by the asymmetry of the crystal field. The central atom lies 0.lA above the best plane through the atoms C2, C5 and C8, C11. The lines joining the atoms C2-C5 and C 8 - C 11 respectively are twisted through 1 '.

A B

Received: November 9,1970 [Z 349b IE] German version: Angew. Chem. 83,250 (1971)

Publication delayed at authors' request

[I] E. Koerner von Gustorf, J. Buchkremer, Z . Pfajier, and F.-W. Grecels, Angew. Chem. 83, 249 (1971); Angew. Chem. internat. Edit. 10,260 (1971). [2] See also. R . E . DaLia, G.L. Cupper, and H . D . Simpson, Amer. Crystallogr. Assoc. Summer Meeting, August 1970 Ottawa, Abstr. N4. [ 3 ] 0. S . Mills and G. Robinson, Acta Crystallogr. 16, 758 (1963); M . R. Churchill and R. Mason, Proc. Roy. SOC. (London) A 301, 433 (1967); R . Eiss, Inorg. Chem. 9, 1650 (1970).

Concerning the Existence of 1-Norbornene

By Reinhart Keese and Ernst-Peter Krebs"'

Bredt's rule categorically denies the possibility of a normal double bond at the bridgehead of the norbornane system"]. However, it remains an open question whether bicyclo- [2.2.l]hept-l-ene (8) with its highly strained double bond['] can be detectedL3], possibly as a metastable intermediate.

In the present communication we report the results of bis-dehalogenation of 1,2-dihalogenonorbornanes. The starting materials (3a)-(36) were prepared as shown in Scheme

Fragmentation of (2,JC6"] in cumene at 130°C gives 2-exo- brom~norbornane['~; this supports both the exo- configu- ration of (I)[81 and that of (3a) [NMR: 4.15 (0, J = 7.5, 3.5, 1.5; 1 H), 2.8-0.7 (ca. 9 H); mass spectrum: 302/300 (M+), 221 (M+-Br)lc91. The constitution and configura- tion of (36)'6b1 are apparent from its formation on thermolysis of (2) in bromotrichloromethane [NMR : 4.15 (0, J = 7.0,3.5,1.8; 1 H), 2.7-1.0 (ca. 9 H); mass spectrum: 256/254/252 (Mf) , 175/173 (M+-Br)].

The constitution of (3c) [NMR: 4.30 (0, J = 8.0,4.0, 1.5; 1 H), 2.8-1.0 (ca. 9 H); mass spectrum: 348 (M'), 221 (M+ - I)], which is formed almost quantitatively from ( S ) , is supported by (7)-obtained via (6) [NMR: 6.18 ( d , J = 5.5; 1 H), 5.88 (q, J = 5.5, 3.0; 1 H), 2.7-1.0 (7 H); mass spectrum 220 (M+), 192 (M+- C,H,)]-whose IR spec- trum is identical with that of I-iodonorbornane[' 21 pre- pared by conventional means ; the probable" 31 exo config- uration of ( 3 c ) remains to be confirmed.

The elimination of halogen from ( 3 a ) , which is induced by n-butyllithium and proceeds via lithium-iodine ex- change['41, gives, in the presence of furan, the isomeric adducts ( 9 a ) and ( 9 6 ) . Three saturated hydrocarbons of composition C,,H,, whose structures are unknown were isolated as by-products (see Scheme 2 and Table).

The furan adducts ( 9 a ) and ( 9 6 ) differ significantly in their NMR coupling constants. In (9b ) H, is exo to H, (.lax = 4.0 Hz), whereas H, in (9a) is endo to the proton at the ether bridge and consequently is not coupled with itri51.

Scheme 1

[*] Dr. R. Keese and E:P. Krebs, Dip].-Natw. ETH Organisch-chemisches Laboratorium der Eidg. Techn. Hochschule CH-8006 Zurich, Universitatsstrasse 6 (Switzerland

Ozonolysis and subsequent chromic acid oxidation of both isomers (9a ) and ( 9 6 ) affords the same 1,2-exo- norbornanedicarboxylic acid The constitution

262 Angew. Chem. internat. Edit. 1 Vol. I0 (1971) No. 4

(3~7). X = J, X’ = Rr (3h), X = X’ = Br ( 3 ~ ) . X = X’ = J

XI & RLi/Pentane/Furane T:-60 + + l o % 1

COOH C O O H

Scheme 2

Cpd. R-Li Furan adducts Hydrocarbons

R yield yield ratio [b] ( 9 4 + ( 9 6 ) 1 9 a ) : ( 9 b ) [a1 CI, H,,

(%) (7%

(30) n-Butyl 55 23: 77 18 37:12:51 n-Butyl [c] 56.5 22:78 40 44:14:42

sec-Butyl 18 25:75 63 49:14:37 n-Butyl -[d] 74 52:15:33

( 3 c ) n-Butyl [fl 62 20 : 80 19 53:10:37 sec-Butyl 28 23177 37 58:11:31

/ 3 b j sec-Butyl 16 22:78 - re1

[a] Gas chromatography area ratios. [b] Arranged in the order of increasing GLC retention times; area ratios. [c] After 84% conversion. [d] In diethyl ether. [el Mixture, not identified [q After 52% conversion.

of this acid is confirmed by independent synthesis starting from the Diels-Alder reaction between methyl cyclo- pentadienecarboxylate“ 71 and ally1 acetate.

All the trapping reactions so far carried out with furan give the same ratio of the adducts (9a) and (9b) (see Table). We regard this result as compelling evidence for the intermediacy of bicyclo[2.2.1 .]hept-I(2)-ene (8). The question whether the highly reactive intermediate (8) is susceptible to detection at all and whether it is a triplet or a singlet molecule warrants further study. Experiments to detect bicyclo[2.2.1.]hept-l(7)-ene are also currently in progress.

Received: December 2, 1970; [Z 350 IE]

German version: Angew. Chem. 83,254 (1971) revised: January 8, 1971

[l] J. Bredt, Liebigs Ann. Chem. 437, 1 (1924). [2] Bredt’s rule in the sense in which it is usually understood nowadays. [3] a) See, e.g., the following studies on larger bicycloalkane systems: P.D. Bartlert and L.H. Knox, J. Amer. Chem. SOC. 61, 3184 (1939); !? Prelog, P. Barmann, and M . Zimmermann, Helv. Chim. Acta 32,

1284 (1949); J.A. Marshall and H. Faubl, J. Amer. Chem. SOC. 92. 948 (1970); J.R. Wiseman and W A . Pletclier. ibid. 92, 962 (1970); b) J.A. Bersoii and M . R Wrilcotr, J. Org. Chem. 30, 3569 (1965). A consideration of the enthalpy of the transltion state and of the pre- exponential term led to the conclusion that: “anti-Bredt species [e .g . (S ) ] would be kinetically inaccessible by way of conventional olefin- forming reactions.” [4] The new compounds are racemic, pure according to GLC and/or NMR spectra, and gave correct elemental analyses; the NMR [6(ppm), TMS internal standard, J(Hz); CDCI, or CCI, as solvent] [5], mass (m/e), and IR spectra support the structures given; b) a detailed de- scription of the experiments mentioned in this communication is planned.

[5] We are grateful to Prof. W c. Philipsborn, Universitat Zurich. for recording some of the NMR spectra. [6] In collaboration with a) P. Biitzer (Diplomarbeit ETH, 1970) and b) J . Frank (Diplomarbeit ETH, 1969). [7] J . D. Roberts, E. R. Trumbull, W Bennet, and R. Armstrong, J. Amer Chem. SOC. 72, 3116 (1950). [8] W R . Boehme, J. Amer Chem. SOC. 81, 2762 (1959); H . Kwurt and G. Null , ihid. 81, 2765 (1959). [9] ( 3 a j is formed directly from ( l j on photolysis in a benzene solution of tert-butyl hypoiodite (E.-P. Krebs, Dlplomarbeit ETH, 1968); cf. D. H.R. Barton, H.P. Faro, E. P. Srrebryakoc. and N . F. Woolsey, J. Chem. SOC. 1965, 2438. [lo] P . D. Bortlett and J . M . McBride, J. Amer. Chem. SOC. 87, 1727 (1965). [I 11 D. H . R. Barton, R. E. O’Brien, and S . Sternhell, J. Chem. SOC. 1962, 270. In those cases of iodination of keto hydrazones by this method that have come to our knowledge no geminal diiodo products were obtained. [12] P. 7: Lansbury, I.: A. Pattison, J.D. Sidler, and J . B. Bieber, J. Amer. Chem. SOC. 88, 78 (1966). [13] a) Compare the isomerization of ( 4 ) and that of 2.2-dichloro- norbornane, which lead predominantly to ( 3 6 ) and 1,2-e.~o-dichloro- norbornane respectively [13 b]; b) A.J. Fry and W E . Farnhom, J. Org. Chem. 34,2314 (1969). [I41 In an elimination experiment, 73% (area of GLC signal) of n- butyl iodide was detected; the n-butyl iodide isolated was identified by comparison of IR spectra [6a]. [15] Cf. P. Laszlo and P.v.R. Schleyer, J. Amer. Chem. SOC. 86, 1171 (1964). [16] Melting point. mixed melting point, and IR spectrum. [I71 H . K . Wiese, US Pat 2781395 (1957); Chem. Abstr. 51, 13913 (1957); D. Peter, J. Chem. SOC. 1959, 1761.

A N e w Route to Derivatives of Bicyclof2.l.l]hexene and Tricyclo[3.1.0.02~6]hexane

By Wolfgang Kirmse and Friedrich Scheidt[’’

In conjunction with our work on bicycloalkyldiazonium ions“’ we have studied the decomposition of N-nitroso-N- exo-bicyclo[3.l.0]hex-2-en-6-ylurea (1). Compound ( 1 ) was prepared, analogously to the saturated compound“], from cyclopentadiene and ethyl diazoacetate. Alkaline cleavage of ( I ) with 2 mol. equiv. of sodium carbonate as base gave benzene as the sole product. Benzene is the product expected from deprotonation of the cyclohexa- dienyl cation (5) formed by a cyclopropyl-ally1 rear- rangement. However, the exo-diazonium ion (2) cannot be transformed into (S) in a concerted process (outward disrotation). We therefore assume that benzene formation is preceded by a base-catalyzed isomerization of the exo- diazonium ion (2) to the endo species (3) . This assumption is confirmed by the incorporation of deuterium in deu- terated solvents.

Under less strongly alkaline conditions, benzene is accompanied by substitution products (Table). In metha- nol the reaction yields exo-6-methoxybicyclo[3.1.0]hex-2-

[*] Prof. Dr. W. Kirmse and Dr. F. Scheidt Abteilung fur Chemie der Universitat Bochum 463 Bochum-Querenburg, Postfach 2148 (Germany)

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