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Spatial orientation effects on the σ-assistance in the solvolysis of methyl substituted 1-norbornyl triflates
Tam&&km &ttew, Vol. 35, No. 3% pp. 7285-7288, 1994
Elsevier Science Ltd
Pefgamon
printed in Great Britain o@40-4039/94 $7.oo+o.00
Spatial Orientation A, Gada
Effects an the a-Mi l-Norbornyl
Mart&z,” J. O&o Barcina,
in the Solvoiysis of Methyl Substituted Triflates
M. E. Rocirlrguez Herrero,
M, Iglesii
de Dies
de Quimics Or@nico, Facultad de Ciencirs Qufmicas, Uuiversidad Complutease, tiudad Universitmia, 28040 Madrid, Spain
-to
E. Teso Viir Deputpmtnto
de QufmicaGrgktica y Biologfn, Facultad de Ciencias, UNED, Ciudad Universitatia, 28040
Madrid,
Spain
L. R. Subramaalaa Instk@ fiir OtgtiecIte
Chemie, UiversitSt
TtWigen, Auf der MorgensteIIe IS, D-72076, Geimaey
Abstmei.- The u-pa&ip&ion of tbe CpC, sod C,-C, bonds in tbe soivolysis of methyl suhtittged 1-norbomyI triflatesis wahated by application of the additivity principle. It is concluded that the u-participation of the G-C, bond is dependent on the splltiat orientation of methyl substitumts.
We have shown that the solvolysis of 2,2,3-, 2,3,3-and 4,7,7-trimethyl in 60% aqueous ethanol at 80 “C proceeds with u-~ci~tion
of C-&
substituted I-norbomyi
triflate
and G&Z, bonds, respectively. u In
order to achieve an estimation of the magnitude of the a-assistance in the solvolysis of 1-norbomyf
triflate,
we report here on the application of the additivity principle (APy’ to this subject. For this purpose we have prepared4 txo- and e~~2-me~yl-I-no~myl dime~yl-l-no~myl
t&late (3 and 4), 2,2-d~methyl-1-no~rnyl~~a~
(5) and 3,3-
triflate (6). The rate constants k of the solvolysis in 60% aqueous ethanol are given in
Table 1. The solvolysis of 3, 4 and 6, lie bridgehead alcohols (-60%) mixture of unrearranged
the solvolysis of 1, 2 and 7, yield only the corresponding
and ethers { -40%).
11 + 12 and ~ng~n~c~
However, the solvolysis of 5, like 8, 9 and 10, affords a products 13 + 14 (Scheme).’ The product ratios were
determinated by GC (OV-101,25m, 150 “C). All compounds were characterized by MS, IR, ‘H- and 13C-NMR spectral analyses.
Scheme 7285
7286
Table 1. Rate Constants of Solvolysis of I-Norbomyi Triflates in Buffered (E&N) 60% Aqueous Ethanol. -----_-___
____I-_________________--____________________*_________________________-___“____
Trifkite
Temp . PC)
&i*‘)”
AH*(Kcal/mol)
AS#(eu)
A~(K~/mol)
k,(at SO.YC)
Ref.b
__-_-____-__1______--__“_“_____________________“__-____-_----*_-______-___________________-__________”
1
80.3
1.08~10-~
26.8”
-2.5”
1.3
I.0
2
2
80.3
4*04x10-5
28.9
2.4
1.3
3.7
2
3
100.5 90.4 80.3
1.97x1O-4 6.21x10-5 2.07~18~
28.4
2.3
1.5
1.9
tw
100.5 90.4 80.3
3.2Oxlrr*o 1.08~10‘~ 3.43x10-5
28.2
2.7
0.5
3.2
tw
80.3 70.0 59.0 50.0
1.65x1@‘* 5.30x10-4 1.45x10-4 4.97X10”5
26. I
2.2
0.1
153.1
tw
6
90.4 80.3 70.0
7.41x10-4 3.10x10”’ 7.oox1O-5
28.7
5.5
1.7
28.7
tW
7
80.3
1.59x1o-s
28.9
-0.8
2.2
I.5
2
8
80.3
22.9
-6.3
1.4
149.0
1
9
80.3
9 . 63~10~~
23.3
-6.4
0.2
89
1
IO
80.3
3.57x10-4
26.3
1.4
2.1
33.0
2
4
s
_v--
.
---mm-
D6z&rmbed by GC (ex~tat
_____~_“___1_“~__^______~~~_~~_11_1______”~”””~~~____“_____~-~_____~“____~_“~~*_~~~~~~-_”
error 55%). btw- This work. %I 50% aquso~~&anoL
dEx@apoki&ed f&n other tempewtu~
‘7287
The AP asserts that the molar values of a property are additive functions of independent assignable
to part-structures
of the molecule.
contributions
The AP is based on the tendency of such quantities as the
standard free energy to be additive functions of molecular st~eture.~ The application of the AP to the solvolysis of 5, 8-18 leads to equation [ 11: In(k,l&J=~~ lnL-,‘ &I where k, represents the caiculated solvolysis rate for a substrate with II methyl groups (n= 2 or 3), kti is the relative solvolysis rate (k, in Table 1) of related substrates with i methyl groups (i= 1 or 2). The calculated k, and the basis substrates are shown in Table 2.
Table 2. Calculated
Solvolysis pates (k,J at 80.3 “C
_~~-~___~~____________~___~_~_____~~~~~__~___~_________~____~___________~~_~_________~______~””~~_____~____
Triflate II Substrates for k, k/k,,” AAG*(&O,lS Kcallmol)b k& ‘)a __~___-_____~__________~_________________________-_“_________~~~~~~~~~~~~~~~~~~_~~~~~~-____~~~~________~______~____~~ S
2
6.57x 105
3-t-4
25.10
-2.26
8
3
5.89x1O-5
3+6
2.73
-0.70
9
3
9.92x10-4
4-i-6
0.97
t-o.02
10
3
5.59x1o-5
2+7
6.39
-1.30
lExpeaimmtal error The
&
lo-15%. bA&G’
= RThk,Jk
AP is only fulfilled in the case of the solvolysis of 9, because the calculated solvolysis rate S,
agrees with the observed k. The observed rate constants of all the other triflates are higher than the calculated pointing to the existence of an accelerating term3 (AAG%Table AE,” Orable 1) excludes any significative term. Thus, the interaction C&s
contribution
2). The lack of relationship between Ink and
of steric effects (F- and B-strain) to the interaction
terms observed in the cases of S, 8 and 10 are due to enhanced o-assitance of the
and C,-C, bonds, respectively.‘*’ The solvolysis of these substrates takes place with formation of
u-bridged carbocations as intermediates, ’ *’ which are stabilized in relation to the corresponding c1assica.t cations for at least the term AA.G# (Table 2)’ Indeed, the total u-participationof a bond, CT,is given by c’+: AAGf + CC+ where Oi is the u-participation in the basis $ubsUates. The Cq fan reach the necessary threshold to provoke a rearrangement. This seems to be the ease for 9,’ The different interaction terms observed in the cases of 8 and 9 show that the u-assistance of the C;-C, bond is dependent not only on the number and position of the methyl groups, but also on their configuration. The very different solvotysis rates of endo- and era-2,2,3+rimethyl- 1-norbomyl triflates I (k, = 3805 and 589, respectively) can also be attributed to a spatial effect on the u-assistance. until now unknownS effect is under progress.
Further work on the nature of this
7288
Acknowkdgment We thank the DGICYT (Spain) for finantial support of this work (Grants PB91-0354 and PB90-0070). References and Notes
I.
Garcia Martfnez, A.; Teso Vilar, J.; Oslo Barcina, J.; Hanack, M. ; Subramanian,
L. R. Tetrahedron
Lett. 1989, 30, 1503. 2.
Garcia Martfnez,
A.; Oslo Barcina, I.; Rodrfguez Herrero,
E.; Subramanian,
L. R. Terrahedron Lett. 1994,3S, 1793. In this reference an extrapolated
the rate of 7 (2.20~10~
M. E.’: Iglesias de Dios, M.; Teso Vilar,
5.‘) instead of the correct experimental
value (1.59x1Bs
vaiue for
s-‘)was given
erroneously. 3.
For a very good discussion
of the AP, see: Leffer, J. E.; Grundwald,
E. Rates and Equilibria of
Organic Reactions; Wiley, New York, 1963. 4.
The triflates 3 and 4 were prepared by catalytic reduction of 2-methylidene-1-norbomyl 5 and 6 from 2,2-dimethyl-3-oxo-I-norbomyl respectively.
‘%-NMR
triflate, and
triflate and 2-oxo-3,3-dimethyl-4-norbomyl
(75 MHz, CDCI,, TMS): 3: 6= 118.90 (q, CF,);
triflate,
103.62 (C,); 39.02 (C,);
38.05 (Cd; 37.15 (C,); 33.06 (C,); 31.43 (Cd; 29.17 (C,); 18.05 (CH,) ppm. 4: 6= 118.00 (q, CF,); 103.89 (C,); 41.93 (C,); 37.37 (C,); 37.30 (C,); 32.61 (C,); 29.05 (C,); 25.86 (C,); 13.80 (CH3) ppm.
5: 6= 118.07 (q, CF,); 105.81 (C,); 45.87 (C,); 39.13 (Q;
(Cd; 28.19 (C,); 27.13 (exe-CH,);
23.66 (err&-CH,)
39.07 (C,); 31.84 (C,); 28.44
ppm. 6: 6= 118.90 (CFJ;
100.50 (C,); 49.90
(Cd; 42.93 (C,); 41.53 (C,); 37.98 (C,); 31.71 (Cd; 30.90 (exe-CH,); 26.96 (C,); 25.08 (endo-CH,) ppm. 5.
Examples of i3C-NMR:
13C-NMR (75 MHz, CDCI,, TMS): 11: 6= 85.66 (C,); 46.96 (C,); 42.01
(C,); 33.22 (Cd; 30.62 (Cd; 29.70 (C,); 29.61 (C,); 27.07 (exe-CH,); 12: 6= 90.01 (C,); 60.82 (-0-CH,-); 27.84 (C,); 25.68 (exe-CH,);
23.94 (en&-CH,)
48.27 (C,); 39.33 (C,); 31.35 (Ccl); 29.8i
25.57 (-0-CH&H3);
16.37 (endo-CH,)
ppm.
(C,); 29.44 (C,);
ppm. 13: 6= 71.16 (-C-OH);
60.00 (C,); 37.81 (C,, C,& 34.92 (C,); 28.79 (C,); 27.22 (Cd); 25.75 (CH,) ppm. 14: b= 74.54 (-c-OEt); (CH,); 6.
7.
59.49 (C,); 57.56 (-0-cH,-); 16.46 (-O-CH&Hs)
AE,, is the difference
ppm.
between the steric energies of the carbocation
and the corresponding
triflate
calculated with the MMX program.
Eksterowicz, J. E.; Houk, K. N. Chem. Rev. 1993, .93, 2439.
For comparison,
in the 2-norbomyl
Schleyer, 8.
39.50 (C,, Cd; 35.38 (C,); 28.43, 26.65 (C,, Cd; 22.49
the u participation
cation amounts to ca. 5 Kcal/mol:
Sieber, S.;
P. v. R. Angew. Chem. 1993, 105, 1673.
For related effects, see: Lenoir, D.; Apeloig, Y.; Arad, D.; Schleyer, P. v. R. J. Org. Chem. 1988, 53, 661.
(Received in UK 25 July 1994: accepted 4 August 1994)
Elsevier Science Ltd
Pefgamon
printed in Great Britain o@40-4039/94 $7.oo+o.00
Spatial Orientation A, Gada
Effects an the a-Mi l-Norbornyl
Mart&z,” J. O&o Barcina,
in the Solvoiysis of Methyl Substituted Triflates
M. E. Rocirlrguez Herrero,
M, Iglesii
de Dies
de Quimics Or@nico, Facultad de Ciencirs Qufmicas, Uuiversidad Complutease, tiudad Universitmia, 28040 Madrid, Spain
-to
E. Teso Viir Deputpmtnto
de QufmicaGrgktica y Biologfn, Facultad de Ciencias, UNED, Ciudad Universitatia, 28040
Madrid,
Spain
L. R. Subramaalaa Instk@ fiir OtgtiecIte
Chemie, UiversitSt
TtWigen, Auf der MorgensteIIe IS, D-72076, Geimaey
Abstmei.- The u-pa&ip&ion of tbe CpC, sod C,-C, bonds in tbe soivolysis of methyl suhtittged 1-norbomyI triflatesis wahated by application of the additivity principle. It is concluded that the u-participation of the G-C, bond is dependent on the splltiat orientation of methyl substitumts.
We have shown that the solvolysis of 2,2,3-, 2,3,3-and 4,7,7-trimethyl in 60% aqueous ethanol at 80 “C proceeds with u-~ci~tion
of C-&
substituted I-norbomyi
triflate
and G&Z, bonds, respectively. u In
order to achieve an estimation of the magnitude of the a-assistance in the solvolysis of 1-norbomyf
triflate,
we report here on the application of the additivity principle (APy’ to this subject. For this purpose we have prepared4 txo- and e~~2-me~yl-I-no~myl dime~yl-l-no~myl
t&late (3 and 4), 2,2-d~methyl-1-no~rnyl~~a~
(5) and 3,3-
triflate (6). The rate constants k of the solvolysis in 60% aqueous ethanol are given in
Table 1. The solvolysis of 3, 4 and 6, lie bridgehead alcohols (-60%) mixture of unrearranged
the solvolysis of 1, 2 and 7, yield only the corresponding
and ethers { -40%).
11 + 12 and ~ng~n~c~
However, the solvolysis of 5, like 8, 9 and 10, affords a products 13 + 14 (Scheme).’ The product ratios were
determinated by GC (OV-101,25m, 150 “C). All compounds were characterized by MS, IR, ‘H- and 13C-NMR spectral analyses.
Scheme 7285
7286
Table 1. Rate Constants of Solvolysis of I-Norbomyi Triflates in Buffered (E&N) 60% Aqueous Ethanol. -----_-___
____I-_________________--____________________*_________________________-___“____
Trifkite
Temp . PC)
&i*‘)”
AH*(Kcal/mol)
AS#(eu)
A~(K~/mol)
k,(at SO.YC)
Ref.b
__-_-____-__1______--__“_“_____________________“__-____-_----*_-______-___________________-__________”
1
80.3
1.08~10-~
26.8”
-2.5”
1.3
I.0
2
2
80.3
4*04x10-5
28.9
2.4
1.3
3.7
2
3
100.5 90.4 80.3
1.97x1O-4 6.21x10-5 2.07~18~
28.4
2.3
1.5
1.9
tw
100.5 90.4 80.3
3.2Oxlrr*o 1.08~10‘~ 3.43x10-5
28.2
2.7
0.5
3.2
tw
80.3 70.0 59.0 50.0
1.65x1@‘* 5.30x10-4 1.45x10-4 4.97X10”5
26. I
2.2
0.1
153.1
tw
6
90.4 80.3 70.0
7.41x10-4 3.10x10”’ 7.oox1O-5
28.7
5.5
1.7
28.7
tW
7
80.3
1.59x1o-s
28.9
-0.8
2.2
I.5
2
8
80.3
22.9
-6.3
1.4
149.0
1
9
80.3
9 . 63~10~~
23.3
-6.4
0.2
89
1
IO
80.3
3.57x10-4
26.3
1.4
2.1
33.0
2
4
s
_v--
.
---mm-
D6z&rmbed by GC (ex~tat
_____~_“___1_“~__^______~~~_~~_11_1______”~”””~~~____“_____~-~_____~“____~_“~~*_~~~~~~-_”
error 55%). btw- This work. %I 50% aquso~~&anoL
dEx@apoki&ed f&n other tempewtu~
‘7287
The AP asserts that the molar values of a property are additive functions of independent assignable
to part-structures
of the molecule.
contributions
The AP is based on the tendency of such quantities as the
standard free energy to be additive functions of molecular st~eture.~ The application of the AP to the solvolysis of 5, 8-18 leads to equation [ 11: In(k,l&J=~~ lnL-,‘ &I where k, represents the caiculated solvolysis rate for a substrate with II methyl groups (n= 2 or 3), kti is the relative solvolysis rate (k, in Table 1) of related substrates with i methyl groups (i= 1 or 2). The calculated k, and the basis substrates are shown in Table 2.
Table 2. Calculated
Solvolysis pates (k,J at 80.3 “C
_~~-~___~~____________~___~_~_____~~~~~__~___~_________~____~___________~~_~_________~______~””~~_____~____
Triflate II Substrates for k, k/k,,” AAG*(&O,lS Kcallmol)b k& ‘)a __~___-_____~__________~_________________________-_“_________~~~~~~~~~~~~~~~~~~_~~~~~~-____~~~~________~______~____~~ S
2
6.57x 105
3-t-4
25.10
-2.26
8
3
5.89x1O-5
3+6
2.73
-0.70
9
3
9.92x10-4
4-i-6
0.97
t-o.02
10
3
5.59x1o-5
2+7
6.39
-1.30
lExpeaimmtal error The
&
lo-15%. bA&G’
= RThk,Jk
AP is only fulfilled in the case of the solvolysis of 9, because the calculated solvolysis rate S,
agrees with the observed k. The observed rate constants of all the other triflates are higher than the calculated pointing to the existence of an accelerating term3 (AAG%Table AE,” Orable 1) excludes any significative term. Thus, the interaction C&s
contribution
2). The lack of relationship between Ink and
of steric effects (F- and B-strain) to the interaction
terms observed in the cases of S, 8 and 10 are due to enhanced o-assitance of the
and C,-C, bonds, respectively.‘*’ The solvolysis of these substrates takes place with formation of
u-bridged carbocations as intermediates, ’ *’ which are stabilized in relation to the corresponding c1assica.t cations for at least the term AA.G# (Table 2)’ Indeed, the total u-participationof a bond, CT,is given by c’+: AAGf + CC+ where Oi is the u-participation in the basis $ubsUates. The Cq fan reach the necessary threshold to provoke a rearrangement. This seems to be the ease for 9,’ The different interaction terms observed in the cases of 8 and 9 show that the u-assistance of the C;-C, bond is dependent not only on the number and position of the methyl groups, but also on their configuration. The very different solvotysis rates of endo- and era-2,2,3+rimethyl- 1-norbomyl triflates I (k, = 3805 and 589, respectively) can also be attributed to a spatial effect on the u-assistance. until now unknownS effect is under progress.
Further work on the nature of this
7288
Acknowkdgment We thank the DGICYT (Spain) for finantial support of this work (Grants PB91-0354 and PB90-0070). References and Notes
I.
Garcia Martfnez, A.; Teso Vilar, J.; Oslo Barcina, J.; Hanack, M. ; Subramanian,
L. R. Tetrahedron
Lett. 1989, 30, 1503. 2.
Garcia Martfnez,
A.; Oslo Barcina, I.; Rodrfguez Herrero,
E.; Subramanian,
L. R. Terrahedron Lett. 1994,3S, 1793. In this reference an extrapolated
the rate of 7 (2.20~10~
M. E.’: Iglesias de Dios, M.; Teso Vilar,
5.‘) instead of the correct experimental
value (1.59x1Bs
vaiue for
s-‘)was given
erroneously. 3.
For a very good discussion
of the AP, see: Leffer, J. E.; Grundwald,
E. Rates and Equilibria of
Organic Reactions; Wiley, New York, 1963. 4.
The triflates 3 and 4 were prepared by catalytic reduction of 2-methylidene-1-norbomyl 5 and 6 from 2,2-dimethyl-3-oxo-I-norbomyl respectively.
‘%-NMR
triflate, and
triflate and 2-oxo-3,3-dimethyl-4-norbomyl
(75 MHz, CDCI,, TMS): 3: 6= 118.90 (q, CF,);
triflate,
103.62 (C,); 39.02 (C,);
38.05 (Cd; 37.15 (C,); 33.06 (C,); 31.43 (Cd; 29.17 (C,); 18.05 (CH,) ppm. 4: 6= 118.00 (q, CF,); 103.89 (C,); 41.93 (C,); 37.37 (C,); 37.30 (C,); 32.61 (C,); 29.05 (C,); 25.86 (C,); 13.80 (CH3) ppm.
5: 6= 118.07 (q, CF,); 105.81 (C,); 45.87 (C,); 39.13 (Q;
(Cd; 28.19 (C,); 27.13 (exe-CH,);
23.66 (err&-CH,)
39.07 (C,); 31.84 (C,); 28.44
ppm. 6: 6= 118.90 (CFJ;
100.50 (C,); 49.90
(Cd; 42.93 (C,); 41.53 (C,); 37.98 (C,); 31.71 (Cd; 30.90 (exe-CH,); 26.96 (C,); 25.08 (endo-CH,) ppm. 5.
Examples of i3C-NMR:
13C-NMR (75 MHz, CDCI,, TMS): 11: 6= 85.66 (C,); 46.96 (C,); 42.01
(C,); 33.22 (Cd; 30.62 (Cd; 29.70 (C,); 29.61 (C,); 27.07 (exe-CH,); 12: 6= 90.01 (C,); 60.82 (-0-CH,-); 27.84 (C,); 25.68 (exe-CH,);
23.94 (en&-CH,)
48.27 (C,); 39.33 (C,); 31.35 (Ccl); 29.8i
25.57 (-0-CH&H3);
16.37 (endo-CH,)
ppm.
(C,); 29.44 (C,);
ppm. 13: 6= 71.16 (-C-OH);
60.00 (C,); 37.81 (C,, C,& 34.92 (C,); 28.79 (C,); 27.22 (Cd); 25.75 (CH,) ppm. 14: b= 74.54 (-c-OEt); (CH,); 6.
7.
59.49 (C,); 57.56 (-0-cH,-); 16.46 (-O-CH&Hs)
AE,, is the difference
ppm.
between the steric energies of the carbocation
and the corresponding
triflate
calculated with the MMX program.
Eksterowicz, J. E.; Houk, K. N. Chem. Rev. 1993, .93, 2439.
For comparison,
in the 2-norbomyl
Schleyer, 8.
39.50 (C,, Cd; 35.38 (C,); 28.43, 26.65 (C,, Cd; 22.49
the u participation
cation amounts to ca. 5 Kcal/mol:
Sieber, S.;
P. v. R. Angew. Chem. 1993, 105, 1673.
For related effects, see: Lenoir, D.; Apeloig, Y.; Arad, D.; Schleyer, P. v. R. J. Org. Chem. 1988, 53, 661.
(Received in UK 25 July 1994: accepted 4 August 1994)