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Decarboxylative Dehydration of -Hydroxycarboxylic Acids by Redox Condensation A Novel Olefin Synthesis.

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CAS Registry numbers:
( l a ) , 3332-08-9; (1 b), 7707-71-3; (1 c), 1077-18-5; ( I d ) , 13652-31-8; ( I f ) ,
40051-50.1 ;(1 g j , 1075-70-3;(2a), 61 701-86-8; (Zb), 61701-87-9; (2c), 6170188-0; (3 d). 61 701-89-1 ;(3f), 61701-90-4; ( 4 g ) , 61701-91-5; butadiene, 106-990; nickel, 7740-02-0
[l] P. Heimbach, G . Wilke, Justus Liebigs Ann. Chem. 727, 183 (1969).
[2] The perturbation [(-I) effect] caused by the introduction of the nitrogen
is compensated by the alkyl substituents [(+I) effect]: compensation
of this perturbation results in a behavior analogous to that of the unperturbed system (ethylene).
[3] A. Rolofi Dissertation, Universitat Bochum 1976; D.Reinehr, B. Hugelin,
E . Troxler, DOS 2507007 (Sep. 4, 1975) Ciba-Geigy AG, Basel (Switzerland).
[4] P . Heimbach, E. F . Nabbefeld, A . Roiofl, unpublished.
[S] The curve was derived using an unpublished method of J . Kluth and
H. Schenkluhn.
[6] An extremely pure Schiff base is necessary if octadienylated Schiff bases
of types ( 3 ) and ( 4 ) are to be synthesized, as traces of water or primary
amines present in the preparation can act as cocatalysts.
[7] These hydrogen transfer reactions are probably sigmatropic rearrangements and not the consequence of p-elimination and -addition steps.
[S] W Brenner, P. Heimbach, C. Wilke, Justus Liebigs Ann. Chem. 727,
194 (1969); K . 4 . Ploner, P. Heimbach, ibid. 1976, 54.
Decarboxylative Dehydration of P-Hydroxycarboxylic
Acids by Redox Condensation: A Novel Olefin Synthesis
which is formed according to eq. (B) in an exergonic process
[es. (C)l.
T"'
Li-C-CO2Li
I
+
R3\
,C=O
R4
R2
-
8 3
8'
Li-O-C--C-C02Li
I
1
R4 R 2
The advantages the new method has over those already
reported in the literature are the mild reaction conditions
(all the transformations ( 1 ) -+ (2) listed in Table 1 are complete within a few seconds at O T ) , the easy workup (only
HzO
+
EtOZC-N=N-COzEt
+
PPh3
-
(C)
EtOzC-NH-NH-COzEt
By Johann Mulzer and Gisela Briintrupp]
By addition of carbonyl compounds to the dilithium salts
of carboxylic acids a wide variety of P-hydroxycarboxylic
acids (I ) can be obtained in good yields[']. The decarboxylative dehydration of (1) according to eq. (B) leads to the
olefins (2), the combination of (A) and (B) being an attractive
alternative to the Wittig reaction.
Depending on the nature of the dehydrating reagent X
eq. (B) can be realized in two variations I or 11. Thus, with
X =dimethylformamide acetal, for example, olefin formation
and elimination of H 2 0 and C 0 2 proceeds in one step (variation I"]). Alternatively, if X = arenesulfonyl chloride, (1 ) is
HzO
--+
+
O=PPh,
nonvolatile and hence easily separable byproducts are formed),
and the low cost of the reagents employed (azodicarboxylate
can be readily prepared on a large scale from hydrazine,
chloroformates and an oxidizing agent[61).The full scope,
the stereochemistry and the mechanism of the reaction are
currently under investigation.
Experimental:
To a stirred solution of (1 a ) (3.0mmol) in anhydrous THF
(3ml) is added a solution of P(C6H5)3(3.0mmol) in THF
Table 1. Examples of p-hydroxycarboxylic acids ( I ) prepared according to Eq. (A) and of olefins ( 2 ) prepared according to Eq. (B/C)
(1 I
R' = R 2 = R 3 = H , R4=C6H5
R1= R 2 = R 3 = H, R4 =p-C6H4CI
R' = R 2 = R 3 =H, R4=p-C6H4CH3
R 1 = R Z = R 3 = H , R4=trans-CH=CHC6H~
R ' = R 2 = R 3 = H , R4=CH2C6H5
R ' = R 3 = H , R2=CH3, R4=2,2-diphenylcyclopropyl
f2)
[%I
M. p- r C ]
Yield
9 G 91
92-94
94-95
77-78
90-91
oil
70
70
75
80
30
50 Cal
B. p. ["C/torr]
Yield
60-70/10
60-70/10
60-70/10
8&90/10
65-75/10
1 10-1 2015. 10- 4
70
65
70
65
60
75
[%I
Ibl
55 Cdl
[a] Diastereomeric mixture. [b] cis-trans Mixture. [c] ( 1 y) was obtained in 40 yield by Diels-Alder addition of 1-acetoxybutadiene to methacrylic acid and
base-catalyzed hydrolysis. [d] Isolated and characterized (NMR, IR) as the TCNE adduct (dec. > 200°C).
first converted into its p-lactone, from which (2) is subsequently obtained by thermal elimination of C 0 2 (variation
IP31). We report here on a novel method for variation I
utilizing the principle of the redox conden~ation[~l.
The reagent
X we use is the adduct of triphenylphosphane and ethyl azodicarbo~ylate[~I.
This adduct is capable of binding the HzO
['I
Dr. J. Mulzer, G. Briintrup
Institut fur Organische Chemie der Universitat
Karlstrasse 23, D-8000 Munchen 2 (Germany)
Angew. Chem. lilt. Ed. Engl. 16 (1977) No. 4
(2 ml) under a nitrogen atmosphere. The resulting mixture
is treated dropwise with a solution of 3.0mmol of ethyl azodicarboxylate in THF (2 ml). The rapid progress of the reaction
is indicated by the slight warming of the mixture and the
instantaneous decoloration of the azoester. After the evolution
of C 0 2 has ceased, the resulting mixture is stirred for an
additional 10 min. The solvent is then evaporated under
reduced pressure and the residue triturated with ether/pentane.
The triphenylphosphane oxide and the hydrazoester crystallize
and are removed by filtration. The filtrate, after stripping
255
off the solvent, is distilled at 10 torr. Spectroscopically and
analytically pure ( 2 a ) is obtained in 70 % yield.
Received: January 12, 1977 [Z 657 IE]
German version: Angew. Chem. 89,265 (1977)
CAS Registry numbers:
(1 a ) , 156-05-8;(1 b ) , 25209-46-5;(1 c ) . 61752-37-2;( I d ) , 61752-38-3;(1 c ) ,
6828-41-7; ( I f ), 61752-39-4;( I g ) , 61752-40-7;( 2 a ) , 100-42-5; ( 2 b ) ,
1073-67-2;(2c), 622-97-9;(2ri), 16939-57-4;( 2 e ) , 300-57-2; 2 - ( 2f),
61752-41-8;E 4 2 f ), 61752-42-9;( Z q ) , 61752-43-0;P(C6H&, 603-35-0;
dietbyl azodicarboxylate, 1972-28-7;1-acetoxybutadiene, 151 5-76-0;methacrylic acid, 79-41-4
Since the calculation of k - requires knowledge of the equillibrium constant of dissociation, only the temperature dependence of k'L1 = I/T~,," (the reciprocal lifetime of all ionic
forms)was considered in the compilation of kinetic data (Table
1) for recombination.
I(.
ki
Rexo
ki
R@
+
PCO"
0.78
1.22
1.70
Xo
free ions
have so far been studied by two different methods: (i) determination of the solvolytic behavior of RXIZ1and (ii) examination of the kinetics of recombination of Re and Xe by flow
methodsr3a]or relaxation techniquesr3b1.All these methods
use time-dependent changes in concentrations in order to
determine kinetic parameters. We now report a study of
the ionization kinetics of triphenylmethyl chloride in SOz
under equilibrium conditions by NMR spectroscopy.
When a solution of trityl chloride in SO2 is cooled down,
the center of gravity of the 'H-NMR signals migrates downfield, indicating a shift of the equilibrium from covalent to
ionic species. In addition, the signals exhibit broadening below
-40°C and ultimately split into a spectrum of ionic and
covalent trityl chloride. In order to allow a quantitative evaluation of the 'H-NMR spectra we used trityl chloride deuterated
in the ortho and para positionsr4]which at low temperatures
only gives rise to singlets at 6=7.37 (covalent trityl chloride)
and 7.93ppm (all ionic forms). Line shape analysis of the
coalescence of these two signals (Fig. 1)results in temperaturedependent values of the average lifetimes T~~~ (all ions) and
T,,, (covalent form). The rate constant kl can easily be calculated from T~~~ according to
activity of free chloride ions
[*I Prof. Dr. H. Kessler, DipLChem. M. Feigel
Institut fur Organische Chemie der Universitat, Laboratorium Niederrad
Theodor-Stern-Kai 7, D-6004 Frankfurt am Main 70 (Germany)
256
0.00107
k-2
ion pair
ma:
=!h
0.43
By Martin Feigel and Horst Kessler[*]
Rate constants for ionization and dissociation of a compound RX via ion pairs into free ions according to the following
simplified Winstein scheme
k- i
0'
in SO,
Ionization Barrier of Trityl Chloride in Sulfur Dioxide"]
RX
H'
0'
H'
G . W! Moersch, A. R. Burkert, J. Org. Chem. 36, 1149 (1971);A. P.
Krapcho, E. G . E. Jahngen Jr., ibid. 39, 1650 (1974).
S.Hara, H. Taguchi, H . Yamamoto, H . Nozaki, Tetrahedron Lett. 1975,
1545; A. Riittimann, A . Wick, A. Eschenmoser, Helv. Chim. Acta 58,
1450 (3975).
W! Adam, J . Baeza, J.-C. Liu, J. Am. Chem. Soc. 94,2000 (1972).
7: Mukaiyama, Angew. Chem. 88, 1 1 1 (1976);Angew. Chem. Int. Ed.
Engl. 15, 94 (1976).
E. Brunn, R. Huisgen, Angew. Chem. 81, 534 (1969); Angew. Chem.
Int. Ed. Engl. 8, 513 (1969); 0.Mitsunobu, M . Eguchr, Bull. Chem.
SOC.Jpn. 44, 3427 (1971);A . K . Bose, B. Lal, W. A. Hoffman, M . S.
Manhas, Tetrahedron Lett. 1973, 1619.
N . Rabjohn, Org. Synth. Coll. Vol. 3, 375 (1955);J . C . Kauer, ibid.
4 , 41 1 (1963).
3.26
6[ppml8.0
1.5
7.0
Fig. 1. Lineshapeanalysis (right)of the FT-'H-NMR spectra (left) of nonadeuteriotrityl chloride in SO2 (0.1 M). The individual mean lifetimes of the ionic
and covalent species are given by T~~~ = r/pcov and rcor= T / P ~ ~ "p.; = population
of the species S; K,on=p,on/peov.
Table 1. Activation parameters for trityl chloride in SO2 (0.1 M).
[kcal/mol]
AH
* [kcal/mol]
AS* [cal/mol.K]
Ionization ( k , )
Recombination ( k - l ) [a]
10.12f0.05
5.34k0.5
-22.9 k 3
10.06+0.05
10.6 k0.5
+ 2.6 +3
[a] Recombination pseudo first order, see text.
Whereas enthalpy contributions are mainly responsible for
the recombination barrier, the ionization barrier is largely
determined by the strong negative activation entropy (Table
1). The higher order of the solvent molecules around the
ions than around covalent RX lowers the entropy. It follows
from our data that in the transition state the solvation is
comparable with that of ion pairsrs1.
Regarding the results obtained in less polar solvents the
value of AG?, in SO2 appears high. For example the barrier
was estimated to be lower than 4 kcal/mol from SNlreactions
of trityl chloride in benzener7! Furthermore, in dichloroethane
the recombination of trityl cations with chloride anions is
diffusion controlledr3b1.Since the population of ions and covalent compound are similar in SOz (measureable populations
p s are an essential condition for kinetic NMR measurements
Angew. Chem. Int. Ed. Engl. 16 (1977) No. 4
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acid, hydroxycarboxylic, synthesis, condensation, redox, olefin, decarboxylative, novem, dehydration
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