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Photochemical (2 + 6)-Cycloadditions. Novel 1 4-Cycloaddition with Formation of the Bicyclo[2.2

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perpendicular to the reacting u orbital and to the n orbitals and
is conserved with respect to the molecular orbitals taking part
in the reaction, as is required for a conrotatory process.
(2a). R
(2b), R
(la), R = H
(Ib), R = CH3
= CH3
Reduction of dimethyldivinylcyclobutane (1 b)I21 under the
same conditions gives 4,5-dimethyl-cis,trans-2,6-octadiene
(Zb) in 72% yield.
The reduction of the two isomeric 3-methyl-cis-1,2divinylcyclobutanes (3) and (4)131 yields different products for
steric reasons. The trans-3-methyl compound (3) affords both
possible methyloctadienes (5a) and (5b) as an approximately
1 : 1 mixture in an overall yield of 73%. However, compound
(4) gives a 1 : 4 mixture of (5a) and (Sb) in 81% yield.
The structures of (Za) and (2 b) were assigned on the basis of
the IR and 'H-NMR spectra. In the case of (5a) and (Sb) the
structures were determined from the spectra and the retention
behavior. The retention times are characteristic of allyl-substituted trans- and cis-2-alkenes respecti~ely[~I.
The examples studied cannot be classed as electrocyclic reactions since n o rearrangement of a cyclic compound into its conjugated polyene isomer takes place. A formal similarity to, e.g.,
conrotatory opening of cis-3,4-disubstituted cyclobutenes to
give cis, rrans-2,4-diene~[',~]nevertheless exists. In both cases
the u bond participating in the reaction occurs in the four-membered ring and the uppermost occupied n orbitals are of the same
symmetry. Steric effects also play a role in determining the absolute rotation on conrotatory opening of the substituted cis-1,2divinylcyclobutanes (3) and (4), thus leading to an unequal distribution of the isomers (5a) and (5b) on reductive ring
General procedure:
cis-1,2-Divinylcyclobutane(11.9 g, 0.11 mole) is dissolved in a
mixture of liquid ammonia (approx. 100 ml) and ether (10 ml),
and sodium metal (6.3 g, 0.274 mole) is added to the solution.
The resulting blue solution is allowed to react for about 4 h at
-33 C. After the ammonia has evaporated overnight through
a reflux condenser cooled to - 25 "C,50 ml of pentane is added
and the reaction mixture is filtered. The solvent is distilled off
and the residue analyzed by gas chromatography.
Received: December 21, 1970 [Z 325 IE]
German version' Angew Chem 83, 144 (1971)
The first step in the reduction of the divinylcyclobutanes probably involves radical anions whose radical part is also transformed to an anion in the next step. During reduction the four-membered rings undergo cleavage between C-1 and C-2 (cf. ref.[']).
The divinylcyclobutanes afford ally1 anions which are then protonated in such a way that thermodynamically favorable compounds having disubstituted double bonds are formed.
The surprisingly high stereospecificity of the reaction becomes
readily understandable when it is regarded as a stereoelectronically controlled process in which conrotatory ring opening forms
two anions having a cis- and a trans-ally1 group. Fig. 1 shows a
correlation diagram for this process.
[*I Dr. H. Hey
Max-Planck-Institut fur Kohlenforschung
433 Miilheim-Ruhr, Kaiser-Wilhelm-Platz 1 (Germany)
Present address: Farbwerke Hoechst AG
623 Frankfurt/Main 80, Postfach (Germany)
[l] P. Heimbachand W. Brenner, Angew. Chem. 79,813 (1967); Angew. Chem. internat. Edit. 6, 800 (1967).
[2] P. Heimbach, and H. Hey, Angew. Chem. 82, 550 (1970): Anens
Chem. internat. Edit. 9, 528 (1970).
[3] P. Heimbach and H. Hey, unpublished.
(41 G. Schomburg, 3. Chromatog. 23, 1 (1966).
[ 5 ] H. Nozakj, I. Otani, R. Nogovi, and M. Kawanisi, Tetrahedron 24,
2183 (1968).
[6] R. Criegee, D. Seebaeh, R.E. Winter, B. Borretzen, and H. A .
Brune, Chem. Ber. 98, 2339 (1965), and further literature cited there.
[7] R. B. Woodward and R. Hoffmann, J. Amer. Chem. SOC.87, 395
Photochemical (2z 6z)-Cycloadditions. Novel
1,4-Cycloaddition with Formation of the Bicyclo[2.2.2]octadiene System
By Gerhard Hesse and Peter LechtkenL']
On irradiation with a high- ressure mercury vapor lampc'l dichlorovinylene carbonate['Padds to aromatic compounds if a
Duran filter is used. The formation of a 1: 1adduct is established
by elemental analysis and mass spectrometry. When benzene
is used as substrate a molecular peak at m/e = 232 (C1 = 35)
is obtained resembling a pattern typical of a dichloro compound.
NMR and UV spectra show that the addition must have taken
place in the 1,4 position.
Fig. 1. Correlation diagram for the conrotatory opening of ( l a ) to ( 2 ) .
A total of four molecular orbitals of cis-l,2-divinylcyclobutane
participate in the rearrangement. The symmetry properties of
the molecular orbitals with regard to a twofold symmetry axis
C2 are shown in the diagram. C2 passes through the molecule
Angew. Chern. internat. Edit. / Vol. I0 (1971) / N o . 2
(la), R = H
(lb), R = CH3
(Za), R' = R3 = H; R2 = R4 = CH,
(Zb), R' = R 2 = R3 = R4 = CH,
R 3 = H ; R2 = R4 = OCH,
(ZC), R'
Rel. RR[a]
Quantum yield
M. p.
(%) [cl
nothing has hitherto been reported regarding the possible conformations and inversion processes of the five-membered
MS,C2 chelate rings in solution.
It is, however, to be expected that an insight into the spatial
structure of metallocene enedithiolate chelates[*]willbe provided by the 'H-NMR spectrum of the cyclopentadienyl ligands,
as in the case of metallocene polychalcogenide chelates13]. In
fact, the titanocene 1,2-enedithiolates (l)L4], ,]sI)?,(
and (3)['1
[a] Reaction rate.
(b] Information regarding the irradiation performance of the TQ150
lamp as a function of wavelength and burning time was taken from the
manufactures specifications. The quantum yields are valid for the first
100 mins' irradiation.
[c]Analytically pure product; referred to dichlorovinylene carbonate.
This 1,4 addition fits in with the series of 1,2 and 1,3 cycloadditi on^[^-^] found previously. The only example reported so far
of a photochemical cycloaddition in the 1,4 position is the reaction of butadiene with benzene to give the bicyclo[4.2.2]decatriene derivativel6], but only fair yields were obtained.
The 1,4 additions carried out by us by direct irradiation of ca.
10% solutions of dichlorovinylene carbonate in aromatic compounds gave relatively good yields and could be accelerated
by a factor of about 40 by addition of acetone or acetophenone.
A purely thermal addition to the hydrocarbon does not occur
after 48 hours' heating at 150°C.
By way of example, proof for the structure of (lb) was obtained
from the following data: NMR: T = 4.40 (2 vinyl H/M); 6.28
(1 bridgeheadH/T);8.09,8.11(2vinylCH3/D);8.37(1bridgehead CH,/S). UV: h,,, = 208 nm (& = 1950). This absorption
indicates unequivocally the presence of a bicyclo[2.2.2]octadiene system, for 1,3-cyclohexadiene absorbs at 258 nm ( E =
1600)[71and values of 220 nm ( E = 3000) were found for 1,3 addition c0mpounds[~1. The analogous norbornadiene, on the
other hand, absorbs at 205 nm ( E = 2100)[*1.IR: the positionof
the carbonyl vibration at 1835 cm-' indicates that the cyclic carbonate remained unchanged.
2,6-Dichloro-7,9,1 O-trimethyl-3,5-dioxatricyclo[]undeca-t?,lO-dien-4-one
( I b)
Dichlorovinylene carbonate (8 g, 51.6 mmole) is dissolved under
N, in anhydrous mesitylene (80 ml) and UV-pure acetone
(10 ml) and then irradiated for 65 hours through a Duran filter.
After removal of acetone and excess mesitylene a viscous oil
is obtained which is then sublimed at 80-10OoC/0.5 torr. The
crystals thus obtained are pressed on an unglazed plate to remove any residual oil and recrystallized from petroleum ether.
Yield 7.0 g ( 5 0 %) , m.p. 90°C,analytically pure.
Received: December 14, 1970 [2322 IE]
German version: Angew. Chern. 83. 143 (1971)
[*] Prof. Dr. G. Hesse and Dipl.-Chem. P. Lechtken,
Institut fur Organische Chemie an der Universitat ErlangenNiirnberg
852 Erlangen, Henkestr. 42 (Germany)
[ I ] TQ 150, Original Hanau, Quarzlampen GmbH, Hanau.
[2] H.-D. Scharf, W. Droste, and R. Liebig, Angew. Chem. 80, 194
(1968); Angew. Chem. internat. Edit. 7, 215 (1968).
[3] H. J. F. Angus and D. Bryce-Smith, Proc. Chem. SOC.1959, 326.
(41 K. E. Wilzbachand L. Kaplan,J. Amer. Chem. SOC.88,2066 (1966).
[5] D. Bryce-Smith, A . Gilbert, and B. H. Orger, Chem. Commun.
[6] K. Kraft and G. Koltzenburg, Tetrahedron Lett. 1967, 4357.
[7] H. Bohme and G. Peters, Z. Natuxforsch. IZb, 5 (1957).
[ 8 ] C. F. WilcoxJr., S. Winstein,and W. G.McMillan, J. Amer. Chem.
SOC.82, 5450 (1960).
Conformational Studies on Enedithiolate
By Hartmut Kopf['l
Although rjs-1,2-enedithiolate (or a-dithiodiketone) complexes of transition metals nowadays number among the most
thoroughly investigated S-coordinated chelate complexes[']
give spectra exhibiting a reversible temperature dependence of
the C,H, proton resonanceF6I, which is independent of the solvent and which is in the same sense for compounds (I)-(3),while
the signals of the groups C,H2, C6H4, and C6H,CH,, respectively, remain unchanged in the temperature range studied.
This observation can be interpreted in the following manner:
1) At -50°C the occurrence of two sharp singlets of equal intensity indicates the presence of the identical conformers (a)
and (c) in which the magnetic equivalence of the two freely
rotating cyclopentadienyl ligands of each molecule is canceled
by a folding of the chelate rings along the S . . S
nonplanar chelate rings are rigid: no measurable conformational
transitions take place.
2) When the temperature of the sample is raised the signals
broaden and finally coalesce between +10 and +20° C. This
would indicate that the mutual interconversion (a)*@) is now
occurring at a detectable rate, probably Via (b) as excited
state"]. The coalescence temperature T, and the signal splitting
A v afford the free energy of activation AG: of this inversion
3) At normal measuring temperature (+ 36°C) a single sharp
singlet appears, as would be expected for a rapid conformational
(*] Dr. H. Kopf
Institut fur Anorganische Chemie der Universitat
87 Wurzburg, Rontgenring 11 (Germany)
[**I Metallocene enedithiolate chelates, Part 2. This work was supported
by the Deutsche Forschungsgemeinschaft. Ref. [2] is to be regarded as
Part 1 of the series.
[ I ] J. A. McCleverty, Progr. Inorg. Chem. 10, 49 (1968).
[2] A. Kutoglu and H. Kopf, J. Organometal. Chem. 25,455 (1970).
[3] H. Kopf, B. Block, and M. Schmidt, Chem. Ber. 101, 272 (1968);
H. Kopf, Angew. Chem. 81,332 (1969); Angew. Chem. internat. Edit.
8, 375 (1969).
[4]H. Kopf, 2. Naturforsch. 23b, 1531 (1968).
[5] H. Kopf and M. Schmidt, J. Organometal. Chem. 4,426 (1965).
[6] I am grateful to Dr. D. Scheutzow and Fraulein H. Feenders,
Wiirzburg, for recording the low temperature NMR spectra.
[7] Other conceivable states with nonplanar S,C, system are energetically unfavorable.
[ S ] Cf. A. E. Smith, G.N. Schrauzer, V. P. Mayweg, and W. Heim'ch,
J. Amer. Chem. SOC.87, 5798 (1965).
Angew. Chem. internat. Edit. / Vol. 10 (1971) / N o . 2
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bicycle, cycloadditions, formation, novem, photochemical
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