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Investigation of Valence Isomerism CyclobutadieneЧBismethylenecyclobuteneЧ[4]Radialene.

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2,5-dibromo-2,5-dimethyl-3-hexyneis treated with Fe2(CO)y (45%
yield).
[8] (5) has previously been isolated from the mixture of photolysis products
of 4-acetyl-5-isopropyl-3,3-dimethyl-3H-pyrazole
using preparative gas
chromatography: C. Dietrich-Buchecker. M . Franck-Neumann, Tetrahedron 33, 751 (1977).
[9]E. g. 2,5-dimethyl-2,4-hexadiene (I,I,4,4-tetramethylbutadiene)reacts
with Fe(CO), to give the tricarbonyliron complex of 1-isopropyl-3-methyl-IJ-butadiene): G. F. Emerson, 1. E. Mahler, R . Kochhar, R . Pettir.
J. Org. Chem. 29, 3620 (1964).
[lo]The diester corresponding to the diketone (6)is known, and this simplified its identification: L. K. Snydes, L. Skattebd, C. 8. Chapleo, D. G.
Leppard, K . L. Suanholt, A. S. Dreiding, Helv. Chim. Acta 58, 2061
(1975);J. M. Mclntosh, R . A . Sieler. J. Org. Chem. 43, 4431 (1978).
Ill] a) See e. g. A. J . P. Deuaquet, R . E. Townshend, W. 1. Hehre. J. Am.
Chem. SOC.98. 4068 (1976);b) H. G. Viehe, R. MerPnyi. L. Stella. Z . Janousek, Angew. Chem. 91, 982 (1979);Angew. Chem. Int. Ed. Engl. 18.
917 (1979).
Table I. IR and 'H-NMR spectroscopic data of compounds (6)-(9)
[a].
(6): IR (CHCI,): v=1700, 1655 c m - ' ( C 4 ) ; 'H-NMR (CDCI,/TMS):
6=2.12 (s, 3H), 2.26 (s, 3H),other H as multiplets between 1.75 and 2.80
(6H), 5.13 (dd, J= 1.3 and 16.6 Hz, 1 H), 5.25 (dd, J= 1.3 and 10.4 Hz, 1 H),
5.90 (dd, J= 10.4and 16.6 Hz, 1 H), 6.93 (m,1 H)
(7)[b]: 'H-NMR (C6D6/TMS): 6- 1.35 (broad s, 2H), 1.51 (dd, J=3.5 and
12Hz, 1 H), 1.80(s, 3 H), 2.17 (broad d, J= 12 Hz, 1 H), 2.58(m,1 H), 2.80(m,
1 H), 4.91(d, J= 1 1 Hz, 1 H), 4.97 (d, J= I7 Hz, 1 H), 5.75(dd, J = 1 I and 17
Hz, 1 H), 5.76-6.06 (m, 2H)
(8): IR (CCI,): v = 1715 ( C d ) , 1645 cm-' (C-C); 'H-NMR(C6D6/TMS):
6=1.91(~,3H),2.32(dd,J=4and12Hz,1H),2.58(m,lH),3.10(m,1H),
4.78 (d, J=17 Hz, IH), 4.86 (d, J=11 Hz, IH), 5.65 (dd, J=11 and 17 Hz,
1 H), other H as multiplets between 0.95 and 1.50 (3 H) as well as 5.80 and
6.10 (2H)
(9): IR (CCI,): v=1675 (CPO), 1635 cm-' ( C d ) ; 'H-NMR (CDCIJ
TMS):6=2.31 (s, 3H),5.64(broad ABm, 2H),7.09 (broad t, J=5 Hz, IH),
other H as multiplets between 1.85 and 3.15 (8H)
[a] The compounds (7).(8) and (9)formed in the ratio 2 :3:5; could be separated by HPLC on silica gel Si 60 (5-15 p) hexandether (20: l). [b] The 1R
spectrum of (7) shows the same characteristic bands as (8).
mL ice-water. After extraction with CH2C12(2 x 50 mL) the
organic extract is dried over MgSO,. The solvent is removed under reduced pressure and the residue chromatographed on silica gel (Merck Si 60) using hexane/ether
(9 :1); (2), 4.47 g (79%) is isolated as a yellow-orange oil.
IR (CCl,): v=2060, 1995, 1985 (CO); 1690 cm-' (C=O);
'H-NMR (CDC13): 6 ~ 0 . 2 3(d, 3=3.0 Hz, 1 H), 0.57 (dd,
5=2.0 and 10.0 Hz, 1 H), 2.06 (dd, 5=2.0 and 7.0 Hz, 1 H),
2.35 (dd, J=3.0 and 1.3 Hz, 1 H), 2.47 (s, 3H), 6.17 (broad
dd, 5=7.0 and 10.0 Hz, 1 H).
Investigation of Valence Isomerism
Cyclobutadieze- Bismethy lenecyclobutene141Radialene'
By Herbert Meier, Toni Echter, and Oswald Zimmer~'l
The short lifetime of highly strained cyclic alkynes often
results from di-, tri-, and oligomerization reactions, which
e. g. occur with cyclohexyne['al or 1,2-didehydrocyclooctatetraene['bl.
The 1,5-cyclooctadien-3-yne (I)['), isolated by us, isomerizes to 1,3,5,7-~yclooctatetraene(2) at high temperatures.
In contrast, at room temperature-by avoiding alkaline
media-an almost quantitative dimerization to the cyclobutadiene (4) is observed. A 0.3 M solution of (1) in chloroform has a half-life of ca. 2 h. (4) can stabilize itself uiu a
conrotatory electrocyclic ring opening process, forming the
bicycle (5). a bismethylenecyclobutene, or even the monocycle (6), a [4]radialene. The 'H- and I3C-NMR spectra of
the dimeric stage indicate an equilibrium whose position
lies almost completely to the side of (5). In contrast to the
--I
H2C=CH-CH=C=C
=CH-CH=CH2
(3)
1
Received: January 19, 1981 [Z 862 IE]
German version: Angew. Chem. 93, 900 (1981)
CAS-Registry-Numbers :
(I), 12211-98-2;
(2). 12082-23-4;
(3)p 12087-05-7;
(4). 12212-46-3;
(5). 5814380-9;(6). 79044-47-6;(7). 79044-48-7;(8). 79044-49-8;(9). 79044-50-1;
CH,COCI, 75-36-5;
C6HSCOCI,98-88-4
[I] E. 0. Greaves, G. R . Knox. P. L. Pauson, Chem. Commun. 1969, 1124;
R. E. Graf, C . P. Lillya. J. Organomet. Chem. 166. 53 (1979).
[21 Cf. e . g . R. Lonrzsch, D. Arlr, Justus Liebigs Ann. Chem. 1976. 1757.
131 M. Franck-Neumann. D. Martina, F. Brian, Angew. Chem. 90, 736
(1978);Angew. Chem. Int. Ed. Engl. 17, 690 (1978).
[4]a) K . K. Joshi, J. Chem. SOC.A 1966, 594;b) D. Bright. 0. S . Milk. J.
Chem. SOC.Dalton Trans. 1972, 2465.
I51 (1) was prepared in 45% yield from a solution of I,&dibromo-Z-butyne
and Fe2(C0)y (I :2.8) at 80°C. (11% from 1,4-dichloro-2-butyne and
FeACO), WI.)
[6j R . N. Greene. C. H . Depuy, T. E. Schroer. J. Chem. SOC.C1971. 3115;s.
M. Nelson. C. M . Regan, M. Sloan. J. Organomet. Chem. 96, 383
(1975).
171 (4) can be obtained, as described in [4a], in 65% yield from free cumulene and Fe3(C0)12.The preparation is, however, more straightforward if
Angew. Chem. Int. Ed. Engl. 20 (1981) No. I0
colorless educt ( I ) , (5) is intensely yellow. The 400 MHz
'H-NMR spectrum[3' demonstrates that six types of chemically non-equivalent olefinic protons are present. The protons Hf and Hy absorb at the lowest field position
(6=6.84). Their coupling with He, H,, and Hhrand He,, H,,,
and Hh' respectively was ascertained by means of decoupling experiments (6=5.90, 5.28, 5.17). The protons of the
[*I
[**I
Prof. Dr. H. Meier, DipLChem. T. Ecbter, Dipl.-Chem. 0. Zimmer
Institut fiir Organische Chemie der UniversitBt
Auf der Morgenstelle 18, D-7400Tiibingen (Germany)
This work was supported by the Deutsche Forschungsgemeinschaft and
by the Fonds der Chemischen Industrie.
0 Verlag Chemie GrnbH, 6940 Weinheim, 1981
0570-0833/81/1010-0865$02.50/0
865
intact eight-membered ring approximately form an ABXX'
system. H, and Ha. appear as a doublet at 6=6.27, and Hb
and H, as a multiplet at 6=6.23. The chemical equivalence of H, and Hc8,as well as that of Hd and Hd,, is based
on an inversion process which occurs at room temperature.
The eight I3C absorptions recorded for (5) yield two singlets, four doublets and two triplets under off-resonance
conditions. The given assignments shown in the formula
are consistent with the I3C data for bis(methy1ene)cyclobutene in the literatureL4].
In principal, (5) could also be formed via an electrocyclic ring opening process of (I) to 1,3,4,5,7-octapentaene (3).
which reacts with (Z) in a [2,+2,]-cycloaddition step. This
route is, however, precluded, since the monomolecular
reaction (1)- (3) would then have to be observed already in
the gas phase in the preparation of (I). In the 'H-NMR
spectrum of a solution of (5) in chloroform kept for a few
days at room temperature, the signals for protons Ha and
Hb become smaller and those of the protons of the open
chain become larger. This indicates a further valence isomerization to the radialene system (6). Unfortunately, this
process is accompanied by polymerization which makes its
investigation difficult.
cis,cis-1,3,5,7-0ctatetraene undergoes extremely rapid
and complete cyclization to 1,3,5-~yclooctatriene'~~~.
Huisgen et uI.['~' were able to extensively investigate the
position of equilibrium and stereochemistry of the dimethyl compounds. The cyclooctatriene was shown to
dominate the equilibrium at room temperature. A low energy barrier for this [,8,]-valence isomerization is also indicated by our example. Because of the energetically unfavorable cyclobutadiene structure of (4). the equilibrium
lies to the side of (5).
In contrast to (I), the dimeric stage reacts spontaneously
with the highly reactive dienophile 4-phenyl- I ,2,4-triazol-
ine-3,s-dione (7). By this means a 20% yield of the bisadduct (lo), a derivative of cyclobutadiene (4), is obtained.
This can be rationalized in two different ways: either the
tricycle (4) reacts preferentially via the monoadduct (8) to
(10) and thereby displaces the position of the equilibrium
( 4 ) ~ ( 5 ) o. r the monoadduct (9) is formed from (5) via selective addition to the side of the eight-membered ring,
which then is further transformed in an electrocyclic ring
closure to (8) and hence leads, via a second cycloaddition,
to (20). The constitution of (10) was elucidated using homonuclear double-resonance experiments. Apart from the
signals of five aromatic protons (6=7.5), the 'H-NMR
spectrum (CDC&) consists of a doublet for Hh (6.9, 3J=6.8
Hz), a multiplet for H, and Hb (6.0), a multiplet for H,
(5.2), and a broad absorption for H,, Hd, He, and Hf
(1.9 5 6 1 2.6). When all couplings to the saturated protons
HCpf are eliminated, residual AB- and AX-systems remain
for Ha,band Hg,h, respectively. The possible structures of
(ZO) are obtained by applying one of the following symmetry operations to the half-molecules shown in formula (ZO):
(ZOa):Reflection in a plane of symmetry 0 lying right angles to the plane of the four-membered ring. (lob): Rotation about a C2 axis lying in the plane of the four-membered ring. ( 1 0 ~ ) :Rotation about a Cz axis perpendicular
to the plane of the four-membered ring. (IOd): Inversion i
through the middle of the four-membered ring.
In principle, the double Diels-Alder reaction could lead
to four adducts. In this connection it is immaterial whether
the direct route (4)-(8)+(10),
or the indirect route
(4)- (5)- (9)+ (10) is followed. The various possible modes
of attack of the dienophile (7) and the point groups of the
resulting adducts are shown in Scheme 1.
Scheme 1
Apart from the C1,Hl,-system with 2.871- o r o-electrons
described here, valence isomerization between cyclobutadiene, bis(methylene)cyclobutene, and [4]radialene systems
is also conceivable in the C12H,2- and C8H8-systems
(Scheme 2). The steric course shown refers to the thermally
allowed synchronous reactions. The behavior is reversed
under photolytic conditions.
Cyclobutdiene
Bidmethyled-
Structure
cyclobutene
[LIRadiolene
Structure
Structure
M p = 211oc
Scheme 2.
866
0 Verlag Chemie GrnbH. 6940 Weinheim. 1981
0570-08;13/81/1010-0866 S. 02.50/0
Angew. Chem. Int. Ed Engl. 20 (1981) No. 10
The experimental verification of the hypotheses appears
to be considerably easier in the C,,H,, series than with
C8H8161.
We hope that our investigations will be an impetus
to finding further electrocyclic reactions at four-membered
rings with four n-centers.
Received: March 13, 1981 [Z 864 IE]
German version: Angew. Chem. 93, 901 (1981)
CAS Registry numbers:
( I ) , 68344-46-7; (4). 79084-09-6; (5). 79084-10-9; (7). 4233-39-4; (lo), 7908411-0
[I] a) G. Witrig, U. Mayer, Chem. Ber. 96, 342 (1963); b) A. Krebs. D. Byrd,
Justus Liebigs Ann. Chem. 707, 66 (1967).
121 H . Meier, T. Echter, H . Petersen, Angew. Chem. 90, 997 (1978); Angew.
Chem. Int. Ed. Engl. 17, 942 (1978).
131 Dr. U. Siehl is thanked for recording the 400 MHz spectra.
[4] A. 3. Jones. P. J . Garratt. K . P. C. Vollhardt. Angew. Chem. 85, 260
(1973); Angew. Chem. Int. Ed. Engl. 12. 241 (1973).
[5] a) W. Ziegenbein. Chem. Ber. 98. 1427 (1965); b) R . Huisgen, A . Dahrnen.
H. Huber. J. Am. Chem. SOC.89, 7130 (1967); Tetrahedron Lett. 1969,
1461; A. Dahmen, R. Huisgen. ibid. 1969, 1465.
[6] The tetrakis(rnethy1ene)cyctcbutane(13) (C. W.Griffin, L. I . Peterson. J.
Am. Chem. SOC.84, 3398 (1962)) and the bicyclo[2.2.0]hex-l(4)-ene (K.B.
Wiberg, G. J . Burgmaier. P. Warner, ibid. 93, 246 (1971)) as basic frameworks of (12) are known. For the tricyclic compound (11) see E. KlosterJensen. J . Wirz, Helv. Chim. Acta 58. 162 (1975).
Reaction of (lc) with methanolic sodium hydroxide produced a product which was sufficiently soluble in CDCl,
to allow the determination of I3C-NMR spectra. It was apparent that a tert-butyl group was still present, but that a
rearrangement had occurred. Hence, in the reaction of (la)
with ethanolic potassium hydroxide the incorporation of
the ethyl group is not necessarily coupled to the rearrangement reaction, but is rather a secondary process, a transesterification which does not occur with the tert-butyl ester.
Additional information on the mechanism was gathered
from the reaction of the rearranged methyl ester with acetic anhydride/triethylarnine/4-dimethylaminopyridine.By
this means, the acetyl derivative (4) of the minor component of the product mixture was isolated; sufficient material was collected in this way to allow structural assignment~'~].
The constitutional changes express themselves
particularly clearly in the I3C-NMR spectra (Table 1). The
Table 1. Selected I3C-NMR data (in CDClr; &-values)of (Ic)-(4c). C-atoms
which are related to each other through the structural changes in the reactions are displayed in the same columns.
(lc)
(2c)
(3c)
(44
45.9
43.0
[a]
27.9
(C-5')
(C-7)
(CH2S)
(CH2S)
158.3
73.2
71.6
68.2
(C-4')
(C-I)
(C-3)
(C-3)
93.1
67.7
156.7
157.1
(C-2')
(C-5)
(C-5)
129.0
140.2
[a]
133.5
((2-5)
(C-2)
(C-4)
(C-6)
(C-6)
[a] Hidden by lines of (2c).
Reactions of a Heterocyclic System Having
Ambidentate Reactivity[**]
By Johann Gasteiger, Ulrich StrauJ3, and
Ulrich Schubert"]
a-Phenylhydrazono-2,5-dihydro-2-thiazole
acetates ( l ) [ ' l
offer various sites for attack, both by electrophilic[*I and
nucleophilic reagents.
This makes them useful models for the study of ambidentate reactivity. Nucleophilic attack could occur at both
C atoms (1 and 2) of the acetic acid system and at C-4' of
the dihydrothiazole ring. A sufficiently basic nucleophile
could abstract the NH-proton followed by rearrangement
or fragmentation processes. We investigated whether, under these circumstances, the ester group could be hydrolyzed in alkaline solution.
Reaction of (la) with ethanolic potassium hydroxide
gave a product in which the methyl group had been lost
and an ethyl group had been incorporated. However, the
product was not (lb), as its independent synthesis proved,
but rather an isomer of (lb). Structure elucidation was aggravated, since 'H-NMR spectra showed that the product
consisted of a mixture of two compounds which were only
moderately soluble in CDC13.
[*I Priv. Doz. Dr. J. Gasteiger I+], Dr. U. StrauB
Organisch-chemisches Institut der Technischen Universitgt Miinchen
Lichtenbergstrasse 4, D-8046 Garching (Germany)
Priv. Doz. Dr. U. Schuben
Anorganisch-chemisches Institut der Technischen Universitgt Miinchen,
Lichtenbergstrasse 4, D-8046 Garching (Germany)
['I Author to whom correspondence should be addressed.
I**] This work was supported by the Deutsche Forschungsgemeinschaft.
Angew. Chem. I n [ Ed Engl. 20 (1981) NO.I 0
course of the reaction is thus as follows: in alkaline media
deprotonation of the hydrazono group takes place first,
followed by nucleophilic attack at the azomethine group to
give the 6-thia-2,3,8-triazabicyclo[3.2.l]oct-3-enesystem
(2). This compound has a thiohemiaminal structure which
can rearrange to the 3-thiomethyl-2,3-dihydro-I ,2,4-triazine derivative (3).
1
AczOINE13IDMAP
C H3
The equilibrium (2)+ (3) is solvent dependent. At room
temperature the amount of (3c) in CDC& is 25%, in
CD3COCD3 5%. Acylation of this equilibrium mixture
only leads to the acetyl derivative (4).
An X-ray structure determination of the rearranged
methyl ester was performedI4', and showed that only (2a)
was present in the crystal (Fig. 1).
In the thiazolidine ring, the atoms C2, S, C7 and C1 are
approximately coplanar (torsion angle C2-S-C7-C
1
4.7'). In the six-membered ring, all atoms except N3 are
also approximately coplanar. This observation, in conjunction with the bond lengths and the trigonal planar configuration of N2, indicates conjugation of the C=N double
bond with N2.
0 Verlag Chemie GmbH, 6940 Weinheim.1981
0570-0833/81/1010-0867S 02.50/0
867
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investigation, valence, cyclobutadieneчbismethylenecyclobuteneч, isomerism, radialene
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