1.1: copper (I) iodide; sodium iodide; potassium carbonate / dimethylformamide / 20 °C 1.2: TBAF; acetic acid / tetrahydrofuran / 20 °C 2.1: 67 percent / [CpRu(CH3CN)3]PF6; LiBr; stannic bromide / acetone / 2 h / 60 °C 3.1: 74 percent / chromium (II) chloride; nickel (II) chloride / dimethylformamide / 20 °C 4.1: 74 percent / pyridinium dichromate / CH2Cl2 / 1 h / 0 °C View Scheme

1: 2-ethoxycarbonyl-2-(2-propynyl)malonic acid diethyl ester With sodium ethanolate in tetrahydrofuran 1.5 h; 2: methanesulfonic acid pent-2-enyl ester in tetrahydrofuran T=20°C; 5 h;