Synergistic interplay of a non-heme iron catalyst and amino acid coligands in H2O2 activation for asymmetric epoxidation of α-alkyl-substituted styrenes

Article abstract of DOI:10.1002/anie.201410557

Highly enantioselective epoxidation of α-substituted styrenes with aqueous H₂O₂ is described by using a chiral iron complex as the catalyst and N-protected amino acids (AAs) as coligands. The amino acids synergistically cooperate with the iron center in promoting an efficient activation of H₂O₂ to catalyze epoxidation of this challenging class of substrates with good yields and stereoselectivities (up to 97% ee) in short reaction times.

Full text of DOI:10.1002/anie.201410557

Angewandte
Chemie
DOI: 10.1002/anie.201410557
Bioinspired Asymmetric Catalysis Very Important Paper
Synergistic Interplay of a Non-Heme Iron Catalyst and Amino Acid
Coligands in H2O2 Activation for Asymmetric Epoxidation of
a-Alkyl-Substituted Styrenes**
Olaf Cussꢀ, Xavi Ribas, Julio Lloret-Fillol, and Miquel Costas*
Abstract: Highly enantioselective epoxidation of a-substituted
styrenes with aqueous H2O2 is described by using a chiral iron
complex as the catalyst and N-protected amino acids (AAs) as
coligands. The amino acids synergistically cooperate with the
iron center in promoting an efficient activation of H2O2 to
catalyze epoxidation of this challenging class of substrates with
good yields and stereoselectivities (up to 97% ee) in short
reaction times.
dependent on the nature of aminopyridine ligands.[1] With
these considerations in mind, we focused our attention on
amino acids (AAs) as putative coligands for the system. While
their large structural diversity finds wide use in organo-
catalytic epoxidation methodologies,[2c,d,4] the compatibility of
amino acids with metal-catalyzed oxidations has few but
notable precedents.[5]
Herein we show that synergistic cooperation between
a non-heme iron coordination complex and amino acid
coligands allows for efficient activation of hydrogen peroxide
leading to highly stereoselective epoxidation reactions in
short reaction times. Remarkable aspects of the current
system are: a) the use of iron as the metal catalyst and
aqueous H2O2 as oxidant, reagents that are attractive because
Biologically inspired catalysts are currently explored with
the aim to produce selective oxidation reactions. The quest for
catalytic methodologies that provide novel reactivities and
selectivities that could complement those attained with
traditional oxidants, or that could represent a more efficient
alternative constitute major reasons of interest
for this approach.[1] Among oxidations, asym-
metric epoxidation is a reaction of broad interest
in synthetic organic chemistry because of the
synthetic value of chiral epoxides.[2] Recently we
reported that iron complexes with electron-rich
aminopyridine ligands catalyze highly stereose-
lective epoxidation of enones and cis-b-substi-
tuted styrenes with H2O2 (Scheme 1, 2-eha = 2-
ethylhexanoic acid, S-Ibp = S-ibuprofen).[3] In
these experiments, carboxylic acids were also
À
key elements for controlling O O breakage and
epoxidation stereoselectivity. The system could
therefore be adapted to cover novel families of
substrates just by employing other carboxylic
acids, without requiring preparation of novel
chiral iron catalysts. We reasoned that this
variability could be an important aspect because
the activity and reaction mechanisms of iron
Scheme 1.
complexes when reacting with peroxides are very
of their availability and low environmental impact.[6–8] b) The
use of amino acids as a versatile source of chirality. c) The
highly stereoselective epoxidation of a-substituted styrenes,
a class of substrates that remain very challenging for other
asymmetric epoxidation methods.[9] Furthermore the present
system can be considered a remarkable approach towards the
mimicking of selective oxidation reactions taking place in
non-heme iron-dependent oxygenases because a number of
[*] O. Cussꢀ, Dr. X. Ribas, Dr. J. Lloret-Fillol, Dr. M. Costas
Institut de Quꢁmica Computacional i Catꢂlisi (IQCC) and
Departament de Quꢁmica
Universitat de Girona
Campus de Montilivi, 17071 Girona, Catalonia (Spain)
E-mail: miquel.costas@udg.edu
[**] We acknowledge group LIPPSO from UdG for providing amino acid
samples and A. Riera (IRB) for access to a polarimeter. We
acknowledge financial support from the European Research Council
(ERC-2009-StG-239910), MINECO of Spain (CTQ2012-37420-C02-
01/BQU, CSD2010-00065), and Generalitat de Catalunya
(2009SGR637). J.L.-F. thanks MICINN for a RyC contract. X.R. and
M.C. thank ICREA-Academia awards.
À
these enzymes rely in controlled breakage of the O O bond,
and amino acids are common biological iron ligands and
provide a main element of chirality regulating stereoselectiv-
ity in the enzymatic transformations.
Initial conditions involved the epoxidation of cis-b-
methylstyrene (S0) employing the electron rich catalyst
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/anie.201410557.
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(S,S)-Me2NPDP-Fe (2 mol%, Scheme 1) and amino acid coli-
gand (3 mol%) in acetonitrile solution at À308C, over which
1.8 equivalents of H2O2 were delivered by syringe pump over
30 min (Table 1). This substrate was chosen to compare the
efficiency of amino acids with respect to simple organic acids
as co-catalyst.[3]
acid was employed in combination with the two enantiomeric
forms of the iron catalyst, the opposite epoxide enantiomer
was obtained as major product. In addition, as a general trend,
small differences in yields and stereoselectivities were
observed for each of these pair of reactions. A different
picture was however observed when the N-Npha-ILeu-OH
derivative was employed (entry 13). This amino acid not only
The initial screening involved the use of a range of amino
acids, and also an analysis of the
nature of the N-protecting group in
Table 1: Screening of amino acids in asymmetric epoxidation reaction (Table continued on next page).[a]
reaction performance. Since both
the amino acid and the iron catalyst
are chiral, each amino acid was
tested with both (S,S)-Me2NPDP-Fe
(3rd–4th columns in Table 1) and
(R,R)-Me2NPDP-Fe (5–6th columns
in Table 1). The first significant
observation is that proline is not
Catalyst
Entry
(S,S’)-Me2NPDPFe[b]
(R,R’)-Me2NPDPFe[b]
Amino acid
Conv.
ee [%]
Conv.
ee [%]
(Yield) [%]
(Yield) [%]
a
valid acid partner (Table 1,
entry 1), presumably because the
unprotected amine poisoned the
catalyst by chelation. However,
when the amine site was protected,
the reaction took place with mod-
erate to excellent yields and good
enantioselectivities (entries 2–4).
No major side product was
1
Pro-OH
–
–
n.d.
n.d.
2
N-Ts-Pro-OH
47 (30)
100 (75)
100 (87)
100 (90)
50 (40)
55(27)
63
74
79
76
32
17
87 (69)
96 (77)
95 (90)
n.d.
76
3
N-Fmoc-Pro-OH
N-Boc-Pro-OH
N-Boc-Pro-OH
N-Boc-Pro-OH
N-Boc-Pro-OH
77
4
77
detected. Boc as
a protecting
group provides the highest enantio-
selectivities of the series. Moreover,
when the reaction was carried out
5[c]
n.d.
n.d.
n.d.
using dMMPDP-Fe (Scheme 1), a cat- 6[d]
n.d.
alyst which has less-electron-donat-
7[e]
n.d.
ing groups in the pyridine rings,
moderate yields were obtained and
the enantioselectivities decrease
(Table 1 entry 6). In the same vein,
the use of the simplest HPDP-Fe
(Scheme 1) produced poor yields
and stereoselectivities (Table 1,
entry 7), thus illustrating the impor-
tant role of the electronic properties
of the aminopyridine ligand in the
activation of H2O2 and in the O-
delivering step. Then, a series of
Boc-protected amino acids were
tested, resulting in an improvement
of the enantioselectivity up to 81
and 80% ee using N-Boc-t-Leu-OH
(entry 8) and N-Boc-ILeu-OH
(entry 10), respectively. Since both
the iron catalyst and the amino acid
coligand are chiral, matching–mis-
matching effects resulting from
combination of the respective chir-
alities were also evaluated by using
the two enantiomeric R,R and S,S
forms of the catalyst (compare col-
umns 4 and 6 in Table 1). Without
exception when the same amino
8
N-Boc-t-Leu-OH
N-Boc-Leu-OH
N-Boc-Ileu-OH
N-Fmoc-Ileu-OH
N-Ac-Ileu-OH
100 (93)
100 (89)
100 (96)
100 (84)
100 (89)
79 (51)
80
71
80
78
78
49
100 (91)
100 (89)
100 (83)
100 (84)
100 (82)
100 (81)
81
75
73
74
74
87
9
10
11
12
13
N-Npha-Ileu-OH
14
15
N-Npha-t-Leu-OH
N-Npha-Ala-OH
72 (57)
92 (74)
70
70
100 (89)
100 (87)
85
76
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Table 1: (Continued)
The benefits of using N-Npha-
(S,S’)-Me2NPDPFe[b]
(R,R’)-Me2NPDPFe[b]
ILeu-OH and N-Npha-t-Leu-OH as
acid coligand partners in asymmet-
ric epoxidations catalyzed by
Me2NPDP-Fe was then tested against
different families of substrates
(Figure 1 and Table S2). Styrenes
S1–S4 differing in the substitution
patterns at the olefinic site were
chosen because these are recog-
nized as a challenge for iron asym-
metric epoxidation catalysis.[6f] Fur-
thermore results were compared
with those obtained with other
carboxylic acids which had previ-
ously proved to be excellent in the
epoxidation of aromatic and cyclic
aliphatic enones, as well as in cis-
aromatic olefins.[3] Most interesting
from this analysis was the observa-
Catalyst
Entry
Amino acid
Conv.
(Yield) [%]
ee [%]
Conv.
(Yield) [%]
ee [%]
16
N-Npha-Phe-OH
98 (79)
68
100 (84)
74
[a] Reaction conditions are Me2NPDP-Fe (2 mol%), H2O2 (1.8 equiv) and amino (3 mol%), cis-b-
methylstyrene (S0, 0.11m) in CH3CN at À308C during 30 min. [b] Conversion and yield were calculated
using an internal standard. The ee values were determined by chiral GC. [c] 1.4 equiv of N-Boc-Pro-OH.
[d] dMMPDP-Fe as catalyst.[3] [e] HPDP-Fe as catalyst. n.d.: not determined. See Supporting Information for
a complete list of the amino acids tested. All the amino acids have S configuration. The absolute
configuration of the epoxide obtained with (S,S’)-Me2NPDPFe was determined as (1R,2S) by comparison
of optical rotation data with that from the literature,[10] in the case of (R,R’)-Me2NPDPFe the configuration
of the epoxide is (1S,2R).
provides the best stereoselection among the series (up
to 87% ee) but also a pronounced difference in
epoxide yield and ee values responding to matching–
mismatching between chiralities of N-Npha-ILeu-OH
and of the iron complex Me2NPDP-PFe were observed
(81 vs 51% in yield and 87 vs 49% in ee). We
interpreted this large difference as a signature that this
amino acid effectively helps in defining the structure of
the active site. For comparison, when the reaction is
performed in the absence of amino acid, epoxide was
obtained in modest 20% yield and 46% ee.[3]
Scheme 2.
tion that an a-substituted styrene
(S3) was epoxidized with values
of stereoselectivity substantially
better than any of the carboxylic
acids previously studied. a-Alkyl
substituted styrenes are particu-
larly challenging for asymmetric
catalysis because of the difficulty
to differentiate between the
enantiotopic faces of these sub-
strates.[11] To our knowledge good
levels of ee values in their epox-
idation is limited to chloroperox-
idase (up to 89% ee)[9a] and
Shiꢀs organocatalysts (up to
88% ee).[9b] Therefore, catalytic
epoxidation of a series of this
class of substrates was evaluated
under optimized conditions using
N-Npha-ILeu-OH.
We
examined
examples
Figure 1. The stereoselectivity on epoxidation of structurally different styrenes with R,R and S,S forms of
Me2NPDP-Fe using different carboxylic acids. See supporting information for details of the reactions. R
and S inside the bars refer to the chirality of Me2NPDP-Fe. When chirality is not specified, S,S-Me2NPDP-Fe
was employed as the catalyst.
of a-methylstyrene derivatives
(Table 2, entries 1–3). In these
cases the yields obtained were
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Table 2: Substrate scope on the asymmetric epoxidation.[a]
excellent (88–94%), but enantioselectivities were moderate
(50–66% ee). On the other hand, replacing the a-methyl by
a trifluoromethyl group (entries 4–5) the enantioselectivity
increased up to 87%, although in this case yields were small
(5–16%), presumably reflecting the poor reactivity of this
electron-deficient olefin with an electrophilic reagent. Most
interestingly, when the a position of styrenes was modified by
sterically more demanding groups such as ethyl, isopropyl,
and tert-butyl the enantioselectivities increased up to 97% ee
(entries 6–20), although the cyclohexyl derivate substrate S17
provided a more modest ee value (75%). The system tolerates
o, m- and p- substitutions in the aromatic ring, and also
different functional groups, such as nitro, esters, and halides.
On the other hand, epoxidation of a,a’-dialkyl substrates
provided very low enantioselectivities (16% ee for 2-methyl-
hept-1-ene; not shown) and pyridine heterocycles inhibit the
catalysis (entry 21).
To illustrate the utility of this methodology, epoxide
resulting from epoxidation of S13 (Scheme 2) was trans-
formed into azido-alcohol P1 with no erosion of the
enantioselectivity (yield 87%, 92% ee), which can then be
converted into unprotected aziridine P2 through a Staudinger
reaction (80%, 88% ee),[12] which can be regarded as an entry
into chiral amines. Alternatively, reduction of the azide using
palladium under hydrogen conditions (see Scheme 2) provide
the corresponding chiral 1,2-amino alcohol P3 (yield 98%,
90% ee), which can be seen as a precursor for the synthesis of
oxazolines, among other interesting products.[13]
Entry
Substrate
Yield [%] Npha-I-Leu-OH
(ee) [%]
1
2
3
R=Cl (S3)
R=NO2 (S4)
R=CF3 (S5)
90
94
88
63
66
50
4
5
R=H (S6)
R=Cl (S7)
ca. 20 (5) 84
16 (16)
87
6
7
8
9
R=Me(S8)
R=OAc (S9)
R=OPiv (S10) 83
R=Ph (S11)
78
80
80
83
81
80
70
10
11
12
13
R=H (S12)
R=Cl (S13)
R=F (S14)
R=CF3 (S15)
60
87
85
77
91
92
91
84
In summary, the present work shows the use of amino
acids as suitable coligands in epoxidation reactions with
aqueous H2O2 using bioinspired non-heme iron catalysts,[14]
extending the substrate scope of these systems to the
challenging terminal olefins. The present approach is appeal-
ing as it provides proof of concept that the versatility of these
systems can be extended straightforwardly towards novel
classes of substrates without requiring an elaborate develop-
ment of novel chiral catalysts.
14
15
S16
S17
90
52
97[b]
75
16
17
18
19
R=Me (S18)
R=H (S19)
R=Cl (S20)
R=F (S21)
79
85
80
85
93
91
94
96
Received: October 29, 2014
Published online: && &&, &&&&
Keywords: amino acids · asymmetric catalysis ·
.
bioinspired catalysis · epoxidation · non-heme iron complexes
20
21
S22
S23
57
–
92
–
[1] a) L. Que, W. B. Tolman, Nature 2008, 455, 333; b) K. P.
Bryliakov, E. P. Talsi, Coord. Chem. Rev. 2014, 276, 73.
[2] a) K. Matsumoto, T. Katsuki in Catalytic Asymmetric Synthesis,
Wiley, Hoboken, 2010, pp. 839; b) G. De Faveri, G. Ilyashenko,
M. Watkinson, Chem. Soc. Rev. 2011, 40, 1722; c) Y. Zhu, Q.
Wang, R. G. Cornwall, Y. Shi, Chem. Rev. 2014, 114, 8199;
d) R. L. Davis, J. Stiller, T. Naicker, H. Jiang, K. A. Jørgensen,
Angew. Chem. Int. Ed. 2014, 53, 7406 – 7426; Angew. Chem.
2014, 126, 7534 – 7556.
[3] O. Cussꢁ, I. Garcia-Bosch, X. Ribas, J. Lloret-Fillol, M. Costas, J.
Am. Chem. Soc. 2013, 135, 14871.
[4] Selected examples of organocatalyzed epoxidations with amino-
acid derivatives; a) S. Juliꢂ, J. Masana, J. C. Vega, Angew. Chem.
Int. Ed. Engl. 1980, 19, 929; Angew. Chem. 1980, 92, 968; b) S.
Banfi, S. Colonna, H. Molinari, S. Juliꢂ, J. Guixer, Tetrahedron
[a] Reaction conditions are (R,R)-Me2NPDP-Fe (2 mol%), H2O2
(1.8 equiv), and N-Npha-ILeu-OH (3 mol%) in CH3CN at À308C during
30 min. The ee values and configuration are determined by chiral GC.
1
[b] The ee values are determined by H NMR with europium tris [3-
(heptafluoropropylhydroxymethylene)-(+)-camphorate] (see Supporting
Information for details). Absolute configuration of epoxides at entries 10
and 11 are (R) and were determined by comparing optical rotation with
that described in the literature.[9b]
4
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Angewandte
Chemie
1984, 40, 5207; c) G. Peris, C. E. Jakobsche, S. J. Miller, J. Am.
Chem. Soc. 2007, 129, 8710.
Wang, C. Xia, W. Sun, Chem. Eur. J. 2012, 18, 7332; j) O. Y.
Lyakin, R. V. Ottenbacher, K. P. Bryliakov, E. P. Talsi, ACS
Catal. 2012, 2, 1196; k) T. Niwa, M. Nakada, J. Am. Chem. Soc.
2012, 134, 13538; l) V. A. Yazerski, A. Orue, T. Evers, H. Kleijn,
R. J. M. K. Gebbink, Catal. Sci. Technol. 2013, 3, 2810; m) L.
Luo, H. Yamamoto, Eur. J. Org. Chem. 2014, 35, 7803.
[9] a) A. F. Dexter, F. J. Lakner, R. A. Campbell, L. P. Hager, J. Am.
Chem. Soc. 1995, 117, 6412; b) B. Wang, O. A. Wong, M.-X.
Zhao, Y. Shi, J. Org. Chem. 2008, 73, 9539; c) O. A. Wong, B.
Wang, M.-X. Zhao, Y. Shi, J. Org. Chem. 2009, 74, 6335; d) O.
Boutureira, J. F. McGouran, R. L. Stafford, D. P. G. Emmerson,
B. G. Davis, Org. Biomol. Chem. 2009, 7, 4285; e) B. Wang, C.
Miao, S. Wang, C. Xia, W. Sun, Chem. Eur. J. 2012, 18, 6750.
[10] H. Tian, X. She, H. Yu, L. Shu, Y. Shi, J. Org. Chem. 2002, 67,
2435.
[11] Representative asymmetric transformations in a-styrenes; a) H.
Becker, S. B. King, M. Taniguchi, K. P. M. Vanhessche, K. B.
Sharpless, J. Org. Chem. 1995, 60, 3940; b) J. Mazuela, P.-O.
Norrby, P. G. Andersson, O. Pꢅmies, M. Diꢃguez, J. Am. Chem.
Soc. 2011, 133, 13634; c) S. Monfette, Z. R. Turner, S. P.
Semproni, P. J. Chirik, J. Am. Chem. Soc. 2012, 134, 4561;
d) E. N. Bess, M. S. Sigman, Org. Lett. 2013, 15, 646; e) S. Song,
S.-F. Zhu, Y.-B. Yu, Q.-L. Zhou, Angew. Chem. Int. Ed. 2013, 52,
1556; Angew. Chem. 2013, 125, 1596; f) L. Zhang, Z. Zuo, X.
Wan, Z. Huang, J. Am. Chem. Soc. 2014, 136, 15501.
[5] a) M. B. Francis, E. N. Jacobsen, Angew. Chem. Int. Ed. 1999, 38,
937; Angew. Chem. 1999, 111, 987; b) N. Makita, Y. Hoshino, H.
Yamamoto, Angew. Chem. Int. Ed. 2003, 42, 941; Angew. Chem.
2003, 115, 971; c) J. W. de Boer, W. R. Browne, S. R. Harutyun-
yan, L. Bini, T. D. Tiemersma-Wegman, P. L. Alsters, R. Hage,
B. L. Feringa, Chem. Commun. 2008, 3747; d) J. C. Lewis, ACS
Catal. 2013, 3, 2954.
[6] a) S. Enthaler, K. Junge, M. Beller, Angew. Chem. Int. Ed. 2008,
47, 3317; Angew. Chem. 2008, 120, 3363; b) A. Correa, O. G.
Mancheno, C. Bolm, Chem. Soc. Rev. 2008, 37, 1108; c) C.-L.
Sun, B.-J. Li, Z.-J. Shi, Chem. Rev. 2011, 111, 1293; d) M.
Darwish, M. Wills, Catal. Sci. Technol. 2012, 2, 243; e) K.
Gopalaiah, Chem. Rev. 2013, 113, 3248; f) S. Rana, A. Modak, S.
Maity, T. Patra, D. Maiti, Prog. Inorg. Chem. 2014, 59, 1; g) F. G.
Gelalcha, Adv. Synth. Catal. 2014, 356, 261.
[7] R. Noyori, M. Aoki, K. Sato, Chem. Commun. 2003, 1977.
[8] Selected examples of iron-catalyzed asymmetric epoxidations;
a) Q. F. Cheng, X. Y. Xu, W. X. Ma, S. J. Yang, T. P. You, Chin.
Chem. Lett. 2005, 16, 1467; b) C. Marchi-Delapierre, A. Jorge-
Robin, A. Thibon, S. Mꢃnage, Chem. Commun. 2007, 1166;
c) F. G. Gelalcha, B. Bitterlich, G. Anilkumar, M. K. Tse, M.
Beller, Angew. Chem. Int. Ed. 2007, 46, 7293; Angew. Chem.
2007, 119, 7431; d) F. G. Gelalcha, G. Anilkumar, M. K. Tse, A.
Brꢄckner, M. Beller, Chem. Eur. J. 2008, 14, 7687; e) H.-L.
Yeung, K.-C. Sham, C.-S. Tsang, T.-C. Lau, H.-L. Kwong, Chem.
Commun. 2008, 3801; f) M. Wu, C.-X. Miao, S. Wang, X. Hu, C.
Xia, F. E. Kꢄhn, W. Sun, Adv. Synth. Catal. 2011, 353, 3014; g) Y.
Nishikawa, H. Yamamoto, J. Am. Chem. Soc. 2011, 133, 8432;
h) F. Oddon, E. Girgenti, C. Lebrun, C. Marchi-Delapierre, J.
Pecaut, S. Menage, Eur. J. Inorg. Chem. 2012, 85; i) B. Wang, S.
[12] C. Molinaro, A.-A. Guilbault, B. Kosjek, Org. Lett. 2010, 12,
3772.
[13] a) G. Desimoni, G. Faita, K. A. Jørgensen, Chem. Rev. 2006, 106,
3561; b) G. C. Hargaden, P. J. Guiry, Chem. Rev. 2009, 109, 2505.
[14] For a discussion on the reaction mechanism and role of the
carboxylic acid in H2O2 activation, see Ref. [3].
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Communications
Bioinspired Asymmetric Catalysis
O. Cussꢁ, X. Ribas, J. Lloret-Fillol,
M. Costas*
&&& — &&&
Synergistic Interplay of a Non-Heme Iron
Catalyst and Amino Acid Coligands in
H2O2 Activation for Asymmetric
Epoxidation of a-Alkyl-Substituted
Styrenes
Come on styrene: Using amino acids as
coligands for bioinspired non-heme iron
catalysts, the substrate scope of epox-
idation reactions with aqueous H2O2 is
extended to the challenging a-styrenes.
Thus, these systems can be adapted for
new substrates classes simple by chang-
ing the amino acid coligand.
6
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