1.1: n-BuLi / tetrahydrofuran / 1.5 h / 20 °C 1.2: 96 percent / tetrahydrofuran / 1 h / 0 °C 2.1: 91 percent / triethylamine; p-toluenesulfonyl azide / acetonitrile / 8 h / 20 °C View Scheme

1: 3,4-dimethylphenyl methyl sulfone With n-butyllithium in tetrahydrofuran T=20°C; 1.5 h; 2: pent-4-enoic acid ethyl ester in tetrahydrofuran T=0°C; 1 h;