1: but-3-enyltriphenylphosphonium bromide With potassium hexamethylsilazane in tetrahydrofuran T=-78°C; 1 h; Inert atmosphere; 2: methyl chloroformate in tetrahydrofuran T=-78 - 20°C; 1.5 h; Inert atmosphere;

1.1: toluene / 24 h / |Inert atmosphere; |Reflux 2.1: potassium hexamethylsilazane / tetrahydrofuran / 1 h / -78 °C / |Inert atmosphere 2.2: 1.5 h / -78 - 20 °C / |Inert atmosphere View Scheme

in ethyl acetate