1874 ences are even more remarkable because the relative spread of the chemical shifts in the case of I3Cis larger than for 'H. The electron-deficient carbon 1 in ion 7a exhibits a chemical shift (6 -7.4 ppm from I C s 2 ) which is deshielded by 64.5 ppm from its position in the neutral hydrocarbon (see Figure 10). A tentative assignment of the carbon absorptions is shown below and is compared with the cmr chemical shifts found for toluenium ion 19, revealing that the unprotonated ring preserves much of its aromatic character.4" @,9
+6*,o@+46,6
00
+m.1
+606 +53.i*"',.4.
+70.9
7
'
+;
114.9
,
t40.6 '\+1508
+145.1
19
7a
The application of the Fourier-transform natural abundance carbon nmr spectroscopy to the investigation of carbocation intermediates thus proves very useful and promises to open up a new dimension in our ability to elucidate in detail structures of even quite complicated and large ions. Experimental Section Materials. All the organic compounds used in this study were commercially available in high purity. Antimony pentafluoride
(Allied Chemical) was triply distilled; fluorosulfuric acid was doubly distilled. Preparation of Ions. The solution of naphthalenium ion was prepared as reported previously in this series for protonations in superacid media and studied directly by nmr spectrometry. The quenching of solutions of naphthalenium ions and the analysis of recovered hydrocarbons (by glc and pmr) were also carried out as described. 4% Nuclear Magnetic Resonance Measurement. Spectra were obtained on Varian Associates Model A56/60A, HA100, and HR300 spectrometers. Fourier-transform spectra were recorded either with a Bruker HX-90 nmr spectrometer (22.63 MHz) or with a Varian HA-100 FT nmr spectrometer (25.16 MHz). With the Bruker instrument lgF was used for locking the system (either C12C===CF2for low-temperature or C6F6 for room-temperature measurements). With the Varian instrument, a 13C lock (13Cenriched CHJ) was used for both low- and high-temperature measurements. In both cases a broad band (2 KHz) noise generator was used for proton noise decoupling.
Acknowledgment. Support of our work by the National Science Foundation and the Petroleum Research Fund, administered by the American Chemical Society, is gratefully acknowledged. We express our thanks to Dr. Toni Keller and Mr. Werner Schittenhelm (Bruker Scientific, Inc.) for the opportunity to record some of the early carbon-13 spectra with their instrument. The assistance of Dr. LeRoy F. Johnson and Mr. Lewis Cary (Varian Associates, Palo Alto, California) in recording the 300-MHz pmr spectra is acknowledged.
Radical Anions of 1,8-Bis-Unsaturated Naphthalene Derivatives Stephen F. Nelsen* and John P. Gillespie
Contribution f r o m the Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706. Received July 13, 1972 Abstract: The synthesis of 7,8-dimethylenenaphtho[lf,8']bicyclo[3.2.0]hept-2-ene and its conversion into 2,3dimethyl- and 2,3-cyclobutapleiadiene are described. The epoxide derived from naphtho[l',8']bicyclo[3.2.0]-
hepta-2,5-diene and the related hydrocarbon give the peri-bridged 1,8-divinylnaphthalenesresulting from cyclobutane cleavage upon pyrolysis. The esr spectra of the radical anions from six pleidaiene derivatives, 1-oxo-4naphtho[l',8'lcycloocta-2,4,7-triene, and 1,8-divinylnaphthalene are reported and discussed. e report here the synthesis of some 1,8-bis-unsaturated derivatives of naphthalene, some limitations on the use of thermal cleavages of acenaphthene derivatives to prepare such compounds, and the esr spectra of several such radical anions. Experimental comparisons of the spin distributions of pleiadiene (l), the related enol ether 2, and 1,8-divinylnaphthalene
W
a& 1
2
radical anions were of particular interest, to see if simple MO calculations would be successful for predictive purposes and, if not, to see what spin distributions actually result.
Journal o j t h e American Chemical Society
95:6
Synthesis. Several derivatives of pleiadiene (1) were prepared using the method of Meinwald and coworkers, who employed the heavy-atom solvent enhanced photocycloaddition of maleic anhydride to acenaphthylene to give 3a after work-up, lead tetraacetate decarboxylation to 4a, and pyrolytic cyclobutene ring opening to give l a . Starting the sequence with 3,6-di-tert-butylacenaphthenegave IC, and preparation of 3b by base-catalyzed exchange (KOD-DzO, 150") on 3a gave l b after completion of the sequence. We were unable to repeat the reported' 28% yields in the bis-decarboxylations and observed serious fallingoff of the yield in runs at a larger scale than 4 g. Attempts to improve conditions showed that saturation of the reaction mixtures with oxygen2 shortened the (1) J. Meinwald, G. E. Samuelson, and M. Ikeda, J . Amer. Chem. SOC.,92, 7604 (1970).
/ March 21, 1973
(2) C . M. Cimarsturi and J. Wolinsky, ibid., 90, 113 (1968).
1875 HO,C
R'
R'
R' 1
3
a, R = R ' = H b, R = D; R' = H c, R = H; R' = tert-butyl
R'
R' 4
reaction time from 2 hr to 5 min, facilitating sequential runs of small scale reactions to build up material. We also prepared two 2,3-dialkylpleiadienes starting from cyclobutanedicarboxylate 3a. Diazomethane esterification (giving 5 ) , lithium aluminum hydride reduction (to 6), mesylation (to 7), and reaction with potassium iodide in HMPA gave the bis-iodide 8, which was dehydrohalogenated to the dimethylenecyclobutane 9 in 91 yield using potassium tertbutoxide in T H F . Reduction of 9 to 11 was accomplished by addition of bromine and cleavage of the dibromide 10 with lithium aluminum hydride. Thermal opening of 11 to 12 was accomplished by subliming and sweeping 11 through a heated column (hereafter referred to as "pyrolysis"). Although 4a was completely converted to l a during one pass at a column temperature of 350", three passes at 380" were required to give a 93 :7 mixture of 12 :11 (by nmr). 9 is a very labile compound, polymerizing rapidly at room temperature in concentrated solution. It is not sublimable but was successfully pyrolyzed by injection as a benzene solution into the heated flask normally used for sublimation. Pyrolysis of 9 gave 2,3-cyclobutapleiadiene (13). This rearrangement is formally analogous ~
RCg
~
although in our case the extra ring should prohibit the preferred conrotatory ring opening3c and also not allow the intermediacy of a perpendicular bisallyl radical. At 515", only a 60 :40 mixture of 9 :13 was observed after the first pass, and an 88 :12 mixture after two passes; a third pass still gave the same product ratio. Unfortunately, we did not succeed in separating the residual 9 from 13, and were unable to establish whether the observed mixture was really an equilibrium mixture, as seems likely. We also investigated the possibility of generating 1,8-divinylnaphthalene derivatives by thermal cleavage of derivatives of cyclobutane 14. Most cyclobutane cleavages appear to be nonconcerted reactions which proceed through diradical intermediate^,^ although Baldwin and Ford; have suggested that about 30% of the decomposition of 7,8-cis-exo-dideuteriobicyclo[4.2.0]octane occurred ciu a concerted mechanism. Bicyclo[3.2.0]heptane itself thermally cleaves both to 1,6-heptadiene and to ethylene and cyclopentene, although the latter process has about a 3.3 kcal/mol lower activation energy.6 Of the three types of cyclobutane bonds in 14, cleavage of the 1-2 bond might be predicted to lead to the stablest diradical, since both radical centers formed would be benzylic. Cleavage of the 1-2 bond is, however, very poor stereoelectronically, since this bond is in the nodal plane of the aromatic rings in 14, and overlap giving benzylic resonance would be very low until far along the reaction coordinate for bond cleavage. In contrast 1,4 cleavage leads to benzylic stabilization at one center, which is available at an early stage on the reaction coordinate. Pyrolysis of 14 gave no detectable amount of 1,8-divinylnaphthalene (18) or its pyrolysis product^,^ but acenaphthalene (19) was formed, demonstrating that 1,4 cleav-
&+&' 16
14
00 5, R = C02Me 6,R = CHzOH 7, R = CH~OMS
\
00 9
18
10,R = Br 11, R = H 17
8,R=CHzI
19
age is in fact strongly preferred over 1,2 or 3,4 cleavage. Fusion of a small ring on the 3,4 positions of 14 was expected to facilitate divinylnaphthalene derivative formation, both because of raising the activation energy for 1-4 bond cleavage, and because 3,4 cleavage would be enhanced by ring strain. Treatment of 4a with m-chloroperbenzoic acid gave the epoxide 20,
H3CxcH3 A 12
13
to the isomerization of 1,2-bis(methylene)cyclobutane, which is only detectable through the use of label^,^ (3) (a) W. {'on E. Doering and W. R. Dolbier, Jr., ibid., 89, 4534 (1967); (b) J. J. Gajewski and C. N. Shih, ;bid.,89, 4532 (1967); (c) ibid., 94, 1675 (1972).
(4) (a) T. A. Bancock, ibid., 91, 1967 (1969); (b) A. T. Cocks and H. M. Frey, J . Chem. SOC.A , 1671 (1969); ( c ) A. T. Cocks, H. M. Frey. and I. D. R. Stevens, J . Chem. Soc. D,458 (1969). ( 5 ) J. E. BaIdwin and P. W. Ford, J. Amer. Chem. Soc., 91, 7192 (1969). (6) R. J. Ellis and H. M. Frey, J . Chem. Soc., 4164 (1964). (7) S. F. Nelsen and J. P. Gillespie, J . Amer. Chem. Soc., 94, 6237 (1972).
Nelsen, Gillespie / Radical Anions of 1,8-Bis- Unsaturated Naphthalenes
1876
which pyrolyzed at 400" to give a J 3 z yield of the divinyl ether derivative 2. No acenaphthalene was observed. The carbon analog 21 proved to be more difficult to prepare. Addition of diazomethane to the cyclobutene 3a was remarkably sluggish, but stirring with ethereal diazomethane for over 2 weeks did give the 1,3-dipolar adduct 22. Although photolysis in
21
20
22
cyclohexane gave a reasonable yield of 21 on a 50-mg scale, the yield plunged upon attempted scale-up, and an alternate route to 21 was sought. We were unable to obtain any methylene addition under ordinary Simmons-Smith conditions8 or using the diazomethanezinc iodide modifi~ation,~ but reaction with diethylzinc-methylene iodide lo was more successful, although complete removal of side products involving addition of methylene to the naphthalene ring was not accomplished. Pyrolysis of bicyclo[2.1 .O]pentane gives almost exclusively the hydrogen shift product derived from the diradical intermediate, although a 0.4% yield of 1,4-pentadiene has been observed. l 1 In contrast, pyrolysis of the bicyclo[2.1 .O]pentane derivative 21 gave an 80% yield of 23. We have not established that the hydrogen shift product 24 is not an inter-
L 2 5 - I
26
in DMSO, using tetrabutylammonium perchlorate as the electrolyte and electrolytic generation. Low temperatures proved to be necessary for the other species studied, and were obtained by sodium-potassium alloy reduction in THF, at -50 to -80". Since l a gave identical splittings to within h0.02 G in DMSO at room temperature, in butyronitrile at -40°, and in D M E at -8O", we believe solvent and temperature effects are negligible for these ions and will make direct comparisons of the splittings obtained. We usually were able to work at high enough temperatures to exchange out important variable line-width effects, such as have been seen with 1,8-dialkylnaphthalenes.l 4 Our esr data are summarized in Table I, using the posiTable I. Esr Splitting Constants (G) for 1,8-Unsaturated Naphthalene Derivatives& Line Compd widthb la.1b.IC.12.13.2.2-d2.-
70 70 70 110 3004 50 40
m
p
1.93 1.93 1.89 1.83 1.68 5.66 5.64
0
0.23 0.17
0.80 0.77 0.87 0.66 0.61 3.75 3.74
0.18 unobsd 0.09$
O.Ogd
.
y
P
6.29 2.62 6.27 6.48 2.62 5.92 6.15 0.24$ 2.48 0.24d
Other 0 . 4 0 (2 D) 2.23(6H) 6.78 (4 H) 0.39 (2 D)
Line width (mG) used *All 2 H triplets except where noted. in simulations (Lorentzian shape), c Some viscosity broadening is probably observed at the -80" temperature necessary for enough stability to allow recording to spectra; this apparently obscured the tiny meta splitting. Arbitrary assignment.
23
24
tional references shown on structure 27. We were
mediate, although we doubt that 24 would completely rearrange to 23 under our reaction conditions, and suggest that cleavage of the 1,4 diradical initially formed might be expected to be substantially more rapid for 21 than for the unsubstituted case. The mass spectral cracking patterns of 14, 20, and 21 show a parallel to the observed thermal chemistry. l 2 Meinwald and Young13 have shown that the base peak in the mass spectrum of 14 appears at mje 152, which is assigned to acenaphthylene cation 25. In contrast, epoxide 21 and its diene isomer 2 show nearly identical spectra, mje 194 (P, 1 2 7 3 , 165 (27, 100%). The case is somewhat less clear-cut for 21, for both types of cleavage are important: mje 192 (P, SO%), 191 (P - 1, loox), 165(27,85%), 152(26,30%). Radical Anions. We studied the esr spectra of the radical anions of l a , lb, and IC at room temperature (8) L. Fieser and M. Fieser, "Reagents for Organic Synthesis," Vol. I, Wiley, New York, N. Y . , 1968, p 1019. (9) G. Wittig and I
