TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preparation (claimed): The preparation of pyrazindithiophene derivative (I) comprises:(A) placing dimethylformamide (DMF) in flask under ice bath, argon degassing for 30 minutes, taking methylthio compound, adding sodium methyl mercaptan or dimethyl disulfide to form methylthio sodium thiomethoxide with N,N,N,N'-tetramethyl ethylene diamine (TMEDA) and copper iodide catalyst, adding dropwise 2,5-dihalo-substituted pyrazine in DMF solution in funnel under constant voltage, reacting with ice bath for 2 hours, keeping reaction at room temperature for 48 hours, removing DMF under vacuum, extracting with chloroform, drying organic phase over anhydrous magnesium sulfate, removing solvent by rotary evaporation, purifying using column chromatography to get product A;(B) adding dropwise 2,2,6,6-tetramethylpiperidine and n-butyllithium mixture at 1:1 mol ratio in tetrahydrofuran under argon gas protection at - 78 degrees C, raising temperature to 0 degrees C for 30-60 minutes, cooling to - 78 degrees C, adding dropwise tetrahydrofuran solution to product A, reacting at - 78 degrees C for 2 hours, quenching reaction with water, raising temperature to room temperature, purifying solvent directly by column chromatography to give product B;(C) adding product B to the flask with catalyst with argon gas for 15 minutes, adding dropwise tetrahydrofuran and triethylamine, bubbling argon for 30 minutes, adding dropwise trimethylsilylacetylene, reacting at 20-60 degrees C for 12-24 hours in the dark, distilling solvent, purifying using column chromatography to give product C;(D) dissolving product C in dichloromethane, argon degassing for 30 minutes, adding iodine, reacting at 20-40 degrees C for 3-16 hours, adding sodium thiosulfate to remove excess iodine, extracting with dichloromethane, drying organic phase over anhydrous magnesium sulfate, removing solvent, purifying using column chromatography to get product D; and(E) dissolving product D and 2-(5-(2-alkyl)thiophene-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane in degassed toluene, argon degassing for 15 minutes, adding tetrakis(triphenylphosphine)palladium(0), adding degassed sodium carbonate, reacting under argon gas at 85 degrees C for 24 hours, extracting with chloroform, drying organic phase over anhydrous magnesium sulfate, removing solvent by rotary evaporation, and purifying using column chromatography.The methylthio compound and 2,5-dihalo-substituted pyrazine mol ratio is 4:1. The halogen is chlorine, bromine or iodine. The product A, n-butyllithium, 2,2,6,6-tetramethylpiperidine feed weight ratio is 1:2-8:2.0-8.0. The trimethylsilylacetylene and product B mass ratio is 2-6:1. The 2-(5-(2-alkyl)thiophene-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane and product D mass ratio is 2-6:1. Preferred Component: The catalyst is palladium catalyst, copper catalyst and base mixture. The palladium catalyst is tetrakis(triphenylphosphine)palladium(0) and/or bis(triphenylphosphine)palladium(II) dichloride. The copper catalyst is copper iodide and/or copper bromide. The base is triethylamine and/or tetrabutylammonium fluoride.