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Triazolinedione additions to alkenes in protic solvents. A remarkable temperature dependence of the competing reaction paths.
00404039191 $3.00 + 00 PergamonPressplc
TetrahedronLetters,Vo1.32,No.23. pp 2667-2670.1991 Printedin GreatBritain
Triazolinedione Additions to Alkenes in Protic Solvents. A Remarkable Temperature Dependence of the Competing Reaction Paths. Yiannis Elemesf- and Michael OrfanopouloP Departmentof Chemistry,Universityof Crete,71110I&lion, Crete, Greece
Key Words:Triaz~linedione;methen
tipping; emreaction; airidinium hi& &xmedia~,
activation parameters.
Abstract: lhe reactivity of the ene and MeOH-adduct reactions from N-Phenyl-1,2,4-triazoline-3,Sdione tetramethylethylene
with
(TME) shows a remarkable temperature dependence. These results are consonant with the
formation of a common intermediate between the two competing reaction paths.
In the course of our investigation of the mechanism of N-phenyl-triazolinedione
(PTAD) additions to
alkenes2, we have obtained results that show a remarkable temperature dependence of the ratio of ene over methanol adducts. PTAD, one of the most reactive enophiles, adds to olefins in aprotic solvents to give the ene products3. However, in alcoholic solvents”, at lower temperatures, the reaction gives RTAD-alkoxy adducts (eq. 1).
n N-NH
s&vent
We present here the results of PTAD reaction with tetra- and trimethylethylene
in protic solvents and
various temperatures. FI’AD was added to a stirred solution of tetramethylethylene (TME) in MeOH at various temperatures. The reaction gave two products, the ene adduct A and the MeOH adduct B. The ratio of these products, determined by tH NMR spectroscopy, depends on the reaction temperature. These results are summarized in Table 1.
2667
2668
TME gives the MeOH adduct B as the only product 299% at -780C. However, as the reaction temperature increases, the product ratio A/B also increases. Indeed, above 13.8oC, the isokinetic point, Figure 1, adduct A predominates. In Figure 2, the logarithmic ratio A/B is ploted as a function of l/T. From these data a AAH#AB (AH#A-AH#B) value of 5.2 kcal/mol is calculated (r=O.983). The enthalpy of activation, therefore, favors the formation of the methanol adduct B. On the other hand, the calculated MS#AB (AS#A -AS#B)value of 17.9 eu favors the formation of the ene product A, as expected, because of the bimolecularity of the path leading to the MeOH adduct B through transition state TS#B vs the monomolecularity of the path leading to the ene product A. via TS#A.
Table 1. Ene over MeOH-Adduct Ratio and MG#AB Values from WAD Additions to TME TOC
% ene
% MeOH add.
WB)
MG’AB
60
78
22
3.46
-0.76
40
67
33
2.07
-0.40
25
57
43
1.32
-0.13 +0.30
0
36
64
0.56
-15
21
79
0.27
+0.58
-40
17
83
0.20
+I.03
-60
4.5
95.5
0.05
+1.39
-78
cl
>99
0.01
+1.71
RH
X
0
A
R= RH >4”
4 N-Ph $ N -+0
OMe 6
It is constructive to emphasize that in entries 1-3, Table I, both MG#AB and AAH#AB have opposite sign, whereas in entries 4-8 have the same sign. Assuming that MH#AB (5.2 Kcal/mol) is constant over the studied range, this result indicates that the large entropy factor MS#AB dictates MG#AB changes and consequently controls the remarkable variations of the reactivity of the two competing reaction paths. Similar
results were obtained by the reaction of FTAD with trimethylethylene in MeOH. Again as the temperature decreases the MeOH adduct increases. Indeed, equal amounts of ene and MeOH adduct products were measured at 25% whereas at -500C the only detected product was the MeOH adduct. In conclusion the data reported here are consonant with the concept of a common intermediate leading to the ene and the MeOH adduct products. We consider this intermediate to be the aziridinium imide (AI), whose intermediacy in the ene reactions of mAD with alkenes has been supported from stereoisotopic studies2a~3a~ and direct spectroscopic observations6.
\
H--0Nle
TS ‘+,,
TS#,
AI
80
-I
-90
-60
-30
0
30
60
Fig.1. Linear plot of ene product (A) and MeOH adduct (B) vs temperature T.
90
2670
l/r x lo-3,(1/w)
Fig. 2. Logarithmic plot of ene adduct (A) over MeOH adduct (B) vs l/T.
Acknowledgment:
We thank professor G. J. Karabatsos for valuable comments. We also thank Mr. K.
Johnson at MSU for taking some NMR spectra. This work was supported by M. & S. Hourdakis SA. REFERENCES. 1.
Present address: Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90024.
2.
(a)
Orfanopoulos, M.; Smonou, I.; Foote, C. S. J. Am. Chem. Sot.
Orfanopoulos,
M.; Elemes,
Y.; Stratakis,
M. Tetrahedron
Lett.
1990, 112, 3607-3614. (b) 1990,
31,
5775-5778.
(c)
Orfanopoulos, M.; Foote, C. S.; Smonou, I. Tetrahedron Leit. 1987,28,2769-2772. 3.
For review paper see: (a) Cheng, C. C.; Seymour, C. A.; Petti, M. A.: Greene. F. D.; Blount, J. F. J. Org.Chem.
1984, 49, 2910. (b) Ohashi, S.; Leong, K.; Matyjaszewski, K.; Butler, G. B. J. Org.
Chem. 1980,45,3467-3471.
4.
Jensen F.; Foote, C. S. J. Am. Chem. Sot. 1987,109,6376-6385.
5.
(a) Elemes Y.; Stratakis M.; Orfanopoulos,
M. Tetrahedron
Lett.
1989,
30. 6903-6906.
(b)
Clennan, E. L.; Koola, J.J.; Oolman, K. A. Tetrahedron Lett. 1990,31,6759-6762. 6.
(a) Squillacote, M.; Mooney, M.; De Felippis J. J. Am. Chem. Sot. 1990, 112. 5365-5366 (b) Nelsen, S. F.; Kapp D. L. J. Am. Chem. Sot. 1985,107,5548-5549.
(Received in UK 8 March 1991)
TetrahedronLetters,Vo1.32,No.23. pp 2667-2670.1991 Printedin GreatBritain
Triazolinedione Additions to Alkenes in Protic Solvents. A Remarkable Temperature Dependence of the Competing Reaction Paths. Yiannis Elemesf- and Michael OrfanopouloP Departmentof Chemistry,Universityof Crete,71110I&lion, Crete, Greece
Key Words:Triaz~linedione;methen
tipping; emreaction; airidinium hi& &xmedia~,
activation parameters.
Abstract: lhe reactivity of the ene and MeOH-adduct reactions from N-Phenyl-1,2,4-triazoline-3,Sdione tetramethylethylene
with
(TME) shows a remarkable temperature dependence. These results are consonant with the
formation of a common intermediate between the two competing reaction paths.
In the course of our investigation of the mechanism of N-phenyl-triazolinedione
(PTAD) additions to
alkenes2, we have obtained results that show a remarkable temperature dependence of the ratio of ene over methanol adducts. PTAD, one of the most reactive enophiles, adds to olefins in aprotic solvents to give the ene products3. However, in alcoholic solvents”, at lower temperatures, the reaction gives RTAD-alkoxy adducts (eq. 1).
n N-NH
s&vent
We present here the results of PTAD reaction with tetra- and trimethylethylene
in protic solvents and
various temperatures. FI’AD was added to a stirred solution of tetramethylethylene (TME) in MeOH at various temperatures. The reaction gave two products, the ene adduct A and the MeOH adduct B. The ratio of these products, determined by tH NMR spectroscopy, depends on the reaction temperature. These results are summarized in Table 1.
2667
2668
TME gives the MeOH adduct B as the only product 299% at -780C. However, as the reaction temperature increases, the product ratio A/B also increases. Indeed, above 13.8oC, the isokinetic point, Figure 1, adduct A predominates. In Figure 2, the logarithmic ratio A/B is ploted as a function of l/T. From these data a AAH#AB (AH#A-AH#B) value of 5.2 kcal/mol is calculated (r=O.983). The enthalpy of activation, therefore, favors the formation of the methanol adduct B. On the other hand, the calculated MS#AB (AS#A -AS#B)value of 17.9 eu favors the formation of the ene product A, as expected, because of the bimolecularity of the path leading to the MeOH adduct B through transition state TS#B vs the monomolecularity of the path leading to the ene product A. via TS#A.
Table 1. Ene over MeOH-Adduct Ratio and MG#AB Values from WAD Additions to TME TOC
% ene
% MeOH add.
WB)
MG’AB
60
78
22
3.46
-0.76
40
67
33
2.07
-0.40
25
57
43
1.32
-0.13 +0.30
0
36
64
0.56
-15
21
79
0.27
+0.58
-40
17
83
0.20
+I.03
-60
4.5
95.5
0.05
+1.39
-78
cl
>99
0.01
+1.71
RH
X
0
A
R= RH >4”
4 N-Ph $ N -+0
OMe 6
It is constructive to emphasize that in entries 1-3, Table I, both MG#AB and AAH#AB have opposite sign, whereas in entries 4-8 have the same sign. Assuming that MH#AB (5.2 Kcal/mol) is constant over the studied range, this result indicates that the large entropy factor MS#AB dictates MG#AB changes and consequently controls the remarkable variations of the reactivity of the two competing reaction paths. Similar
results were obtained by the reaction of FTAD with trimethylethylene in MeOH. Again as the temperature decreases the MeOH adduct increases. Indeed, equal amounts of ene and MeOH adduct products were measured at 25% whereas at -500C the only detected product was the MeOH adduct. In conclusion the data reported here are consonant with the concept of a common intermediate leading to the ene and the MeOH adduct products. We consider this intermediate to be the aziridinium imide (AI), whose intermediacy in the ene reactions of mAD with alkenes has been supported from stereoisotopic studies2a~3a~ and direct spectroscopic observations6.
\
H--0Nle
TS ‘+,,
TS#,
AI
80
-I
-90
-60
-30
0
30
60
Fig.1. Linear plot of ene product (A) and MeOH adduct (B) vs temperature T.
90
2670
l/r x lo-3,(1/w)
Fig. 2. Logarithmic plot of ene adduct (A) over MeOH adduct (B) vs l/T.
Acknowledgment:
We thank professor G. J. Karabatsos for valuable comments. We also thank Mr. K.
Johnson at MSU for taking some NMR spectra. This work was supported by M. & S. Hourdakis SA. REFERENCES. 1.
Present address: Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90024.
2.
(a)
Orfanopoulos, M.; Smonou, I.; Foote, C. S. J. Am. Chem. Sot.
Orfanopoulos,
M.; Elemes,
Y.; Stratakis,
M. Tetrahedron
Lett.
1990, 112, 3607-3614. (b) 1990,
31,
5775-5778.
(c)
Orfanopoulos, M.; Foote, C. S.; Smonou, I. Tetrahedron Leit. 1987,28,2769-2772. 3.
For review paper see: (a) Cheng, C. C.; Seymour, C. A.; Petti, M. A.: Greene. F. D.; Blount, J. F. J. Org.Chem.
1984, 49, 2910. (b) Ohashi, S.; Leong, K.; Matyjaszewski, K.; Butler, G. B. J. Org.
Chem. 1980,45,3467-3471.
4.
Jensen F.; Foote, C. S. J. Am. Chem. Sot. 1987,109,6376-6385.
5.
(a) Elemes Y.; Stratakis M.; Orfanopoulos,
M. Tetrahedron
Lett.
1989,
30. 6903-6906.
(b)
Clennan, E. L.; Koola, J.J.; Oolman, K. A. Tetrahedron Lett. 1990,31,6759-6762. 6.
(a) Squillacote, M.; Mooney, M.; De Felippis J. J. Am. Chem. Sot. 1990, 112. 5365-5366 (b) Nelsen, S. F.; Kapp D. L. J. Am. Chem. Sot. 1985,107,5548-5549.
(Received in UK 8 March 1991)