Pd-Catalyzed Cross-Coupling Of Diazo Compounds And Isocyanides

Ketenimine represents an important class of speciesand useful synthetic intermediates or synthons.It Includes C=C and C=N,two cumulative active functional groups.It'smainly used for the synthesis of nitrogen-containing molecules.In the earlydays,the availability of ketenimines was rather limited,which significantly constrained their synthetic applications.It has developed rapidly in recent years.This type of cumulated double bonds has a variety of resonance structures and it can be used as both electrophile and nucleophile.In addition,C = C and C = N of ketenimine can be used as 1,3-dipoles to perform [m+n] cycloaddition reaction to obtain corresponding cyclic or heterocyclic compounds.Accordingly,the preparation of these molecules has received great attention.The existing methods were limited inherently by the use of scarcely available starting materials,harsh reaction conditions,narrow substrate scope,functional group tolerance and poor atom-economy.Therefore,it is very attractive to develop a mild and simple solution for their preparation.The use of diazo compounds in organic synthesis has played a vital role in the generation of molecular complexity.Especially,the transition-metal-catalyzed cross-coupling of diazo compounds through the carbene migratory insertion process has emerged as one of the most powerful and reliable synthetic tools for the construction of C–C and C=C bonds.However,the formation of highly reactive cumulated double bonds from diazo compounds remains underdeveloped.In the text,the development of a mild and operationally simple protocol for their preparation is highly appealing.Herein,we report atom-economical preparation of ketenimines via the direct cross-coupling of diazo compounds with isocyanides using Pd catalysis.The practicality of this method is highlighted by its mild conditions,broad substrate scope,excellent functional group tolerance,high product yields,and the rich chemistry associated with the obtained products.The combined experimental and DFT studies provide unambiguous support for the initial formation of a Pd(II)-isocyanide complex as an active catalytic species,and the cross-coupling occurs through the migratory insertion of Pd(II)-carbenoid species with free isocyanides.Moreover,the DFT calculations also support the preservation of the oxidation state of palladium throughout the catalytic cycle.