J. Chem. Research (S), 1997, 70–71 J. Chem. Research (M), 1997, 0501–0508 Attempted Synthesis of Cyclopenta-1,2-diene and Wurtz-like Condensation Products in the Reaction of 2,3-Dibromocycloalkenes with Zinc Mustafa Ceylan,*a Hasan Se6cenb and Ya6sar S�utbeyazb aDepartment of Chemistry, Faculty of Science, Gaziosmanpa6sa University, 60110 Tokat, Turkey bDepartment of Chemistry, Faculty of Science, Atat�urk University, 25240 Erzurum, Turkey Fluoride ion-promoted elimination of 2-bromo-3-trimethylsilylcyclopentene 5 and the reaction of five-, six- and sevenmembered 2,3-dibromocycloalkenes with zinc gave Wurtz-like dimeric products instead of the expected cyclic allenes.Allenes are an important class of unsaturated hydrocarbons which contain two cumulative orthogonal double bonds. In cyclic allenes, ring constraints bend and twist the normally linear, perpendicular allene and result in substantial strain and kinetic reactivity.1 Recently, we reported the synthesis of an allene unit in six- and seven-membered rings by fluoride ion-promoted elimination of a b-halogenosilane.4 In this paper, we applied fluoride ion-promoted elimination of halogenosilane to 5 and zinc catalysed elimination to 4 to synthesise the highly strained cyclic allene cyclopenta-1,2-diene 8.In addition, we applied zinc catalysed elimination to 12 and 13. To synthesise 5, cyclopent-2-enone 1 as starting material was used. Addition of bromine and triethylamine to 1 followed by reduction of 2 with NaBH4 afforded the bromoalcohol 3.Substitution of 3 with PBr3 gave dibromoalkene 4. To convert 4 to 5, a published procedure was used.4 In this reaction, 6 and 7 were also obtained in a combined yield of 13%. When the same reaction was carried out at µ70 °C, the yield of 6 and 7 increased to 55% (Scheme 1). Treatment of 5 with tetrabutylammonium fluoride (Bu4NF) and KF under different conditions resulted in the formation of two isomeric Wurtz-like condensation products 6 and 7 in a combined yield of 48–50% (Scheme 2).Treatment of 4 with activated zinc in DMSO at 85 °C gave 6 and 7 in a combined yield of 58% (Scheme 3). The structures of 6 and 7 were determined on the basis of 1H and 13C NMR spectral data. The identical product distribution from the three different reactions, implies a common intermediate 11. 12 and 13 were synthesised according to literature procedures.4,6 Treatment of 12 and 13 with activated zinc in THF at 65 °C resulted in the formation of two isomeric Wurtz-like condensation products 18,19 (combined yield, 73%) and 20,21 (combined yield, 68%), respectively.The same condensation products 18, 19, 20, 21 were also obtained in the synthesis of silyl compounds 167 and 174 from 70 J. CHEM. RESEARCH (S), 1997 *To receive any correspondence. Scheme 1 Scheme 2 Reagents and conditions: i, Bu4NF, DMSO, 85 °C; ii, Bu4NF, toluene, 110 °C; iii, KF, AgNO3, HMPA, 110 °C; iv, Bu4NF, THF, DBI, 65 °C; v, Bu4NF, toluene, DBI, 110 °Cdibromides 12 and 13 and the mesylate compound 22 which was synthesised by a literature procedure.3a,8 Treatment of 12 and 13 with trimethylsilylcopper (CuSiMe3) gave the silyl compounds 16 (54%) and 17 (20%) and the condensation products 18,19 (combined yield, 10%) and 20,21 (combined yield, 28%), respectively.In addition, treatment of 22 with trimethylsilylcopper at µ40 °C also gave 17 (6%) and 20,21 (combined yield, 35%).In contrast, reaction of 16 and 17 with Bu4NF had resulted in the formation of 14 and 15 in good yield4 (Scheme 5). We are indebted to the Atat�urk University for financial support of this work (Project No: 1991/4) and the State Planning Organization of Turkey (DPT) for purchasing a 200 MHz NMR. Techniques used: 1H and 13C NMR, IR spectrometry References: 8 Schemes: 5 Received, 8th August 1996; Accepted, 11th November 1996 Paper E/6/05543E References cited in this synopsis 1 R. P. Johnson, Chem. Rev., 1989, 89, 1111; H. F. Schuster and G. M. Coppola, Allenes in Organic Synthesis, Wiley, New York, 1984. 3 (a) M. Balci and W. M. Jones, J. Am. Chem. Soc., 1980, 102, 7607. 4 Y. S�utbeyaz, M. Ceylan and H. Seçen, J. Chem. Res., 1993, (S) 293; (M) 2189. 6 J. Sonnenberg and S. Winstein, J. Org. Chem., 1962, 27, 748. 7 S. E. Denmark and C. Klix, Tetrahedron, 1988, 44, 4043. 8 Leo A. Paquette and A. Leone-Bay, J. Am. Chem. Soc., 1983, 105, 7352. J. CHEM. RESEARCH (S), 1997 71 Scheme 3