Study On The Synthesis Of Aryl Thiocyanates And Aryl Selenides By CHAN-lAM Cross-coupling Reactions

Aryl thiocyanates and aryl selenides are two kinds of important compounds which are widely used in fields of pharmceuticals,agrochemicals and materials science.They are also acted as building blocks in the synthesis of a number of sulfur-containing or selenium-containing organic compounds.As a result,the development of efficient and practical methods for the synthesis of aryl thiocyanates and aryl selenides are very desirable.Chan-Lam cross-coupling is a class of important organic reactions.It provides a mild and efficient approach for the synthesis of a number of functionalized organic compounds by direct C–X?X = C,H,N,O,S,Se,Te,Cl,Br,I,P?bonds formation.In this work,novel methods for the synthesis of aryl thiocyanates and aryl selenides have been developed by Chan-Lam cross-coupling reactions.Part 1.With the cross-coupling of 4-methylphenylboronic acid and TMSNCS to form 4-methylphenyl thiocyanate as model reaction,the reaction conditions,including the kinds of catalysts,ligands,solvents and so on,were screened.When the ratio of 4-methylphenylboronic acid andTMSNCS was 2 : 1,the optimal conditions was obtained that the reaction was carried out with 20 mol% of CuCl,20 mol% of TMEDA,1 equiv.of NaF and 4 equiv.of K₂CO₃ in CH3 CN at room temperature for 12 h and under oxygen balloon,together with 3? molecular sieves.Under this optimal reaction conditions,4-methylphenyl thiocyanate was isolated in89% yield.The proposed reaction system was also suitable in the cross-coupling of a variety of substituted arylboronic acids and TMSNCS,and a broad range of corresponding aryl thiocyanates were synthesized in45-89%.Moreover,the reaction mechanism of this reaction was studied and a plausible reaction pathway was proposed.Part 2.With the cross-coupling of arylboronic acid and benzyl selenocyanate to form phenyl benzyl selenide as model reaction,the reaction conditions,including the kinds of catalysts,ligands and so on,were screened.When the ratio of arylboronic acid and benzyl selenocyanate was 1.5 : 1,the optional reaction was obtained that the reaction was carried out with 50 mol% of Cu?TFA?2,10 mol%8-Hydroxyquinoline,3 equiv.of K₂CO₃ in refluxing CH3 CN for 2 h.Under this optimal reaction conditions,the phenyl benzyl selenide was obtained in 90% yield.The proposed reaction system was also suitable in the cross-coupling of a variety of electron-rich arylboronic acids and benzyl selenocyanate,and corresponding aryl benzyl selenides were obtained in 57-90% yields.Unfortunately,the proposed reaction systemwas inefficient in the cross-coupling of electron-poor arylboronic acids,and much lower yields were resulted.In conclusion,novel routes for the synthesis of aryl thiocyanates and aryl selenides have been proposed from commercial available raw materials.The newly developed methods were facile,mild and easy to operate.