1: methyl 2-methylphenyl sulphone 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;

4-toluenesulfonyl azide; triethylamine in acetonitrile T=20°C; 8 h;