A new environmentally benign catalytic process for the asymmetric synthesis of lactones: Synthesis of the flavouring δ-decalactone molecule

Article abstract of DOI:10.1002/adsc.200303234

The system Sn-Beta/hydrogen peroxide is applied to the Baeyer-Villiger oxidation of delfone to δ-decalactone, which is an industrial fragrance. The reaction is carried out without solvent and with a substrate/catalyst ratio > 200 (wt/wt). Starting with an enantiomerically enriched delfone it is shown that the rearrangement occurs with retention of configuration at the migrating asymmetric carbon atom, and enantiomerically enriched δ-decalactone is obtained as product. This process offers clear advantages over the actual industrial production that uses peracids as oxidants.

Full text of DOI:10.1002/adsc.200303234

FULL PAPERS
A New Environmentally Benign Catalytic Process for the
Asymmetric Synthesis of Lactones: Synthesis of the Flavouring
d-Decalactone Molecule
Avelino Cormaa,*, Sara Iborraa, MarÌa Mifsuda, Michael Renza, Manuel Susarteb
a
Instituto de TecnologÌa QuÌmica, UPV-CSIC, Avda. de los Naranjos s/n, 46022 Valencia, Spain
Fax: ( ‡ 34)-96-387-7809; e-mail: acorma@itq.upv.es
b
Acedesa-Takasago, Murcia, Spain
Received: December 17, 2003; Accepted: February 7, 2004
Abstract: The system Sn-Beta/hydrogen peroxide is enantiomerically enriched d-decalactone is obtained
applied to the Baeyer Villiger oxidation of delfone to as product. This process offers clear advantages over
d-decalactone, which is an industrial fragrance. The the actual industrial production that uses peracids as
reaction is carried out without solvent and with a oxidants.
substrate/catalyst ratio > 200 (wt/wt). Starting with an
enantiomerically enriched delfone it is shown that the Keywords: Baeyer Villiger oxidation, d-decalactone,
rearrangement occurs with retention of configuration heterogeneous catalysis, hydrogen peroxide, tin, zeo-
at the migrating asymmetric carbon atom, and lites
Introduction
molecular sieves are less effective catalysts for the
activation of hydrogen peroxide for oxidation reactions.
In spite of the lack of activity for an effective hydrogen
Lewis acids have been used for a long time to catalyse
selective oxidations.[1] An important breakthrough in peroxide activation, we have presented recently a very
the design of heterogeneous oxidation catalysts was the chemoselective oxidation reaction with hydrogen per-
discovery of Ti-silicalite (TS-1).[2] Titanium was incor- oxide catalysed by Sn-Beta,[8,10] namely the Baeyer
porated in the framework of silicalite zeolite as isolated Villiger oxidation. This is an important reaction for
tetrahedral Ti(IV) sites. These metal centres are able to organic synthesis which finds many applications in the
form titanium-peroxy species and, thereby, to activate fine chemical industry.[11] It has been demonstrated that
hydrogen peroxide for oxidation reactions such as the water-resistant heterogeneous Lewis acid Sn-Beta is
epoxidation, ammoximation or CH oxidation.[1]
able to activate the carbonyl group of cyclic ketones and
In the course of the exciting oxidation chemistry with aromatic aldehydes for the nucleophilic attack of
TS-1, other metals have been incorporated into mo- hydrogen peroxide to give the corresponding Baeyer
lecular sieves, such as vanadium, chromium, zinc, iron, Villiger reaction products.[8b,12] In the case that double
and tin, the latter with an increasing number of bonds were present in the substrate molecules, no
applications in recent years. Several patents and reports epoxidation was observed in contrast to reactions with
have appeared on the hydroxylation of phenol with Sn- other classical oxidants such as peracids or MTO/H2O2.
silicalite,[3] Sn-MCM-41[4] and tin incorporated in other With tin incorporated into the mesoporous molecular
zeolite structures.[5] However, when the results are sieve MCM-41 during synthesis or in a post-synthesis
compared with titanium incorporated into the same treatment, two materials were available without the
molecular sieve the titanium-containing materials al- limitation of molecular size introduced by the pores of
ways perform better[3b] or much better.[6] Sn-Beta the Beta zeolite (6.2 7.2 ä).[13] By in situ IR spectro-
however, was found to be particularly active for scopy it was established that Sn-Beta has the highest
À
Meerwein Ponndorf Verley and Oppenauer reactions Lewis acid strength of the three materials so that
in which carbonyl groups are reduced and alcohols are substrates that were able to diffuse within both channel
oxidised.[7] With respect to epoxidation only the oxida- systems without steric impediments were oxidised
tion of the very reactive norbornene has been reported fastest in the presence of Sn-Beta.
with tert-butyl hydroperoxide as oxidant and Sn-MCM-
These in situ IR measurements provided also valuable
41 as catalyst, while Sn-Beta was found to be absolutely information for the proposal of a catalytic cycle. By the
inactive for epoxidation reactions with hydrogen per- coordination of the carbonyl group to the Sn Lewis acid
oxide.[8,9] These results indicate that tin-containing site, the corresponding IR band of the C O group is
ˆ
Adv. Synth. Catal. 2004, 346, 257 262
DOI: 10.1002/adsc.200303234
¹ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
257

Avelino Corma et al.
FULL PAPERS
shifted towards lower wavenumbers indicating that the means of a Baeyer Villiger reaction. Percarboxylic
double bond character of the carbonyl bond was acids are used as oxidants involving a well-established
decreased, and a higher positive charge appears on the retention of the stereochemistry of an asymmetric
carbon atom. A subsequent nucleophilic attack of the migrating centre.[11] However, for the design of a process
hydrogen peroxide forms a coordinated ™Criegee inter- adapted to the actual environmental demands, peracids
mediate∫ or perhydrate. This type of intermediate is in should be substituted since they involve several draw-
accordance with labelling experiments involving oxygen backs such as: a low active oxygen content and therewith
18.[8] After a rearrangement step the ester product is important by-product formation, requirement of strong
obtained. This mechanism has been supported and acids,[11] and potential explosions.[20]
refined by theoretical calculations revealing further
A catalytic system like Sn-Beta/hydrogen peroxide
details.[14] A second dative coordination of the Criegee could be, in principle, valuable for producing d-deca-
intermediate to the metal centre has been proposed via lactone from the Baeyer Villiger oxidation of 2-pentyl-
the peroxy oxygen neighbouring the hydrogen atom, cyclopentanone enriched with the R-isomer, if the Sn-
with formation of a five-membered ring species. This Beta catalyst would allow the migration of the asym-
additional coordination lowers the Gibbs activation metric carbon centre with retention of configuration. In
barrier for the irreversible Baeyer Villiger rearrange- spite of the theoretical and experimental work on the
ment (which has been determined in the theoretical mechanism mentioned above, it is still unknown if this
work to be the rate-limiting step) since now the leaving catalyst can be used for oxidation steps in stereo-
group is not the unfavourable water (or hydroxide) but selective synthesis. It is clear that if this point could be
an MOH species. However, these calculations have to be clarified and a stereoselective rearrangement could be
treated cautiously since they have been performed with established and, furthermore, the reaction could be also
a very limited zeolite model wherein the whole zeolite carried out with aqueous H2O2 in absence of any organic
network has been substituted by four OH ligands[14] and co-solvent, a new process for the asymmetric synthesis
potential influence or effects of the zeolite structure of lactones and more specifically for the industrial
have been neglected. Furthermore, the results for the preparation of d-decalactone could be provided.
epoxidation, where the calculations predict identical
behaviour for tin and titanium zeolites, differ signifi-
cantly from the experimental observations.
In any case, the discovery of Sn-Beta as an active and
Results and Discussion
ecofriendly solid catalyst for Baeyer Villiger oxidations In order to test the stereochemical behaviour of the
has opened the possibility for application of the Sn- rearrangement step, we startedwith an enantiomerically
Beta/H2O2 system to the production of some fine enriched delfone (87:13) and the Baeyer Villiger
chemicals. In this sense, a potential interesting applica- oxidation of this molecule with hydrogen peroxide
tion involves the oxidation of delfone (2-pentylcyclo- (35%, 1.5 equivs.) was carried out first in dioxane and
pentanone, 1) to d-decalactone (tetrahydro-6-pentyl- with 50 mg of Sn-Beta catalyst for 1 mmol of ketone
2H-pyran-2-one, 2) which has a creamy-coconut and (ratio ketone/Sn ˆ 150 mol molÀ1). Time was prolonged
peach-like aroma and is an important flavour constitu- to 24 h and reaction temperature lowered to 608C with
ent of many types of fruit, cheese and other dairy respect to earlier experiments.[8]
products [Eq. (1)].[15]
Under these experimental conditions, 18% conver-
sion was achieved with a selectivity > 98%. Although
the yield was still low, we could already test with the
product obtained whether the reaction occurs with
retention of configuration at the migrating centre. The
two enantiomers were separated with a chiral GC
column and an 87:13 ratio was observed, which
corresponds to the nominal isomer distribution in the
ꢀ1†
The importance of d-decalactone is evidenced by the starting ketone (Figure 1). This result proves unequiv-
number of bioorganic syntheses[16] or chemical process- ocally that the Baeyer Villiger reaction of ketones with
es[17] which have been patented for its production. The a migrating asymmetric carbon atom occurs with
lactone has two different enantiomers, the R-isomer retention of the configuration when the oxidation is
being the one found preferentially in nature.[18] As it carried out with hydrogen peroxide and catalysed by Sn-
occurs with other fragrances, in the case of d-decalac- Beta (Figure 2).
tone the two isomers and their racemic mixture have
Following our second objective, i.e., to avoid the use of
different aromas,[19] and for practical uses the R-isomer any organic co-solvent, the reaction was carried out in a
is the preferred one. Based on this, the industrial tri-phasic system involving a liquid aqueous phase
production starts with the R-isomer enriched ketone, (hydrogen peroxide), a liquid organic phase (the
that is transformed into the corresponding lactone by ketone) and the solid catalyst. Reaction temperature
258
¹ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
Adv. Synth. Catal. 2004, 346, 257 262

Synthesis of the Flavouring d-Decalactone Molecule
FULL PAPERS
was varied from 60 to 1108C (Table 1) and it is found
that increasing the reaction temperature produces a
decrease in the reaction selectivity, due to the formation
of 5-oxodecanoic acid (3), Eq. (2). However, we found
that this by-product is not formed catalytically, but by
the direct oxidation of the reactant with H2O2. Indeed,
the blank experiment (Table 1, entry 1) shows that at
high reaction temperature 5-oxodecanoic acid as well as
other oxidised by-products are formed to a large extent.
Therefore, we decreased the reaction temperature to
608C, working with a substrate/zeolite ratio of 60 (wt/
wt) and a molar ratio H2O2/ketone of 1.6. When working
without an organic co-solvent under these reactions
conditions, the selectivity to the lactone was 86% (with
87:13 enantiomeric ratio, Figure 1), while the oxo acid 3
was strongly suppressed (3%). However, the total
conversion was 15% after 7 h (Table 1, entry 10). The
lactone product obtained with the Sn-MCM-41 catalyst
under the same experimental conditions showed the
same enantiomeric excess (Figure 1).
Figure 1. Chromatograms of d-decalactone obtained from the
racemate of delfone by Baeyer Villiger oxidation with Sn-
Beta/H2O2 (a) and from the enantiomerically enriched
delfone by Baeyer Villiger oxidation with peracetic acid
(b), with Sn-Beta/H2O2 in dioxane (c), Sn-Beta/H2O2 (d), and
with Sn-MCM-41/H2O2 (e).
ꢀ2†
It should be noticed that although the oxo acid is an
undesired by-product it may be transformed into
lactone 2 by NaBH4 reduction with subsequent H2SO4
catalysed cyclisation[21] or by asymmetric reduction
providing the R-isomer exclusively by use of fermenting
baker×s yeast.[22] Nevertheless, we attempted to decrease
the yield of 3 by decreasing by 50% the concentration of
oxidant (H2O2). Thus, by doing this and working at 908C
the selectivity towards lactone 2 could be improved from
61% to 80% and the yield increased from 26% to 30%
(Table 2, entries 2 and 3). A further reduction of the
oxidant to only 0.3 equivalents improved further the
Figure 2. Proposed mechanism for the Sn-Beta catalysed,
stereoselective Baeyer Villiger oxidation with hydrogen
peroxide involving an interaction of the hydrogen peroxide
with the metal centre improving the leaving group abilities.
Table 1. Conversions and selectivities for the Baeyer Villiger oxidation of delfone with hydrogen peroxide (35%)/Sn-Beta in a
tri-phasic system after 7 h at different temperatures. Reaction conditions: 3.0 g (19 mmol) of delfone, 3.0 g (30 mmol) of 35%
aqueous hydrogen peroxide, and 50 mg of Sn-Beta catalyst were mixed and heated to the desired reaction temperature.
Entry
Catalyst [mg]
Temp. [0C]
Conv. [%]
Selectivity [%]
Yield [%]
2
3
other
2
3
1
2
3
4
5
6
7
8
9
110
110
90
90
80
80
70
70
60
36
57
21
43
10
37
3
21
1
15
27
52
32
61
24
69
24
73
41
86
36
30
43
22
42
14
28
7
37
18
25
17
34
17
48
20
48
11
10
30
7
26
2
25
1
15
0.4
13
13
17
9
9
4
5
1
2
0.1
0.5
50
50
50
50
50
11
3
10
60
Adv. Synth. Catal. 2004, 346, 257 262
asc.wiley-vch.de
¹ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
259

Avelino Corma et al.
FULL PAPERS
Table 2. Conversions and selectivities for the Baeyer Villiger oxidation of delfone with different amounts of hydrogen
peroxide (35%) and Sn-Beta in a tri-phasic system after 7 h at 908C. Reaction conditions: 3.0 g (19 mmol) of delfone, the
corresponding amount of 35% aqueous hydrogen peroxide, and 50 mg of Sn-Beta catalyst were mixed and heated to 908C.
Entry
1/cat[a] [wt/wt]
H2O2 [equiv.]
Conv. [%]
Selectivity [%]
Yield [%]
2
3
other
2
3
1
2
3
60
60
60
0.3
0.8
1.6
17
38
43
92
80
61
0
11
22
8
9
17
16
30
26
0
4
9
[a]
Substrate/catalyst ratio.
Table 3. Conversions and selectivities for the Baeyer Villiger oxidation of delfone with hydrogen peroxide (1.6 equivs., 35%)
and Sn-Beta in a tri-phasic system after 7 h at 808C in the presence of different amounts of Na2HPO4. Reaction conditions:
3.0 g (19 mmol) of delfone, 3.0 g (30 mmol) of 35% aqueous hydrogen peroxide, 50 mg of Sn-Beta catalyst, and the
corresponding amount of Na2HPO4 were mixed and heated to 808C.
Entry
Na2HPO4 [mg]
Conv. [%]
Selectivity [%]
Yield [%]
2
3
other
2
3
1
2
3
4
0
152
303
600
37
23
10
10
69
75
80
77
14
14
5
17
11
15
20
25
17
5
5
3
0.5
0.3
3
3
selectivity towards lactone 2, however, the conversion Conclusion
and therewith the yield dropped significantly (Table 2,
entry 1). A slow addition during seven hours of the In summary, we can say that during the Baeyer Villiger
hydrogen peroxide did not improve the catalytic per- oxidation of ketones with only one enantiomer or in an
formance.
enantiomerically enriched mixture, using an Sn-Beta
In another attempt to reduce the formation of the oxo catalyst and H2O2, the migration of the asymmetric
acid 3, the acidity of the H2O2 was reduced by adding carbon centre occurs with retention of configuration.
Na2HPO4. The results from Table 3 show an increase of We have also shown that the Baeyer Villiger oxidation
the selectivity to lactone, but the conversion was of 2-pentylcyclopentatone (1) to d-decalactone (2) can
negatively affected.
be performed with H2O2 and Sn-Beta zeolite catalyst,
At this point, and in order to increase conversion and without requiring any co-solvent. A process such as the
selectivity, always working with a tri-phasic system, we one reported here appears interesting also from an
increased the catalyst to substrate ratio in order to industrial point of view.
improve the relative rates of the catalysed (lactone)
versus the uncatalysed (oxy acid) reaction, while work-
ing at different reaction times. From the results given in
Experimental Section
Hydrogen peroxide (50%) was purchased from Aldrich and
hydrogen peroxide (35%) from Fluka. Delfone and enantio-
Table 4, it can be seen that it is possible to achieve near
100% conversion of the ketone, with a selectivity of 84%
to the lactone at 608C and with a substrate to zeolite
ratio of 10, which results in a molar ratio of substrate to merically enriched delfone were provided by Acedesa. As the
enantiomeric excess of the enriched ketone was not known
exactly, the Baeyer Villiger oxidation was carried out with
peracetic acid and the lactone product analysed as in the other
cases (Figure 1). The obtained ratio was taken also for the
ketone substrate since it is well known in the literature that the
Baeyer Villiger oxidation with peracids occurs with retention
of configuration.[11] Sn-Beta was synthesised according to the
literature procedure.[8] The Sn content (2.0 wt % of SnO2) was
determined by atomic absorption. The Sn-Beta zeolite was
calcined at 853 K for 3 h. A high crystallinity of the zeolite was
observed by XRD, and no peaks of SnO2 were found in the
active Sn site of 488. In a further up-scale at prolonged
reaction time, 107 g of ( Æ )-delfone were employed
along with 2.1 equiv. of 50% aqueous hydrogen per-
oxide and 500 mg of Sn-Beta at 608C. With the resulting
substrate/catalyst ratio of 200 (wt/wt) full conversion
was achieved after 54 h and 86% of the desired product
was observed.
260
¹ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
Adv. Synth. Catal. 2004, 346, 257 262

Synthesis of the Flavouring d-Decalactone Molecule
FULL PAPERS
Table 4. Conversions and selectivities for the Baeyer Villiger oxidation of delfone with hydrogen peroxide (1.6 equivs., 35%)
and Sn-Beta in a tri-phasic system after 7 h at 608C with different catalyst amounts. Reaction conditions: 3.0 g (19 mmol) of
delfone, 3.0 g (30 mmol) of 35% aqueous hydrogen peroxide, and 0 mg, 50 mg, 100 mg, and 200 mg of Sn-Beta catalyst (for
entries 1 to 4, respectively) were mixed and heated to 608C. For entries 5 to 7, 1.0 g (6.5 mmol) of delfone, 1.0 g (15 mmol) of
50% aqueous hydrogen peroxide, and 100 mg of Sn-Beta catalyst were mixed and heated to 608C.
Entry
1/cat[a] [wt/wt]
Time [h]
Conv. [%]
Selectivity [%]
Yield [%]
2
3
other
2
3
[b]
1
2
3
4
5
6
7
7
7
7
7
7
1
15
26
29
58
32
95
41
86
76
78
84
96
84
11
3
10
8
4
0
48
11
14
16
12
4
0.4
13
20
22
49
0.1
0.5
2
2
2
60
30
15
10[c]
10[c, d]
10[c]
7
24
31
80
0
7
8
8
[a]
Substrate/catalyst ratio.
Without catalyst.
2.3 equivs. hydrogen peroxide were used as 50% aqueous solution.
With dioxane as solvent.
[b]
[c]
[d]
diffractogram. Nitrogen adsorption experiments on the cal-
cined Beta samples gave an isotherm very similar to that of
pure silica Beta with values of micropore volume of 0.20
0.21 cm3 gÀ1 and BET surface areas of 450 475 m2 gÀ1. GC
analyses were carried out on an HP5890 gas chromatograph
equipped with a 25 m HP-5 column. GC-MS analyses for the
identification of products were carried out on an Agilent
Technologies 6890N apparatus coupled with an Agilent Mass
Selective Detector 5973 Network. 1H NMR spectra were
recorded with a Bruker spectrometer at a frequency of
300 MHz and 13C NMR spectra at a frequency of 75 MHz.
The two enantiomers of d-decalactone were separated on a
Fisons Instruments GC 8035 equipped with an Chiraldex G-TA
(gamma-cyclodextrin, trifluoroacetylated) column from Astec
(30 m, 0.25 mm, 0.25 mm film) at 125 C isothermally.
Acknowledgements
The authors thank Acedesa, CICYT (MAT2003 07945-C02
01), and the Generalitat Valenciana for financing this work.
M. R. is grateful to the Spanish Ministry of Science and
¬
Technology for a ™Ramon y Cajal∫ Fellowship.
References and Notes
[1] a) A. Corma, H. GarcÌa, Chem. Rev. 2002, 102, 3837
3892; b) A. Corma, H. GarcÌa, Chem. Rev. 2003, 103,
4307 4365.
[2] M. Taramasso, G. Perego, B. Notari, US Patent 4,410,501,
1983.
[3] a) M. Costantini, J.-L. Guth, A. Lopez, J.-M. Popa, Eur.
Patent 0466545, 1991; b) N. K. Mal, V. Ramaswamy, S.
Ganapathy, A. V. Ramaswamy, J. Chem. Soc. Chem.
Commun. 1994, 1933 1934; c) N. K. Mal, V. Ramasw-
amy, S. Ganapathy, A. V. Ramaswamy, Appl. Catal. A:
Gen. 1995, 125, 233 245; d) N. K. Mal, A. V. Ramasw-
amy, J. Mol. Catal. A: Chem. 1996, 105, 149 158.
[4] K. Chaundhari, T. K. Das, P. R. Rajmohanan, K. Lazar,
S. Sivasanker, A. J. Chandwadkar, J. Catal. 1999, 183,
281 291.
[5] N. K. Mal, A. Bhaumik, V. Ramaswamy, A. A. Belhekar,
A. V. Ramaswamy, St. Surf. Sci. Catal. 1995, 94, 317 324.
[6] R. Klaewkla, S. Kulprathipanja, P. Rangsunvigit, T.
Rirksomboon, L. Nemeth, Chem. Commun. 2003,
1500 1501.
General Procedure for the Baeyer Villiger Oxidation
Delfone, aqueous hydrogen peroxide (35% or 50%), optionally
3.0 g of dioxane and Sn-Beta catalyst (normally 50 mg) were
stirred magnetically and heated to the desired reaction
temperature. The reaction was followed by gas chromatogra-
phy, and the products were identified by comparison with
reference samples, by GC-MS, or after purification by
1H NMR spectroscopy.
1
Lactone 2: H NMR (CDCl3, 300 MHz): d ˆ 0.89 (t, J ˆ
6.7 Hz, 3H, 10-H), 1.3 1.9 (m, 12H, 3-H, 4-H, 6-H, 7-H, 8-H,
9-H), 2.4 2.7 (m, 2H, 2-H), 4.3 (m, 1H, 5-H).
For the identification of the oxo acid 3, the organic phase of
the catalytic run at 708C was distilled in an oil-pump vacuum.
The residue, colourless crystalline material, was submitted to
1
[7] a) A. Corma, M. E. Domina, S. Valencia, J. Catal. 2003,
215, 294 304; b) A. Corma, M. E. Domina, L. Nemeth,
S. Valencia, J. Am. Chem. Soc. 2002, 124, 3194 3195.
[8] a) A. Corma, L. T. Nemeth, M. Renz, S. Valencia, Nature
2001, 412, 423 425; b) M. Renz, T. Blasco, A. Corma, V.
NMR analysis: H NMR (CDCl3, 300 MHz): d ˆ 0.89 (t, J ˆ
7.1 Hz, 3H, 10-H), 1.29 (m, 4H, 9-H, 8-H), 1.65 (m, 2H, 7-H),
1.90 (quin., J ˆ 7.1 Hz, 2H, 3-H), 2.39 (t, J ˆ 7.2 Hz, 2H, 4-H or
6-H), 2.40 (t, J ˆ 7.8 Hz, 2H, 4-H or 6-H), 2.50 (t, J ˆ 7.2 Hz,
2H, 2-H); 13C NMR (CDCl3, 75 MHz): d ˆ 13.9 (q, C-10), 18.5
(t, C-3), 22.4 (t, C-9), 23.5 (t, C-7), 31.4 (t, C-8), 33.0 (t, C-2),
41.3 (t, C-4), 42.8 (t, C-6), 178.9 (s, C-1), 210.5 (s, C-5).
¬
Fornes, R. Jensen, L. Nemeth, Chem. Eur. J. 2002, 8,
4708 4717.
Adv. Synth. Catal. 2004, 346, 257 262
asc.wiley-vch.de
¹ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
261

Avelino Corma et al.
FULL PAPERS
[9] A. Corma, unpublished results; when Sn-Beta (2.2 wt %
of SnO2; 100 mg) is employed as catalyst together with
16.5 mmol of 1-hexene, 4.1 mmol of aqueous hydrogen
peroxide solution and 11.8 g of acetonitrile no conver-
sion is observed after 5 hours at 508C. With Ti-Beta
(0.4 wt % of TiO2) under the same conditions the
conversion is already 7.5% of the maximum and with a
Ti-Beta sample with 1.4 wt % of TiO2 around 30%.
[10] S. Valencia, A. Corma, US Patent 5,968,473, 1999.
[11] a) M. Renz, B. Meunier, Eur. J. Org. Chem. 1999, 737
750; b) G. R. Krow, Org. React. 1993, 43, 251 798.
[12] A. Corma, S. Iborra, M. Mifsud, M. Renz, J. Catal. 2004,
221, 67 76.
[13] a) A. Corma, M. T. Navarro, L. Nemeth, M. Renz, Chem.
Commun. 2001, 2190 2191; b) A. Corma, M. T. Nav-
arro, M. Renz, J. Catal. 2003, 219, 242 246.
[14] a) R. R. Sever, T. W. Root, J. Phys. Chem. B 2003, 107,
10521 10530; b) R. R. Sever, T. W. Root, J. Phys. Chem.
B 2003, 107, 10848 10862.
[15] K. Bauer, D. Garbe, H. Suburg, Common Fragrance and
Flavor Materials; Wiley-VCH, Weinheim, 1997.
[16] a) G. Bretler, C. Dean, Eur. Patent 899342, 1998; b) S.
Ushiwata, R. Kitazawa, T. Komai, Jap. Patent 10042889,
1996; c) R. Cardillo, C. Fuganti, M. Barbeni, G. Alle-
grone, Eur. Patent 577463, 1993; d) W. T. A. M. De Laat,
P. H. Van der Schaft, Can. Patent 2025678, 1990.
[17] R. Kayama, H. Suzuki, Jap. Patent 09104681, 1995.
[18] a) D. Lehmann, B. Maas, A. Mosandl, Zeitschrift fuer
Lebensmittel-Untersuchung und -Forschung 1995, 201,
55 61; b) S. Hashimoto, S. Hayshi, Y. Ueyama, T. Giga,
Jap. Patent 10158257, 1996.
[19] H. Nohira, K. Mizuguchi, T. Murata, Y. Yazaki, M.
Kanazawa, Y. Aoki, M. Nohira, Heterocycles 2000, 52,
1359 1370.
[20] H. Heaney, Aldrichimica Acta 1993, 26, 35 44.
[21] Sumitomo Chemical Co., Jap. Patent 56161348, 1981.
[22] M. Utaka, H. Watabu, A. Takeda, J. Org. Chem. 1987, 52,
4363 4368.
262
¹ 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
Adv. Synth. Catal. 2004, 346, 257 262