J . Org. Chem. 1988,53, 152-161
152
of BH4-, strongly suggests the participation of 8. In-cage transfer of hydrogen at this stage can explain the lack of a primary isotope effect. Acrylonitrile quenches the borohydride reactions to a very small extent. It is likely that aryl radicals are formed when 7 fragments. In the case of 8, the caged radical pair may abstract a hydrogen from within the cage or diffuse into the solvent in the form of a radical. It is likely that acrylonitrile, which appears to be an inefficient quencher of the aryl radical generated from 1, has a lower rate of quenching than the rate of hydrogen transfer from the borohydride in 8 within the radical pair cage. Experimental Section General Procedures. Reagent grade acetonitrile (Baker Chemical Co.) was freshly distilled from phosphorus pentoxide, and its purity was greater than 99% by GLC analysis. Sodium borohydride and borodeuteride (Aldrich) were 99% and 98 atom %, respectively. General Procedure for Photolysis. Irradiations of 1 were carried out in a Rayonet merry-go-round reactor (The Southern New England Co.) equipped with eight 2537-A lamps. A steady stream of air was passed into the reactor to maintain a constant
temperature of 40 "C. The photolysis samples (1mL) were placed in quartz tubes (Ace Glass, 170 mm X 15 mm), each screwed to a nylon adapter bushing containg a Pyrex glass sliding stopper valve, and degassed through three or four freeze-pump-thaw cycles. The tubes were sealed under vacuum and irradiated a t 254 nm for 6 min. Quantum yields of products were determined by using the potassium ferrioxalate'* actinometer. Product Analysis. The photolysis mixtures were analyzed by GLC on a Varian 3300 capillary gas chromatograph equipped with an FID with a 30 m X 0.25 mm DB-225 capillary column (J & W Scientific Inc.) and a Varian 4290 integrator. The column was held a t 60 "C for 5 min and raised to 180 "C at a rate of 5 "C/min with an injection port temperature of 200 "C and detector temperature of 250 "C. Helium was used as carrier gas at 30 mL/min. The photoproducts were identified by comparing their retention times with those of commercially obtained authentic samples. The mass spectral analyses were carried out with a Finnigan 4023 mass spectrometer equipped with a Finnigan 9610 gas chromatograph. Dodecane was used as an internal standard in the determination of yields of products.
Acknowledgment. Support of this research by the National Instituite of Environmental Health Sciences (Grant ES00040) is gratefully acknowledged. Registry No. 1, 608-93-5; NaBH,, 16940-66-2.
Bicyclopropylidene: Cycloadditions onto a Unique Olefin A. de Meijere,*qt Ihsan Erden,t Walter Weber,+and Dieter Kaufmannt Institut fur Organische Chemie, Universitat Hamburg, 0-2000 Hamburg 13, West Germany, and S u n Francisco S t a t e University, Department of Chemistry, S a n Francisco, California 94132 Received M a y 11, 1987
Bicyclopropylidene (1) is capable of undergoing cycloadditions in a t least six different modes, depending on the nature of the cycloaddend. In analogy to its [2 21 cyclodimerization, 1 adds in a [2 21 and [2 41 fashion to 1,3-dienes,most probably via diradical intermediates to a large extent. A concerted mode of formation is likely for a t least fractions of the [2 41 cycloadducts 11, 14, 17, and 45 and the [2 + 21 cycloadducts 22 and 23 of chloroketenes. 1 readily undergoes cycloaddition to electron-deficient olefins, both with u- and a-electronwithdrawing groups, to give cyclobutane derivatives 18-20 and 24 via 1,4-diradical intermediates all retaining the two cyclopropyl groups of 1. Chlorosulfonyl isocyanate (CSI), N-phenyltriazolinedione (PTAD), and tetracyanoethylene (TCNE), all known for their propensity to form zwitterionic intermediates with electron-rich olefins, yield three types of products with 1 in different proportions. All three arise from the same type of initial 1,4-dipolar intermediates 25,29, and 36 and ring closure yields 27 and 35, while cyclopropyl to cyclobutyl ring enlargement and cyclopropylcarbinyl to homoallyl ring opening with subsequent closure lead to 32,40 and 31, 41 respectively. The products 33,51, and 59, obtained from 1 upon photooxidation and ozonolysis, can also best be rationalized by assuming zwitterionic intermediates. This body of results helps to constitute a plausible and general scheme for the classification of various [2a]-cycloaddends according to their preferred reaction modes.
+
+
+
+
Cross-conjugated polyenes, such as fulvene and fulvalenes, can partake in diverse modes of cycloadditions (i.e., [2 + 21, [4 + 21, [6 + 21, [8 + 21, [14 + 21, etc.), depending on the nature of the olefinic reaction ~ a r t n e r . l - ~ Normal monoalkenes, on the other hand, are confined to only two types of pericyclic reactions, namely, the [,2, + ,2J and [2 + 41 including the 1,3-dipolar cycloaddition^.^^^ Thermal cyclodimerizations of alkenes are rare, because the orbital symmetry conservation rules preclude a concerted [2, + 2,] reaction, and the [2, + 2,] transition state is energetically unfavorable; the relatively facile thermal cyclodimerizations of fluoroalkenes have been explained by a stepwise mechanism involving diradical intermediates which are stabilized by the fluoro substituent^.^^^ Methylenecyclopropanes and its 1,l-dihalo- and l-halo-substituted derivativesga as well as the cyclopropylidene-
'Universitat Hamburg.
* S a n Francisco State University. 0022-3263/88/1953-Ol52$01.50/0
acetatesgbbehave in an entirely analogous manner: they all give head to head dimers upon heating, and the 1,ldichloro derivative also cycloadds to 1,3-butadiene in a [2 + 21 mode. The role of the cyclopropane ring on the high propensity of methylenecyclopropanes to undergo cyclo(1)Dunn, L.C.; Chang, Y.-M.; Houk, K. N. J . Am. Chem. SOC.1976, 98,7095 and references cited therein. (2) Prinzbach, H. Pure Appl. Chem. 1971,28,281. (3)Erden, I.; Kaufmann, D. Tetrahedron Lett. 1981,215. (4)Woodward, R. B.; Hoffmann, R. The Conservation of Orbital Symmetry; Verlag Chemie: Weinheim, Germany, 1970. (5)Fleming, I. Grenzorbitale und Reaktionen organischer Verbindungen; Verlag Chemie: Weinheim, Germany, 1979. (6) Sharts, C. M.; Roberts, J. D. J . Am. Chem. SOC.1961,83, 871. (7)Sharts, C. M.; Roberts, J. D. Org. React. (N.Y.) 1962,12,1. (8)Binper, P. Angew. Chem. 1972,84,483;Angew. Chem., Int. Ed. Engl. 1972,11, 433. (9) (a) Dolbier, W. R., Jr.; Lomas, D.; Tarrant, P. J. Am. Chem. Soc. 1968,90,3594.Bottini, A. T.; Cabral, L. J. Tetrahedron 1978,34,3187; (b) de Meijere, A.; Wenck, H.; Seyed-Mahdavi, F.; Viehe, H. G.; Gallez, V.; Erden, I. Tetrahedron 1986,42,1291. Liese, Th.; Teichmann, S.; de Meijere, A. submitted for publication in Synthesis.
0 1988 American Chemical Society
J. Org. Chem., Vol. 53, NO.'^,
Bicyclopropylidene
1988 153
Scheme I
D=a
44
+1 -1
HOMO
1
Figure 1. Concerted [,2,
+1
3
+
Table I. Cycloadditions of Bicyclopropylidene (1) to 1,3-Dienes
4
reaction conditions
It
+
,2,] combination of two bicyclo2bl,(Walsh)] inpropylidene molecules with HOMO-[LUMO teraction.
diene
2'. "C
9
150 170 180
12
15
t. h 10 11 12
products (re1 yields, % ) 12 + 21 14 + 21 13 (78) 16 (92)
Based on GLPC-isolated amounts. consumed completely (50%).
+
dimerizations and thermal [2 21 cycloadditions is not fully understood as yet. In view of the considerable double bond character of the cyclopropane ring, as evidenced by its chemical behaviorlo and explained by the various theoretical models describing its bonding properties," it is probably more appropriate to draw parallels between methylenecyclopropanes and allenes, as the latter compounds likewise cyclodimerize readily.12 Bicyclopropylidene (l)13J4 is a unique olefin, combining the structural features of a tetrasubstituted ethylene and two methylenecyclopropane units. As unraveled by its He I photoelectron spectrum,15*1 has a much higher HOMO energy than methylenecyclopropane. As the length of its symmetrically substituted central bond is significantly shorter than a regular C(sp2)=C(sp2)double bondlsband the 13C,13Ccoupling constant is considerably larger,lsc bicyclopropylidene (1) conforms to the predictions based on the bonding properties in methylenecyclopropane. The central C(sp)=C(sp) bond in 1 should impart properties which more closely resemble those of the central double bond in butatriene than of that in a simple tetrasubstituted ethylene. In this full account16 we wish to report our observations that bicyclopropylidene (1) combines with numerous cycloaddendsin such a variety of cycloadditions which no other alkene has previously been capable of. (10) Cf.: de Meijere, A. Angew. Chem. 1979,91,867; Angew. Chem., Znt Ed. Engl. 1979, 18, 809 and references cited therein. (11) Walsh, A. D. Trans. Faraday SOC. 1949,45,179. Sugden, T. M. Nature (London) 1947,160,364. Schoeller, W. W. Tetrahedron 1973,29, 929. Forster, Th. 2. Phys. Chem. (Leipzig) 1939,58, 1343. Coulson, C. A.; Moffit, W. E. J. Chem. Phys. 1947,15,151; Philos. Mag. 1949,40,1. (12) Cf.: Murray, M. In Methoden der Organischen Chemie (Houben-Weyl);Thieme: Stuttgart; Vol. 5/2a, p 1067 ff and references cited therein. Hopf, H. In The Chemistry of the Allenes; Landor, S. R., Ed.; Academic: New York, 1982; p 525 ff. (13) Le Perchec, P.; Conia, J.-M. Tetrahedron Lett. 1970, 1587. Fitjer, L.; Conia, J.-M. Angew. Chem. 1973, 85, 345; Angew. Chem., Znt. Ed. Engl. 1973,12,332. Schmitt, A. H.; Schirmer, U.; Conia, J.-M. Chem. Ber. 1976, 109, 2588. (14) Weber, W.; de Meijere, A. Synth. Commun. 1986,16, 837. (15) (a) Gleiter, R.; Haider, R.; Conia, J.-M.; Barnier, J.-P.;de Meijere, A.; Weber, W. J . Chem. SOC., Chem. Commun. 1979,130. (b) Traetteberg, M.; Simon, A.; de Meijere, A. J . Mol. Struct. 1984, 118,333. (c) SeyedMahdavi, F.: Machinek, R.: Gleiter, R.: Flotow. A.: SDiekermann. M.: de Meijere, A., to be published. (16) (a) Cf. preliminary communications on cycloadditions of 1, with 1,3-dienes: Kaufmann, D.; de Meijere, A. Angew. Chem. 1973,85, 151; Angew. Chem., Int. Ed. Engl. 1973,12,159. (b) With electron-deficient cycloaddends: Weber, W.; Erden, I.; de Meijere, A. Angew. Chem. 1980, 92, 387; Angew. Chem., Int. Ed. Engl. 1980, 19, 387. (c) With singlet oxygen: Erden, I.; de Meijere, A.; Rousseau, G.; Conia, J.-M. Tetrahedron Lett. 1980, 2501. (d) With monoenes under nickel(0) catalysis: Kaufmann, D.; de Meijere, A. Chem. Ber. 1984, 117, 3134.
total yields,a %
11 (>97) 14 (22) 17 (8)
* In this reaction
16b
50 54 1 was not
Moreover, our results should contribute significantly to the growing body of experimental studies aimed at grouping cycloaddends according to their mode of cycloaddition.
Results Cycloadditions of Bicyclopropylidene to Olefinic Hydrocarbons. Le Perchec and Conia13 previously reported that 1 upon heating to 210 "C in a sealed tube, gives a 54.5:35:10.5 mixture of 6,8, and 1,respectively (Scheme I). A normal methylenecyclopropane rearrangement" after homolysis of the C2-C3 bond in 1 via the trimethylenemethane diradical3 easily accounts for methylenespiropentane 6. As to the cyclodimer 8, the authors ruled out a thermal concerted [2 + 21 reaction for being orbital symmetry forbidden. Instead, they held the combination of two vinyl radicals 4 to 7 responsible for the formation of [4]rotane (8). It appears unlikely, however, that the diradical7 would lead to 8 as the sole product, taking into account that three new rings have to be formed. If this cyclodimerization were to proceed stepwise, it is more probable that the diradical 4 would add onto 1 to form 5, unless it were a regular olefin dimerization via a l,Cdiradical, in this case 2. The latter would have to close only one ring, 5 in turn would have to close two rings to arrive at 8. An attractive alternative would be a thermally allowed concerted [,2, + ,2a + .2,] pericyclic reaction (see Figure 1). This description corrresponds to a concerted equivalent of the stepwise diradical pathway via the intermediate 5 (see Scheme I). 1 also undergoes cycloadditions with 1,3-dienes,and these showed an interesting dependence on the structure of the diene. Whereas cyclopentadiene (9) gave the [4 + 21 cycloadduct only, 1,3cyclohexadiene (12) and 1,3-butadiene (15) led to mixtures of the [4 + 21 and [2 + 21 cycloadducts, with the proportion of the [2 + 21 adduct increasing in this order (Table I). The products from each reaction were isolated by gas chromatographyand identified mainly on the basis of their 'H NMR spectra. The spectral data of 11 and 17 were identical with those of authentic materials prepared by independent syntheses.18-20 The observation that the overwhelming product from the cycloaddition of 1 to 1,3-butadiene (15) is 16 and the (17) Cf.: Gajewski, J. J. Hydrocarbon Thermal Z s o m e r & i & s ; ~ ~ a demic: New York, 1981, p 51 ff. (18) An authentic sample of 11 was prepared from the Diels-Alder adduct of ethylenetetracarboxylic dianhydride to cycl~pentadiene,'~ essentially following the procedure applied for 17.20 (19) Sauer, 3.; Schroder, B.; Mielert, A. Chem. Ber. 1967, 100, 315. (20) Magrill, D. S.; Altmann, J.; Ginsburg, D. Isr. J. Chem. 1969, 7, 479.
154 J. Org. Chem., Vol. 53, No. 1, 1988
c
de Meijere et al. Scheme I1
1
pN
lCH21n
9
" E l
1 2 n.2
Q 15
A
'"C N
10
" - 1
11
n = 1
13
" - 2
14
n = 2
-1 $ 4
16
^.
^.
19
20
+q 17
1
c=c=o
21
proportion of the [4 + 21 adduct increases in the order 15 < 12
