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Cycloadditions of Vinylcarbenes.

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B-l'-B-&B-5
and its chemical equivalent in the asymmetric
unit of the molecule. Likewise, the B-H-B
bonds are not
characteristic open three-center bonds. I n such a case the
bonding electrons are supposed to be concentrated on the
lines connecting the atoms B-H-B.
Fig. 3 clearly shows that
this is not so.
Received: April 8, 1970
[ Z 212 IE]
German version: Angew. Chem. 82, 519 (1970)
[*I Prof. Dr. R. Brill, Dr. H . Dietrich, and Dr. H. Dierks
Fritz-Haber-Institut der Max-Planck-Gesellschaft
1 Berlin 33, Faradayweg 4-6 (Germany)
[ l ] J . S . Kasper, C. M . Lucht, and D . Harker, Acta crystallogr.
3, 436 (1950).
[2] M. Dettke, Dissertation, Technische Universitat Berlin
1966.
[ 3 ] A. Tippe and W . C. Hamilton, Inorg. Chem. 8, 464 (1969).
[4] H . Dietrich, Messtechnik 76, 303 (1968).
[5] H . Dietrich and H . Dierks, Messtechnik 78 (1970), in press.
161 Internat. Tab. X-Ray Crystallogr., Vol. 3, 202. Kynoch
Press, Birmingham 1962.
[7] R. &if/, Zeitschrift Elektrochem. 63, 1088 (1959); Acta
Crystallogr. 13, 275 (1960).
[S] W. N . Lipscomb: Boron Hydrides. W. A. Benjamin, New
York 1963.
Isothiocyanato Carboxylic Acids and
2-Thioxo-5-oxazolidones
By Hans R . Kricheldorfr*]
Isothiocyanato carboxyIic acids ( 3 ) and 2-thioxo-5-oxazolidones ( 4 ) can be polymerized with loss of COS to give polyamides or peptides.
The hitherto unknown trimethylsilyl isothiocyanato carboxylates (2), which proved accessible by silylation of N-dithiocarboxy amino acid derivatives ( I ) , appeared suitable as
starting materials for the preparation of (3) and ( 4 ) (R1 :=
C O - O C Z H ~ ~ ~C2H5[21,
],
C H Z - C ~ H[31;
~ for R and n, see
Table).
S
-
I1
2(CH,)3SiCII2N(CzHs),
4
- - - z N ( ~ ~ ~ ~ ~ ~HCI
.
t
R'-S-C-NH-(CHR)n-COOH
14)
m.p.( "C)
-
C
d
e
f
g
[a]
1
H
CH3
CH*CH(CH&
CHzC6Hs
H
H
H
U
b
D,L
form.
67-7011
52-55/10-2 [a]
75-78110-3 [b]
122--125/10-3 [bl
1
1
1
2
3
81-84/1
5
95-98/10-3
70-73/10-*
-
-
70-72
93-95
-
10-12
18-20
32-34
[b] L form.
(2) + C,H,OH
I
SCN-(CHR), - C 0 2 H
+
TT:
s o
(41
526
All the new compounds listed were characterized by C, H, N
elemental analysis and IR spectra, and some of them by
N M R spectra.
Isocyanato carboxylic acids (3) and 2-thioxo-5-oxazolidones(4)
Triethylamine (2.1 moles) is added dropwise to a warm
mixture of ( I ) (1 mole), having R1 = CO-OCzH5, CzH5, or
C H ~ - C G H ~ ,and trimethylchlorosilane (2 moles) in dry
toluene (ca. 1.5 I) and the reaction mixture is heated to
boiling for 2 h. Precipitated triethylammonium chloride is
filtered off and the esters ( 2 ) are isolated in 7 6 9 0 % yield by
fractional dist i I lat ion.
A solution of ( 2 ) (0.1 mole) in light petroIeum (10&150 ml)
is treated at 0 ° C with dry ethanol 10.1 mole) and a catalytic
amount of dry hydrogen halide, and the solution is stirred at
0"Cuntil theproduct [ ( 3 )or ( 4 ) ] hasprecipitated(5-30min).
The 2-thioxo-5-oxazolidones (4) must be filtered off, dried in
a high vacuum, and used immediately. At 20 "C compound
(46) yields a solid foam of poly-D,L-alanine within about
20 min of isolation.
Received: April 21, 1970; revised: May 8, 1970 I
2 220 IE]
German version: Angew. Chern. 82, 550 (1970)
[*] Dr. H . R. Kricheldorf
Institut fur makromolekulare Chemie der Universitat
78 Freiburg, Stefan-Meier-Strasse 31 (Germany)
[I] T . Higashimura, H . Karo, K . Suzuoki, and S . Okamura,
Makromolekulare Chem. 90, 243 (1966).
121 A . Fredga, Svensk kem. Tidskr. 5 4 , 2 6 (1942); Chem. Abstr.
40, 2797 (1946).
[3] Ch. E . Dalgliesh, J. chem. SOC.(London) 1949, 2373.
[4] A. D . Grabenko, V . V . Stophan, M . N . Danchenko, T . I .
Cherepenko, and P. S . Pel'kis, Fiziol. Aktiv. Veshehestva, Akad.
Nauk Ukr. SSR, Repub. Mezhvedom. Sb. 1966, 104; Chem.
Abstr. 67, 3037 (1967).
[5] The p-, y-, and c-isothiocyanato carboxylic acids and
their silyl esters have an extremely powerful urticating action
and give rise to painful blisters and wounds, even in high
dilution.
Cycloadditions of Vinylcarbenes
By Michel Franck-Neumann and Chrisriane Buchecker * I
The carboxylic acids (3) can be liberated in 85-95 % yield
from the silyl esters (2) by treatment with ethanol at 0 "C.
C,H,0Si(CH3),
The cc-compounds ( 2 a ) to ( 2 d ) gave only the 2-thioxo-5oxazolidones ( 4 ) . These compounds have a low thermal
stability; for example, (4a) and (4b) decompose within a few
hours at room temperature, and, although slower, also at
temperatures as Iow as about -20 "C. Those bearing larger
substituents, e.g., ( 4 c ) and ( 4 d ) , exhibit a definite melting
point and can be kept at -20 "C for several weeks. Decomposition involves loss of COS to give peptides; a concurrent
isomerization gives the morestable thiazolidin-2,5-diones, but
in far smaller yield.
,!3-Isothiocyanatopropionicacid (3e) also polymerizes in the
course of a week at +25 "C to give oligo-P-alanine. In contrast, y-isothiocyanatobutyric acid (3f)and E-isothiocyanatohexanoic acid ( 3 g ) (which has already been prepared by
another rnethodr41) are stable at room temperature. The
compounds polymerize readily only above about 150 "C or,
in the presence of triethylamine (not pyridine!), above 50 "C.
Copolymers can be isolated from mixtures of monomers [51.
(31, n>,2
Carbenes that can undergo intramolecular stabilization
generally react very reluctantly with other molecules [I]. This
appears to be the case, for example, with vinylcarbenes which
can give cyclopropenes by intramolecular addition [2,31 and
which, to our knowledge, exhibit no intermolecular additions
providing proof of carbenoid structure 141.
We have now been able to intercept the vinylcarbenes supposed to give rise to cyclopropenes via diazoalkenesc31 on
photolysis of 5-cyano-3H-pyrazoles 151. This was accomplished by intermolecular cycloaddition to alkenes, alkynes,
and dienes to give vinylcyclopropanes, vinylcyclopropenes,
and divinylcyclopropanes, respectively.
Angew. Chem. internat. Edit.
I Vol. 9 (1970) I N o . 7
Two special cases will serve as illustrations: (i) Stereospecific
addition t o furan and (ii) addition t o benzene, which gives a
new stable norcaradiene derivative.
If irradiation of 5-cyano-3H-pyrazole ( I ) , which gives only
the highly unstable 3,3-dimethyl-l-cyanocyclopropene (2)
[v (C=C) = 1720 cm-I] when performed in ethereal solution,
is carried out in furan, the resulting Diels-Alder adduct (3)
of cyclopropene (m.p. 52 OC, J < 0.4 Hz) is accompanied
solely by the 1,2-divinylcyclopropane derivative (4) (cis or
trrms).
(3)
1:2.5
(4)
6-Cyano - 6 - (2-methyl-l-propenyl)-2-oxabicyclo
[3.1 .O] hex-3ene (41, v (C=C) (vinyl ether) = 1685 cm-1; 8 = 1.67 ppm
1.4 Hz; 1.78 (3 Hid), J = 1.2 Hz; 4.54 (1 vinyl
(3 Hid), J
H!heptuplet); 3.04 (Hl/dd), J = 2.8 and 5.5 Hz; 4.94 (Hz/d),
J .= 5.5 Hz; 5.16 (H3/t), J = 2.8 Hz; 6.24 (H4,d), J = 2.8 H z [ ~ ] .
i
( 4 ) is sufficiently stable to be isolated in pure form (yield
42"/,), although i t gradually rearranges at room temperature
t o three new substances (halflife 65 min at 50 O C and 23 min
at 60 "C). Divinylcyclopropane rearrangement 171 gives
2-cyano-4,4-dimethyl-8-oxabicyclo[3.2.1]octa-2,6-diene( S ) ,
6 = 0.88 (3 H); 1.28 (3 H); 4.52 (1 bridgehead H/t), J = 2 Hz;
4.68 (1 bridgehead H!m); 5.95-6.70 (3 vinyl Him), and
furanocyclopropane rearrangement 181 affords a cis-trans
mixture (1 : 3.4) of two trienealdehydes, v ( G O ) = 1680
cm-1; v (C=C) = 1600 and 1640 cm-1;, , ,A
(CH30H) =
330nm (E- 8050); S (0-dichlorobenzene)= 9,60ppm(aldehyde
H;d), J = 7.4 Hz; 10.10 (aldehyde Hjd), J = 6.4 Hz.
+
T-\[CH=CCNImCHO
CN
cis
+ trans
The ready divinylcyclopropane rearrangement cannot be
regarded as proof of the cis structure of ( 4 ) in this case
(cyan0 substituent, concomitant isomerization).
Photolysis of 4,5-dicyano-3H-pyrazole ( 6 ) gives a much more
reactive vinylcarbene which even undergoes a C-H insertion
reaction with ether. Unlike the carbenes generated from ( I ) ,
it reacts with benzene t o give both the cyclopropene [S (CH3)
= 1.531, which was not isolated, and the stable norcaradiene
derivative (7) (one isomer, pure yield 45 %), which isomerizes
mainly t o ( 8 ) only at elevated temperatures (halflife at
160 O C about 60 min).
265 nm ( E
3320); 6 = 2.07ppm (3 H); 2.12 (3 H), 2.93
(2 cyclopropane H'm); 6.20 (4 vinyl Him).
~
1,2-Dicyano-3-methyl-l-phenyl-2-butene
( 8 ) , 8 = 2.03 ppm
(3 H), 2.15 (3 H); 4.95 (1 ally1 H), 7.36 (5 arom. H).
Received: April 29, 1970; revised: May 21, 1970 [Z 221 IE]
German version: Angew. Chem. 82, 549 (1970)
~
_
..
.-
-
["I Dr. M. Franck-Neumann and C. Buchecker
lnstitut de Chimie, Universite de Strasbourg
1 rue Blaise Pascal, F-67 Strasbourg (France)
[ l ] W. Kirmse: Carbene Chemistry. Academic Press, New
York 1964.
[2] G. L . Closs. Advances alicyclic Chem. 1, 53 (1966), page 62.
[3] G. L . Closs and W . A . Boll, J. Amer. chem. SOC.85, 3904
(1965); A . C. D a y and M . C. Whiting, J. chem. SOC.(London)
C 1966, 1719; G . L . Closs, W . A . Boll, H . Heyn, and V . Dev,
J. Amer. chem. SOC.90, 173 (1968); M . Franck-Neumann and
C. Bucherker, Tetrahedron Letters 1969, 15; A . C. Dav and
R. N . Inwood, J. chem. SOC.(London) C 1969, 1065.
[4] Photolysis of 3 H-indazoles proceeds via 1,3-diradicals
which were intercepted with butadiene; G. L . Closs, L. R.
Knplan, and V . I . Bendall, J. Amer. chem. SOC.89, 3376 (1967).
[S] The 5-cyano-3H-pyrazoles ( I ) and ( 6 ) are accessible from
2-diazopropane and cyanoacetylene (yield 70°:) and dicyanoacetylene (yield 62:/,) respectively ( M . Franck-Neumann and
C. Buchecker, to be published). Only the cyano substituent
permits intermolecular reactions in good yields: The ester
group has a much weaker effect, and oxopyrazoles appear to
react differently.
[6] L . M . Jackman: Applications of Nuclear Magnetic Resonance Spectroscopy in Organic Chemistry. Pergamon Press,
London 1959, p. 87.
[7] E. Vogel, Angew. Chem. 7 4 , 829 (1962); J . M . Brown,
Chem. Commun. 1965, 226.
[8] G . 0. Schenk and R . Steinmetz, Liebigs Ann. Chem. 668,
19 (1963).
[9] E. Ciganek, J. Amer. chem. SOC.87, 652 (1965).
Cyclooctatetraene Systems Flattened by Steric
Constraints[**]
By Dieter Hellwinkel and Gunther Reiff[*]
Cyclooctatetraene[I] is a tub-shaped molecule which can
assume a planar conformation with predominantly localized
double bonds (symmetry D4h) only in a relatively energyrich transition state (12-15 k c a l h o l e ) during a ring inversion [21. Flattening of the cyclooctatetraene ring can also
be achieved by alteration of the Tc-electron skeleton (i.e. by
addition of two electrons [21 and formation of transition metal
complexes [31) the dianion then being structure determining.
The same is true for the symmetrical dibenzocyclooctene [41.
The ESR data of the radical anions of the cyclooctatetraene
derivatives mentioned above and of the tub-shaped tetrabenzocyclooctene (o-tetraphenylene), on the other hand, d o
not afford definite information about the structure [4,51.
In order t o force tetraphenylene, and hence the inherent
cyclooctatetraene skeleton, t o assume a planar conformation
by purely steric means we used as starting materials the tetra-
7-Cyano-7-(1-cyano-2-methyl-l-propenyl)norcaradiene
(7),
colorless crystals, m.p. 91 "C (from dimethoxyethane),
spectroscopic properties similar t o those of 7,7-dicyanonor(CH3OH) =
caradiene[gI: v(C=C) = 1630cm-1;, , ,A
Angew. Chem. internat. Edit.
Vol. 9 (1970) 1 No. 7
(21
R
= COOH;
( c ) , R = COOCH,
527
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