Pergamon Tetrahedron Letters 41 (2000) 161–163 TETRAHEDRON LETTERS Stereoselective addition of sodium organyl chalcogenolates to alkynylphosphonates: synthesis of diethyl 2-(organyl)-2-(organochalcogenyl)vinylphosphonates Antonio L. Braga, * Elenilson F. Alves, Claudio C. Silveira and Leandro H. de Andrade Departamento de Química, Universidade Federal de Santa Maria, 97105-900, Santa Maria, RS, Brazil Received 30 July 1999; revised 20 October 1999; accepted 21 October 1999 Abstract Organyl thiolate, selenolate or tellurolate anions reacted with alkynylphosphonates 1 to give diethyl 2-(organyl)- 2-(organochalcogenyl)vinylphosphonates [β-organochalcogenyl vinylphosphonates] 2 in satisfactory yields. The reaction was stereoselective, giving predominantly or exclusively the (Z)-stereoisomer. © 1999 Elsevier Science Ltd. All rights reserved. In the last few decades, there has been remarkable interest in the synthesis of vinylic chalcoge- nides and their synthetic applications. 1a Diethyl 2-(organyl)-2-(organochalcogenyl)vinylphosphonates [β-organochalcogenyl vinylphosphonates] 2 are intermediates of great synthetic potential since they combine the well-known chemical reactivity of vinylic chalcogenides 1a and vinylic phosphonates. 1b The selenium derivatives were recently prepared by Pd-mediated stereoselective selenophosphorylation of alkynes. 2 Hydrometallation of acetylenes is a widely used method for the synthesis of vinylic metal and metalloid derivatives. 1a In this communication we describe a new, general and stereoselective method to synthesize β-organochalcogenyl vinylphosphonates 2 by means of the hydrochalcogenation of diethyl 1-alkynylphosphonates 1. We started our investigations with the hydrotelluration of alkynylphosphonates. 3 The reaction was performed by addition of alkynylphosphonates to a solution of sodium organyl tellurolate, prepared by reduction of diorganyl ditellurides with sodium borohydride in ethanol at room temperature 4 (Scheme 1). The β-organotelluranyl vinylphosphonates were formed in satisfactory yields with total regio- and Z-stereoselectivity (Table 1). The same procedure was used for the synthesis of β-organosulfanyl and organoselanyl vinylphosphonates. However, in these cases, the stereoselectivity was lower than for the tellurium analogues, probably as a result of the lower nucleophilicity of the organyl thiolate and selenolate anion. In all cases studied, only the regioisomer shown in Scheme 1 was obtained. This result can be * Corresponding author. E-mail: albraga@quimica.ufsm.br (A. L. Braga) 0040-4039/00/$ - see front matter © 1999 Elsevier Science Ltd. All rights reserved. PII: S0040-4039(99)02044-4 tetl 15972