Ligand-controlled α- And β-arylation of acyclic N-boc amines

Article abstract of DOI:10.1002/anie.201310904

The palladium-catalyzed ligand-controlled arylation of α-zincated acyclic amines, obtained by directed α-lithiation and transmetalation, is described. Whereas PtBu₃ gave rise to α-arylated Boc-protected amines, more flexible N-phenylazole-based phosphine ligands induced major β-arylation through migrative cross-coupling. All manner of control: The arylation of α-zincated acyclic Boc-protected amines was selectively performed at the α- or β-position in a ligand-controlled manner. α-Arylation occurs by direct reductive elimination of the α-palladated intermediate whereas β-arylation involves palladium migration along the alkyl chain. Boc=tert-butoxycarbonyl.

Full text of DOI:10.1002/anie.201310904

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Angewandte
Communications
DOI: 10.1002/anie.201310904
Cross-Coupling
Ligand-Controlled a- and b-Arylation of Acyclic N-Boc Amines**
Anthony Millet, David Dailler, Paolo Larini, and Olivier Baudoin*
Dedicated to Max Malacria on the occasion of his 65th birthday
Abstract: The palladium-catalyzed ligand-controlled arylation
of a-zincated acyclic amines, obtained by directed a-lithiation
and transmetalation, is described. Whereas PtBu3 gave rise to
a-arylated Boc-protected amines, more flexible N-phenyl-
azole-based phosphine ligands induced major b-arylation
through migrative cross-coupling.
prefunctionalized amino reagents. In contrast, the directed
lithiation of Boc-protected piperidines and pyrrolidines a to
the nitrogen atom, with subsequent in situ transmetalation to
zinc and Negishi coupling, has been established as a powerful
and direct entry into a-aryl nitrogen heterocycles (Scheme
1b).[3] However, to the best of our knowledge this method has
never been extended to acyclic Boc-protected amines. Based
on a seminal observation by Knochel and co-workers,[4] we
have recently described the selective b-arylation of Boc-
protected piperidines, which occurs through the generation of
a-zincated piperidines and ligand (L1)-induced migrative
Negishi coupling (Scheme 1b).[5] Herein, we report the
ligand-controlled a- and b-arylation of acyclic Boc-protected
amines, which are potentially more challenging substrates for
these cross-coupling reactions because of a higher degree of
conformational freedom (Scheme 1c). This approach pro-
vides a one-step entry into synthetically useful arylmethyl-
and arylethylamines from simple precursors.
Acyclic arylmethyl and arylethylamines are found in count-
less bioactive molecules. In addition to classical methods
which are employed to access these motifs, the palladium-
catalyzed cross-coupling of a- and b-metalated amines with
aryl electrophiles has emerged as an efficient and chemo-
selective alternative.[1,2] In particular, the Suzuki–Miyaura
coupling of a- and b-aminotrifluoroborates, as developed by
Molander and co-workers, has proven effective and versatile
(Scheme 1a). However, this approach involves the use of
We first studied the arylation of the organozinc reagent,
which was generated in situ by a-lithiation of the Boc-
protected dimethylamine 1a[6] and transmetalation with
ZnCl2, with p-trifluoromethylbromobenzene to give the
product 2a (Scheme 2). A quick optimization[7] revealed
that the Pd/PtBu3 catalytic system described for the Negishi
coupling of Boc-protected piperidines and pyrrolidines[3]
performed exquisitely at 258C, thus furnishing 2a in 88%
yield by using an equimolar amount of 1a and p-trifluor-
omethylbromobenzene. Aryl bromides were coupled more
efficiently than the corresponding chlorides and iodides at
258C, as shown with 2a. However, upon heating to 408C p-
trifluoromethylchlorobenzene proved a competent coupling
partner, thus delivering 2a in 71% yield. A variety of aryl
(2a–i) and heteroaryl (2j,k) bromides were coupled success-
fully, including electrophiles bearing relatively sensitive func-
tional groups (2c,f) or an ortho-substituent (2g,h). In addition
to (hetero)aryl bromides, acid chlorides (2l,m), bromoalkenes
(2n), and bromoalkynes (2o) were found to be competent
coupling partners, thereby extending the scope of this
reaction beyond arylation and allowing access to synthetically
useful nitrogenated building blocks.
The a-arylation of other acyclic Boc-protected amines was
next studied (Scheme 3). We found that the same reaction
conditions could be applied to the Boc-protected alkylmethyl-
amines 1b–d bearing a primary or secondary alkyl group (R1),
thereby delivering the arylmethylamines 3–5 in moderate to
high yields. As expected, a-lithiation[6b] and arylation at the
secondary carbon atom of 1e were found to be more difficult,
but upon increasing both the lithiation time (3 h) and the
coupling temperature (408C), the products 6a–d were iso-
Scheme 1. Palladium-catalyzed a- and b-arylation of cyclic and acyclic
amines. Boc=tert-butoxycarbonyl.
[*] A. Millet, D. Dailler, Dr. P. Larini, Prof. Dr. O. Baudoin
Universitꢀ Claude Bernard Lyon 1, CNRS UMR 5246, Institut de
Chimie et Biochimie Molꢀculaires et Supramolꢀculaires, CPE Lyon
43 Boulevard du 11 Novembre 1918, Lyon (France)
E-mail: olivier.baudoin@univ-lyon1.fr
Homepage: http://cosmo.univ-lyon1.fr/Index.html
[**] Computational work performed by Dr. P. Larini. We thank the
Agence Nationale de la Recherche (programme blanc “EnolFun”)
and Institut Universitaire de France for financial support of this
work. We also thank Prof. B. Andrioletti and L. Sandjong-Kuigwa for
free access to and assistance with in situ IR instrument and Dr. E.
Clot for fruitful discussions and comments.
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201310904.
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lated with satisfying yields. In addition, the reaction per-
formed equally well on a gram scale (6c, 1.77 g, 66%). Of
note is that no trace of b-arylation was observed under these
reaction conditions. Finally, the a-arylation of the more
functionalized 1 f was attempted. The initial a-lithiation
occurred regioselectively on the propyl ether fragment,
likely as a result of the combined directing effects of the
Boc and OMe groups. Subsequent Li–Zn transmetalation and
Negishi coupling allowed isolation of the a-arylated product
7a in moderate yield.
To study each individual step of this reaction and to
compare the reactivity of different aryl electrophiles and Boc-
protected amines, we turned to the use of in situ IR
spectroscopy. This technique has been recently employed to
monitor the directed a-lithiation and electrophilic quenching
of cyclic Boc-protected amines,[8] including a-lithiation/
Negishi coupling.[8a] First, we found that the a-lithiation of
1a with sBuLi/TMEDA occurred within 2 minutes at ꢀ608C,
as monitored by the disappearance of the nC O band of 1a at
=
1701 cmꢀ1 and appearance of a new band at 1655 cmꢀ1, which
was ascribed to the organolithium species.[7] Similarly, upon
addition of zinc chloride, transmetalation occurred in less
than a minute, as shown with the appearance of a band at
1624 cmꢀ1.[7] An aryl halide was then added, and resulted in
Scheme 2. a-Functionalization of Boc-protected dimethylamine. Reac-
tion conditions: 1a (1.0 equiv), sBuLi (1.2 equiv), TMEDA (1.2 equiv),
Et2O, ꢀ608C, 1 h, then ZnCl2 (1.2 equiv), ꢀ60!208C, then removal of
volatiles under vacuum, then toluene, [Pd2dba3] (2.5 mol%),
PtBu3·HBF4 (5 mol%), R-X (1.0 equiv), 258C, 17 h. [a] Coupling per-
formed at 408C instead of 258C. [b] X=Br. [c] X=Cl. [d] Coupling
performed at 808C instead of 258C. dba=dibenzylideneacetone,
TIPS=triisopropylsilyl, TMEDA=N,N,N’,N’-tetramethylethylenedi-
amine.
the appearance of a nC O band at about 1700 cmꢀ1, which was
=
ascribed to the coupling product. The reaction was complete
in 3–7 hours with the studied aryl bromides. This method was
employed to compare the kinetics of the Negishi coupling of
1a with different aryl halides. A Hammett plot was con-
structed from the individual kinetic curves obtained with aryl
bromides bearing various para substituents (Figure 1).[7,9] The
concave-down shape of the plot is indicative of a change in the
rate-limiting step of the reaction for the considered substitu-
ents.[10] More specifically, the current trend suggests that the
Scheme 3. a-Arylation of other acyclic Boc-protected amines. Reaction
conditions: Boc-protected amine (1.0 equiv), sBuLi (1.2 equiv), TMEDA
(1.2 equiv), Et2O, ꢀ608C, 1 h (3 h for 1e), then ZnCl2 (1.2 equiv),
ꢀ60!208C, then removal of volatiles under vacuum, then toluene,
[Pd2dba3] (2.5 mol%), PtBu3·HBF4 (5 mol%), Ar-Br (1.0 equiv), 258C,
17 h. [a] Coupling performed at 408C instead of 258C. [b] Deprotona-
tion performed at ꢀ408C instead of ꢀ608C.
Figure 1. Hammett plot of the relative rates of product formation for
the Negishi coupling of a-zincated Me2NBoc with p-substituted aryl
&
bromides, as monitored by in situ IR spectroscopy ( ). The relative
rate of the coupling of a-zincated Et2NBoc with PhBr (product 6a) is
^
also reported on the same plot for comparison ( ). The product 2p
was obtained with 4-fluorobromobenzene as the aryl halide, similar to
examples in Scheme 2.
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rate-limiting step is reductive elimination with electron-
deficient aryl bromides, and transmetalation with electron-
rich ones.[11] In addition, the coupling of the a-zincated 1e and
bromobenzene (giving rise to 6a, Scheme 3) was found to be
significantly slower (krel = 0.67) than the coupling of the a-
zincated 1a (giving 2b), thereby reflecting the greater steric
hindrance of 1e at Ca (Figure 1). Although a more complete
kinetic analysis should be performed to draw more precise
conclusions, these data clearly show how changes in the
substitution of both coupling partners affect their reactivity.
We next turned our attention towards migrative arylation
at the b position of Boc-protected ethylamines (Scheme 4).
Mechanistically, this reaction initially proceeds by formation
selectivities and yields with Boc-protected piperidines. How-
ever, a 1:1 (approximately) mixture of the b-arylated product
8a and its a-arylated isomer 6d was obtained in the coupling
of 1e with p-trifluoromethylbromobenzene. In light of
previous mechanistic data,[5] we reasoned that less sterically
hindered ligands might further improve the coupling selec-
tivity by disfavoring reductive elimination at the more
crowded a position. Indeed, the ligand L2, containing n-
butyl substituents at the phosphorus atom instead of the
isopropyl groups as in L1, furnished an improved selectivity
(87:13) in favor of 8a, which was isolated in 52% yield after
separation from the minor a-arylated isomer. The enecarba-
mate 9 and trifluorotoluene were also observed in the crude
reaction mixture, and consistent with previous work and
mechanistic considerations.[5,14] Further variations of the
ligand structure led to the imidazole-based ligand L3 con-
taining isobutyl P substituents of intermediate bulkiness,[7]
and it afforded an enhanced product yield (63%) compared
to that of L2. Other reaction parameters such as the molarity
of each reagent were also optimized.[7]
These reaction conditions were applied to different
amines and aryl electrophiles (Scheme 4). Both L2 and L3
were tested in each case to obtain optimal yields. L2
consistently afforded better selectivity albeit often in lower
yield than L3. It is important to note that in all cases, despite
the fact that b/a-isomeric mixtures were obtained, we were
able to isolate the major b-arylated isomer in good purity and
acceptable yield after standard chromatography. Thus, yields
in the 50–63% range were obtained for the b-arylated
products 8a–g containing either an electron-withdrawing or
electron-donating substituent at the para or meta position,
including relatively sensitive or reactive functional groups
(8b, 8d, 8g). Moreover, similar to the corresponding a-
arylation (6c, Scheme 3), the b-arylation of 1e with p-
fluorobromobenzene to give 8c could be performed on
a gram scale (0.95 g, 51%; Scheme 4). In contrast, a lower
yield was obtained for ortho-substituted aryl bromides such as
2-fluorobromobenzene (8h) and heteroaryl bromides such as
3-bromopyridine (8j), and was attributed to the formation of
larger amounts of the enecarbamate 9. In these cases,
switching back to the bulkier ligand L1 gave a higher
efficiency without loss of selectivity, thereby providing the
b-arylated products 8h–j with satisfying yields (54–64%).
Electrophiles other than (hetero)aryl halides were also tested,
but they mainly gave a-functionalization. The b-arylation of
other Boc-protected amines was attempted, but a major
limitation came from the initial a-lithiation step, which was
found to be very sensitive to steric hindrance. For instance,
iPrN(Boc)Et and CyN(Boc)Et failed to undergo a-lithiation
whereas the a-lithiation/transmetalation/migrative Negishi
coupling sequence could be applied to the slightly less
crowded iBuN(Boc)Et (1g; product 8k). When the same
reaction conditions were applied to iBuN(Boc)CH2CD3, the
corresponding b-arylated product 8l was obtained with
complete transfer of a deuterium atom from the b to the
a position. This transfer is consistent with the migrative
mechanism involving b-hydride(deuteride) elimination and
Scheme 4. b-Arylation of acyclic Boc-protected amines. Reaction con-
ditions: Boc-protected amine (1.0 equiv), sBuLi (1.0 equiv), TMEDA
(1.0 equiv), Et2O, ꢀ608C, 3 h, then ZnCl2 (1.0 equiv), ꢀ60!208C,
then removal of volatiles under vacuum, then toluene, [Pd2dba3]
(2.5 mol%), ligand (5 mol%), Ar-Br (0.7 equiv), 808C, 17 h. Yields
refer to the isolated b-arylated product, calculated against the aryl
bromide (unless otherwise stated). Ratios of b- and a-arylated
products were determined by GCMS analysis of the crude reaction
mixture. [a] Deprotonation performed at ꢀ408C instead of ꢀ608C.
[b] Yield of the mixture of a- and b-arylated products.
of the a-palladated Boc-amine, which is a common inter-
mediate for a- and b-arylation.[5] a-Arylation occurs by
reductive elimination whereas rearrangement to the b-
palladated isomer (by the well-characterized b-hydride elim-
ination/rotation/insertion manifold),[12] and reductive elimi-
nation affords the linear b-arylated product.[13] We initially
tested L1, which was found to give optimal b/a arylation
ꢀ
Pd H(D)/olefin insertion, which was previously reported
with Boc-protected piperidines[5] and esters.[12]
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as shown both by the
Pd···Cortho short dis-
tance of 2.654 ꢀ and
by the incipient pira-
midalization at Cortho
(dihedral angle 7.18).
Finally, reductive
elimination to give
the b-arylated product
8a occurs via TS-III-b
(DG° = 19.1 kcal
molꢀ1). The compari-
son of TS-III-b and
TS-Ia-a shows that
2
ꢀ
the forming C(sp ) C-
(sp3) bond is shorter
(2.02 ꢀ vs. 2.12 ꢀ)
and the C(sp2)-Pd-C-
(sp3) angle is smaller
(578 vs. 608) in the
former, thus account-
ing for the observed
lower DG° value.
These
calculations
suggest that by using
L2 as the ligand, the
two selectivity-deter-
mining steps are TS-
Ia-a and TS-IIa-IIb,
Figure 2. Comparison of the energy profiles for the a- and b-arylation pathways from the complex Ia with L2 and
PtBu3 as the ligands.
On this basis, DFT calculations were employed to study
the ligand effect on the a/b selectivity (Figure 2).[15] To this
purpose, the reaction mechanism was computed both with
PtBu3 (a-selective) and L2 (b-selective), and using Et2NBoc
and (p-CF3)PhBr as coupling partners (the corresponding
products being 6d, Scheme 3, and 8a, Scheme 4). Results
obtained with L2 are discussed first. The initial a-palladated
intermediate Ia, resulting from the Zn–Pd transmetalation
step, is coordinated to the Boc group (Pd···O 2.179 ꢀ), as
observed previously with Boc-protected piperidine.[5] In the
present case, the pathway leading to a-arylated product 6d
involves decoordination of the Boc group from palladium,
thus leading to the T-shaped ML3 complex Ia-a, with
reductive elimination occurring via TS-Ia-a (DG° = 21.6 kcal
molꢀ1). In contrast, the b-arylation pathway involves several
sequential steps. First, decoordination of the Boc group from
palladium and the establishment of a b-CH agostic interaction
(Pd···H 2.025 ꢀ, Cb-H 1.14 ꢀ) lead to the intermediate Ib.
Then, b-hydride elimination from Ib via TS-Ib-IIa (DG° =
18.5 kcalmolꢀ1) leads to the p-complex IIa. Rotation of the
coordinated olefin through TS-IIa-IIb (DG° = 21.6 kcal
molꢀ1) produces the isomeric p-complex IIb. The complex
IIb is more stable than IIa by 2.9 kcalmolꢀ1, and this is
possibly a result of lower steric constraints in the former.
that is, the reductive elimination at the a-carbon atom and
the rotation of the p-complex, with a DDG° value of
0 kcalmolꢀ1. This value is consistent with the observed
experimental a/b ratio of 13:87, when considering the
uncertainties of the computational method. We experimen-
tally observed that the a-arylation pathway was favored using
PtBu3 as the ligand, thus leading exclusively to 6d (Scheme 3).
Similar calculations were thus conducted with PtBu3 as the
ligand, and allowed analysis of the impact of the ligand on the
different steps of the mechanism. First, reductive elimination
occurring via TS-Ia-a is significantly favored (5.1 kcalmolꢀ1)
compared to the case of L2. Along the b-arylation pathway,
two transiton states, TS-Ib-IIa and TS-IIa-IIb, were found to
be higher in energy by 0.2 and 1.5 kcalmolꢀ1, respectively.
This higher energy can be attributed to the increased steric
repulsion between the more bulky PtBu3 ligand and the Boc-
protected amine substrate. The two other transition states,
that is, TS-IIb-IIc and especially TS-III-b, were found to be
lower in energy compared to the case of L2. The known
ꢀ
propensity of bulky and rigid ligands to favor C C reductive
elimination[16] is translated into the lower TS-Ia-a and TS-III-
b observed with PtBu3 compared to L2. Importantly, the two
selectivity-determining steps are TS-Ia-a and TS-IIa-IIb as in
the above-mentioned case for L2, but now the DDG° is
6.6 kcalmolꢀ1 in favor of a-arylation, and is in accordance
with the observed experimental selectivity. Overall, the
calculations reproduce well the selectivity difference
observed experimentally with L2 and PtBu3, and can be
mainly attributed to the markedly different rigidity and steric
bulk of these ligands.
ꢀ
Insertion of the olefin into the Pd H bond via TS-IIb-IIc
(DG° = 16.2 kcalmolꢀ1) leads to the T-shaped b-palladated
intermediate IIc. The latter is more stable than Ib by
2.8 kcalmolꢀ1, even though no stabilizing agostic interaction
is present in IIc. This stability could be due to stronger
interactions between the phenyl group of L2 and palladium,
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[5] A. Millet, P. Larini, E. Clot, O. Baudoin, Chem. Sci. 2013, 4,
2241 – 2247.
[6] a) P. Beak, W.-K. Lee, Tetrahedron Lett. 1989, 30, 1197 – 1200;
b) V. Snieckus, M. Rogers-Evans, P. Beak, W. K. Lee, E. K. Yum,
J. Freskos, Tetrahedron Lett. 1994, 35, 4067 – 4070.
In conclusion, we have reported for the first time the
direct a- and b-arylation of acyclic Boc-protected amines
proceeding by a sequence of directed a-lithiation, trans-
metalation with zinc, and palladium-catalyzed cross-coupling,
with the latter occurring under the normal or migrative mode
in a ligand-controlled manner. These studies lay the ground-
work for site-selective cross-couplings on other acyclic
systems.
[7] See the Supporting Information for supplementary Tables and
Figures.
[8] a) G. Barker, J. L. McGrath, A. Klapars, D. Stead, G. Zhou,
K. R. Campos, P. OꢃBrien, J. Org. Chem. 2011, 76, 5936 – 5953;
b) N. S. Sheikh, D. Leonori, G. Barker, J. D. Firth, K. R. Campos,
A. J. H. M. Meijer, P. OꢃBrien, I. Coldham, J. Am. Chem. Soc.
2012, 134, 5300 – 5308; c) X. Li, D. Leonori, N. S. Sheikh, I.
Coldham, Chem. Eur. J. 2013, 19, 7724 – 7730.
Received: December 16, 2013
Published online: February 6, 2014
[9] For sp values: C. Hansch, A. Leo, R. W. Taft, Chem. Rev. 1991,
91, 165 – 195.
[10] J. O. Schreck, J. Chem. Educ. 1971, 48, 103 – 107.
[11] a) J. F. Hartwig, Inorg. Chem. 2007, 46, 1936 – 1947; b) L. Jin, A.
Lei, Org. Biomol. Chem. 2012, 10, 6817 – 6825.
ꢀ
Keywords: arylation · C C coupling · cross-coupling ·
density functional calculations · palladium
.
[1] a) M. S. Jensen, C. Yang, Y. Hsiao, N. Rivera, K. M. Wells,
J. Y. L. Chung, N. Yasuda, D. L. Hughes, P. J. Reider, Org. Lett.
2000, 2, 1081 – 1084; b) G. A. Molander, D. L. Sandrock, Org.
Lett. 2007, 9, 1597 – 1600; c) G. A. Molander, P. E. Gormisky,
D. L. Sandrock, J. Org. Chem. 2008, 73, 2042 – 2057; d) G. A.
Molander, M.-A. Hiebel, Org. Lett. 2010, 12, 4876 – 4879;
e) G. A. Molander, I. Shin, Org. Lett. 2011, 13, 3956 – 3959;
f) N. Fleury-Brꢁgeot, J. Raushel, D. L. Sandrock, S. D. Dreher,
G. A. Molander, Chem. Eur. J. 2012, 18, 9564 – 9570.
[2] a) R. F. W. Jackson, M. J. Wythes, A. Wood, Tetrahedron Lett.
1989, 30, 5941 – 5944; b) J. Barluenga, J. M. Montserrat, J. Flꢂrez,
J. Org. Chem. 1993, 58, 5976 – 5980; c) A. Kamatani, L. E.
Overman, J. Org. Chem. 1999, 64, 8743 – 8744; d) G. A.
Molander, F. Vargas, Org. Lett. 2007, 9, 203 – 206; e) G. A.
Molander, L. Jean-Gꢁrard, J. Org. Chem. 2007, 72, 8422 – 8426.
[3] a) K. R. Campos, A. Klapars, J. H. Waldman, P. G. Dormer, C.-y.
Chen, J. Am. Chem. Soc. 2006, 128, 3538 – 3539; b) I. Coldham,
D. Leonori, Org. Lett. 2008, 10, 3923 – 3925; c) T. K. Beng, R. E.
Gawley, Org. Lett. 2011, 13, 394 – 397.
[12] a) A. Renaudat, L. Jean-Gꢁrard, R. Jazzar, C. E. Kefalidis, E.
Clot, O. Baudoin, Angew. Chem. 2010, 122, 7419 – 7423; Angew.
Chem. Int. Ed. 2010, 49, 7261 – 7265; b) P. Larini, C. E. Kefalidis,
R. Jazzar, A. Renaudat, E. Clot, O. Baudoin, Chem. Eur. J. 2012,
18, 1932 – 1944; c) S. Aspin, A.-S. Goutierre, P. Larini, R. Jazzar,
O. Baudoin, Angew. Chem. 2012, 124, 10966 – 10969; Angew.
Chem. Int. Ed. 2012, 51, 10808 – 10811.
[13] Secondary alkylzinc halides are well known to give linear
products alongside desired branched products in Negishi cou-
plings: a) E. Negishi, L. F. Valente, M. Kobayashi, J. Am. Chem.
Soc. 1980, 102, 3298 – 3299; b) T. Hayashi, M. Konishi, Y. Kobori,
M. Kumada, T. Higuchi, K. Hirotsu, J. Am. Chem. Soc. 1984, 106,
158 – 163.
[14] Reductive elimination from the intermediate ArPd(H)(9)L
affords Pd0L, ArH, and 9 in an irreversible manner.
[15] Gaussian09, RevisionD.01, M. J. Frisch et al., Gaussian, Inc.,
Wallingford CT, 2009. See the Supporting Information for
computational details.
[16] U. Christmann, R. Vilar, Angew. Chem. 2005, 117, 370 – 378;
Angew. Chem. Int. Ed. 2005, 44, 366 – 374.
[4] S. Seel, T. Thaler, K. Takatsu, C. Zhang, H. Zipse, B. F. Straub, P.
Mayer, P. Knochel, J. Am. Chem. Soc. 2011, 133, 4774 – 4777.
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