2528 J . Org. Chem., Vol. 63, No. 8, 1998
Aranyos and Szabo´
on the heavy atoms (LANL2DZ+P)29 leading to a theo-
retical model, which is denoted as B3PW91/LANL2DZ+P/
/B3PW91/LANL2DZ. All calculations were performed on
a Digital Alphastation 500 using Gaussian94 software
package.30
Exp er im en ta l Section
NMR spectra were recorded for CDCl3 solutions (1H at 400
MHz and 13C at 100.5 MHz) using chloroform-d (7.26 ppm,
1H, 77.0 ppm, 13C) as internal standard. Coupling constants
were evaluated using J -doubling31 technique. Mass spectra
were obtained in GC/MS mode (EI, 70 eV). Dichloromethane
was distilled over CaH2. Other solvents were used without
further purification. Pd(OAc)2 was purchased from Fluoro-
chem. All other chemicals were bought from Lancaster or
Aldrich and were used without further purification. Merck
silica gel 60 (240-400 mesh) was used for flash chromatog-
raphy.
F igu r e 2. Calculated relative B3PW91/LAN2DZ+P//B3PW91/
LAN2DZ energies of complexes 11b-13b as a function of
C4-O bond distances.
in two additional points of the potential energy surface.
Freezing the C4-O distance at 1.8 Å led to a sharp
decrease of total energies (Figure 2). When the C4-O
bond was constrained at 2.0 Å, which would be expected
for the transition state of a C-O bond cleavage, a further
decrease of the total energy occurred for all three
complexes. The energy decrease was considerably greater
for the trifluoroacetoxy substituted complex (17.8 kcal/
mol) than the acetoxy (11.7 kcal/mol) or methoxy (5.8
kcal/mol) substituted ones.
The results clearly show the expected trend, namely
that the reactivity order of these groups in the acid-
catalyzed C4-O bond cleavage is the following: CF3COO-
> AcO- > MeO-.21 This means that in any combination
of these nucleophiles, the more reactive22 will form a
kinetically less stable 4-substituted [η3-(1,2,3)-allyl]pal-
ladium intermediate, and under sufficiently acidic reac-
tion conditions, unsymmetrical functionalization is pos-
sible.
tr a n s-1-Acetoxy-4-(tr iflu or oacetoxy)-2-cycloh exen e (2).
Pd(OAc)2 (16.8 mg, 0.075 mmol), lithium trifluoroacetate (180
mg, 1.5 mmol), CF3COOH (230 µL, 3 mmol), (CF3CO)2O (320
µL, 2.25 mmol), MnO2 (157 mg 1.65 mmol), and p-benzo-
quinone (24 mg, 0.225 mmol) were dissolved in a mixture of 5
mL of CH2Cl2 and 2 mL of acetic acid. To this stirred solution
freshly distilled 1,3-cyclohexadiene (147 µL, 1.5 mmol) was
added via a syringe pump during 6-8 h. The reaction mixture
was stirred for another 8 h at room temperature and then
diluted with 50 mL pentane/ether (50/50). The resulting
mixture was extracted with water (2 × 15 mL), brine (2 × 15
mL), saturated aqueous Na2CO3 (3 × 15 mL), and brine. The
organic phase was dried over MgSO4 and concentrated in
vacuo. Rapid flash chromatography using an 85:15 mixture
of pentane and ether as eluent gave 0.278 g (74%) of compound
2 as a colorless oil (93% trans). 1H NMR: δ 6.05 (ddd, 1H, J
) 10.0, 3.4, 1.5 Hz), 5.94 (ddd, 1H, J ) 10.0, 3.7, 1.4 Hz), 5.52-
5.47 (m, 1H), 5.36-5.30 (m, 1H), 2.27-2.11 (m, 2H), 2.06 (s,
3H), 1.92-1.82 (m, 1H), 1.82-1.72 (m, 1H); 13C NMR: δ 170.3,
2
1
157.1 (q J C-F ) 41.9 Hz), 132.5, 127.5, 114.4 (q J C-F ) 286.1
Hz), 72.0, 66.6, 25.1, 25.0, 21.1; IR (in CDCl3 solution): 3048,
2963, 2942, 1779, 1729, 1373, 1225, 1157, 1032, 1010 cm-1
;
Con clu d in g Rem a r k s
MS m/z (%): 252 (M+, <1), 219 (<1), 209 (1) 192 (1), 139 (6),
96 (100), 79 (63), 69 (30). Anal. Calcd: C, 47.62; H 4.39.
Found: C, 47.52; H, 4.32.
In the above study we have described a new method
for preparation of some unsymmetrically substituted
cycloalkenes. These products can be further functional-
ized selectively by for example Pd(0)-catalyzed allylic
substitutions.23 A mechanism for the alkoxy- and ac-
etoxy-trifluoroacetoxylations has been suggested, which
is supported by theoretical calculations performed on the
proposed allylpalladium intermediates.
Com p u ta tion a l Deta ils. The geometries were opti-
mized employing Density Functional Theory using a
Becke24 type three-parameter model B3PW9125-27 in
connection with the LANL2DZ basis set28 (denoted as
B3PW91/LANL2DZ). For single-point energy calcula-
tions of the protonated species the LANL2DZ basis set
was augmented with one set of d polarization functions
cis-1-Acet oxy-4-(t r iflu or oa cet oxy)-2-cycloh exen e (3).
Pd(OAc)2 (16.8 mg, 0.075 mmol), CF3COOLi (900 mg, 7.5
mmol), CF3COOH (230 µL, 3 mmol), MnO2 (157 mg, 1.65
mmol), p-benzoquinone (35 mg, 0.33 mmol), (CF3CO)2O (420
µL, 3 mmol), and acetonitrile (160 µL, 3 mmol) were dissolved
in 5 mL of acetone/acetic acid (1:1). To this stirred solution
was added 1,3-cyclohexadiene (147 µL, 1.5 mmol) via a syringe
pump during 10 h. The reaction mixture was stirred for
additional 12 h at room temperature, and then it was diluted
with 50 mL of ether/pentane (50:50). The resulting mixture
was worked up the same way as in the case of compound 2,
giving 0.148 g (40%) of colorless oil 2 (83% cis). 1H NMR: δ
6.03 (dm, 1H, J ) 10.1 Hz), 5.93 (dm, 1H, J ) 10.1 Hz), 5.47-
5.37 (m, 1H), 5.29-5.23 (m, 1H), 2.08 (s, 3H), 2.05-1.84 (m,
2
4H). 13C NMR: δ 170.5, 157.1 (q J C-F ) 42.7 Hz), 133.0,
1
127.1, 114.5 (q J C-F ) 285.8 Hz), 71.7, 67.0, 24.5, 24.3, 21.1;
(20) The relationship between the geometrical parameters and the
intensity of the â-substituent effects is discussed in ref 12.
(21) Even if the solvation effects raise an activation barrier to the
C4-O bond cleavage, the intrinsic stabilization by the 4-substituent
effect will lower most effectively the activation energy in case of the
trifluoracetoxy substituted complex 12b.
IR (in CDCl3 solution): 2962, 1780, 1727, 1374, 126, 1161, 1036
cm-1; MS m/z (%): 192 (M+ - 60, 1), 139 (12), 96 (100), 79
(56), 69 (34).
(29) (a) Huzinaga, S.; Andzelm, J .; Klobukowski, M.; Radzio-
Andzelm, E.; Sakai, Y.; Tatewaki, H. Gaussian Basis Sets for Molecular
Calculations; Elsevier: Amsterdam, 1984. (b) Exponents for the d
functions: C, 0.630; O, 1.154; F, 1.496; Pd (diffuse d function), 0.0628.
(30) Gaussian 94, Revision B.3; Frisch, M. J .; Trucks, G. W.;
Schlegel, H. B.; Gill, P. M. W.; J ohnson, B. G.; Robb, M. A.; Cheeseman,
J . R.; Keith, T.; Petersson, G. A.; Montgomery, J . A.; Raghavachari,
K.; Al-Laham, M. A.; Zakrzewski, V. G.; Ortiz, J . V.; Foresman, J . B.;
Peng, C. Y.; Ayala, P. Y.; Chen, W.; Wong, M. W.; Andres, J . L.;
Replogle, E. S.; Gomperts, R.; Martin, R. L.; Fox, D. J .; Binkley, J . S.;
Defrees, D. J .; Baker, J .; Stewart, J . P.; Head-Gordon, M.; Gonzalez,
C.; Pople, J . A.; Gaussian, Inc., Pittsburgh, PA, 1995.
(22) In the sense of the cleavage reaction.
(23) The allylic trifluoroacetate is a highly reactive group in Pd(0)-
catalyzed allylic substitutions: (a) Tsuji, Y.; Funato, M.; Ozawa, M.;
Ogiyama, H.; Kajita, S.; Kawamura, T. J . Org. Chem. 1996, 61, 5779.
Rajanbabu, T. V. J . Org. Chem. 1985, 50, 3642. (c) Ba¨ckvall, J . E.;
Granberg, K. L.; Heumann, A. Israel. J . Chem. 1991, 31, 17.
(24) Becke, A. D. J . Chem. Phys. 1993, 98, 5648.
(25) Kohn, W.; Sham, L. J . Phys. Rev. 1965, 140, 1133.
(26) Becke, A. D. Phys. Rev. A 1988, 38, 3098.
(27) Perdew, J . P.; Wang, Y. Phys. Rev. B 1992, 45, 13244.
(28) (a) Dunning, T. H.; Hay, P. J . Modern Theoretical Chemistry;
Plenum: New York, 1977. (b) Hay, P. J .; Wadt, W. R. J . Chem. Phys.
1985, 82, 270. (c) Hay, P. J .; Wadt, W. R. Ibid. 1985, 82, 299.
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