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Intramolecular Cl H Disproportionation of an Oxamide Chloride.

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Table I . N M R data (8 values) of
1/(1)-1/CJ
and 14) in CDCI,
~
NCH CI
NCHCl
3.76
4.05
2.77
5 21
5 68
49.6
38.4
72.9
79.9
[H-NMR
OCH?
CH,
NCH,
/ l u J [a]
4.45
45
4.51
4.2X
1.2s
I .4
I .47
1.32
66.7
62.5
13.3
Ilh) Ibl
( 1 1 ) [cl
(4)
N
CCI
~
COO
'J(NCH,)[Hi]
154.2
I65
I46 7
13x.4
2.98
"C-NMR
l/<i
14)
[a] At
~
13.9
160.9
20 C . [b] In CD,CN. [c] If less than 1 equiv. is present on formation of / / c ) ,intermediate values are observed for S ( N C H , ) indicating occurrence of fast exchange
/luJd/cJ
1 h at room temperature. (4) is characterized by its NMR
data (Table 1); as a 1,3-biselectrophile it reacts withp-toluidine to give the ben7pyrimidine derivative (5).
recrystallized from CH3CN; yield 0.85 g (37%). m. p. 219 "C
(decomp.); 'H-NMR (CDCl,): 6=1.18 (3H, t), 2.32 (3H, s),
3.33 (3H, s), 4.19 (2H, q), 5.76 (1 H, s), 7.17 (1 H, $), 7.24
(2H, s), 8.78 (1 H, s).
Received: May 21, 1979 [Z 254a IE]
German version: Angew. Chem Y / . 650 (1979)
CAS Registry numbers:
( l u ) . 70941-59-2.
( / h J . 7lJY4/-61-6: / / < I , 70941-62-7;
/ I ) . 16703-48-3:(.IJ. 16703(5) HCI. 70941-64-9,
52-9:14). 70941-63-8:
p-toluidine. 106-49-0
Intramolecular C1,H disproportionations such as ( l a )+ (4),
apparently represent a general type of reaction. Thus amide
chlorides (6) bearing electron-withdrawing substituents
isomerize to (8)f3'.
-Y
=
-co-R',
-CN,
0
-cci,, - c F ~R'C=NR;
,
xo
This disproportionation formally corresponds to a 1,3 hydride shift. However, the fact that the hexachlorophosphate
( l b ) does not isomerize, and that the weakly complexed salt
( l c ) isomerizes much more slowly (several days) than ( l a )
excludes this possibility. Although a concerted or ionic
mechanism cannot be ruled out, the most probable pathway
involves homolysis of the C C1 bond favored by the captodative substitution of the presumed radical intermediate
(7) [('I .
Procedure
Synthesis of (Ib): T h i o ~ x a m a t e [(2)
~ l (0.8 g, 5 mmol) is added to a stirred suspension of PC1, (2.08 g, 10 mmol) in dry
CHzC12 (15 ml). The resulting clear solution is stirred for 30
min, concentrated, and the residue is washed with ether.
3.95 g (98%) of (16) is obtained. Hydrolysis with aqueous
N a H C 0 3 yields the known oxamate (3)f51in 68% yield.
Disproportionation ( l a )+ (4): Thiooxamate (2) (1.61 g, 10
mmol) in CHzCla(30 ml) is treated with COCl, in 2-4 fold
excess. After about 1 h at room temperature, chlorination to
( l a ) and its isomerization are complete. The solvent is removed to give 1.64 g (82%) of (4) as a very hygroscopic, ether-soluble oil.
Reaction (4)+(5): p-Toluidine (3.21 g. 30 mmol) and (4)
(2 g, 10 mmol) are stirred in dry CH2CI2(75 ml) for 2 h. The
hydrochloride is filtered off and the solvent is evaporated.
The residue is washed with benzene/ether (1 : l), dried, and
exposed to air for 12 h. The resulting hydrochloride of (5) is
[ I ] H . Bohme. H. G Viehe: lminium Salts in Organic Chemistry. i n Advances in
Organic Chemistry. Vol 9/1 und 9/2. Wiley-Interscience. New York 1976
and 1979.
[2] a ) L Stellu. 2. Junuuseh. R . Mcrinyi. If. G. Vfehe. Angew Chem. 90. 741
(1978):Angew. Chem Int. Ed. Engl. 17.691 (1978).b) L. Srellu. P Turdu, Z.
Junuusrk. R. Merenvr. H G. Viehe. A . Munu;. J. Phy\. Chem.. in press.
131 F. Huvs. M . R o w r . Part of Disertations. Univerrite Louvain-la-Neuve 1979;
Z.Junousek. F Huv.~.L. Rene. M. Musyuehrr. L. SteIiu. R. Mer6nt.i. 11. G
Vfehe. Angew. Chem. 'I/,651 (1979):Angew. Chem. Int. Ed. Engl /8.616
(1979).For analogous sulfur compounds- J. C. Pummeler. C N m s . E l-. L N hous.re, R. MrrPn1.i. H . G. Vfehc.unpublished
[4] W Wulrer, K D . Bode. Justus Liebigs Ann. Chem. hhfl. 74 (1962).
IS] I / . M. A l k i n w n . J Chem. Soc. 105. 1290 (1914).
161 Note udded in proof: For helerocyclizations using [(lb), X = FSO'Y] see D.
Barrholumew. I. T. Kqr', Tetrahedron Lett.. in press.
Intramolecular CI,H Disproportionation of an
Oxamide Chloride.
An Entry to Imidazole Derivatives[*-]
By Zdenek Janousek, Fabienne Huys, Loic Rene. Michele
Masquelier, Lucien Stella, Robert Merenyi, and Heinz Gunter
Viehe"'
Radicals can be stabilized by capto-dative substitution" 21;
capto-dative substitution of compounds in which the central
CClz moiety is linked to a dimethylamino group and a n
electron-withdrawing group have been observed to undergo
CI,H disproportionation"'. Compound (2). an amide chloride of oxalic acid, is a further substrate capable of such rearrangement. We have now been able to synthesize and trap,
but not isolate, the highly unstable compound (2) and to elucidate reaction sequences in which i t occurs as intermediate.
['I
Prof. Dr. H. G. Viehe. Dr. Z . Janousek. Lic. Chem F. Huys. Dr. L. Rene.
Lic. Chem. M. Masquelier. Dr L. Stella. Dip1 -1ng. R. Merenyi
Laboramire d e Chimie Organique. Universite de Louvain
Place Louis Pasteur I. B-134X Louvain-la-Neuve (Belgium)
[**I Capto-dative Substitution Effects. Part 4. Part 3. F. Hui..\. R. Merenvr. Z .
Januuvek. L. Strllu. H . G Viehe. Angew Chem. 9 1 . 650 (lY7Y);Angew. Chem.
Int. Ed. t n g l . / X 615 (1979).
~
r
II
I
II
s s
14)
Attempts to synthesize (2) by exhaustive chlorination of
tetramethyldithiooxamide (4) led instead to the new stable
trichloroimidazolium salt (8). The disproportionation
(2)+ (3) can be envisaged as the key step of this reaction. Although the monoamide chloride (5) could be detected on
chlorination of (4) in the molar ratio 1 :2, the reaction could
not be stopped at the stage of (2). Chemical proof for the
structure of (8) is provided by its smooth thermolysis to the
known imidazole derivative (7) (m.p. 76°C; ref. [41: 7576 "C). This new synthesis resembles the Wallach reaction
which has been employed for the synthesis of chloroimidazolesl'l.
The formation of (7) and more highly chlorinated products on chlorination of dimethylaminoacetonitrile is already
knowni4I.This reaction can also be explained in terms of intramolecular CI,H disproportionation.
We finally succeeded in preparing the oxamide chloride
(2) by chlorination of the highly reactive bis(dimethy1amino)acetylene (/) at - 60 "C under high-dilution conditions in
CHZC1,. Compound (2) precipitates but is too unstable to be
isolated. The structure of (2) was established by hydrolysis to
tetramethyloxamide (6) and reaction with o-phenylenediamine to give the known quinoxaline derivative (9) (m.p.
66-67
C).
CAS Registry numbers.
i i ) ,5907-90-4: (?a).70941-52-5: izhj. 70941-53-6: f i i . 70941-54-7: (4). 35x40-7x9; (.70941.55.~;
i),
(6). 1608-14-6; (7). 873-25-6: (8).70941-57-0: ( 0 ) . 70~41-5x-I:
u-phenylenediamine. 95-54-5
[I] L. Srellu. Z . Junousek. R . Mer4nti. I / . 6. Viehe. Angew. Chem WI, 741
(197X): Angew. Chem. Int. Ed. Engl 17. 6Yl (lY7X).
[2] L. Srellu. P Turdo. Z Jnnoiicek. R. MerPnrr. 11. G. Viehe. A Mnno:. .I. Phys.
.
Chem in press
131 F. l l n ~ , sPart
,
of Distertation. Universite Louvain-la-Neuve 147').
[4] TI Pat. 154x390 (1969). Bayer. Chem Ahbtr 74. 3 h Z w (1971).
[ 5 ] K. Shimudu. J Kurr/umo. T. Kono:aw~u. M . Saruh. S. ~ ' ( J I Y J . ~ ~ UYekugaku
.
Zasshi 91. 221 (1971).
Acidity of Acetophenone Enol in Aqueous Solution'"'
By Pave1 Haspra, Alfred Sutter, and Jakob Wirrl']
Thermodynamically unstable enols are of importance as
reactive intermediates and are often the primary products of
photochemical reactions. The formation of enols during the
Norrish type I1 cleavage of ketones was first demonstrated
directly by Henne and Fischerl'l. The subsequent transformation of the enols into stable ketones necessitates protonation
of a carbon and proceeds much slower than the establishment of the acid-base enol-enolate equilibrium. This would
suggest the possibility, hitherto not exploited, of determining
the acidity of enols directly b y flash spectroscopy. Since enolization constants, K, = [enol]/[ketone], are accessible from
thermochemical[2"1or
data, the a -CH acidity constant K, of the corresponding ketone in aqueous solution can
be calculated according to eq. (a).
Experimental
Synthesis of (8) from (4): A fast stream of chlorine is
passed through a solution of (4) (1.76 g, 10 mmol) in dry
CHzClz(30 ml) such that the solution boils under reflux. After about 30 min the precipitate is collected and washed with
benzene containing some styrene to remove excess Clz; yield
2.26 g (96%); m. p. 186 "C (acetonitrile); 'H-NMR (S0Cl2):
6=3.85; 1R (KBr): 1580, 1510, 1390, 1330, 1155, 1070, 840
cm I .
Synthesis of (2): A solution of chlorine (2.8 g , 40 mmol) in
CH2C12(250 ml) is transferred at -78 " C to a 1-1 flask equipped with a dry-ice cooler and a dropping funnel. After dropwise addition of ( I ) (1.12 g, 10 mmol) in CH2C12 (250 ml)
with stirring at - 78 "C, a precipitate of (2) appears; it is hydrolyzed by aqueous N a H C 0 3 to (6) (63%).
Received: May 21. 1979 [Z 254h IE]
German version: Angew Chem. 91, 651 (1979)
AIIRCM..
('hem. Inr. Ed. Engl I X ( I Y 7 V ) No. A
pK,,(ketone) = pY,(enol)
+ pK,
(a)
Novak and L ~ u d o n ~have
~ " ~recently estimated the pK, of
acetophenone enol (1) in aqueous solution by a somewhat tedious indirect method to be l l -C 1, from which the pK, of
acetophenone (2) was calculated as 15.8f 1.0. Since this value deviates considerably from the result of an earlier measurement (19.2141) and since the pK, value of ( I ) serves as a
reference for relative measurements[3h1on derivatives of (f),
we decided to test the feasibility of the flash-spectroscopic
"titration" method on (1) as a n example.
[*] Priv.-Dor. Dr. J. Wlrz. Dipl.-Chem. P. Haspra. Dip1.-Chem. A. Sutter
Physikalisch-chemisches Institut der Universitat
Klingelhergstrasse 80. CH-4056 Basel (Switzerland)
["I This work constitutes part of Project No. 2.012.78 of the Swiss National
Science Foundation.
0 Verlug Chemie. GmbH. 6940 Weinheim.
1979
0.5 71)-OXH/79/01Xf)X-/~~/
7 .$ OZ.SOI/O
617
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intramolecular, disproportionate, oxamide, chloride
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