Chiral schiff bases synthesized from terpenes of pinane series in asymmetric metall complex oxidation of sulfi des

Article abstract of DOI:10.1134/S1070428012020108

The absolute confi guration of α-hydroxyaldehyde obtained from verbenol epoxide in the presence of clay was determined. Two new Schiff bases were synthesized from the aldehyde obtained. The compounds can be used as ligands in the asymmetric vanadium-catalyzed oxidation of sulfi des to sulfoxides. The structure of initial sulfi des signifi cantly affects the value of the enantiomeric excess in the obtained sulfoxides: the highest enantiomeric excess is observed in the oxidation of thioanisole. Pleiades Publishing, Ltd., 2012.

Full text of DOI:10.1134/S1070428012020108

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2012, Vol. 48, No. 2, pp. 214−220. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © I.V. Il’ina, E.A. Koneva, D.V. Korchagina, G.E. Sal’nikov, A.M. Genaev, K.P. Volcho, N.F. Salakhutdinov, 2012, published in Zhurnal
Organicheskoi Khimii, 2012, Vol. 48, No. 2, pp. 226−232.
Chiral Schiff Bases Synthesized from Terpenes of Pinane Series
in Asymmetric Metall Complex
Oxidation of Sulfides
I. V. Il’ina, E. A. Koneva, D. V. Korchagina, G. E. Sal’nikov, A. M. Genaev,
K. P. Volcho, and N. F. Salakhutdinov
Vorozhtsov Novosibirsk Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences,
Novosibirsk, 630090 Russia
e-mail: volcho@nioch.nsc.ru
Received July 19, 2011
Abstract—The absolute configuration of α-hydroxyaldehyde obtained from verbenol epoxide in the presence
of clay was determined. Two new Schiff bases were synthesized from the aldehyde obtained. The compounds
can be used as ligands in the asymmetric vanadium-catalyzed oxidation of sulfides to sulfoxides. The structure
of initial sulfides significantly affects the value of the enantiomeric excess in the obtained sulfoxides: the highest
enantiomeric excess is observed in the oxidation of thioanisole.
DOI: 10.1134/S1070428012020108
Optically active sulfoxides play an important role in
the modern organic chemistry. They are widely used in the
asymmetric synthesis [1–5], a number of chiral sulfoxides
exhibits a large pharmacologic activity [6–10]. The prep-
aration methods of nonracemic sulfoxides were treated in
detail in several recent reviews [11–14]. One among the
most efficient and general synthetic procedures for the
synthesis of optically active sulfoxides is the asymmetric
metal complex oxidation of prochiral sulfides. During
recent years a constant attention was paid to the use as
ligands in the asymmetric vanadium-catalyzed oxidation
of sulfides of compounds prepared from monoterpenoids
[15–22] preferably with pinane skeleton [15–17, 19–21].
oxidation of several sulfides as compared with the previ-
ously obtained ligands Ia–Ic.
In the isomerization of verbenol epoxide (V) alongside
diol VI and hydroxyketone VII α-hydroxyaldehyde VIII
with a cyclopentane skeleton formed as a minor product
[23–25] (Scheme 2). Although the configuration at the
atom C6 was not established, it was shown [23] that the
isomerization of epoxide V into compound VIII pro-
ceeded stereospecifically giving a single diastereomer.
We formerly demonstrated [15] that the reaction
Scheme 1.
We showed recently [16] that the use of ligands Ia–Ic
in the vanadium-catalyzed oxidation of methyl phenyl
sulfide (II) led to the formation of the corresponding
sulfoxide III with the enantiomeric excess (ee) up to
32% (Scheme 1).
R
O
SO2Me
S
S
R
[O]
+
OH
OH
N
VO(acac)2,
Iа_Ic
The aim of this study was the synthesis of new ligands
on the basis of the terpenoid of the pinane series, verbenol
epoxide (V) and the investigation of the applicability
of these ligands to the vanadium-catalyzed asymmetric
IV
II
(S)-III
Ia_Ic
214

CHIRAL SCHIFF BASES SYNTHESIZED FROM TERPENES
O
215
OH
V
3
8
2
OH
OH
4
9
10
5
1
+
+
6
CHO
7
HO
VIII
RR-1
O
VII
OH
VI
R = H (a), t-Bu (b), NO2 (c).
of optically active aldehydes with 2,4-di-tert-butyl-6-
aminophenol (IXb) afforded compounds suitable for
the application as ligands in the vanadium-catalyzed
asymmetric oxidation of sulfides. The presence of the
aldehyde group in compound VIII makes it possible to
obtain from it the ligands of this type.
RS-1
RS-2
Before synthesizing ligands using α-hydroxyaldehyde
VIII as the source of chirality the absolute configura-
tion of this compound should be established. This was
performed combining the calculation methods and NMR
spectroscopy.
Fig. 1. Spatial arrangement of the most stable conformers of
(1R,6R)- and (1R,6S)-diastereomers of hydroxyaldehyde VIII.
(1R,6S)-diastereomer are respectively 0.91, 1.29 and
23.1, 26.9 ppm.2 Their comparison with experimental
data [0.86 (1H) and 23.6 ppm (13C)] suggests the (1R,6R)-
configuration for the obtained α-hydroxyaldehyde VIII.
The conformational analysis of aldehyde VIII along
the procedure [26] predicted for (1R,6R)- and (1R,6S)-
diastereomers 22 and 20 conformers respectively. In
the event of (1R,6R)-isomer the single conformer RR-1
proved to be significantly more stable than others (its
contribution was 93%, Fig. 1), and in the case of (1R,6S)-
diastereomer the main contribution originates from
the conformers RS-1 and RS-2 (57 and 40% according
to Boltzmann’s distribution at 25°C). The energies of
formation of the most stable (1R,6R)- and (1R,6S)-
diastereomers calculated by DFT method possess close
values: RR-1 only by 0.3 kcal mol−1 is more stable than
RS-1. Consequently, the formation of a single diastereo-
mer of α-hydroxyaldehyde VIII does not result from the
thermodynamic control of the reaction. The calculation by
the method GIAO1 showed that the most sensitive to the
change in the configuration of the atom C6 should be the
signal of the group C9H3. The calculated 1H and 13C NMR
chemical shifts of this methyl group for (1R,6R)- and
In the NOESY spectrum of hydroxyaldehyde VIII
among the existing cross-peaks the characteristic ones
correspond to NOE between H1 and H7, H1 and C8H3,
H7 and C8H3, H5cis and C9H3, H5trans and C8H3, and NOE
cross-peaks between H1 and C9H3, H7 and C9H3, H5cis
and C8H3, H5trans and C9H3 are absent (Fig. 2). All set
of the present or absent NOE cross-peaks between the
mentioned protons is well consistent with that expected
for the most stable RR-1conformer, and at the same time
some of these cross-peaks cannot belong to the relatively
stable conformers RS-1 or RS-2. Thus the spatial structure
RR-1 is the only one among the most stable conforma-
tions according to the calculations by DFT method which
totally and consistently corresponds to the NOESYspec-
2 In calculating these values the signal of another methyl group (6-
CH3, δ 23.7 ppm) was used as “internal reference”. This was done
to avoid the systematic underestimation of the chemical shifts of
methyl groups in the 13C NMR spectra obtained by the calculations
along the equation from [27] we used.
1 The chemical shifts used were obtained by “averaging by Boltzmann”
including all found conformers of each diastereomer.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 2 2012

IL’INA et al.
216
Scheme 3.
OH
R
R
NH2
H
H
H
H3C 8
Htrans
CHO
+
7
1
O
CH3
9
HO
5
CH3
H3C
Hcis
OH
IXа, IXb
VIII
RR-1
8
R
16
17
9
Fig. 2. NOE between the protons of the most stable (1R,6R)-
diastereomer of hydroxyaldehyde VIII.
2
1
15
14
H
6
7
12
5
3
N
R
4
13
11
trum of hydroxyaldehyde VIII. This proves its spatial
(1R,6R)-configuration and besides allows unambiguous
assignment of the NMR signals of diastereotopic protons
H5cis and H5trans and diastereotopic methyl groups C8H3
and C9H3.
CH3
HO
OH
10
Xа, Xb
R = H (a), t-Bu (b).
In this study we used as the initial compound for the
synthesis of α-hydroxyaldehyde the (–)-verbenone of the
ee 70%; the ee of compound VIII also proved to be 70%
(as showed the data of GLC-MS on a chiral phase). For the
preparation of compound VIII with higher ee and for the
synthesis of the other isomer the procedure from [28] may
be used applying as the initial compounds commercially
available (+)- and (–)-α-pinenes of high optical purity.
The use of ligand Xa in the vanadium-catalyzed oxi-
dation of methyl phenyl sulfide (II) furnished sulfoxide
III with a slight exsess of the (S)-enantiomer (7%) (see
the table). Going over to the more spatially hindered
ligand Xb resulted in the doubling of the enantiomeric
excess, and taking into account the enantiomeric purity
of compound VIII and of ligand Xb, respectively, the
calculated ee was 20%.
Compound VIII was obtained by isomerization of
verbenol epoxide V in the presence of montmorillonite
clay in the 11% yield. Schiff bases Xa, Xb were pre-
pared by the reaction of α-hydroxyaldehyde VIII with
2-aminophenol (IXa) or compound IXb (Scheme 3).
The reactions were carried out in acetonitrile at room
temperature over 24 h.
Both the decrease and the increase in the reaction
temperature (see the table, runs nos. 5–8) led to the con-
Scheme 4.
O
SO2Me
S
S
The structure of compounds Xa, Xb was established
H2O2
1
using the data of H, 13C NMR spectroscopy and high
+
VO(acac)2,
resolution mass-spectrometry. The results of the confor-
mational analysis and of the calculation of the chemical
shifts of compound Xa, like those of aldehyde VIII, are
in a better agreement with the (1R,6R)-configuration of
this compound.
Iа_Ic
Br
Br
XI
Br
(S)-XIII
XIV
We studied the possibility to apply compounds Xa,
Xb as ligands in the vanadium-catalyzed asymmetric
oxidation of sulfides using as substrates methyl phenyl
sulfide (II), (p-bromophenyl) methyl sulfide (XI), and
benzyl phenyl sulfide (XII) (Scheme 4). For the sake
of comparison we used previously obtained compounds
Ia–Ic which had not been applied as ligands in the asym-
metric oxidation of sulfides XI, XII.
SO2CH2Ph
O
H2O2
S
S
+
VO(acac)2,
Iа_Ic
(S)-XV
XII
XVI
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 2 2012

CHIRAL SCHIFF BASES SYNTHESIZED FROM TERPENES
217
Asymmetric oxidation of sulfides in the presence of compounds Ia–Ic, Xa, Xb as ligands in the oxidant complexa
Yield, %b
Run no.
Sulfide
Ligand no.
Time, h Conversion, %
ee, %c
sulfoxide
98 (III)
sulfone
2 (IV)
2 (IV)
4 (IV)
10 (IV)
7 (IV)
0
1d
2d
3d
4
II
II
Ia
Ib
2
84
44
4 (S)
32 (R)
19 (S)
2.5
3.5
2
98 (III)
II
Ic
96
96 (III)
II
Xa
Xb
Xb
Xb
Xb
Ia
98
90 (III)
7 {10} (S)
14 {20} (S)
3 {4} (S)
8 {11} (S)
7 {10} (S)
0
5
II
2
99
93 (III)
6e
7f
II
2
74
100 (III)
97 (III)
II
2
92
3 (IV)
3 (IV)
31 (XIV)
36 (XIV)
10 (XIV)
8 (XIV)
2 (XIV)
14 (XVI)
0
8g
9
II
2
86
97 (III)
XI
XI
XI
XI
XI
XII
XII
XII
XII
XII
2
100
100
100
99
69 (XIII)
64 (XIII)
90 (XIII)
92 (XIII)
98 (XIII)
86 (XV)
100 (XV)
100 (XV)
91 (XV)
95 (XV)
10
11
12
13
14
15
16
17
18
Ib
2
12 (R)
Ic
2
2 (S)
Xa
Xb
Ia
2
3 {4} (S)
7 {10} (S)
34 (S)
2
81
3
86
Ib
3
92
37 (S)
Ic
3
87
0
30 (S)
Xa
Xb
2
100
100
9 (XVI)
5 (XVI)
0
2
0
a
Molar ratio VO(acac)2–ligand–sulfide–H2O2 1 : 1.5 : 106 : 132, 20ºC, solvent 5 ml of CH2Cl2.
b With respect to the reacted sulfide, according to the data of 1H NMR spectra.
c
1
Enantiomeric excess in sulfoxides was measured from the H NMR spectra recorded with a chiral shift reagent (R)-(–)-3,5-dinitro-N-(1-
phenylethyl)benzamide. The absolute configuration was established by comparison of the sign of the optical rotation of sulfoxides with
published data [29, 30]. In braces the calculated ee values are given with accounting for the enantiomeric purity of ligands Xa, Xb.
d Data from [16].
e
Reaction was performed at –20ºC.
Reaction was performed at 10ºC,
f
g Reaction was performed at 30ºC.
siderable reduction of the ee in sulfoxide III. A similar
temperature dependence of ee was formerly observed
in the asymmetric oxidation of sulfide II in the system
VO(acac)2–ligand (Ib)–H2O2 [16].
the formation of a large amount (>30%) of sulfone XIV.
At the application of ligands Xa, Xb in the oxidation
of sulfide XI the enantioselectivity also was lower than
in the reaction with sulfide II but the fraction of sulfide
XIV did not grow.
In the oxidation of sulfide XI using ligands Ia–Ic the
ee sharply decreased as compared to the reaction with un-
substituted sulfide II. The most efficient was the catalytic
system including ligand Ib that contained in the aromatic
ring two tert-butyl substituents; the enantiomeric excess
reached 12%. The use of less spatially hindered ligand
Ia and ligand Ic containing two nitro groups resulted in
the formation of materially racemic sulfoxide XIII. At
the use of ligands Ia, Ib the reaction was accompanied by
In the oxidation of benzyl phenyl sulfide (XII) using
ligands Ia–Ic the ee did not notably depend on the struc-
ture of the substituents in the aromatic ring and attained
30–37%, the catalyst using ligand Ib gave the best result.
Going over to ligands Ia, Ic resulted in a slight decrease
in the ee of the formed sulfoxide XV. Whereas at the
oxidation of sulfides II, XI in the presence of ligand Ib
the (R)-isomer formed in excess, in sulfoxide XV the
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 2 2012

IL’INA et al.
218
(S)-enantiomer prevailed.
0.25 μm). Oven temperature 50°C (2 min), heating rate 2
deg/min till 220°C (5 min). Temperature of the vaporizer
and the interface 250°C. Carrier gas helium (flow rate
2 ml min–1, flow splitting 99 : 1). Scanning of m/z from 29
to 500. The purity of initial compounds was checked and
the reaction products were analyzed by GLC on a chro-
matograph Agilent 7820A (USA), quartz column HP-5
30 m long, flame-ionization detector, carrier gas helium.
In the oxidation of sulfide II using as ligands Schiff
bases obtained proceeding from α-pinene [16], 2- and
3-carenes [18, 22] the replacement in the aromatic ring
of the ligand of tert-butyl substituents by nitro groups
led to the reversion of the absolute configuration of the
prevailingly formed sulfoxide III. Yet in the oxidation of
benzyl phenyl sulfide (XII) the structure of substituents
in the aromatic ring of ligands Ia–Ic did not affect the
configuration of sulfoxide XV.
The conformational analysis of diastereomers of
compounds VIII and Xa was performed by the procedure
described in [26] using for conformers generation the
programs ChemAxon Marvin (conformers plugin) [31],
VeraChem Vconf [32]. The optimization of the geometry
parameters of all conformers obtained was carried out by
the DFT method {functional PBE [33], basis L1 (Λ01
[34], analog cc-pVDZ), program PRIRODA [35]}. The
chemical shifts were calculated by the method GIAO/
DFT/PBE, basis L22 (Λ22, analog cc-pCVTZ), pro-
gram PRIRODA. Quantum-chemical calculations were
performed on a cluster of the Novosibirsk University
Scientific Computing Center [http://www.nusc.ru/]. The
visualization of the optimized structure, their Cartesian
coordinates, and the calculated chemical shifts are avail-
able on the site http://limor1.nioch.nsc.ru/quant/conform-
ers/hydroxyaldehyde/.
The use of ligands Xa, Xb in the oxidation of benzyl
phenyl sulfide (XII) was inefficient, sulfoxide XV in
both cases proved to be racemic. The reactions occurred
notably faster, the conversion was quantitative already
after 2 h, whereas in analogous reactions with ligands
Ia–Ic after 3 h from the start of the process the conver-
sion reached 86–92%.
EXPERIMENTAL
NMR spectra were registered on a spectrometer
Bruker DRX-500 at operating frequencies 500.13 (1H)
and 125.76 MHz (13C) for solutions of compounds in
a mixture CDCl3–CCl4, ~1 : 1, v/v. NMR spectra of the
solution of hydroxyaldehyde VIII in CDCl3 was taken
on a spectrometer Bruker Avance-III 600 at operating
frequencies 600.3 (1H) and 150.95 MHz (13C). The
chloroform signals (δH 7.24, δC 76.90 ppm) served as
internal references. The structures of compounds ob-
tained were established using the 1H NMR spectra with
the assistance of the spectra of double resonance 1H–1H,
and also applying the 13C NMR spectra registered in the
J-modulation mode (JMOD), with the off-resonance
proton decoupling and 2D spectra of 13C–1H correlation
on the direct constants (C–H COSY, 1JC,H 160 Hz). For
the complete assignment of the NMR signals and for the
establishment of the spatial arrangement of hydroxyal-
dehyde VIII the 2D spectra HSQC, HMBC, COSYDQF,
and NOESYwere recorded. High resolution mass spectra
were measured on a spectrometer DFS Thermo Scientific
(USA) in the mode of total scanning in the range 0–500
m/z, electron impact ionization, 70 eV, direct admission
of the sample. The specific rotation was determined on
an instrument polAAr 3005.
Verbenol epoxide (V) was prepared from (–)-ver-
benone (Aldrich, ee 70%) by procedure [36], 2-amino-
4,6-di-tert-butylphenol (IXb), by the method [15]. The
montmorillonite clay K10 (Fluka) was calcined for 3 h
at 110°C directly before use. CH2Cl2 was passed through
a column packed with the calcined Al2O3.
(R)-2-[(R)-2,2-Dimethylcyclopent-3-enyl]-2-hy-
droxypropanal (VIII). To a dispersion of 20 g of clay
K10 in 150 ml of CH2Cl2 was added a solution of 10 g
of verbenol epoxide in 150 ml of CH2Cl2, the mixture
was stirred for 1 h at room temperature, then 75 ml of
ethyl acetate was added. The catalyst was filtered off,
washed with ethyl acetate, the solvent was distilled off
in a vacuum. The residue was subjected to separation on
a column packed with 100 g of silica gel (60–200 μ, Ma-
cherey-Nagel), gradient elution with hexane containing
ethyl acetate from 0 to 100%. We obtained 1.13 g (11%)
of compound VIII (ee 70%), 1.68 g (17%) of 2-hydroxy-
1-[(1S)-2,2,3-trimethylcyclopent-3-enyl]ethanone (ee
70%), and 2.77 g (28%) of (1R,2R,6S)-3-methyl-6-(prop-
1-en-2-yl)cyclohex-3-en-1,2-diol (ee 70%).
The chirospecific GLC-MS analysis was carried
out on a gas chromatograph 6890N (Agilent Tech.,
USA) equipped with a mass-selective detector 5973
INERT, capillary column Cyclosil-B (0.32 mm × 30 m ×
Compound VIII. 1H NMR spectrum, δ, ppm: 0.86 s
(C9H3), 1.03 s (C8H3), 1.27 s (C10H3), 2.21 d.d (H1,
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 2 2012

CHIRAL SCHIFF BASES SYNTHESIZED FROM TERPENES
219
J1,5cis 10.0, J1,5trans 8.1 Hz), 2.43 d.d.d.d (H5trans, 2J 15.9,
J5trans,1 8.1, J5trans,4 3.0, J5trans,3 1.5 Hz), 2.63 d.d.d.d (H5cis
J
5',4 1.8 Hz), 5.37 d.d.d (H3, J3,4 5.8, J3,5' 2.5, J3,5 1.3 Hz),
5.62 d.d.d (H4, J4,3 5.8, J4,5 2.8, J4,5' 1.8 Hz), 7.04 d (H17,
J17,15 2.2 Hz), 7.26 d (H15, J15,17 2.2 Hz), 8.24 s (H7).
13C NMR spectrum, δ, ppm: 23.65 q (C9), 27.34 q (C10),
29.34 q (3 C19), 29.93 q (C8), 31.45 q (3 C21), 32.95 t (C5),
33.95 s and 34.41 s (C18,20), 46.50 s (C2), 56.11 d (C1),
75.53 s (C6), 110.88 d (C17), 123.35 d (C15), 126.12 d (C4),
132.76 s (C12), 135.67 s (C14), 141.58 d (C16), 142.70 d
(C3), 147.84 s (C13), 165.74 d (C7). Found [M]+ 371.2818.
C16H21O2N. Calculated M 371.2787.
,
2J 15.9, J5cis,1 10.0, J5cis,3 2.6, J5cis,4 2.0 Hz), 5.32 d.d.d
(H3, J3,4 5.8, J3,5cis 2.6, J3,5trans 1.5 Hz), 5.55 d.d.d (H4,
J4,3 5.8, J4,5trans 3.0, J4,5cis 2.0 Hz), 9.65 s (H7). 13C NMR
spectrum, δ, ppm: 23.30 q (C9), 23.66 q (C10), 29.66 q
(C8), 32.45 t (C5), 46.21 s (C2), 53.77 d (C1), 79.35 s (C6),
125.81 d (C4) 142.40 d (C3), 203.68 d C7).
2-{(R)-2-[(R)-2,2-Dimethylcyclopent-3-enyl]-2-
hydroxypropylideneamino}phenol (Xa). To a solution
of 0.080 g (0.7 mmol) of 2-aminophenol (IXa) (Aldrich)
in 3 ml of acetonitrile was added a solution of 0.080 g
(0.5 mmol) of compound VIII in 2 ml of acetonitrile.
The mixture was stirred at room temperature for 24 h.
The solvent was distilled off in a vacuum, the residue
was diluted with 4 ml of CHCl3. The precipitate was
filtered off, the filtrate was evaporated. Yield 0.119 g
Asymmetric oxidation of sulfides II, XI, XII.
A mixture of 2 mg (8 μmol) of VO(acac)2 and 12 μmol
of an appropriate ligand in 2 ml of CH2Cl2 was stirred
till complete dissolution of the crystals of VO(acac)2
(~20 min). To the solution obtained was added at stirring
847 μmol of an appropriate sulfide in 3 ml of CH2Cl2, the
reaction mixture was cooled or heated as required. Then
45 μl (1060 μmol) of 70% aqueous H2O2 was added. The
reaction progress was monitored by GLC. On the comple-
tion of the reaction the reaction mixture was diluted with
10 ml of water, the organic layer was separated, the water
layer was extracted with CH2Cl2 (2 × 5 ml), the combined
organic solutions were washed with water (2 × 10 ml),
dried with MgSO4. The conversion and the ratio of the
reaction products was determined from the H NMR
spectra. The enantiomeric excess was calculated from
the H NMR spectra (solvent CCl4–CDCl3) registered
in the presence of an equal in weight amount of (R)-(–)-
3,5-dinitro-N-(1-phenylethyl)benzamide. The oxidation
results are presented in the table.
23
1
(96%), [α]D 113° (c 0.4, CHCl3). H NMR spectrum,
δ, ppm: 0.97 s (C9H3), 1.07 s (C8H3), 1.41 s (C10H3),
2.20 d.d (H1, J1,5' 10.2, J1,5 8.0 Hz), 2.48 d.d.d.d (H5,
2J 16.0, J5,1 8.0, J5,4 2.8, J5,3 1.3 Hz), 2.76 d.d.d.d (H5',
2J 16.0, J5',1 10.2, J5',3 2.4, J5',4 1.8 Hz), 5.35 d.d.d (H3,
J3,4 5.8, J3,5' 2.4, J3,5 1.3 Hz), 5.61 d.d.d (H4, J4,3 5.8,
J
4,5 2.8, J4,5' 1.8 Hz), 6.87 d.d.d (H16, J16,17 8.0, J16,15 7.4,
J16,14 1.4 Hz), 7.00 d.d (H14, J14,15 8.1, J14,16 1.4 Hz),
7.13 d.d (H17, J17,16 8.0, J17,15 1.5 Hz), 7.18 d.d.d (H15,
1
J
15,14 8.1, J15,16 7.4, J15,17 1.5 Hz), 8.22 s (H7). 13C NMR
1
spectrum, δ, ppm: 23.62 q (C9), 27.14 q (C10), 29.96 q
(C8), 32.86 t (C5), 46.41 s (C2), 56.07 d (C1), 75.65 s
(C6), 115.72 d (C14), 116.85 d (C17), , 120.10 d (C16)
126.16 d (C4), 128.86 d (C15), 133.65 s (C12), 142.57 d
(C3), 151.50 s (C13), 166.65 d (C7). Found [M]+ 259.1570.
C16H21O2N. Calculated M 259.1567.
REFERENCES
1. Carreno, M.C., Hernandez-Torres, G., Ribagorda, M. and,
2,4-Di-tert-butyl-6-{(R)-2-[(R)-2,2-dimethyl-cy-
clopent-3-enyl]-2-hydroxypropylideneamino}phenol
(Xb). To a solution of 0.135 g (0.6 mmol) of 2-amino-
4,6-di-tert-butylphenol (IXb) in 3 ml of acetonitrile was
added a solution of 0.100 g (0.5 mmol) of compound VIII
in 3 ml of acetonitrile. The mixture was stirred at room
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