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Dimerization of УPush-PullФ Substituted Allenes.

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Treatment of ( 2 ) with 7.8 rnole-O/o of dicarbonyl-2,4-pentanedionatorhodium(1) (16 h at O’C in chloroform) leads to 57%
of ( I ) (pale yellow needles, m. p. 23.5-24.5cC)171, which was
purified by low-temperature column chromatography on alumina (deactivated with 5 % water) at -20°C. All manipulations during work-up have to be carried out below - 10°C
in order to avoid contamination with naphthalene. The structure of ( I ) was established by a combination of elemental
analysisL71,UV and NMR spectroscopy: The UV spectrum
of ? I ) [h,,,,, (cyclohexane)=217 nm (log ~=4.07),256 (4.07),
295 sh (2.96), 345 nm (broad, weak) (2.55)] is closely similar
to those reported for the substituted l-benzothiepins‘2a1.The
NMR spectrum [lo0 MHz (CDCI,), TMS int., -20°C:
6=5.90 (2-H), 6 . 3 U . 5 6 (3-H, 4-H), and 7.09 (5-H), 7.15-7.5
(aromat. H)] was assigned on the basis of relative chemical
shifts, shielding of 2-H being larger than that of 3-HL2”].[3,4D,]-I-Benzothiepin ( I a ) , obtained from ( 2 ~ ) [ exhibited
~~],
in addition to the multiplet of the four aromatic protons
(6 = 7.05-7.4), two equally intense broad singlets (1 H) at
F = 5.85 and 7.00.
Chemical proof of the structure of ( I ) was gained by catalytic
hydrogenation in ethanol over a large amount of palladium-charcoal. This reduction yielded 2,3,4,5-tetrahydro-lbenzothiepin, which was identical with an authentic sample[*].
Warming of (1) in carbon tetrachloride leads to formation
of naphthalene and sulfur with a (NMR spectroscopically
determined) half-life of transformation of 80 min at 40°C.
Treatment of ( I ) with m-chloroperbenzoic acid in CH2Clz
at - 2 0 T afforded I-benzothiepin-1,l-dioxide
in 87% yield,
m. p. 138--139°C ([S]: 140-141 T ) . NMR, 6=6.6-7.1 (m,
3H), 7.4-7.9 (m. 4 H ) and 8.1-8.4 (m, 1 H). Irradiation of
( I ) in T H F (450-W high-pressure mercury arc lamp, pyrex
filter, 4 h at 0 ’C) yielded the known valence isomer (3)r5‘]
along with a small amount of naphthalene. (3) is also formed
from ( 2 ) by irradiation or by AgC104
Far less attention has been paid to allene dimerizations proceeding with substituent participation, such as the formation
of dehydroacetic acid from allenecarboxylic acidL2]or the
dimerization of triphenylchloroallenes to give derivatives of
rubreneL3! The present communication reports the dimerization of the diethoxyvinylidene-tetrahydrofuranones( 1 a ) and
-cyclopentanones ( I h ) affording the tetracyclic compounds
( 2 a ) and ( 2 b ) respectively, which resembles the dimerization
of triphenylchloroallenes mentioned above.
(la), x
(fh),
= 0
x = CH2
K
=
C2Hs
(2L7), X = 0
l2b), X
7
CFiz
The allenes (1) can be described in terms of the resonance
structures A and B. It is assumed that 1 &dipolar cycloaddition
of the cx$-unsaturated keto system of one allene molecule
to the ketene acetalic double bond of another leads initially
to the cisoid 2,2-diethoxypyran intermediate (3). This intermediate then undergoes an electrocyclic reaction analogous to
hexatriene-cyclohexadieneisomerization to give the dimer (2)
whose structure follows unequivocally from the spectroscopic
data listed in Table 1.
Received: November 27, 1973 [Z 966 IE]
German version: Angew. Chem. 86, 161 (1974)
[ I ] L. A. Paqurrte in J . P. Snyder Nonbenzenoid Aromatics. Academic
Press, New York 1969, Vol. 1 , Ch. 5.
[2] a) H . Hofmann, B. Meyer, and P. Hofmann, Angew. Chem 84. 477
(1972): Angew. Chem. internat. Edit. 11, 423 (1972); b) H. Hofmann and
H. Wrstrrnachrr, Chem. Ber. 102, 205 (1969); c) D. N . Reinhoudt and C.
G. Kouwmhooen, J. C S. Chem. Comm. 1972, 1232; d ) V. J . Troynefis in
A . Weissbrrger and E. C. Tapfor;The Chemistry of Heterocyclic Compounds.
Wiley-Interscience, New York 1972, Vol. 26, Ch. I I.
[3] !l J . Traynrlis and J . R. Lirmyston, Jr., J. Org. Chem. 29, 1092 (1964).
[4] V. J . Trayneiis and Z Yoshikawa, Abstracts, 164th National Meeting
of the American Chemical Society, New York, N. Y., 1972, No. ORGN-56.
151 a ) I . Murara and K . Nakasuji, Tetrahedron Lett. 1973, 43; b) ibid. 1973,
1591: c)
Murara, K . Nakasuji. and H. Kurnr, ibid. 1973, 3401, 3405; d )
I . Murato, 71 Tarsuoka, and Y Sugihara, ibid. 1973, 4261: e) ibid., in the
press.
161 For a review see: D J . Cardin, B. Crfinskaya, M . J . Doyle. and M
F . Lupperr. Chem. SOC.Rev. 2. 99 (1973).
[7] Satisfactory C, H analytical values were obtained for ( I J.
In boiling glacial acetic acid the diethoxypyrans ( 2 ) are converted almost quantitatively into the fused x-pyrones ( 4 ) .
[ 8 ] V. J . Truynelis and R. f.L o w , J. Org. Chem. 26, 2728 (L961), M! E.
Trircr and J . P. Milionis, J. Amer. Chem. SOC.74, 974 (1952).
Dimerization of “Push-Pull” Substituted Allenes
By Rolf W Saalfmnk[*l
The dirnerization of allenes in a [2 + 2]cycloadditionL’]leading
to 1,2-bis(methylene)cyclobutane derivatives is well known.
[*] Dr. R. W. Saalfrank
lnstitut fur Organische Chemie der Universitat
Erlangen-Numberg
852 Erlangen, Henkestrasse 42
Angew. Chem. intrrnar. Edit. 1 Vof. 13 ( 1 9 7 4 )
No. 2
These strongly fluorescing substances exhibit powerful emission on excitation of their saturated methylene chloride solutions by a nitrogen laser. Owing to their remarkable stability
they are particularly suited for use as laser dyes. The following
spectroscopic data not listed in Table 1 were obtained for
compounds ( 4 a ) and ( 4 6 ) : UV spectrum (CzHsOH):
A, =410nm ( E = 10500) and 420nm (12100) respectively; dye
143
Table I. Data of the compounds ( 2 a ) . ( Z b ) , f 4 a ) . ( 4 6 ) , ( S a ) , and ( 5 6 ) [ S ] .
i0/.I
r Cl
IR (KBr)
[cm-I]
(2a)
(26)
48 [a]
45 [a]
140
144
1634
1621
(40)
(46)
96
93
65
63
291 [b]
252 [b]
1730, 1608
1727, 1590
1773, 1704
1764, 1695
Cpd.
(50)
(56)
Yield
M. p.
215
179
'H-NMR (60 MHz,
T
values, TMS internal, in CDC13)
8.91 (I2H. t); 8.55 (12H, s). 8.25 (12H, s); 6.33 (8H. q)[c]
8.85 (12H, t); 8.84 (12H, s): 8.70 (12H. s): 8.35 (4H, s); 642
l8H, 4)
8.55 (12H. s); 8.34 (12H. s)
8.73 (12H. s); 8.55 (12H. s); 8.09 (4H, s)
8.81 (12H, s ) . 8.71 (6H, s); 8.68 (6H, s); 7.06 (2H, s) [c]
8.85 (24H, s); 8.25 (4H, s): 6.54 (2H. s)
[a] Based on the amount of 2,2-diethoxyvinylphosphonium salt.
[b] Slow sublimation above about 200' C.
[c] In C6D6.
laser emission spectrum (CH,Cl,): h,,, laser -485 and 510 nm,
and 495 and 515 nm respectively[6!
Reduction of the x-pyrones (4) with zinc in glacial acetic
acid gives the fused lactones (5) in good yieldst''.
ESR Spectrum of a Perpendicular Benzyl Radical"]
By Kurt Schreiner and Armin Berndt"]
In the same way as the planar benzyl radical constitutes a
textbook example for K-K delocalization or conjugation, the
perpendicular benzyl radical ( I a ) represents a prototype for
4,4,9,9-Tetraethoxy-1,1,3,3,6,6,8,8-octamethyl-1,3,4,6,8,9-hexaK-CJ delocalization or hyperconjugation, whose significance
hydro-2,5,7,10- tetraoxaindeno [S,l-e]indene
(2 a)
and
in chemistry has recently received increasing recognition'''.
-1,2,3,4,6,7,8,9-octahydro-S,l0-dioxaindeno[5,4-e]indene(2 b)
INDO calculationst3. on ( I a ) predict ESR coupling constants of considerable magnitude for the ortho C atoms
A benzene solution of 2,2,5,5-tetramethyltetrahydrofuran-3,4dione (5.5 g, 35 mmol) or 3,3,5,5-tetramethyl- 1,2-cyclopentane(1 7.05 G), ortho H atoms (1.97 G), and meta H atoms (2.78G)
dione (5.4g, 35mmol) is rapidly added dropwise to a stirred,
which arise almost exclusively from K-CJ delocalization since
cooled benzene solution of 2,2-diethoxyvinylidenetriphenylthe minimal K spin densities at the ring C atoms would lead
only to coupling constants of 0.5, 0.3, and 0.2G by spin
phosphorane[l"] prepared from 2,2-diethoxyvinyltriphenylpolarization.
phosphonium tetrafluoroborate (1 8.0 g, 40 mmol). The solvent
is drawn off at room temperature, the resinous residue extracted several times with light petroleum, and triphenylphosphane
oxide is filtered off. After removal of the light petroleum
and subsequent bulb distillation (ca. 11OoC/0.5torr), 2-(2,2-diethoxyvinylidene)-3,3,5,5-tetramethylcyclopentanone ( I bj
(5.1 g, 20mmol) is obtained which undergoes almost complete
Experimental checks of the INDO results have hitherto been
dimerization to (2b) on prolonged heating at about 140limited to model r a d i c a l ~ [ ~ having
-~]
relatively small spin
160°C. 4-(2,2-Diethoxyvinylidene)-2,2,5,5-tetramethyltetrahydensities at the exocyclic K center and angles of twist of
drofuran-3-one ( I a) cannot be isolated under the above experonly about 60".
imental conditions and (Za) is obtained directly on removal
The 1,l -di-tert-butylbenzyl radical ( 1 b) represents the first
of the light petroleum. The dimers (2) can be recrystallized
benzyl radical twisted through 90". We prepared it by reaction
from ether.
of the oxalic diester''] of 1,l -di-tert-butylbenzyl alcohol with
potassium/sodium alloy in benzene. Since ( I b) is stable for
I ,I ,3,3,6,6,8,8-0ctamethyl- 1,3,6,8-tetrahydro-2,5,7,lO-tetraoxa- several days at room temperature under the conditions of
its preparation, it can be generated in concentrations high
indeno[5,4-e]indene-4,9-dione ( 4 aj and -1,2,3,6,7,8-hexahydroenough to determine coupling constants of 13C in naturajt
5,10-dioxaindeno[5,4-e]indene-4,9-dione(4b j
isotopic abundance. These coupling constants together with
( 2 a ) or (2b) ( 5 mmol) is refluxed in glacial acetic acid (20ml)
the g factor of 2.0024 provide proof of the structure and
for 30min. After cooling and filtration, the greenish yellow,
the stereochemistry of the radical ( I b).
strongly fluorescing crystals of (4a) or (4b) are washed with
The following coupling constants can be deduced from the
methanol.
ESR spectrum shown in Figure 1;aH=0.47 G for 18 equivalent
Received: December 3, 1973 [Z 967 I€]
protons (2 tBu). a" = 0.31 G (1 H, i. e. para proton), and a" = 0.82
German version: Angew. Chem. 86,162 (1974)
and aH=0.91G for two sets of two equivalent protons (ortho
and meta). An ESR spectrum recorded at higher concentration
[ I ] a) H . J. Brstmann, R . W Saalfrank, and J . P. Snyder, Chem. Ber. 106,
2601 (1973); b) 0.J . Muscio Jr. and 7: L. Jacobs, Tetrahedron Lett. 1969,
and amplification reveals 3C coupling constants of 45 (1 C),
2867; c) 7: L. Jacobs and 0.J . Muscio Jr., ibid. 1970, 4829; d) E . V. Dehmlow
18.2 (2C), and 11.7G (7C). We assign the largest constant
and G . C . Ezimora, ibid. 1972, 1265.
to C' since it shows excellent agreement with aC=45.2GrsJ
[2] G. Eglinton, E. R . H . Jones, G. H . Mansfidd, and M . C . Whiting, J.
of the central C atom of the tert-butyl radical. a'= 18.2G
Chem. Soc. 1954, 3197.
(2C) lies in the range expected for the ortho C atoms of
[3] P. D. Landor and S. R . Landor, J. Chem. SOC.1963, 2707.
a highly twisted benzyl radical from the known relationship
[4] R . W Saalfrank, Tetrahedron Lett. 1973, 3985.
ac=19 p , c 0 s ~ 8 ~ ~
The
] . assignment of ac=11.7 G to the six C
[ 5 ] All compoundsgavecorrect valueson C,H analysis. The expected molecuatoms of the methyl groups of the teut-butyl substituents
lar peak was observed in the mass spectra.
follows from a comparison with the I3C coupling constants
[6] I am grateful to Prof. Dr. F. P. Schafer, Gottingen, for recording the
dye laser emlssion spectrum. See also D. Basting, F. P. Schafrr, and B.
Steyrr, Appl. Phys. 3.81 (1974).
[7] Determination of the stereochemistry of the lactones (5) by X-ray crystal
structure analysis is still in progress.
144
[*] Prof. Dr. A. Berndt and Dip].-Chem. K . Schreiner
Fachbereich Chemie der Universitat
355 Marburg, Lahnberge (Germany)
Angew. Chem. internal. Edit.
1 Val. 13 (1974) 1 No. 2
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