1: dimethyl diselenide With 1,4-dithio-DL-threitol in N,N-dimethyl-formamide T=20°C; 0.5 h; Inert atmosphere; 2: 2-chloro-5-nitro-benzaldehyde in N,N-dimethyl-formamide T=20°C; 0.25 h; Inert atmosphere; 3: With potassium carbonate in N,N-dimethyl-formamide T=20°C; 1 h; Inert atmosphere;