3-(Trifluoromethyl)indenyl Cation: Ion Pair Return in the Formation of an Antiaromatic and Electron-Deficient Doubly Destabilized Carbocation

Article abstract of DOI:10.1021/jo961387k

The solvolysis of 3-(trifluoromethyl)-3-indenyl tosylate (15) occurs with extensive isomerization to 1-(trifluoromethyl)-3-indenyl tosylate (16), which reacts in a slower process to give the substitution product 17. Kinetic analysis of a model involving an intermediate allyl cation/tosylate ion pair 18 gave a partitioning ratio in CD₃CO₂D at 99.6°C for 18 of 7.7 for return with allylic rearrangement compared with solvent capture. Studies of 15 with specific ¹⁸O labeling show no scrambling in recovered 15 and partial scrambling in rearrangement to 16. The m value measuring the dependence of the reactivity of 15 on the solvent-ionizing parameter Y_OTs is 0.78, which is significantly less than that of 1.23 for the analogous 9-(trifluoromethyl)-9-fluorenyl tosylate 7. Normal salt effects in CF₃CO₂H predominate for 15, and the special salt effect involves no more than 14% capture of solvent-separated ion pairs by 0.551 M KO₂CCF₃. The substrate 15 has a net diminution in reactivity of more than 109 relative to the secondary indanyl tosylate 22, with factors of 10⁶ and 10³ attributable to antiaromaticity and to the electron-withdrawing CF₃ group, respectively. The solvolysis of 15 is proposed to occur by formation of an ion pair with significant nucleophilic solvation at the relatively unhindered allylic carbon, but internal return occurs in preference to solvent or salt capture. Solvolysis of the rearranged tosylate 16 occurs with a strong rate retardation by the γ-CF₃ group, a large extent of internal return, and with a normal salt effect.

Full text of DOI:10.1021/jo961387k

246
J . Org. Chem. 1997, 62, 246-252
Articles
3-(Tr iflu or om eth yl)in d en yl Ca tion : Ion P a ir Retu r n in th e
F or m a tion of a n An tia r om a tic a n d Electr on -Deficien t Dou bly
Desta bilized Ca r boca tion
Annette D. Allen,† Mizue Fujio,‡ Nageib Mohammed,† Thomas T. Tidwell,*,† and
Yutaka Tsuji‡
Department of Chemistry, University of Toronto, Toronto, Ontario, M5S 3H6, Canada, and Institute for
Fundamental Research of Organic Chemistry, Kyushu University, Hakozaki, Fukuoka 812, J apan
Received J uly 22, 1996X
The solvolysis of 3-(trifluoromethyl)-3-indenyl tosylate (15) occurs with extensive isomerization to
1-(trifluoromethyl)-3-indenyl tosylate (16), which reacts in a slower process to give the substitution
product 17. Kinetic analysis of a model involving an intermediate allyl cation/tosylate ion pair 18
gave a partitioning ratio in CD3CO2D at 99.6 °C for 18 of 7.7 for return with allylic rearrangement
compared with solvent capture. Studies of 15 with specific 18O labeling show no scrambling in
recovered 15 and partial scrambling in rearrangement to 16. The m value measuring the
dependence of the reactivity of 15 on the solvent-ionizing parameter YOTs is 0.78, which is
significantly less than that of 1.23 for the analogous 9-(trifluoromethyl)-9-fluorenyl tosylate 7.
Normal salt effects in CF3CO2H predominate for 15, and the special salt effect involves no more
than 14% capture of solvent-separated ion pairs by 0.551 M KO2CCF3. The substrate 15 has a net
diminution in reactivity of more than 109 relative to the secondary indanyl tosylate 22, with factors
of 106 and 103 attributable to antiaromaticity and to the electron-withdrawing CF3 group,
respectively. The solvolysis of 15 is proposed to occur by formation of an ion pair with significant
nucleophilic solvation at the relatively unhindered allylic carbon, but internal return occurs in
preference to solvent or salt capture. Solvolysis of the rearranged tosylate 16 occurs with a strong
rate retardation by the γ-CF3 group, a large extent of internal return, and with a normal salt effect.
There has been increasing interest in the concepts of
recent studies of 3,3b,5g but 2 has been comparatively
neglected. We now report the results of our studies of a
doubly destabilized indenyl carbocation.
aromaticity and antiaromaticity,1 and the study of car-
bocations and carbanions that display these properties
continues to be a particularly challenging area for both
theoretical2 and experimental3 studies. Because of our
interest in destabilized carbocations,4,5 we have been
attracted to the study of the cyclopentadienyl (1),5h
indenyl (2), and fluorenyl (3)5g cations. Of these, 1 has
received particular attention,1,2a,c,d,5h and there have been
The solvolytic generation of the indenyl cation (2) has
been studied by Friedrich and co-workers.6 The relative
solvolytic reactivities of 4, 5, and 6 were estimated as 1,
10, and 105-106, respectively, and on the basis of these
data, rate retardations due to antiaromatic destabiliza-
tion by factors of 1011 and 108 were estimated for
formation of 2 and the 9-fluorenyl cation, using the
cyclopentyl system as a reference.6
† University of Toronto.
‡ Kyushu University.
X Abstract published in Advance ACS Abstracts, December 15, 1996.
(1) (a) Garratt, P. J . Aromaticity; Wiley-Interscience: New York,
1986. (b) Minkin, V. I.; Glukhovtsev, M. N.; Simkin, B. Ya. Aromaticity
and Antiaromaticity; Wiley-Interscience: New York, 1994.
(2) (a) Schleyer, P. v. R.; Freeman, P. K.; J iao, H.; Goldfuss, B.
Angew. Chem., Int. Ed. Engl. 1995, 34, 337-340. (b) Byun, Y.-G.;
Saebo, S.; Pittman, C. U., J r. J . Am. Chem. Soc. 1991, 113, 3689-
3696. (c) Feng, J .; Leszczynski, J .; Weiner, B.; Zerner, M. C. J . Am.
Chem. Soc. 1989, 111, 4648-4655. (d) Glukhovtsev, M. N.; Reindl, B.;
Schleyer, P. v. R. Mendeleev Commun. 1993, 100-102.
(3) (a) Sachs, R. K.; Kass, S. R. J . Am. Chem. Soc. 1994, 116, 783-
784. (b) Amyes, T. L.; Richard, J . P.; Novak, M. J . Am. Chem. Soc.
1992, 114, 8032-8041.
(4) Tidwell, T. T. Angew. Chem., Int. Ed. Engl. 1984, 23, 20-34.
(5) (a) Kirmse, W.; Wonner, A.; Allen, A. D.; Tidwell, T. T. J . Am.
Chem. Soc. 1992, 114, 8828-8835. (b) Allen, A. D.; Krishnamurti, R.;
Prakash, G. K. S.; Tidwell, T. T. J . Am. Chem. Soc. 1990, 112, 1291-
1292. (c) Allen, A. D.; Tidwell, T. T.; Tee, O. S. J . Am. Chem. Soc. 1993,
115, 10091-10096. (d) Allen, A. D.; Fujio, M.; Tee, O. S.; Tidwell, T.
T.; Tsuji, Y.; Tsuno, Y.; Yatsugi, K. J . Am. Chem. Soc. 1995, 117, 8974-
8981. (e) Begue, J .-P.; Benayoud, F.; Bonnet-Delpon, D.; Allen, A. D.;
Cox, R. A.; Tidwell, T. T. Gazz. Chim. Ital. 1995, 125, 399-402. (f)
Allen, A. D.; Kanagasabapathy, V. M.; Tidwell, T. T. J . Am. Chem.
Soc. 1986, 108, 3470-3474. (g) Allen, A. D.; Colomvakos, J . D.; Tee,
O. S.; Tidwell, T. T. J . Org. Chem. 1994, 59, 7185-7187. (h) Allen, A.
D.; Sumonja, M.; Tidwell, T. T. J . Am. Chem. Soc. 1997, 119, in press.
We have been interested in the destabilizing effects of
CF3 and C2F5 groups on carbocationic reactivity,5 includ-
ing the effects on the reactivity of molecules substituted
with two such groups to produce doubly destabilized
(6) (a) Friedrich, E. C.; Taggart, D. B. J . Org. Chem. 1978, 43, 805-
808. (b) Friedrich, E. C.; Tam, T. M. J . Org. Chem. 1982, 47, 315-
319.
S0022-3263(96)01387-4 CCC: $14.00 © 1997 American Chemical Society

3-(Trifluoromethyl)indenyl Cation
J . Org. Chem., Vol. 62, No. 2, 1997 247
carbocations.5f Recently, we have extended this approach
to include double destabilization by antiaromaticity and
electron-withdrawing R-substitution and have examined
the solvolysis of tosylate 7 to generate the 9-(trifluorom-
ethyl)fluorenyl cation 8.5g The results indicated that 7
is 4 × 107 times less reactive than Ph2CHOTs, and rate
factors of 104 and 103 may be attributed to the effect of
the electron-withdrawing effect of the CF3 group and the
destabilizing effect of the 12 π-electron antiaromatic1
system, respectively, in the generation of cation 8.
Ta ble 1. Solvolysis Ra te Con sta n ts for
15 a n d 16 a t 25 °C
a
a
solvent
TFA
[salt]
k1 (s-1
)
15
k (s-1
)
16
k 7/k 15 k 15/k 16
2.06 × 10-3
8.30 × 10-5
1.12 × 10-4
1.19 × 10-4
2.14 × 10-4
1.86 × 10-4
3.13 × 10-4
3.56 × 10-4
149e
24.8
23.1
22.4
20.5
19.4
18.6
19.7
51.2
0.0587b 2.59 × 10-3
0.0588c 2.66 × 10-3
0.201c
0.201d
0.421c
0.592c
4.38 × 10-3
3.61 × 10-3
5.82 × 10-3
7.00 × 10-3
97 HFIP
HCO2H
97 TFE
50 TFE
80 EtOH
HOAc
5.89 × 10-4f 1.15 × 10-5g
9.57 × 10-5
226e
86e
1.61 × 10-5h
55e
2.27 × 10-5i (4.59 × 10-4
)
4.2i
1.5l
i
(3.20 × 10-5
)
7.7j
0.87
j
(1)
2.00 × 10-7k
a
Duplicate runs measured by UV unless noted at each tem-
b
perature, reproducible (5%. NaO2CCF3. c KO2CCF3; for 15 k1 )
(8.52 ( 0.35) × 10-3 M-1 s-1 [KO2CCF3] + (2.18 ( 0.11) × 10-3
s-1, for 16 k ) (4.88 ( 0.24) × 10-4 M-1 s-1 [KO2CCF3] + (9.16 (
d
0.77) × 10-5 s-1
.
NaO3SCF3. e Derived using redetermined values
The tosylate 7 was also found to have a very high
dependence of reactivity on the solvent ionizing power
YOTs, with an m value of 1.23, and was found to display
very large accelerations of trifluoroacetolysis on addition
of NaO2CCF3. The effects were attributed to a high
demand for solvent stabilization and a special salt effect
with scavenging of solvent-separated ion pairs by the
added salt.5g We have now extended these studies to the
potentially more highly destabilized indenyl system,
which shows markedly different behavior from 7.
of k (7). kobs(s-1 × 103), (T, °C): 5.30 (56.6), 2.78 (45.9), 1.28 (35.8);
f
∆Hq ) 13.0 kcal/mol; ∆Sq ) -29.6 cal K-1 mol-1
.
kobs (s-1 × 105),
g
(T, °C): 21.0 (56.6), 8.83 (45.9), 3.24 (35.8); ∆Hq ) 17.4 kcal/mol;
∆Sq ) -22.6 cal K-1 mol-1
.
kobs (s-1 × 104), (T, °C): 7.61 (62.7),
h
1.95 (47.6); ∆Hq ) 19.8 kcal/mol, ∆Sq ) -14.1 cal K-1 mol-1
.
kobs
i
15 (65.1 °C) ) 1.94 × 10-3 s-1; kobs 16 (65.1 °C) ) 4.59 × 10-4 s-1
,
k 15/k 16 ) 4.2. j 60.8 °C. k Extrapolated value from measurements
at higher temperatures, kobs s-1 × 105 (T, °C) 40.0 (99.6), 4.86
(75.4), 1.31 (63.0); ∆Hq ) 22.6 kcal/mol, ∆Sq ) -13.9 cal K-1 mol-1
.
Rate at 99.6 °C measured by 1H NMR in CD3CO2D. See text.
l
be monitored by UV and by NMR, and 16 could be
obtained on a preparative scale by stopping the reaction
at a suitable time and then isolating and characterizing
the purified material. After extended reaction times, the
acetates 17a and 17b were isolated and characterized,
along with small amounts of the alcohol 17c.
Rate constants for the reaction of 15 and for the
subsequent solvolysis of 16 to 17 were measured by both
UV and NMR spectroscopy, as collected in Table 1. The
rates for both processes could be measured by continuous
monitoring of the same sample, and good agreement in
the rates was found by using isolated and purified 16 to
measure the rate of the second step.
Resu lts
The indenyl tosylate 15 was prepared using a mod-
ification7a of the Marvel and Hinman synthesis of inde-
none (12),7b,c followed by CF3 transfer using CF3SiMe3
(eqs 2-4).7d
For the reaction of 15 in acetic acid the reaction
mixture in CD3CO2D was sealed in an NMR tube and
heated at 99.6 °C. The tube was cooled at intervals, and
the 1H NMR spectrum was measured. The change in the
CH3 peak of 16 with time as a function of the total
tosylate concentration (15 + 16 + TsOH) was measured,
as collected in Table 2 (Supporting Information), and
illustrated in Figure 1.
The effects of added salts on the rates of trifluoroac-
etolysis of 15 and 16 as measured by UV are reported in
Table 1. Addition of NaO2CCF3, KO2CCF3, and NaO3-
SCF3 gave similar changes in the reactivity of 15, and
linear correlations of the dependence on [KO2CCF3] of
the rates of 15 and 16 gave slopes (s-1 M-1) of (8.52 (
0.35) × 10-3 and (4.88 ( 0.24) × 10-4. A plot for 15 at
25 °C is shown in Figure 2, along with comparative data5g
for 9-(trifluoromethyl)fluorenyl tosylate (7) at 6.1 °C. For
direct comparison the latter rates have been multiplied
by 0.0532 to give the same rates at [salt] ) 0.0.
The solvolysis of 15 in trifluoroacetic acid or acetic acid
gave rearrangement to the secondary tosylate 16, which
reacted further in a slower process to the corresponding
substitution products 17 (eq 5). These processes could
To determine the effect of added salt on the competition
between rearrangement of 15 to 16 and solvolysis to 17,
solutions of 15 in CF3CO2D without salt and with 0.551
M KO2CCF3 were observed at intervals by 1H NMR (400
MHz) at 22 °C, as reported in Table 3 (Supporting
Material). Kinetic analysis of the data in the absence of
salt gave similar rate constants of 1.24 × 10-3 and 1.48
(5)

248 J . Org. Chem., Vol. 62, No. 2, 1997
Allen et al.
F igu r e 3. 13C NMR signal for the carbinyl carbon of partially
scrambled 1-(trifluoromethyl)-3-indenyl tosylate-18O2 (16-18O2).
F igu r e 1. Fraction of 1-(trifluoromethyl)-3-indenyl tosylate
(16) vs time in the acetolysis of 3-(trifluoromethyl)-3-indenyl
tosylate (15) in CD3CO2D at 99.9 °C (curve fit by eq 6).
Discu ssion
These results are consistent with the solvolysis of 15
proceeding to an ion pair 18 that can partition between
return to the rearranged tosylate 16 and solvent capture
to form 17, but without return to the less stable starting
tosylate 15 (eq 5). There have been numerous previous
demonstrations of return in allylic systems,8ab but the
conversion of 15 to 16 is unusual in that there is an
isomerization of a tertiary to a secondary substrate.
The kinetic rate expressions for the reaction scheme
corresponding to eq. 5 have been derived previously.9 For
the reaction in CD3CO2D (Table 2, Supporting Informa-
tion), the appropriate expression for the measured quan-
tity [16]/([15] + [16] + [17]) is given in eq 6, and fitting
this equation to the measured results (Figure 1) gave ka
+ kb () k1) of (4.00 ( 0.07) × 10-4 s-1, ka/(ka + kb) ) 0.886
( 0.005, and kc ) (3.09 ( 0.04) × 10-5 s-1, and these
give values ka ) 3.54 × 10-4 s-1 and kb ) 4.60 × 10-5
s-1. The fraction ka/kb is 7.7 and is equal to k-2/k3, which
is the extent to which the initial ion pair partitions
between rearranged tosylate 16 and solvent capture. The
value of k2 () k1kckb-1, eq 5), is 2.69 × 10-4 s-1, so the
ionization rate ratio k1/k2 ) 1.5, considerably less than
the rate ratio (ka + kb)/kc of 13 for product formation from
15 and 16.
F igu r e 2. Effects of added salts MO2CCF3 on the trifluoro-
acetolysis of 9-(trifluoromethylfluorenyl)tosylate 7 (NaO2CCF3
at 6.1 °C, k × 0.517) and 3-(trifluoromethyl)-3-indenyl tosylate
15 (KO2CCF3 at 25 °C).
× 10-3 s-1 for the disappearance of 15 and the appearance
of 16 at 22 °C, respectively, in reasonable agreement with
the UV rate 2.06 × 10-3 s-1 at 25 °C for reaction of 15.
For the data in the presence of 0.551 M KO2CCF3, a value
of k1 of 3.3 × 10-3 s-1 at 22 °C was estimated, which is
2.6 times greater than the value in the absence of salt,
and this acceleration in the rate is comparable to that of
3.4 observed by UV for 0.592 M KO2CCF3 (Table 1).
ka
98 16
15
15
To examine the extent of oxygen equilibration during
the reaction in CF3CO2H, a sample of 15 with sulfonyl-
18O2 labeling was prepared using sulfonyl-18O2-labeled
4-tosyl chloride made using H218O with 98.8% 18O, as we
have done previously.5d The solvolysis was carried out
for 9 min (1.6 half-lives) at 25 °C and then quenched,5d
kb
98 17
kc
98 17
16
1
and the H NMR spectrum showed the presence of the
[16]/([15] + [16] + [17]) ) ka[exp(-(ka + kb)t) -
exp(-kct)](kc - ka - kb)-1 (6)
starting tosylate 15 and the rearranged tosylate 16 in a
ratio of 1:1.5. The 13C NMR spectrum of the recovered
tosylate 15 showed no detectable 18O-induced isotope shift
in the peak for the alkoxy carbon at δ 90.6, indicating
no 18O scrambling had occurred. The 13C NMR spectrum
of the rearranged tosylate 16 showed signals for 13C
bonded to 16O at δ 80.089 and to 18O at 80.058 ppm, in a
ratio of 1.142:1.000, respectively (Figure 3), correspond-
ing to 53% bonding of 16O-labeled oxygen to the allylic
carbon.
For the kinetic data (Table 1) in CF3CO2H k(15) () ka
+ kb) is 2.06 × 10-3 s-1 and k(16) () kc) is 8.30 × 10-5
s-1
.
From the product data in CF3CO2D (Table 3,
Supporting Information) the first observed product ratio
[16]/([16] + [17]) [) ka/(ka + kb)] is 0.88, giving values
for ka of 1.80 × 10-3 s-1, kb of 2.6 × 10-4 s-1, k1/k2 ()
kb/kc) of 3.1, and ka/kb () k-2/k3) of 6.9.

3-(Trifluoromethyl)indenyl Cation
J . Org. Chem., Vol. 62, No. 2, 1997 249
The trifluoroacetolysis of 15 labeled with 98.8% sulfo-
nyl-18O2 for 1.6 half-lives showed no scrambling of the
label in recovered 15, consistent with the absence of
return of the ion pair 18 to 15, as shown in eq 5. The
rearranged tosylate 16 showed the oxygen bonded to the
allylic carbon contained 53% 16O, while complete scram-
bling of the 18O label would result in 34% 16O incorpora-
tion at this position, and selective migration of the 16O
at C-3 of 15 to the allylic carbon would result in 100%
16O at this position. This result indicates a preference
(memory effect) for rebonding of the originally carbon-
bonded oxygen to the extent of 30%, with 70% scrambling
of the oxygens. For comparison, in one previous study8d
of an allylic rearrangement of a p-nitrobenzoate ester 18O
equilibration to the extent of 90-100% was observed,
while for 2-pent-3-enyl p-nitrobenzoate there was a
preference for bonding of the carbonyl oxygen during the
symmetrical allylic rearrangement8e by a factor of 3.8 to
4.9. Preferential return of an original tertiary carbon
bonded oxygen to a secondary carbon following Wagner-
Meerwein rearrangement to the extent of 6.1:1 in an 18O-
labeled hexafluorobutyrate ester has also been observed.8f
0.059 M produces a rate acceleration of 5.4,5g 4.2 times
greater than for 15. For the indenyl tosylate 15 the
added salts cause mainly normal salt effects and inter-
cept no more than 14% of solvent separated ion pairs,
and predominant internal return to rearranged tosylate
16 still occurs, even at 0.59 M salt. By contrast, the much
larger salt effects for the fluorenyl tosylate 7 have been
characterized kinetically as special salt effects5g and
result in formation of solvolysis product. The compara-
tive salt effects on the trifluoroacetolysis of 7 and 15 are
shown in Figure 2. The different behavior of the indenyl
tosylate 15 is due to the availability of the unhindered
allylic position, which provides a ready point of return
for the tosylate anion. The steep initial curvature of rate
vs [salt] plots characteristic of the special salt effect is
too weak in the case of 15 to be reliably observed.
The strikingly different m values of 1.23 and 0.78 for
the fluorenyl tosylate 7 and the indenyl tosylate 15,
respectively, lead to a steady decrease in the fluorenyl/
indenyl rate ratio k 7/k 15 with decreasing solvent
polarity from 226 (HFIP) to 0.87 (HOAc). The large m
value for the fluorenyl tosylate 7 was attributed5g to
destabilization due to antiaromaticity effects, which
therefore led to a rather localized carbocation that
showed enhanced stabilization by polar solvents.
The significantly lower m value for 15 may be ex-
plained on the basis of extensive charge delocalization
to the relatively unhindered allylic carbon, which under-
goes significant nucleophilic interaction with the solvent.
However, this solvation does not advance to the stage of
nucleophilic solvent participation, as even in the rather
nucleophilic acetic acid formation of the rearranged
tosylate exceeds solvent capture by a factor of 7.7 (vide
supra).
The alternative mechanism of formation of the rear-
ranged tosylate 16 without ionization but by a sigmat-
ropic rearrangement of 15 appears highly unlikely, as
the strong dependence of the reaction rate on solvent
polarity, and the significant normal salt effect, indicate
a very polar transition state, and such pathways have
not been demonstrated in other allylic rearrangements.8
The rates of solvolysis of the rearranged secondary
tosylate 16 in TFA (25 °C), 97% HFIP (25 °C), 50% TFE
(65.1 °C), and CD3CO2D (99.6 °C) are 25, 51, 4.2, and 13
times slower, respectively, than the rate of rearrange-
ment of 15 to 16. The lower rate ratios in the more
nucleophilic 50% TFE and CD3CO2D are consistent with
some nucleophilic solvent assistance in the case of 16,
which is not unexpected for this secondary substrate. In
CD3CO2D the kinetic analysis shows that the ionization
rate ratio k1/k2 is only 1.5, but because of the extensive
reformation of 16 by ion pair return the rate of consump-
tion of the reactant is considerably less.
The values of k1 for the initial reaction of 15 in 6
solvents (Table 1) are well correlated by YOTs values at
25 °C by the relation log k1 ) (0.78 ( 0.03)YOTs -6.25 (
0.09, r ) 0.997. The initial ion pair presumably has the
tosylate anion in proximity to the original point of
attachment, and there is likely to be a barrier to the
movement of the tosylate to the γ-position, as it has been
demonstrated by Nordlander and Gassman et al.,10 that
allylic ion pairs in which the termini differ only in isotopic
labeling and the initial position of the counterion do not
undergo equilibration as fast as collapse to covalent
products. A plausible contributing factor for this barrier
is the presence of a node at Câ in the HOMO of the allylic
carbocation, which causes an impediment to the move-
ment of the counterion. Despite this barrier the extent
of tosylate internal return with rearrangement is still
quite large. The fraction return in CD3CO2D at 99.6 °C
ka/(ka + kb) is 0.88, and in CF3CO2D in the absence of
salt the initial observed fraction of return observed is also
0.88 (Table 3, Supporting Information). In the presence
of 0.551 M KO2CCF3 the initial observed fraction of
rearrangement to 16 decreases to 0.74, and the change
of 14% caused by the salt may be interpreted as a very
modest special salt effect in which solvent separated ion
pairs are captured by salt. The similarity of the extent
of ion pair return in CF3CO2D and CD3CO2D is sugges-
tive that there is only a similar and small extent of
formation of solvent separated ion pairs in both of these
media, so that the nucleophilic CD3CO2D or the added
salts in CF3CO2D do not capture major portions of the
initial ion pair.
(7) (a) Bellamy, F. D.; Chazan, J . B.; Ou, K. Tetrahedron 1983, 39,
2803-2806. (b) Marvel, C. S.; Hinman, C. W. J . Am. Chem. Soc. 1954,
76, 5435-5437. (c) Galatsis, P.; Manwell, J . J .; Blackwell, J . M. Can.
J . Chem. 1994, 72, 1656-1659. (d) Krishnamurti, R.; Bellew, D. R.;
Prakash, G. K. S. J . Org. Chem. 1991, 56, 984-989.
(8) (a) Goering, H.; Koerner, G. S.; Linsay, E. C. J . Am. Chem. Soc.
1971, 93, 1230-1233. (b) Goering, H. L.; Anderson, R. P. J . Am. Chem.
Soc. 1978, 100, 6469-6474. (c) Gassman, P. G.; Harrington, C. K. J .
Org. Chem. 1984, 49, 2258-2273. (d) Goering, H. L.; Linsay, E. C. J .
Am. Chem. Soc. 1969, 91, 7435-7439. (e) Goering, H. L.; Pombo, M.
M.; McDaniel, K. D. J . Am. Chem. Soc. 1963, 85, 965-970. (f) Wilgis,
F. P.; Neumann, T. E.; Shiner, V. J ., J r. J . Am. Chem. Soc. 1990, 112,
4435-4446.
Added KO2CCF3 in CF3CO2H gives normal salt effects
on the rates of both 15 and 16, with increases of 3.4 and
4.3, respectively, for 0.592 M salt. These increases are,
however, much less than those observed for either
5d
secondary or tertiary substrates ArCH(OTs)CF3 and
ArC(OTs)(CH3)CF3;5c for example, in the latter case5d
0.586 M KO2CCF3 gives a rate acceleration of 27.1, which
is 8.0 times greater than the effect on 15. Similarly, for
the fluorenyl tosylate 7, a concentration of KO2CCF3 of
(9) McClelland, R. A.; Watada, B.; Lew, C. S. Q. J . Chem. Soc.,
Perkin Trans. 2 1993, 1723-1727.
(10) (a) Nordlander, J . E.; Owuor, P. O.; Haky, J . E. J . Am. Chem.
Soc. 1979, 101, 1288-1289. (b) Gassman, P. G.; Singleton, D. A.;
Kagechika, H. J . Am. Chem. Soc. 1991, 113, 6271-6272.

250 J . Org. Chem., Vol. 62, No. 2, 1997
Allen et al.
As described above, the kinetic analysis indicates that
the rate ratio k-2/k3 for internal return relative to solvent
capture for the ion pair 18 is 7.7, even in the highly
nucleophilic solvent CD3CO2D. This is rather larger than
values that have been obtained for other allylic systems,
for example, a value of 2.1 in 90/10 acetone/H2O found
using 18O equilibration.8a The value of 7.7 is remarkable
since this is a relatively unhindered substrate that should
be rather accessible for backside solvent attack. This
substrate has the advantage that the ratio of ion pair
return and solvent capture can be assessed from the
kinetic analysis.
Comparison of the rate of rearrangement in trifluoro-
ethanol of 1.61 × 10-5 s-1 for the tertiary CF3-substituted
indenyl tosylate 15 to the rate of trifluoroethanolysis of
2.1 × 10-2 s-1 estimated for the secondary indenyl
tosylate 216b,11a reveals that 15 is 1.3 × 103 less reactive,
showing a strong decelerating effect for the CF3 group.
The magnitude of this rate ratio kH/kCF3 is comparable
to those reported for some substrates ArCH(OTs)CF3.5f
A trifluoroethanolysis rate of 2.3 × 104 s-1 may be
estimated for the indanyl tosylate 22,6b,11b which implies
a retardation in rate by a factor of 1.1 × 106 for 21
relative to 22, and this was attributed6b to destabilization
of the cation 2 derived from 21 due to the potentially
antiaromatic 8π-electron cation system of the indenyl
moiety. Thus, there are major decelerating effects of both
the CF3 substituent and the antiaromatic effect of the
extra double bond in 15, resulting in a net deceleration
of more than 109 for 15 compared to 22.
the presence of electron-withdrawing fluoroalkyl and
sulfonate groups on the same carbon.
In contrast to 15 and 16, studies by Gassman and
Harrington8c of the solvolysis of acylic (trifluoromethyl)-
allylic triflates 23 and 24 showed that the R-(trifluorom-
ethyl) isomers 23 were 50-100 times less reactive than
the primary γ-(trifluoromethyl) isomers 24, and the
trifluoroethanolysis of 23 gave the E/ Z stereoisomeric
trifluoroethyl ethers of general structure 24, while tri-
flates 24 gave only the corresponding ethers. Evidently,
solvent displacement in the solvolysis is a major con-
tributor to the higher reactivity of 24. The solvolyses of
23 were interpreted as involving largely rate-limiting
ionization with solvent substitution at the γ-carbon of the
ion pair.
In summary, the doubly destabilized indenyl tosylate
15 shows a strong rate retardation by a factor of more
than 109 due to the combined effects of antiaromaticity
and the electron-withdrawing CF3 group. In contrast to
the relatively localized ion from fluorenyl tosylate 7, the
indenyl tosylate undergoes allylic delocalization permit-
ting nucleophilic solvation at the relatively unhindered
allylic carbon resulting in a much less marked depen-
dence of rate on solvent ionizing power compared to 7,
so that 15 is slightly more reactive than 7 in the rather
weakly ionizing HOAc solvent. The initial ion pair from
15 undergoes predominantly internal return to the
secondary allylic tosylate 16, even in the rather nucleo-
philic solvent CD3CO2D, or in the presence of 0.59 M
added salt in CF3CO2D, and the lower reactivity of 16
provides further evidence for the importance of geminal
ground-state destabilization in the reactivity of R-(trif-
luoromethyl) tosylates.
From the rates of solvolysis of the rearranged tosylate
16 in TFA and 97% HFIP a rate of reaction in TFE at 25
°C of 2 × 10-7 s-1 may be estimated, and comparison of
this rate to that for 2111c shows that the allylic CF3 group
decreases the reactivity of 16 by a factor of 105. This may
be contrasted to the effect of a γ-CH3 group in accelerat-
ing the solvolysis of indenyl dinitrobenzoate (4) by a
factor of 103 at 21 °C,6a so the γ-CH3 group is 108 more
effective than γ-CF3 in promoting the reactivity of these
indenyl substrates. The greater effect of a γ as compared
to a R-trifluoromethyl group in decreasing the reactivity
of the allylic tosylate is a strong argument for the
importance of geminal ground-state destabilization of
R-trifluoromethyl tosylates partially counterbalancing the
electronic destabilization of the carbocation and thus
Exp er im en ta l Section
Reagents for preparative experiments were obtained from
commercial suppliers and used as received unless noted.
Procedures and solvents for kinetics measurements have been
described previously.5
Ether and THF for use as reaction solvents were dried by
refluxing over Na/benzophenone and distilling. Glassware was
either dried in an oven at 150 °C and then cooled under N2 or
Ar, or flame dried under N2 or Ar before use.
2-Br om oin d a n on e (9).7a,b To indanone (6.0 g, 0.045 mol)
in 150 mL of CCl4 was added 5,5-dibromo-2,2-dimethyl-4,6-
dioxo-1,3-dioxane (dibromo Meldrum’s acid, DBMA) (14.5 g,
0.047 mol), and the solution was refluxed for 3.5 h. Analysis
of the mixture by 1H NMR revealed the presence of 6% starting
material, 78% 9, and 16% 2,2-dibromoindanone. The solution
was extracted with saturated NaHCO3 solution, and the
aqueous layer was extracted twice with ether. The combined
organic layers were dried over CaSO4, and the solvent was
evaporated to give a bluish viscous solution, which was purified
twice eluting on a column of silica gel with 3/2 CH2Cl2/hexane
and final purification by radial chromatography with the same
solvent to give 9 (3.71 g, 39%) as a pale yellow solid: mp 32-
giving kH/kCF rate ratios greater than would be expected
3
in the absence of this effect. We have previously argued
that such ground-state destabilization led to enhanced
kH/kCF rate ratios in 2-(trifluoromethyl)-2-adamantyl tos-
3
ylate5b and 2-(pentafluoroethyl)-exo-2-norbornyl brosylate.5a
Both of these substrates rearrange to less reactive sec-
ondary sulfonates in reactions suggested5a to be acceler-
ated by the ground-state destabilizing effect caused by
(11) (a) Multiplying the rate constant for 21-ODNB in TFE at 25
°C of 8.32 × 10-12 s-1 (extrapolated from data in ref 6b) by the
k(ROPNB)/k(ROTs) conversion factor of 2.5 × 109 (Lowry, T. H.;
Richardson, K. S. Mechanism and Theory in Organic Chemistry, 3rd
ed.; Harper and Row: New York, 1987; p 374) gives 2.08 × 10-2 s-1
for 21 in TFE at 25 °C. (b) Based on the rate constant of 9.4 × 10-6 s-1
for 22-ODNP in TFE at 25 °C extrapolated from data in ref 6b. (c)
Solvolysis rates are compared since the ionization rate of 21 has not
been determined.
1
34 °C; H NMR (CDCl3) δ 3.43 (dd, 1, J ) 3.2 Hz, 18.1 Hz),
3.85 (dd, 1, J ) 7.5, 18.1 Hz), 4.66 (dd, 1, J ) 3.2, 7.5 Hz),
7.4-7.9 (m, 4).
2-Br om oin d a n on e Eth ylen e Keta l (10).7a,b A solution of
9 (3.71 g, 0.0176 mol), ethylene glycol (17 mL, 0.305 mol), and
toluenesulfonic acid monohydrate (0.10 g, 0.53 mmol) in 200
mL of toluene was refluxed in a 500 mL round-bottomed flask

3-(Trifluoromethyl)indenyl Cation
J . Org. Chem., Vol. 62, No. 2, 1997 251
equipped with a Dean-Stark trap for 5 h. Workup of a small
sample showed 7% 9 remained, so additional toluenesulfonic
acid (0.022 g, 0.12 mmol) and ethylene glycol (10 mL, 0.18 mol)
were added and the solution was refluxed for an additional 8
h. The organic layer was washed with NaHCO3 and NaCl
solutions, dried over CaSO4, and evaporated to give crude 10
(3.9 g, ca. 87%), which contained 6% 9 by 1H NMR. The
identity of 10 was confirmed by H NMR (CDCl3) δ 3.26 (dd,
1, J ) 7.3, 16.1 Hz), 3.48 (dd, 1, J ) 7.3, 16.1 Hz), 4.2-4.4 (m,
4), 4.55 (t, 1, J ) 7.3 Hz), 7.1-7.5 (m, 4).
suspension of NaH (0.3 g, 6.3 mmol), previously washed with
pentane, in 8 mL of ether was added alcohol 14 (0.0252 g, 0.126
mmol) in 2 mL of ether. After the mixture was stirred for 1
h, TsCl (0.023 g, 0.121 mmol) in 2 mL ether was added, the
solution was stirred for 30 min, and the TLC showed no trace
of residual TsCl. Ice and H2O were added, the solution was
extracted three times with ether, and the combined ether
layers were washed with NaHCO3 and NaCl solution, dried
over CaSO4, and evaporated to give crude 15 (0.047 g, 0.13
mmol, ca. 100%), which after radial chromatography (10/90
EtOAc/hexanes) and recrystallization from pentane gave mp
72.5-73 °C: 1H NMR (CDCl3) δ 2.39 (s, 3, CH3), 6.31 (d, 1, J
) 5.8 Hz, CdCH), 6.94 (d, 1, J ) 5.8 Hz), 7.08-7.63 (m, 8,
1
2-In d en on e Eth ylen e Keta l (11).7a,b The crude ketal 10
(1.0 g, ca. 3.9 mmol) was added to freshly opened potassium
tert-butoxide (0.84 g, 7.5 mmol) in a flame-dried three-neck
round-bottomed flask. After an initial exothermic reaction,
the mixture was heated for 3 h at 90 °C, cooled, added to
aqueous NH4Cl solution, and extracted three times with ether.
The combined ether layers were washed with NaCl, dried, and
evaporated to give crude 11 (0.502 g, ca. 73%) as a brown oil:
1H NMR (CDCl3) δ 4.1-4.4 (m, 4), 6.14 (d, 1, J ) 5.8 Hz), 6.64
(d, 1, J ) 5.8 Hz), 7.02-7.35 (m, 4).
2
Ar); 13C NMR (CDCl3) δ 21.6, 90.6 (q, J CF ) 32.2 Hz), 122.4,
1
122.8 (q, J CF ) 283.4 Hz), 124.7, 127.2, 128.0, 128.8, 129.4,
130.8, 133.9, 136.3, 139.4, 142.6, 145.0; 19F NMR (CDCl3) δ
-77.5; EIMS m/ z 354 (M+, 20), 334 (M+ - HF, 6), 199 (M+
-
Ts, 100), 183 (M+ - TsO, 43), 164 (M+ - TsO, F, 46), 155 (Ts+,
61); HRMS m/ z calcd for C17H13F3O3S 354.0537, found 354.0523.
1-(Tr iflu or om eth yl)-3-in d en yl Tosyla te (16). A solution
of tosylate 15 (20.1 mg, 0.0568 mmol) in 3 mL of CF3CO2H
was left at 25 °C for 35 min and then poured into ice-water
and extracted twice with ether, and the ether layers were
washed with NaHCO3 and NaCl, dried over CaSO4, filtered,
and evaporated to give 14.1 mg of crude product that by 1H
contained 10% of trifluoroacetate 17a and 90% 16. Radial
chromatography (20/80 EtOAc/hexanes) gave 17a (Rf ) 0.56)
and 16 (Rf ) 0.35), which after recrystallization from pentane
2-In d en on e (12).7b The crude ketal 11 (0.474 g, 2.72 mmol)
was added with stirring to 1.5 g of silica gel (70-230 mesh),
4.5 mL of CHCl3, and 5 drops of 1 N HCl. After 30 min of
stirring, NaHCO3 (0.054g) was added, and after 5 min of
stirring the mixture was filtered through silica gel on a
sintered glass funnel to give a bright yellow solution. Analysis
1
by H NMR showed the presence of 30% residual 11 with the
product 12, and so the above procedure was repeated with 7
drops of 1 N HCl to give a solution shown to contain only 12
by 1H NMR:1H NMR (CDCl3) δ 5.89 (d, 1, J ) 5.9 Hz), 7.2-
7.5 (m, 4), 7.58 (d, 1, J ) 5.9 Hz): IR (CDCl3) 1736 (m), 1711
(s, CdO), and 1607 (m, CH)CH) cm-1. For the next step it
was essential to remove all CHCl3, and this was done by drying
the solution first with Drierite and then with 4A molecular
sieves, evaporating, and adding CCl4 followed by evaporation
again.
1
gave white needles: mp 92.5-93 °C; H NMR (CDCl3) δ 2.49
(s, 3, CH3), 5.88 (broad quintet, 1, J ) 1.5, 2.0 Hz), 6.63
(quintet, 1, J ) 1.9 Hz, CF3CdCH), 7.24-7.95 (m, 8); 13C NMR
(CDCl3) δ 21.7, 80.1, 121.3 (2), 121.4 (q, 1J CF ) 270.9 Hz), 125.1,
128.1, 130.0, 130.1, 133.1, 133.5 (q, 3J CF ) 5.1 Hz), 136.4, 137.9
2
(q, J CF ) 35.2 Hz), 139.9, 145.5; 19F NMR (CDCl3) δ -65.70
(t, J HF 1.9 Hz); EIMS m/ z 354 (M+, 9), 334 (M+ - HF, 13),
290 (M+ - SO2, 23), 199 (M+ - Ts, 46), 183 (M+ - OTs, 34),
164 (M+ - OTs - F, 100), 155 (Ts+, 65), 91 (C7H7+, 100); HRMS
m/ z calcd for C17H13F3O3S 354.0537, found 354.0541.
3-(Tr iflu or om et h yl)-3-[(t r im et h ylsilyl)oxy]-1-in d en e
(13). A solution of indenone 12 (0.123 g, 0.945 mmol) in 3
mL of THF was added to KF (0.011 g, 0.189 mmol) in 12 mL
of THF cooled to -78 °C in a 25 mL round-bottomed three-
neck flask, followed by the addition of CF3SiMe3 (0.30 mL, 2.0
mmol). Then, 10 drops of a saturated solution of t-BuOK in
THF was added with a syringe. After 10 min TLC (10/90
EtOAc/hexane on silica gel) showed 13 (Rf ) 0.6), and no
residual 12 (Rf ) 0.3). The solution was warmed to room
temperature, water was added, and the solution was extracted
three times with hexanes. The combined organic layers were
dried over CaSO4 and evaporated to give 13 (0.23 g, 0.84 mmol,
90%, at least 95% pure by 1H NMR), which was purified by
VPC (OV-17, 170 °C, tR 5 min): 1H NMR (CDCl3) δ -0.07 (s,
9), 6.28 (d, 1, J ) 5.8 Hz), 6.88 (d, 1, J ) 5.8 Hz), 7.2-7.6 (m,
1-(Tr iflu or om eth yl)-3-in d en yl Tr iflu or oa ceta te (17a ).
Reaction of tosylate 15 in CF3CO2H as above for 25 h gave
after workup a product containing alcohol 17c and 17a in a
1/4 ratio. On separation by radial chromatography 17a
decomposed to some extent, and only a small sample of slightly
impure material was obtained: 1H NMR (CDCl3) δ 6.38 (broad
3
quintet, 1), 6.80 (quintet, 1, J CF ) 1.9 Hz), 7.00-7.60 (m, 4);
19F NMR (CDCl3) δ -65.8, -74.9; IR (CDCl3) 1788 cm-1 (CdO);
EIMS m/ z 296 (M+, 43), 199 (M+ - COCF3, 100), 151 (M+
-
O2CCF3, 66), 69 (CF3+, 74); HRMS m/ z calcd for C12H6F6O2
296.0272, found 296.0259. 1-(Tr iflu or om eth yl)-3-in d en ol
(17c): 1H NMR (CDCl3) δ 1.71 (d, 1, J ) 10.0 Hz, OH), 5.31
2
4); 13C NMR (CDCl3) δ 1.4, 85.5 (q, J CF ) 31.0 Hz), 122.0,
2
(broad quintet, 1, J CF ) 11.5, 2 Hz, CHO), 6.84 (quintet, 1, J
1
) 1.8, 1.9 Hz, CdCH), 7.0-7.6 (m, 4, Ar); 13C NMR (CDCl3) δ
76.2, 121.0, 124.0, 127.6, 129.0, 138.6, 145.1 (3 C not visible);
IR (CDCl3) 3690 cm-1 (OH); EIMS m/ z 200 (M+, 77), 180 (M+
- HF, 31), 131 (M+ - CF3, 100), 103 (M+ - CF3CO, 41); HRMS
m/ z calcd for C10H7F3O 200.0449, found 200.0447.
124.4, 124.8 (q, J CF ) 284.1 Hz), 126.8, 129.9, 134.2, 136.6,
141.8, 142.6; 19F NMR (CDCl3) δ -79.4; EIMS m/ z 274 (M+,
34), 203 (M+ - CF3, 44), 180 (M+ - Me3SiF, 30), 161 (M+
-
Me3Si, F2, 48), 133 (M+ - Me3SiO, CF2, 100), 73 (Me3Si+, 56);
HRMS m/ z calcd for C13H15F3OSi 272.0844, found 272.0853.
3-(Tr iflu or om eth yl)-3-in d en ol (14). In a 10 mL flask was
stirred 13 (0.023 g, 0.09 mmol) overnight in 2 mL of THF and
3 mL 1 M HCl until TLC revealed no starting material
remained. The reaction mixture was added to H2O and
extracted three times with ether, the combined ether layer was
washed with H2O and saturated NaCl and dried over CaSO4,
and the solvent was evaporated. The product was purified by
radial chromatography with 20/80 EtOAc/hexane to give 14
(12 mg, 0.058 mmol, 66%), which after recystallization from
pentane gave mp 46.5-47 °C: 1H NMR (CDCl3) δ 2.53 (bs, 1,
OH), 6.29 (d, 1, J ) 5.7 Hz), 6.90 (d, 1, J ) 5.7 Hz); 13C NMR
Tr iflu or oa cetolysis of 15. A solution of 15 (4 mg, 0.011
mmol) and KO2CCF3 (83.7 mg, 0.550 mmol) in 1 mL of CF3-
1
CO2D was observed at intervals by H NMR (400 mHz) at 22
°C. The signals due to the vinyl protons of 15-17 were
integrated and used to calculate the relative amounts of 15-
17 present. A similar experiment was carried out in the
absence of salt. The amounts of 15-17 could also be evaluated
from the integration of the CH3 protons of the tosylate group,
and sample spectra are included in the Supporting Informa-
tion.
2
1
Acetolysis of 15. Kin etics. A solution of tosylate 15 (6.1
mg) in 650 µL of CD3CO2D in a sealed NMR tube was heated
at 99.6 °C, and 24 data points were measured for the change
(CDCl3) δ 84.0 (q, J CF ) 30.7 Hz), 122.3, 123.6, 124.8 (q, J CF
) 283.4 Hz), 127.2, 130.4, 133.1, 137.2, 140.9, 142.8; 19F NMR
(CDCl3) δ -78.5; IR (CDCl3) 3592 cm-1 (OH); EIMS m/ z 200
1
(M+, 67), 180 (M+ - HF, 31), 152 (35), 151 (29), 131 (M+
-
in the H NMR spectrum of the CH3 in the tosylate group 16
CF3, 100), 103 (M+ - CF3CO, 52), 77 (43); HRMS m/ z calcd
for C10H7F3O, 200.0449, found 200.0450. Anal. Calcd C, 59.99;
H, 3.53. Found C, 60.06; H, 3.61.
at δ 2.4 and of 15 plus TsOH (corresponding to 17), which were
both near δ 2.5. The rate constant for formation of the
rearranged tosylate 16 was 4.00 × 10-4 s-1, and this disap-
peared to form the acetate 16b-O2CCD3 with a rate constant
3-(Tr iflu or om eth yl)-3-in den yl Tosylate (15). To a cooled

252 J . Org. Chem., Vol. 62, No. 2, 1997
Allen et al.
of 3.09 × 10-5 s-1
.
Kinetic analysis as reported in the text
3-(Tr iflu or om eth yl)-3-in d en yl Tosyla te-su lfon yl-18O2.
The labeled tosylate was prepared from indenol 14 and 4-tosyl-
sulfonyl-18O2 chloride5d following the procedure for unlabeled
15.
using the programs ENZFITTER, distributed by Elsevier-
BIOSOFT, and Sigma Plot, from J andel Scientific, gave rate
ratios of the individual steps. P r od u cts. A solution of 15
(19.8 mg, 0.0559 mmol) in 2 mL of CH3CO2H was heated at
18O Exch a n ge. The reaction of 15 in TFA at 25 °C was
carried out for 9 min and quenched and worked up for 13C
NMR analysis in CDCl3 by the procedure utilized previously.5d
The tosylate-bonded carbon in residual 15 appeared at 90.6
ppm, with no detectable signal due to an isotope shift from
bonding to 18O, while the tosylate-bonded carbon in the
rearranged tosylate 16 showed a signal at 80.089 ppm due to
bonding to 16O and a signal at 80.058 ppm due to bonding to
18O in a ratio of 1.142:1.00, respectively.
1
100 °C for 26 h, and after workup the H NMR of the product
showed the presence of the rearranged acetate 17b and the
corresponding alcohol 17c in a 4/1 ratio. Radial chromatog-
raphy (1/9 EtOAc/hexanes) gave 3-(trifluoromethyl)-1-indenyl
1
acetate (17b): mp near 0 °C; H NMR (CDCl3) δ 2.18 (s, 3),
6.31 (br quintet, 1), 6.81 (quintet, 1, J ) 1.9 Hz), 7.25-7.54
(m, 4); 13C NMR (CDCl3) δ 20.9, 75.6, 121.1, 121.7 (q, J CF
)
1
3
270.3 Hz, CF3), 124.8, 127.7, 129.4, 134.6 (q, J CF ) 5.1 Hz,
2
CF3CC), 137.0, 137.2 (q, J CF ) 35.1 Hz, CCF3), 141.7, 170.9;
IR (CDCl3) 1739 cm-1 (CdO); 19F NMR (CDCl3) δ -65.58;
Ack n ow led gm en t. Financial support by the Natu-
ral Sciences and Engineering Research Council of
Canada and helpful discussions regarding the kinetic
analysis with Professors R. A. McClelland and O. S. Tee
are gratefully acknowledged.
EIMS m/ z 242 (M+, 13), 200 (M+ - CH2CO, 100), 183 (M+
-
AcO, 24), 131 (69); HRMS m/ z calcd for C12H9F3O2 242.0555,
found 242.0548.
Kin etic m ea su r em en ts were carried out by injecting 10
µL of a 0.028 M solution of 15 in CH3CN into 1.2 mL of solvent
in the UV cell and monitoring the change in the absorption at
310 nm. Solvolysis rate constants for the disappearance of
15 were derived by fitting the observed absorbance data to a
double exponential linear least-squares fit and correspond to
the initial rate process observed. Rates for the reaction of 16
were obtained beginning with pure 16 and gave reasonable
agreement with those obtained for the second process observed
beginning with 15.
1
Su p p or tin g In for m a tion Ava ila ble: Copies of H NMR
spectra and Tables 2 and 3, kinetic derivation (11 pages). This
material is contained in libraries on microfiche, immediately
follows this article in the microfilm version of the journal, and
can be ordered from the ACS; see any current masthead page
for ordering information.
J O961387K