Conformationally Driven Ru(II)-Catalyzed Multiple ortho-C–H Bond Activation in Diphenylpyrazine Derivatives in Water: Where Is the Limit?

Sara Hrovat,Uroš Grošelj,Franc Požgan,Jurij Svete,Bogdan Štefane,Miha Drev,Franc Perdih

doi:10.3390/catal10040421

Abstract

Ru(II)/carboxylate/PPh3 catalyst system enabled the preparation of highly conjugated pyrazine derivatives in water under microwave irradiation. Both nitrogen atoms efficiently dictated cleavage of the ortho-C–H bonds in both benzene rings of 2,3-diphenylpyrazine substrates through chelation assistance. In conformationally more flexible diphenyldihydropyrazine 1, the arylation of four ortho-C–H bonds was possible, while in the aromatic analog 2, the triarylation was the limit.

Highlights

Catalytic C–H bond activation and subsequent formation of new C–C bonds, or C–heteroatom bonds, have remarkably contributed to the development of chemical transformations which enable the construction of complex molecular architectures from readily available precursors by shortening synthetic pathways and reducing waste production [1,2,3,4,5,6,7]
We have investigated the functionalization of ortho-C–H bonds of diphenylpyrazine derivatives with ruthenium(II) catalysts
Even though we intended to directly apply the previously established catalytic conditions [37] for the present arylation of dihydropyrazine substrate 1, the effect of base, solvent, ligands, and temperature was briefly investigated under conventional heating

Summary

Introduction

Catalytic C–H bond activation and subsequent formation of new C–C bonds, or C–heteroatom bonds, have remarkably contributed to the development of chemical transformations which enable the construction of complex molecular architectures from readily available precursors by shortening synthetic pathways and reducing waste production [1,2,3,4,5,6,7]. Pd [10,11,12,13,14] and Rh [15,16,17,18] catalysts are very efficient in enabling the selective functionalization of C–H bonds, the use of easy-to-prepare, air-stable, often stable in water and functional groups tolerant Ru(II) complexes have attracted much interest in the development of efficient catalytic systems for these processes [19,20,21,22,23,24,25,26]. Požgan and co-workers have demonstrated that the quinazolinyl [34,35]

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