reported elsewhere.
[12] For reviews on the synthesis of allylsilanes, see: a) C. E. Masse, J. S.
Panek, Chem. Rev. 1995, 95, 1293–1316; b) I. Fleming, A. Barbero, D.
Walter, Chem. Rev. 1997, 97, 2063–2192; c) L. Chabaud, P. James, Y.
Landais, Eur. J. Org. Chem. 2004, 3173–3199.
[13] For the synthesis of enantioenriched allylsilanes through Cu-catalyzed
enantioselective allylic substitutions of prochiral g-silylated primary al-
lylic alcohol derivatives with organozinc or organoaluminum reagents,
see: a) M. A. Kacprzynski, T. L. May, S. A. Kazane, A. H. Hoveyda, Angew.
Chem. Int. Ed. 2007, 46, 4554–4558; Angew. Chem. 2007, 119, 4638–
4642; b) F. Gao, K. P. McGrath, Y. Lee, A. H. Hoveyda, J. Am. Chem. Soc.
2010, 132, 14315–14320. For the synthesis of allylsilanes via copper-
catalyzed allylic substitutions with silylating reagents, see: c) D. J. Vyas,
M. Oestreich, Chem. Commun. 2010, 46, 568–570; d) D. J. Vyas, M. Oes-
treich, Angew. Chem. Int. Ed. 2010, 49, 8513–8515; Angew. Chem. 2010,
122, 8692–8694.
(JST) to M.S. and S.M., and CREST (JST) to M.S. K.N. thanks JSPS
for scholarship support.
Keywords: allylic substitution · copper catalysis · coupling ·
secondary alkylborane · stereoselectivity
[1] For a review on transition-metal-catalyzed allylic substitutions with or-
ganoboron compounds, see: F. C. Pigge, Synthesis 2010, 1745–1762.
[2] For reviews on Cu-catalyzed enantioselective allylic substitutions with
organomagnesium, organozinc, or organoaluminum reagents, see:
a) A. H. Hoveyda, A. W. Hird, M. A. Kacprzynski, Chem. Commun. 2004,
1779–1785; b) C. A. Falciola, A. Alexakis, Eur. J. Org. Chem. 2008, 3765–
3780; c) A. Alexakis, J. E. Bäckvall, N. Krause, O. Pàmies, M. DiØguez,
Chem. Rev. 2008, 108, 2796–2823; d) S. R. Harutyunyan, T. den Hartog,
K. Geurts, A. J. Minnaard, B. L. Feringa, Chem. Rev. 2008, 108, 2824–
2852.
[3] For Cu-catalyzed g-selective and stereospecific allylic substitutions be-
tween primary alkyl-9-BBN and enantioenriched secondary allylic phos-
phates, see: a) H. Ohmiya, U. Yokobori, Y. Makida, M. Sawamura, J. Am.
Chem. Soc. 2010, 132, 2895–2897; b) K. Nagao, H. Ohmiya, M. Sawa-
mura, Synthesis 2012, 44, 1535–1541; c) K. Nagao, U. Yokobori, Y.
Makida, H. Ohmiya, M. Sawamura, J. Am. Chem. Soc. 2012, 134, 8982–
8987. See also: d) A. M. Whittaker, R. P. Rucker, G. Lalic, Org. Lett. 2010,
12, 3216–3218.
[4] For Cu-catalyzed enantioselective allylic substitutions between alkyl-9-
BBN and prochiral primary allyl chlorides, see: a) Y. Shido, M. Yoshida,
M. Tanabe, H. Ohmiya, M. Sawamura, J. Am. Chem. Soc. 2012, 134,
18573–18576; b) K. Hojoh, Y. Shido, H. Ohmiya, M. Sawamura, Angew.
Chem. Int. Ed. 2014, 53, 4954.
[5] For Cu-catalyzed g-selective allylic substitutions with aryl-, alkenyl-, and
allenylboronates, see: a) H. Ohmiya, N. Yokokawa, M. Sawamura, Org.
Lett. 2010, 12, 2438–2440; b) R. Shintani, K. Takatsu, M. Takeda, T. Haya-
shi, Angew. Chem. Int. Ed. 2011, 50, 8656–8659; Angew. Chem. 2011,
123, 8815–8818; c) B. Jung, A. H. Hoveyda, J. Am. Chem. Soc. 2012, 134,
1490–1493; d) F. Gao, J. L. Carr, A. H. Hoveyda, Angew. Chem. Int. Ed.
2012, 51, 6613–6617; Angew. Chem. 2012, 124, 6717–6721; e) M.
Takeda, K. Takatsu, R. Shintani, T. Hayashi, J. Org. Chem. 2014, 79, 2354–
2367.
[14] For the synthesis of enantioenriched allylsilanes through palladium-cat-
alyzed allylic substitutions of enantioenriched g-silylated secondary al-
lylic alcohol derivatives with organoboronic acids, see: D. Li, T. Tanaka,
H. Ohmiya, M. Sawamura, Org. Lett. 2010, 12, 3344–3347.
[6] For a review on copper-mediated 1,3-syn selective allylic substitutions
of organometallic reagents by employing reagent-directing leaving
groups, see: B. Breit, Y. Schmidt, Chem. Rev. 2008, 108, 2928–2951.
Received: March 18, 2015
Published online on May 26, 2015
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