Rhodium-catalyzed Selective N-H Bond Insertion Reaction

Sulfoxonium ylide derived metal carbenes have been extensively used in constructing various carbon carbon and carbon heteroatom bonds.Typically,compared with traditional carbene precursors,diazo compounds,sulfoxonium ylides are stable,safe,and can be stored for longer time.Therefore,these compounds have been utilized as diazo alternatives in diverse carbene transfer reactions,including the formal X H（X=N,O,S,B）bond insertion reactions.N-Alkylated 2-pyridones are important motifs in natural products and biologically active pharmaceuticals.Since the 2-pyridone molecule exists in equilibrium（tautomerism）with 2-hydroxypyridine,the direct alkylation of 2-pyridones remains elusive and often suffers poor chemoselectivity,leading to a mixture of N-and O-alkylated products.Thus,the highly chemoselective N-alkylation of 2-pyridones remains a great challenge.Given that diazo compounds can readily undergo X-H insertion reactions,the alkylation of 2-pyridones with diazo compounds has been previously investigated.However,the O-alkylation proved to be the dominant insertion reaction under either rhodium or gold catalysis.Recently,using 2-oxypyridines as the substrates,this article have developed a rhodium-catalyzed synthesis of N-alkylated pyridones via a novel O-to-N acyl rearrangement.Inspired by the pioneering reports and our own group interest in metal-carbene chemistry,The research content of this article focuses on the following two aspects:（1）Selective N-H bond insertion reaction between 2-pyridones and sulfoxonium ylides.A ruthenium-catalyzed highly chemoselective N-alkylation of2-pyridones has been developed,affording N-alkylated 2-pyridone derivatives in good yields and excellent N-selectivity.The key to achieve this unprecedented N-H rather than O-H insertion reaction is the use of Cp Ru（PPh₃）₂Cl as the catalyst and sulfoxonium ylides as the alkylation reagents.（2）Selective N-H bond insertion reaction between 7-azaindoles and sulfoxonium ylides.This protocol is also amenable to 7-azaindoles by slightly varying the reaction conditions（lowering the temperature）,It was found that 93%of the N7-position alkylation products can be obtained,and the substrate adaptability is good.