Rearrangement of bornyl phenyl ether

Full text of DOI:10.1134/S1070428013070233

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2013, Vol. 49, No. 7, pp. 1087–1088. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © I.Yu. Chukicheva, O.A. Shumova, A.V. Kutchin, 2013, published in Zhurnal Organicheskoi Khimii, 2013, Vol. 49, No. 7,
pp. 1101–1102.
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COMMUNICATIONS
Rearrangement of Bornyl Phenyl Ether
I. Yu. Chukicheva, O. A. Shumova, and A. V. Kutchin
Institute of Chemistry, Komi Research Center, Ural Branch, Russian Academy of Sciences,
ul. Pervomaiskaya 48, Syktyvkar, 167982 Russia
e-mail: chukicheva-iy@chemi.komisc.ru
Received December 5, 2012
DOI: 10.1134/S1070428013070233
We previously studied rearrangement of isobornyl
phenyl ether under catalysis by acids and aluminum
phenoxide [1]. Comparison of the experimental data
obtained in the reaction catalyzed by acids and in the
presence of aluminum phenoxide led us to presume
that in the first case the rearrangement follows mainly
intermolecular mechanism, and in the second, intra-
molecular. As a result, high regio- and stereoselectivity
of the process were rationalized by tandem Claisen and
Wagner–Meerwein rearrangements occurring intramo-
lecularly in the initially formed aluminum complex
with isobornyl phenyl ether [1].
Bornyl phenyl ether underwent rearrangement only
in the presence of AlCl3 or boron trifluoride–ether
complex on heating to 100 and 160°C, respectively
(see table). However, the rearrangement was accom-
panied by isomerization of the bornyl fragment. The
reaction in the presence of AlCl3 (100°C) afforded
2-isocamphylphenol (IIa) in 65% yield and a difficult-
ly separable mixture of ortho- and para-substituted
phenols IIa–IId and IIIa–IIId (30%) with different
structures of the terpene substituent. When the reaction
temperature was raised to 160°C, the yield of 2-iso-
camphylphenol (IIa) increased to 75%. The rearrange-
ment in the presence of BF3·Et2O was less selective. In
this case, 30% of 2-isocamphylphenol (IIa) and a mix-
ture of 2- and 4-substituted phenols IIa–IId and IIIa–
IIId were formed.
The alkylation of phenol with excess β-pinene in
the presence of aluminum phenoxide afforded mainly
optically active bornyl phenyl ether (I) and 2-bornyl-
phenol (IIc) in approximately equal amounts (35–46
and 22–49%, respectively, depending on the reaction
temperature) [2]. Our attempt to promote rearrange-
ment of bornyl phenyl ether with the use of Al(OPh)3
as catalyst, as in the rearrangement of isobornyl phenyl
ether, was unsuccessful. We also failed to obtain
phenol IIc by heating ether I in boiling methylene
chloride in the presence of KSF montmorillonite.
Our experimental data confirm intermolecular char-
acter of the rearrangement of ether I. The fact that no
rearrangement occurred in the presence of Al(OPh)3
may be rationalized by steric factor. Coordination of
bornyl phenyl ether to the aluminum atom in the cata-
lyst leads to such orientation of the phenoxy group that
the rearrangement becomes impossible.
Me
Me
Me
H
OH
OH
R
O
Catalyst
+
R
I
IIa–IId
IIIa–IIId
Me
Me
Me
Me
Me
Me
Me
Me
Me
Catalyst = Al(OPh)3, KSF, AlCl3, BF3 ·Et2O; R =
(a),
(b),
(c),
(d).
H
H
H
Me
i-Pr
1087

CHUKICHEVA et al.
1088
Rearrangement of bornyl phenyl ether (I)
Yield, %
Catalyst
Reaction time, h
Temperature, °C
Conversion, %
IIa
II + III
Al(OPh)3
KSF clay
AlCl3
49
56
02
04
04
160–180
CH2Cl2, reflux
160
00
00
95
90
89
–
–
–
–
78
70
35
22
30
65
AlCl3
100
BF3·Et2O
160
To conclude, we have studied the rearrangement of
phenyl bornyl ether in the presence of Al(OPh)3, AlCl3,
BF3 ·Et2O, and KSF clay. No reaction occurs in the
presence of Al(OPh)3 and KSF clay, whereas the rear-
rangement in the presence of AlCl3 and BF3 ·Et2O
occurs intermolecularly, and it yields mainly 2-isocam-
phylphenol.
detected by treatment with a solution of vanillin in
alcohol, followed by heating to 100–150°C, or by
treatment with a solution of potassium permanganate
(15 g of KMnO4 in 300 ml H2O containing 0.5 ml of
concentrated sulfuric acid). The products were isolated
by column chromatography on silica gel (70–230 μm,
Alfa Aesar); gradient elution with petroleum ether–
diethyl ether with increasing fraction of the latter.
General procedure. A mixture of 0.20 g of bornyl
phenyl ether (I) and 0.02 g of BF3·Et2O or AlCl3 was
heated to 160 or 100°C, respectively, under argon in
the absence of a solvent. When the reaction was com-
plete, the mixture was cooled and dissolved in chloro-
form, the solution was passed through a thin layer of
Al2O3, the solvent was removed under reduced pres-
sure, and the residue was separated by column chroma-
tography. The yields of compounds IIa–IId and IIIa–
IIId thus isolated are given in table. Their structure
was confirmed by NMR spectroscopy and by compar-
ing with published data [1, 3].
Commercial KSF montmorillonite (Acros
Organics), AlCl3 (Alfa Aesar), and phenol (Alfa Aesar)
were used without additional purification; Al(OPh)3
was generated in situ.
This study was performed under financial support
by the Russian Foundation for Basic Research (project
no. 12-03-00900).
REFERENCES
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1
The H and 13C NMR spectra were recorded on
Russ. J. Org. Chem., 2008, vol. 44, p. 62.
a Bruker Avance II 300 spectrometer at 300.17 and
75.5 MHz, respectively, using CDCl3 as solvent and
reference (CHCl3, δ 7.26 ppm; CDCl3, δC 76.90 ppm).
The products were analyzed by GLC on a Shimadzu
GC-2010AF chromatograph equipped with a flame
ionization detector (HP-1 capillary column, 60 m×
0.25 mm, film thickness 0.25 μm; oven temperature
programming from 100 to 240°C at a rate of 6 deg×
min–1; carrier gas helium). The progress of reactions
was monitored by TLC using Sorbfil plates; spots were
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RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 7 2013