1: butyl ethanesulfonate With n-butyllithium in hexane T=-78°C; 0.5 h; 2: 5-chloro-2-thiophenecarboxaldehyde in tetrahydrofuran; hexane T=-78 - 0°C; 3: With water in tetrahydrofuran; hexane T=0°C; 0.166667 h;