TETRAHEDRON LETTERS Tetrahedron Letters 42 (2001) 3515–3518 Pergamon anti -Selective Heck-type cyclotrimerization of polycyclic bromoalkenes Sergio Cossu,* Ottorino De Lucchi,* Antonio Paulon, Paola Peluso and Cristiano Zonta Dipartimento di Chimica, Universita ` Ca’ Foscari di Venezia, Dorsoduro 2137, I -30123 Venice, Italy Received 19 February 2001; revised 5 March 2001; accepted 21 March 2001 Abstract—Vinyl halides can react as both substrate and reagent in the Heck reaction. In the case of bicyclic vinyl halides, the reaction leads to cyclotrimers through an anti -selective process. © 2001 Elsevier Science Ltd. All rights reserved. The addition reaction between a bromoalkene or bro- moarene and an olefin in the presence of a palladium catalyst is referred to as the Heck reaction. 1 Since its discovery, the Heck reaction has been extensively exploited because of its synthetic potential and recent studies have shown that besides the traditional reagents, it is also possible with a large variety of haloalkenes or triflates and that the addition occurs even on unactivated olefins. 2 For the sake of discussion in this work, it is important to point out three features of the mechanism of Scheme 1: (i) the syn -addition to the olefin [step (B)], (ii) the syn -coplanar -hydride elimination from the palladium -complex 2 [step (C)], and (iii) the need of the base to regenerate the active Pd(0) catalyst [step (D)]. Under these circumstances, one may expect that a bromoalkene may also react with itself, i.e. a bro- moalkene may act both as the addend and the receiving olefin, as shown in Scheme 1. If this is indeed the case, at the stage of the palladium complex 2 the reaction may bias either towards -hydride elimination or ‘standard’ base-induced E 2 elimination of HBr. Scheme 1. Keywords : aromaticity; cross-coupling; cyclotrimerization; Heck reaction; palladium. * Corresponding authors. Tel.: 39 041-2578647; fax: 39 041-2578517 (S.C.); tel.: 39 041-2578546; fax: 39 041-2578517 (O.D.L.); e-mail: cossu@unive.it; delucchi@unive.it 0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved. PII:S0040-4039(01)00495-6