Pergamon Tetrahedron 55 (1999) 4969--4978 TETRAHEDRON Halogen-Dependent Coupling Reaction of Alkynes with (Z)-3-Halopropenoates Catalyzed by Nickel Martin Kotora, Masanori Ishikawa, Fu-Yu Tsai and Tamotsu Takahashi* Catalysis Research Center and Graduate School of Pharmaceutical Sciences, Hokkaido University, Kita-ku, Sapporo 060 Japan Received 4 December 1998; accepted 23 February 1999 Abstract: Ni-catalyzed coupling reaction of alkynes with (Z)-3-halopropenoates depended on the halogen of halopropenoates. The reaction with (Z)-3-bromopropenoate afforded cyclopentadienes and the reactionwith (Z)-3-iodopropenoates gave pyrones. © 1999 ElsevierScienceLtd. All rights reserved. Introduction The formation of useful compounds from commercially available, simple starting materials is an important task of organic chemistry. One such example is cyclopentadienes that have wide application as ligands in transition metal chemistry. I Recently, we reported that the coupling reaction of two alkynes and (Z)-3- iodopropenoate through zirconacyclopentadiene intermediates afforded pentasubstituted cyclopentadienes.2 A critical limitation of our procedure is the use of a stoichiometric amount of zireonocene dichloride for each molecule of the formed cyclopentadiene. In order to develop a more economical procedure we investigated nickel-catalyzed 3 coupling reaction of alkynes and halopropenoates, giving pentasubstituted cyclopentadiene derivatives. During the course of our study, we found that the outcome of this nickel-catalyzed coupling reaction substantially depends on the halogen of halopropenoates. In this paper we report halogen-dependent catalytic reaction of alkynes with halopropenoates (Scheme 1), where (Z)-3-bromopropenoate afforded cyclopentadienes and (Z)-3-iodopropenoate gave pyrones. Scheme 1 R 0 R ~ C Brff':-~COO Et ,/~COOMe ,[~/O R OOEt " NiBr2(cat)/Zn R ~ R NiCI2(PPha)2(cat)/Zn" R R R 1 2 Results and discussion Formation of cyclopentadlenes. The most efficient method for the preparation of cyclopentadienes would be a catalytic coupling of alkynes. Trimerization of alkynes to cyclopentadienes in the presence of Pd4 and Ni 5 catalysts is well known. However, this process is hampered by the fact that the trimerization proceeds only with internal alkynes to give bexasubstituted cyclopentadienes, whereas it is desirable to gain access to penta- or less substituted ones. 0040-4020/9915 - see front matter © 1999 Elsevier Science Ltd. All rights reserved. Pll: S0040-4020(99)00182-9