Iron-Catalyzed Michael Addition of Ketones to Polar Olefins

Article abstract of DOI:10.1002/adsc.201600278

The base metal complex tetrabutylammonium nitrosyltricarbonylferrate {Bu₄N[Fe(CO)₃(NO)] (TBA[Fe])} – catalyzes the conjugate addition of ketones to polar olefins. The reaction is applicable to a wide range of substrates leading to interesting building blocks for organic synthesis. Clear indications for an acid-base type rather than a C?H activation pathway exist. (Figure presented.).

Full text of DOI:10.1002/adsc.201600278

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DOI: 10.1002/adsc.201600278
Iron-Catalyzed Michael Addition of Ketones to Polar Olefins
Di-Han Zhang,a Jakob Knelles,a and Bernd Plietkera,*
a
Institut fꢀr Organische Chemie, Universitꢁt Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany
E-mail: bernd.plietker@oc.uni-stuttgart.de
Received: March 11, 2016; Revised: June 8, 2016; Published online: && &&, 0000
Dedicated to Prof. Dieter Enders on the occasion of his 70th birthday.
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201600278.
À
Abstract: The base metal complex tetrabutylammo- tions for an acid-base type rather than a C H activa-
nium nitrosyltricarbonylferrate {Bu4N[Fe(CO)3(NO)] tion pathway exist.
(TBA[Fe])} – catalyzes the conjugate addition of ke-
tones to polar olefins. The reaction is applicable to
a wide range of substrates leading to interesting Keywords: activation; addition; catalysis; iron; syn-
building blocks for organic synthesis. Clear indica- thesis
À
Introduction
the C N bond formation [Eq. (1), Figure 1]. With
these results in mind we were wondering if the elec-
The conjugate addition of ketones to a,b-unsaturated tron-rich ferrate would be able to activate more polar
3
À
carboxylic acid esters is a versatile method for gener- C(sp ) H bonds. From a mechanistic point of view
ating building blocks with an interesting 1,5-dicarbon- two distinct activation pathways could be operative,
yl motif.[1] Classical procedures largely rely on the use i.e., the C H insertion or the deprotonation mecha-
À
of a strong base, which can cause undesirable side re- nism [Eq. (2), Figure 1]. Whereas in the former sce-
À
actions. To circumvent these problems, efficient cata- nario the ferrate would insert oxidatively into the C
lytic protocols based on the use of transition metals, H bond to give an Fe H species that undergoes a car-
À
Brønsted or Lewis catalysts have been developed.[2] bometallation with polar olefins, the latter scenario
The high atom economy of these catalytic transforma- reflects the classical acid-base type reactivity in which
tions plus the chance to induce stereoselectivity in the the ferrate acts as a Brønsted base to generate an
À
À
C C bond forming process by employing catalytic enolate and an Fe H species. Michael addition of the
À
amounts of a chiral ligand make these processes more enolate generates the new C C bond. Protonation of
advantegous compared to the classical protocols.[3,4] the resulting carbanion by the Fe H species regener-
À
Recently, an iron-based Lewis acid has been used as ates the catalyst.
an alternative efficient catalyst to carry out the conju-
As a result of this study an efficient iron-catalyzed
gate addition.[5]
conjugate addition of 2-acylimidazoles[9] and electron-
For the past years our group has developed an deficient olefins was developed that is broadly appli-
array of processes in which the nucleophilic Fe com- cable and has good indications of the more classical
plex tetrabutylammonium nitrosyltricarbonylferrate acid-base type mechanism to be operative.
{Bu4N[Fe(CO)3(NO)] (TBA[Fe])} was used as a cata-
lyst.[6] More recently, we became interested in explor-
À
ing the reactivity of this electron-rich ferrate in C H Results and Discussion
activation chemistry and developed an efficient ami-
2
À
nation of C(sp ) H bonds through activation of Our preliminary investigation started with a reaction
azides.[7] In line with the detailed mechanistic studies between 2-acylimidazole 1 and benzyl acrylate 2 with
that were performed by Driver on the related Rh-cat- 5 mol% TBA[Fe] as a catalyst at 808C, which resulted
alyzed version,[8] we suggested an electrocyclization in isolation of the desired adduct 3 in 72% (entry 1,
followed by a proton transfer as a mechanism. Hence, Table 1). Control experiments indicated that no prod-
at the current state of research it appears as if the Fe uct was observed in the absence of iron catalyst
À
complex is not inserting into the C H bond prior to (entry 2, Table 1). Examination of solvent effects re-
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Table 1. Optimization of the reaction conditions.
Entry TBA[Fe]
Solvent Ligand
[mol%]
Temp. Yield
[8C]
[mol%]
[%][a]
1
5
DMF
–
80
76
(72)[b]
0
2
3
4
5
–
5
5
5
5
5
5
5
5
5
2
DMF
MeCN
THF
MTBE
toluene –
MeCN
MeCN PPh3
MeCN L1
MeCN L2
MeCN L3
–
–
–
–
80
80
80
80
84
61
36
83
90
88
88
76
6
80
7[c]
8[c]
9[c]
10[c]
11[c]
12[d]
–
100
100
100
100
100
100
68
MeCN
–
90
(88)[b]
63
13[d]
1
MeCN
-
100
À
Figure 1. TBA[Fe]-catalyzed C H transformation: Fe-cata-
[a]
1
Yields were determined by H NMR using mesitylene as
2
À
lyzed C(sp ) H amination and mechanistic dichotomy in the
an internal standard.
Isolated yield.
18 h.
3
À
activation of C(sp ) H bonds.
[b]
[c]
[d]
30 h.
vealed that MeCN was the solvent of choice, and 3
was formed in lower yield in other organic solvents,
such as THF, MTBE or toluene (entries 3–6). Elevat- cation due to the presence of water was observed as
ing the temperature to 1008C did improve the reac- a minor side-reaction.
tion outcome, which produced 3 in 90% yield
With these optimized conditions established, we
(entry 7). On the other hand, adding phosphine li- subsequently initiated a survey of various substituted
À
gands did not promote the reaction (entries 8 and 9). 2-acylimidazoles in this type of C C bond formation.
Moreover, yields of the product decreased by using The results are summarized in Scheme 1. For benzimi-
NHC ligands (entries 10 and 11). Lowering the cata- dazole, the corresponding product 4 was formed in
lyst loading (2 mol%) did not decrease the yield of 85% yield. Remarkably, imidazole having an isopro-
the product, but the reaction took a longer time to pyl group was a suitable substrate as well, affording
complete (entry 12). Further reduction of the catalyst adduct 5 in excellent yield. In the case of substrates
loading (1 mol%) indicated that the yield decreased containing an electron-donating group on the benzene
considerably (entry 13). Interestingly, changing the ring, such as methoxy or methyl groups, the reactions
catalyst from Bu4N[Fe(CO)3(NO)] to more common proceeded smoothly to furnish the corresponding ad-
bases like K2CO3 (stoichiometric) or Bu4NOAc ducts 6–9 in 69–94% yields. With regard to substrates
(5 mol%) led to the formation of product 3 in good with electron-withdrawing groups on the benzene
yields (80 and 86%, respectively), however, saponifi- ring, the corresponding adducts 10–13 could be ob-
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Scheme 1. Substrate scope of ketones. Reagents and conditions: ketone (0.2 mmol), 2 (0.24 mmol), TBA[Fe] (5 mol%),
MeCN (0.5 mL), 1008C, 18–30 h. Isolated yields).
tained in high yields. Also, the naphthyl substituent sion that these substrates are particularly sensitive
was well tolerated, which could produce adduct 14 in toward oxidation. Having in hand a powerful catalytic
88% yield. In addition, the thienyl-substituted imida- protocol for the conjugate addition of acylimidazoles
zole reacted successfully to deliver 15 in 90% yield. to acrylates, we were wondering whether we could
Using aryl groups instead of imidazolyl, led to the de- extend the substrate scope also to quinones. These
sired products 16–19 efficiently. Further examination substrates are potent oxidants that are known to cata-
revealed that conjugate addition occurred very slowly lyze the in-situ oxidation of precious metals. On the
to give the desired 20 in low yield along with more other hand side they are also attractive Michael ac-
than 99:1 dr. Unfortunately, no desired product 21 ceptors. To analyze the competition between oxida-
was formed when an aliphatic ketone was used as tion versus Michael-addition, 2,3-dimethylbenzoqui-
a substrate. The starting materials were reisolated in none was subjected to the standard conditions, under
good yields.
which only low yields of the Michael product were
Subsequently, we turned our interest to investigate observed. However, upon changing the solvent to eth-
the scope of reactive olefins. As shown in Scheme 2, anol the undesired oxidation of the ferrate was signifi-
a series of acrylates underwent the conjugate addition cantly reduced and, to our surprise, benzofuranone 39
successfully to produce the corresponding products in was formed as the sole product. To our delight the re-
high yields (22–26). Broad functional group tolerance action proved to be applicable to various quinones
and excellent yields were observed, such as nitriles using different acylimidazoles (Scheme 3). To the best
(28 and 29), aldehydes (31–33), ketones (34 and 35) of our knowledge this catalytic one-pot transforma-
and sulfone (36). Notably, even nitro groups (30) tion represents a new approach toward substituted 4-
proved to be stable. Furthermore, oxazolidinone was hydroxybenzofuranones, most literature reported
also a competent acceptor and gave the correspond- methods rely on the use of overstoichiometric
ing adduct 27 in 66% yield. Interestingly, the use of amounts of acid or base plus extended heating peri-
sorbic acid ester under otherwise identical reaction ods.
conditions gave the desired 1,6-addition product ex-
clusively in good combined yield of 61% as a 2:1-mix- the desired products in moderate to good yields. In
ture of p-bond isomers (37 and 38). the case of electron-poor benzoquinones however
The method proved to be broadly applicable giving
The catalyst employed in this study possesses an a fast oxidation of the catalyst and no conversion to
electron-rich ferrate as active center. One could envi- the corresponding benzofuranone 45 was observed.
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Scheme 2. TBA[Fe]-catalyzed conjugate addition – olefin scope. Reaction conditions A: 1 (0.4 mmol), olefin (0.48 mmol),
TBA[Fe] (2 mol%), MeCN (1 mL), 1008C, 30 h. Reaction conditions B: 1 (2 mmol), olefin (2.4 mmol), TBAFe (5 mol%),
MeCN (5 mL), 1008C, 60 h. Reaction conditions C: 1 (0.2 mmol), olefin (0.24 mmol), TBAFe (5 mol%), MeCN (0.5 mL),
1
1008C, 20-48 h. Isolated yields. The dr values were determined by H NMR of crude products.
From a mechanistic point of view, we propose a Mi- Conclusions
chael-type addition of the acylimidazole plus a con-
À
comitant transesterification with C C bond scission to Herein we report the Bu4N[Fe(CO)3(NO)]-catalyzed
be operative. In order to support this model we per- Michael-type addition of acylimidazoles to olefins.
formed several test experiments. Treating 2,6-dime- The reaction proceeds in good to excellent yields on
thylbenzoquinone with 2-acylimidazole 1 at 408C for a broad scope of substrates. In the case of quinone-
one hour under microwave conditions led to the for- type substrates a fast Michael addition is observed
mation of the Michael addition product 46 in good that is followed by an internal cyclization with substi-
yield [Eq. (1), Scheme 4]. Product 46 collapses upon tution of the imidazole moiety upon heating. A range
heating to 808C to give the observed benzofuranone of substituted benzofuranones were obtained in good
39 in good yield even in the absence of TBA[Fe] [Eq. to excellent yields. Experimental indications for an
À
(2), Scheme 4].
acid-base-type rather than a reductive C H bond acti-
Finally, heating one equivalent of acylimidazole vation were obtained. Hence, these results provide
1 with one equivalent of TBA[Fe] and subsequent ad- another insight into probable mechanistic pathways in
À
dition of D2O to the reaction mixture led to quantita- TBA[Fe]-catalyzed C H activations and will serve as
tive generation of the a-monodeuterated acylimida- guidelines for further studies in this field.
zole 1-D [Eq. (3), Scheme 4]. This result indicates an
acid-base-type mechanism to be operative.
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Scheme 4. TBA[Fe]-catalyzed conjugate addition to qui-
nones.
column chromatography on silica gel completed the proce-
dure.
Benzyl 5-(1-methyl-1H-imidazol-2-yl)-5-oxo-4-phenylpen-
tanoate (3): 30 h; yield: 62 mg (86%); colorless oil; Rf: 0.66
(petroleum ether/ethyl acetate 1:1); 1H NMR (300 MHz,
CDCl3): d=7.41 (d, J=6.9 Hz, 2H), 7.32–7.25 (m, 7H),
7.22–7.17 (m, 1H), 7.11 (s, 1H), 6.96 (s, 1H), 5.18 (t, J=
6.6 Hz, 1H), 5.07 (s, 2H), 3.92 (s, 3H), 2.51–2.19 (m, 4H);
13C NMR (75 MHz, CDCl3): d=191.8, 172.8, 142.6, 138.4,
135.9, 129.3, 128.7, 128.6, 128.5, 128.15, 128.10, 127.4, 127.1,
66.2, 51.8, 36.1, 32.2, 27.7; IR (film): n=3063, 3031, 2950,
1731, 1670, 1401, 1153, 911, 740, 698 cmÀ1; MS (EI, 70 eV):
m/z (%)=362 (30), 271 (5), 213 (100), 199 (33), 109 (27), 91
(45), 65 (3); HR-MS (ESI): m/z=385.1538, calcd. for
C22H22N2NaO3 [M+Na]+: 385.1523.
Scheme 3. TBA[Fe]-catalyzed conjugate addition to qui-
nones. Reagents and conditions: benzoquinone (0.4 mmol),
2-acylimidazole (0.48 mmol), TBA[Fe] (2 mol%), EtOH
(1 mL), microwave (808C, 1 h). Isolated yields. 15–35% of
hydroquinones were formed.
Experimental Section
General Remarks
All reactions sensitive to moisture and/or air were carried
out under an atmosphere of dry nitrogen (N2) using anhy-
drous solvents. Solvents were either dried by passing them
through commercially available columns (n-pentane,
CH2Cl2) or distilling them from CaH2 (CCl4, C2H2Cl4,
C2H4Cl2, PhH). THF was freshly distilled from Na/benzo-
phenone (ketyl radical).
Benzyl
5-(1-methyl-1H-benzo[d]imidazol-2-yl)-5-oxo-4-
phenylpentanoate (4): 20 h; yield: 70 mg (85%); colorless
oil; Rf: 0.53 (petroleum ether/ethyl acetate 4:1); 1H NMR
(500 MHz, CDCl3): d=7.86 (d, J=8.8 Hz, 1H), 7.45 (d, J=
7.6 Hz, 2H), 7.36 (t, J=7.4 Hz, 1H), 7.31–7.24 (m, 9H), 7.17
(t, J=7.4 Hz, 1H), 5.44–5.41 (m, 1H), 5.08 (d, J=12.5 Hz,
1H), 5.05 (d, J=12.5 Hz, 1H), 3.99 (s, 3H), 2.57–2.29 (m,
4H); 13C NMR (125 MHz, CDCl3): d=194.5, 172.7, 145.7,
141.6, 137.7, 137.1, 135.8, 128.8, 128.6, 128.4, 128.1, 128.0,
127.2, 125.8, 123.5, 122.0, 110.3, 66.2, 52.5, 32.1, 32.0, 27.5;
IR (film): n=3063, 3032, 2948, 1732, 1681, 1456, 907,
727 cmÀ1; MS (EI, 70 eV): m/z (%)=412 (16), 263 (100),
249 (19), 159 (16), 91 (28); HR-MS (ESI): m/z=435.1696,
calcd. for C26H24N2NaO3 [M+Na]+: 435.1679.
General Procedure for Michael Addition
Under a nitrogen atmosphere, a dried Schlenk tube was
charged with the catalyst TBA[Fe] (2 or 5 mol%), the corre-
sponding 2-acylimidazole (0.4 mmol). Then MeCN (1 mL,
0.4M) was added via syringe, followed by the corresponding
olefin (0.48 mmol, 1.2 equiv.). The reaction mixture was
stirred at 1008C for the indicated time. Purification via
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Benzyl 5-(1-isopropyl-1H-imidazol-2-yl)-5-oxo-4-phenyl-
pentanoate (5): 30 h; yield: 70 mg (90%); colorless oil; Rf:
0.50 (petroleum ether/ethyl acetate 2:1); 1H NMR
(300 MHz, CDCl3): d=7.42–7.39 (m, 2H), 7.34–7.25 (m,
7H), 7.22–7.14 (m, 3H), 5.53–5.39 (m, 1H), 5.24–5.19 (m,
1H), 5.07 (s, 2H), 2.51–2.19 (m, 4H), 1.43 (d, J=6.6 Hz,
3H), 1.30 (d, J=1.4 Hz, 3H); 13C NMR (75 MHz, CDCl3):
d=191.9, 172.8, 142.0, 138.6, 135.9, 129.7, 128.7, 128.6, 128.4,
128.14, 128.09, 127.0, 121.5, 66.2, 52.3, 49.2, 32.2, 27.9, 23.5,
23.4; IR (film): n=3031, 2965, 1732, 1669, 1391, 1151,
697 cmÀ1; MS (EI, 70 eV): m/z (%)=390 (50), 241 (100),
227 (30), 137 (29), 91 (50); HR-MS (ESI): m/z=413.1836,
calcd. for C24H26N2NaO3 [M+Na]+: 413.1836.
Benzyl 4-(4-methoxyphenyl)-5-(1-methyl-1H-imidazol-2-
yl)-5-oxopentanoate (6): 30 h; yield: 74 mg (94%); white
solid; mp 86–878C; Rf: 0.60 (petroleum ether/ethyl acetate
1:1); 1H NMR (300 MHz, CDCl3): d=7.34–7.29 (m, 7H),
7.11 (s, 1H), 6.96 (s, 1H), 6.83–7.80 (m, 2H), 5.14–5.07 (m,
3H), 3.92 (s, 3H), 3.74 (s, 3H), 2.45–2.16 (m, 4H); 13C NMR
(75 MHz, CDCl3): d=192.0, 172.8, 158.7, 142.6, 135.9, 130.3,
129.7, 129.2, 128.4, 128.12, 128.08, 127.3, 114.0, 66.1, 55.1,
50.8, 36.1, 32.2, 27.6; IR (film): n=3033, 2954, 1731, 1669,
1509, 1400, 1246, 1152, 697 cmÀ1; MS (EI, 70 eV): m/z (%)=
392 (68), 243 (100), 91 (96); HR-MS (ESI): m/z=415.1645,
calcd. for C23H24N2NaO4 [M+Na]+: 415.1639.
(96);
HR-MS
(ESI):
m/z=399.1693,
calcd.
for
C23H24N2NaO3 [M+Na]+: 399.1679.
Benzyl 4-(4-bromophenyl)-5-(1-methyl-1H-imidazol-2-yl)-
5-oxopentanoate (10): 24 h; yield: 83 mg (94%); colorless
oil; Rf: 0.57 (petroleum ether/ethyl acetate 1:1); 1H NMR
(300 MHz, CDCl3): d=7.39 (d, J=8.5 Hz, 2H), 7.32–7.25
(m, 7H), 7.11 (s, 1H), 6.98 (s, 1H), 5.18–5.02 (m, 3H), 3.92
(s, 3H), 2.47–2.17 (m, 4H); 13C NMR (75 MHz, CDCl3): d=
191.1, 172.6, 142.4, 137.4, 135.8, 131.6, 130.4, 129.4, 128.4,
128.12, 128.11, 127.6, 121.1, 66.2, 51.1, 36.1, 32.0, 27.5; IR
(film): n=3033, 2953, 1731, 1670, 1399, 1153, 729 cmÀ1; MS
(EI, 70 eV): m/z (%)=442 (37), 440 (37), 293 (90), 291 (91),
109 (65), 91 (100); HR-MS (ESI): m/z=463.0658, calcd. for
C22H21BrN2NaO3 [M+Na]+: 463.0639.
Benzyl 4-(4-chlorophenyl)-5-(1-methyl-1H-imidazol-2-yl)-
5-oxopentanoate (11): 24 h; yield: 72 mg (91%); colorless
oil; Rf: 0.59 (petroleum ether/ethyl acetate 1:1); 1H NMR
(300 MHz, CDCl3): d=7.39–7.32 (m, 7H), 7.28–7.24 (m,
2H), 7.14 (s, 1H), 7.01 (s, 1H), 5.19 (t, J=7.8 Hz, 1H), 5.10
(s, 2H), 3.95 (s, 3H), 2.50–2.20 (m, 4H); 13C NMR (75 MHz,
CDCl3): d=191.3, 172.6, 142.4, 136.9, 135.8, 133.0, 130.0,
129.4, 128.7, 128.5, 128.2, 128.1, 127.6, 66.2, 51.0, 36.1, 32.1,
27.6; IR (film): n=3032, 2952, 1730, 1670, 1399, 1152,
696 cmÀ1; MS (EI, 70 eV): m/z (%)=396 (35), 247 (100),
109 (39), 91 (55); HR-MS (ESI): m/z=419.1122, calcd. for
C22H21ClN2NaO3 [M+Na]+: 419.1133.
Benzyl
5-(1-methyl-1H-imidazol-2-yl)-5-oxo-4-(p-tolyl)-
Benzyl 4-(4-fluorophenyl)-5-(1-methyl-1H-imidazol-2-yl)-
5-oxopentanoate (12): 24 h; yield: 72 mg (95%); colorless
oil; Rf: 0.62 (petroleum ether/ethyl acetate 1:1); 1H NMR
(300 MHz, CDCl3): d=7.40–7.27 (m, 7H), 7.12 (s, 1H),
7.00–6.92 (m, 3H), 5.17 (t, J=7.8 Hz, 1H), 5.09 (d, J=
12.5 Hz, 1H), 5.05 (d, J=12.5 Hz, 1H), 3.93 (s, 3H), 2.49–
2.15 (m, 4H); 13C NMR (75 MHz, CDCl3): d=191.6, 172.7,
161.9 (d, J=243.9 Hz), 142.4, 135.8, 134.1 (d, J=3.1 Hz),
130.2 (d, J=7.9 Hz), 129.3, 128.5, 128.14, 128.12, 127.5, 115.4
(d, J=21.2 Hz), 66.2, 50.8, 36.1, 32.1, 27.8; 19F NMR
(376 MHz, CDCl3): d À115.50 to À115.53 (m); IR (film): n
() 3034, 2927, 1731, 1670, 1400, 1154, 697 cmÀ1; MS (EI,
70 eV): m/z (%)380 (44), 231 (100), 109 (39), 91 (59); HR-
MS (ESI): m/z=403.1429, calcd. for C22H21FN2NaO3 [M+
Na]+: 403.1428.
Benzyl 5-(1-methyl-1H-imidazol-2-yl)-4-(4-nitrophenyl)-5-
oxopentanoate (13): 24 h; yield: 68 mg (83%); light yellow
oil; Rf: 0.51 (petroleum ether/ethyl acetate 1:1); 1H NMR
(300 MHz, CDCl3): d=8.13 (d, J=8.7 Hz, 2H), 7.59 (d, J=
8.7 Hz, 2H), 7.37–7.30 (m, 5H), 7.13 (s, 1H), 7.03 (s, 1H),
5.34 (t, J=7.6 Hz, 1H), 5.08 (s, 2H), 3.95 (s, 3H), 2.57–2.18
(m, 4H); 13C NMR (75 MHz, CDCl3): d=190.2, 172.4, 147.1,
146.1, 142.2, 135.7, 129.7, 129.6, 128.5, 128.2, 128.0, 123.8,
66.4, 51.5, 36.2, 32.0, 27.6; IR (film): n=3033, 2952, 1731,
1671, 1344, 1155, 698 cmÀ1; MS (EI, 70 eV): m/z (%)=407
(19), 258 (100), 244 (47), 109 (75), 91 (59); HR-MS (ESI):
m/z=430.1397, calcd. for C22H21N3NaO5 [M+Na]+:
430.1373.
pentanoate (7): 30 h, yield: 67 mg (89%); colorless oil; Rf:
0.69 (petroleum ether/ethyl acetate 1:1); 1H NMR
(300 MHz, CDCl3): d=7.36–7.26 (m, 7H), 7.10–7.07 (m,
3H), 6.94 (s, 1H), 5.13 (t, J=7.9 Hz, 1H), 5.06 (s, 2H), 3.90
(s, 3H), 2.46–2.20 (m, 7H); 13C NMR (75 MHz, CDCl3): d=
191.9, 172.8, 142.6, 136.7, 135.9, 135.3, 129.3, 129.2, 128.5,
128.4, 128.1, 128.0, 127.3, 66.1, 51.4, 36.1, 32.2, 27.6, 21.0; IR
(film): n=3031, 2949, 1731, 1669, 1400, 1152, 696 cmÀ1; MS
(EI, 70 eV): m/z (%)=376 (38), 227 (100), 109 (15), 91 (77);
HR-MS (ESI): m/z=399.1669, calcd. for C23H24N2O3Na
[M+Na]+: 399.1679.
Benzyl 5-(1-methyl-1H-imidazol-2-yl)-5-oxo-4-(m-tolyl)-
pentanoate (8): 30 h; yield: 64 mg (85%); colorless oil; Rf:
0.73 (petroleum ether/ethyl acetate 1:1); 1H NMR
(300 MHz, CDCl3): d=7.36–7.27 (m, 5H), 7.22–7.13 (m,
3H), 7.11 (s, 1H), 7.01 (d, J=7.2 Hz, 1H), 6.96 (s, 1H), 5.14
(t, J=7.9 Hz, 1H), 5.07 (s, 2H), 3.93 (s, 3H), 2.49–2.18 (m,
7H); 13C NMR (75 MHz, CDCl3): d=191.9, 172.8, 142.6,
138.3, 138.2, 135.9, 129.3, 129.2, 128.4, 128.12, 128.07, 127.9,
127.4, 125.7, 66.1, 51.7, 36.1, 32.2, 27.8, 21.4; IR (film): n=
3033, 2953, 1731, 1670, 1402, 907, 726 cmÀ1; MS (EI, 70 eV):
m/z (%)=376 (24), 227 (100), 109 (18), 91 (49); HR-MS
(ESI): m/z=399.1677, calcd. for C23H24N2NaO3 [M+Na]+:
399.1679.
Benzyl
5-(1-methyl-1H-imidazol-2-yl)-5-oxo-4-(o-tolyl)-
pentanoate (9): 30 h; yield: 52 mg (69%); colorless oil; Rf:
0.68 (petroleum ether/ethyl acetate 1:1); 1H NMR
(300 MHz, CDCl3): d=7.36–7.27 (m, 6H), 7.15–7.07 (m,
3H), 7.05 (s, 1H), 6.93 (s, 1H), 5.40 (t, J=7.3 Hz, 1H), 5.07
(s, 2H), 3.92 (s, 3H), 2.56 (s, 3H), 2.46–2.12 (m, 7H);
13C NMR (75 MHz, CDCl3): d=192.4, 172.9, 143.0, 137.2,
137.1, 135.9, 130.6, 129.2, 128.5, 128.2, 128.1, 127.2, 127.0,
126.9, 126.1, 66.2, 47.2, 36.0, 32.1, 28.1, 20.0; IR (film): n=
3032, 2954, 1731, 1670, 1401, 1152, 696 cmÀ1. MS (EI,
70 eV): m/z (%)=376 (23), 227 (96), 199 (100), 109 (29), 91
Benzyl 5-(1-methyl-1H-imidazol-2-yl)-4-(naphthalen-2-yl)-
5-oxopentanoate (14): 30 h; yield: 73 mg (88%); colorless
oil; Rf: 0.54 (petroleum ether/ethyl acetate 1:1); 1H NMR
(300 MHz, CDCl3): d=7.85 (s, 1H), 7.79–7.74 (m, 3H), 7.57
(dd, J=8.5 Hz, J=1.7 Hz, 1H), 7.44–7.37 (m, 2H), 7.34–7.30
(m, 5H), 7.10 (s, 1H), 6.92 (s, 1H), 5.35 (t, J=7.5 Hz, 1H),
5.08 (d, J=12.4 Hz, 1H), 5.03 (d, J=12.4 Hz, 1H), 3.90 (s,
3H), 2.59–2.30 (m, 4H); 13C NMR (75 MHz, CDCl3): d=
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191.6, 172.8, 142.6, 135.9, 135.8, 133.4, 132.5, 129.3, 128.4,
128.3, 128.12, 128.08, 127.8, 127.7, 127.5, 127.4, 126.6, 126.0,
125.7, 66.2, 51.9, 36.1, 32.2, 27.6; IR (film): n=3057, 2955,
1730, 1668, 1400, 1154, 730 cmÀ1; MS (EI, 70 eV): m/z (%)=
412 (55), 263 (100), 109 (12), 91 (48); HR-MS (ESI): m/z=
435.1699, calcd. for C26H24N2NaO3 [M+Na]+: 435.1690.
Benzyl 5-(1-methyl-1H-imidazol-2-yl)-5-oxo-4-(3-thienyl)-
pentanoate (15): 30 h; yield: 68 mg (92%); colorless oil; Rf:
0.56 (petroleum ether/ethyl acetate 1:1); 1H NMR
(300 MHz, CDCl3): d=7.36–7.29 (m, 5H), 7.23–7.22 (m,
2H), 7.14–7.12 (m, 2H), 6.99 (s, 1H), 5.36–5.31 (m, 1H),
5.07 (s, 2H), 3.94 (s, 3H), 2.45–2.29 (m, 4H); 13C NMR
(75 MHz, CDCl3): d=191.4, 172.8, 142.4, 138.6, 135.9, 129.3,
128.5, 128.2, 128.1, 127.6, 125.6, 122.8, 66.2, 47.1, 36.2, 32.1,
27.7; IR (film): n=3033, 2950, 1730, 1670, 1401, 1154,
697 cmÀ1; MS (EI, 70 eV): m/z (%)=368 (61), 219 (100),
205 (41), 109 (38), 91 (93); HR-MS (ESI): m/z=391.1083,
calcd. for C20H20N2NaO3S [M+Na]+: 391.1098.
Benzyl 5-[(S)-4-isopropyl-2-oxooxazolidin-3-yl]-5-oxo-4-
phenylpentanoate (20): 48 h; yield: 18 mg (12%); colorless
oil; Rf: 0.48 (petroleum ether/ethyl acetate 3:1); 1H NMR
(300 MHz, CDCl3): d=7.35–7.22 (m, 10H), 5.14–5.03 (m,
3H), 4.46 (dt, J=8.6 Hz, J=3.5 Hz, 1H), 4.20 (t, J=8.7 Hz,
1H), 4.08 (dd, J=9.1 Hz, J=3.4 Hz, 1H), 2.44–2.10 (m,
5H), 0.78 (d, J=7.1 Hz, 3H), 0.40 (d, J=6.9 Hz, 3H);
13C NMR (75 MHz, CDCl3): d=173.2, 172.7, 153.3, 137.8,
135.9, 128.6, 128.5, 128.25, 128.19, 127.5, 66.3, 62.9, 58.0,
48.1, 32.0, 28.2, 27.8, 17.7, 14.0; IR (film): n=3032, 2963,
1774, 1732, 1694, 1372, 1203, 698 cmÀ1; MS (EI, 70 eV): m/z
(%)=409 (10), 318 (12), 280 (14), 171 (11), 130 (19), 91
(100); HR-MS (ESI): m/z=432.1782, calcd. for
C24H27NNaO5 [M+Na]+: 432.1781.
Ethyl 5-(1-methyl-1H-imidazol-2-yl)-5-oxo-4-phenylpenta-
noate (22): 30 h; yield: 95 mg (79%); colorless oil; Rf: 0.54
(petroleum ether/ethyl acetate 1:1); 1H NMR (250 MHz,
CDCl3): d=7.45–7.41 (m, 2H), 7.31–7.25 (m, 2H), 7.23–7.16
(m, 1H), 7.11 (s, 1H), 6.96 (s, 1H), 5.20–5.14 (m, 1H), 4.08
(q, J=7.2 Hz, 2H), 3.92 (s, 3H), 2.47–2.16 (m, 4H), 1.21 (t,
J=7.2 Hz, 3H); 13C NMR (75 MHz, CDCl3): d=191.9,
173.0, 142.6, 138.5, 129.3, 128.7, 128.6, 127.4, 127.1, 60.3,
51.8, 36.1, 32.3, 27.8, 14.1; IR (film): n=2979, 1728, 1670,
1400, 1154, 739, 698 cmÀ1; MS (EI, 70 eV): m/z (%)=300
(18), 255 (16), 213 (100), 199 (19), 117 (21), 109 (21), 82 (5);
HR-MS (ESI): m/z=323.1364, calcd. for C17H20N2NaO3
[M+Na]+: 323.1366.
Phenethyl 5-(1-methyl-1H-imidazol-2-yl)-5-oxo-4-phenyl-
pentanoate (23): 30 h; yield: 112 mg (75%); colorless oil; Rf:
0.58 (petroleum ether/ethyl acetate 1:1); 1H NMR
(300 MHz, CDCl3): d=7.43–7.40 (m, 2H), 7.31–7.17 (m,
8H), 7.12 (s, 1H), 6.97 (s, 1H), 5.18–5.13 (m, 1H), 4.24 (t,
J=7.2 Hz, 2H), 3.93 (s, 3H), 2.89 (t, J=7.2 Hz, 2H), 2.44–
2.15 (m, 4H); 13C NMR (75 MHz, CDCl3): d=191.8, 172.9,
142.6, 138.4, 137.8, 129.3, 128.8, 128.7, 128.6, 128.4, 127.4,
127.1, 126.5, 64.8, 51.8, 36.2, 35.0, 32.2, 27.7; IR (film): n=
3028, 2955, 1729, 1670, 1400, 1154, 742, 698 cmÀ1. MS (EI,
70 eV): m/z (%)=376 (15), 213 (100), 199 (22), 105 (35);
HR-MS (ESI): m/z=399.1683, calcd. for C23H24N2NaO3
[M+Na]+: 399.1690.
tert-Butyl 5-(1-methyl-1H-imidazol-2-yl)-5-oxo-4-phenyl-
pentanoate (24): 30 h; yield: 108 mg (82%); white solid; mp
108–1098C; Rf: 0.69 (petroleum ether/ethyl acetate 1:1);
1H NMR (300 MHz, CDCl3): d=7.44–7.41 (m, 2H), 7.31–
7.26 (m, 2H), 7.22–7.17 (m, 1H), 7.11 (s, 1H), 6.97 (s, 1H),
5.17 (t, J=7.5 Hz, 1H), 3.94 (s, 3H), 2.44–2.31 (m, 1H),
2.22–2.14 (m, 3H), 1.41 (s, 9H); 13C NMR (75 MHz,
CDCl3): d=192.0, 172.3, 142.7, 138.6, 129.2, 128.7, 128.6,
127.4, 127.0, 80.2, 51.8, 36.1, 33.5, 28.0; IR (film): n=2976,
1723, 1671, 1401, 1144, 740, 698 cmÀ1; MS (EI, 70 eV): m/z
(%)=328 (10), 272 (18), 255 (28), 213 (100), 199 (30), 109
(16), 82 (13); HR-MS (ESI): m/z=351.1686, calcd. for
C19H24N2NaO3 [M+Na]+: 351.1690.
Benzyl 5-oxo-4,5-diphenylpentanoate (16): 30 h; yield:
63 mg (88%); colorless oil; Rf: 0.33 (petroleum ether/ethyl
1
acetate 10:1); H NMR (300 MHz, CDCl3): d=7.91–7.88 (m,
2H), 7.48–7.42 (m, 1H), 7.37–7.16 (m, 12H), 5.12 (d, J=
12.3 Hz, 1H), 5.07 (d, J=12.3 Hz, 1H), 4.64 (t, J=7.2 Hz,
1H), 2.53–2.42 (m, 1H), 2.35 (t, J=6.9 Hz, 2H), 2.24–2.13
(m, 1H); 13C NMR (75 MHz, CDCl3): d=199.2, 173.0, 138.7,
136.5, 135.9, 132.9, 129.0, 128.7, 128.5, 128.4, 128.26, 128.21,
127.2, 66.2, 52.2, 31.8, 28.7; IR (film): n=3030, 2939, 1730,
1678, 1150, 694 cmÀ1; MS (ESI): m/z=381.2 (M+Na)+; HR-
MS (ESI): m/z=381.1455, calcd. for C24H22NaO3 [M+Na]+:
381.1461.
Benzyl 5-(4-chlorophenyl)-5-oxo-4-phenylpentanoate (17):
30 h; yield: 153 mg (97%); colorless oil; Rf: 0.4 (petroleum
1
ether/ethyl acetate 10:1); H NMR (300 MHz, CDCl3): d=
7.83–7.80 (m, 2H), 7.35–7.18 (m, 12H), 5.14–5.06 (m, 2H),
4.57 (t„ J=7.18 Hz, 1H), 2.51–2.40 (m, 1H), 2.36–2.31 (m,
2H), 2.22–2.11 (m, 1H); 13C NMR (75 MHz, CDCl3): d=
198.0, 172.9, 139.3, 138.4, 130.1, 129.2, 128.8, 128.7, 128.3,
128.3, 128.2, 127.5, 66.3, 52.3, 31.7, 28.6; IR (film): n=3063,
3030, 2943, 1731, 1255, 1092, 698 cmÀ1.
Benzyl 5-oxo-4-phenyl-5-(p-tolyl)pentanoate (18): 30 h;
yield: 124 mg (84%); colorless oil; Rf: 0.38 (petroleum
1
ether/ethyl acetate 10:1); H NMR (400 MHz, CDCl3): d=
7.80 (d, J=8.28 Hz, 2H), 7.37–7.13 (m, 12H), 5.09 (d, J=
3.72 Hz, 2H), 4.61 (t, J=7.32 Hz, 1H), 2.51–2.42 (m, 1H),
2.36–2.32 (m, 5H), 2.22–2.13 (m, 1H); 13C NMR (100 MHz,
CDCl3): d=198.8, 173.1, 143.7, 138.9, 135.9, 134.0, 129.2,
128.9, 128.8, 128.5, 128.3, 128.2, 127.2, 66.2, 52.1, 312.9, 28.7,
21.6; IR (film): n=3061, 3030, 2941, 1730, 1674, 1150,
697 cmÀ1; MS (ESI): m/z=395.16 (M+Na)+; HR-MS (ESI):
m/z=395.1611, calcd. for C25H24NaO3 [M+Na]+: 395.1618.
Benzyl
5-(4-methoxyphenyl)-5-oxo-4-phenylpentanoate
(19): 30 h; yield: 131 mg (85%); colorless oil; Rf: 0.16 (pe-
troleum ether/ethyl acetate 10:1); 1H NMR (400 MHz,
CDCl3): d=7.91–7.88 (m, 2H), 7.37–7.16 (m, 10H), 6.85–
6.80 (m, 2H), 5.09 (d, J=2.84 Hz, 2H), 4.59 (t, J=7.32 Hz,
1H), 3.80 (s, 3H), 2.50–2.41 (m, 1H), 2.34 (t, J=14.00 Hz,
2H), 2.21–2.12 (m, 1H); 13C NMR (100 MHz, CDCl3): d=
197.7, 173.1, 163.3, 139.2, 135.9, 131.0, 129.6, 128.9, 128.6,
128.3, 128.2, 127.2, 113.7, 66.2, 55.4, 51.9, 31.9, 28.8; IR
(film): n=3062, 3030, 2936, 2839, 1729, 1668, 1254, 1164,
697 cmÀ; MS (ESI): m/z=411.16 (M+Na)+; HR-MS (ESI):
m/z=411.1467, calcd. for C25H24NaO4 [M+Na]+: 411.1563.
Ethyl 5-(1-methyl-1H-imidazol-2-yl)-5-oxo-2,4-diphenyl-
pentanoate (25): 30 h; yield: 70 mg (93%); dr=45:55; color-
less oil; Rf: 0.43 (petroleum ether/ethyl acetate 1:1);
1H NMR (300 MHz, CDCl3): d=7.40–7.36 (m, 2H), 7.30–
7.16 (m, 8H), 7.08 (d, J=0.7 Hz, 0.48H), 7.04 (d, J=0.7 Hz,
0.52H), 6.93 (s, 0.48H), 6.89 (s, 0.52H), 5.16–5.06 (m, 1H),
4.17–3.97 (m, 2H), 3.91 (s, 1.44H), 3.83 (s, 1.56H), 3.50–3.42
(m, 1H), 2.95–2.27 (m, 2H), 1.21–1.10 (m, 3H); 13C NMR
(75 MHz, CDCl3): d=191.6, 191.5, 173.46, 173.36, 142.54,
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142.51, 139.0, 138.7, 138.6, 138.3, 129.3, 129.1, 128.8, 128.66,
128.58, 128.53, 128.50, 128.4, 128.2, 127.8, 127.21, 127.19,
127.0, 60.72, 60.70, 50.5, 50.4, 49.7, 49.2, 36.3, 36.2, 36.1, 36.0,
14.0, 13.9; IR (film): n=3030, 3031, 2980, 1726, 1671, 1401,
1154, 908, 727, 697 cmÀ1; MS (EI, 70 eV): m/z (%)=376 (3),
213 (100), 109 (6), 91 (4); HR-MS (ESI): m/z=399.1684,
calcd. for C23H24N2NaO3 [M+Na]+: 399.1679.
white solid; mp 188–1898C; Rf: 0.52 (petroleum ether/ethyl
acetate 1:1); H NMR (300 MHz, CDCl3): d=7.66–7.60 (m,
1
2H), 7.44–7.32 (m, 4H), 7.27–7.19 (m, 3H), 7.12–7.00 (m,
2.49H), 6.88 (s, 0.51H), 6.08 (d, J=12.3 Hz, 0.51H), 5.91 (d,
J=11.8 Hz, 0.49H), 4.41 (d, J=5.0 Hz, 0.49H), 4.20–4.12
(m, 1H), 3.96 (s, 1.47H), 3.71 (s, 1.53H), 3.64 (d, J=3.8 Hz,
0.51H); 13C NMR (75 MHz, CDCl3): d=189.4, 187.7, 142.1,
142.0, 135.2, 134.8, 134.4, 130.3, 129.84, 129.79, 129.2, 129.04,
129.00, 128.96, 128.9, 128.8, 128.7, 128.5, 128.2, 127.8, 127.5,
112.0, 111.8, 111.5, 110.9, 54.6, 53.8, 48.4, 47.6, 36.2, 35.8,
28.2, 28.0; IR (film): n=3033, 2904, 1667, 1400, 909,
697 cmÀ1; MS (EI, 70 eV): m/z (%)=354 (3), 289 (100), 199
(26), 109 (56); HR-MS (ESI): m/z=377.1390, calcd. for
C22H18N4NaO [M+Na]+: 377.1373.
1-(1-Methyl-1H-imidazol-2-yl)-4-nitro-2,3-diphenylbutan-
1-one (30): 20 h; yield: 28 mg (40%); dr=45:55; colorless
oil; Rf: 0.62 (petroleum ether/ethyl acetate 1:1); 1H NMR
(300 MHz, CDCl3): d=7.61 (d, J=7.0 Hz, 2H), 7.40–7.35
(m, 4H), 7.31–7.22 (m, 3H), 7.16 (d, J=7.2 Hz, 1H), 7.06 (s,
1H), 6.85 (s, 1H), 5.77–5.68 (m, 1H), 4.55–4.31 (m, 3H),
3.72 (s, 3H); 13C NMR (75 MHz, CDCl3): d=188.8, 142.5,
137.8, 135.7, 129.4, 129.3, 129.0, 128.7, 128.21, 128.17, 127.7,
127.5, 79.5, 54.9, 46.4, 35.9; IR (film): n=3063, 2959, 1672,
1550, 1400, 909, 697 cmÀ1; MS (EI, 70 eV): m/z (%)=349
(6), 303 (52), 199 (100), 171 (23), 109 (61), 91 (9); HRMS
(ESI): m/z=372.1303, calcd. for C20H19N3NaO3 [M+Na]+:
372.1319.
Methyl 5-(1-methyl-1H-imidazol-2-yl)-5-oxo-3,4-diphenyl-
pentanoate (26): 48 h; yield: 52 mg (72%); dr=67:33; color-
less oil; Rf: 0.56 (petroleum ether/ethyl acetate 1:1). Major
1
isomer: H NMR (300 MHz, CDCl3): d=7.62–7.59 (m, 2H),
7.40–7.31 (m, 4H), 7.27–7.18 (m, 3H), 7.13–7.07 (m, 1H),
7.04 (s, 1H), 6.82 (s, 1H), 5.62 (d, J=12.0 Hz, 1H), 4.15–
4.06 (m, 1H), 3.70 (s, 3H), 3.39 (s, 3H), 2.54–2.39 (m, 2H);
13C NMR (75 MHz, CDCl3): d=190.6, 172.3, 142.9, 141.8,
137.1, 129.4, 129.1, 128.8, 128.26, 128.20, 127.5, 127.1, 126.6,
57.5, 51.3, 44.6, 39.5, 35.9; IR (film): n=3062, 3029, 2951,
1736, 1673, 1402, 1155, 700 cmÀ1; MS (EI, 70 eV): m/z (%)=
362 (70), 289 (64), 200 (100), 121 (47), 109 (26), 82 (13);
HR-MS (ESI): m/z=385.1539, calcd. for C22H22N2NaO3
[M+Na]+: 385.1523. Minor isomer: 1H NMR (300 MHz,
CDCl3): d=7.26–7.23 (m, 2H), 7.15 (s, 1H), 7.13–6.98 (m,
9H), 5.49 (d, J=11.6 Hz, 1H), 4.13–4.03 (m, 1H), 3.97 (s,
3H), 3.48 (s, 3H), 2.77 (d, J=7.4 Hz, 2H); 13C NMR
(75 MHz, CDCl3): d=191.6, 172.0, 143.1, 140.9, 137.0, 129.4,
129.3, 128.3, 128.1, 127.9, 127.6, 126.8, 126.4, 57.9, 51.4, 44.9,
39.8, 36.3; IR (film): n=3062, 3029, 2951, 1736, 1668, 1401,
699 cmÀ1; MS (EI, 70 eV): m/z (%)=362 (97), 289 (100),
200 (95), 121 (61), 109 (34), 82 (19); HR-MS (ESI): m/z=
385.1530, calcd. for C22H22N2NaO3 [M+Na]+: 385.1523.
1-(1-Methyl-1H-imidazol-2-yl)-5-(2-oxooxazolidin-3-yl)-2-
phenylpentane-1,5-dione (27): 30 h; yield: 45 mg (66%);
white solid; mp 171–1728C; Rf: 0.22 (petroleum ether/ethyl
acetate 1:2); 1H NMR (500 MHz, CDCl3): d=7.43 (d, J=
7.2 Hz, 2H), 7.29–7.26 (m, 2H), 7.21–7.18 (m, 1H), 7.11 (s,
1H), 6.97 (s, 1H), 5.22 (t, J=7.7 Hz, 1H), 4.33 (t, J=8.6 Hz,
2H), 3.96–3.93 (m, 5H), 2.93–2.90 (m, 2H), 2.51–2.44 (m,
1H), 2.31–2.24 (m, 1H); 13C NMR (125 MHz, CDCl3): d=
191.8, 172.7, 153.3, 142.7, 138.6, 129.2, 128.7, 128.5, 127.4,
127.0, 61.9, 51.6, 42.4, 36.1, 32.9, 27.2; IR (film): n=2925,
1772, 1695, 1669, 1385, 700 cmÀ1; MS (EI, 70 eV): m/z (%)=
341 (15), 213 (100), 109 (17), 88 (13); HR-MS (ESI): m/z=
364.1272, calcd. for C18H19N3NaO4 [M+Na]+: 364.1268.
3-Methyl-5-(1-methyl-1H-imidazol-2-yl)-5-oxo-4-phenyl-
pentanenitrile (28): 48 h; yield: 45 mg (84%); dr=55:45;
colorless oil; Rf: 0.33 (petroleum ether/acetone 3:1);
1H NMR (300 MHz, CDCl3): d=7.46–7.39 (m, 2H), 7.33–
7.20 (m, 3H), 7.14 (s, 0.47H), 7.13 (s, 0.53H), 6.99 (s, 1H),
5.08 (d, J=11.2 Hz, 0.47H), 5.03 (d, J=10.8 Hz, 0.53H),
3.944 (s, 1.41H), 3.939 (s, 1.59H), 2.87–2.75 (m, 1H), 2.52
(dd, J=16.7 Hz, J=3.9 Hz, 0.53H), 2.34 (dd, J=16.7 Hz, J=
8.6 Hz, 0.53H), 2.23 (dd, J=16.7 Hz, J=3.8 Hz, 0.47H),
1.99 (dd, J=16.7 Hz, J=8.3 Hz, 0.47H), 1.23 (d, J=6.5 Hz,
1.41H), 0.98 (d, J=6.8 Hz, 1.41H); 13C NMR (75 MHz,
CDCl3): d=191.1, 190.8, 142.8, 142.7, 137.0, 136.7, 129.6,
129.5, 129.03, 128.99, 128.9, 128.7, 127.79, 127.76, 127.73,
127.45, 118.49, 118.36, 57.7, 57.6, 36.2, 33.2, 33.0, 23.2, 22.5,
18.4, 17.4; IR (film): n=3030, 2963, 1667, 1398, 738,
699 cmÀ1; MS (ESI): m/z=268.1 (M+H)+; HR-MS (ESI):
m/z=290.1253, calcd. for C16H17N3NaO [M+Na]+: 290.1264.
2-[3-(1-Methyl-1H-imidazol-2-yl)-3-oxo-1,2-diphenylpro-
pyl]malononitrile (29): 30 h; yield: 48 mg (68%); dr=70:30;
5-(1-Methyl-1H-imidazol-2-yl)-5-oxo-4-phenylpentanal
(31): 24 h; yield: 16 mg (31%); colorless oil; Rf: 0.34 (petro-
1
leum ether/ethyl acetate 1:1); H NMR (300 MHz, CDCl3):
d=9.71(s, 1H), 7.44–7.40 (m, 2H), 7.32–7.26 (m, 2H), 7.21–
7.18 (m, 1H), 7.13 (s, 1H), 6.99 (s, 1H), 5.18–5.13 (m, 1H),
3.95 (s, 3H), 2.49–2.17 (m, 4H); 13C NMR (75 MHz,
CDCl3): d=201.6, 191.8, 142.6, 138.3, 129.3, 128.7, 127.5,
127.2, 51.7, 41.8, 36.2, 25.1; IR (film): n=3030, 2959, 1718,
1670, 1400, 910, 728, 699 cmÀ1; MS (ESI): m/z=257.1 (M+
H)+; HR-MS (ESI): m/z=279.1100, calcd. for C15H16N2NaO2
[M+Na]+: 279.1104.
2-Methyl-5-(1-methyl-1H-imidazol-2-yl)-5-oxo-4-phenyl-
pentanal (32): 30 h; yield: 41 mg (80%); dr=55:45; colorless
oil; Rf: 0.50 (petroleum ether/ethyl acetate 1:1); 1H NMR
(300 MHz, CDCl3): d=9.62 (d, J=1.8 Hz, 0.65H), 9.57 (d,
J=1.4 Hz, 0.35H), 7.46–7.42 (m, 2H), 7.33–7.18 (m, 3H),
7.13 (s, 1H), 6.99 (s, 1H), 5.34–5.26 (m, 1H), 3.94 (s, 3H),
2.68–2.58 (m, 0.65H), 2.49–2.17 (m, 1.35H), 2.10–2.00 (m,
0.35H), 1.90–1.81 (m, 0.65H), 1.15–1.11 (m, 3H); 13C NMR
(75 MHz, CDCl3): d=204.1, 204.0, 191.65, 191.62, 142.6,
142.4, 138.8, 138.1, 129.4, 129.3, 128.73, 128.67, 128.64,
128.62, 127.5, 127.23, 127.15, 49.9, 49.8, 44.4, 44.2, 36.1, 33.5,
32.9, 13.8, 13.2; IR (film): n=3030, 2966, 1721, 1671, 1402,
700 cmÀ1; MS (ESI): m/z=271.1 (M+H)+; HR-MS (ESI):
m/z=293.1254, calcd. for C16H18N2NaO2 [M+Na]+:
293.1260.
3-Phenyl-5-(1-methyl-1H-imidazol-2-yl)-5-oxo-4-phenyl-
pentanal (33): 30 h; yield: 31 mg (47%); dr=85:15; colorless
oil. Major isomer: Rf: 0.49 (petroleum ether/ethyl acetate
1:1); 1H NMR (400 MHz, CDCl3): d=9.41–9.40 (m, 1H),
7.58 (d, J=7.2 Hz, 2H), 7.40–7.32 (m, 4H), 7.28–7.20 (m,
3H), 7.11 (t, J=7.2 Hz, 1H), 7.05 (s, 1H), 6.84 (s, 1H), 5.63
(d, J=12.0 Hz, 1H), 4.22–4.16 (m, 1H), 3.72 (s, 3H), 2.69–
2.62 (m, 1H), 2.50–2.45 (m, 1H); 13C NMR (100 MHz,
CDCl3): d=201.0, 190.5, 142.8, 141.8, 137.0, 129.3, 129.1,
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129.0, 128.5, 128.2, 127.7, 127.2, 126.8, 57.6, 48.4, 42.9, 36.0;
IR (film): n=3029, 2956, 1721, 1672, 1402, 701 cmÀ1; MS
(EI, 70 eV): m/z (%)=332 (37), 289 (39), 200 (89), 199
(100), 109 (40); HR-MS (ESI): m/z=355.1394, calcd. for
C21H20N2NaO2 [M+Na]+: 355.1417.
91 (100); HR-MS (ESI): m/z=425.1833, calcd. for
C25H26N2NaO3 [M+Na]+: 425.1836.
(E)-Benzyl 5-methyl-7-(1-methyl-1H-imidazol-2-yl)-7-oxo-
6-phenylhept-2-enoate (38): 30 h; yield: 17 mg (20%); dr=
60:40; colorless oil. Major isomer: Rf: 0.62 (petroleum
ether/ethyl acetate 1:1); 1H NMR (400 MHz, CDCl3): d=
7.44 (d, J=6.8 Hz, 2H), 7.37–7.27 (m, 7H), 7.19 (t, J=
7.6 Hz, 1H), 7.14 (s, 1H), 6.99 (s, 1H), 6.93–6.85 (m, 1H),
5.74 (d, J=15.6 Hz, 1H), 5.15 (s, 2H), 5.00 (d, J=11.2 Hz,
1H), 3.94 (s, 3H), 2.68–2.60 (m, 1H), 2.14–2.08 (m, 1H),
1.92–1.84 (m, 1H), 1.00 (d, J=6.8 Hz, 3H); 13C NMR
(100 MHz, CDCl3): d=192.3, 166.2, 148.0, 137.7, 136.1,
129.2, 128.7, 128.5,128.2, 128.1, 127.5, 127.3, 122.4, 66.0, 58.8,
36.8, 36.4, 35.5, 18.3; IR (film): n=2961, 1728, 1669, 1398,
1154, 696 cmÀ1; MS (EI, 70 eV): m/z (%)=402 (25), 227
(100), 199 (56), 109 (30), 91 (90); HR-MS (ESI): m/z=
425.1844, calcd. for C25H26N2NaO3 [M+Na]+: 425.1836.
5-Hydroxy-4,6-dimethyl-3-phenylbenzofuran-2(3H)-one
(39): Yield: 63 mg (62%); white solid; mp 133–1348C; Rf:
0.44 (petroleum ether/ethyl acetate 3:1); 1H NMR
(500 MHz, CDCl3): d=7.35–7.29 (m, 3H), 7.17 (d, J=
8.0 Hz, 2H), 6.84 (s, 1H), 4.78 (s, 1H), 4.52 (s, 1H), 2.30 (s,
3H), 1.90 (s, 3H); 13C NMR (125 MHz, CDCl3): d=175.7,
149.0, 147.4, 134.8, 129.1, 128.12, 128.10, 124.2, 124.0, 121.3,
110.0, 50.1, 16.5, 12.5; IR (film): n=3490, 3064, 3030, 1771,
1145, 1019, 700 cmÀ1; MS (EI, 70 eV): m/z (%)=254 (67),
225 (100), 105 (7); HR-MS (ESI): m/z=277.0830, calcd. for
C16H14NaO3 [M+Na]+: 277.0835.
1-(1-Methyl-1H-imidazol-2-yl)-2,3,5-triphenylpentane-1,5-
dione (34): 30 h; yield: 70 mg (86%); dr=60:40; colorless
oil; Rf: 0.59 (petroleum ether/ethyl acetate 1:1); 1H NMR
(300 MHz, CDCl3): d=7.85–7.81 (m, 1H), 7.68–7.62 (m,
2H), 7.50–6.92 (m, 13.51H), 6.78 (s, 0.49H), 5.74 (d, J=
12.0 Hz, 0.51H), 5.60 (d, J=11.6 Hz, 0.49H), 4.41–4.28 (m,
1H), 3.92 (s, 1.47H), 3.65 (s, 1.53H), 3.51 (dd, J=16.0 Hz,
J=9.9 Hz, 0.51H), 3.36–3.26 (m, 0.98H), 2.96 (dd, J=
16.4 Hz, J=3.2 Hz, 0.49H); 13C NMR (75 MHz, CDCl3): d=
198.5, 198.1, 191.8, 190.8, 143.2, 142.9, 142.3, 141.4, 137.4,
137.10, 137.07, 136.9, 132.7, 132.6, 129.43, 129.36, 129.3,
129.0, 128.8, 128.4, 128.34, 128.27, 128.1, 127.9, 127.8, 127.6,
127.5, 127.1, 126.7, 126.4, 126.2, 58.3, 57.5, 44.5, 44.1, 44.0,
43.4, 36.2, 35.8; IR (film): n=3029, 2958, 1670, 1399, 732,
697 cmÀ1; MS (ESI): m/z=409.2 (M+H)+; HR-MS (ESI):
m/z=431.1739, calcd. for C27H24N2NaO2 [M+Na]+:
431.1730.
3-[2-(1-Methyl-1H-imidazol-2-yl)-2-oxo-1-phenylethyl]cy-
clohexanone (35): 24 h; yield: 17 mg (29%); dr=90:10; col-
orless oil. Major isomer: Rf: 0.30 (petroleum ether/ethyl ace-
tate 1:1); 1H NMR (400 MHz, CDCl3): d=7.39 (d, J=
7.2 Hz, 2H), 7.29–7.25 (m, 2H), 7.20 (t, J=7.2 Hz, 1H), 7.15
(s, 1H), 7.01 (s, 1H), 5.10 (d, J=10.8 Hz, 1H), 3.95 (s, 3H),
2.79–2.69 (m, 1H), 2.38–2.33 (m, 1H), 2.30–2.22 (m, 1H),
2.11–2.03 (m, 2H), 1.99–1.96 (m, 2H), 1.76–1.66 (m, 1H),
1.52–1.46 (m, 1H); 13C NMR (100 MHz, CDCl3): d=211.1,
191.9, 143.1, 136.6, 129.4, 129.0, 128.8, 127.7, 127.4, 58.4,
45.5, 41.4, 41.3, 36.3, 30.2, 25.0; IR (film): n=3029, 2931,
1710, 1670, 1402, 700 cmÀ1; MS (EI, 70 eV): m/z (%)=296
(100), 225 (39), 200 (26), 109 (42), 82 (20); HR-MS (ESI):
m/z=319.1426, calcd. for C18H20N2NaO2 [M+Na]+:
319.1417.
1-(1-Methyl-1H-imidazol-2-yl)-2-phenyl-4-(phenylsulfo-
nyl)butan-1-one (36): 24 h; yield: 47 mg (64%); colorless
oil; Rf: 0.29 (petroleum ether/ethyl acetate 1:1); 1H NMR
(300 MHz, CDCl3): d=7.88–7.85 (m, 2H), 7.67–7.62 (m,
1H), 7.57–7.52 (m, 2H), 7.32–7.18 (m, 5H), 7.09 (s, 1H),
6.98 (s, 1H), 5.15 (dd, J=8.7 Hz, J=6.9 Hz, 1H), 3.91 (s,
3H), 3.15–2.93 (m, 2H), 2.47–2.25 (m, 2H); 13C NMR
(75 MHz, CDCl3): d=190.5, 142.2, 138.8, 137.2, 133.6, 129.4,
129.2, 128.8, 128.5, 128.1, 127.7, 127.5, 54.1, 50.8, 36.1, 25.5;
IR (film): n=3063, 2956, 1671, 1403, 1152, 739 cmÀ1; MS
(ESI): m/z=369.1 (M+H)+; HR-MS (ESI): m/z=391.1085,
calcd. for C20H20N2NaO3S [M+Na]+: 391.1087.
(E)-Benzyl 5-methyl-7-(1-methyl-1H-imidazol-2-yl)-7-oxo-
6-phenylhept-3-enoate (37): 30 h; yield: 33 mg (41%); dr=
55:45; colorless oil. Major isomer: Rf: 0.62 (petroleum
ether/ethyl acetate 1:1); 1H NMR (400 MHz, CDCl3): d=
7.38–7.29 (m, 7H), 7.22 (t, J=7.6 Hz, 2H), 7.16–7.12 (m,
2H), 6.99 (s, 1H), 5.44–5.29 (m, 2H), 5.05–5.02 (m, 3H),
3.94 (s, 3H), 3.18–3.10 (m, 1H), 2.94–2.82 (m, 2H), 1.10 (d,
J=6.8 Hz, 3H); 13C NMR (100 MHz, CDCl3): d=192.3,
171.6, 143.1, 137.9, 137.0, 135.9, 129.4, 128.5, 128.3, 128.13,
128.06, 127.5, 126.8, 121.9, 66.2, 58.5, 39.5, 38.0, 36.3, 19.0;
IR (film): n=2959, 1732, 1670, 1399, 1153, 696 cmÀ1; MS
(EI, 70 eV): m/z (%)=402 (31), 227 (78), 199 (52), 109 (33),
5-Hydroxy-4,7-dimethyl-3-phenylbenzofuran-2(3H)-one
(40): Yield: 61 mg (60%); white solid; mp 195–1968C; Rf:
0.44 (petroleum ether/ethyl acetate 3:1); 1H NMR
(300 MHz, CDCl3): d=7.38–7.31 (m, 3H), 7.20–7.16 (m,
2H), 6.63 (s, 1H), 4.80 (s, 1H), 4.69 (brs, 1H), 2.29 (s, 3H),
1.85 (s, 3H); 13C NMR (75 MHz, CDCl3): d=175.7, 150.5,
146.3, 134.7, 129.1, 128.1, 126.2, 119.1, 118.9, 116.8, 50.5,
14.8, 12.0; IR (film): n=3362, 2923, 1754, 1147, 704 cmÀ1
;
MS (EI, 70 eV): m/z (%)=254 (55), 225 (100); HR-MS
(ESI): m/z=277.0842, calcd. for C16H14NaO3 [M+Na]+:
277.0835.
5-Hydroxy-4-methyl-3-phenylnaphtho[1,2-b]furan-2(3H)-
one (41): Yield: 59 mg (51%); white solid; mp 145–1468C;
Rf: 0.42 (petroleum ether/ethyl acetate 3:1); 1H NMR
(400 MHz, CDCl3): d=8.19–8.17 (m, 1H), 8.02–7.99 (m,
1H), 7.57–7.55 (m, 2H), 7.35–7.33 (m, 3H), 7.20–7.18 (m,
2H), 5.07 (brs, 1H), 4.97 (s, 1H), 2.04 (s, 3H); 13C NMR
(100 MHz, CDCl3): d=175.8, 145.9, 143.5, 134.7, 129.2,
128.3, 128.2, 126.4, 126.3, 124.7, 121.7, 121.2, 121.1, 118.9,
113.6, 51.1, 12.3; IR (film): n=3417, 2924, 1784, 1699, 1049,
712 cmÀ1; MS (EI, 70 eV): m/z (%)=290 (38), 278 (95), 261
(76), 105 (100), 77 (45); HR-MS (ESI): m/z=313.0815,
calcd. for C19H14NaO3 [M+Na]+: 313.0835.
5-Hydroxy-3-(4-methoxyphenyl)-4,6-dimethylbenzofuran-
2(3H)-one (42): Yield: 75 mg (66%); white solid; mp 150–
1518C; Rf: 0.36 (petroleum ether/ethyl acetate 3:1);
1H NMR (400 MHz, CDCl3): d=7.08 (d, J=8.8 Hz, 2H),
6.87–6.82 (m, 3H), 4.73 (s, 1H), 4.58 (s, 1H), 3.79 (s, 3H),
2.30 (s, 3H), 1.90 (s, 3H); 13C NMR (100 MHz, CDCl3): d=
176.2, 159.3, 149.0, 147.3, 129.1, 126.8, 124.14, 124.12, 121.3,
114.5, 109.9, 55.2, 49.3, 16.5, 12.4; IR (film): n=3511, 2912,
1771, 1510, 1146, 1010, 780 cmÀ1; MS (EI, 70 eV): m/z (%)=
284 (84), 255 (100), 225 (89), 128 (10); HR-MS (ESI): m/z=
307.0934, calcd. for C17H16NaO4 [M+Na]+: 307.0941.
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FULL PAPERS
asc.wiley-vch.de
5-Hydroxy-4,6-dimethyl-3-(4-nitrophenyl)benzofuran-
Angew. Chem. 2013, 125, 12933; Angew. Chem. Int. Ed.
2013, 52, 12701; c) F. Zhong, X. Dou, X. Han, W. Yao,
Q. Zhu, Y. Meng, Y. Lu, Angew. Chem. 2013, 125, 977;
Angew. Chem. Int. Ed. 2013, 52, 943; d) T. Buyck, Q.
Wang, J. Zhu, Angew. Chem. 2013, 125, 12946; Angew.
Chem. Int. Ed. 2013, 52, 12714; e) T. Poisson, Y. Yama-
shita, S. Kobayashi, J. Am. Chem. Soc. 2010, 132, 7890;
f) M. Weber, S. Jautze, W. Frey, R. Peters, J. Am. Chem.
Soc. 2010, 132, 12222; g) B. M. Trost, J. Hitce, J. Am.
Chem. Soc. 2009, 131, 4572.
2(3H)-one (43): Yield: 38 mg (32%); white solid; mp 185–
1868C; Rf: 0.28 (petroleum ether/ethyl acetate 3:1);
1H NMR (400 MHz, CDCl3): d=8.22 (d, J=8.8 Hz, 2H),
7.39 (d, J=8.8 Hz, 2H), 6.88 (s, 1H), 4.92 (s, 1H), 4.55 (s,
1H), 2.33 (s, 3H), 1.90 (s, 3H); 13C NMR (100 MHz,
CDCl3): d=174.1, 149.2, 147.8, 147.4, 141.9, 129.1, 124.9,
124.3, 122.6, 121.3, 110.4, 49.7, 16.6, 12.8; IR (film): n=3444,
2915, 1775, 1515, 1348, 1156, 1014, 728 cmÀ1; MS (EI,
70 eV): m/z (%)=299 (100), 254 (35), 224 (89), 165 (7);
HR-MS (ESI): m/z=322.0685, calcd. for C16H13NNaO5 [M+
Na]+: 322.0686.
5-Hydroxy-4,6-dimethyl-3-(3-thienyl)benzofuran-2(3H)-
one (44): Yield: 47 mg (45%); white solid; mp 144–1458C;
Rf: 0.40 (petroleum ether/ethyl acetate 3:1); 1H NMR
(300 MHz, CDCl3): d=7.32 (dd, J=5.1 Hz, J=3.0 Hz, 1H),
7.11–7.10 (m, 1H), 6.93 (dd, J=5.1 Hz, J=1.2 Hz, 1H), 6.82
(s, 1H), 4.91 (s, 1H), 4.58 (s, 1H), 2.29 (s, 3H), 1.97 (s, 3H);
13C NMR (75 MHz, CDCl3): d=175.0, 149.0, 147.2, 143.3,
126.8, 126.7, 124.2, 123.8, 123.4, 121.3, 110.1, 45.5, 16.5, 12.4;
IR (film): n=3438, 3103, 2890, 1767, 1462, 1150, 1011,
781 cmÀ1; MS (EI, 70 eV): m/z (%)=260 (56), 231 (100),
217 (10); HR-MS (ESI): m/z=283.0391, calcd. for
C14H12NaO3S [M+Na]+: 283.0399.
[3] For selected reviews on catalytic asymmetric Michael re-
actions, see: a) C. Palomo, M. Oiarbide, J. M. Garcꢃa,
Chem. Soc. Rev. 2012, 41, 4150; b) B. Weiner, W. Szy-
´
manski, D. B. Janssen, A. J. Minnaard, B. L. Feringa,
Chem. Soc. Rev. 2010, 39, 1656; c) T. Jerphagnon, M. G.
Pizzuti, A. Minnaard, B. L. Feringa, Chem. Soc. Rev.
2009, 38, 1039; d) D. Enders, C. Wang, J. X. Liebich,
Chem. Eur. J. 2009, 15, 11058; e) A. Alexakis, J.-E.
Bꢁckvall, N. Krause, O. Pꢄmies, M. Diꢅguez, Chem. Rev.
2008, 108, 2796; f) S. R. Harutyunyan, T. Den Hartog, K.
Geurts, A. J. Minnaard, B. L. Feringa, Chem. Rev. 2008,
108, 2824; g) J. L. Vicaris, D. Badꢃa, L. Carrillo, Synthesis
2007, 2065; h) T. Hayashi, K. Yamasaki, Chem. Rev.
2003, 103, 2829; i) N. Krause, A. Hoffmann-Rçder, Syn-
thesis 2001, 2001, 171; j) M. P. Sibi, S. Manyem, Tetrahe-
dron 2000, 56, 8033; k) B. E. Rossiter, N. M. Swingle,
Chem. Rev. 1992, 92, 771.
2-(3,6-Dihydroxy-2,4-dimethylphenyl)-1-(1-methyl-1H-
imidazol-2-yl)-2-phenylethanone (46): Yield: 54 mg (80%);
light yellow solid; mp 138–1398C; Rf: 0.08 (petroleum ether/
1
ethyl acetate 3:1); H NMR [500 MHz, (CD3)2CO]: d=9.11
[4] For selected examples of asymmetric Michael reactions,
see: a) T. Kano, H. Sugimoto, H. Maruyama, K. Maruo-
ka, Angew. Chem. 2015, 127, 8582; Angew. Chem. Int.
Ed. 2015, 54, 8462; b) A. D. Gammack Yamagata, S.
Datta, K. E. Jackson, L. Stegbauer, R. S. Paton, D.
Dixon, Angew. Chem. 2015, 127, 4981; Angew. Chem.
Int. Ed. 2015, 54, 4899; c) P. Lu, J. J. Jackson, J. A.
Eickhoff, A. Zakarian, J. Am. Chem. Soc. 2015, 137,
656; d) K. S. Yang, A. E. Nibbs, Y. E. Tꢀrkmen, V. H.
Rawal, J. Am. Chem. Soc. 2013, 135, 16050; e) T. Kano,
F. Shirozu, M. Akakura, K. Maruoka, J. Am. Chem. Soc.
2012, 134, 16068.
(brs, 1H), 7.41 (s, 1H), 7.31–7.20 (m, 5H), 7.11 (s, 1H), 6.71
(brs, 1H), 6.63 (s, 1H), 6.59 (s, 1H), 4.06 (s, 3H), 2.18 (s,
3H), 2.16 (s, 3H); 13C NMR [125 MHz, (CD3)2CO]: d=
191.5, 149.8, 148.1, 144.3, 139.6, 129.5, 128.9, 128.8, 128.7,
127.0, 126.3, 125.9, 124.0, 118.4, 52.8, 36.4, 16.8, 13.8; IR
(film): n=3313, 2920, 1688, 1401, 1210, 1034, 739 cmÀ1; MS
(EI, 70 eV): m/z (%)=336 (4), 254 (57), 225 (100), 82 (19);
HR-MS (ESI): m/z=337.1538, calcd. for C20H21N2O3 [M+
H]+: 337.1547.
[5] For selected examples of iron-catalyzed conjugate addi-
tion reactions, see: a) J. D. White, S. Shaw, Chem. Sci.
2014, 5, 2200; b) H. Li, X. Xu, J. Yang, X. Xie, H.
Huang, Y. Li, Tetrahedron Lett. 2011, 52, 530; c) G.
Chai, Z. Lu, C. Fu, S. Ma, Adv. Synth. Catal. 2009, 351,
1946; d) M. Fujiwara, M. Kawatsura, S. Hayase, M.
Nanjo, T. Itoh, Adv. Synth. Catal. 2009, 351, 123; e) J.
Christoffers, H. Frey, Chimica Oggi/Chem. Today 2008,
26, 26; f) Z. Lu, G. Chai, S. Ma, J. Am. Chem. Soc. 2007,
129, 14546: g) M. Bauer, T. Kauf, J. Christoffers, H. Ber-
tagnolli, Phys. Chem. Chem. Phys. 2005, 7, 2664; h) S.
Pelzer, T. Kauf, C. van Wꢀllen, J. Christoffers, J. Orga-
nomet. Chem. 2003, 684, 308; i) J. Christoffers, Chem.
Commun. 1997, 943.
[6] a) J. E. M. N. Klein, B. Miehlich, M. S. Holzwarth, M.
Bauer, M. Milek, M. Khusniyarov, G. Knizia, H.-J.
Werner, B. Plietker, Angew. Chem. 2014, 126, 1820;
Angew. Chem. Int. Ed. 2014, 53, 1790; b) C.-H. Lin, D.
Pursley, J. E. M. N. Klein, J. Teske, J. Allen, F. Rami, A.
Kçhn, B. Plietker, Chem. Sci. 2015, 6, 7034;
c) J. E. M. N. Klein, G. Knizia, B. Miehlich, J. Kꢁstner,
B. Plietker, Chem. Eur. J. 2014, 20, 7254; d) A. P. Die-
skau, M. S. Holzwarth, B. Plietker, J. Am. Chem. Soc.
Acknowledgements
Financial support by the Alexander von Humboldt-founda-
tion (postdoc fellowship for D.Z.) is gratefully acknowl-
edged.
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12 Iron-Catalyzed Michael Addition of Ketones to Polar
Olefins
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Di-Han Zhang, Jakob Knelles, Bernd Plietker*
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These are not the final page numbers!