A mild catalytic oxidation system: Ruthenium porphyrin and 2,6-dichloropyridine n-oxide applied for alkene dihydroxylation

Article abstract of DOI:10.1002/adsc.201000455

A new method was developed to transform alkenes into three types of functional molecules, including epoxides, aldehydes and 1,2-diols by using dichlororuthenium(IV) meso-tetrakis(2,6-dichlorophenyl)porphyrin [Ru(IV)(TDCPP)Cl₂] as catalyst and 2,6-dichloropyridine N-oxide (Cl₂pyNO) as the oxidant, in which the 1,2-diols were afforded via "one-pot" reactions in moderate yields. Copyright

Full text of DOI:10.1002/adsc.201000455

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DOI: 10.1002/adsc.201000455
A Mild Catalytic Oxidation System: Ruthenium Porphyrin
and 2,6-Dichloropyridine N-Oxide Applied for Alkene
Dihydroxylation
Wen-Xiang Hu,a,* Pei-Rong Li,a Gaoxi Jiang,b,c Chi-Ming Che,b,c,* and Jian Chend,*
a
Department of Chemistry, College of Life Science, Capital Normal University, Beijing 100048, Peopleꢀs Republic of China
Fax : (+86)-10-6890-4756; e-mail: huwx66@163.com
Department of Chemistry and Open Laboratory of Chemical Biology of the Institute of Molecular Technology for Drug
b
Discovery and Synthesis, The University of Hong Kong, Pokfulam Road, Hong Kong, Peopleꢀs Republic of China
Fax : (+852)-2857-1586; e-mail: cmche@hku.hk
Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, Peopleꢀs
c
Republic of China
d
Key Laboratory of Pesticide & Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal
University, 152 Luoyu Road, Wuhan 430079, Peopleꢀs Republic of China
Fax : (+86)-27-6786-7786; e-mail: jianc@mail.ccnu.edu.cn
Received: June 10, 2010; Published online: December 7, 2010
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.201000455.
Abstract: A new method was developed to trans-
form alkenes into three types of functional mole-
cules, including epoxides, aldehydes and 1,2-diols by
using dichlororuthenium(IV) meso-tetrakis(2,6-di-
proved the synthetic utility of this transformation by
reducing the catalyst loading of RuO4.[6] Then, a new
catalytic system lowered further the amount of the
catalyst to 0.25–0.5 mol% through the combination of
RuCl3, NaIO4 and CeCl3·7H2O.[7] Che and co-workers
recently presented the cis-dihydroxylation of various
chlorophenyl)porphyrin [Ru(IV)
ACHTUNGTRENNUNG
catalyst and 2,6-dichloropyridine
(Cl2pyNO) as the oxidant, in which the 1,2-diols
were afforded via “one-pot” reactions in moderate
yields.
unfunctionalized
alkenes
by
using
[Ru(II)-
AHCUTNRTGEG(NNUN Me3tacn)Cl3] as catalyst and H2O2 as the terminal ox-
idant.[8] Despite these acheviements, developing
milder and more efficient methods for alkene dihy-
droxylation reactions is still an attractive topic.
Keywords: alkenes; catalytic oxidation; 2,6-dichlo-
G
Since cytochrome P-450,[9] one of the most attrac-
tive metalloenzymes containing the porphyrin struc-
ture in nature, was found to catalyze metabolic
oxygen transfer processes, porphyrins have been dem-
onstrating a wide range of applications in catalytic ox-
idation reactions, including alkene cyclopropana-
[11]
1,2-Diols are useful building blocks in organic synthe- tion,[10] C N bond formation, saturated C H bond
sis. This subunit can be synthesized from alkenes amination,[12] and alkene epoxidation.[13] In previous
through alkene dihydroxylation.[1] Several group VIII work, the combination of dichlororuthenium(IV)
transition metal oxides, such as: Fe,[2] Ru, Os, have meso-tetrakis(2,6-dichlorophenyl)porphyrin [Ru(IV)-
À
À
been employed to promote these reactions, in which,
ACHTUNGTRNE(NUNG TDCPP)Cl2] (1) and 2,6-dichloropyridine N-oxide
OsO4 is the most commonly used catalyst. In 1988, (Cl2pyNO) (2) (Figure 1) afforded aldehydes in high
Sharpless and Jacobsen[3] developed the OsO4/NMO yields via epoxide rearrangement.[14] We envisioned
(N-methylmorpholine N-oxide) oxidation system for that this reaction could provide an efficient method
asymmetric dihydroxylation of alkenes. Several simi- to prepare different types of products. For example,
lar studies[4] have been made based on this system in aldehydes can be obtained from epoxide rearrange-
recent years. The industrial use of OsO4, however, is ment, while expoxides can be obtained by the block-
thwarted by its expensive price and toxic properties. ing of this rearrangement process. The 1,2-diols can
In 1953, the less toxic RuO4 was introduced into this be prepared by utilizing epoxide ring opening and hy-
field by Carl Djerassi.[5] Shing and co-workers im- drolysis.
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A Mild Catalytic Oxidation System: Ruthenium Porphyrin and 2,6-Dichloropyridine N-Oxide
Under the same optimized conditions, a series of
styrenes were tested to prepare epoxides and diols.
As depicted in Table 2, all the epoxide derivatives
were obtained in high yields. Most of the epoxidation
reactions were complete in less than 1 hour, giving
the desired products in moderate to good yields. The
substituent(s) on the phenyl ring was found to affect
the reaction time dramatically. For example, the reac-
tion of compounds c, f and i took only ten minutes,
while the reactions of compounds b and d took 17 h
to give the corresponding products in 96% and 97%
yields respectively.
Almost all the diol products were synthesised in 2 h
in good yields (Table 2). The reaction of compound k
took 3 h to give the diol, possibly because of the pres-
ence of the methyl group attached at the double
bond. It was interesting to mention that compound h
took 22 h. The total yields were higher than 80%
except for compounds f and i.
Figure 1. [Ru(IV)ACHTUNGTRENNUNG(TDCPP)Cl2] and Cl2pyNO.
Table 1. Oxidation of 4-methoxystyrene catalyzed by
[Ru(IV)
(TDCPP)Cl2] with varying loadings of Cl2pyNO.[a]
ACHTUNGTRENNUNG
A plausible mechanism has been proposed. In the
process, [Ru(IV)ACTHUNTGRENUNG(TDCPP)Cl2] is supposed to be a
precatalyst, not the effective or active one, which, as
illustrated in Figure 2, is transformed into the real cat-
alyst, [Ru
from the reaction system, probably containing the ele-
ments Cl or O. [Ru(TDCPP)LL’] promotes the trans-
ACHTUNGTRENN(UNG TDCPP)LL’]. L and L’ are other ligands
Entry Cl2pyNO [equiv.] Conversion [%]
Yield [%][b]
AHCTUNGTRENNUNG
4
5
formation of the alkenes into aldehydes, epoxides and
diols. When the loading of oxidant was increased
from 1.03 equivalents to 2.0 equivalents, the aldehyde
formation was prohibited. We speculated that
Cl2pyNO acts as ligand coordinated to the ruthenium
atom of the catalyst. Therefore, there is a competition
between oxidant and epoxide for this coordination re-
action. In the case of 1.03 equivalents of oxidant, the
epoxide interacts with Ru complex again, which ini-
tiates the epoxide rearrangement. On the other hand,
1
2
3
2.0
1.03
0.9
100
100
90
76
0
0
24
99
>99
[a]
Reaction conditions: 3: 0.1 mmol, 1: 0.5 mol%, CDCl3:
0.5 mL; 258C, open to the air.
[b]
Determined by 1H NMR spectroscopy (based on con-
sumed substrate).
The reaction of 4-methoxystyrene was chosen as excess oxidant interacts with the Ru complex, which
the model system for our initial investigation. A pushes away the resulting epoxide and shifts the equi-
series of experiments were performed and representa- librium to epoxide formation. The ring-opening re-
tive results are listed in Table 1. As shown in Table 1, agent, such as protic acid, was added to give diols
the amount of oxidant loading affected the reaction through epoxide hydrolysis.
pathway. The optimal conditions for the formation of
In summary, a mild oxidation system has been de-
the aldehyde were to use 1.03 equivalents of oxi- veloped to convert alkenes into various types of func-
dant.[14] However, when 2.0 equivalents of oxidant tional molecules, including aldehydes, epoxides, and
was used, the epoxide 4 was obtained as the major diols in moderate to excellent yields by controlling
product in 76% yield, along with the formation of al- the loadings of oxidant and reaction procedures. This
dehyde 5 in 24% yield.
is the first time, to the best of our knowledge, that an
We reasoned that the in-situ ring opening (epoxide efficient method has been developed to prepare three
hydrolysis) would prevent the synthesis of aldehyde different types of compounds from alkenes by using a
and epoxide. In order to get the optimal reaction con- single catalytic system via “one-pot” cascade reac-
ditions for the formation of the diols, a carboxylic tions.
acid was introduced to promote the reaction. Indeed,
when AcOH and 1.5 equivalents of Cl2pyNO were
added, the ring-opened diol products were obtained
as a mixture of regioisomers in excellent yield (95%).
Formic acid was later found to be a better promoter
for the ring opening process.
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Table 2. Alkenes that were oxidized with [Ru(IV)ACTHNUTRGNEUNG
(TDCPP)Cl2] and Cl2pyNO.[a]
Compound
R1
R2
R3
Time[b]
Yield[d] of epoxide
Time[c]
Yield[d] of diol
a
b
c
d
e
f
g
h
i
MeO
H
Me
H
H
H
H
H
H
H
H
H
Me
H
H
H
H
H
H
H
H
H
H
H
Me
15 min
17 h
10 min
17 h
11 min
10 min
48 min
52 min
10 min
15 min
19 min
76%
96%
97%
97%
82%
90%
46%
75%
90%
2 h
2 h
2 h
2 h
2 h
2 h
2 h
22 h
2 h
2 h
3 h
95%
85%
92%
81%
90%
63%
98%
88%
63%
86%
83%
F
i-Bu
t-Bu
i-PrO
PhO
BnO
Me
[e]
j
k
–
[e]
H
–
[a]
Yields of the aldehydes were reported in the previous works.[14]
The reaction times of epoxidation.
[b]
[c]
[d]
[e]
The reaction times for the nucleophilic ring opening of epoxides.
1
The yields were determined by H NMR with internal standard of trimethylphenylsilane.
Epoxides from j and k were crudely obtained and directly used for their conversions to diols.
Figure 2. Probable mechanism leading to aldehydes, epoxides and diols.
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Adv. Synth. Catal. 2010, 352, 3190 – 3194

A Mild Catalytic Oxidation System: Ruthenium Porphyrin and 2,6-Dichloropyridine N-Oxide
troleum ether and EtOAc (1:1–1:2) as eluent giving the pure
diol.
Experimental Section
1-(4-Methoxyphenyl) ethane-1,2-diol: yield: 32 mg (95%).
[Ru(II)ACHTUNGTRENNUNG(TDCPP)(CO)]
1H NMR (600 MHz, CDCl3): d=2.17 (brs, 1H), 2.56 (brs,
1H), 3.65 (m, 2H), 3.81 (s, 3H), 4.77 (m, 1H), 6.90 (d, J=
8.5, 2H), 7.28 (d, J=8.5, 2H); 13C NMR (150 MHz, CDCl3):
d=55.30, 68.07, 74.28, 113.93, 127.35, 132.62, 159.42; IR: n=
3310 cmÀ1 (br). MS: m/z=168.0 [M+].
A mixture of Ru3(CO)12 (178 mg, 0.28 mmol) and porphyrin
H2TDCPP (165 mg, 0.19 mmol) was heated to reflux in
1,2,4-trichorobenzene under an argon atmosphere for 4–6 h.
After the mixture was cooled to room temperature, the resi-
due was loaded onto an alumina column and the column
was first eluted with hexane to remove the trichlorobenzene,
followed by eluting with dichloromethane. A dark red band
containing the desired ruthenium complex was collected;
1-Phenylethane-1,2-diol: yield: 23 mg (85%). 1H NMR
(600 MHz, CDCl3): d=2.04 (brs, 1H), 2.50 (brs, 1H), 3,70
(m, 2H), 4.85 (m, 1H), 7.35 (m, 2H), 7.40 (m, 3H);
13C NMR (150 MHz, CDCl3): d=68.03, 74.67, 126.03,
128.60, 140.45; IR: n=3306 cmÀ1 (br); MS: m/z=138.1
[M+].
1
yield: 187 mg (99%). H NMR (300 MHz, CDCl3): d=8.48
(s, 8H), 7.73–7.80 (m, 8H), 7.65 (dd, 4H, J=7.8 Hz); IR
(KBr): n=2921, 2851, 1951, 1429, 1009, 799 cmÀ1; UV-vis
(CH2Cl2): lmax (log e)=410, 531, 609 nm; MS (FAB) m/z=
1018 (M+1), 990 (M+1ÀCO).
1-p-Tolylethane-1,2-diol: yield: 28 mg (92%). 1H NMR
(600 MHz, CDCl3): d=2.34 (s, 3H), 2.53 (brs, 1H), 2.90
(brs, 1H), 3.70 (m, 2H), 4.76 (m, 1H), 7.16 (d, J=7.8, 2H),
7.24 (d, J=7.8, 2H); 13C NMR (150 MHz, CDCl3): d=21.12,
68.07, 74.56, 126.01, 129.02, 137.73; IR: 3251 cmÀ1 (br); MS:
m/z=152.1 [M+].
[Ru(VI)
ACHTUNGTRENNUNG
A
dichloromethane solution of [Ru(II)ACTHUNGETRNNU(G TDCPP)(CO)]
1-(4-Fluorophenyl)ethane-1,2-diol: yield: 25 mg (81%).
1H NMR (600 MHz, CDCl3): d=2.11 (brs, 1H), 2.62 (brs,
1H), 3,75 (m, 2H), 4.80 (m, 1H), 7.05 (m, 2H), 7.35 (m,
2H); 13C NMR (150 MHz, CDCl3): d=70.70, 76.66, 118.00,
130.41, 138.85, 164.30, 165.33; IR: n=3313 cmÀ1 (br); MS:
m/z=156.0 [M+].
1-(4-tert-Butylphenyl)ethane-1,2-diol: yield: 24 mg (63%).
1H NMR (600 MHz, CDCl3): d=1.31 (s, 9H), 2.35 (brs, 1H),
2.70 (brs, 1H), 3.70 (m, 2H), 4.78 (m, 1H), 7.29 (d, J=8.2,
2H), 7.39 (d, J=8.2, 2H); 13C NMR (150 MHz, CDCl3): d=
33.97, 37.20, 70.68, 77.16, 128.40, 140.14, 153.68; IR: n=
3404 cmÀ1 (br); MS: m/z=194.1 [M+].
(150 mg) was added to a well stirred solution of m-chloro-
peroxybenzoic acid in dichloromethane (50 mL). After
10 min, the solution was chromatographed on a short alumi-
na column. The product was eluted by dichloromethane.
The solution obtained was evaporated to dryness by rotary
evaporation. A dark purple residue was obtained; yield:
123 mg (82%). 1H NMR (300 MHz, CDCl3): d=8.89 (s,
8H), 7.83–7.86 (m, 8H), 7.73–7.78 (m, 4H); IR (KBr): n=
1557, 1533, 1428, 1018, 824, 801, 776 cmÀ1; UV-vis (CH2Cl2):
lmax (log e)=420, 516 nm.
[Ru(IV)ACHTUNGTRENNUNG(TDCPP)Cl2]
1-(4-Isopropoxyphenyl)ethane-1,2-diol:
yield:
38 mg
(98%). 1H NMR (600 MHz, CDCl3): d=1.32 (d, J=6 Hz,
6H), 2.46 (brs, 1H), 2.80 (brs, 1H), 3.68 (m, 2H), 4.53 (m,
1H), 4.74 (m, 1H), 6.85 (d, J=8.5 Hz, 2H), 7.20 (d, J=
8.5 Hz, 2H); 13C NMR (150 MHz, CDCl3): d=24.75, 70.51,
72.56, 76.86, 118.47, 130.10, 135.03, 160.35; IR: n=3289 cmÀ1
(br); MS: m/z=196.1 [M+].
TMSCl (0.4 mL) was added into a well stirred solution of
[Ru(VI)(TDCPP)O2] (150 mg) in dichloromethane
ACHTUNGTRENNUNG
(350 mL). After 10 min, the solution was concentrated to
small volume by rotary evaporation and was filtered offering
a dark purple residue; yield: 139 mg (90%). 1H NMR
(300 MHz, CDCl3): d 9.56 (d, 8H, J=8.1 Hz), 8.85 (t, 4H,
J=8.1 Hz), À53.5 (br, 8H); IR (KBr): n=1557, 1429, 1194,
1072, 999, 802, 776 cmÀ1; UV-vis (CH2Cl2): lmax (loge)=408,
1-[4-(Benzyloxy)phenyl]ethane-1,2-diol: yield: 31 mg
1
(63%). H NMR (600 MHz, CDCl3): d=2.05 (brs, 1H), 2.43
517 nm; MS (FAB): m/z=1060 (M+), 1025 (M+À Cl), 1023
35
(brs, 1H), 3.73 (m, 2H), 4.78 (m, 1H), 5.03 (s, 2H), 6.97 (d,
J=8.6 Hz, 2H), 7.29 (d, J=8.6 Hz, 2H), 7.33 (t, J=7.3 Hz,
1H), 7.38 (m, 2H), 7.43 (d, J=7.3 Hz, 2H); 13C NMR
(150 MHz, CDCl3): d=68.05, 70.03, 74.27, 114.96, 127.40,
127.98, 128.58, 132.91, 136.90, 159.66; IR: n=3336 cmÀ1
(br); MS: m/z=243.9 [M+].
37
35
37
(M+À Cl), 990 (M+À235Cl), 988 (M+À ClÀ Cl).
General Procedure for the Preparation of Diols
To a solution of styrene (0.2 mmol) in CHCl3 (1–2 mL), cat-
alyst [Ru(IV)ACHTUNGTRENNUNG(TDCPP)Cl2] (2 mg, 1 mmol%), oxidant
1-(2,4-Dimethylphenyl)ethane-1,2-diol:
yield:
28 mg
1
(86%). H NMR (600 MHz, CDCl3): d=2.30 (s, 6H), 2.56
(brs, 1H), 2.76 (brs, 1H), 3.65 (m, 2H), 5.01 (m, 1H), 6.96
(s, 1H), 7.04 (d, J=7.8 Hz, 1H), 7.35 (d, J=7.8 Hz, 1H);
13C NMR (150 MHz, CDCl3): d=21.55, 23.60, 69.80, 74.15,
128.40, 129.60, 133.85, 137.31, 138.12, 140.03; IR: 3242 cmÀ1
(br); MS: m/z=166.1 [M+].
Cl2pyNO (48 mg, 0.3 mmol), and HCOOH (22–37 mL, 0.6–
1 mmol) were added at the same time. The system needs to
be covered with aluminium foil paper as protection from
light. With stirring, the reaction solution was kept at room
temperature for 2.5–3 h. After the completion of the reac-
tion, the mixture was diluted with 6–8 mL of petroleum
ether and purified by silica gel column chromatography
using petroleum ether and EtOAc (3:1–2:1) as eluent to
give mixture of mono-protected diols. Then K2CO3
(0.3 mmol) was added to a solution of mono-protected diols
(0.2 mmol) in methanol (10 mL). The mixture was stirred
for 3–4 h and then concentrated with silica gel (200–
300 mesh) under vacuum. The mixture was then purified by
silica gel column chromatography (300–400 mesh) using pe-
2-Phenylpropane-1,2-diol: yield: 25 mg (83%). 1H NMR
(600 MHz, CDCl3): d=1.52 (s, 3H), 2.01 (brs, 1H), 2.70
(brs, 1H), 3.70 (m, 2H), 7.27 (t, J=7.3 Hz, 1H), 7.36 (m,
2H), 7.45 (d, J=7.8 Hz, 2H); 13C NMR (150 MHz, CDCl3):
d=25.98, 71.05, 74.82, 125.05, 127.16, 128.40, 144.92; IR: n=
3391 cmÀ1 (br); MS: m/z=152.1 [M+].
1-(4-Isobutylphenyl)ethane-1,2-diol: yield: 35 mg (90%).
1H NMR (400 MHz, CDCl3): d=0.89 (d, J=6.6 Hz, 6H),
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1.84 (m, 1H), 2.31 (brs, 1H), 2.46 (d, J=7.1 Hz, 2H), 2.69
(brs, 1H), 3.69 (m, 2H), 4.78 (m, 1H), 7.13 (d, J=8 Hz,
2H), 7.25 (d, J=8 Hz, 2H); 13C NMR (150 MHz, CDCl3):
d=22.36, 30.21, 45.09, 68.07, 74.61, 125.85, 129.29, 137.73,
141.62; IR: 3365 cmÀ1 (br); HR-MS: m/z=194.1302, calcu-
lated for C12H18O2: 194.1307.
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1H NMR (600 MHz, CDCl3): d=2.23 (brs, 1H), 2.67 (brs,
1H), 3,70 (m, 2H), 4.81 (m, 1H), 7.00 (m, 4H), 7.11 (t, J=
7.4 Hz, 1H), 7.33 (m, 4H); 13C NMR (150 MHz, CDCl3):
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Acknowledgements
This work was supported by the National Nature Science
Foundation of China (Nos. 20872095and 20802023), Univer-
sity Grants Council of HKSAR (the Area of Excellence
Scheme: AoE 10/01P), and the Hong Kong Research Grants
Council (HKU 1/CRF/08).
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