Controlling factors determining the regiochemistry of intramolecular alkoxymercuration

Article abstract of DOI:10.1039/a608003k

The intramolecular alkoxymercuration of (E)-5-arylpent-4-en-1-ols indicated that the regioselectivity is closely related to the Hammett constants of the para-substituents on the benzene ring. Large solvent effects on the regioselectivity were also observe

Full text of DOI:10.1039/a608003k

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Controlling factors determining the regiochemistry of intramolecular
alkoxymercuration
Yasuhisa Senda,* Hiroko Kanto and Hiroki Itoh
Department of Material and Biological Chemistry, Faculty of Science, Yamagata University,
Yamagata 990, Japan
The intramolecular alkoxymercuration of (E )-5-arylpent-4-en-1-ols indicated that the regioselectivity is
closely related to the H ammett constants of the para-substituents on the benzene ring. Large solvent
effects on the regioselectivity were also observed. These results were compared with those of the
methoxymercuration of β-methylstyrene analogues. The regioselectivity is discussed in terms of steric
effects as well as the electronic effects which are suggested by the M O calculation for the mercurinium ion
intermediates.
Table 1 Alkoxymercuration–demercuration of 5-arylpent-4-en-1-ols
and β-methylstyrenes
Introduction
The oxymercuration–demercuration procedure provides
a
O
convenient synthetic method for effecting the Markovnikoff
hydration of a carbon–carbon double bond. The reaction of
(E)-pent-2-ene, which has a symmetrically substituted carbon–
carbon double bond, preferably yielded pentan-2-ol, but there
is no clear explanation of this regiochemistry.1 In a cyclic
system, 3-methylcyclohexene exclusively gave 3-methylcyclo-
hexanol, the regiochemistry of which was explained in terms
of the relative stabilities of the two possible regiochemical
transition states during the attack of the nucleophiles on their
mercurinium ion intermediates.2 In contrast to the cyclo-
hexene series, the results for the flexible cyclopentenes are not
attributable to any reasonable explanation.
In order to examine the factors determining the regiochemis-
try of symmetrically substituted carbon–carbon double bonds
in the formation of oxacyclic compounds by intramolecular
alkoxymercuration, the reaction of (E)-5-phenylpent-4-en-1-
ol (1), the p-methyl analogue, (E)-5-(p-methylphenyl)pent-4-
en-1-ol (2) and the p-methoxy analogue, (E)-5-(p-methoxy-
phenyl)pent-4-en-1-ol (3), were carried out with mercuric
acetate and their regioselectivity was compared with that
obtained from the methoxymercuration of (E)-β-methyl-
styrene (4) and (E)-anethole (5). The products were character-
ized by demercuration with NaBH4.
R
R
α-attack
OH
7
+
R
α
O
β
C
H2
β-attack
6
1–3
OCH3
R
CHCH2CH3
α-attack
R
α
β
4,5
Hammett
constant
(σp)
Regioselectivity
α-attack (%)
In MeOH
Compound
R
H
In ButOH
1
2
3
4
5
0.00
Ϫ0.17
Ϫ0.27
0.00
Ϫ0.27
52
82
100
100
100
19
53
100
100
100
CH3
OCH3
H
OCH3
Results and discussion
Table 2 Solvent effect on regioselectivity of intramolecular alkoxy-
mercuration of 1
Although the introduction of solvent into the product was also
expected in the reaction of the unsaturated alcohols employed
here, no such product was detected.
Since the resulting mixture included unidentified polymer-
like substances as well as the intramolecular reaction products,
the yields of the latter were relatively low (Tables 1 and 2).
For comparison, the benzylic carbon is denoted Cα and the
atom at the other end of the double bond is Cβ for the mercurin-
ium ion moiety in the series of substrates here. The nucleophile
Regioselectivity
α-attack (%)
and (yield)a
Swain’s
solvent
polarity
Solvent
H2O–THF (1:1)
MeOH
EtOH
65 (39)
52 (34)
56 (33)
46 (46)
33 (54)
22 (48)
19 (40)
—
1.25
1.11
1.08
1.04
1.04
0.95
PrOH
BuOH
PriOH
H
ButOH
R
X
2′
C
CH2X
1′
H
CH
OCH
H
OCH
CH2CH2OH
CH2CH2OH
CH2CH2OH
H
a
1:
2:
3:
4:
5:
The values in parentheses are the isolated yields of the intramolecular
C β
H
α
3
reaction products. THF = tetrahydrofuran.
3
R
H
3
ration of 1 in tert-butyl alcohol (under intramolecular reaction
conditions), however, predominantly proceeded to give 2-
benzyltetrahydrofuran (6). The minor product was 2-phenyl-
tetrahydropyran (7). The reaction of 2 also gave a mixture of
both five- and six-membered oxacyclic products, but the former
was exclusively introduced to Cα irrespective of the para-
substituent on the benzene ring during the reaction of β-
methylstyrenes in methanol. The intramolecular alkoxymercu-
J. Chem. Soc., Perkin Trans. 2, 1997
1143

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Table 3 The formal electronic charges for the structure-optimized
mercurinium ion intermediates of para-substituted β-methylstyrenes in
some alcohols by PM3-COSMO calculation a
Substituent
(Hammett
constant,
σp)
Formal electronic charge
∆Charge
(Cα Ϫ Cβ)
Solvent
Cα
Cβ
H
(0.00)
MeOH
EtOH
Ϫ0.0654
Ϫ0.0662
Ϫ0.0669
Ϫ0.0685
Ϫ0.0598
Ϫ0.0816
Ϫ0.0811
Ϫ0.0805
Ϫ0.0794
Ϫ0.1015
0.0162
0.0149
0.0136
0.0109
0.0417
PriOH
ButOH
ButOH
Me
(Ϫ0.17)
MeO
(Ϫ0.27)
MeOH
ButOH
Ϫ0.0419
Ϫ0.0499
Ϫ0.1161
Ϫ0.1078
0.0742
0.0579
a
MOPAC93 was used. Main parameters adopted are as follows: PM3,
EF PRECISE (or GNORM = 0.2), RSOLV (1.0), NSPA (60), VDW
(HG; 1.55 × 1.1 = 1.70), EPS (for MeOH, EtOH, PriOH and ButOH,
32.70, 24.55, 19.92 and 12.47, respectively).
Fig. 1 Correlation between the dihedral angle and the heat of for-
mation for (E)-β-methylstyrene mercurinium ion intermediate in
methanol
no longer predominated. The amount of the six-membered
product was slightly larger than that of the five-membered
product (53:47). When a methoxy group was introduced at the
para-position of the benzene ring, the reaction of 3 exclusively
proceeded to give 2-(p-methoxyphenyl)tetrahydropyran. No
product of the methoxymercuration was found but an appre-
ciable amount of intramolecular reaction products was isolated
for these three substrates in methanol. The substrate, 1, pro-
vided the opposite regioselectivity in the case of tert-butyl
alcohol. The major product was then 7. The intramolecular
nucleophilic attack on the benzylic position appreciably
increased from 19 to 52% for 1 and 53 to 82% for 2 by replacing
the solvent tert-butyl alcohol with methanol. The p-methoxy
compound again exclusively gave the tetrahydropyran
derivative as in tert-butyl alcohol. These results are shown in
Table 1.
In order to investigate the solvent effects on the regioselectiv-
ity, the reaction of 1 was examined in various kinds of hydroxy-
lic solvents. The regioselectivity of the reaction is shown in
Table 2. The product distribution depended on Swain’s solvent
polarity.3 Increasing the solvent polarity tends to decrease the
amount of β-attack (Table 2). Such variation in regioselectivity
depending on the solvent implies that the interaction of the
mercurinium ion intermediate with the solvent affects the elec-
tron density of the reaction site. We accept the premise that the
oxymercuration of olefins involves the rapid pre-equilibrium
formation of a mercurinium ion as an unstable intermediate,
followed by rate- and product-determining attack of the nucleo-
phile.4 The regioselectivity of the hydration of unsymmetrical
carbon–carbon double bonds by oxymercuration obeys Mark-
ovnikoff’s rule. The position of the nucleophilic attack on the
mercurinium ion derived from a symmetrically substituted
olefinic bond is considered to be controlled by the following two
factors. First, an electronic factor; the relative electron densities
on the two carbon atoms in the mercurinium ion moiety.
Secondly, steric factors; the steric environment of the two car-
bon atoms in the mercurinium ion moiety and the ring size
formed.
Because the steric factor which controls the regioselectivity
is considered to be negligible during the methoxymercuration
of simple hydrocarbons such as 4 and 5, the attacking
position of the nucleophile on the mercurinium ion moiety
is practically determined by the electronic factor. In order to
examine the factors determining the regiochemistry of
these inter- and intra-molecular alkoxymercuriations, the
optimised structures and the formal electronic charges of
the mercurinium ion intermediates of 4, 5 and the para-methyl
analogue were obtained using semiempirical MO (MNDO/
PM3) calculations.5 The COSMO method 6 was used for the
calculation because the relative permittivities of tert-butyl
alcohol, isopropyl alcohol, ethanol and methanol, which are
Fig. 2 Correlation between the dihedral angle and the heat of for-
mation for (E)-anethole mercurinium ion intermediate in tert-butyl
alcohol
employed in the reaction, are 12.47, 19.92, 24.55 and 32.70,
respectively.7
The heats of formation for the conformers were monitored
by changing the dihedral angles (Cβ᎐Cα᎐C1Ј᎐C2Ј) every 15Њ; C1Ј
is the phenyl carbon connected to Cα and C2Ј is one of the ortho
carbon atoms of the phenyl ring. The correlation between the
dihedral angle and the heat of formation for each conformer is
shown in Figs. 1 and 2. Further detailed analysis of the corre-
lation between the heats of formation and the dihedral angles in
the vicinity of the roughly energy-minimized conformation
indicated that, in the obtained optimized conformation, the
Cα᎐C1Ј bond rotated counterclockwise with respect to the Cα᎐Cβ
bond by approximately 20Њ. No apparent effect of the methoxy
substituent was found on examining the optimized conformer
of 5, which also showed that the dihedral angle of counter-
clockwise rotation was ca. 20Њ closer to that of 4. The formal
electronic charges on Cα and Cβ in the structure-optimized
mercurinium ion intermediates of 4 and 5, together with the
Hammett constants8 of the para-substituents, are summarized
in Table 3.
The regioselectivity of the reaction may be discussed on the
basis of the energy-minimized structure of the mercurinium ion
intermediates. The electron density of Cα for 4 was lower than
those of Cβ in all solvents used here and the differences between
them are large in methanol which has a higher solvent polarity.
Decreasing the solvent polarity decreases the differences in the
electron density on Cα and Cβ. Finally, the difference becomes
smallest and the electron density on Cα is highest in tert-butyl
alcohol. When a methoxy group is introduced to the para-
position of the benzene ring, decreasing the solvent polarity
1144
J. Chem. Soc., Perkin Trans. 2, 1997

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decreases the difference in the electron density on Cα and Cβ
similar to what happens with 4. The difference is, however,
larger than that in 4. This indicates that the electrons lie more
on Cβ by replacement of the hydrogen at the para-position of
the benzene ring with the electron donative methoxy group.
It is not necessary to take into account the participation of
the steric factor on the reaction of β-methylstyrenes; therefore,
the electronic factor plays a role in determining the regio-
selectivity of the reaction. As a consequence, it is reasonable for
the methoxylation to take place at Cα which has a lower electron
density.
vacuo to give ethyl 4-(p-methoxybenzoyl)butanoate (23.17 g,
0.090 mol, 24%); mp 56–58ЊC.
The keto ester (9.97 g, 0.040 mol) was hydrogenated over
Raney Ni prepared from Ni–Al alloy (6 g) in methanol for 12 h.
The catalyst and solvent were removed and distillation gave
ethyl 5-hydroxy-5-(p-methoxyphenyl)pentanoate (9.10 g, 96%).
The hydroxy ester (9.10 g, 0.037 mol) was heated in refluxing
benzene with toluene-p-sulfonic acid (1.01 g, 0.005 mol) by
using Dean–Stark trap for 10 min. The solution was washed
with 5% sodium carbonate solution and dried over sodium
sulfate. Distillation gave ethyl (E)-5-(p-methoxyphenyl)pent-
4-enoate (6.8 g, 0.030 mol, 81%); mp 59–61 ЊC.
The intramolecular attack of the nucleophile occurred on Cβ
as well as Cα in the reaction of 5-arylpent-4-en-1-ols, different
from the case of 4 and 5. Because the electronic situation of
5-arylpent-4-en-1-ols is considered to be not very different
from that of β-methylstyrenes, the MO parameters of 4, 5 and
the p-methyl analogue were applied to the examination of 5-
arylpent-4-en-1-ols. In the reaction of 1, the intramolecular
nucleophilic attack preferably occurred on Cα with a lower elec-
tron density in methanol and ethanol, while the attack appar-
ently occurred more on Cβ with a higher electron density than
Cα in less polar solvents. The experimental evidence suggests
that the regioselectivity is controlled by another factor as well
as electronic factors in the intramolecular nucleophilic reaction.
There is no appreciable difference in the steric environment
of the two carbon atoms in the mercurinium ion intermediate
for the 5-arylpent-4-en-1-ols employed here. It is generally
accepted that the formation of a five-membered ring is kinetic-
ally preferable to that of a six-membered ring.9 Baldwin pro-
posed that the opening of three-membered rings to form
cyclic structures generally follows the exo-mode.10 From a
stereochemical point of view, the five-membered ring should be
formed rather than the six-membered one in this reaction. The
experimental evidence for 1 showed that electronic and steric
factors operate competitively and that the latter becomes pre-
dominant when the difference in the electron density is small at
the carbon atoms in the mercurinium ion moiety. The intra-
molecular nucleophile predominantly attacks at Cβ with a high-
er electron density to give the five-membered ring compounds.
The attack of an intramolecular nucleophile exclusively
occurred on Cα in the reaction of the para-methoxy compounds
irrespective of the nature of the solvent. Because the electron-
donating ability of the methoxy group is large, an appreciable
difference in the electron density between Cα and Cβ is main-
tained in the solvents used and the regioselectivity of the intra-
molecular nucleophilic attack is preferably controlled by the
electronic factor.
Treatment of the pentenoate with LiAlH4 in diethyl ether
gave (E)-5-(p-methoxyphenyl)pent-4-en-1-ol (2.79 g, 70%), mp
72–74 ЊC; δH (400 MHz; CDCl3; J values in Hz), 1.72 (2 H, m,
2-H), 1.98 (1 H, s, OH), 2.26 (2 H, m, 3-H), 3.67 (2 H, t, J
6.4, 1-H), 3.79 (3 H, s, aromatic-OCH3), 6.07 (1 H, dt, J 15.8,
6.8, 4-H) and 6.35 (1 H, d, J 5.6, 5-H), 6.81 (2 H, d, J 12.8,
aromatic) and 7.26 (2 H, d, J 12.8, aromatic).
(E)-5-Phenylpent-4-en-1-ol: bp 115–122 ЊC (0.6 mmHg);
δH (400 MHz; CDCl3), 1.73 (2 H, m, 2-H), 1.93 (1 H, s, OH),
2.29 (2 H, m, 3-H), 3.67 (2 H, t, J 6.8, 1-H), 6.22 (1 H, dt, J
16.0, 6.8, 4-H), 6.41 (1 H, d, J 16.0, 5-H), 7.15–7.34 (5 H, m,
aromatic); δC(100 MHz; CDCl3), 29.2 (C2), 32.1 (C3), 62.2
(C1), 130.3 (C5), 130.0 (C4), 125.6, 125.9, 126.9, 128.3, 128.4,
137.6 (aromatic).
(E)-5-(p-Methylphenyl)pent-4-en-1-ol: bp 140–141 ЊC (0.5
mmHg) (Found: C, 81.50; H, 8.95. C12H16O requires C, 81.77;
H, 9.15); δH (400 MHz; CDCl3), 1.73 (2 H, m, 2-H), 1.79 (1 H, s,
OH), 2.31 (3 H, s, aromatic-CH3), 2.48 (2 H, m, 3-H), 3.68 (2 H,
t, J 6.6, 1-H), 6.16 (1 H, dt, J 15.6, 6.8, 4-H), 6.38 (1 H, d, J
15.6, 5-H), 7.06–7.24 (4 H, m, aromatic); δC(100 MHz;
CDCl3), 21.1 (CH3), 29.2 (C2), 32.2 (C3), 62.3 (C1), 129.1 (C4),
130.1 (C5), 125.8, 126.4, 128.2, 128.9, 134.8, 136.6 (aromatic).
Methoxymercuration
Methoxymercuration of (E)-1-arylprop-1-ene. (E)-1-Phenyl-
prop-1-ene (1.53 g, 0.013 mol) in methanol (30 cm3) was added
to a mixture of Hg(OAc)2 (5.30 g, 0.016 mol) in methanol (100
cm3) at room temp. and stirred for 24 h. Sodium hydroxide
(3.0 , 16 cm3) was added, followed by NaBH4 (0.32 g, 0.008
mol) in NaOH (3.0 , 16 cm3) at 0 ЊC. The precipitated Hg was
removed by filtration. The product was isolated by diethyl ether
extraction. After drying over Na2SO4, solvent was removed and
distillation gave the product, which was subjected to analytical
GLC.
The product from (E)-1-phenylprop-1-ene, 1-methoxy-1-
phenylpropane, had bp 71–72 ЊC (25 mmHg); an authentic
sample was prepared from commercially available 1-phenyl-
propan-1-ol by the Williamson synthesis; δH (400 MHz; CDCl3),
0.87 (3 H, t, J 7.0, 3-H), 1.67–1.83 (2 H, m, 2-H), 3.21 (3 H, s,
OCH3), 4.01 (1 H, t, J 6.4, 1-H), 7.18–7.45 (5 H, m, aromatic);
δC(100 MHz; CDCl3), 10.2 (C3), 30.8 (C2), 56.6 (OCH3), 85.5
(aromatic-OCH3), 126.7, 127.4, 128.2, 142.1 (aromatic).
That from the para-methoxy compound, 1-methoxy-1-(p-
methoxyphenyl)propane had bp 71–72 ЊC (25 mmHg); an
authentic sample was prepared from 1-(p-methoxyphenyl)-
propan-1-ol13 by the Williamson synthesis; δH (400 MHz;
CDCl3), 0.85 (3 H, t, J 7.1, 3-H), 1.63–1.82 (2 H, m, 2-H), 3.15
(3 H, s, OCH3), 3.80 (3 H, s, aromatic-OCH3), 3.96 (1 H, t, J 6.4,
1-H), 7.18–7.45 (4 H, m, aromatic); δC(100 MHz; CDCl3), 10.2
(C1), 30.8 (C2), 55.2 (OCH3), 56.3 (aromatic-OCH3), 85.0 (C1),
113.6, 127.9, 134.1, 159.0 (aromatic).
The para-methyl analogue showed regioselectivity between
that of 1 and 3 due to the order of the electron donating ability
of the substituents.
In summary, the electronic factor operates mainly to deter-
mine the regioselectivity of the intermolecular alkoxy-
mercuration, whereas the regioselectivity is controlled by a
delicate balance of both steric and electronic factors in the
intramolecular reaction.
Experimental
Materials
(E)-1-Phenyl- and (E)-1-(p-methoxyphenyl)-pent-1-ene are
commercially available. 5-(p-Methoxyphenyl)pent-4-en-1-ol was
prepared by the method in the literature.11 5-Phenyl12 and 5-(p-
methylphenyl) analogues were prepared in a similar manner.
(E)-5-(p-Methoxyphenyl)pent-4-en-1-ol.
Ethyl-4-chloro-
Intramolecular alkoxymercuration of (E)-5-arylpent-4-en-1-ol
The (E)-5-arylpent-4-en-1-ol (0.06 mol) in the appropriate
solvent (10 cm3) was added to a Hg(OAc)2 (23.5 g, 0.07 mol) in
the same solvent (50 cm3) at room temp. and stirred for 24 h.
Sodium hydroxide (3.0 , 10 cm3) was added, followed by
NaBH4 (0.2 g, 0.005 mol) in NaOH (3.0 , 10 cm3) at 0 ЊC. The
formylbutanoate (42.70 g, 0.24 mol) was slowly added to a
stirred mixture of anisole (25.84 g, 0.24 mol) and AlCl3 (63.48
g, 0.49 mol) in dichloromethane (100 cm3) at 0 ЊC. The mixture
was stirred at 0–5 ЊC for 3 h and quenched with cold dil. HCl.
The solvent was evaporated and the residue was distillated in
J. Chem. Soc., Perkin Trans. 2, 1997
1145

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precipitated Hg was removed by filtration. The product was
isolated by diethyl ether extraction. After drying over Na2SO4,
solvent was removed and the residual oil was subjected to ana-
lytical GLC. The residual oil was also column chromato-
graphed (SiO2, 95:1 hexane–ethyl acetate) to give the pure
compound.
δC(100 MHz; CDCl3), 24.0, 25.9, 33.8 (C3), 55.2 (OCH3), 69.0
(O᎐C), 79.7 (O᎐C), 113.6, 127.1, 135.6, 158.8 (aromatic).
NMR and GC analyses
1H NMR and 13C NMR spectra were obtained with a JEOL
JNM α-400 instrument operating at 400 MHz and 100.13 MHz,
respectively, in the pulse Fourier mode. Gas chromatographic
analyses were performed on a Shimadzu model GC-8AIF
with a Carbowax 20M chemical bonded silica capillary column
(0.25 mm × 25 m or 11 m) at 120 and 140 ЊC.
The products from (E)-5-phenylpent-4-en-1-ol were: 2-
benzyltetrahydrofuran,14 bp 110–112 ЊC (10 mmHg); δH (400
MHz; CDCl3), 1.56 (1 H, dd, J 10.5, 7.5), 1.88 (3 H, m), 2.74 (1
H, dd, J 13.4, 6.4, benzyl), 2.92 (1 H, dd, J 13.4, 6.4, benzyl),
3.48 (1 H, q, J 7.1, 5-H), 3.73 (1 H, dt, J 8.3, 7.1, 5-H), 3.89 (1
H, m, 2-H), 7.19–7.30 (5 H, m, aromatic); 2-phenyltetra-
hydropyran,15 bp 105–108 ЊC (10 mmHg); δH (400 MHz;
CDCl3), 1.63 (4 H, m), 1.83 (1 H, br d, J 10.2), 1.93 (1 H, m),
3.61 (1 H, dt, J 10.2, 2.7, 6-H), 4.13 (1 H, dt, J 8.1, 2.0, 6-H),
4.31 (1 H, dd, J 10.2, 2.0, 2-H), 7.22–7.37 (5 H, m, aromatic).
The products from (E)-5-(p-methylphenyl)pent-4-en-1-ol
were: 2-(p-methylbenzyl)tetrahydrofuran, bp 108–111 ЊC (10
mmHg) (Found: C, 82.01; H, 8.98. C12H16O requires C, 81.77;
H, 9.15%); δH (400 MHz; CDCl3), 1.56 (1 H, m), 1.87 (2 H, m),
2.31 (3 H, s, aromatic-CH3), 2.33 (1 H, t, J 3.4), 2.70 (1 H, dd, J
13.8, 6.2, benzyl), 2.88 (1 H, dd, J 13.8, 6.0, benzyl), 3.73 (1 H,
m, 5-H), 3.89 (1 H, m, 5-H), 4.04 (1 H, m, 2-H), 7.07–7.26
(4 H, m); δC(100 MHz; CDCl3), 21.1 (CH3), 25.7, 26.0, 38.7
(benzyl), 66.9 (C5), 80.9 (C2), 125.6, 129.4, 137.5, 142.1 (aro-
matic); 2-(p-methylphenyl)tetrahydropyran, bp 108–111 ЊC (10
mmHg) (Found: C, 81.94; H, 8.81. C12H16O requires C, 81.77;
H, 9.15%); δH (400 MHz; CDCl3), 1.67 (4 H, m, 3-H, 4-H),
1.80 (1 H, br d, J 9.6, 3-H), 1.93 (1 H, dd, J 6.4, 3.2, 3-H), 2.32
(3 H, s, aromatic-CH3), 3.60 (1 H, dt, J 15.6, 2.4, 6-H), 4.12 (1
H, dd, J 11.2, 4.0, 6-H), 4.28 (1 H, br d, J 9.6, 2-H), 7.13 (2 H,
d, J 8.0, aromatic), 7.23 (2 H, d, J 8.0, aromatic); δC(100 MHz;
CDCl3), 21.1 (CH3), 24.0, 25.9, 30.0, 69.0 (C6), 80.0 (C2), 125.9,
128.9, 136.8, 140.4 (aromatic).
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The product from (E)-5-(p-methoxyphenyl)pent-4-en-1-ol
was 2-(p-methoxyphenyl)tetrahydropyran,16 bp 138 ЊC (10
mmHg); δH (400 MHz; CDCl3), 1.55–1.70 (4 H, m), 1.74 (1 H,
br d, J 9.6), 1.92 (1 H, br s), 3.60 (1 H, t, J 11.6), 3.78 (3 H, s,
aromatic-OCH3), 4.11 (1 H, br t, J 10.0), 4.26 (1 H, dd, J 10.0,
2.0), 6.86 (2 H, d, J 8.8, aromatic), 7.27 (2 H, d, J 8.8, aromatic);
Paper 6/08003K
Received 26th November 1996
Accepted 13th February 1997
1146
J. Chem. Soc., Perkin Trans. 2, 1997