β-Hydroxy carbocation intermediates in solvolyses of di- and tetra-hydronaphthalene substrates

Article abstract of DOI:10.3762/bjoc.6.118

Solvolysis of trichloroacetate esters of 2-methoxy-1,2-dihydro-1-naphthols shows a remarkably large difference in rates between the cis and trans isomers, k_cis/k_trans = 1800 in aqueous acetonitrile. This mirrors the behaviour of the acid-catalysed dehydration of cis- and trans-naphthalene-1, 2-dihydrodiols to form 2-naphthol, for which k_cis/k_trans = 440, but contrasts with that for solvolysis of tetrahydronaphthalene substrates, 1-chloro-2-hydroxy-1,2,3,4-tetrahydronaphthalenes, for which k _cis/k_trans = 0.5. Evidence is presented showing that the trans isomer of the dihydro substrates reacts unusually slowly rather than the cis isomer unusually rapidly. Comparison of rates of solvolysis of 1-chloro-1,2,3,4-tetrahydronaphthalene and the corresponding (cis) substrate with a 2-hydroxy group indicates that a β-OH slows the reaction by nearly 2000-fold, which represents a typical inductive effect characteristic also of cis-dihydrodiol substrates. The slow reaction of the trans-dihydrodiol substrate is consistent with initial formation of a β-hydroxynaphthalenium carbocation with a conformation in which a C-OH occupies an axial position β to the carbocation centre preventing stabilisation of the carbocation by C-H hyperconjugation, which would occur in the conformation initially formed from the cis isomer. It is suggested that C-H hyperconjugation is particularly pronounced for a β-hydroxynaphthalenium ion intermediate because the stability of its no-bond resonance structure reflects the presence of an aromatic naphthol structure.

Full text of DOI:10.3762/bjoc.6.118

β-Hydroxy carbocation intermediates in solvolyses of
di- and tetra-hydronaphthalene substrates
Jaya S. Kudavalli and Rory A. More O'Ferrall*
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2010, 6, 1035–1042.
School of Chemistry and Chemical Biology, University College Dublin,
Belfield, Dublin 4, Ireland
doi:10.3762/bjoc.6.118
Received: 02 September 2010
Accepted: 25 October 2010
Published: 03 November 2010
Email:
Jaya S. Kudavalli - kjsnarayana@yahoo.co.in;
Rory A. More O'Ferrall* - rmof@ucd.ie
Guest Editor: J. Murphy
* Corresponding author
© 2010 Kudavalli and More O'Ferrall; licensee Beilstein-Institut.
License and terms: see end of document.
Keywords:
aromaticity; β-hydroxycarbocations; hyperconjugation; solvolysis
Abstract
Solvolysis of trichloroacetate esters of 2-methoxy-1,2-dihydro-1-naphthols shows a remarkably large difference in rates between
the cis and trans isomers, kcis/ktrans = 1800 in aqueous acetonitrile. This mirrors the behaviour of the acid-catalysed dehydration of
cis- and trans-naphthalene-1,2-dihydrodiols to form 2-naphthol, for which kcis/ktrans = 440, but contrasts with that for solvolysis of
tetrahydronaphthalene substrates, 1-chloro-2-hydroxy-1,2,3,4-tetrahydronaphthalenes, for which kcis/ktrans = 0.5. Evidence is
presented showing that the trans isomer of the dihydro substrates reacts unusually slowly rather than the cis isomer unusually
rapidly. Comparison of rates of solvolysis of 1-chloro-1,2,3,4-tetrahydronaphthalene and the corresponding (cis) substrate with a
2-hydroxy group indicates that a β-OH slows the reaction by nearly 2000-fold, which represents a typical inductive effect character-
istic also of cis-dihydrodiol substrates. The slow reaction of the trans-dihydrodiol substrate is consistent with initial formation of a
β-hydroxynaphthalenium carbocation with a conformation in which a C–OH occupies an axial position β to the carbocation centre
preventing stabilisation of the carbocation by C–H hyperconjugation, which would occur in the conformation initially formed from
the cis isomer. It is suggested that C–H hyperconjugation is particularly pronounced for a β-hydroxynaphthalenium ion intermedi-
ate because the stability of its no-bond resonance structure reflects the presence of an aromatic naphthol structure.
Introduction
Cis-arenedihydrodiols are products of fermentation of aromatic A surprising finding is that the reactivity of cis-dihydrodiols is
molecules by mutant strains of soil bacteria containing dioxyge- much greater than that of the synthetically accessible trans
nase enzymes such as Pseudomonas putida UV4 [1]. A charac- isomers, e.g., kcis/ktrans = 4500 for cis- and trans-benzene di-
teristic reaction they undergo is acid-catalysed dehydration to hydrodiols (1), despite the expectation that the two reactions
form phenols [2], as illustrated for benzene-1,2-dihydrodiol in proceed through a common β-hydroxycarbocation intermediate
Scheme 1.
(2) [3]. This contrasts with reactions of cis- and trans-dihydro-
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Beilstein J. Org. Chem. 2010, 6, 1035–1042.
Scheme 1: Mechanism of dehydration of benzene-1,2-dihydrodiol.
Figure 1: Reactivity ratios for acid-catalyzed reaction of arene dihydrodiols.
diols of non-aromatic double bonds for which only a small Finally, to allow the influence of the β-hydroxy group on the
advantage for the cis-diol is observed. Indeed, the cis/trans rate rate of solvolysis to be assessed, a rate constant for solvolysis of
ratio decreases regularly as the aromaticity of the double bond the corresponding tetrahydronaphthalene substrate lacking a
decreases, as shown for the dihydrodiols of benzene, naphtha- β-hydroxy group, namely 1-chloro-1,2,3,4-tetrahydronaph-
lene (1,2), phenanthrene (9,10) and 3,4-dihydronaphthalene in thalene (5), has been measured.
Figure 1 [3].
Results
Cis- and trans-1-trichloroacetoxy-2-methoxy-
1,2-dihydro-naphthalenes (3)
The purpose of the present work was to determine whether the
same differentials apply to solvolysis reactions of dihydrodiol
derivatives for which one of the hydroxy groups has been
converted to a more reactive leaving group. In the case of
benzene dihydrodiol it is hard to functionalise the hydroxy
group without triggering aromatisation to phenol, at least in the
case of the cis-diol. The same is true of the cis-1,2-dihydrodiol
of naphthalene. However, prior methylation of the 2-hydroxy
group of this substrate led to the preparation of cis- and trans-1-
trichloroacetoxy-2-methoxy-1,2-dihydronaphthalenes (3) which
were stable enough to be isolated and purified (Figure 2). This
allowed us to compare a ratio of rate constants for the solvol-
yses of these two isomers with the corresponding ratio for
solvolyses of cis-and trans-1-chloro-2-hydroxy-1,2,3,4-tetra-
hydronaphthalene (1-chloro-2-tetralol, 4), which are similar in
structure but lack a 3,4-double bond and yield carbocations
which cannot undergo deprotonation to form aromatic products.
Rate constants for solvolyses of cis- and trans-1-trichloroacet-
oxy-2-methoxy-1,2-dihydronaphthalene (3) were measured
spectrophotometrically in aqueous acetonitrile and were
recorded for different solvent compositions (Table 1). Addition
of the acetonitrile to water solubilised the substrates which are
precipitated in pure water. A rate constant in water for the cis-
substrate was extrapolated from measurements at different
solvent compositions plotted as log k against YOTs (Supporting
Information File 1, Figure S1) [4,5]. For the trans isomer the
solvolysis was too slow for measurements over a wide range of
solvent compositions and rate constants could conveniently be
measured only for 10 and 20% (v/v) acetonitrile. A rate
constant in water was crudely extrapolated from the ratio of rate
constants for the cis and trans isomers at these two solvent
compositions. Values in water are shown in brackets in Table 1.
In the case of the more slowly reacting trans isomer there was a
competing hydrolysis of the trichloroacetate ester group to give
trans-2-methoxy-1,2-dihydro-1-naphthol (6-trans), as shown in
Scheme 2. The fraction of hydrolysis was determined by HPLC
and was found to increase with increasing water content and
amounted to 67% in 10% acetonitrile.
Surprisingly, 10% of the hydrolysis product was also identified
Figure 2: Substrates for solvolysis measurements.
in the products from solvolysis of the cis-trichloroacetate
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Beilstein J. Org. Chem. 2010, 6, 1035–1042.
Table 1: Rate constants for solvolysis of cis- and trans-1-trichloroacetoxy-2-methoxy-1,2-dihydronaphthalene (3) in acetonitrile-water mixtures at
25 °C.
% MeCN
103 kobs(s−1)
103 kobs(s−1)
% solvolysisa
YOTsb
kcis/ktrans
cis
trans
trans
50
40
30
20
10
0
0.63
0.84
2.31
6.75
20.1
(35)
1.4
1.8
2.3
3.2
3.7
3.9
0.0053c
0.0122c
(0.019)c
33
16
1.28 × 103
1.65 × 103
(~1.8 × 103)
aMeasured by HPLC. bValues interpolated from measurements recorded for solvent mixtures made up by weight from [5] cRate constant for solvol-
ysis corrected for competing hydrolysis.
because loss of a β-proton from a naphthalenium ion intermedi-
ate to form the aromatic product (naphthol) is expected to be
too fast [6,7]. This conclusion is confirmed by the lack of satu-
ration of the effect and the normal salt effects observed for
sodium acetate and sodium azide, which would be expected to
trap a carbocation intermediate more effectively than the tri-
chloroacetate anion. The normal salt effect exerted by the
sodium azide also confirms that the solvolysis proceeds via the
Scheme 2: Products of solvolysis and (ester) hydrolysis of trans-1-tri-
chloroacetoxy-2-methoxy-1,2-dihydronaphthalene.
formation of a carbocation intermediate rather than by an SN2
mechanism.
1-Chloro- and 1-chloro-2-hydroxy-1,2-
(3-cis). This was unexpected because the solvolysis of this sub-
strate is more than one thousand times faster than that of its tetrahydronaphthalenes
trans isomer whereas the rate of hydrolysis should remain prac- Rate constants for solvolysis of cis- and trans-1-chloro-2-
tically unchanged. In so far as the hydrolysis product was not hydroxy-1,2,3,4-tetrahydronaphthalenes (4) were measured in
present in the reactants and the fraction of hydrolysis was inde- aqueous solution by monitoring small but easily measurable
pendent of solvent composition, the most likely explanation changes in the UV absorbance. Values obtained were 8.1 × 10−3
would seem to be that the hydrolysis is catalysed by the cis- s−1 and 1.6 × 10−2 s−1 for the cis and trans isomers, respective-
methoxy group.
ly. Product analyses showed the formation of practically the
same ratio of cis to trans diols from cis and trans reactants
The supplementary data record salt effects for the solvolysis of together with a small amount of 2-tetralone. The product distri-
the cis-trichloroacetate ester (3-cis). For sodium acetate, the rate bution for the trans isomer is shown in Scheme 3. The corres-
in 20% acetonitrile increased by a factor of close to two at a ponding figures for the cis isomer are 76% cis and 20% trans
concentration of 0.4 M, whilst smaller effects were observed for dihydrodiols plus 4% 2-tetralone.
both sodium perchlorate and sodium azide. A little surprisingly,
sodium trichloroacetate showed a small negative salt effect The similarity of the product ratios for cis and trans isomers
leading approximately to a halving of the rate at a salt concen- argues for a common carbocation intermediate in the solvolysis
tration of 1 M. This is unlikely to be a common ion effect, reactions. The possibility of significant reaction via an epoxide
Scheme 3: Products of solvolysis of trans-1-chloro-2-hydroxy-1,2,3,4-tetrahydronaphthalene.
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Beilstein J. Org. Chem. 2010, 6, 1035–1042.
intermediate is made unlikely by the predominant formation cis-
dihydrodiol from the trans-chlorohydrin reactant and the forma-
tion of similar products from both isomers. Evidence of partial
reaction via an epoxide intermediate in buffers at higher pH,
which could favour epoxide formation, will be reported else-
where [8].
For the 1-chlorotetrahydronaphthalene (5), solvolysis in water
could not be measured directly, but a value of 14 s−1 was
obtained by extrapolation of a plot of log k against YOTs for
aqueous acetonitrile mixtures (Supporting Information File 1,
Figure S1). The measured and extrapolated rate constants in
water for the five substrates studied are summarised under the
appropriate structures in Figure 3.
Figure 4: Cis/trans reactivity ratios for β-hydroxycarbocation forming
reactions.
Comparison of rate constants for the aqueous solvolysis of cis-
and trans-1-chloro-2-hydroxy-1,2-dihydronaphthalenes (4) with
the rate constant for the corresponding substrate lacking a
hydroxy group (5) in Figure 3 shows that the hydroxy slows the
rate by a factor of 860 in the case of the trans isomer and 1700
in the case of the cis. These rate retardations seem a little large
when compared with early estimates of the effect of a
β-hydroxy or methoxy group in solvolysis reactions, which
gave kH/kOH ~100 [9-11]. However, for β-oxy substituents it is
difficult to separate a rate-retarding (inductive) effect from a
competing acceleration arising from participation of oxygen as
a neighbouring group [12,13].
As shown in Table 2, more recent estimates of the rate-retarding
effect have been based on incorporating oxygen into a struc-
tural framework which prevents its participation as a neigh-
bouring group. An example of this constraint is provided by
Figure 3: Rate constants for aqueous solvolyses.
Discussion
The major conclusion to be drawn from the measurements comparison of solvolyses of the exo- and endo-norbornyl
described above is that solvolysis of cis and trans 1-trichloro- brosylate with an oxygen atom at the 7-position (9) with the
acetoxy-2-methoxy-1,2-dihydronaphthalenes (3) show an even corresponding substrate lacking an oxygen. This leads to a rate
larger advantage for reaction of the cis isomer, with kcis/ktrans = retardation of 2000- fold for the exo-isomers and 6000 fold for
~1800, than the acid-catalysed reaction of the corresponding di- the endo [14] which is comparable to the differences we
hydrodiols 7 (kcis/ktrans = 440) or the similar 2-methoxy-1,2- observed and, indeed, is similar to the effect of oxygen reported
dihydronaphthols 8 (kcis/ktrans = 415) [8]. Moreover, this advan- for the monocyclic tetrahydrofuranyl ring of 10 which solvol-
tage is lost for the chlorohydrins of the non-aromatic double yses 1030 times more slowly than cyclopentyl brosylate [15].
bond of 3,4-dihydronaphthalene (as it is for the corresponding
dihydrodiol). These measurements are summarised in Figure 4. These effects are much larger than that of oxygen in the 3-posi-
tion of the tetrahydropyranyl brosylate (11), which slows the
It is clear that the β-OH and β-OMe substituents exert a rate only by a factor of 18. However, in this case, participation
profound influence on the relative reactivity of cis- and trans- of oxygen as a neighbouring group is well established [15]. Par-
dihydrodiol isomers and their derivatives functionalised at the ticipation by oxygen in a six-membered ring is excluded for
1-position when the dihydrodiol is derived from an aromatic solvolysis of endo (although not exo) norbornyl brosylate
double bond. A question that arises is: does this selectivity substituted with oxygen at the 4-position (12). Comparison with
derive from an unusually reactive cis isomer or an unusually the carbocyclic substrate in this case shows a rate retardation of
unreactive trans isomer? Evidence on this point comes from 80,000 [16]. This value has been considered exceptionally large
examining the effect of the β-hydroxy group on the rate of reac- and an additional rate-retarding effect has been attributed to
tions of the cis and trans isomers.
ring strain induced by the presence of oxygen in the six-
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Beilstein J. Org. Chem. 2010, 6, 1035–1042.
Table 2: Solvolysis reactions: oxygen substituent effects on reactivitya.
9
10
11
12
kCH2/kO
Temp
2000
1030
18
80000
25 °C
AcOH
85 °C
85 °C
AcOH
85 °C
AcOH
Solvent
20% aq EtOH
adata from [14-16].
membered ring of the bicyclic carbocation. Surprisingly, while It can be seen from this figure that a β-hydroxy substituent has
the solvolysis of trans-2-methoxycyclohexyl tosylate has been similar effects on the reactivity of cis-dihydro and tetrahydro
well studied [17], there appear to have been no measurements substrates, with a rate retarding effect of 5000 for 13-cis in
reported for its cis isomer.
Figure 5, compared with 2800 for solvolysis of the cis
β-hydroxychlorotetrahydronaphthalene 4. In contrast, the effect
We cannot compare these rate ratios directly with those for the is much greater in the dihydro case for the trans-substituent,
solvolyses of cis- and trans-1-trichloroacetoxy-2-methoxydihy- i.e., 2.3 × 106 for 13-trans compared with 1400 for solvolysis ot
dronaphthalenes (3) because, as noted in the introduction, the 4-trans. Measurements for benzene and phenanthrene dihydro-
parent 1-trichloroacetoxy-1,2-dihydronaphthalene is too reac- diols confirm that, whereas the ratio of cis-rate constants to
tive to allow isolation and kinetic measurements. However, rate those of the corresponding alcohols, which lack a β-hydroxy
constants have been measured for the acid-catalysed reactions group, remains roughly constant, those for the trans-dihydro-
of cis and trans-naphthalene 1,2-dihydrodiols 13-cis and diols increase sharply as the aromaticity of the double bond
13-trans (reacting at the 1-position) and may be compared with increases [18].
the corresponding alcohol lacking a β-hydroxy substituent,
namely the 1-hydroxy-1,2-dihydronaphthalene (14) [3], as These comparisons suggest that that the rate of reaction of the
shown in Figure 5.
cis-dihydrodiol is ‘normal’ while that of its trans isomer is
abnormally slow. This is consistent with the interpretation
already given for the difference in reactivities between the cis
and trans isomers 3, namely that the arenium ion intermediates
are strongly stabilised by hyperconjugation between the carbo-
cationic charge centre and a β-C–H bond, and that this effect is
amplified by the contribution of an aromatic structure to the
no-bond resonance form (15b) of the valence bond representa-
tion of this interaction 15a↔15b in Scheme 4 [3].
Scheme 4: ‘Aromatic’ hyperconjugation for the benzenium ion.
The interaction operates effectively for arenium ion intermedi-
ates formed from alcohols (arene hydrates) and cis-dihydro-
diols or their derivatives which, as illustrated in Scheme 5, can
be formed in a conformation in which an axial C–H bond bond
is positioned for hyperconjugation with the positive charge.
Figure 5: Comparison of the effect of a β-hydroxy group on the re-
activity of cis and trans di- and tetrahdronaphthalene substrates.
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Beilstein J. Org. Chem. 2010, 6, 1035–1042.
This is a consequence of a stereochemical constraint requiring hydroxy-2-methoxy-1,2-dihydronaphthalene (6-trans) were
that the leaving group departs from an axial position to facili- prepared as described by Jerina and co-workers [20]. Trans-1,2-
tate delocalisation of the carbocationic charge. However, for the dihydroxy-1,2-dihydronaphthalene was prepared by the method
trans-dihydrodiols, or the trans-1-trichloroacetoxy-2-methoxy- of Platt and Oesch [21]. Cis- and trans-1,2-dihydroxy-1,2,3,4-
1,2-dihydronaphthol 3-trans, the same constraint forces the tetrahydronaphthalene [22-24], the corresponding trans-1-
β-OH group into an axial position. Although delocalisation of chloro-2-hydroxy-1,2,3,4-tetrahydronaphthalene [25,26] and
the charge appears to be highly effective when this position is 1-chloro-1,2,3,4-tetrahydronaphthalene [25] were also prepared
occupied by a β-hydrogen atom (C–H bond), the interaction by literature methods.
becomes very much less favourable when occupied by a β-OH
group (C–OH bond).
cis-1-Hydroxy-2-methoxy-1,2-dihydronaphthalene (6-cis).
To a solution of cis-1,2-dihydroxy-1,2-dihydronaphthalene (0.5
g, 3.1 mmol) in DMF (20 mL), was added sodium hydride as a
60% dispersion on mineral oil (0.15 g, 6.2 mmol) followed over
10 min by dimethyl sulfate (0.77 g, 6.18 mmol). The mixture
was stirred at room temperature for 20 h, quenched with 1 mL
of acetic acid and diluted with water (50 mL). It was then
extracted with diethyl ether (2 × 50 mL) and the combined ether
layers washed with water (2 × 50 mL) and dried over sodium
sulfate. The solvent was removed under reduced pressure to
yield a residue consisting of two regioisomeric monomethyl-
Scheme 5: Stereochemistry of carbocation formation from solvolysis
of cis-1-trichloroacetoxy-2-hydroxy-1,2-dihydronaphthalene.
The work describing these favourable and unfavourable hyper- ated products and the dimethylated product (cis-1,2-dimethoxy-
conjugative interactions has hitherto been based largely on 1,2-dihydronaphthalene). Purification by chromatography
carbocation formation involving an H2O leaving group charac- allowed separation of the dimethylated product but the mono-
teristic of acid-catalysed dehydration of alcohols and cis and methylated products were obtained as a three to one mixture of
trans dihydrodiols of aromatic and aliphatic carbon–carbon the desired product with its regioisomer (0.08 g, 15%) (Rf 0.65,
double bonds (3). The purpose of the present study was to deter- 20% ethyl acetate in pentane). NMR data for the principal
mine whether the same dependence on stereochemistry of a isomer and analytical data for the mixture were as follows.
β-hydroxy group would be observed for solvolytic reactions.
Our conclusion, that it is, is based on a comparison of measure- 1H NMR (CDCl3) δ 2.6 (bs, 1H, OH), 3.45 (s, 3H), 4.0 (t, J =
ments of absolute and relative reactivities of cis and trans 4.4 Hz, 1H), 4.78 (bs, 1H), 6.08 (dd, J = 9.6, 3.9 Hz, 1H), 6.59
isomers in conventional solvolytic reactions with chloride ion as (dd, J = 9.6 Hz, 1H), 7.1–7.54 (m, 4H); m/z GC-MS) 156
a leaving group (yielding a carbocation not corresponding to a (M-H2O); (Found C 74.3, H 7.0; C11H12O2 requires C 75.0, H
protonated aromatic molecule) with the solvolytic formation of 6.9).
naphthalenium ions in which the leaving group is a trichloro-
acetate anion. The only noteworthy difference between the two cis-1-Trichloracetoxy-2-methoxy-1,2-dihydronaphthalene
classes of reactions (i.e., dehydrations and solvolyses) is a (3-cis). To a 3:1 mixture (0.1 g, 0.56 mmol) of cis-1-hydroxy-2-
slightly larger difference in reactivity between cis and trans methoxy-1,2-dihydronaphthalene (6-cis) and its regioisomer
methoxy groups for the solvolytically generated arenium ions (see above) in dichloromethane (10 mL), were added pyridine
(2000 compared with 415) which perhaps represents a more (45 mg, 0.57 mmol), DMAP (7 mg 0.05 mmol) and
product-like transition for the poorer trichloroacetate than the trichloroacetic anhydride (0.21 g, 0.68 mmol) and the solution
H2O leaving group. In sum, the influence of an enhanced hyper- was stirred at room temperature for 2 h. Evaporation of the
conjugation identified in the reactions of arene dihydrodiols is solvent gave a crude product mixture from which the desired
fully corroborated by the present study of β-hydroxy carbo- product was separated by flash chromatography (Rf 0.61, 10%
cation-forming solvolysis reactions.
ethyl acetate in pentane) to give a light yellow oil (0.08g, 73%).
1H NMR (CDCl3) δ 3.4 (s, 3H), 4.31 (m, 1H), 6.05 (dd, J =
9.91, 2.39 Hz, 1H), 6.11 (d, J = 4.35 Hz, 1H), 6.58 (dd, J =
Experimental
Purchased reagents were generally used without purification. 9.81, 1.81 Hz, 1H) 7.15–7.31 (m, 4H).
Cis-naphthalene dihydrodiol (cis-1,2-dihydroxy-1,2-dihydro-
naphthalene) was prepared by oxidative fermentation of naph- trans-1-Trichloracetoxy-2-methoxy-1,2-dihydronaphthalene
thalene [19] and was kindly provided by D. R. Boyd of the (3-trans). To a solution of trans-1-hydroxy-2-methoxy-1,2-di-
Queen’s University of Belfast. Naphthalene oxide and trans-1- hydronaphthalene (6-trans) (0.1 g, 0.56 mmol) in
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Beilstein J. Org. Chem. 2010, 6, 1035–1042.
dichloromethane (10 mL), pyridine (45mg, 0.57 mmol) and
DMAP (7 mg, 0.05 mmol) were added. The mixture was stirred
for 5 min and trichloroacetic anhydride (0.21g, 0.68 mmol) was
added over 5 min followed by stirring for 2 h at room tempera-
ture. Evaporation of the solvent gave a crude product which was
purified by preparative TLC (5% ether in pentane) to yield the
desired product as a light yellow-coloured liquid (0.14 g 77%);
(Rf 0.73 10% ether in hexane); 1H NMR (CDCl3) δ 3.4 (s, 3H),
4.29 (ddd, J = 7.53, 3.24, 1.48 Hz, 1H), 6.09 (dd, J = 9.87, 3.32
Hz, 1H), 6.28 (d, J = 7.55 Hz, 1H), 6.59 (dd, J = 9.89, 1.00 Hz,
1H) 7.15–7.31 (m, 4H); m/z (GC-MS) 158.1 (321.5
–Cl3CCOOH).
Supporting Information
Supporting Information File 1
Experimental part.
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-6-118-S1.pdf]
Acknowledgements
This work was supported by The Science Foundation Ireland
(Grant No. 04/IN3/B581). We thank A. Cagney for assistance
with the kinetic measurements.
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Kinetic measurements and product ratios. In general, rate
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2 mL of water or aqueous acetonitrile in a cuvette and moni-
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1-chloro-1,2,3,4-tetrahydronaphthalene rate constants (s−1)
were measured for the following acetonitrile water solvent
mixtures: 50% MeCN, 0.0320; 60% MeCN, 0.0106; 70%
MeCN, 0.00335; 80% MeCN, 0.00082. A plot of log k versus
YOTs and extrapolation gave a rate constant of ~2.3 s−1 for pure
water.
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For both the trichloroacetate esters of 2-methoxy-1,2-dihydro-1-
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acetonitrile were injected into 150 μL of water or aqueous
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were required to partition measured rate constants between
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