Acid-catalyzed transformations of diepoxy derivatives of terpinolene

Article abstract of DOI:10.1134/S1070428011100046

Transformations of diepoxy derivatives of terpinolene under conditions of homogeneous and heterogeneous acid catalysis were studied. Qualitative and quantitative compositions of the reaction mixtures were found to depend on the acidity of the medium and m

Full text of DOI:10.1134/S1070428011100046

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ISSN 1070-4280, Russian Journal of Organic Chemistry, 2011, Vol. 47, No. 10, pp. 1479–1486. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © O.V. Salomatina, O.I. Yarovaya, D.V. Korchagina, Yu.V. Gatilov, V.A. Barkhash, 2011, published in Zhurnal Organicheskoi
Khimii, 2011, Vol. 47, No. 10, pp. 1455–1461.
Acid-Catalyzed Transformations of Diepoxy
Derivatives of Terpinolene
O. V. Salomatina, O. I. Yarovaya, D. V. Korchagina, Yu. V. Gatilov, and V. A. Barkhash
Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Division, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 9, Novosibirsk, 630090 Russia
e-mail: ana@nioch.nsc.ru
Received March 2, 2011
Abstract—Transformations of diepoxy derivatives of terpinolene under conditions of homogeneous and
heterogeneous acid catalysis were studied. Qualitative and quantitative compositions of the reaction mixtures
were found to depend on the acidity of the medium and mutual orientation of the epoxide rings in the
p-menthane skeleton. The experimental data were compared with the results of computer simulation of the
most probable transformation pathways in terms of molecular mechanics and quantum-chemical methods.
DOI: 10.1134/S1070428011100046
Epoxide ring is fairly readily formed by oxidation
of double bonds and is an important building block in
organic synthesis due to its high reactivity in both
acidic and basic media [1]; furthermore, epoxide ring
is a structural fragment of many biologically active
compounds of natural and synthetic origin [2]. Epoxy
derivatives of terpenes constitute a very important
source of cheap and accessible chemicals possessing
unique structure and biological activity. Their trans-
formations could led to organic compounds belonging
to various classes, whereas the use of zeolites, clays,
and solid superacids to catalyze reactions of terpenes
and their epoxy derivatives makes it possible to not
only reduce activation barriers of known transforma-
tions but also initiate different reaction paths than
under homogeneous conditions [3].
homogeneous and heterogeneous acidic media with
a view to elucidate how mutual orientation of the
epoxy groups in the p-menthane skeleton affects the
reaction outcome. Terpinolene (I) is an isomer of
limonene with different position of the double bond in
the isopropyl group; it is a component of coriander,
Monterey cypress, and tea tree essential oils [7]. It is
known that terpinolene in acidic medium does not
undergo skeletal rearrangement but isomerizes into
compounds of the p-menthane series via migration of
double bonds [8]; on the other hand, acid-catalyzed
transformations of terpinolene monoepoxides lead to
diols as a result of opening of the epoxide ring [9, 10].
Stereoisomeric terpinolene diepoxides II and III at
a ratio of 5:1 were synthesized according to the proce-
dure described in [11] by oxidation of terpinolene (I)
with 2 equiv of peroxyacetic acid (Scheme 1). Com-
pounds II and III were isolated as individual sub-
stances by column chromatography on silica gel.
We previously examined transformations of diep-
oxy derivatives of limonene in various homo- and
heterogeneous acid media [4–6]. It was shown that
homogeneous reactions in media with considerably
different acidities (HCOOH–dioxane, CF3COOH,
etc.) led to the formation of only 6-oxabicyclo[3.2.1]-
octane derivatives. By contrast, solid catalysts, such as
β-zeolite, askanite–bentonite, K-10 clay, and solid
superacid TiO2/SO42–, gave rise to a wide series of com-
pounds with various bi- and tricyclic skeletons.
Taking into account that the results of acid-cata-
lyzed transformations of diepoxy derivatives depend
on mutual orientation of the epoxide rings, the most
stable conformations of compounds II and III were
found by molecular mechanics and using Dreiding
models; the relative energies of formation (ΔE, kcal×
mol–1) are given in Scheme 1. Quantum-chemical cal-
culations in terms of the density functional theory
(DFT, BPE/TZ2P) for the gas phase were performed
using PRIRODA software [12]. It is seen that the
In the present work we studied transformations of
cis- and trans-diepoxy derivatives of terpinolene in
1479

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SALOMATINA et al.
1480
Scheme 1.
Me
Me
Me
O
O
MeCO3H
+
O
O
Me
Me
Me
Me
Me
Me
I
II
III
Me
Me
O
Me
Me
O
Me
O
Me
O
Me
Me
Me
O
O
IIa
IIb
IIc
PBE/TZ2P, ΔE (kcal/mol)
0.0
0.8
5.1
(E = –540.606606)
Me
Me
Me
O
Me
Me
Me
Me
O
O
Me
Me
O
O
O
IIIa
IIIb
IIIc
PBE/TZ2P, ΔE (kcal/mol)
(E = –540.606606)
0.0
1.7
4.4
stabilities of different conformers of II and III are
directly related to the stabilities of cyclohexane con-
formers; conformers IIa and IIIa in which the six-
membered ring has half-chair structure are more stable
than boat conformers IIc and IIIc.
confirmed by the absence of the corresponding prod-
ucts in the reaction mixture. Further transformation of
cation A follows paths a or b: the cationic center gen-
erated by opening of the 4,8-epoxy ring reacts with the
1,2-epoxy group to give oxonium ions C and D. Cation
C is then converted into stable tertiary cation E which
takes up ROH molecule, and subsequent deprotonation
yields 6-oxabicyclo[3.2.1]octane derivative IV or V.
Direct reaction of ROH with oxonium ion C with
formation of product IV or V is also possible. Nucle-
ophilic attack by water molecule on cation D at the C2
atom leads to structure VI. The fact that the reaction
mixture contained no products corresponding to nucle-
ophilic attack by ROH on the C2 atom in cation C may
be rationalized in terms of higher reactivity of cation
D. Cation B undergoes rearrangement to produce the
same cation D, thus leading to compound VI.
Like diepoxy derivatives of limonene [4], trans-
formations of trans isomer II in homogeneous acid
medium lead to compounds having a 6-oxabicyclo-
[3.2.1]octane skeleton. Compound V was formed as
the only product in formic acid–dioxane, whereas diol
IV was obtained in acetone–water–sulfuric acid. In the
latter case, 7-oxabicyclo[2.2.1]heptane derivative VI
was also isolated (Scheme 2). cis Isomer III gave rise
only to compound VI in both formic acid–dioxane and
acetone–water–sulfuric acid. Scheme 2 shows a prob-
able mechanism of transformations of isomers II and
III, which was confirmed by the calculation data. The
relative energies (ΔE, kcal/mol) of different con-
formers and cations are given below the corresponding
formulas, and calculated (PBE/TZ2P) ΔE≠ values for
rearrangements are given near the arrows [12].
We also examined transformations of isomeric di-
epoxy derivatives II and III over solid catalysts. trans
Isomer II over β-zeolite and solid superacid (sulfated
titanium oxide) gave rise to compounds VII and VIII
at ratios of ~5:2 and ~6:1, respectively (according to
the GLC data). The transformation of compound II
over K-10 clay afforded 6-oxabicyclo[3.2.1]octane
derivative IV as the major product (Scheme 3). Com-
pound IX was formed from cis isomer III in the pres-
Presumably, both trans (II) and cis isomers (III)
undergo protonation of the 4,8-epoxy ring with forma-
tion of cations A and B, respectively. According to the
calculations, protonation of the 1,2-epoxy ring in II
and III is less thermodynamically favorable. This is
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 10 2011

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ACID-CATALYZED TRANSFORMATIONS OF DIEPOXY DERIVATIVES OF TERPINOLENE
Scheme 2.
1481
Me
Me
Me
Me
O
Me
O
Me
O
Me
Me
Me
Me
O
O
Me
O
H
O
H
Me
H
O
H
26.2
24.7
26.3
23.6
H+
H+
H+
H+
Me
Me
Me
Me
O
2
2
1
1
Me
Me
4
O
O
8
4
Me
Me
Me
Me
8
O
O
O
Me
O
Me
O
0.0
1.7
0.8
0.0
IIIa
IIIb
IIb
IIa
H+
H+
H+
H+
H
Me
Me
Me
O
H
Me
Me
Me
Me
b
Me
O
b
a
O
O
a
O
Me
O
Me
Me
H
H
Me
O
O
19.6
20.2
21.0
22.3
B
A
2.0
1.9
6.4
b
0.7 a
a
b
H2O
2
2
1
1
Me
Me
Me
Me
Me
OH
Me
Me
OH
Me
Me
Me
O
O
O
O
OH
OH
12.8
Me
Me
17.7
0.0
E
D
C
H2O –H+
ROH –H+
Hsyn
Hanti
HO
8
2
3
9
Me
RO
Hexo
5
5
9
4
6
M1e0
O6
7
Me
Me
1
4
8
3
Hax
1
10
OH
7
O
Me
Me11
2
HO
IV, V
Heq
VI
IV, R = H; V, R = CHO.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 10 2011

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SALOMATINA et al.
1482
Scheme 3.
Hanti
Hsyn
9 Me
8
4
5
O6
M1e0
3
H
1
2
–H+
7
11
Me
OH
H'
VII
Me
Me
O
O
HO
Me
Me
1
H+
H2O
–H+
2
O
O
Me
Me
4
HO
HO
O
HO
Me
8
Me
Me
Me
Me
IV
Me
II
E
9
8
H2C
H'
5
3
4
2
O
10
Me
H
1
7
–H+
H
Me11
OH
H'
VIII
Me
Me
Me
O
O
OH
H+
H+
–H+
–H+
7
Me
Me
OH
Me
OH
Me
OH
Me
O
O
Me
H2C
H2C
1
1
4
2
6
2
3
5
4
OH
10
Me
Me
Me
O
8
8
9
Me
H2C
Me
OH
O
O
Me
H+
~H
–H+
H+
III
IX
–H+
O
O
OH
Me
Me
Me
Me
Me
Me
ence of both K-10 clay and TiO2/SO42– (Scheme 3),
whereas the reaction catalyzed by β-zeolite resulted in
the formation of a mixture of unidentified products.
Thus isomeric diepoxides II and III in homogene-
ous acid medium are converted into bicyclic com-
pounds as a result of reaction of initially formed cat-
ionic center with the second epoxy group. A different
pattern is observed in their transformations over solid
catalysts. Cation generated from trans isomer II is
capable of intramolecularly interacting with the second
epoxy group, yielding 6-oxabicyclo[3.2.1]octane
derivatives, whereas cis isomer III is converted into
compound IX as a result of independent opening of the
epoxide rings.
Therefore, it is reasonable to presume that trans-
formations of diepoxy derivatives of terpinolene under
conditions of heterogeneous catalysis are determined
mainly by their conformation fixed on the catalyst
surface (or in its cavity).
Probable mechanisms of transformations of isomers
II and III are shown in Scheme 3. Cationic center gen-
erated by opening of the 4,8-epoxy ring in trans isomer
II reacts the 1,2-epoxy group to form bicyclic cation
E. Deprotonation of the latter leads to compounds VII
and VIII, while its reaction with water gives bicyclic
diol IV. Opening of the epoxy rings in cis isomer III is
likely to occur independently. Cleavage of the 1,2-ep-
oxy ring yields stable tertiary cation, and the subse-
quent hydride shift and deprotonation give rise to car-
bonyl group. Opening of the 4,8-epoxy ring, followed
by deprotonation, leads to formation of α,β-unsaturated
alcohol fragment in final product IX.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 47 No. 10 2011