Selective catalysis for the oxidation of alcohols to aldehydes in the presence of cucurbit[8]uril

Article abstract of DOI:10.1016/j.catcom.2011.03.029

Efficient selectivity for the supramolecular catalysis by cucurbit[8]uril (Q[8]) for the oxidation of aryl, allyl, and alkyl alcohols to corresponding aldehydes by o-Iodoxybenzoic acid (IBX) in aqueous solvent is reported. The relationship between the catalytic ability of Q[8] and the structure of the substrate has revealed that the catalyst prefers aryl and allyl alcohols to alkyl alcohols, and the conversions of most aryl and allyl alcohols have been increased by 30-50% in the presence of Q[8]. The catalytic selectivity suggests that the IBX oxidation proceeds via a stabilized α-Carbanion intermediate and the supramolecular catalysis should be mechanistically related to the electron density and reactivity of the α-Carbanion.

Full text of DOI:10.1016/j.catcom.2011.03.029

Catalysis Communications 12 (2011) 1127–1130
Contents lists available at ScienceDirect
Catalysis Communications
journal homepage: www.elsevier.com/locate/catcom
Short Communication
Selective catalysis for the oxidation of alcohols to aldehydes in the presence
of cucurbit[8]uril
a
a
a
Yong-Huan Wang a, Hang Cong a, , Fang-Fang Zhao , Sai-Feng Xue , Zhu Tao ,
⁎
Qian-Jiang Zhu a, Gang Wei b,
⁎
a
Key Laboratory of Macrocyclic and Supramolecular Chemistry of Guizhou Province, Guizhou University, Guiyang 550025, PR China
b
CSIRO Materials Science and Engineering, P.O. Box 218, Lindfield, NSW 2070, Australia
a r t i c l e i n f o
a b s t r a c t
Article history:
Efficient selectivity for the supramolecular catalysis by cucurbit[8]uril (Q[8]) for the oxidation of aryl, allyl,
and alkyl alcohols to corresponding aldehydes by o-Iodoxybenzoic acid (IBX) in aqueous solvent is reported.
The relationship between the catalytic ability of Q[8] and the structure of the substrate has revealed that the
catalyst prefers aryl and allyl alcohols to alkyl alcohols, and the conversions of most aryl and allyl alcohols
have been increased by 30–50% in the presence of Q[8]. The catalytic selectivity suggests that the IBX
oxidation proceeds via a stabilized α-Carbanion intermediate and the supramolecular catalysis should be
mechanistically related to the electron density and reactivity of the α-Carbanion.
Received 10 January 2011
Received in revised form 5 March 2011
Accepted 19 March 2011
Available online 26 March 2011
Keywords:
Cucurbituril
Oxidation
© 2011 Elsevier B.V. All rights reserved.
Supramolecular catalysis
Alcohol
IBX
1. Introduction
alcohols to carbonyl products with IBX in a mixed solvent of ionic
liquid and water in spite of the stoichiometric excess of IBX [14]. Rao
The oxidation of alcohols to their corresponding aldehydes [1,2],
especially the dependence of selectivity on the structure of the
substrate [3,4], is one of the most important synthetic processes in
organic chemistry. Numerous investigations into the easy isolation of
the product and recycling of the catalyst emphasise the importance of
the development of an efficient heterogeneous catalysis system [5,6].
From the economical and environmental viewpoint, such stoichio-
metric, safe and eco-friendly oxidizing reagents are thus extremely
valuable [7,8]. o-Iodoxybenzoic acid (IBX, Scheme 1), a precursor in
the preparation of Dess–Martin periodinane, was already known in
1893 [9], but it had little use in synthetic chemistry until an awareness
of its solubility in DMSO was observed [10].
In the last 5 years, IBX has attracted amazing attention due to its
unique combination of a mild and extraordinarily efficient oxidizing
reagent with high selectivity to perform a number of oxidation
reactions, especially alcohol oxidation [11,12]. In fact, IBX can carry out
the oxidation of alcohols as a suspension in many common solvents
besides DMSO. Finney et al. observed that the suspended IBX showed a
satisfying capability to transform primary and second alcohols to the
corresponding carbonyl compounds in ethyl acetate, trichloro-
methane, acetone and so on, close to the refluxing temperature of
the solvent [13]. Chen and co-workers described the oxidation of
et al. described an efficient oxidation of various alcohols by IBX with β-
cyclodextrin catalysis in water/acetone mixture [15]. IBX has been
proved to be able to carry out the efficient oxidation of various
substrates other than alcohols, such as phenols [16,17], ethers [18],
amines and sulfides [19,20]. Since most of these oxidations have
inevitably been carried out in organic solvents, since a hydrophobic
solvent can promote the removal of water in the oxidation reaction, we
have recently built a clean oxidation process with this hypervalent
iodine reagent via cucurbituril-mediated catalysis for the transforma-
tion in water of benzylic alcohols into the corresponding aldehydes
[21].
Cucurbit[n]uril (Q[n], n=5–8 and 10, Scheme 1) are macrocyclic
compounds with carbonyl groups on both portals and a hydrophobic
cavity enclosed with the glycoluril wall [22]. The cavity can be filled
with organic molecules involving amino groups, alcohols, phenols and
some small biomolecules with weak ion-dipole, hydrogen binding,
hydrophobic or hydrophilic properties [23,24]. Depending on the
host–guest chemistry, cucurbituril-induced supramolecular catalysis
has made a significant contribution to organic synthesis [25]. The
cucurbit[8]uril host, in particular, is always able to accommodate
sizeable guests in its cavity to form ternary complexes in a ratio of 1:2
or 1:1:1 [26,27], giving the unique property of stereoselective
cycloaddition reactions within the “nano-reaction vessels” of Q [8]
[28,29]. The encapsulation of substrates within Qs has been
considered to be mechanistically connected to the easy formation of
a transition state, since the distance between reagents was expected
⁎
Corresponding authors. Tel.: +86 851 3623903; fax: +86 851 3620906.
E-mail addresses: ecnuc@163.com (H. Cong), Gang.Wei@csiro.au (G. Wei).
1566-7367/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.catcom.2011.03.029

1128
Y.-H. Wang et al. / Catalysis Communications 12 (2011) 1127–1130
have precipitated our previous success in the exploration of the Q [8]-
catalyzed oxidation of benzylic alcohol [21]. Further studies of the
universality and selectivity of the supramolecular catalysis are
reported in this work.
2. Results and discussion
The goal of this work is to develop the supramolecular catalysis of
Q [8] as described above, various alcohols, such as aryl alcohols, allyl
alcohols and alkyl alcohols, were used to investigate the catalytic
efficiency on IBX oxidations by Q[8]. With the optimized reaction
conditions of our previous work [21], the oxidation of alcohols with
IBX in the presence and absence of Q[8] has been carried out,
and Table 1 illuminates the scope of the procedures as well as the
transformation results of the alcohols.
As a general rule, the Q[8]-induced supramolecular catalysis of the
oxidations is clearly affected by the species of aryl and allyl alcohols
(entry 1–10). However, the oxidations by IBX of the alkyl alcohols
(entry 11–14) are very inefficient, for the transformation is barely
observable, either in the absence or in the presence of the macrocyclic
compound Q[8], and even if the reaction time for the oxidation is
extended to as long as 1 h. In each case, for a random selection of
alkyl alcohols, the isolated conversion was within 5% of the value
determined by gas chromatography. In our previous work [21], we
have shown that the equilibrium conversions of veratryl alcohol with
catalysis of Q[8] were always higher than those in the absence of Q[8]
at different temperatures, indicating that the supramolecular catalysis
should be under thermodynamic control. It is impossible to form
Scheme 1. Structures of cucurbiturils and o-Iodoxybenzoic acid, and Q[8]-catalyzed
oxidation of alcohols.
to be reduced as a result of encapsulation [30]. The host–guest
interactions between alcohols and Q [6] have been determined in the
work of Buschmann's group [31,32], and other pioneering studies
Table 1
Q[8]-catalytic oxidation of alcohols with IBX.
Entry
1
Substituent
Product
Time
(min)
Conversion(%) to aldehyde
With Q[8]
74.6
Without Q[8]
46.0
15
O
O
O
OH
O
H
O
O
2
3
4
20
20
10
79.6
68.8
74.9
34.3
42.9
25.2
OH
H
O
OH
O
H
O
O
O
O
O
OH
OH
O
O
H
H
5
6
30
15
58.3
87.1
44.9
20.3
O
OH
O
H
O
O
7
8
30
30
73.6
64.2
34.3
49.7
OH
S
H
S
O
OH
H
O
9
30
30
79.4
83.7
50.5
44.8
OH
OH
H
H
O
10
11
60
b5
b5
OH
O
12
13
14
60
60
60
b5
b5
b5
b5
b5
b5
O
OH
O
OH
OH
O

Y.-H. Wang et al. / Catalysis Communications 12 (2011) 1127–1130
1129
stable alpha-carbanions with alkyl alcohols so that the Q[8]-induced
supramolecular catalysis on the IBX oxidation is generally invalid to
these alcohols.
benzyl and allyl alcohols but makes no improvement to the oxidation
of alkyl alcohols. The catalytic ability of Q[8] for benzyl and allyl
alcohols is relevant to the substrate structure. The analysis of
the electronic effect of the alcohols indicates that the electron-rich
α-Carbanion contributes to the improvement of the supramolecular
catalysis. No steric effects have been clearly observed in the above
cases.
For the team of aryl alcohols (entries 1–7), the catalysis by Q [8] of
the oxidization of an alcohol with IBX is, on the whole, satisfactory. The
highest degree of supramolecular catalysis is shown by the improved
conversion of 2-furyl alcohol (entry 6), by up to about 67% in the
presence of Q [8], and the oxidizing conversion of 3-methoxybenzyl
alcohol (entry 4) is also increased from 25.2% to 74.9% with catalysis by
Q[8]. It is evident that the supramolecular catalytic ability of Q [8] on the
other aryl alcohols (entries 1–3, 5, 7) is very different from the above
two species. For veratryl alcohol, benzylic alcohol, 2-methoxybenzyl
alcohol (entries 1–3) and 2-thenyl alcohol (entry 7), the conversions to
the corresponding aldehydes are always improved by about 30–40%
with Q [8] catalysed oxidation. In particular, for 4-methoxybenzyl
alcohol (entry 5), only 13.4% improvement is found when the
macrocyclic compound Q[8] is used as supramolecular catalyst, even
with a longer reaction time. The above interesting results, namely that
the catalytic ability of Q [8] is seriously dependent on the substrate
structures of the aryl alcohols, tend to prove that an electronic effect of
the substrates seems to exist for these aryl alcohol systems. Taking the
methoxybenzyl alcohols, for example, a strong negative inductive effect
and weak conjugated effect on the α-C occurs in the 3-methoxybenzyl
alcohol, and both positive conjugated effect and negative inductive
effect are present in the substituent of 2-methoxybenzyl alcohol, but
only the conjugated effect is noticeable in 4-methoxybenzyl alcohol.
Obviously, the catalysis of Q [8] for substrates with predominantly
negative inductive effect is significantly stronger, and the high
conjugated effort generally causes a reduction of Q[8] catalytic activity.
A similar electronic effect is also found in the team of allyl alcohols
(entries 8–10). Comparing cinnamyl alcohol (entry 8) to the other
allyl alcohols, the improvement of conversion is particularly poor in
the presence of Q[8] under the same reaction conditions, which
correspond to the conjugated effect of the styryl group in the
cinnamyl alcohol. Only about 15% improvement with Q [8] was
found. Nerol (entry 9) and geraniol (entry 10) are a pair of geometric
isomers, and the similar conversion of about 30–35% has been
improved in the presence of Q[8]. The identical conversion suggests
that the stereo effect of substrates is not relevant to the cucurbituril-
induced catalysis system.
Based on the discovered electronic effect on the supramolecular
catalysis in the above cases, a plausible mechanism is proposed. The
analysis of conjugated and inductive effect drops a hint that the
formation of the intermediate of a stable α-Carbanion of substrate and
an electron transfer-mediated mechanistic pathway is crucial.
Accordingly, the alkyl alcohols, which cannot be stabilized to form
an α-Carbanion, exhibit chemical interactions in their oxidation with
IBX. With powerful manipulation possibilities for the electron on the
α-Carbanion, aryl and allyl alcohols always show different improve-
ment of transformation to aldehydes in the presence of Q [8]. It is well
known that Q [8] is able to induce electron transfer between electron–
donor and acceptor guests in the formation of a ternary supramolec-
ular assembly [27,28]. With this rule, the supramolecular catalysis of Q
[8] on the oxidation of alcohols with IBX is not difficult to understand,
since it means that the electron transfer between the stabilized
carbanion and the hypervalent iodine in IBX should be enhanced in
the cavity of Q [8], and the selectivity of the catalyst is essential to the
electron transfer ability of the reaction intermediate.
4. Experimental
4.1. Materials and apparatus
Cucurbit[8]uril was prepared and purified according to the methods
developed in our laboratory [33]. Alcohols and aldehydes were
purchased from Alfa Aesar (Tianjing) Chemical Co., Ltd. and used
without further purification. IBX was prepared with 2-iodobenzoic acid
and ozone [34]. 1H NMR (d6-DMSO, δ): 7.20 (t, 1H), 7.44 (t, 1H), 7.66 (d,
1H), 7.94 (d, 1H). Mp: 230–233 °C with explosive decomposition.
Gas chromatography (GC) was performed using an Angilent
6820 with a HP-Innovax quartz capillary column (30 m×0.32 mm×
0.25 μm) and flame ionization detector (FID) using ultrapure nitrogen
as the carrier gas.
4.2. Catalytic oxidation experiments
The alcohol (0.2 mmol) was added to a suspension of 0.2 mmol IBX
and Q[8] in 25 ml distilled water. The reaction was carried out at a
temperature of 95 °C [21]. When cooled to room temperature, the
product was separated from the mixture by filtration under vacuum and
extracted with ethyl acetate (3×5.0 ml). The organic phase wasbrought
to volume (25 ml) before GC analysis. The reaction conversions were
determined by gas chromatographic analysis using the external
standard. The products were identified by comparing their retention
time in GC with the aldehydes obtained commercially.
Acknowledgement
We acknowledge the support of the “Chun Hui” Project of the
Chinese Ministry of Education (No. Z2008-1-5501), the International
Collaboration Project of Guizhou Province, the Natural Science
Foundation of Guizhou Province (Nos. [2008]75 and [2009]2073),
and the Natural Science Project of the Department of Education of
Guizhou Province (No. (2008)10).
Appendix A. Supplementary data
Supplementary data to this article can be found online at
doi:10.1016/j.catcom.2011.03.029.
References
[1] P. Lahtinen, J.U. Ahmad, E. Lankinen, P. Pihko, M. Leskelä, T. Repo, J. Mol. Catal. A
275 (2007) 228.
[2] V.V. Namboodiri, V. Polshettiwar, R.S. Varma, Tetrahedron Lett. 48 (2007) 8839.
[3] W. Hou, N.A. Dehml, R.W.J. Scott, J. Catal. (2007) 1.
[4] Z. Ye, Z. Fu, S. Zhong, F. Xie, X. Zhou, F. Liu, D. Yin, J. Catal. 261 (2009) 110.
[5] S. Farhadi, Z. Momeni, J. Mol. Catal. A 277 (2007) 47.
[6] H. Tsunoyama, H. Sakurai, Y. Negishi, T. Tsukuda, J. Am. Chem. Soc. 127 (2005)
9374.
[7] M.G. Buonomenna, E. Drioli, Appl. Catal. B 79 (2007) 35.
[8] J.T. Su, W.A. Goddard, J. Am. Chem. Soc. 127 (2005) 14146.
[9] C. Hartman, V. Meyer, Chem. Ber. 26 (1893) 1727.
[10] M. Frigerio, M. Santagostino, Tetrahedron Lett. 35 (1994) 8019.
[11] R. Bernini, E. Mincione, M. Barontini, F. Crisante, J. Agric. Food Chem. 56 (2008)
8897.
[12] I.N. Lykakis, I.-P. Zaravinos, C. Raptis, M. Stratakis, J. Org. Chem. 74 (2009) 6339.
[13] J.D. More, N.S. Finney, Org. Lett. 4 (2002) 3001.
[14] Z. Liu, Z.-C. Chen, Q.-G. Zheng, Org. Lett. 5 (2003) 3321.
[15] K. Surendra, N.S. Krishnaveni, M.A. Reddy, Y.V. Nageswar, K.R. Rao, J. Org. Chem.
68 (2003) 2058.
3. Conclusion
Selectivity of an efficient supramolecular catalysis system for
cucurbit[8]uril-mediated oxidation of alcohol with the hypervalent
iodine reagent, IBX, is investigated in detail. The Q[8]-induced
transformation of aryl, allyl and alkyl alcohols into the corresponding
aldehydes reveals that the macrocyclic compound catalytically favors

1130
Y.-H. Wang et al. / Catalysis Communications 12 (2011) 1127–1130
[16] D. Magdziak, A.A. Rodriguez, R.W. Van De Water, T.R.R. Pettus, Org. Lett. 4 (2002)
285.
[26] Y.H. Ko, K. Kim, J.-K. Kang, H. Chun, J.W. Lee, S. Sakamoto, K. Yamaguchi, J.C.
Fettinger, K. Kim, J. Am. Chem. Soc. 126 (2004) 1932.
[17] Y. Huang, J. Zhang, T.R.R. Pettus, Org. Lett. 7 (2005) 5841.
[18] A. Ozanne, L. Pouységu, D. Depernet, B. Francüois, S. Quideau, Org. Lett. 5 (2003)
2903.
[19] K.C. Nicolaou, C.J.N. Mathison, T. Montagnon, J. Am. Chem. Soc. 126 (2004) 5192.
[20] V.G. Shukla, P.D. Salgaonkar, K.G. Akamanchi, J. Org. Chem. 68 (2003) 5422.
[21] H. Cong, F.-F. Zhao, J.-X. Zhang, X. Zeng, Z. Tao, S.-F. Xue, Q.-J. Zhu, Catal. Commun.
11 (2009) 167.
[22] A. Day, A.P. Arnold, R.J. Blanch, B. Snushall, J. Org. Chem. 66 (2001) 8094.
[23] J.W. Lee, S. Samal, N. Selvapalam, H.J. Kim, K. Kim, Acc. Chem. Res. 36 (2003) 621.
[24] J. Lagona, P. Mukhopadhyay, S. Chakrabarti, L. Isaacs, Angew. Chem. Int. Ed. 44
(2005) 4844.
[27] J.W. Lee, I. Hwang, W.S. Jeon, Y.H. Ko, S. Sakamoto, K. Yamaguchi, K. Kim, Chem.
Asian J. 3 (2008) 1277.
[28] S.P. Gromov, A.I. Vedernikov, L.G. Kuz'mina, D.V. Kondratuk, S.K. Sazonov, Y.A.
Strelenko, M.V. Alfimov, J.A.K. Howard, Eur. J. Org. Chem. (2010) 2587.
[29] B.C. Pemberton, N. Barooah, D.K. Srivatsava, J. Sivaguru, Chem. Commun. 46
(2010) 225.
[30] W.L. Mock, T.A. Irra, J.P. Wepsiec, M. Adhya, J. Org. Chem. (1989) 5302.
[31] H.-J. Buschmann, K. Jansen, E. Schollmeyer, Thermochim. Acta 317 (1998) 95.
[32] H.-J. Buschmann, K. Jansen, E. Schollmeyer, Thermochim. Acta 346 (2000) 33.
[33] G.-L. Zhang, Z.-Q. Xu, S.-F. Xue, Q.-J. Zhu, Z. Tao, Chin. J. Inorg. Chem. 19 (2003) 655.
[34] M. Frigerio, M. Santagostino, S. Sputore, J. Org. Chem. 64 (1999) 4537.
[25] H. Cong, Z. Tao, S.-F. Xue, Q.-J. Zhu, Curr. Org. Chem. 15 (2011) 86.