Synthesis of Ferrocene-Based Pyridinones through Rh(III)-Catalyzed Direct C-H Functionalization Reaction

Article abstract of DOI:10.1021/acs.organomet.6b00020

Synthesis of ferrocene-based pyridinones via Rh(III)-catalyzed annulation of ferrocenecarboxamides with internal alkynes has been developed using a directing group as the internal oxidant. This method displays good functional group tolerance and delivers ferrocene-based pyridinones generally in moderate to good yields. Additionally, an asymmetric reaction can be achieved in the presence of a chiral catalyst Rh1.

Full text of DOI:10.1021/acs.organomet.6b00020

Article
pubs.acs.org/Organometallics
Synthesis of Ferrocene-Based Pyridinones through Rh(III)-Catalyzed
Direct C−H Functionalization Reaction
Shao-Bo Wang,† Jun Zheng,‡ and Shu-Li You*,†,‡
†School of Physical Science and Technology, ShanghaiTech University, 100 Haike Road, Shanghai 201210, China
‡State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345
Lingling Lu, Shanghai 200032, China
S
* Supporting Information
ABSTRACT: Synthesis of ferrocene-based pyridinones via
Rh(III)-catalyzed annulation of ferrocenecarboxamides with
internal alkynes has been developed using a directing group as
the internal oxidant. This method displays good functional
group tolerance and delivers ferrocene-based pyridinones
generally in moderate to good yields. Additionally, an
asymmetric reaction can be achieved in the presence of a
chiral catalyst Rh1.
INTRODUCTION
■
Ferrocene derivatives, because of their unique structural and
electronic character, have been extensively used in organic
synthesis, materials science, and medicinal chemistry.1 Partic-
ularly, ferrocenes with planar chirality have drawn considerable
attention in asymmetric catalysis as either ligands or catalysts.2
To date, the notable strategies to construct planar chirality
include diastereoselective directed ortho-metalation (DoM),3
enantioselective DoM,4 and resolution of racemic substrates.5
In these cases, a preinstalled chiral auxiliary, a stoichiometric
amount of external chiral base, or chiral resolution reagents
were required. In addition, the methods to introduce functional
Figure 1. Synthesis of ferrocene-based pyridinones.
groups into the Cp ring rely mainly on lithiation/quenching
with electrophiles. Therefore, to access the planar chiral
ferrocene derivatives by efficient, catalytic methods has been
group on nitrogen, which facilitates the further transformation.
Moreover, the introduction of chiral Cp ligands14 might be able
to provide enantioselective control. Herein, we report a Rh-
catalyzed external oxidant free annulation of ferrocenecarbox-
amides with internal alkynes via direct C−H bond function-
alization (Figure 1, eq 2).
a longstanding challenge.6
Recently, transition metal-catalyzed asymmetric C−H bond
functionalization has been applied for constructing planar
chirality into the ferrocene backbone.7,8 Most of these studies
were achieved through palladium-catalyzed asymmetric C−H
bond functionalization reported by our group7e−h and others,
such as Cui and Wu,7c,d Kang and Gu,7j,k and Liu and Zhao,7l
respectively. In 2014, Wang and co-workers reported an elegant
Pd-catalyzed annulation of ferrocenecarboxamides with internal
alkynes using stoichiometric copper acetate and air as the
terminal oxidants, affording ferrocene derived pyridinones
(Figure 1, eq 1).8f Notably, N-methoxy hydroxamic acid was
first introduced as a directing group in C−H activation by Yu9
and was discovered capable as an internal oxidant independ-
ently by Fagnou10 and Glorius.11 Inspired by previous works12
and based on our recent development on rhodium-catalyzed
C−H bond functionalization reactions,13 we decided to study
the C−H bond activation/annulation reaction toward ferrocene
substrates bearing an internal oxidant group by employing a Rh
catalyst. The resulting pyridinone products have no protecting
RESULTS AND DISCUSSION
■
Optimization of the Reaction Conditions. Initially, N-
methoxy ferrocenecarboxamide (1a) and 1-phenyl-1-propyne
(2a) were chosen as the model substrates to optimize the
reaction conditions. As shown in Table 1, in the presence of 2.5
mol % of [RhCp*Cl2]2 and 2.0 equiv of NaOAc, the reaction of
1a (0.2 mmol) with 2a (1.6 equiv) in MeOH at 40 °C afforded
the annulated product (3aa) in 25% NMR yield (Table 1, entry
1). The structure of 3aa was confirmed by X-ray crystallo-
Special Issue: Organometallics in Asia
Received: January 13, 2016
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.6b00020
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a
a
Table 1. Optimization of Reaction Conditions
Table 2. Substrate Scope of Alkynes
b
b
Entry T (°C)
Base (x equiv)
Solvent
Conv (%)
Yield (%)
1
2
3
4
5
6
40
60
80
60
60
60
NaOAc (2.0)
NaOAc (2.0)
NaOAc (2.0)
Cu(OAc)2 (2.0)
NaOAc (0.6)
NaOAc (0.6)
Et3N (1.0)
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
48
49
61
-
25
30
24
trace
27
43
73
51
7
60
60
60
60
60
60
60
60
60
NaOAc (0.6)
Et3N (1.0)
DMF
CH3CN
PhMe
THF
47
17
<5
24
20
95
95
90
--
<5
12
--
8
NaOAc (0.6)
Et3N (1.0)
9
NaOAc (0.6)
Et3N (1.0)
10
11
12
13
14
15
NaOAc (0.6)
Et3N (1.0)
6
a
NaOAc (0.6)
Et3N (1.0)
dioxane
TFE
6
Conditions: 1a (0.3 mmol), 2 (1.6 equiv), [RhCp*Cl2]2 (2.5 mol %),
NaOAc (0.6 equiv), Et3N (1.0 equiv), TFE (1.5 mL), 60 °C. Yields of
b
c
isolated products are reported. [RhCp*Cl2]2 (5 mol %).
NaOAc (0.6)
Et3N (1.0)
91 (77 )
c
NaOAc (0.6)
Et3N (1.5)
TFE
(78 )
to the steric effect. With methoxy or free hydroxyl group-
containing 1-phenylalkynes 2e−f, good yields ranging from
80% to 85% were obtained. 2-(1-Propynyl)thiophene (2g) was
also a suitable substrate, giving product in 63% yield in the
presence of 5 mol % of [RhCp*Cl2]2. However, 2-(1-
propynyl)pyridine (2h) was ineffective under the present
reaction conditions. Substituted phenylpropynes, with electron-
donating groups at the para- or meta-position (2i, 2j, 2k, 2n) of
benzene ring, could proceed smoothly in good yields (76−
82%), whereas the reactivity of this reaction deceased in the
cases of 2l and 2m bearing electron-withdrawing groups. A
slightly lower yield (55%) was resulted for substrate 2p, likely
due to steric hindrance caused by 2-methyl group. Notably, for
all these unsymmetrical alkynes, excellent regioselectivity was
observed. The alkyl-substituted terminal of alkynes is
exclusively attached to the ferrocene moiety. Based on previous
DFT studies on related reactions,15 the regioselectivity is
established during the alkyne insertion step, and the intrinsic
electronic and steric bias of unsymmetrical alkynes contributes
significantly. Finally, alkyne 2q could also react under enhanced
conditions by increasing the reaction temperature (70 °C).
Unfortunately, terminal alkynes were not tolerated, with no
expected products being isolated.
Besides 1a, various substituted ferrocenecarboxamides (1b−
1h) were also tested under the optimized conditions with 2a.
The results are summarized in Table 3. The reactions of
substrates 1b-1f gave desired products with good yields (74−
95%) regardless of their electronic properties. For substrate 1g
bearing two directing groups at both Cp rings, monoannulated
compound 3ga was obtained as the sole product with 3.2 equiv
of 2a. Interestingly, for 1h bearing a pentamethyl Cp ring, the
reaction could also proceed well to give 3ha in 43% yield in the
presence of 5 mol % of [RhCp*Cl2]2.
c
NaOAc (0.6)
Et3N (0.6)
TFE
(78 )
d
c
NaOAc (0.6)
Et3N (1.0)
TFE
(82 )
a
Conditions: 1a (0.2 mmol), 2a (1.6 equiv), [RhCp*Cl2]2 (2.5 mol
b
1
%), bases (x equiv), solvent (1.0 mL), 40−80 °C. Detected by H
NMR integration methods with CH2Br2 as an internal standard.
c
d
Isolated yield. 1a (0.3 mmol) was used. TFE = CF3CH2OH.
graphic analysis (Table 2, see the Supporting Information for
details). The yield was slightly improved when temperature was
elevated to 60 °C. However, further increase of temperature did
not provide a better result (Table 1, entry 3). When 2.0 equiv
of Cu(OAc)2 were used, only trace amount of product 3aa was
detected (Table 1, entry 4). Decreasing the amount of NaOAc
from 2.0 equiv to 0.6 equiv, no notable effect on the reaction
outcome was observed (Table 1, entry 5). To our delight, when
the combination of NaOAc (0.6 equiv) and Et3N (1.0 equiv)
was employed, 51% NMR yield could be achieved (Table 1,
entry 6). After screening the solvents (Table 1, entries 7−12),
CF3CH2OH was found to be the optimized one, in which 77%
isolated yield was obtained (Table 1, entry 12). Changing the
amount of Et3N had no deleterious effect on the yield (Table 1,
entries 13−14). When the reaction was performed in 0.3 mmol
scale, the yield of 3aa was increased to 82% (Table 1, entry 15).
Thus, the optimal reaction conditions were obtained as the
following: [RhCp*Cl2]2 (2.5 mol %), NaOAc (0.6 equiv), Et3N
(1.0 equiv), CF3CH2OH (0.2 M) at 60 °C.
Substrate Scope. With the optimized reaction conditions
in hand, we then explored the substrate scope. As summarized
in Table 2, 1-phenylalkynes 2a−c reacted with 1a, smoothly
affording their desired products in good yields (79−84%). For
cyclopropyl substituted alkyne (2d), 5 mol % [RhCp*Cl2]2 was
required to ensure a reasonable yield (3ad, 74%), probably due
Synthetic Application. To demonstrate the practicality of
the methodology, a gram-scale reaction was carried out
(Scheme 1, eq 1). Reaction of ferrocenecarboxamide 1b on a
B
DOI: 10.1021/acs.organomet.6b00020
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a
is needed to realize an efficient asymmetric reaction, these
preliminary results provide a proof of concept for an
asymmetric reaction.
Table 3. Substrate Scope of Ferrocenecarboxamide
Mechanistic Study. To probe the reaction mechanism, a
series of deuteration experiments were carried out. First, 1a was
conducted in d4-CH3OH without alkyne at room temperature
(Scheme 3, eq 1). The deuteration was incorporated exclusively
Scheme 3. Deuteration Experiments for the Mechanistic
Study
a
Conditions: 1 (0.3 mmol), 2a (1.6 equiv), [RhCp*Cl2]2 (2.5 mol %),
NaOAc (0.6 equiv), Et3N (1.0 equiv), TFE (1.5 mL), 60 °C. Yields of
b
isolated products are reported. [RhCp*Cl2]2 (5 mol %) and 0.1
mmol scale.
Scheme 1. Gram Scale Synthesis of 3ba and Transformation
of 3aa
at the ortho position of the directing group after 24 h. When
the reaction of 1a-d2 with 2a under standard conditions was
quenched after 8 min, partially deuterated product and 1a-d2
with decreased deuteration ratio were obtained (Scheme 3, eq
2). These results suggested that the C−H bond activation step
might be reversible with or without the alkyne, which was
distinct from the results reported by Rovis16 and Fagnou
groups.10 In their works, the cyclometalation step is largely
irreversible in the presence of alkynes. Then we further
conducted a parallel experiment using 1a and 1a-d2,
respectively, under standard reaction conditions, the lack of
kinetic isotope effect (kH/D = 1.04) indicated the C−H bond
cleavage should not be involved in the rate-determining step
(Scheme 3, eq 3).
2.7 mmol scale with 2a gave 3ba in 93% yield. The product 3aa
could be converted to trifluoromethanesulfonate in the
presence of 1.8 equiv of Tf2O and 3.0 equiv of Et3N, and
then ferrocene[1,2-c]pyridine 4aa could be obtained under
reductive coupling conditions in 61% total yield (Scheme 1, eq
2). This method leads to a facile synthetic route for planar
chiral ferrocenylpyridine, which could be potential organo-
catalyst or ligand for various transition metals.
Asymmetric Reaction Investigation. A preliminary
investigation for enantioselective annulation of ferrocenecar-
boxamide with alkyne was conducted by using a chiral Rh1
catalyst (Scheme 2). The desired product 3aa was obtained in
moderate enantioselectivity (46% ee) and yield (37%).
Although further optimization of the catalysts and conditions
CONCLUSION
■
In conclusion, we have developed a Rh(III)-catalyzed C−H
bond functionalization/annulation of ferrocenecarboxamides
with internal alkynes using a directing group as an internal
oxidant. Various substituted groups can be tolerated on alkynes
and ferrocenecarboxamides. Importantly, an enantioselective
reaction could also be achieved in the presence of a chiral Rh
complex (Rh1), providing planar chiral ferrocene in moderate
enantioselectivity. Further mechanistic investigations and the
development of a more efficient asymmetric catalytic system are
currently underway in our laboratory.
Scheme 2. Enantioselective Synthesis of 3aa
EXPERIMENTAL SECTION
■
General Procedure for the Synthesis of Ferrocene-Based
Pyridinones. The N-methoxy ferrocenecarboxamide 1 (0.3 mmol, 1.0
equiv), alkyne (1.6 equiv), [Cp*RhCl2]2 (4.6 mg, 2.5 mol %) and
NaOAc (14.8 mg, 0.18 mmol) were added in a sealed tube with a
stirring bar. To this tube was added TFE (1.5 mL) and followed
immediately by Et3N (41.7 μL, 0.3 mmol). Then the resulting mixture
C
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was stirred at 60 °C. After the reaction was complete (monitored by
TLC), the reaction mixture was diluted with EtOAc and filtered
through a short pad of silica gel. Volatiles were evaporated under
reduced pressure. The residue was purified by column chromatog-
raphy on silica gel (ethyl acetate/petroleum ether =1/3, v/v).
Compound 3aa. Red solid, mp = 157−159 °C, 84.4 mg, 82% yield.
1H NMR (400 MHz, CDCl3) δ 7.94 (br s, 1H), 7.53−7.33 (m, 5H),
5.17 (d, J = 1.6 Hz, 1H), 4.79 (d, J = 1.2 Hz, 1H), 4.39 (t, J = 2.4 Hz,
1H), 4.07 (s, 5H), 2.17 (s, 3H); 13C NMR (100 MHz, CDCl3) δ
169.1, 135.4, 132.3, 128.74, 128.7, 128.5, 110.2, 90.7, 71.6, 71.5, 69.7,
65.5, 64.7, 14.2; IR (thin film): νmax (cm−1) = 3290, 3204, 3097, 3057,
1638, 1333, 1304, 1172, 1000, 840, 815, 777, 706; HRMS (ESI) calcd
for C20H1856FeNO [M + H]+: 344.0732; Found: 344.0732.
Compound 3ab. Red solid, mp = 154−156 °C, 89.7 mg, 84% yield.
1H NMR (400 MHz, CDCl3) δ 8.02 (br s, 1H), 7.52−7.35 (m, 5H),
5.16 (s, 1H), 4.81 (s, 1H), 4.40 (s, 1H), 4.06 (s, 5H), 2.67−2.37 (m,
2H), 1.33 (m, 3H); 13C NMR (100 MHz, CDCl3) δ 169.0, 135.5,
132.6, 128.7, 128.6, 128.5, 116.1, 89.8, 71.6, 71.5, 69.9, 65.1, 64.8 22.0,
15.1; IR (thin film): νmax (cm−1) = 2961, 1644, 1495, 1334, 1297,
1173, 1000, 816, 763, 698; HRMS (ESI) calcd for C21H2056FeNO [M
+ H]+: 358.0889; Found: 358.0888.
90.8, 71.4, 69.6, 65.3, 64.5, 21.2, 14.1; IR (thin film): νmax (cm−1) =
2919, 1643, 1514, 1331, 1301, 1172, 1000, 817, 727; HRMS (ESI)
calcd for C21H2056FeNO [M + H]+: 358.0889; Found: 358.0889.
Compound 3aj. Red solid, mp = 191 °C (decomposed), 85.6 mg,
76% yield. 1H NMR (400 MHz, CDCl3) δ 7.70 (br s, 1H), 7.31 (d, J =
8.8 Hz, 2H), 6.99 (d, J = 8.4 Hz, 2H), 5.17 (d, J = 1.2 Hz, 1H), 4.77
(d, J = 1.2 Hz, 1H), 4.39 (t, J = 2.4 Hz, 1H), 4.07 (s, 5H), 3.87 (s,
3H), 2.16 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 169.1, 159.7,
132.1, 130.0, 127.8, 114.1, 109.8, 91.0, 71.5, 69.7, 65.5, 64.6, 55.4, 14.2;
IR (thin film): νmax (cm−1) = 3170, 3079, 2956, 2927, 2858, 1643,
1512, 1304, 1245, 1184, 1027, 809, 676; HRMS (ESI) calcd for
C21H2056FeNO2 [M + H]+: 374.0838; Found:374.0837.
Compound 3ak. Red solid, mp = 160 °C (decomposed), 89.1 mg,
82% yield. 1H NMR (400 MHz, CDCl3) δ 8.34 (br s, 1H), 7.44−7.31
(m, 2H), 7.23−1.08 (m, 2H), 5.15 (s, 1H), 4.78 (s, 1H), 4.39 (s, 1H),
4.05 (s, 5H), 2.14 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 169.3,
162.5 (d, J = 247.5 Hz), 131.5, 131.4 (d, J = 3.4 Hz), 130.7 (d, J = 8.2
Hz), 115.7 (d, J = 21.5 Hz), 110.4, 90.6, 71.6, 69.7, 65.5, 64.7, 14.1; 19F
NMR (376 Hz, CDCl3) δ −112.3 (m); IR (thin film): νmax (cm−1) =
3929, 3167, 1633, 1510, 1332, 1303, 1219, 1163, 1003, 847, 816, 730,
675; HRMS (ESI) calcd for C20H17F56FeNO [M + H]+: 362.0638;
Found: 362.0637.
Compound 3ac. Yellow solid, mp = 138−139 °C, 91.4 mg, 79%
1
Compound 3al. Red solid, mp = 204 °C (decomposed), 60 mg,
46% yield. 1H NMR (400 MHz, CDCl3) δ 8.55 (br s, 1H), 7.59 (d, J =
8.4 Hz, 2H), 7.28 (d, J = 8.0 Hz, 2H), 5.14 (s, 1H), 4.78 (s, 1H), 4.39
(t, J = 2.4 Hz, 1H), 4.04 (s, 5H), 2.15 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ 169.4, 134.1, 131.8, 131.3, 130.5, 122.6, 110.8, 90.4, 71.7,
69.7, 65.6, 64.7, 14.2; IR (thin film): νmax (cm−1) = 3034, 1639, 1492,
1332, 1305, 1173, 1105, 1070, 1002, 814, 723; HRMS (ESI) calcd for
C20H17Br56FeNO [M + H]+: 421.9837; Found: 421.9837.
yield. H NMR (400 MHz, CDCl3) δ 7.95 (br s, 1H), 7.49−7.34 (m,
5H), 5.18−5.13 (m, 1H), 4.81−4.75 (m, 1H), 4.40 (t, J = 2.4 Hz, 1H),
4.06 (s, 5H), 2.57−2.38 (m, 2H), 1.84−1.58 (m, 2H), 1.40−1.27 (m,
2H), 0.89 (t, J = 7.6 Hz, 3H); 13C NMR (100 MHz, CDCl3) δ 169.0,
135.6, 132.8, 128.63, 128.6, 115.0, 90.1, 71.6, 69.9, 65.0, 64.9, 32.5,
28.4, 22.8, 13.8; IR (thin film): νmax (cm−1) = 2926, 1645, 1494, 1335,
1300, 1172, 1000, 817, 770, 698; HRMS (ESI) calcd for
C23H2456FeNO [M + H]+: 386.1202; Found: 386.1202.
Compound 3am. Red solid, mp =178 °C (decomposed), 20.4 mg,
17% yield. 1H NMR (400 MHz, CDCl3) δ 8.19 (br s, 1H), 8.14 (d, J =
7.6 Hz, 2H), 7.49 (d, J = 8.0 Hz, 2H), 5.18 (s, 1H), 4.81 (s, 1H), 4.42
(s, 1H), 4.07 (s, 5H), 3.97 (s, 3H), 2.19 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ 169.2, 166.4, 139.7, 131.3, 130.0, 129.9, 128.9, 111.5, 90.3,
71.8, 71.6, 69.8, 65.8, 65.0, 52.3, 14.2; IR (thin film): νmax(cm−1) =
3171, 1716, 1637, 1432, 1275, 1180, 1102, 815, 777, 715, 650; HRMS
(ESI) calcd for C22H2056FeNO3 [M + H]+: 402.0787; Found:
402.0787.
Compound 3an. Red solid, mp = 176 °C (decomposed), 84.6 mg,
79% yield. 1H NMR (400 MHz, CDCl3) δ 8.18 (br s, 1H), 7.33 (t, J =
8.0 Hz, 1H), 7.24−7.16 (m, 3H), 5.15 (d, J = 1.6 Hz, 1H), 4.77 (d, J =
1.6 Hz, 1H), 4.37 (t, J = 2.8 Hz, 1H), 4.05 (s, 5H), 2.42 (s, 3H), 2.17
(s, 3H); 13C NMR (100 MHz, CDCl3) δ 169.1, 138.3, 135.2, 132.5,
129.3, 129.1, 128.4, 125.9, 109.9, 90.8, 71.5, 71.4, 69.6, 65.4, 64.5, 21.4,
14.1; IR (thin film): νmax (cm−1) = 3168, 3099, 3030, 2902, 1644,
1493, 1439, 1334, 1307, 1174, 1131, 1000, 819, 786, 710, 667; HRMS
(ESI) calcd for C21H2056FeNO [M + H]+: 358.0889; Found: 358.0889.
Compound 3ao. Red foam, 90.0 mg, 71% yield with 5 mol %
[RhCp*Cl2]2. 1H NMR (400 MHz, CDCl3) δ 8.29 (br s, 1H), 7.57 (s,
2H), 7.34 (d, J = 3.2 Hz, 2H), 5.18 (s, 1H), 4.79 (s, 1H), 4.40 (s, 1H),
4.07 (s, 5H), 2.18 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 169.4,
137.1, 131.9, 131.3, 131.03, 131.0, 127.7, 122.4, 111.0, 90.3, 71.6, 69.6,
65.6, 64.7, 14.1; IR (thin film): νmax (cm−1) = 2921, 1643, 1590, 1485,
1331, 1298, 1172, 998, 817, 787, 726, 659; HRMS (ESI) calcd for
C20H1779Br56FeNO [M + H]+: 421.9837; Found: 421.9838.
Compound 3ad. Red solid, mp = 167 °C (decomposed), 82.5 mg,
74% yield with 5 mol % [RhCp*Cl2]2. 1H NMR (400 MHz, CDCl3) δ
7.99 (br s, 1H), 7.54−7.35 (m, 5H), 5.15 (s, 1H), 5.00 (s, 1H), 4.40
(s, 1H), 4.05 (s, 5H), 1.93−1.76 (m, 1H), 0.77−0.65 (m, 2H), 0.53−
0.41 (m, 1H), 0.33−0.16 (m, 1H); 13C NMR (100 MHz, CDCl3) δ
169.2, 135.7, 134.7, 128.6, 128.4, 128.37, 114.7, 90.9, 71.6, 71.1, 70.0,
65.5, 65.0, 10.2, 7.6, 7.2; IR (thin film): νmax (cm−1) = 3052, 1644,
1495, 1329, 1216, 1012, 828, 807, 773, 703, 673; HRMS (ESI) calcd
for C22H2056FeNO [M + H]+: 370.0889; Found: 370.0888.
1
Compound 3ae. Red foam, 95.7 mg, 85% yield. H NMR (400
MHz, CDCl3) δ 8.47 (br s, 1H), 7.53−7.41 (m, 5H), 5.12 (s, 1H),
4.92 (s, 1H), 4.40 (s, 1H), 4.35 (d, JAB = 10.8 Hz, 1H), 4.19 (d, JBA
=
10.8 Hz, 1H), 4.05 (s, 5H), 3.38 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ 169.6, 136.5, 134.4, 129.0, 128.60, 128.58, 111.2, 89.3, 71.9,
71.2, 69.9, 69.0, 65.2, 65.1, 57.9; IR (thin film): νmax (cm−1) = 3189,
2924, 2893, 1893, 1646, 1495, 1335, 1296, 1169, 1081, 816, 772, 700;
HRMS (ESI) calcd for C21H2056FeNO2 [M + H]+: 374.0838; Found:
374.0837.
Compound 3af. Red solid, mp = 181 °C (decomposed), 86.0 mg,
80% yield with 5 mol % [RhCp*Cl2]2. 1H NMR (400 MHz, CD3OD)
δ 7.54−7.47 (m, 5H), 5.16−5.10 (m, 2H), 4.60 (d, JAB = 11.6 Hz, 1H),
4.51 (t, J = 2.8 Hz, 1H), 4.39 (d, JBA = 11.6 Hz, 1H), 4.10 (s, 5H); 13
C
NMR (100 MHz, CD3OD) δ 172.6, 137.5, 135.7, 130.4, 130.0, 129.6,
115.8, 90.9, 79.5, 73.4, 72.5, 71.1, 66.8, 65.8, 59.6; IR (thin film): νmax
(cm−1) = 3402, 3194, 1644, 1299, 1002, 803, 774, 703; HRMS (ESI)
calcd for C20H1856FeNO2 [M + H]+: 360.0681; Found: 360.0681;
Compound 3ag. Red solid, mp = 161 °C (decomposed), 66.1 mg,
63% yield with 5 mol % [RhCp*Cl2]2. 1H NMR (400 MHz, CDCl3) δ
8.15 (br s, 1H), 7.41 (d, J = 4.8 Hz, 1H), 7.18 (d, J = 3.2 Hz, 1H), 7.12
(dd, J = 4.0, 3.6 Hz, 1H), 5.17 (d, J = 1.2 Hz, 1H), 4.78 (d, J = 1.2 Hz,
1H), 4.39 (t, J = 2.4 Hz, 1H), 4.05 (s, 5H), 2.29 (s, 3H); 13C NMR
(100 MHz, CDCl3) δ 168.9, 136.3, 127.4, 127.2, 126.4, 125.7, 112.3,
90.1, 71.7, 71.5, 69.7, 65.8, 65.0, 14.5; IR (thin film): νmax (cm−1) =
3918, 2919, 1643, 1330, 1296, 1171, 997, 843, 809, 727, 657; HRMS
(ESI) calcd for C18H1656FeNOS [M + H]+: 350.0297; Found:
350.0297.
Compound 3ap. Red solid, mp = 194 °C (decomposed), 59.4 mg,
1
55% yield. Two rotamers were observed by NMR. H NMR (400
MHz, CDCl3) δ 7.81 (br s, 1H), 7.43−7.11 (m, 4H), 5.17 (s, 1H),
4.77 (s, 1H), 4.38 (s, 1H), 4.12 and 4.08 (s, 5H), 2.31 and 2.22 (s,
3H), 1.94 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 169.0, 136.9,
126.2, 134.6, 131.9, 131.8, 130.4, 130.3, 129.7, 129.0, 128.9, 126.0,
125.9, 110.4, 90.6, 90.4, 71.7, 71.3, 71.2, 69.7, 69.3, 65.5, 65.4, 64.4,
64.2, 19.5, 19.3, 13.6; IR (thin film): νmax (cm−1) = 3158, 3025, 1646,
1497, 1334, 1305, 1176, 1105, 999, 818, 766, 730, 689; HRMS (ESI)
calcd for C21H2056FeNO [M + H]+: 358.0889; Found: 358.0889.
1
1
Compound 3ai. Red foam, 87.8 mg, 82% yield. H NMR (400
Compound 3aq. Red foam, 22.1 mg, 30% yield. H NMR (400
MHz, CDCl3) δ 7.97 (br s, 1H), 7.38−7.21 (m, 4H), 5.16 (s, 1H),
4.77 (s, 1H), 4.37 (s, 1H), 4.05 (s, 5H), 2.41 (s, 3H), 2.17 (s, 3H); 13C
NMR (100 MHz, CDCl3) δ 169.2, 138.3, 132.4, 129.2, 128.5, 109.8,
MHz, CDCl3) δ 8.36 (br s, 1H), 5.09 (s, 1H), 4.69 (s, 1H), 4.32 (s,
1H), 3.99 (s, 5H), 2.58−2.30 (m, 4H), 1.76−1.53 (m, 4H), 1.44 (m,
4H), 1.03−0.98 (t, J = 7.2 Hz, 3H), 0.98−0.93 (t, J = 7.2 Hz, 3H); 13C
D
DOI: 10.1021/acs.organomet.6b00020
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Article
NMR (100 MHz, CDCl3) δ 169.8, 132.9, 112.7, 91.2, 71.0, 69.7, 64.7,
64.0, 32.3, 31.2, 30.0, 27.9, 22.9, 22.3, 14.0, 13.9; IR (thin film): νmax
(cm−1) = 2925, 2862, 1652, 1490, 1463, 1343, 1300, 1105, 1001, 815,
736; HRMS (ESI) calcd for C21H2856FeNO [M + H]+: 366.1515;
Found: 366.1514.
Enantioselective Synthesis of Ferrocene-Based Pyridinone.
To a Schlenk tube were added Rh1 (2.8 mg, 5 μmol), (BzO)2 (1.2 mg,
5 μmol) and TFE (0.5 mL). After the mixture was stirred at room
temperature for 30 min, 1a (25.9 mg, 0.1 mmol), NaOAc (4.9 mg,
0.12 mmol), Et3N (13.8 μL, 0.1 mmol), 2a (18.6 mg, 0.16 mmol) and
TFE (0.5 mL) were added successively. The mixture was stirred at 60
°C for 50 h. The mixture was diluted with EtOAc and filtered through
a short pad of silica gel. Volatiles were evaporated under reduced
pressure. The residue was purified by column chromatography on
silica gel affording 3aa (12.7 mg, 37% yield). [Daicel CHIRALPAK
AD-H (0.46 cm × 25 cm), n-hexane/2-propanol =80/20, v = 1.0 mL·
min−1, λ = 254 nm, t (minor) = 6.60 min, t (major) = 7.59 min], 46%
Compound 3ba. Orange solid, mp = 101−103 °C, 119.9 mg, 95%
1
yield. H NMR (400 MHz, CDCl3) δ 7.89 (br s, 1H), 7.50−7.39 (m,
5H), 5.22 (dd, J = 2.4, 1.2 Hz, 1H), 4.80 (dd, J = 2.4, 1.2 Hz, 1H), 4.45
(t, J = 2.4 Hz, 1H), 4.35 (dt, J = 2.4, 1.2 Hz, 1H), 4.16 (dd, J = 2.4, 1.2
Hz, 1H), 4.14 (td, J = 2.4, 1.2 Hz, 1H), 4.09 (td, J = 2.4, 1.2 Hz, 1H),
2.17 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 168.1, 135.2, 133.7,
128.8, 128.52, 128.5, 108.4, 93.2, 78.7, 73.3 72.9, 72.3, 70.5, 68.6, 67.4,
66.8, 66.5, 14.4; IR (thin film): νmax (cm−1) = 3026, 2925, 1643, 1497,
1302, 1175, 868, 821, 770, 703; HRMS (ESI) calcd for
C20H1779Br56FeNO [M + H]+: 421.9837; Found: 421.9838.
27
ee; [α]D = +957.1 (c = 0.20, CHCl3).
ASSOCIATED CONTENT
* Supporting Information
■
1
Compound 3ca. Sticky oil, 92.9 mg, 80% yield. H NMR (400
S
MHz, CDCl3) δ 8.16 (br s, 1H), 7.44 (m, 5H), 5.13 (s, 1H), 4.76 (s,
1H), 4.38 (s, 1H), 4.13 (s, 1H), 4.10 (s, 3H), 4.07 (s, 2H), 3.25 (s,
3H), 2.16 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 168.7, 135.2,
132.7, 128.7, 128.66, 128.5, 109.6, 91.6, 83.1, 70.5, 70.0, 69.8, 69.2,
57.7, 14.2; IR (thin film): νmax (cm−1) = 2920, 2241, 1645, 1496, 1444,
1332, 1301, 1173, 1085, 1030, 905, 816, 771, 730, 703; HRMS (ESI)
calcd for C22H2256FeNO2 [M + H]+: 388.0994; Found: 388.0995.
Compound 3da. Red solid, mp = 146−148 °C, 85.4 mg, 76% yield.
1H NMR (400 MHz, CDCl3) δ 8.73 (br s, 1H), 7.50−7.35 (m, 5H),
5.14 (s, 1H), 4.79 (s, 1H), 4.39 (s, 1H), 4.34−4.18 (m, 3H), 4.10 (s,
2H), 3.72 (s, 1H), 3.65 (br s, 1H), 2.15 (s, 3H); 13C NMR (100 MHz,
CDCl3) δ 170.0, 135.0, 132.7, 128.8, 128.6, 128.5, 110.4, 91.1, 89.9,
72.0, 71.5, 69.5, 69.2, 68.4, 67.4, 66.0, 65.0, 59.3, 14.1; IR (thin film):
νmax (cm−1) = 3169, 3037, 1627, 1496, 1342, 1305, 1184, 1055, 1016,
913, 833, 776, 706; HRMS (ESI) calcd for C21H2056FeNO2 [M + H]+:
374.0838; Found: 374.0839.
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.6b00020.
Experimental procedures and analysis data for all new
compounds (PDF)
Details of X-ray crystallographic analysis for 3aa (CIF)
AUTHOR INFORMATION
Corresponding Author
*E-mail: slyou@sioc.ac.cn.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
1
Compound 3ea. Red foam, 101.1 mg, 84% yield. H NMR (400
We thank the National Basic Research Program of China (973
Program 2015CB856600) and National Natural Science
Foundation of China (21332009, 21421091) for generous
financial support.
MHz, CDCl3) δ 8.36 (br s, 1H), 7.56- 7.35 (m, 5H), 5.16 (s, 1H), 4.79
(s, 1H), 4.71 (s, 1H), 4.57 (s, 1H), 4.43−4.32 (m, 3H), 3.67 (s, 3H),
2.10 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 169.9, 167.8, 135.0,
134.1, 129.0, 128.5, 128.46, 108.3, 92.3, 72.8, 72.4, 72.37, 72.2, 71.4,
70.6, 66.0, 65.7, 51.5, 14.0; IR (thin film): νmax (cm−1) = 2948, 1710,
1648, 1497, 1464, 1278, 1189, 1137, 1028, 967, 900, 823, 772, 730,
704; HRMS (ESI) calcd for C22H2056FeNO3 [M + H]+: 402.0787;
Found: 402.0788.
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■
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̌ ̌
1
Compound 3fa. Sticky oil, 82.1 mg, 74% yield. H NMR (400
̌
MHz, CDCl3) δ 9.70 (s, 1H), 8.53 (br s, 1H), 7.54−7.37 (m, 5H),
5.20 (s, 1H), 4.88 (s, 1H), 4.75 (s, 1H), 4.60 (s, 1H), 4.58 (s, 1H),
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79.2, 74.2, 73.2, 72.2, 71.8, 70.0, 66.3, 65.4, 14.0; IR (thin film): νmax
(cm−1) = 2922, 2852, 1645, 1497, 1448, 1366, 1332, 1301, 1243, 1174,
1031, 826, 772, 738, 703; HRMS (ESI) calcd for C21H1856FeNO2 [M
+ H]+: 372.0681; Found: 372.0683.
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Compound 3ga. Red foam, 54.8 mg, 44% yield. H NMR (400
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417.0896; Found: 417.0897.
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(400 MHz, CDCl3) δ 7.99 (br s, 1H), 7.53−7.34 (m, 5H), 4.59 (s,
1H), 4.25 (s, 1H), 4.02 (d, J = 2.4 Hz, 1H), 2.08 (s, 3H), 1.76 (s,
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[M + H]+: 414.1515; Found: 414.1510.
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F
DOI: 10.1021/acs.organomet.6b00020
Organometallics XXXX, XXX, XXX−XXX