Synthesis of 1,3-diynes via detelluration of bis(ethynyl)tellurides

Abstract

Neste artigo é descrita a síntese de sistemas diínicos conjugados contendo substituintes elétron-atratores e elétron-doadores via a deteluração catalizada por paládio de bis-(ariletinil)teluretos e bis-(alquiletinil)teluretos. Este procedimento foi realizado sob condições atmosféricas em DMF usando Pd(Oac) 2 como catalisador e AgOAc como um aditivo na presença de trietilamina. Esta rota oferece acesso eficiente a sistemas diínicos conjugados em um curto período de tempo. A estrutura cristalográfica por difração de raios X do telureto de bis(p-toluiletinila) e a conformação no estado sólido mostram uma cadeia supramolecular alinhada ao longo do eixo b, sustentada por interações CH…p.The synthesis of symmetric conjugated diyne systems with electron-withdrawing or electrondonating substituents via a palladium-catalyzed detelluration of bis(arylethynyl)tellurides and bis(alkylethynyl)tellurides is described. This procedure is effected under atmospheric conditions in DMF using Pd(OAc) 2 as a catalyst and AgOAc as an additive in the presence of triethylamine. This route offers efficient access to conjugated diyne systems in short reaction time. X-ray crystallographic structure and solid-state conformation of bis(p-tolylethynyl)telluride show a supramolecular chain aligned along the b axis, sustained by C-H…p interactions.Keywords: tellurium, bis(phenylethynyl)tellurides, bis(alkynylethynyl)tellurides, detelluration, diynes, palladium IntroductionOrganotellurium compounds play an important role in organic synthesis, and they have received considerable attention because of their potential availability and useful biological activity. 1 As reported by Bergman and co-workers 2 more than three decades ago, aryltelluriums undergo detelluration upon treatment with degassed Raney nickel to afford biaryl compounds. Although the reaction is interesting and synthetically useful, the necessity of more than a stoichiometric amount of the required metal is still a serious drawback. However, attempted transition metalcatalyzed detellurations have been unsuccessful to date. 2,3 Compounds containing chains of conjugated triple bonds 4,5 are of paramount importance as versatile and useful building blocks in organic synthesis. Among these compounds, 1,3-butadiynes 6 have been prominently utilized as substructures in the formation of valuable intermediates for natural products 7 and pharmaceuticals such as antitumor, 8 antibacterial, 9 anti-inflammatory, 10 and antifungal agents. 11 These conjugated diynes also serve as the core functional group in organic molecular materials such as linearly σ-conjugated acetylenic oligomers and polymers, 12 macrocycles 13 (Figure 1), and supramolecular scaffolds. 14 Oxidative dimerization of sp-hybridized terminal alkynes mediated by Cu(I) or Cu(II) salts under either catalytic or stoichiometric conditions is the most commonly used synthetic methodology for obtaining symmetrically substituted 1,3-butadiyne.These approaches include Glaser's coupling, 15 Eglinton's coupling, 16 and Hay's coupling. 17 In t...