Studies On Transition-metal Catalyzed C-H Bond Functionalizations Using N Atom As Directing Group

Transition-metal-catalyzed functionalizations of C–H bonds have come across a tremendous development over the last decades.In particular,great progress has been made in site-selective chemical transformations of unactivated C-H bonds.Among all of the methods developed,directing group has proven to be an ingenious strategy to improve reactivity and control selectivity.Various functional groups,especially nitrogen-containing groups,are widely served as directing groups because of their excellent coordination ability with transition metals.However,the directing groups usually have high molecular weight,making the procedures poor in terms of atom economy.Moreover,formation of di-functionalized products is difficult to avoid.We employ azine?Ar?R?C=N-N=C?R?Ar?as a directing group for the Rh-catalyzed ortho-C-H carbenoid insertion of arylketone or aldehyde.In this protocol,the hydrazine,a small molecule,is envisaged as both a directing group via formation of azine and a bridging unit between two reacting aryl rings?Ar?.Two equivalent mono-substituted?-aryl malonates were obtained in one step,which exhibits not only high atom economy,but also superior site selectivity.This reaction proceeds smoothly at room temperature with excellent regioselectivity and functional group compatibility.Hydrolysis of the products can release ketones or aldehydes,which easily access to aromatic 1,5-keto-diesters as valuable synthons for further chemical transformations.On the other hand,tremendous progress in transition-metal-catalyzed functionalization of C-H bonds have been achieved in the past decade,main breakthroughs relying on the use of noble metals,such as Rh,Ru,Pd or Ir.Focus is,however,currently shifting towards first-row transition metals for their high natural abundance,low cost,low toxicity,and recently disclosed promising catalytic activities.Continuing efforts for the development of economically and ecologically valuable strategies for the synthesis of functional aromatics and heterocycles,we have developed a novel Mn?III?-catalyzed three-component cyclizing cascade C-H/N-H functionalization of 2-aminopyridines with dialkyl butynedioates to prepare 2,11-diazatricyclo[5.3.1.0^4,11]undeca-1?10?,4,6,8-tetraen-3-ones.In this protocol,nitrogen atoms not only serve as directing groups,but also get ultimately involved in two new C–N bonds,with parallel formation of two C–C bonds in a one pot manner,using a manganese salt as catalyst.