Study On The Diboronic Acid(Pinacolate)Mediated Borylation And Reduction Reaction

This thesis mainly focuses on the research of two commonly used diboron reagents B₂pin₂ and B₂?OH?₄.A series of pyrazine boronicesters were synthesized from the corresponding chloropyrazines by using palladium-catalyzed Miyaura borylation reaction;A metal-free reduction of aryl nitro compounds to the corresponding amines has been achieved by using B₂pin₂ as reductant;Cu?II?-catalyzed reduction of aryl azides to the corresponding aryl amines has been completed via diboron reagent as reductant.1.Efficient synthesis of pyrazine boronic esters via palladium-catalyzed Miyaura borylationA facile and efficient method for palladium-catalyzed Miyaura borylation reaction of chloropyrazines with B₂pin₂ has been developed.The optimal reaction condition was obtained as the combination of Pd?OAc?2?2 mol%?,PCy3?4 mol%?,Ac OK?2.5 eq?and B₂pin₂?1.1 eq?in dioxane at 110 °C under N2 for 10 min?Scheme 1?.A series of pyrazineboronic ester derivatives were easily prepared from the corresponding chloropyrazines in moderate to good yields.The notable advantages of the protocol are its short reaction times,high yields,broad functional group compatibility and easy purification.The reaction is also suitable for decagram scale synthesis.2.A metal-free reduction of aromatic nitro compounds to the corresponding aminesA metal-free reduction of aryl nitro compounds to the corresponding amines has been developed.The optimized reaction conditions for the reduction of aryl nitro compounds?1.0 eq?to the corresponding arylamines were determined as the combination of B₂pin₂?3.1 eq?with KOt Bu?1.2 eq?in i Pr OH at 110 oC for 2 h.A series of aryl nitro compounds containing various reducible functional groups could be chemoselectively reduced in good to excellent yields?Scheme 2?.The notable features of the protocol is short reaction times,broad functional group tolerance?halide,cyano,ester,ether,et al.?,and generally high yields.3.Cu?II?-catalyzed reduction of aryl azides to amines by using diboron reagent.The copper-catalyzed reduction of aryl azide compounds to the corresponding aryl amines has been explored.The optimal reaction condition was obtained as the combination of?1 eq?aryl azide compounds,?1.5 eq?B₂?OH?₄ or?1.3 eq?B₂pin₂,1 mol% Cu?OAc?2 in methanol/water at 40 °C for 10 min.A broad range of aryl azide compounds were selectively reduced to the corresponding primary aryl amines?Scheme 3?.The method features low catalytic loading,simple operation,mild reaction conditions,good selectivity,and broad functional group tolerance?such as halogen,ether,cyano and other functional groups?.