Heterogeneous platinum catalytic aerobic oxidation of cyclopentane-1,2- diols to cyclopentane-1,2-diones

Article abstract of DOI:10.1016/j.tet.2014.03.104

A method for the aerobic oxidation of cyclopentane-1,2-diols to the corresponding diketones over a commercial heterogeneous Pt/C catalyst is described. Unsubstituted and 3- or 4-substituted cyclopentane-1,2-diols are oxidized to 1,2-dicarbonyl compounds in good yields under the reported optimized reaction conditions (atmospheric air, 1 mol % of catalyst, 1 equiv of LiOH, aqueous solvents and 60 °C temperature). The method is applicable for producing cyclopentane-1,2-diketones in a scalable manner.

Full text of DOI:10.1016/j.tet.2014.03.104

Tetrahedron 70 (2014) 3608e3613
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Heterogeneous platinum catalytic aerobic oxidation of
cyclopentane-1,2-diols to cyclopentane-1,2-diones
y
z
€
Indrek Reile , Sigrid Kalle, Franz Werner , Ivar Jarving, Marina Kudrjashova, Anne Paju,
*
Margus Lopp
Talllinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia
a r t i c l e i n f o
a b s t r a c t
Article history:
A method for the aerobic oxidation of cyclopentane-1,2-diols to the corresponding diketones over
a commercial heterogeneous Pt/C catalyst is described. Unsubstituted and 3- or 4-substituted cyclo-
pentane-1,2-diols are oxidized to 1,2-dicarbonyl compounds in good yields under the reported optimized
reaction conditions (atmospheric air, 1 mol % of catalyst, 1 equiv of LiOH, aqueous solvents and 60 ꢀC
temperature). The method is applicable for producing cyclopentane-1,2-diketones in a scalable manner.
Ó 2014 Elsevier Ltd. All rights reserved.
Received 21 January 2014
Received in revised form 16 March 2014
Accepted 31 March 2014
Available online 4 April 2014
Keywords:
1,2-Diols
Heterogeneous catalysis
1,2-Diketones
Aerobic oxidation
Platinum catalyst
1. Introduction
Oxidative catalytic dehydrogenation is a common way of selec-
tively converting alcohols to their carbonyl derivatives (Scheme 1).
Catalytic oxidation, especially the catalytic aerobic oxidation, is
preferred over the traditional stoichiometric oxidation processes,
since it does not produce hazardous byproducts.1 Starting from the
1970s, when the first reports on the metal-catalyzed aerobic oxi-
dations appeared,2 steady progress has occurred in this field.3
Several catalyst systems, such as homogeneous metal complexes
dissolved in water,4,5 ionic liquids6 or organic solvents7 and het-
erogeneous systems where the catalytic metal particles are em-
bedded on various supports, have been developed.8 Known
catalyst supports include, for example, polymers,9e12 silica,13
TiO2,14 Al2O3,15 hydrotalcite,16 hydroxyapatite,17 metaleorganic-
frameworks18 and carbonaceous materials,19e22 which are used in
organic solvents,13,14,18,20,21 water9e12,16,20,22,23 or super-critical
CO2.19 Examples of metals used as the catalytically active species
include, but is not limited to, platinum,9,19,20 palladium,12,13,15,18,19,22
ruthenium,21,24 gold14,23 and various bimetallic systems.10,11,16
Scheme 1. Oxidative catalytic dehydrogenation of alcohols.
While most of the known methods can be applied for the con-
version of allylic or benzylic alcohols, only a few can be used for the
oxidation of non-activated aliphatic alcohols.8,18,21,22 Furthermore,
there are even fewer aerobic oxidation methods suitable for the
oxidation of vic-diols to their corresponding diketones25,26 because
of the easy cleavage of the carbonecarbon bond between the vic-
inal hydroxyl groups under oxidative conditions.27e30 In our pre-
liminary report, we described the first experiments on the aerobic
Pt-catalyzed oxidation of cyclopentane-1,2-diols to their corre-
sponding cyclopentane-1,2-diones (isolated as their monoenol
tautomers).31 In the present report we summarize the results of
our study on the oxidation method, concerning optimization of
reaction conditions and broadening the selection of reaction
substrates.
* Corresponding author. Tel.: þ372 5136083; e-mail addresses: margus.lopp@ttu.
2. Results and discussion
ee, lopp@chemnet.ee (M. Lopp).
y
Present address: National Institute of Chemical Physics and Biophysics, Aka-
In testing different activated carbon supported platinum group
metal catalysts, we found that cis-1,2-diols 1 (Scheme 2) can be
converted to 1,2-diones 3, and isolated in their thermodynamically
deemia tee 23, 12618 Tallinn, Estonia.
Present address: Vienna University of Technology, Institute of Applied Synthetic
Chemistry, Getreidemarkt 9, 1060 Vienna, Austria.
z
0040-4020/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2014.03.104

I. Reile et al. / Tetrahedron 70 (2014) 3608e3613
3609
Table 1
Aerobic catalytic oxidation of 1,2-cyclopentanediol 1a to 4a over Pt/C catalyst
Entry
Alkali equiv
Time h
Product yield, %
131
2
3
4
5
0
20
4
4
4
4
4
4
5.5
4
5.5
66
61
67
69
70
70
68
63
59
39
0.2
0.4
0.6
0.8
1
1
1
1
0.5
6
7a
8b
9b,c
10b
All experiments were run in 1:1 MeCN/H2O at 60 ꢀC with 5 mol % Pt/C catalyst
loading in an open glass reactor equipped with a condenser; 1 equiv of LiOH/H2O.
a
Regenerated catalyst.31
Pt/C (1 mol %) catalyst.
CsOH (1 equiv).
b
c
Scheme 2. Aerobic catalytic oxidation of 1,2-cyclopentanediols over Pt/C catalyst.
we achieved a stable process in acetonitrile/water with un-
restricted access of atmospheric air to the reaction medium.
When the substrate was oxidized in a 1:1 mixture of acetoni-
trile/water in the presence of different amounts of LiOH and 5 mol %
Pt/C loading (Table 1, entries 1e6), it was found that the optimal
amount of alkali was around 1 M equiv to the substrate. In the
presence of base, no formation of hydroxyketone 2 was detected.
Presence of alkali considerably enhanced the reaction rate: without
alkali we obtained 66% of product 4a in 20 h, while adding 1 equiv
of LiOH provided 70% of product 4a in 4 h (Table 1, entries 1 and 6).
Prolonging the reaction time further had no beneficial effect on the
conversion of the remaining 1a but caused a gradual degradation of
the product 4a.
When the Pt/C catalyst was filtered from the reaction mixture
and reused for the oxidation of diol 1a under the conditions de-
scribed above, only a minor decrease of the yield was observed and
the product 4a was isolated in 68% yield (Table 1, entry 7). Thus the
catalyst could be reused at least once without a noticeable decrease
in the catalyst activity.
Reducing the catalyst loading to 1 mol % slightly decreased the
yield when compared to 5 mol % loading (Table 1, entries 6 vs 8). At
the same time the TON value increased from 14 to 63, making the
lower catalyst loading highly feasible. The same tendency was ob-
served for all substrates, with the highest observed TON being
approximately 72 in the case of substrate 1e (Table 2, entries 4 and
5). The reduction of catalyst loadings below 1 mol % resulted in an
excessive decrease in the yield. In all investigated cases the
unreacted starting material could be easily separated and recovered
when deemed necessary.
The product yield with 1 mol % of Pt/C catalyst depended sim-
ilarly on the amount of LiOH, as with 5 mol % of catalyst. However,
with lower catalyst loadings the yield was more sensitive to the
alkali amount (Table 1, entries 3 and 10). Replacing LiOH with CsOH
resulted in a small reduction in the product yield (to 59%), ac-
companied by a complete loss of starting material (Table 1, entry 9).
We suggest that CsOH does considerably influence the reaction, but
the product 4a decomposes with CsOH under reaction conditions.
The optimal reaction temperature was around 60e70 ꢀC: below
60 ꢀC the reaction became significantly slower and above 70 ꢀC the
product started to decompose, resulting in reduced yields.
The substrate scope of the reaction was studied by oxidizing
cyclopentane-1,2-diols with different structures (Table 2). In most
cases, 1,2-diones 4 formed in good yield (around 70%). In the case of
hydroxyalkyl substituent 1c with an unprotected OH group,
a modest yield of compound 4c was observed (49%, Table 2, entry
2). However, it is noteworthy that only the secondary OH groups in
the cyclopentane moiety in the substrate 1c were oxidized, leaving
the primary hydroxyl group in the hydroxyethyl side chain intact.
preferred monoenol form 4, by an aerobic oxidation reaction over
a commercially available Pt/C catalyst.32 The presence of water in
the catalyst and/or in the reaction medium is essential for the re-
action to occur. Out of several commercial Pt/C catalysts tested, only
those two that contained around 50% (w/w) of water were active. A
similar wet Pd/C catalyst showed only low catalytic activity, which
may have been due to the lower oxidizing ability of Pd compared to
that of Pt.9
When the active catalyst was dried before use and the reaction
was run in dry toluene, a complete loss of activity was observed,
demonstrating the significant role of water in the reaction. It has
been suggested that water may serve as a weak base, assisting the
abstraction of the alcohol proton and thus helping the alcohol to
absorb on the metal surface.33
It was found that the main consideration in selecting the solvent
for the oxidation is the solubility of the substrate: a variety of sol-
vents, such as toluene, H2O or a mixture of MeCN and H2O can be
used. When running the reaction in toluene, small amounts of
hydroxyketones 2 and 20 were also detected among the reaction
products,31 indicating that the hydroxyl groups are oxidized in two
steps via formation of the intermediate hydroxyketone.
The yield of ketoenol 4 depended on the amount of air available.
The activated carbon supported catalyst initially contains some
oxygen and dissolved oxygen is usually present in solvents. We
have previously observed that this amount of oxygen is not suffi-
cient for the optimal conversion of 1 to 4.31 At the same time, we
have observed that an unrestricted access of atmospheric air may
hinder the oxidation of diols, probably due to the excessive oxi-
dation of the Pt surface, which will deactivate the catalyst.33,34
The beneficial effect of adding inorganic bases as additives to the
€
oxidation system has been described by Backvall for the hetero-
geneous catalytic dehydrogenations35 and Mueller and Sigman for
the aerobic oxidations.36 Following these suggestions, we in-
vestigated the influence of alkali on the oxidation of 1,2-diol 1a
(Scheme 2, Table 1). We found that the addition of an inorganic
base significantly influences the process by increasing the reaction
rate and catalyst turnover, allowing us to reduce the reaction time
and the catalyst loading. In the presence of a base the process was
also less sensitive to higher oxygen concentration, which made it
possible to use a simple open top vertical condenser on the reaction
vessel and obtain stable yields. The sensitivity drop towards oxygen
concentration was similar to that discussed by Steinhoff and Stahl
for the aerobic homogeneous Pd catalysis.37 Our observations are in
good accordance with earlier findings on the role of the base in the
dehydrogenation process38 where base facilitates the
elimination step during the reaction.39 By adding 1 equiv of LiOH,
b-hydrogen

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I. Reile et al. / Tetrahedron 70 (2014) 3608e3613
Table 2
Aerobic oxidation of alcohols to carbonyl compounds over Pt/C catalyst
Entry
Substrate
Time h
Product yield, %
1a
1b
1c
1d
1e
1e
1f
1g
1h
1i
5
5
1.3
4
4
3.5
3
5
5
5
74
49
28
76
72
69
0
65
63
61
62
19
2a
3a
4a
5b
631
7a,b
8b
9b
10b
11b
12b
1j
1k
1l
5
4
13b
14b
15b
16b
1m
1n
5
4
38
Fig. 1. Molecular moieties in the crystal structures of the racemic enols 4j (left) and 4k
(right). Displacement ellipsoids for non-H atoms are drawn at the 50% probability level.
4
36
acid 70 in 33% yield were obtained (Table 2, entry 16). The total yield
of the dehydration reaction was 61%. This hints that the described
oxidation procedure can also be applied to cyclopentanols in order
to get cyclic ketones.
4
0
We also checked the possibility to scale up the reaction volume
from 100-mg scale to gram scale. When larger reaction volumes
were simply run in larger reaction vessels with unrestricted air
access, the obtained reaction yield remained low and most of the
starting material was left unreacted (Table 3, entry 1), most prob-
ably due to insufficient oxygen transfer from the surrounding at-
mosphere into the reaction mixture. Indeed, bubbling a constant air
flow of 0.2e0.3 mL/min into the reaction mixture in the reactor was
sufficient to successfully oxidize 1,2-diols to 1,2-diones with a rea-
sonable yield (Table 3; to avoid loss of the reaction medium the air
flow was saturated with reaction solvent vapours by passing
through an identical solvent mixture in a separate flask prior to
entering the reactor). Unreacted material was separated and re-
covered in all cases. Thus, although quantitative turnover was not
achieved, overall loss in material was small.
6
3.5
28 (þ33c)
All experiments were run in 1:1 MeCN/H2O at 60 ꢀC with Pt/C and 1 equiv of
LiOH$H2O in an open glass reactor equipped with a vertical condenser.
Catalyst loadings:
a
Pt/C (5 mol %) catalyst.
Pt/C (1 mol %) catalyst.
Yield of corresponding carboxylic acid 70.
b
c
The oxidation of tert-amylcarbonyloxydiol 1d proceeded quickly
during 1 h, until a yield of 4d reached 28% after which no further
conversion occurred (Table 2, entry 3). Boc-aminoalkyl substrate 1e
resulted in the best isolated yield of dione 4 (76%, Table 2, entry 4).
At the same time the carbamoyl group bearing diol 1g did
not oxidize and the expected dione 4g was not detected (Table 2,
entry 7).
The oxidation tolerates different substitutions in the cyclo-
pentane ring. Both, 3- and 4-substituted diols were successfully
oxidized with good yields (Tables 1 and 2). Oxidation of 4-
substituted diols 1j and 1k afforded the corresponding diketones
4j and 4k. The latter two readily formed single crystals suitable for
X-ray diffraction studies (Fig. 1). The low yield in the case of
unsubstituted cyclopentane-1,2-dione 4l was probably due to the
loss of the volatile product during the standard work-up and pu-
rification steps.
Table 3
Scaled up oxidation of diols 1 to diketones 4
Entry
1a
2
3
4
Substrate
Time h
Product yield, %
Regenerated 1 %
1i
1i
1j
1e
1k
5
6
6
4
6
34
64
51
66
53
62
28
46
26
40
5
All experiments were run in 1:1 MeCN/H2O at 60 ꢀC with 1 mol % Pt/C catalyst in an
open glass reactor equipped with a condenser. A 0.3 mL/min flow of atmospheric air
saturated with solvent mixture was maintained through the reactor during the
reaction.
a
Without additional air flow.
3. Conclusion
The spatial arrangement of the substituents in the cyclopentane
ring influenced the reactivity of the substrate. We observed that
trans-diol afforded a lower yield than the cis-diol (Table 1, entry 8 vs
Table 2, entries 13 and 14). At the same time, no noticeable differ-
ence was observed when the alkyl substituent was either cis or
In summary a practical method for the catalytic aerobic oxida-
tion for cyclopentane-1,2-diols to cyclopentane-1,2-diones was
developed. The reaction was run under relatively mild conditions
(60 ꢀC in MeCN/H2O) in the presence of 1 mol % of a heterogeneous
Pt/C catalyst and 1 equiv of LiOH. The method tolerates a wide
choice of solvent systems, ranging from organic solvents to aqueous
mixtures to water. Under the described reaction conditions, only
secondary hydroxyl groups of cyclopentane rings were selectively
oxidized. A number of different functional groups on the cyclo-
pentane ring tolerated well the oxidation conditions. The reaction
method could also be scaled up for preparative use.
trans with the a-hydroxyl group (Table 2, entries 13 and 14).
A non-cyclic vic-diol 5 was completely consumed after 4 h, but
did not afford any of the expected dicarbonyl compound. Instead,
formation of a complex mixture of different carbonyl compounds
was observed (Table 2, entry 15). When the cyclic secondary alcohol
6 was subjected to oxidation, 3-oxo-cyclopentyl acetic acid t-Bu
ester 7 in 28% yield together with the corresponding carbocyclic

I. Reile et al. / Tetrahedron 70 (2014) 3608e3613
3611
4. Experimental section
4.1. General remarks
4.2.2.2. 4-(Benzyloxymethyl)cyclopentane-cis-1,2-diol
1i. Compound 1i was prepared by the general dihydroxylation
procedure over 2 days (868 mg, 98%) as a 1:2.8 mixture of di-
astereomers. The preceding cyclopentene was prepared from 3-
cyclopentene carboxylic acid according to a known procedure.41
Compound 1i was obtained as a white crystalline material with
spectral and physical properties matching literature values.42
All reagents purchased from common suppliers were used
without further purification. All solvents were distilled according
to common procedures prior to use. Silica gel 40e100 mm was used
for column chromatography. All NMR spectra were measured at
room temperature on a Bruker Avance III 400 MHz instrument. MS
(EI) spectra were obtained on a Shimadzu GCMS-QP2010 spec-
trometer, FT-IR spectra were recorded on a PerkineElmer Spec-
trum BX spectrometer, HRMS (APCI-MS) measurements were
performed on an Agilent Technologies 6450 UHD Accurate-Mass
Q-TOF LC/MS instrument. Single crystal X-ray diffraction data
were collected on a Bruker SMART X2S. The Supplementary data
contains additional synthetic procedures for the preparation of
oxidation substrates, NMR spectra and the crystallographic data
for this paper (compounds 4j and 4k, deposited with the Cam-
bridge Crystallographic Data Centre (CCDC 833165 (4j) and 833166
(4k))).
4.2.2.3. 4-(tert-Butoxymethyl)cyclopentane-cis-1,2-diol
1j. Compound 1j was obtained by the general dihydroxylation
procedure over 3 days (467 mg, 62%) as a colourless oil (1:2.5
mixture of diastereomers). Major diastereomer: 1H NMR
(400 MHz, CDCl3):
d
¼4.08e4.04 (m, 2H, H1, H2), 3.91 (broad s, 2H,
2ꢂOH), 3.17 (d, J¼6.3 Hz, 2H, eCH2Oe), 2.48e2.37 (m, 1H, H4),
1.89e1.79 and 1.62e1.56 (m, 2ꢂ2H; H3, H5), 1.16 (s, 9H, t-Bu). 13
C
NMR (100 MHz, CDCl3):
d
¼73.7 (C1, C2), 72.2 (eC(CH3)3), 65.8
(eCOHe), 34.7 (C4), 34.4 (C3, C5), 27.4 (t-Bu). Minor diastereomer:
1H NMR (400 MHz, CDCl3):
d
¼3.91 (broad s, 4H, 2ꢂOH, H1, H2),
3.31 (d, J¼3.4 Hz, 2H, eCH2Oe), 2.31e2.23 (m, 1H, H4), 2.07e2.00
and 1.53e1.47 (m, 2ꢂ2H, H3, H5), 1.21 (s, 3.6H, t-Bu0). 13C NMR
(100 MHz, CDCl3):
d
¼74.0 (C1, C2), 73.5 (eC(CH3)3), 64.3 (eCOHe),
33.9 (C4), 33.5 (C3, C4), 27.3 (t-Bu). IR: 3405, 2973, 1391, 1363,
1200, 1083, 1021 cmꢁ1; MS (EI): m/z¼188, 173, 155, 131, 113, 102, 97,
83, 69, 57. APCI-MS: m/z observed 192.1145, calcd for C7H14O3
192.1150.
4.2. Preparation of oxidation substrates
Diols 1b and 1l were purchased from Aldrich. The preparation of
diols 1a and 1ceg was described earlier.31,40 Diols 1hek were
prepared from their preceding cyclopentenes by the general dihy-
droxylation procedure described below. The preparation of the
above mentioned cyclopentenes is described in the Supplementary
data. The preparation of diols 1m, 1n, 5 and alcohol 6 is described in
the Supplementary data.
4.2.2.4. 4-(Methoxymethyl)cyclopentane-cis-1,2-diol
1k. Compound 1k was obtained by the general dihydroxylation
procedure over 2 days (325 mg, 56%) as a colourless oil (1:0.4
mixture of diastereomers). Major diastereomer: 1H NMR (400 MHz,
CDCl3):
d
¼4.09 (t, J¼4.8 Hz, 2H, H1, H2), 3.33 (s, 3H, OMe), 3.23 (d,
J¼6.5 Hz, 2H, eCH2OMe), 2.54 (tt, J¼9.2, 6.5 Hz, 1H; H4), 1.88e1.81
(m, 2H, H3, H5), 1.64e1.57 (m, 2H, H3, H5). 13C NMR (100 MHz,
4.2.1. General procedure for the dihydroxylation of cyclopentenes
used for the preparation of diols 1hek. Corresponding cyclopentene
(4 mmol) was dissolved in 13 mL of 3:1 mixture of t-BuOH and
water. 1.1 mL of 50% w/w aqueous NMO solution (5.2 mmol) and
13.5 mg of 7.5% solid supported OsO4 catalyst (0.004 mmol) were
added. The mixture was stirred at 60 ꢀC until no more of the cor-
responding cyclopentene was observed in the reaction mixture.
The catalyst was filtered off, 20 mL of EtOAc was added and the
mixture was washed with 10 mL of 10% Na2S2O3. The aqueous
phase was separated and extracted with EtOAc. All organics were
combined and dried over MgSO4, the solvent was evaporated and
the product was purified by column chromatography over silica gel.
CDCl3):
d
¼77.3 (eCH2OMe), 73.9 (C1, C2), 58.8 (OMe), 34.6 (C3, C5),
34.5 (C4). Minor diastereomer: 1H NMR (400 MHz, CDCl3):
d¼3.92
(q, J¼5.5 Hz, 2H, H1, H2), 3.40 (s, 3H, OMe), 3.34 (d, J¼4.0 Hz, 2H,
eCH2OMe), 2.30e2.20 (m, 1H, H4), 2.10e2.02 (m, 2H, H4, H5), 1.51
(dt, J¼13.9, 5.5 Hz, 2H, H4, H5). 13C NMR (100 MHz, CDCl3):
¼76.4
d
(eCH2OMe), 74.1 (C1, C2), 59.1 (OMe), 34.2 (C5), 34.0 (C3, C4). IR:
3396, 2930, 1442, 1388, 1338, 1115, 927 cmꢁ1; MS (EI): m/z¼146,
128, 114, 101, 96, 83, 69, 55, 45. APCI-MS: m/z observed 146.0942,
calcd for C7H14O3 146.0943.
4.2.2.5. (1S,2S,3R)-3-(2-(Benzyloxy)ethyl)cyclopentane-trans-1,2-
diol 1m. Compound 1m was obtained as white crystals (186 mg,
20%), mp 34e35 ꢀC. 1H NMR (400 MHz, CDCl3):
d
¼7.33e7.25 (m,
4.2.2. Characterization of the prepared diols 1
4.2.2.1. 3-Benzylcyclopentane-cis-1,2-diol 1h. Compound 1h was
obtained by the general dihydroxylation procedure over 3 days
(711 mg, 93%) as a 1:0.6 mixture of diastereomers (white crystals,
mp 46e47 ꢀC). Major diastereomer: 1H NMR (400 MHz, CDCl3):
5H, Ph), 4.50 (s, 2H, Bn), 4.05 (tt, J¼4.3, 2.3 Hz, 1H, H1), 3.89 (dd,
J¼5.3, 2.3 Hz, 1H, H2), 3.61e3.56 (m, 1H, CH2CH2OBn), 3.49e3.42
(m, 1H, CH2CH2OBn), 2.18e2.03 (m, 2H, H3, H5), 1.88e1.77 (m, 2H,
H4, CH2CH2OBn), 1.69e1.61 (m, 1H, CH2CH2OBn), 1.48e1.33 (m,
d
¼7.31e7.16 (m, 5H, Ph), 4.07 (dd, J¼8.8, 5.3 Hz, 1H, H1), 3.64 (t,
2H, H4, H5). 13C NMR (100 MHz, CDCl3):
127.8 (Ph), 127.8 (Ph), 79.7 (C2), 79.0 (C1), 73.4 (Bn), 70.1
d
¼137.9 (Ph), 128.5 (Ph),
J¼5.6 Hz, 1H, H2), 2.88 (dd, J¼13.5, 6.3 Hz, 1H, Bn), 2.59 (dd, J¼13.5,
8.5 Hz, 1H, Bn), 2.42 (broad s, 1H, OH1), 2.25e2.16 (m, 2H, H3, OH2),
2.01e1.82 (m, 2H, H4, H5), 1.68e1.57 (m, 1H, H5), 1.25e1.14 (m, 1H,
(eCH2CH2OBn), 41.0 (C3), 31.7 (C5), 29.4 (eCH2CH2OBn), 28.3 (C4);
(assignment of diastereomers based on
g-syn effect between
H4). 13C NMR (100 MHz, CDCl3):
d¼140.8 (Ph), 129.0 (Ph), 128.6
C2eOH and eCH2CH2OBn groups when comparing 13C chemical
shifts of compounds 1m and 1n). IR: 3375, 2937, 1454, 1364, 1095,
956, 738, 698 cmꢁ1; MS (EI): m/z¼236, 218, 200, 174, 156, 145, 127,
107, 91. APCI-MS: m/z observed 236.1412, calcd for C14H20O3
236.1412.
(Ph), 126.2 (Ph), 78.9 (C2), 73.0 (C1), 45.5 (C3), 39.8 (Bn), 30.4 (C5),
26.5 (C4). Minor diastereomer: 1H NMR (400 MHz, CDCl3):
d
¼7.31e7.16 (m, 5H, Ph), 4.16e4.10 (m, 1H, H1), 3.83 (t, J¼4.0 Hz,1H,
H2), 2.92 (dd, J¼13.5, 7.9 Hz, 1H, Bn), 2.66 (dd, J¼13.6, 7.6 Hz, 1H,
Bn), 2.42 (broad s, 1H, OH2), 2.34 (broad s, 1H, OH1), 2.14e2.02 (m,
1H, H3), 2.01e1.82 (m, 1H, H5), 1.68e1.57 (m, 3H, H4, H5). 13C NMR
4.2.2.6. (1S,2S,3S)-3-(2-(Benzyloxy)ethyl)cyclopentane-trans-1,2-
(100 MHz, CDCl3):
d
¼141.6 (Ph), 128.9 (Ph), 128.5 (Ph), 125.9 (Ph),
diol 1n. Compound 1n was obtained as a colourless oil (77 mg,
74.7 (C1), 74.3 (C2), 44.3 (C3), 36.0 (Bn), 30.9 (C5), 27.3 (C4). IR:
3409, 2924, 1604, 1495, 1453, 1341, 1100, 1038, 752, 701 cmꢁ1; MS
(EI): m/z¼192, 174, 156, 145, 130, 117, 91, 83. Anal. Calcd for C7H14O3:
C, 74.97; H, 8.39. Found: C, 74.95; H, 8.44.
9%). 1H NMR (400 MHz, CDCl3):
d
¼7.36e7.25 (m, 5H, Ph), 4.50 (s,
2H, Bn), 3.95 (q, J¼7.3 Hz, 1H, H1), 3.60e3.55 and 3.53e3.49 (m,
2H, eCH2CH2OBn), 3.48e3.43 (m, 1H, H2), 1.98e1.89 (m, 1H, H5),
1.87e1.68 (m, 3H, H3, H4, eCH2CH2OBn), 1.64e1.57 (m, 1H,

3612
I. Reile et al. / Tetrahedron 70 (2014) 3608e3613
eCH2CH2OBn), 1.55e1.46 (m, 1H, H5), 1.40e1.32 (m, 1H, H4). 13C
NMR (100 MHz, CDCl3):
(Ph), 84.3 (C2), 78.1 (C1), 73.1 (Bn), 70.0 (eCH2CH2OBn), 42.6 (C3),
34.4 (C5), 29.0 (eCH2CH2OBn), 26.4 (C4); (assignment
4.5. Characterization of oxidation products
d
¼137.7 (Ph), 128.5 (Ph), 127.8 (Ph), 127.8
4.5.1. 2-Hydroxy-3-(2-benzyloxyethyl)-2-cyclopenten-1-one 4a. The
compound (68 mg, 70%) spectral properties coincided with a liter-
ature example.40
of diastereomers based on
g-syn effect between C2eOH and
eCH2CH2OBn groups when comparing 13C chemical shifts of
compounds 1m and 1n). IR: 3368, 2869, 1454, 1363, 1099,
738, 699 cmꢁ1; MS (EI): m/z¼236, 218, 200, 174, 156, 145, 127,
107, 91. APCI-MS: m/z observed 236.1415, calcd for C14H20O3
236.1412.
4.5.2. 2-Hydroxy-3-methyl-2-cyclopenten-1-one 4b. The compound
(35 mg, 74%) was identical to a commercial sample.
4.5.3. 2-Hydroxy-3-(2-hydroxyethyl)-2-cyclopenten-1-one 4c. The
compound (29 mg, 49%) spectral properties coincided with a liter-
ature example.45
4.2.2.7. 2,7-Dimethyloctane-4,5-diol 5. Compound 5 was pre-
pared from isovaleric aldehyde by pinacol coupling,43 the com-
pound was obtained as white needles (379 mg, 63%), mp 72e74 ꢀC.
4.5.4. 2-Hydroxy-3-oxo-1-cyclopentene-1-acetic acid-1,1-
dimethylpropyl ester 4d. The compound (27 mg, 28%) spectral
properties coincided with a literature example.45
1H NMR (400 MHz, CDCl3)
d
¼3.44 (ddd, J¼7.7, 3.1, 1.7 Hz, 2H, H4,
H5), 2.52 (broad s, 2H, 2ꢂOH), 1.86e1.81 (m, 2H, H2, H7), 1.41 (ddd,
J¼14.0, 9.4, 4.6 Hz, 2H, H3, H6),1.22 (ddd, J¼12.5, 9.5, 3.0 Hz, 2H, H3,
H6), 0.93 (dd, J¼10.2, 6.6 Hz, 12H, 4ꢂMe). 13C NMR (100 MHz,
4.5.5. N-[2-(2,3-Dioxocyclopentyl)ethyl]-carbamic acid-1,1-
dimethylethyl ester 4e. The compound (78 mg, 76%) spectral prop-
erties coincided with a literature example.31
CDCl3):
d
¼73.0 (C4, C5), 42.7 (C3, C6), 24.5 (C2, C7), 23.8 and 21.7
(4ꢂMe). IR: 3347, 2957, 1469, 1367, 1058, 844, 719 cmꢁ1; MS spectra
coincides with public database values.44
4.5.6. 2-Hydroxy-3-phenyl-2-cyclopenten-1-one 4f. The compound
(51 mg, 69%) spectral properties coincided with an authentic
sample.46
4.2.2.8. tert-Butyl-(3-hydroxycyclopentyl)acetate 6. Compound
6 was prepared from the corresponding carboxylic acid over two
steps (110 mg, 18%). 1H NMR (400 MHz, CDCl3):
d
¼4.27e4.22 (m,
1H, CeOH), 2.28e2.26 (m, 2H, CH2COOtBu), 2.23e2.07 (m, 2H, H1,
H2), 1.80e1.66 (m, 2H, H4, H5), 1.64e1.56 (m, 1H, H4), 1.46e1.38 (m,
1H, H5), 1.37 (s, 9H, t-Bu), 1.23e1.14 (m, 1H, H2). 13C NMR (100 MHz,
4.5.7. 2-Hydroxy-3-(benzyl)-2-cyclopenten-1-one 4h. The com-
pound (52 mg, 65%) spectral properties coincided with an authentic
example.47
CDCl3):
d
¼171.6 (COO), 79.2 (C(CH3)3), 72.6 (C3), 40.9 (CH2COOtBu),
40.7 (C2), 34.5 (C4), 33.8 (C1), 28.9 (C5), 27.1 (t-Bu). MS (EI): m/
z¼200, 144, 127, 109, 81.
4.5.8. 4-[(Benzyloxy)methyl]-2-hydroxycyclopent-2-en-1-one
4i. The compound was obtained, following the general pro-
cedures described above, as a colourless oil (58 mg, 63%): 1H
4.3. General procedure for the catalytic aerobic oxidation of
diols
NMR (400 MHz, CDCl3):
d
¼7.38e7.26 (m, 5H, Ph), 6.53 (d,
J¼3.0 Hz, 1H, H3), 5.73 (broad s, 1H, eOH), 4.53 (s, 2H, Bn),
3.50e3.40 (m, 2H, eCH2Oe), 3.12e3.06 (m, 1H, H4), 2.59 (dd,
J¼19.4, 6.0 Hz, 1H, H5), 2.22 (dd, J¼19.4, 1.6 Hz, 1H, H5). 13C NMR
Diol (0.424 mmol), Pt/C catalyst (1 or 5 mol % metal loading
compared to diol),32 LiOH$H2O (1.0 equiv, 0.424 mmol) and sol-
vent (2 mL, MeCN/H2O 1:1) were added to a 10 mL glass reactor,
equipped with a condenser and stirred at 60 ꢀC for the appro-
priate time. The reaction progress was monitored by TLC. When
the product formation had stopped, the catalyst was filtered off
and rinsed with EtOAc (3ꢂ3 mL), resulting in a biphasic solution.
The aqueous phase was acidified to pH 5 with 1 M HCl and the
layers were separated. The aqueous layer was extracted twice
with EtOAc (20 mL). All organics were combined and dried over
MgSO4 and were concentrated in a vacuum. The crude product
was purified by column chromatography (EtOAc/petroleum ether
or MeOH/CH2Cl2) to give the product diketone as its ketoenol
tautomer 4.
(100 MHz, CDCl3):
d
¼203.3 (C1), 153.4 (C2), 138.0 (Ph), 130.5 (C3),
128.6 (Ph), 127.9 (Ph), 127.8 (Ph), 73.4 (Bn), 73.2 (eCH2Oe), 36.5
(C5), 35.4 (C4). IR: 3343, 2860, 1686, 1654, 1455, 1395, 1198, 1100,
740, 700 cmꢁ1; MS (EI): m/z¼218, 200, 188, 172, 160, 145, 134, 121,
107, 91. APCI-MS: m/z observed 218.0937, calcd for C13H14O3
218.0943.
4.5.9. 4-(tert-Butoxymethyl)-2-hydroxycyclopent-2-en-1-one
4j. The compound was obtained, following the general pro-
cedures described above, as colourless crystals (48 mg, 61%),
mp 64e66 ꢀC: 1H NMR (400 MHz, CDCl3):
d
¼6.57 (d, J¼3.0 Hz, 1H,
H3), 6.04 (broad s, 1H, eOH), 3.38e3.28 (m, 2H, eCH2Oe),
3.00e2.95 (m, 1H, H4), 2.58 (dd, J¼19.4, 6.0 Hz, 1H, H5), 2.18 (dd,
J¼19.4, 1.6 Hz, 1H, H5), 1.18 (s, 9H, t-Bu). 13C NMR (100 MHz,
4.4. General procedure for larger scale catalytic aerobic oxi-
dation of diols
CDCl3):
d
¼203.8 (C1), 153.3 (C2), 131.5 (C3), 73.2 (eC(CH3)3), 65.2
(eCH2Oe), 36.7 (C5), 35.8 (C4), 27.6 (t-Bu). IR: 3334, 1707, 1644,
1395, 1375, 1193, 1077, 1058, 842 cmꢁ1; MS (EI): m/z¼184, 169,
153, 128, 111, 98, 87, 80, 57. APCI-MS: m/z observed 184.1103, calcd
for C10H16O3 184.1099.
Diol (9 mmol) was dissolved in 45 mL of solvent (MeCN/H2O
1:1) and the Pt/C catalyst catalyst32 was added (1 mol % metal
loading based on diol), followed by
1 equiv of LiOH$H2O
(9 mmol). A 0.3 mL/min flow of solvent-saturated air was bubbled
through the reaction mixture and the reaction was stirred at
60 ꢀC for 6 h. The catalyst was filtered from the reaction mixture,
rinsed three times with 10 mL of EtOAc and the biphasic solution
was adjusted to pH 5 with 1.0 M HCl. The phases were separated
and the aqueous phase was extracted twice with 20 mL of EtOAc.
All organics were combined and dried over MgSO4, the solvent
was evaporated and the product and the regenerated starting
material were purified by column chromatography (MeOH/
CH2Cl2).
4.5.10. 4-(Methoxymethyl)-2-hydroxycyclopent-2-en-1-one 4k. The
compound was obtained, following the general procedures de-
scribed above, as colourless crystals (37 mg, 62%), mp 46e48 ꢀC:
1H NMR (400 MHz, CDCl3):
d
¼6.53 (d, J¼3.0 Hz, 1H, H3),
6.46e6.21 (broad s, 1H, eOH), 3.41e3.33 (m, 2H, eCH2OMe), 3.37
(s, 3H, OMe), 3.08e3.05 (m, 1H, H4), 2.59 (dd, J¼19.4, 6.0 Hz, 1H,
H5), 2.21 (dd, J¼19.3, 1.6 Hz, 1H, H5). 13C NMR (100 MHz, CDCl3):
d
¼203.5 (CO), 153.6 (COH), 130.7 (C3), 75.8 (eCH2OMe), 59.2
(OMe), 36.5 (C5), 35.2 (C4). IR: 3222, 2910, 1705, 1654, 1394, 1200,

I. Reile et al. / Tetrahedron 70 (2014) 3608e3613
3613
1099, 957, 860 cmꢁ1; MS (EI): m/z¼142, 112, 97, 83, 69, 45. APCI-
MS: m/z observed 142.0629, calcd for C7H14O3 142.0630.
5. Buffin, B. P.; Clarkson, J. P.; Belitz, N. L.; Kundu, A. J. Mol. Catal. A: Chem. 2005,
225, 111e116.
6. Seddon, K. R.; Stark, A. Green Chem. 2002, 4, 119e123.
7. Steinhoff, B. a; King, A. E.; Stahl, S. S. J. Org. Chem. 2006, 71, 1861e1868.
8. Matsumoto, T.; Ueno, M.; Wang, N.; Kobayashi, S. Chem.dAsian J. 2008, 3,
196e214.
4.5.11. 2-Hydroxy-2-cyclopenten-1-one, 4l. The compound (8 mg,
19%) spectral properties coincided with an authentic sample.48
9. Yamada, Y. M. A.; Arakawa, T.; Hocke, H.; Uozumi, Y. Angew. Chem., Int. Ed. 2007,
46, 704e706.
10. Miyamura, H.; Matsubara, R.; Kobayashi, S. Chem. Commun. 2008, 2031e2033.
11. Murugadoss, A.; Sakurai, H. J. Mol. Cat. A: Chem. 2011, 341, 1e6.
12. Giachi, G.; Oberhauser, W.; Frediani, M.; Passaglia, E.; Capozzoli, L.; Rosi, L. J.
Polym. Sci., Part A: Polym. Chem. 2013, 51, 2518e2526.
13. Karimi, B.; Zamani, A.; Clark, J. H. Organometallics 2005, 24, 4695e4698.
14. D’Agostino, C.; Kotionova, T.; Mitchell, J.; Miedziak, P. J.; Knight, D. W.; Taylor, S.
H.; Hutchings, G. J.; Gladden, L. F.; Mantle, M. D. Chem.dEur. J. 2013, 19,
11725e11732.
15. Wu, H.; Zhang, Q.; Wang, Y. Adv. Synth. Catal. 2005, 347, 1356e1360.
16. Tongsakul, D.; Nishimura, S.; Ebitani, K. ACS Catal. 2013, 3, 2199e2207.
17. Mori, K.; Hara, T.; Mizugaki, T.; Ebitani, K.; Kaneda, K. J. Am. Chem. Soc. 2004,
126, 10657e10666.
18. Chen, G.; Wu, S.; Liu, H.; Jiang, H.; Li, Y. Green Chem. 2013, 15, 230e235.
19. Steele, A. M.; Zhu, J.; Tsang, S. C. Catal. Lett. 2001, 73, 9e13.
20. Korovchenko, P.; Donze, C.; Gallezot, P.; Besson, M. Catal. Today 2007, 121,
13e21.
4.5.12. 3-oxo-Cyclopentaneacetic acid-tert-butyl ester 7. The com-
pound was obtained, following the general procedures described
above, as a yellow oil (22 mg, 28%). Compound 7 had been isolated
earlier.49 1H NMR (400 MHz, CDCl3):
d¼2.57e2.45 (m, 1H, H1),
2.43e2.36 (m, 1H, H2), 2.35e2.27 (m, 2H, eCH2COOe), 2.27e2.19
(m, 1H, H4), 2.19e2.07 (m, 2H, H4, H5), 1.82 (ddd, J¼18.2, 10.1,
1.4 Hz, 1H, H2), 1.56e1.45 (m, 1H, H5), 1.38 (s, 9H, t-Bu). 13C NMR
(100 MHz, CDCl3):
d
¼218.7 (C3), 171.5 (eCOOe), 80.8 (eC(CH3)3),
44.7 (C2), 41.2 (eCH2COOe), 38.4 (C4), 33.8 (C1), 29.3 (C5), 28.2 (t-
Bu); IR: 2976, 1729, 1458, 1368, 1154, 842 cmꢁ1; MS (EI): m/z¼183,
142, 125, 97, 83, 57.
4.5.13. 3-oxo-Cyclopentaneacetic acid 70. The compound was ob-
tained, following the general procedures described above, as a yel-
low oil (20 mg, 33%). Compound 70 has been isolated by others
21. Mori, S.; Takubo, M.; Makida, K.; Yanase, T.; Aoyagi, S.; Maegawa, T.; Monguchi,
Y.; Sajiki, H. Chem. Commun. 2009, 5159e5161.
22. Karimi, B.; Behzadnia, H.; Bostina, M.; Vali, H. Chem.dEur. J. 2012, 18,
8634e8640.
earlier.50 1H NMR (400 MHz, CDCl3):
d
¼2.68e2.57 (m, 1H, H1),
ꢀ
23. Abad, A.; Concepcion, P.; Corma, A.; García, H. Angew. Chem., Int. Ed. 2005, 44,
4066e4069.
2.56e2.44 (m, 3H, H2, eCH2eCOOH), 2.36e2.15 (m, 3H, H4, H5),
1.91 (ddd, J¼18.3, 10.2, 1.4 Hz, 1H, H2), 1.67e1.54 (m, 1H, H5). 13C
24. Yamaguchi, K.; Mizuno, N. Chem.dEur. J. 2003, 9, 4353e4361.
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28. Ishii, Y.; Yamawaki, K.; Ura, T.; Yamada, H.; Yoshida, T.; Ogawa, M. J. Org. Chem.
1988, 53, 3587e3593.
NMR (100 MHz, CDCl3):
d
¼218.7 (C3), 177.2 (COOH), 44.7 (C2), 39.6
(eCH2eCOOH), 38.5 (C4), 33.4 (C1), 29.3 (C5). IR: 3352, 3209, 2963,
1733, 1660, 1403, 1161, 757 cmꢁ1; MS (EI): m/z¼142, 113, 97, 85, 83,
60, 55, 41.
29. Takezawa, E.; Sakaguchi, S.; Ishii, Y. Org. Lett. 1999, 1, 713e715.
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2059e2062.
Acknowledgements
We are grateful for the help of the following co-workers from
the Tallinn University of Technology: Tiiu Kailas for FT-IR spectra
and Aleksander-Mati Muurisepp for GCeMS. We also thank the
31. Reile, I.; Paju, A.; Eek, M.; Pehk, T.; Lopp, M. Synlett 2008, 347e350.
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€€
Estonian Science Foundation (Grant No. 8289 and 8880), the Es-
tonian Ministry of Education and Research (Grant No. 0142725s06),
the EU European Regional Development Fund (3.2.0101.08-0017),
grant agreement No. 229830 IC-UP2 under the seventh Framework
Programme of the European Commission and the “Functional ma-
terials and technologies” graduate school, receiving funding from
the European Social Fund under project 1.2.0401.09-0079 in Esto-
nia, for their financial support.
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Supplementary data
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44. Wiley Mass Spectroscopy Database.
Additional detailed synthesis procedures, NMR spectra and
crystallographic data are available in the included Supplementary
data. Supplementary data related to this article can be found at
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€€
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~
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